Non-Conventional Starches: Properties and Potential Applications in Food and Non-Food Products

Abstract

The increasing industrial demand and the search for novel ingredients in food and non-food sectors have driven research efforts toward alternatives to traditional commercial starches, emphasizing sustainability and the valorization of native crops, thereby promoting income generation for small-scale farmers. The extraction of these starches through aqueous methods, employing reductive and/or alkaline agents, can impact their structure and technological properties. These starches exhibit distinct physicochemical, morphological, crystalline, thermal, and nutritional characteristics, influenced by factors such as botanical origin. Although certain limitations may exist in their technological applications, physical, chemical, and/or enzymatic modification methods, or a combination thereof, are employed to enhance these properties for specific uses. These alternative starch sources present potential applications across the food, pharmaceutical, paper, medicinal, and cosmetic industries, underscoring their versatility and unique advantages. Nonetheless, ongoing research is essential to fully explore their composition and potential applications. This review serves as a valuable resource for researchers and professionals interested in sustainable and innovative alternatives to conventional starches.

1. Introduction

Starch is a complex and abundant reserve polysaccharide found in plant tissues, stored in the form of semicrystalline granules, and serves as a critical component of the human diet, contributing 70–80% of daily caloric intake as a primary energy source. Its molecular structure consists of α-glucan units linked by glycosidic bonds, forming the polyglucans amylose and amylopectin, along with intermediate materials [1]. Amylose is essentially a linear biopolymer of α-glucan, predominantly linked through α-(1→4) glycosidic bonds. In contrast, amylopectin exhibits a highly branched structure, comprising a linear portion of α-D-glucose units connected by α-(1→4) linkages and 2–4% side chains attached to the linear backbone through α-(1→6) glycosidic bonds [2,3,4]. The third polyglucan component, known as the intermediate material, consists of glucose molecules arranged in short or long chains, displaying properties that are distinct from those of amylose and amylopectin [5].

The composition and physicochemical properties of starch vary significantly depending on its botanical source, typically presenting an average proportion of amylose between 20 and 30% and amylopectin between 70 and 80%. However, exceptions are observed, such as in waxy corn starch, which comprises approximately 99% amylopectin, or high-amylose starches containing 50–70% amylose. The granular structure of starch comprises both crystalline and amorphous regions, influenced by the presence of highly branched amylopectin chains. The amylose-to-amylopectin ratio is a critical factor affecting various starch properties, including gelatinization behavior, thermal stability, retrogradation, water absorption capacity, and stability under freeze–thaw conditions [5,6,7].

Although corn, wheat, rice, and potato are the predominant commercial sources of starch, increasing industrial demand has led to the exploration of non-conventional or underutilized sources derived from various plant parts and species/varieties. These sources include seeds, roots, and metamorphic plant stems, such as tubers, rhizomes, and shoots, which are isolated and investigated for their physicochemical, morphological, structural, and nutritional characteristics. This trend presents innovative opportunities for developing potential markets in both food and non-food products [4,8].

Understanding the properties of these non-conventional starch sources is essential for determining their applicability. Therefore, this review examines starch sources that are not yet widely available commercially, or that may be available in specific regions, analyzing their morphological, chemical, thermal, and nutritional characteristics, as well as recent studies on their utilization in both food and non-food products. This analysis provides new insights into these starchy sources, emphasizing their potential for commercial development, promoting sustainable practices, enhancing the value of native crops, and contributing to job creation and income generation for local communities.

2. Methodology

The bibliographic research was conducted across five databases: Web of Science, ScienceDirect, Scopus, Scielo, and Google Scholar. Studies were selected using the following search descriptors: “non-conventional AND sources AND starch”, “starch AND food AND application”, “starch”, “starch AND food AND products”, “starch AND non-food AND products”, in the title, abstract, and keywords. Only articles written in English and published in scientific journals were included, with an atemporal period being considered.

3. Non-Conventional Starch Sources

Non-conventional starch sources are characterized by atypical extraction and utilization patterns. These crops are typically cultivated for purposes other than starch production, with their cultivation often restricted to specific regions of origin and yielding smaller volumes compared to conventional starch sources, such as corn, potato, and rice [9,10].

Several alternative sources of starch have been identified in the literature, both in their native form and after undergoing chemical, physical, and/or enzymatic modifications. These starches exhibit varying morphological, physicochemical, thermal, rheological, and nutritional properties, influenced by factors such as environmental conditions, genetic variability, agricultural practices, crop varieties, extraction techniques, and post-harvest processing methods [11,12].

The exploration of these alternative starch sources is motivated by global population growth, the need for more sustainable production practices, the valorization of by-products from food and non-food industries, the promotion of regional products, and various sociocultural, economic, and technological factors associated with these starches [12,13,14]. Additionally, technical advantages in the modification and application of these starches, when compared to conventional varieties, have also been reported [15,16].

Various non-conventional starch sources have been investigated, as depicted in Figure 1, encompassing a diverse array of plant parts. These sources include fruit seeds, such as mango, jackfruit, loquat, jabuticaba, annatto, and avocado [10,17]; fruit pulp, including cupuaçu, babassu, green banana, breadfruit, wolf fruit, and peach palm [10,18]; rhizomes, such as ginger, cocoyam, turmeric, lotus, and chayote [19]; and peels, including banana and peach palm [20]. Other sources comprise culms (bamboo) [21], tubers (parsnip and yam), by-products from the food industry (e.g., fibrous peel and cassava bagasse), cereals (pigmented corn and pigmented rice), and stems, including pineapple stem, arrowroot, cassava, yam, and sweet potato [22,23,24].

Legumes, such as the navy bean, pea, chickpea, and lentil, as well as nuts, including the horse chestnut, water chestnut, Brazil nut, Chinese ginkgo, and acorn, have also been examined [25,26]. Additionally, pseudocereals such as buckwheat, quinoa, and amaranth; seaweed species, including Gracilariopsis, Rhodophyta, and Cladophora [1,27]; and underutilized grasses and millets have been explored. These emerging starch sources are garnering significant interest from both the scientific community and the commercial sector due to their potential applications in various industrial processes. [16].

In addition to technological variations, non-conventional starches have been reported to exhibit unique properties. Recent studies have identified the presence of bioactive compounds, including phenolic compounds, carotenoids, chlorophylls, sesquiterpenes, and lactones. Many of these substances demonstrate significant bioactive properties, particularly antioxidant activity and pro-vitamin A potential. The concentration of these compounds has been found to vary depending on factors such as the degree of maturity, botanical source, purity, post-harvest conditions, and the extraction methods applied [13,14,28,29]. Antioxidant activity ranging from 1.9 to 3.6 mg trolox equivalents·g⁻¹ and a carotenoid content of 549.4 to 780.2 mg of total carotenoids·g⁻¹ have been reported in starch extracted from annatto seeds (Bixa orellana L.) [30]. Similarly, phenolic compounds in starch derived from the endocarp of pitomba (Talisia esculenta) have been quantified at 6062.6 mg gallic acid equivalents·100 g⁻¹ [31]. Additionally, phenolic acids, such as kaempferol (330.46 μg·kg⁻¹) and 5-caffeoylquinic acid (up to 135.00 μg·kg⁻¹), have been identified in starch extracted from loquat seeds (Eriobotrya japonica), with antioxidant activity ranging from 24.43 to 108.20 μmol trolox equivalents·100 g⁻¹ [32].

4. Starch Extraction from Non-Conventional Sources

Starch is extensively utilized across food and non-food industries and can be derived from various botanical sources. Each crop requires specific extraction processes to remove non-starch components and facilitate the production of pure starch. The isolation process is significantly influenced by differences in plant sources, genotypes, chemical composition (including proteins, lipids, minerals, non-starch polysaccharides, phenolic compounds, and fibers), and matrix structure. Prominent extraction techniques include enzymatic, acidic, alkaline, and aqueous methods [5,33,34].

Among these, the aqueous extraction method is the most widely used due to its simplicity and minimal waste generation. However, depending on the starch source, this method may result in lower recovery rates and starch granules with higher levels of residual non-starch components. For instance, a study by Pires et al. [34] comparing alkaline extraction (0.1% NaOH) to aqueous extraction for peach palm fruits (Bactris gasipaes Kunth) demonstrated that the alkaline method achieved yields 15–39% higher than aqueous extraction and reduced lipid content by up to 39% in macrocarpa starch.

Chemical reagents are commonly employed during the maceration phase of starch extraction to solubilize proteins, lipids, and other non-starch components. This enhances leaching, increases purity, and improves recovery efficiency. Alkaline methods, using reagents such as NaOH and sodium metabisulfite (Na₂S₂O₅), are widely implemented in commercial processes due to their ability to achieve higher yields and purity. These methods also reduce cell wall rigidity and disrupt bonds between starch and non-starch components, particularly disulfide bonds in protein bodies, thereby enhancing extraction efficiency. However, the use of such reagents may alter the crystalline structure of starch, affect its morphological, thermal, and rheological properties, and generate waste requiring treatment [5,33,34].

A study by De Melo et al. [35] on bacupari seeds (Garcinia brasiliensis (Mart.)) highlighted the impact of extraction methods on starch properties. Aqueous extraction yielded a higher amylose content (13.07%) compared to alkaline extraction (10.13%), along with reduced lipid (2.38%) and ash (0.15%) contents. Additionally, starch extracted through the aqueous method exhibited greater thermal stability (ΔT = 100–217 °C) and a higher peak temperature (Tp = 70.47 °C), demonstrating the distinct influence of extraction techniques on starch properties.

The process of extracting starch from non-conventional crops typically involves multiple steps. Initially, a starchy paste is produced through cutting or grinding, disintegration, homogenization, and sieving to expose granular starch to water or an extraction solution, facilitating its removal from storage cells. The resulting slurry is filtered and decanted to allow sedimentation. The sediment is repeatedly washed, centrifuged, and dried at approximately 40 °C before being milled, sieved, and stored in airtight containers.

This methodology was demonstrated by Tulu et al. [36] during the extraction of starch from anchote roots (Coccinia abyssinica). The roots were sanitized, peeled, cut, and ground, followed by filtration and sedimentation. The sediment was washed with distilled water, dried in an oven at 45 °C for 24 h, milled, and stored. Similarly, Martins et al. [37] extracted starch from avocado seeds by washing and cutting the seeds, soaking them in 0.2% SO₂ solution for 24 h, and grinding the material in the same solution. The homogenized mixture was sieved, decanted, and centrifuged, with the starch subsequently dried at 40 °C for 12 h. These examples illustrate that variations in starch extraction methods are necessary to accommodate the unique characteristics of each source, often requiring additional steps to optimize the process.

As shown in

Table 1. Selected non-conventional sources of starch and their physicochemical, morphological, and crystalline characteristics.

Botanical Source	Extraction Method	Yield (%)	Morphology	Granule Size	Amylose Content (%)	Proximal Composition (%)	Crystallinity	References
Jabuticaba Seed (Plinia cauliflora)	H2O	22.65	Trimodal—smooth surface and irregular shape	2–10 µm	34.50	M: 7.19, P: 1.19, L: 118, A: N.	Type C—35.4% Peaks at 2θ = 5.69°, 15.11°, 17.02°, and 23.19°	[17]
Pineapple Stems (Ananas comosus)	H2O (1:1)	30	Semi-angular with partially rounded segments	3–14 μm	35.15	M: 10.64, P: 0.71, L: 0.55, A: 0.54	Type A—Peaks at 2θ = 12.8°, 14.6°, 15.4°, and 19.8°.	[22]
Red Rice (Oryza sativa)	H2O (1:2)	35.7–47.0	Polyhedral with irregular shapes, acute angles, and edges	15–30 µm	25.75	M: 6.89, P: 3.73, L: 0.51, A: 0.80	Type A—25.50% Peaks at 2θ = 15.3°, 17.1°, 18.2°, and 23.5°	[29]
Black Rice (Oryza sativa)						M: 13.29, P: 2.60, L: 0.28, A: 0.68
Annatto Seeds (Bixa orellana L.)	H2O	19.0	Oval, spherical, smooth surface, no aggregates	5–20 µm	27.8	M: 12.5, P: 14.7, L: 3.4, A: 5.8	Type C—H2O = 35.4%, NaOH = 41.6% Peaks at 2θ = 10°, 15°, 17°, 20°, 23°, and 26°	[30]
	NaOH (0.25%)	32.0			23.9	M: 11.2, P: 17.4, L: 6.5, A: 3.8
Loquat Seed (Eriobotrya japonica)	H2O (1:15)	N	Oval and cylindrical	29.05–43.66 μm	10.53	M: 7.36, P: 0.61, L: 0.80, A: 0.36	Type C—24.30% Peaks at 2θ = 15°, 17°, 22°, and 23°.	[32]
Microalga Chlorella sp. MBFJNU-17	Na2S2O5 (0.45%)	N	Unimodal—smooth surface with irregularities and ellipsoid shape	400–1300 nm	13.45	M: N, P: 0.96, L: 0.23, A: 0.91	Type A and V—25.93% Peaks at 2θ = 15°, 17°, 18°, 20°, and 23°	[38]
Bamboo Stem (Bambusa tuldoides)	Na2S2O5 (0.2%)	2.51–3.55	Polyhedral with rounded and spherical shapes	5–12 µm	19.26 to 33.35	M: 7.25–7.89, P: 3.12–4.66, L: 0.23–0.61, A: 1.47–5.46	Type A—22.07 to 26.42% Peaks at 2θ = 15°, 17°, 18°, 20°, and 23°	[39]
Pea (Pisum sativum L.)	NaOH (0.33%)	53.20	Rounded or elliptical with a smooth surface	130–160 µm	72.91	M: N, P: 0.29, L: N, A: N	Type C—Peaks at 2θ = 15.35°, 17.38°, 18.28°, and 22.95°	[40]
Peach Palm (Bactris gasipaes var. gasipaes)—pulp	H2O (1:3)	N	Bimodal—irregular shapes (oval, conical, and spherical)	5.2–12.5 µm	18.92	M: 10.76, P: 0.54, L: 2.69, A: 0.19	Type C—23.56% Peaks at 2θ = 5.3°, 15.1°, 17.2°, 18.0°, 21.4°, and 23°	[41]
White Ginger Rhizome (Hedychium coronarium J. Koenig)	Na2S2O5 (0.02%)	22.0	Flat, thin, and smooth	E: 2–6 μm, C: 12–38 μm	59.16	M: 10.13, P: 0.97, L: 0.84, A: 0.28	Type B—19.30% Peaks at 2θ = 16.9°, 21.9°, 23.8°, 14.6°, and 19.4°	[42]
Chestnut (Castanea mollissima Blume)	Na2SO3 (0.025 M)	N	Oval to spherical, elliptical, smooth surfaces, and edges	1.2–517.2 μm	34.17	M: 13.5, P: 0.35, L: N, A: N	Type C—Peaks at 2θ = 5.6°, 15°, 17°, 22–24°	[43]
Black Pepper (Piper nigrum)	Na2SO3 (0.5%)	N	Polygonal and polyhedral with irregular shapes and smooth surface	Dm: 4.05 μm	23.8	M: N, P: N, L: N, A: N	Type A—21.50% Peaks at 2θ = 15°, 17°, and 23°	[44]
White Pepper (Piper nigrum)				Dm: 3.57 μm	25.6	M: N, P: N, L: N, A: N	Type A—21.18% Peaks at 2θ = 15°, 17°, and 23°
Ginkgo Seeds (Ginkgo biloba L.)	H2O	N	Spherical and elliptical	5–20 μm	30.5	M: 9.30, P: 0.44, L: 0.42, A: N	Type C—42.4% Peaks at 2θ = 5.6°, 15.2°, 17.1°, 22.1°, and 24.4°	[45]
Orchid Tuber (Bletilla striata (Thunb.) Reichb.)			Spherical with irregularities	3–20 μm	16.7	M: 9.06, P: 0.61, L: 0.40, A: N	Type C—20.7% Peaks at 2θ = 5.6°, 15.2°, 17.1°, 22.1°, and 24.4°
Flower Tuber (Angelica dahurica (Fisch. ex Hoffm.) Benth.)			Irregular, spherical with smooth surfaces	2–16 µm	21.3	M: 10.1, P: 0.46, L: 0.44, A: N	Type C—20.7% Peaks at 2θ = 5.6°, 15.2°, 17.1°, 22.1°, and 24.4°
Bacuri Seed (Garcinia brasiliensis (Mart.)) Green	NaOH (0.25%)	40.56	Oval with a smooth surface	42.21–56.88 μm	10.13	M: 8.88, P: 3.15, L: 3.58, A: 0.46	Type C—NaOH = 15.68%, H2O = 13.49 Peaks at 2θ = 15°, 17°, and 23°	[35]
	H2O	44.42			13.07	M: 9.49, P: 4.28, L: 2.38, A: 0.15
Green Mang Seed (Mangifera indica L.)	Na2SO3 (1%)	N	Unimodal—oval and spherical	50 μm	23.00	M: N, P: N, L: N, A: N	Type A—26.02% Peaks at 2θ = 15°, 17°, 18° and 23°.	[46]
Bamboo Seeds (Phyllostachys heterocycla var. Pubescens (Mazel) Ohwi)	H2O	N	Polyhedral with irregular shapes and edges	Dm: 5.0 µm	24.1	M: N, P: 18.6, L: 1.1, A: N	Type A—32.1% Peaks at 2θ = 15°, 17.1°, 17.5°, 18°, and 23°.	[47]
Lotus Seeds (Euryale ferox)	NaOH (0.17%)	N	Unimodal—polyhedral and irregular shape	0.50–5.60 μm	45.85	M: 11.67, P: 0.09, L: 0.13, A: 0.08	Type A—38.84% Peaks at 2θ = 15°, 17°, 18°, and 23°.	[48]
Ariá (Goeppertia allouia)	H2O	11	Unimodal—spherical with irregular sizes and smooth surface	15–40 μm	39	M: 8.45, P: 2.04, L: 0.39, A: 0.15	Type C—32% Peaks at 2θ = 5.8°, 10.4°, 18°, 18.5°, and 23°.	[49]
Gold Whisker Seed (Talisia floresii Standl)	NaHSO3 (0.1%)	N	Spherical, uniform, and fracture-free	10–25 μm	33.6	M: 9.49, P: ND, L: 1.60, A: 1.17	Type C—32% Peaks at 2θ = 15°, 17°, 18°, 23°, and 24°.	[50]
Pumpkin (Cucurbita maxima Duch.)	H2O	N	Spherical, polyhedral with irregular granules, and dome-shaped	10–20 μm	30.17	M: 15.90, P: 0.16, L: 1.01, A: 0.19	Type B—28.64% Peaks at 2θ = 5.6°, 15°, 17.2°, 19.8°, 22.3°, and 24.0°.	[51]
Pumpkin (Cucurbita moschata Duch. ex Poir.)				15–30 μm	21.35	M: 14.69, P: 0.47, L: 1.38, A: 0.29	Type B—31.31% Peaks at 2θ = 5.6°, 15°, 17.2°, 19.8°, 22.3°, and 24.0°.
Cocoyam Root (Xanthosoma sagittifolium)	H2O	N	Polyhedral, oval, and irregular at the ends	2–14.55 μm	21.80	M: 12.53, P: 0.17, L: 0.26, A: 0.55	Type A—38.3% Peaks at 2θ = 17°, 18°, and 23°.	[52]
Chickpea (Cicer arietinum L.)	NaOH (0.05%)	28.4	Oval, small, and spherical with a smooth surface	2–30 μm	30.2	M: 10.7, P: 0.75, L: N, A: 0.06	Type C—ND Peaks at 2θ = 6.5°, 15°, 18°, and 23°.	[53]
Mango Seeds (Tommy Atkins)	NaHSO3 (0.5%)	N	Oval, disc-shaped, and spherical	3.6–19.3 μm	25.26	N	Type A and V—28.3% Peaks at 2θ = 5.8°, 12.3°, 15.2°, 17.3°, 18.1°, 20.3°, and 23.2°.	[54]

M: Moisture; P: Protein; L: Lipids; A: Ashes; N: Not Determined; ND: Not Detected; E: Thickness; C: Length; Dm: Average Diameter.

, which summarizes potential sources of non-conventional starches for industrial applications, the aqueous extraction method remains the most commonly employed technique. Its popularity is attributed to its established knowledge base, low cost, and minimal environmental impact, aligning with the growing emphasis on sustainable practices. Furthermore, its economic feasibility and scalability make it a preferred choice, particularly when considering the cost of reagents and equipment [33].

Recently, the use of lactic acid, enzymes (such as proteases), L-cysteine, ultrasound, extrusion pretreatment, supercritical extraction, pulsed electric fields, and high-pressure maceration has emerged as environmentally friendly alternatives for starch extraction [4,33,36,37,55]. Wang et al. [40] evaluated ultrasound-assisted alkaline extraction conditions for pea starch (Pisum sativum L.), reporting a yield increase of 13.72% compared to conventional alkaline extraction, without altering the molecular structure or crystal type.

5. Morphological and Chemical Properties

The properties of starch are closely related to its chemical composition, molecular structure, and morphology, particularly the proportion of amylose. These properties vary according to the botanical source and the extraction method applied, with variations being more pronounced in non-conventional starches. Applications in both the food industry and other sectors depend on the characteristics of the products derived from this composition and the interactions between their components within the starch granules. Additionally, factors such as granule size, uniformity, and rheological and thermal properties play a critical role in determining these applications [6,56]. Table 1 presents various characteristics of non-conventional starches, including their degree of crystallinity, morphological and chemical characteristics, and extraction methods.

The yield of starch extraction is a critical factor for its commercial viability. As indicated in Table 1, a considerable number of studies fail to report extraction yields, revealing a significant gap in the literature. This information is essential for assessing the economic feasibility of extraction processes, optimizing methodologies, and ensuring efficiency and sustainability in large-scale production. Reported yields vary widely, ranging from 2.51% to 53.20%. Notably, sources such as peas (Pisum sativum L.) and bacupari seeds (Garcinia brasiliensis) demonstrate satisfactory yields of 53.20% and 40.56–44.42%, respectively. Conversely, lower yields have been reported for bamboo culm (Bambusa tuldoides), jabuticaba seeds (Plinia cauliflora), white ginger lily rhizome (Hedychium coronarium J. Koenig), ariá (Goeppertia allouia), and chickpea (Cicer arietinum L.) [17,39,42,49,53].

For commercial applications, a yield exceeding 30% is generally considered desirable, as highlighted by Tagliapietra et al. [12]. This benchmark can be influenced by the extraction method employed, the concentration of chemical reagents, and the intrinsic characteristics of the raw material. For instance, bacupari seeds exhibit varying yields depending on the method used: 44.42% for aqueous extraction and 40.52% for alkaline extraction (0.25% NaOH) [35]. Additionally, sources with low amylose content tend to yield lower amounts, as increased water absorption by starch granules can impede the separation of proteins adhering to the granule surface [33].

Table 1 also underscores the heterogeneity in starch granule morphologies obtained from different botanical sources. These granules exhibit a range of characteristics, including unimodal, bimodal, and trimodal distributions, as well as diverse shapes such as polyhedral, spherical, elliptical, oval, flat, and disk-shaped forms. Surface textures vary from smooth and uniform to irregular, with or without pores. This diversity highlights the significant influence of botanical origin on granule size, which can range from nanometric scales (400–1300 nm) in algae [38] to micrometric scales (2–160 µm). An exception is observed in starch derived from chestnuts (Castanea mollissima, Blume variety), where granule sizes range from 1.2 to 517.2 µm. This broader size range is attributed to minimal disruption during the isolation process, which preserves the granules more effectively [43].

Granule morphology and size are critical for determining starch functionality and identifying its botanical origin. Each source exhibits unique characteristics in terms of granule size, shape, and distribution, influenced by the biochemical, physicochemical, and biological properties of the plant. As noted by BeMiller and Whistler [5], these distinctions underscore the diverse origins and properties of starches from different plant species.

The linear structure of amylose plays a significant role in influencing the technological properties of starch, particularly its thermal and rheological characteristics. As presented in Table 1, the amylose content in non-conventional starch sources ranged from 10.13 to 72.91%. Starches from the white ginger lily rhizome (Hedychium coronarium J. Koenig) and pea (Pisum sativum L.) exhibited high amylose contents of 59.16 and 72.91%, respectively, with the latter being comparable to high-amylose corn starch (71.0%), making it a potentially viable alternative for applications requiring high viscosity and thermal stability. Starches derived from legumes, such as peas, typically contain higher amylose levels (24% to 88%) than those found in cereals (15 to 45%), as reported by BeMiller and Whistler [5]. This variation in amylose content is influenced by factors such as genetic variability, cultivation conditions (including temperature, humidity, soil type, and agricultural practices), maturation stage, extraction and analytical methods, post-harvest treatments (drying, storage, and processing), and the presence of lipids, proteins, and minerals, which may interfere with the accurate determination of amylose content.

Blazek and Copeland [57] highlighted that starches with varying amylose compositions are of particular interest in food processing due to their ability to influence the texture and other technological properties of food products. Starches with higher amylose content hold significant nutritional importance, as they are associated with the formation of resistant starch, which provides beneficial physiological effects. As observed by Obadi et al. [6], the gelatinization temperature of starch is generally correlated with its amylose concentration, with higher amylose content necessitating elevated temperatures to disrupt the granular structure. For instance, Wang et al. [40] reported that pea starch requires higher temperatures (78 °C) to initiate gelatinization.

Barros et al. [49] investigated the pasting properties of ariá starch (Goeppertia allouia) and compared them to those of commercial corn and potato starches. Their study revealed that ariá starch exhibited significantly higher pasting temperatures (Tp = 88.3 °C) compared to corn (Tp = 75.8 °C) and potato (Tp = 70.2 °C). This behavior was attributed to its higher amylose content and the presence of a Type C crystalline pattern. Furthermore, ariá starch demonstrated enhanced paste stability (28.7%), likely due to its amylose content, which supports continuous shear resistance at a constant temperature of 95 °C.

Starch purity, as determined by the levels of lipids, ash, and proteins, is a critical factor influencing its isolation, quality, and application. To achieve high purity, these components must be present in amounts below 10% [58]. The protein, fat, and mineral content of non-conventional starch sources, as summarized in Table 1, ranged from 0.29 to 18.6%, 0.13 to 6.5%, and 0.15 to 5.8%, respectively, reflecting significant variability among different sources. Some plant sources exhibited exceptionally high purity levels, such as lotus seeds (Euryale ferox) with >99%, pumpkin (Cucurbita maxima Duch.), pineapple stems (Ananas comosus), and loquat seeds (Eriobotrya japonica), each exceeding 98%. These findings suggest that the extraction methods applied to these sources are highly effective, producing starches of exceptional purity suitable for commercial applications.

However, notable exceptions include starches from annatto seeds (Bixa orellana L.), which have reported protein, fat, and mineral contents of 14.7–17.4%, 3.4–6.5%, and 3.8–5.8%, respectively, resulting in purity levels below 90%. This reduced purity is attributed to protein–starch and lipid–starch interactions, as well as the presence of non-starch components such as cellulose, lignin, fibers, phenolic compounds, and carotenoids. Additionally, variations in purity can arise from botanical characteristics, fruit size, and the extraction method employed, as noted by Silveira and Tapia-Blácido [30] and Yu et al. [59]. Understanding the botanical source is, therefore, essential for selecting the most suitable extraction method, as different sources present varying levels of complexity in starch isolation. For instance, the extraction of legume starch is more complex due to the relatively higher cotyledon cell wall fiber content, which complicates starch isolation and impacts yields, compared to other sources.

The crystalline structure of starch molecules is typically analyzed using X-ray diffraction (XRD) techniques. The degree of crystallinity in native starch generally ranges from 15 to 45%, though it can be altered or reduced by processes such as extraction, modification, and gelatinization, as well as other treatments. Several factors influence starch crystallinity, including the amylopectin content, the length of its side chains, and the organization of its double helices. In contrast, amylose content exhibits an inverse relationship with crystallinity, as amylose is primarily associated with the amorphous regions of the starch granule. The classification of crystallinity types is determined by the packing arrangement of amylopectin double helices, as identified by the peaks observed in X-ray diffraction (XRD) patterns. Starches are currently classified into four types: A, B, C, and V [60,61,62,63,64].

Type A crystallinity is typically observed in starches derived from cereals, such as corn, wheat, and oats. This type is characterized by shorter amylopectin side chains, closely spaced branching points, and a compact packing of double helices, resulting in an orthorhombic structure. Type B crystallinity, on the other hand, is commonly found in starches with longer amylopectin side chains, more distant branching points, and a more open structure, which represents a hexagonal arrangement. This type is frequently associated with starches from roots and tubers, such as cassava and potatoes. Type C crystallinity is a combination of the characteristics of types A and B, and it can be further subdivided into Ca (closer to type A) and Cb (closer to type B). Lastly, type V crystallinity is linked to native or gelatinized starches that contain compounds such as lipids and emulsifiers. This type is further classified into type VI (single intra-helical starch–lipid complex, or inclusion complex) and type VII (semi-crystalline structure resembling lamellae) [60,63,65,66,67,68]. However, compared to type A and B starches derived from plants, type C starches are less commonly found in commercial sources.

Type C starch is widely found in various plant sources. As shown in Table 1, its prevalence is particularly notable in some potential commercial sources, including certain legumes (such as peas and chickpeas) and fruit seeds (such as loquat, jabuticaba, annatto, and bacupari), which may be available commercially, though not on a large scale or in significant quantities. However, starches derived from metamorphic seeds and stems, including tubers and rhizomes, are highlighted as primary sources. This was demonstrated in studies by Da Costa et al. [69], where starch was extracted from pine nut seeds (Araucaria angustifolia), revealing Type C crystallinity with relative crystallinity ranging from 25.43 to 28.43%. Similarly, Pelissari et al. [70] extracted starch from green plantains (Musa paradisiaca), which exhibited 22.8% relative crystallinity, also displaying Type C crystallinity.

In addition, Type V crystallinity has been observed in non-conventional native starches, such as those extracted from microalgae [38] and mango seeds [61]. This crystallinity type originates from the formation of complexes with endogenous lipids during biosynthesis, resulting in a distinctive helical conformation that produces a Type V diffraction pattern. It should be noted, however, that diffraction patterns can be influenced by several factors, including amylose and amylopectin content, cultivation conditions, physiological state at harvest, biological origin, and botanical source [63,71,72].

6. Nutritional and Functional Characteristics of Non-Conventional Starches

Starch is regarded as a macronutrient of high nutritional importance, playing a pivotal role in human diets. Its digestibility is influenced by various factors, including differences in crystalline structures (Types A, B, C, and V), granule morphology, the amylose-to-amylopectin ratio, and other physicochemical properties. Starches are categorized based on their digestibility rates into three fractions: rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) [66,73,74].

These fractions are classified according to their glycemic response. RDS is rapidly hydrolyzed by enzymes in the small intestine, typically within 20 min, leading to a swift increase in blood glucose levels. SDS follows a similar digestive pathway but at a slower rate, taking between 20 and 120 min to release glucose, which results in a more moderate glycemic response. In contrast, RS is resistant to enzymatic degradation in the gastrointestinal tract. It escapes digestion in the small intestine, acting instead as dietary fiber and serving as a fermentative substrate in the colon [73,75,76].

The prebiotic potential of RS is linked to its fermentation in the colon by beneficial bacteria, such as those from the Bifidobacterium and Lactobacillus genera. This process produces short-chain fatty acids (SCFAs), including acetic, succinic, and butyric acids, which are absorbed in the colon. These SCFAs confer numerous health benefits, such as improving cholesterol levels and reducing the pH of the intestinal environment, thereby enhancing mineral absorption. Additionally, starches rich in RS have been employed in managing type 2 diabetes and obesity due to their low glycemic response and associated health benefits [63,77].

Currently, RS is classified into five distinct types, each characterized by specific mechanisms of resistance to digestion in the human body, as detailed in Table 2. For example, the resistance of Type 1 resistant starch (RS1) is primarily due to the structural matrix in which the starch is embedded, rather than the properties of the starch granules themselves. A novel concept has emerged in the study of resistant starches, referred to as multiple resistant starches. This term describes starches that exhibit resistance characteristics of two or more different types within a single sample. Although a clear classification does not yet exist, this concept may present unique functional implications [78].

Non-conventional starch sources, especially those containing Type 2 RS, are gaining attention for their potential commercial applications. Some of these sources are also categorized as Type 1 resistant starch [48,79]. However, many studies in the literature often report these starches in their native form, which may not accurately reflect their behavior in practical applications. Since starch is typically consumed after cooking, it is essential to account for the effects of processing, such as gel formation and retrogradation, to provide a more accurate representation of how these starches perform in the human body.

Zhang and Hamaker [80] demonstrated this phenomenon with green banana starch, highlighting it as a promising market source. In its native form, green banana starch contains 84.5% RS, but when cooked, it transforms into a significant source of SDS, with its SDS content increasing from 8.7% to 19.1%. In comparison, commercial starches from waxy corn decreased from 42.8% to 14.7%, while normal corn starches decreased from 48.4% to 14%, and potato starch saw only a slight increase from 8.4% to 9.3%.

Further studies by Purwandari et al. [81] and Patiño-Rodríguez et al. [46] on kidney bean starch (Canavalia ensiformis) and mango seed starch, respectively, confirmed that cooking increases starch digestibility and alters the distribution of starch fractions. For kidney bean starch, digestibility rose by over 25% with extended cooking times, while mango seed starch exhibited slower digestion in the cooked form, with a significant increase in SDS and RDS fractions, but a 61% reduction in RS content.

Green bananas, with RS content exceeding 80%, are among the most extensively studied non-conventional starch sources [82]. Other significant sources of RS include plantains (Musa sp.), with 90.0% RS, and pumpkin species (Cucurbita moschata Duch. ex Poir. and Cucurbita maxima Duch.), with RS levels around 92.7% [51,83]. The amylose content in these starches plays a crucial role in determining their RS fractions. Studies by Gani et al. [84] found that an amylose content ranging from 31.8% to 40.7% results in RS levels between 85.4% and 92.8%. In contrast, Mondal et al. [85] reported low RS levels (0.4% to 2.3%) in native starches from aromatic rice varieties, which had amylose contents ranging from 0.7% to 29.1%.

Table 2. Classification of resistant starch (RS) according to its basic characteristics and classification system.

Type	Characteristic	Description	Sources	Figure	References
RS I—Resistant Starch Type 1	Physically inaccessible starch	Barrier effect of cell walls or protein isolation.	Coarsely ground or whole grains (Durum wheat), legumes, and seeds		[86,87,88]
RS II—Resistant Starch Type 2	Granular starch with B or C polymorph	Naturally occurring resistant starch granules.	High-amylose corn starch, raw potato, green bananas, some legumes like brown lentils (Lens culinaris Medikus), high-amylose starches		[75,89]
RS III—Resistant Starch Type 3	Retrograded starch	Resulting from crystallization formed during cooling and storage after starch granule gelatinization.	Cooked and cooled starch-rich foods		[73,89,90]
RS IV—Resistant Starch Type 4	Chemically modified starches	Introduction of chemical functional groups to starch	Cross-linked starch and octenyl succinate starch, carboxymethylated starch		[40,86]
RS V—Resistant Starch Type 5	Amylose-lipid complex	Resulting from the interaction between starch and lipids, where amylose and the long-branched chains of amylopectin form single-helix complexes with free fatty acids.	High-amylose starch complexed with stearic acid		[87,89,90]

Table 2. Classification of resistant starch (RS) according to its basic characteristics and classification system.

Type	Characteristic	Description	Sources	Figure	References
RS I—Resistant Starch Type 1	Physically inaccessible starch	Barrier effect of cell walls or protein isolation.	Coarsely ground or whole grains (Durum wheat), legumes, and seeds		[86,87,88]
RS II—Resistant Starch Type 2	Granular starch with B or C polymorph	Naturally occurring resistant starch granules.	High-amylose corn starch, raw potato, green bananas, some legumes like brown lentils (Lens culinaris Medikus), high-amylose starches		[75,89]
RS III—Resistant Starch Type 3	Retrograded starch	Resulting from crystallization formed during cooling and storage after starch granule gelatinization.	Cooked and cooled starch-rich foods		[73,89,90]
RS IV—Resistant Starch Type 4	Chemically modified starches	Introduction of chemical functional groups to starch	Cross-linked starch and octenyl succinate starch, carboxymethylated starch		[40,86]
RS V—Resistant Starch Type 5	Amylose-lipid complex	Resulting from the interaction between starch and lipids, where amylose and the long-branched chains of amylopectin form single-helix complexes with free fatty acids.	High-amylose starch complexed with stearic acid		[87,89,90]

7. Thermal Properties of Non-Conventional Starches

The thermal characteristics of starches, encompassing both conventional and non-conventional varieties, include properties such as thermal conductivity, thermal diffusivity, and specific heat. Significant functional properties include gelatinization and retrogradation, which represent molecular-level changes occurring within the starch granule. Gelatinization is initiated by supplying energy (typically in the form of heat) to a mixture of water and starch, resulting in structural changes or transitions within the starch granules. These changes may include swelling, loss of crystallinity, leaching of amylose, and granule rupture. Conversely, retrogradation refers to the progressive realignment or reassociation of amylose/amylose, amylose/amylopectin, or amylopectin/amylopectin chains into an ordered structure during storage at low temperatures [6,91,92].

The composition of starches is directly related to their thermal properties, with several major factors influencing these properties. Key factors include the amylose-to-amylopectin ratio, which is characterized by an inverse relationship between amylose content and granule swelling. Additionally, agronomic factors such as botanical origin, climate, geographical location, management practices, harvesting techniques, and ripeness play significant roles. The type and degree of starch modification—whether chemical, physical, or enzymatic—also contribute to these thermal properties. Furthermore, the presence of proteins, lipids, and phosphorus, as well as the size and shape of starch granules, the degree of double helix packing, and crystallinity are critical factors that influence starch thermal characteristics [6,8,92,93].

Thermal properties, such as gelatinization, are commonly assessed using differential scanning calorimetry (DSC). Gelatinization temperatures, including onset (To), peak (Tp), and conclusion (Tc), are associated with the energy required for the initial gelatinization of starch. The gelatinization enthalpy (ΔH) reflects the extent of double helix disruption during the gelatinization process, indicating the degree of molecular disorder. Non-conventional starches may exhibit superior thermal properties compared to conventional starches. A study conducted by Zhu et al. [93] analyzed the thermal characteristics of black and white pepper starches in comparison to commercial corn starch. The gelatinization temperatures for black and white pepper starches were found to be significantly higher (Tp = 84 °C and 85 °C, Tc = 91.8 °C and 94 °C, ΔH = 13.05 and 13.09 J·g⁻¹, respectively) than those of corn starch (To = 66.5 °C, Tc = 80.0 °C, ΔH = 15.53 J·g⁻¹). This difference was attributed to the higher porosity of corn granules, which compromises granule integrity and may lower gelatinization temperatures. Furthermore, the degree of packing of adjacent double helices and the chain length of the pepper starches were significantly greater than those observed in corn starch.

High values were also reported by Felisberto et al. [39], where starch extracted from three different parts of young bamboo (Bambusa tuldoides) exhibited an onset thermal transition temperature (To) ranging from 81.47 to 82.20 °C, with the peak thermal transition temperature approaching 85.2 °C. These findings indicate that bamboo starch demonstrates greater thermal stability compared to conventional starches, such as corn and potato.

Another study conducted by Felisberto et al. [21] on starch extracted from peach palm fruit (Bactris gasipaes var. gasipaes) revealed lower calorimetric values compared to commercial starches, with a To of 52.87 °C, Tp of 58.30 °C, and ΔH of 8.76 J·g⁻¹. In terms of retrogradation rate, peach palm starch exhibited a To of 47.57 °C, Tp of 54.69 °C, and ΔH of 1.98 J·g⁻¹, resulting in a retrogradation rate of 22.64%. These findings contrast with the values reported by Barros et al. [49], which indicated retrogradation rates of 49.3% for ariá starch and 31.4% for corn starch. This suggests that peach palm starch is suitable for food applications where stability and texture retention over time are critical, including baked goods (due to its lower retrogradation rate), dairy products (enhancing creaminess and preventing syneresis), and frozen foods.

This heterogeneity in starch properties, whether commercial or non-commercial, underscores the potential for unique and varied characteristics. This diversity positions these starches as viable alternatives for substitution in both food and non-food products, enabling the selection of starches based on the specific requirements of each application. Studies have demonstrated the diversity in thermal properties of non-conventional starches, which may exhibit varying thermal stabilities and retrogradation rates. The definition of these characteristics should be guided by specific applications, highlighting the urgent need for further research to understand and optimize the use of these starches in commercial products.

8. Modification of Non-Conventional Starches

The use of potential alternative starch sources presents several advantages, including sustainability, recycling of residues, utilization of by-products, availability, and technological benefits compared to conventional starch. However, the diverse botanical origins of these sources result in unique morphological, physicochemical, thermal, and paste properties, which may present limitations. Notable limitations include low water solubility, rapid retrogradation, low thermal stability, low stability during freezing and thawing cycles, reduced emulsification capacity, high syneresis, and low shear capacity, all of which restrict their applicability in food and non-food matrices. Nevertheless, the application of various modification techniques emerges as a viable alternative to enhance or adapt one or more characteristics of native starches for specific uses [7,34,64,69].

The modification of native starches aims to alter their physicochemical properties and confer additional functional attributes. Several modification procedures have been employed, including pre-gelatinization, esterification, acid hydrolysis, and oxidation, which are among the most commonly used methods. These techniques are generally categorized into three groups: physical modification, chemical modification, and enzymatic modification, as illustrated in Figure 2. These techniques have become increasingly prevalent due to the superior results achieved when applied either individually or in combination. However, several factors, such as starch availability, cost, starch recovery, and intended application, are key considerations that influence the selection of the technique and starch source to be utilized [7,63,94,95]

In enzymatic modification, various hydrolytic enzymes are utilized to act on the starch molecule, promoting the hydrolysis of glycosidic bonds, the debranching of starch granules, and/or the formation of new glycosidic bonds. This enzymatic action results in alterations to the starch structure and its properties, producing products with varying molecular sizes, amylose/amylopectin ratios, molecular weights, degrees of polymerization, and branching chain distributions. These modifications impact starch properties, leading to reduced retrogradation during storage and a lower glycemic index. Furthermore, enzymatic modification can impart antimicrobial and antioxidant properties. The process is also noted for its sustainability, high specificity, and the ability to produce products with targeted functionalities [7,96,97,98,99,100].

The selection of enzymes used in starch modification significantly impacts the physicochemical and biological properties of starches and is determined based on specific application requirements. The primary enzymes used include α-amylase, β-amylase, cyclodextrinase, pullulanase, and isoamylase. Despite the numerous advantages of enzymatic modification, challenges such as high costs and extended processing times persist, hindering industrial implementation. Recent studies have reported the combined use of enzymatic modification with other techniques to mitigate these disadvantages and maximize the benefits of enzymes. Such approaches may be employed in conjunction with physical and/or chemical methods [98,99,101].

Physical modification is characterized by its simplicity, low cost, and absence of chemical reagents, rendering it a sustainable technology. This process involves altering the packing arrangements of starch molecules, which impact functional properties, including molecular arrangement, degree of crystallinity, particle size, and, consequently, technological properties such as texture, solubility, gelatinization behavior, and paste characteristics [7,102,103].

Physical modification processes can be categorized into two main types: thermal and non-thermal. Thermal processes utilize heat to break intermolecular bonds, leading to the destruction of starch granule structures in the presence of water and heat, resulting in pregelatinized and granular starches. Key techniques within this category include cooking, pre-gelatinization, autoclaving, and hydrothermal treatments. An illustrative example is the physical modification of sweet potato starch (Ipomoea batatas L.), where a moisture content of 30% at 110 °C for 8 h significantly increased the resistant starch (RS) content by over 100% when used to replace 20% of wheat flour in biscuit formulations. This modification also reduced the glycemic index of the biscuits, shifting it from high to medium, without altering sensory acceptance, thickness, or spreadability compared to the control samples, although a 7.04% reduction in diameter was observed [104]. Conversely, non-thermal processes alter the physicochemical properties of starch without breaking intermolecular bonds, thereby preserving its granule structure. This category encompasses techniques such as ultrasound, high hydrostatic pressure, pulsed electric fields, freezing and thawing, cold plasma, electron beam treatment, and gamma irradiation [60,91,105,106,107,108,109].

Chemical modification involves the application of various chemical reagents to alter the starch structure by introducing functional groups, such as hydroxypropyl, amine, and carboxyl groups, into the starch hydroxyl groups without affecting size distribution or morphology. This results in changes to the physicochemical properties, rendering the starch suitable for specific industrial applications. The type of chemical modification employed is contingent upon the chemical product utilized and the bonds formed between the functional groups and the hydroxyl groups. Key methods include acid hydrolysis, oxidation, cross-linking, esterification, and etherification, which may be used alone or in combination [98,109,110].

Chemical modification employs reagents classified as mono- and bifunctional, with monofunctional reagents introducing a single functional group into the starch structure, while bifunctional reagents interact with two or more hydroxyl groups of the starch. Key changes induced by chemical modification in non-conventional starches include alterations in viscoamylographic properties, retrogradation rate, morphological characteristics, mechanical strength, gelatinization temperature, emulsification, and resistance to freezing and thawing. The degree of modification is influenced by factors such as reagent type, starch structure (granule size), and botanical source [109,111,112,113].

The modification of non-conventional starches aims to enhance their properties for specific industrial applications by overcoming inherent limitations such as low freeze–thaw stability, high syneresis, and reduced emulsification capacity.

Table 3. Applications of potential non-conventional starches in food and non-food systems and their effects on the technological characteristics of these products.

Botanical Source	Starch	Quantity Applied	Applied Matrices	Technological Effect	References
Avocado Seed (Persea americana Mill.)	Native and Modified—Cross-linking (sodium tripolyphosphate at 6%)	25	Instant Soup	- Greater viscosity stability during storage; - High acceptance (5.29) on a 1–7 scale, with both starch types well evaluated, especially the modified starch, particularly for viscosity.	[115]
Arrowroot (Maranta arundinaceae L.)	Native	10, 15, 20%	Panettone	- Higher substitutions increased L*, a*, and b* parameters by up to 100% compared to the standard sample; - Up to 20% increase in hardness; - No changes in panettone firmness; - Higher starch additions decreased pH by 7.37%, showing a protective effect from a microbiological perspective; - Starch reduced water activity by 5%, improving product shelf-life; - Dough had elongated alveoli grains with ideal hydration; - Increased flavonoid content (from 0.3 to 1.83 mg of quercetin) and anthocyanins (0.03 to 1.41 mg/g).	[116]
Pine Nut Seeds (Araucaria angustifolia)	Native and Modified (Acid hydrolysis—HCl)	Native Starch, 6 Dextrose, and 12 Dextrose hydrolyzed starch	β-Carotene Preservation	- Up to 50% increase in β-carotene stability; - Incorporation of 12% pine nut starch maintained color characteristics (L*, a*, b*) during storage, with a color loss reduction of up to 15%; - Pine nut starch effectively preserved β-carotene stability.	[117]
Sago (Metroxylon sp.)	Native and Modified (Hydrolyzed-Hydroxypropylated)	10% wheat flour substitution with native, hydrolyzed, hydroxypropylated, and doubly modified starch	Frozen Dough and Hamburger Buns	- Hydroxypropylated and doubly modified starches maintained dough characteristics and water absorption, while native and hydrolyzed starches increased development time by over 100%; - Native and chemically modified starches decreased dough extensibility and energy by up to 20%; - No change in freeze–thaw stability; - Native and chemically modified starches reduced bun moisture by up to 8%, enhancing microbiological stability; - Up to 40% reduction in bun specific volume; - Hydroxypropylated starch maintained superior texture characteristics (hardness, elasticity, cohesiveness) with losses of less than 15% compared to the standard sample’s 75%; - Hydrolyzed sago starch had good scores and acceptable sensory characteristics, with hydroxypropylated starch scoring over 10% higher than the standard sample in analyzed parameters.	[118]
Sweet Potato (Ipomoea batatas) and Red Bean (Phaseolus vulgaris)	Chemically Modified (3%, octenyl succinic anhydride (OSA))	Up to 75% oil substitution	Mayonnaise	- No changes in color, aroma, or taste; - Over 10% increase in color parameters (L* and a*) compared to the standard sample; - Starch use resulted in a structure less gel-like than standard mayonnaise; - Samples containing potato and bean starch showed no phase separation; - Higher acceptance in texture (↑ 16.62%), consistency (↑ 11.64%), and overall acceptability (6.55%); - Successfully replicated the structure, texture, and taste of real mayonnaise.	[119]
Fava Bean (Vicia faba L.)	Native	3%	Panela Cheese	- Fava bean starch addition did not alter probiotic strain viability compared to the control; - Increased moisture by up to 10%, without altering fat and protein content; - Produced a very open amorphous microstructure, indicating low adhesion to the food matrix; - Up to 35% reduction in cheese firmness; - Lower sensory acceptance for compactness, hardness, moisture, softness, and creamy flavor compared to standard cheese.	[120]
Sweet Potato (Ipomoea batatas L.)	Modified: Chemically (citric acid 0.2 M) and Physically (moisture content of 30% at 110 °C for 8 h.)	20% wheat flour substitution with physically and chemically modified starch	Biscuit	- Over 100% increase in resistant starch (RS) content compared to the control sample; - Reduced glycemic index, shifting from high to medium; - Decrease in average biscuit diameter (7.04%); - No changes in thickness, spreadability, or sensory acceptance compared to the control biscuit.	[104]
Kiwi (Actinidia deliciosa ‘Huayou’)	Native	10–20% wheat flour substitution with native kiwi starch	Chinese Steamed Bread	- Kiwi starch (KS) diluted gluten network, reducing dough resistance by up to 20% with higher substitution levels; - Excellent performance in controlling postprandial glucose (up to 10% reduction) without significant differences in sensory quality (appearance, smell, taste, and overall acceptability); - Substitution promoted less/no mold proliferation until the 5th working day, extending shelf life.	[121]
Acorn (Quercus ilex)	Native	0.5, 1, 2, 3%	Fermented Dairy Beverage	- Lower concentrations (0.5% and 1%) resulted in over 7% increase in total solids content; - Lower concentrations (0.5% and 1%) resulted in lower syneresis rates (percentage reduction); - Starch incorporation decreased brightness L* (26.31%) and red a* (516%) in the dairy product and increased yellow b* values (41.71%); - Amounts less than 1% did not alter product characteristics.	[122]
Acorn (Quercus Suber L.)	Native (extraction with H2O and NaOH 0.3%)	100% commercial corn starch substitution	Cream	- Decreased cream brightness by up to 35%, attributed to carotenoid presence, promoting nutritional and functional enhancement of the cream; - Reduced syneresis stability compared to conventional starch by up to 50%; - Substitution created a homogeneous protein matrix with uniformly distributed starch granules.	[123]
Sweet Potato (Sree Arun)	Native	10, 20, 30%	Noodles	- 10% substitution formulation had the lowest cooking losses; - Sweet potato starch fortification reduced RDS fraction by over 12%; - RS content increased by over 25%, with the 30% formulation having the highest levels; - Glycemic index decreased by up to 12% in formulations fortified with sweet potato starch; - Promoted firmness increase in noodles by up to 40%; - Sweet potato starch substitutions had higher acceptance than the control for appearance, taste, mouthfeel, and overall acceptance, with score increases of up to 40%.	[124]
White Sorghum (Sorghum bicolor (L.) Moench)	Modified—Physically (extrusion) and chemically (phosphorylation with sodium trimetaphosphate and sodium tripolyphosphate)	17%	Extruded Snacks	- Modification was within FDA limits; - No changes in sensory acceptability.	[125]
Glutinous Rice (Oryza sativa)	Native	4, 6%	Plant-Based Egg Analog	- Adding rice starch at the given proportions resulted in lower hardness, cohesiveness, chewiness, and elasticity, but significantly increased specific gravity (by 100%); - Rice starch replicated the viscoelastic properties (storage and loss modulus) and specific volume of native eggs; - Displayed a digestion speed of over 20% compared to native eggs.	[126]
Quinoa Seeds (Chenopodium quinoa)	Modified (Chemically—Octenyl Succinate at 1, 3, 5%)	-	Pickering Emulsion	- Improved emulsifying properties at intermediate proportions; - Modified starches were better adsorbed at the oil/water interface than native starch; - Formation of predominantly elastic emulsions; - Modified starch indicated gel-like network formation with higher mechanical resistance than protein-based emulsions.	[127]
Non-Food Matrices
Champedak seeds (Artocarpus integer) and jackfruit seeds (Artocarpus heterophyllus L.)	Native	Partial substitution of 65.3% rice starch and 20% talc	Compact powder	- Maintained uniform adhesion to both paper and skin in all formulations; - Maintained adhesive properties; - Improved resistance to common transport and handling; - Promoted a smoother surface; - No significant change in color and texture characteristics; - Alternative substitutes to talc in compact powder formulations.	[128]
Taro Root (Xanthosoma sagittifolium)	Native	100%	Bioethanol	- Maximum ethanol production of 48.38 g·L−1 and productivity exceeding 55.0 g·L−1·h−1; - High yield coefficient of 0.46 and efficiency of 90%; - Taro starch was considered a promising raw material for ethanol production.	[52]
Banana Peel (Musa spp.)	Native	1.5 to 5.7%	Intravenous Tubes	- ↑ in tensile strength, being superior to 106 N/mm² and ↑ in stiffness with results exceeding 14.2 N·mm−1; - Presented as a biodegradable material, offering an alternative for the production of intravenous tubes, significantly reducing the generation and accumulation of biomedical/hospital waste; - Substitution with 2.5% yielded the best formulation for all evaluated parameters.	[129]
Water Chestnut (Trapa bispinosa)	Modified (Acid Hydrolysis—HCL 3.16 M)	0.5, 1, 2, 5, and 10%	Composite films	- Incorporation of nanoparticles ↓ water vapor permeability by 52.22%, solubility by 9.97%, and moisture by 35.05%; - Incorporation of starch nanoparticles ↑ thickness by up to 117% and ↑ tensile strength by 52.48%; - Water chestnut starch nanoparticles improved water vapor permeability, solubility, and tensile strength compared to native starch.	[130]
Rice (Assam bora)	Native and Modified Chemically (citric acid 40%)	100%	Model Medication (Paracetamol)	- No alteration in tablet uniformity; - Modified (0.39%) and native (0.39%) rice starches showed greater friability compared to native starch (0.32%); - Modified and native rice starches stood out as better disintegrants, with an efficiency of over 30%; - ↑ dissolution efficiency (up to 84.72%) compared to corn starch (76.19%); - ↓ in average dissolution time; - ↑ bioavailability of drugs, with ↑ up to 10.2% in paracetamol dissolution rate.	[131]
Avocado Seed (Persea americana Mill)	Native	100%	Textile application in cotton threads	- ↑ of 12.98% in wash resistance compared to standard starch; - ↓ an average of 50% in hairiness, resulting in improved weaving capacity and textile processing productivity; - Reduction in force and elongation capabilities showed values slightly below the performance of standard starch.	[132]
Green Bananas (Musa paradisiaca L.)	Native and Chemically Modified (Acetylation with 0.33% substitution)	100%	Nanocarriers for curcumin for oral drug delivery	- Retention ↑ to 80% of curcuminoid compounds for both nanoparticles; - Modified starch showed 15% higher controlled release compared to standard starch in SGF and SIF; - Potential source for use in the administration of curcuminoid-based drugs and nutraceuticals.	[133]
Sago	Native and Modified (Esterification—citric acid 1% (w/v))	-	Nanocarrier for Paracetamol	- Capacity of 4.00 mg·L−1 paracetamol concentration for encapsulation; - Modified starch nanoparticles promoted the controlled release ↑ of 1 h compared to native starch in 4 h; - HaCaT cytotoxicity study showed that starch citrate nanoparticles are non-toxic.	[134]
Palm Trunk (Elaeis guineensis)	Native	500 mg·L−1	Coagulant	- Removal of 100% of chemical elements manganese, zinc, and polonium; - Removal of 95.60% of copper; - Viable coagulant for semi-aerobic treatment of landfill leachates.	[135]
Mango (Mangifera indica)	Native	7 g	Bioethanol	- Production of 0.224 to 0.267% v/v ethanol through saccharification and simultaneous co-fermentation methods; - Production of 0.47 to 0.57% ethanol through separate hydrolysis and fermentation; - Production of 0.224 to 0.267% v/v ethanol through saccharification and co-fermentation methods; Production of 0.31 to 3.99% v/v ethanol through saccharification and simultaneous fermentation.	[136]
Duckweed (Landoltia punctata)	Native	100 g	Glycerol Production	- 102.72 g·L−1 in 28 h of fermentation; - Productivity of 3.67 g·L−1·h−1, the highest reported in the literature for glycerol production; - Conversion of duckweed starch to glycerol is viable and shows potential to improve the competitiveness of the glycerol industry.	[137]
Green Banana (Musa paradisiaca L.) and Dessert Banana (Musa cavendishii)	Native	0.1 g	Adsorbent	- Both starches promoted the removal of 7.4% of Thiophene; - Removal of 4.2 of 4,6-dimethyl dibenzothiophene for both starches.	[138]

SGF: Simulated Gastric Fluid; SIF: Simulated Intestinal Fluid; HaCaT: Human skin cells; FDA: Food and Drug Administration.

provides significant examples of how different modification techniques have been applied to non-conventional starches to improve their functionality. For instance, the cross-linking of avocado seed starch improved viscosity stability in instant soups, while hydrolyzed pine nut starch preserved up to 50% of β-carotene in food matrices [114]. These cases demonstrate how tailored modification approaches can adapt non-conventional starches for specific uses, extending their applicability beyond conventional systems.

While techniques such as enzymatic hydrolysis and physical pre-gelatinization are commonly used, recent studies show that combining these methods yields superior results. For example, according to Kumari and Sit [98], the combined application of methods such as physical–physical, chemical–chemical, enzymatic–enzymatic, physical–enzymatic, and chemical–enzymatic has emerged as an effective strategy for enhancing the properties of non-conventional starches for both food and non-food applications. This integrated approach can result in more significant improvements in starch properties compared to isolated modifications. For instance, Almeida et al. [115] conducted dual modification (hydrothermal treatment and α-amylase hydrolysis) on pigmented rice starch, observing increased oil absorption capacity (up to 7.8%) and milk absorption capacity (up to 5.31%), elevated gelatinization temperatures (up to 12.8 °C), and reduced cohesiveness (up to 20%), adhesiveness (up to 34%), and apparent viscosity compared to native samples or those subjected to only one of these modifications.

Table 3 illustrates various applications of non-conventional starches in both food and non-food products. It is evident that both native and modified starches, irrespective of the modification method employed, lead to substantial changes in their physicochemical characteristics, thereby influencing their technological and nutritional properties. Chemical modification, particularly through methods such as cross-linking and acid hydrolysis, remains one of the most widely utilized approaches for altering starch properties to adapt them for specific applications.

9. Recent Applications in Food and Non-Food Products

Starch is a highly versatile biomolecule with applications across a wide range of commercial and industrial sectors. In the food industry, it is utilized in various products, including sauces, jams, ice creams, candies, puddings, and meat preserves. Furthermore, its applications extend to non-food products such as adhesives, aerogels, films, and bioplastics [4,95]. These applications can be derived from different starch sources, whether native or modified, facilitating the production of a broad spectrum of products.

Table 3 illustrates the diversity of applications of non-conventional starches, encompassing both food and non-food sectors, thereby underscoring their significant industrial importance. Non-conventional starches are applied in various fields, including medicine, cosmetics, bioethanol production, and nanostructures, while also playing essential roles in diverse food products with unique characteristics, as well as in pharmaceuticals and the textile industry. Even in small quantities, the incorporation of these starches can lead to substantial changes in product properties, including texture, rheology, stability, and improved sensory acceptance, among others.

Due to their non-toxic properties and high availability, non-conventional starches have garnered interest not only in the food industry but also in the healthcare sector. They are particularly recognized for their potential applications in biodegradable medical products and as carriers for various substances in drug delivery systems. However, it is essential to note that research on the use of these non-conventional starches remains limited. This scarcity of studies can be attributed, in part, to the established presence of conventional starches in the market, whose properties are well-documented and widely recognized.

10. Final Remarks and Perspectives

Non-conventional starches are emerging as a promising alternative to conventional starches, particularly in the context of increasing demand for sustainable and multifunctional ingredients. Their unique properties, such as varying levels of amylose and amylopectin, diverse crystalline patterns, and distinct granule morphologies, enable applications that extend beyond the food sector, reaching areas such as cosmetics, pharmaceuticals, and biodegradable materials.

Despite their numerous advantages, several constraints related to their properties must still be overcome to enable industrial use. Technological limitations include low stability during freeze–thaw cycles, high syneresis, and challenges in achieving high-purity extraction. Additionally, the properties of non-conventional starches are often highly influenced by agronomic factors, seasonal variations, and processing methods, complicating the standardization required for commercial applications.

Future perspectives point to the need for integrated research exploring new combinations of physical, chemical, and enzymatic modification techniques, with an emphasis on sustainability and economic efficiency. The use of emerging technologies, such as ultrasound, cold plasma, and pulsed electric fields, combined with conventional modifications, has the potential to enhance the properties of these starches, tailoring them for specific uses and maximizing their performance.

11. Conclusions

The diversity of non-conventional starch sources reveals unique characteristics regarding morphology, chemical composition, thermal properties, and nutritional value. These attributes position them as potential candidates for commercial use, providing alternatives to conventional starches. This not only underscores the importance of regional products but also promotes the sustainable exploration and full utilization of specific raw materials, thereby creating income opportunities for small-scale producers.

Despite the existence of numerous underutilized or non-conventional starch sources, it is essential to conduct new studies that include detailed analyses of their characteristics, functional properties, and applicability in food and non-food systems. Such research is fundamental for assessing the potential of these sources and identifying necessary modifications. The utilization of non-conventional starch sources with commercial potential could play a critical role in reducing environmental impact, enhancing the value of small producers, promoting regional development, and supporting family farming through sustainable practices, while simultaneously addressing the growing industrial demand for starch and decreasing reliance on conventional sources of this component.