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Re-Valorization of Waste and Food Co-Products

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A Special Issue of Molecules (ISSN 1420-3049) belonging to the section "Green Chemistry".

Deadline for manuscript submissions: 30 November 2026 | Viewed by 12061

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Editors

Prof. Dr. Adriana Dabija

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Guest Editor

Faculty of Food Engineering, Stefan cel Mare University of Suceava, 720229 Suceava, Romania
Interests: food science and technology; food microbiology and safety; food biotechnology
Special Issues, Collections and Topics in MDPI journals

Dr. Ancuța Chetrariu

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Guest Editor Assistant

Faculty of Food Engineering, Stefan cel Mare University of Suceava, 720229 Suceava, Romania
Interests: food chemistry; food waste; valorization; food by-products

Special Issue Information

Dear Colleagues,

We are pleased to invite you to contribute to a Special Issue dedicated to the “Re-Valorization of Wastes and Food Co-Products”.

In developed nations, the overproduction of food is a growing concern, contrasting starkly with the global reality of hunger that continues to affect millions. Alongside this imbalance, a significant portion of food production results in by-products and wastes that are often underutilized or discarded, despite their potential value.

These by-products—originating from fruits, vegetables, dairy, meat, seafood, and cereals—can be rich sources of proteins, lipids, carbohydrates, dietary fiber, and complex nutraceuticals with health-promoting properties. Rather than being seen as waste, these materials can serve as valuable raw inputs for new food formulations, functional ingredients, bio-based materials, biofuels, and other bioproducts.

The emerging bioeconomy provides a strategic framework to address this opportunity. It emphasizes the sustainable transformation of renewable biological resources into value-added products, fostering circular economic models and reducing environmental impact. This approach aligns with the global goals of reducing food waste, lowering greenhouse gas emissions, and promoting sustainable development.

This Special Issue focuses on papers advancing original research and review papers for the re-valorization of food by-products and zero waste. Aspects such as agri-food by-product composition, their functional and nutritional characteristics, and their use in order to obtain new food products may be developed in this Special Issue.

In this Special Issue, original research articles and reviews are welcome. Research areas may include (but are not limited to) the following:

Extraction and recovery of bioactive compounds from food waste;
Bioconversion processes and fermentation of food by-products;
Development of functional foods and ingredients from co-products;
Waste valorization pathways;
Chemical modification and functionalization of food by-products;
Green chemistry approaches for food waste valorization.

We look forward to receiving your contributions

Prof. Dr. Adriana Dabija
Guest Editor

Dr. Ancuța Chetrariu
Guest Editor Assistant

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-anonymized peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

by-products
valorization
reutilization
zero waste
application of functional ingredients
circular economy

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Published Papers (10 papers)

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Research

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17 pages, 2880 KB

Open AccessArticle

Changes in Phenolic Compounds, Antioxidant Capacity, Color, and Microstructure of Hass Avocado (Persea americana) Peel During Ripening

by Madeleine Perucini-Avendaño, Lorraine Salgado-León, Alberto Peña-Barrientos, Vanessa Sánchez-Quezada, Rocio Campos-Vega and Guadalupe Loarca-Piña

Molecules 2026, 31(18), 3280; https://doi.org/10.3390/molecules31183280 - 16 Sep 2026

Abstract

Avocado peel is a high-value by-product rich in bioactive compounds; however, its structural and chemical integrity undergoes critical transitions during postharvest ripening. This study evaluated the influence of ripening stage (unripe, ripe, and overripe) on the chemical composition, color attributes, antioxidant capacity, and microstructural evolution of Hass avocado peel. Significant differences (p < 0.05) were observed in proximate composition and color coordinates among ripening stages. Overripe peel exhibited the highest concentration of total phenolic compounds (168.02 ± 3.28 mg GAE/g) and antioxidant capacity, determined by ABTS•+ (410.25 ± 1.01 µM TE/g) and FRAP (782.84 ± 2.62 µM TE/g). Environmental scanning electron microscopy (ESEM) and confocal laser scanning microscopy (CLSM) revealed progressive degradation of cuticular layers and chlorophyll-containing cells during ripening. Surface fractal dimension texture (FDT) significantly decreased from 1.54 ± 0.02 in unripe peel to 1.47 ± 0.01 in overripe peel, indicating a reduction in surface structural complexity. Principal component analysis (PCA) explained 99.0% of the total variance and revealed a clear association between FDT, chlorophyll fluorescence (λex = 450 nm), and color parameters, while total phenolic content and antioxidant capacity were associated with advanced ripening stages. These findings demonstrate that FDT is a promising indicator of peel senescence and suggest that structural disassembly during ripening is closely associated with enhanced phenolic extractability and antioxidant potential. This work provides a comprehensive framework for monitoring postharvest quality and supports the valorization of avocado peel as a source of bioactive compounds for food applications. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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23 pages, 5795 KB

Open AccessArticle

Technofunctional Properties and Proteomic Profiling of Sesame Cake Protein Isolates Obtained by Green Extraction Methods and Treated with Cold Plasma

by Emine Gizem Acar, Ozge Nur Ozturk, Celale Kırkın, Ekin Sonmez, Huseyin Cimen and Derya Kahveci

Molecules 2026, 31(15), 2638; https://doi.org/10.3390/molecules31152638 - 29 Jul 2026

Viewed by 648

Abstract

The demand for plant-based proteins has been steadily increasing; however, their functionality when applied in food product formulations requires comprehensive evaluation and, when necessary, deliberate modification to ensure that it mimics that of animal-derived proteins. In the present study, protein was extracted from sesame cake, a by-product of sesame oil production, through conventional alkaline extraction, with or without ultrasound or enzymatic pretreatments. Cold plasma treatment was subsequently applied to sesame cake proteins (SCPs) to induce structural modifications. Both the extraction method and cold plasma treatment markedly influenced the compositional and technofunctional properties of the SCPs, including the protein purity, amino acid profile, color, structural integrity, thermal stability, solubility, emulsifying capacity, foaming behavior, and proteomic profile. Importantly, combined ultrasound and cold plasma treatments altered the proteomic landscape, leading to the downregulation of proteins associated with allergenicity and thereby mitigating the adverse effects of SCPs. Notably, this study provides the first demonstration of the interplay between the extraction method and protein responsiveness to cold plasma treatment. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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14 pages, 6290 KB

Open AccessArticle

Fruit Pomace as a Functional Ingredient in Wheat Biscuits: Mineral Composition, Colour Characteristics, and Quality Evaluation of Peach Pomace-Enriched Biscuits

by Sina Cosmulescu and Maria Bianca Mandache

Molecules 2026, 31(15), 2633; https://doi.org/10.3390/molecules31152633 - 29 Jul 2026

Viewed by 399

Abstract

Fruit pomace represents a valuable by-product of the fruit processing industry that can be reutilized to improve the nutritional quality of bakery products while contributing to sustainable waste valorisation. This study evaluated the effect of partially replacing wheat flour with apple, sour cherry, and peach pomace (5–15%) on the mineral composition and colour characteristics of biscuits and performed a detailed physicochemical and sensory assessment of biscuits enriched with peach pomace. Biscuits were prepared by substituting wheat flour with 5%, 10%, and 15% fruit pomace. Mineral composition and colour parameters were determined for biscuits containing all three pomace types. Based on the initial screening, peach pomace was selected for further physicochemical and sensory analyses. Fruit pomace significantly improved the mineral composition of biscuits. Sour cherry pomace increased Ca, Cu, and Mg contents, whereas peach pomace enhanced Fe, K, Mg, and Zn levels. Pomace addition also affected colour, resulting in lower lightness (L*) and higher redness (a*) and yellowness (b*), depending on pomace type and concentration. In peach pomace biscuits, increasing the substitution level led to higher moisture and acidity, while biscuit diameter and thickness decreased because of gluten network dilution. Sensory evaluation showed that biscuits containing 5–10% peach pomace achieved the highest scores for colour, aroma, taste, and overall acceptability. Fruit pomace can be successfully incorporated into wheat biscuits to improve their mineral composition while maintaining satisfactory quality attributes at appropriate substitution levels. The applied two-step approach identified peach pomace as the most suitable ingredient for biscuit fortification and supports the sustainable valorisation of fruit processing by-products in bakery applications. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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19 pages, 1219 KB

Open AccessArticle

Comparative Analysis of Oligosaccharide and Phenolic Profiles in White and Red Grape Pomace from California

by Bruna Paviani, Xueqi Li, Han Peng, Mara Baller, Selina C. Wang and Daniela Barile

Molecules 2026, 31(14), 2530; https://doi.org/10.3390/molecules31142530 - 21 Jul 2026

Viewed by 720

Abstract

The substantial volume of agrifood processing side streams represents a global sustainability challenge that requires transformation of agricultural residues into high-value molecular components. Grape pomace (GP) is a major winemaking co-product whose chemical diversity remains underutilized due to a lack of high-resolution structural data. This study applies advanced analytical platforms to provide a comprehensive molecular characterization of oligosaccharides (OS) and phenolics in GP from four grape varieties (Chardonnay, Sauvignon Blanc, Pinot Noir, and Merlot) from California. Results demonstrate that the molecular signature of the material is highly dependent on the variety and its corresponding processing; white wine pomaces exhibited significantly higher residual sugars and generally greater OS diversity compared to red wine pomaces. Using LC-Q-ToF-MS, 39 oligosaccharides were identified, primarily composed of hexoses and pentoses. Characterization of the OS building blocks via LC-QqQ-MS revealed the dominance of glucose and fructose, followed by arabinose and xylose. In parallel, targeted phenolics quantification by UPLC-DAD showed that (+)-catechin and (−)-epicatechin accounted for up to 50% of quantified phenolics in Chardonnay pomace and 45% in Pinot Noir pomace. This work highlights the molecular intricacies of GP, providing a compositional foundation for its targeted valorization. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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19 pages, 11179 KB

Open AccessArticle

Valorization of Animal-Derived By-Products Through Microencapsulation of Heme and Non-Heme Iron by Vacuum Foam Drying: Development of Functional Gummy Candies

by Carlos A. Ligarda-Samanez, Eliana Villano-Limache, David Choque-Quispe, Elibet Moscoso Moscoso, Henry Palomino Rincón, Fredy Taipe Pardo, José C. Arévalo-Quijano, Dante Fermín Calderón Huamaní, Jackson M’coy Romero Plasencia, Justina Cervantes Carrión, Reynaldo Sucari-León, Jorge Apaza-Cruz and Daniela Isabel Dayan Ortega-Révolo

Molecules 2026, 31(13), 2322; https://doi.org/10.3390/molecules31132322 - 2 Jul 2026

Viewed by 632

Abstract

Iron deficiency and associated anemia remain major public health concerns, requiring innovative food fortification systems with adequate technological and sensory performance. This study aimed to develop a multicomponent fortified gummy candy using heme iron from Cavia porcellus erythrocytes, non-heme iron from Feranin^®, and elderberry juice, integrated through microencapsulation and stabilized by vacuum foam drying. Erythrocytes were isolated, dehydrated, and microencapsulated in a tara gum–maltodextrin matrix, yielding a powder with 1.49 mg Fe/g dry matter. The microencapsulates exhibited compact morphology, lower polydispersity, and negative ζ potential, indicating suitable surface stability. Three gummy formulations (F1–F3) were prepared with different proportions of encapsulated erythrocytes, non-heme iron, and elderberry juice. Iron content increased significantly from 0.21 to 0.89 mg Fe/g of gummy candy. The formulations showed variations in water activity (0.84–0.88), moisture (33.79–40.22%), pH (4.64–6.15), soluble solids (41.00–46.67 °Brix), phenolic compounds (0.80–1.14 mg GAE/g), flavonoids (0.13–0.27 mg QE/g), and antioxidant capacity (1.53–3.75 µmol TE/g). FTIR and SEM confirmed structural preservation and matrix integration. Sensory evaluation showed comparable overall acceptability among formulations, with F3 showing higher mean ranks for flavor and texture. Overall, vacuum foam drying was a feasible strategy for valorizing animal-derived by-products in fortified gelled confectionery. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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12 pages, 642 KB

Open AccessArticle

Development of a Hop Functional Analog Derived from a Global Agrofood By-Product: Roasted Coffee Silverskin

by Nadia Guzińska, Maria Dolores del Castillo and Edyta Kordialik-Bogacka

Molecules 2026, 31(7), 1099; https://doi.org/10.3390/molecules31071099 - 27 Mar 2026

Viewed by 917

Abstract

Roasted coffee silverskin (RCSS) is a by-product of coffee production characterized by its content of phenolic compounds, including those contributing to bitterness. The aim of this study was to evaluate RCSS as an analog for hops in the production of non-alcoholic beer. Beers were developed using hops, RCSS, or a combination of both. Their sensory and physicochemical properties were evaluated, including bitterness, total phenolic content, and antioxidant capacity. Compared to hopped beer, the RCSS beer exhibited a significantly higher original gravity (7.11°P vs. 6.70°P), apparent extract (6.52°P vs. 6.20°P), and darker color (18.02 vs. 4.65 EBC). The total phenolic content was also significantly higher in the RCSS beer, reaching 0.51 ± 0.03 mg CGA/mL, which represents a 34% increase compared to the hopped variant. Importantly, the addition of RCSS had no negative effect on fermentation process. Moreover, the RCSS beer was characterized by improved overall sensory quality. These results indicate that RCSS is an innovative, sustainable alternative to hops, enhancing both sensory and functional properties while supporting zero-waste brewing strategies. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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26 pages, 1448 KB

Open AccessArticle

Unlocking the Potential of Natural Deep Eutectic Solvents for the Valorization of Different Biological Materials

by Jovana Grbić, Slađana Davidović, Mihajlo Bogdanović, Miona Miljković, Predrag Petrović, Dušan Mijin and Aleksandra Djukić-Vuković

Molecules 2026, 31(5), 835; https://doi.org/10.3390/molecules31050835 - 2 Mar 2026

Viewed by 1336

Abstract

Extractions with natural deep eutectic solvents (NADESs) as tunable, biocompatible and green solvents are a new widely applicable platform in cascading fractionation of highly complex biological materials. Roles of NADESs can be multiple, from extraction of phenolics and polysaccharides to stabilization or even support of biocatalysts and extracted compounds in further bioprocessing. Their utilization offers alternative valorization routes in comparison to conventional extractions, decreasing the GHG emissions of underexploited wasted biomass and fossil-based solvents. This study examined the potential of different NADESs as solvents in fractionation of three distinctive biological materials—corn stalks, common nettle, and mycelium of the higher fungus Fomes fomentarius. NADESs were used for delignification and extraction processes, and selected extracts were tested as substrates for lactic acid bacteria (LAB) with an aim to enhance them through microbial biotransformation. For this purpose, D-glucose–glycerol (1:3), betaine–1,3 propanediol (1:4), and betaine–glycerol (1:2) NADESs were selected. According to the results, betaine–glycerol NADES was the most promising solvent for achieving the highest delignification rate and the highest yields of extracted polyphenols and polysaccharides. Moreover, the obtained extracts showed the ability to serve as growth media for LAB, emphasizing the possibility of establishing novel LAB-fortified products, aligning with circular and zero-waste biorefinery principles. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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20 pages, 3139 KB

Open AccessArticle

Yeast as a By-Product from Wine and Beer Production: Comparative Evaluation of Physico-Chemical Composition

by Ionuț Avrămia, Adriana Dabija, Mircea Oroian, Larisa Caisin, Vitalii Agapii, Aurelian Rotaru and Ancuta Chetrariu

Molecules 2026, 31(2), 280; https://doi.org/10.3390/molecules31020280 - 13 Jan 2026

Viewed by 1045

Abstract

The trend toward sustainable protein substitutes is driven by growing concerns about food security, sustainability, and human health. Spent brewer’s yeast and wine lees are two by-products of the beer and wine industry with high potential, owing to their complex composition, which remains insufficiently exploited. The purpose of this study was to perform a comparative analysis of the two by-products under two different drying techniques to observe if there are significant changes in composition: oven-drying and freeze-drying. Two samples of wine lees from producers in the Republic of Moldova were used—Asconi Winery and Cricova Winery (Republic of Moldova)—as well as a sample of spent brewer’s yeast offered by Efes Vitanta Moldova Brewery. The samples were characterized in terms of physicochemical properties, antioxidant activity (total polyphenol content (TPC), individual polyphenol content, and DPPH assay scavenging activity), color, mineral content, structural composition (FT-IR analysis), and microstructure, as well as organic acid and B vitamin content. The highest protein content was recorded in the samples from Cricova (45.35–46.81%). Regarding the polyphenols, the oven-dried Efes sample exhibited a TPC value of 3.98 mg GAE/g, while the highest DPPH value of 88.92% was observed in the Asconi sample. All analyzed samples showed a diverse composition of individual phenolic compounds, including 4-hydroxybenzoic acid, vanillic acid, caffeic acid, and rosmarinic acid. Wine lees samples have the highest content of B vitamins, with vitamin B3 being the most abundant across all samples, followed by vitamin B6. The microstructural examination revealed autolyzed yeast cells, with more permeable cell walls, favorable to subsequent valorization treatments, and in some cases, cells form clusters in a mother-daughter junction due to serial re-pitching. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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27 pages, 4066 KB

Open AccessArticle

Brewers’ Spent Grain from Different Types of Malt: A Comprehensive Evaluation of Appearance, Structure, Chemical Composition, Antimicrobial Activity, and Volatile Emissions

by Aleksander Hejna, Joanna Aniśko-Michalak, Katarzyna Skórczewska, Mateusz Barczewski, Paweł Sulima, Jerzy Andrzej Przyborowski, Hubert Cieśliński and Mariusz Marć

Molecules 2025, 30(13), 2809; https://doi.org/10.3390/molecules30132809 - 30 Jun 2025

Cited by 7 | Viewed by 2607

Abstract

Beer is the third most popular beverage in the world, and its production is distributed uniformly between the biggest continents. Considering the environmental aspects, the utilization of brewing by-products, mainly brewers’ spent grain (BSG), is essential on a global scale. The beer revolution, lasting over a few decades, significantly diversified the beer market in terms of styles, and therefore, also its by-products, which should be characterized appropriately prior to further application. Herein, the presented study investigated the unprecedented number of 22 different variants of brewers’ spent grain, yielded from the production of various beer styles, enabling their proper comparison. A comprehensive by-product characterization revealed an almost linear relationship (Pearson correlation coefficients exceeding 0.9) between the color parameters (L*, a*, browning index) of beer and generated spent grain, enabling a prediction of BSG appearance based on beer color. Applying wheat or rye malts increased the content of extractives by over 40%, reducing cellulose content by as much as 45%. Thermal treatments of malts (kilning or smoking) also reduced extractive content and limited antioxidant activity, often by over 30%. A lack of husk for wheat or rye reduced the crystallinity index of spent grain by 21–41%, while the roasting of barley efficiently decomposed the less stable compounds and maintained the cellulose crystalline structure. All the analyzed BSG samples were characterized by low volatile emissions and very limited antimicrobial activity. Therefore, their harmfulness to human health and the environment is limited, broadening their potential application range. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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Review

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25 pages, 2410 KB

Open AccessReview

Valorization of Plant-Based Food By-Products Through Green Extraction of Bioactive Compounds for Functional Food

by Cristina-Anca Danciu, Alina-Georgeta Mag, Cristian Stanciu, Livia Vidu and Mirela Stanciu

Molecules 2026, 31(4), 646; https://doi.org/10.3390/molecules31040646 - 13 Feb 2026

Cited by 11 | Viewed by 2669

Abstract

The revalorization of food processing by-products represents a critical strategy for enhancing resource efficiency and advancing circularity within the food system. This review examines the potential of three major plant-based agro-industrial by-products—fruit and vegetable residues, brewer’s spent grain, and spent coffee grounds—as sources of high-value functional ingredients. These by-products contain bioactive compounds, including dietary fibers, polyphenols, proteins, peptides, oils, and antioxidants, that can be recovered using emerging green extraction and bioprocessing technologies. Conventional extraction methods are progressively being replaced or hybridized with enzyme-assisted, ultrasound-assisted, microwave-assisted, and deep eutectic solvent techniques to improve yield, reduce solvent consumption, and preserve bioactivity. The recovered compounds have demonstrated promising applications as gelling agents (pectin), natural colorants and antioxidants, protein-enriched flours, prebiotic fibers, and bioactive extracts for functional food and nutraceutical formulations. However, challenges persist in standardizing feedstock composition, scaling continuous extraction processes, ensuring safety and regulatory compliance, and generating robust techno-economic and life-cycle assessments to validate sustainability claims. This review synthesizes biochemical composition data, processing pathways, food applications, and regulatory considerations, and identifies research priorities for developing integrated, scalable biorefinery models that valorize food by-products into market-ready functional ingredients. Full article

(This article belongs to the Special Issue Re-Valorization of Waste and Food Co-Products)

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