Mechanistic Insights into Pigmented Rice Bran in Mitigating UV-Induced Oxidative Stress, Inflammation, and Pigmentation

Abstract

As an agri-food by-product, the rice bran of pigmented rice, encompassing varieties such as red, black, and purple rice, has garnered increasing attention due to its richness in terms of bioactive compounds. Being mainly composed of the pericarp, aleuron, seed coat, and germ, the brown outer layer of the rice kernel offers potential health benefits and has applications in skincare. Human skin serves as the primary barrier against external threats, including pathogens, pollutants, and ultraviolet (UV) radiation. Notably, UV radiation accelerates the aging process and contributes to various skin issues. Recent trends suggest a heightened interest in incorporating pigmented rice into skincare regimens, motivated by its potential to mitigate oxidative stress, inflammation, and pigmentation, which are pivotal factors in skin aging and photodamage. With increasing consumer demand for natural and sustainable ingredients, pigmented rice has emerged as a promising candidate within the skincare and personal care sectors, effectively bridging the gap between nutrition and dermatological health. This review examines the applications of pigmented rice in skincare, with a particular focus on its bioactive components and potential mechanisms of action that contribute to skin health. The unique chemical composition of pigmented rice, which includes compounds such as anthocyanins, flavonoids, phenolic acids, and vitamin E, underlies its antioxidant, anti-inflammatory, and skin-protective properties. Despite the increasing recognition of its benefits, a comprehensive understanding of the underlying mechanisms remains limited, underscoring the necessity for further research to exploit the potential of pigmented rice in skincare applications fully.

1. Introduction

As a primary concern in dermatology and esthetic science, skin photoaging (photodamage), refers to the premature aging of the skin caused by chronic exposure to ultraviolet (UV) radiation. This process leads to visible signs such as wrinkles, hyperpigmentation, a loss of elasticity, and the breakdown of collagen and elastin fibers [1]. At the molecular level, UV radiation induces oxidative stress, generating excessive reactive oxygen species (ROS) that damage cellular structures, including lipids, proteins, and DNA [2]. Antioxidants have emerged as a critical line of defense against skin photoaging by neutralizing ROS and mitigating oxidative damage. These compounds, both endogenous and exogenous, play a pivotal role in protecting the skin, preserving its structure, and promoting rejuvenation. Recent advancements in dermatological research have focused on identifying and formulating potent antioxidant therapies to combat the deleterious effects of photoaging, offering promising strategies for maintaining healthy, youthful skin.

Skin photoaging, primarily caused by UV-induced oxidative stress, underscores the essential function of antioxidants in mitigating cellular damage and maintaining skin health. Within this framework, natural sources of bioactive compounds have attracted considerable scholarly interest. Notably, pigmented rice varieties—such as red, black, purple, and brown rice—and specifically their rice bran, a nutrient-dense byproduct of rice milling, have emerged as promising candidates for further investigation [3]. Rich in antioxidants such as anthocyanins, flavonoids, and phenolic acids [4,5,6], pigmented rice not only serves as a nutritious dietary staple but also offers potential applications in skincare and cosmetic formulations. By leveraging the antioxidative properties of these compounds, innovative approaches to mitigating photoaging and promoting skin rejuvenation are increasingly being explored. Recent trends show a growing interest in leveraging pigmented rice for skincare, particularly due to its potential to combat oxidative stress [7,8], inflammation [9,10], and pigmentation [11], all of which are key contributors to skin aging and photodamage. With consumers and industries prioritizing natural and sustainable ingredients, pigmented rice emerges as an exciting candidate in the skincare and personal care markets, bridging the gap between nutrition and dermatological health. This expanding scope calls for a comprehensive review of its applications and underlying mechanisms.

The significance of pigmented rice lies in its distinctive chemical composition, which includes anthocyanins [5,12], flavonoids [13], phenolic acids [14,15], γ-oryzanol [16], fatty acids [17], vitamin E (tocopherols and tocotrienols) [18,19], etc. These compounds exhibit powerful antioxidant and anti-inflammatory activities, making them valuable in neutralizing ROS and reducing chronic inflammation. For instance, anthocyanins, responsible for the vivid pigments of pigmented rice, not only scavenge free radicals but also protect against lipid peroxidation, which is associated with skin cell damage [20,21]. Phenolic acids and γ-oryzanol further contribute by inhibiting tyrosinase activity, a key enzyme involved in melanin synthesis [22]. This action helps prevent hyperpigmentation, promoting even skin tone. Collectively, these properties highlight the therapeutic potential of pigmented rice in addressing skin health concerns, particularly those linked to aging and environmental stress.

Beyond these bioactive properties, the potential applications of pigmented rice in sun protection and antiphotoaging are particularly compelling. UV radiation is a major contributor to photoaging, leading to collagen degradation, increased pigmentation, and oxidative stress. The antioxidants in pigmented rice can mitigate these effects by protecting skin cells from DNA damage and reducing UV-induced inflammation [10,23,24]. Additionally, their tyrosinase-inhibiting activity offers a natural solution for preventing and treating UV-induced hyperpigmentation [25,26]. These properties suggest that pigmented rice could be integrated into sunscreen formulations or antiphotoaging skincare products, offering a natural and effective alternative to synthetic compounds. With the demand for multifunctional and plant-based ingredients rising, pigmented rice presents a promising avenue for innovation in the cosmetics industry.

This review aims to synthesize current knowledge on the chemical composition and mechanisms of action of pigmented rice, with a specific focus on its applications in skincare. By exploring the antioxidant, anti-inflammatory, and antipigmentation properties of pigmented rice, we aim to provide a foundation for its use in sun protection and antiphotoaging. Furthermore, this review seeks to inspire future research into its bioactive components and their potential for developing novel skincare formulations. Through this analysis, we aim to underscore the transformative potential of pigmented rice as a natural, multifunctional ingredient in both the food and cosmetic industries.

2. Materials and Methods

2.1. Data Retrieval

In this study, the Web of Science (WOS) platform, a global provider of comprehensive scientific documentation, was utilized to compile a dataset of papers focused on constituent analysis or molecular mechanisms associated with pigmented rice. Papers published prior to 15 November 2024 were retrieved in accordance with the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), which is an evidence-based minimum set of items for reporting in systematic reviews and meta-analyses [27].

The search query was performed in the WOS core collection based on the keywords pigmented rice, constituent analysis, and molecular mechanisms. Then, we conducted the search strategy Topic = (“colored-rice” OR “pigmented-rice” OR “Black-rice” OR “Oryza sativa L. indica” OR “Red-rice” OR “Oryza sativa L. japonica” OR “Purple-rice” OR “Oryza sativa L. ” OR “brown-rice”) AND Topic = (“antioxidant*” OR “antioxidant*” OR “photo-aging” OR “photo-damage*” OR “skincare” OR “skin-care” OR “skin-aging” OR “skin anti-aging” OR “cosmetics” OR “cosmetic application” OR “UV protection” OR “UVB” OR “UVA” OR “moisturizing” OR “bioactive-compounds” OR “phytochemical-profile” OR “metabolite profiling” OR “HPLC” OR “UPLC” OR “GC-MS” OR “GC/MS”).

2.2. Screening and Eligibility

After publications were extracted from the WOS database, we listed all the search results and systematically integrated and screened the listed sources, and carefully labeled each item with the reason for including or excluding it in Excel. Firstly, duplicates were screened. Secondly, eligibility criteria were determined prior to the commencement of this review. As shown in

Table 1. Eligibility criteria of selected articles.

No.	Eligibility Criteria
1	Article types not included, e.g., reviews, proceedings, features, editorial material
2	Not in the life sciences
3	Irrelevant object/topic
4	Full text not available
5	Not in English

.

2.3. Annotated Bibliography

Upon completing the initial screening, all eligible papers were downloaded, and the abstract or full text of each research article was reviewed to assess continued relevance. Subsequently, each qualifying research article was annotated with manually extracted information, encompassing the study objectives, methodologies employed, animal or cell models utilized, biomolecules involved (including targets or genes), and the specific mechanisms of action reported. Additionally, key points from each review article were systematically extracted. The statistical data were then generated to describe the current status of research in this field.

3. Results

3.1. Search Results and Study Inclusion

The literature survey and screening process resulted in the inclusion of 248 full-text studies for this review, as depicted in Figure 1. Initially, a comprehensive search of the Web of Science (WOS) database yielded a total of 3969 items. Papers not pertinent to the life sciences (n = 304) were subsequently excluded, and the abstracts of the remaining articles were evaluated for relevance. Further exclusions were made for various reasons, including articles not classified as research or review papers (n = 293), those with irrelevant subjects or topics (n = 3095), articles not published in English (n = 26), and those for which the full text was unavailable (n = 3). These exclusion criteria provide both theoretical and experimental support for the subsequent development of skincare products, facilitating the identification of bioactive compounds in pigmented rice that can be effectively utilized in areas such as anti-aging, hydration, and sun protection.

3.2. Study Characteristics

The majority of the papers included in the analysis were research articles (210, approximately 85.0%), with the remainder being review articles (38, approximately 15.0%). This emerging topic is attracting increasing attention within the global scientific community. An analysis of publication output by country revealed that Thailand is the most prolific contributor, followed by China, Korea, India, the United States, Indonesia, Japan, Italy, Brazil, and Canada, as illustrated in Figure 2. This figure presents the geographical distribution of publications addressing the components, bioactivities, and mechanisms of pigmented rice, highlighting the top ten countries by publication volume. Although this topic has attracted interest from a wide range of countries, the majority of the publications have originated from Asian nations, particularly Thailand and China.

3.3. Chemical Composition of Pigmented Rice Bran

Unlike conventional white rice, pigmented rice owes its distinctive pigmentation to an abundance of bioactive compounds, including anthocyanins, proanthocyanidins, flavonoids, and carotenoids, primarily found in the outer bran layer. These compounds are not only responsible for the vibrant hues but also contribute to the rice’s antioxidant, anti-inflammatory, and potential disease-preventing properties. This section aims to delve into the chemical composition of pigmented rice. By exploring these components, we aim to provide a comprehensive understanding of the scientific basis for the growing popularity and significance of pigmented rice byproducts in skincare. Pigmented rice contains high levels of flavonoids as well as high levels of the terpenoids (carotenoids, tocopherols, phytosterols, and monoterpenes) associated with plant color [28]. Particular anthocyanins, proanthocyanidins, and carotenoids play crucial roles in determining the distinct color of different rice varieties while also contributing significantly to their skincare benefits.

3.3.1. Pigment Compounds

Anthocyanins, a subclass of soluble flavonoids, are the primary pigments responsible for the deep red, purple, and black colors observed in pigmented rice bran [29]. Structurally, these compounds are glycosides composed of anthocyanidins and sugar moieties, with cyanidin-3-O-glucoside being the most prominent anthocyanin identified in purple and black rice bran, contributing to its strong free radical-scavenging activities [30,31,32]. Recent studies have demonstrated that the anthocyanin profile in rice bran is significantly influenced by genetic factors, growing environment, cropping conditions, and germination. Germination influences a significant increase in the overall levels of pigment constituents including six anthocyanins and three proanthocyanidins [12]. The concentration of anthocyanins and proanthocyanidins varies between cultivars, with red, black, and purple rice exhibiting higher levels than milled rice [33]. For purple rice, the anthocyanin content of glutinous highland rice varieties was higher than those of lowland rice varieties [26].

From a functional perspective, anthocyanins are potent antioxidants, capable of scavenging free radicals and chelating metal ions. These properties are attributed to their hydroxyl groups and conjugated structures, which stabilize oxidative species [34]. Six anthocyanins including cyanidin, pelargonidin, malvidin, petunidin, delphinidin, and peonidin are commonly found in plants [35]. The content and composition of these anthocyanins may vary among different pigmented rice varieties [4]. Figure 3 summarizes the types of anthocyanins identified in different pigmented rice, the blue bars represent the presence of the specific compounds in certain pigmented rice varieties.

Proanthocyanidins are found abundantly in red and purple rice and are primarily responsible for their antioxidant properties and red pigmentation, with anthocyanidins serving as crucial intermediates in their synthesis. These bioactive compounds contribute to the red and purple pigmentation observed in rice bran. Proanthocyanidins are primarily composed of flavan-3-ol units, including 3-O-gallates, catechin, epicatechin, and epigallocatechin, which are linked through interflavanol bonds [36]. The structure of proanthocyanidins in red and purple rice can vary, with oligomers consisting of 2–10 flavan-3-ol units and polymers being larger, often more complex structures. The level of polymerization significantly affects the compound’s antioxidant capacity, with more polymerized proanthocyanidins demonstrating greater antioxidant potential, and extractable proanthocyanidins negatively correlated with whole-grain rice’s red color [37].

Recent studies have highlighted that red rice bran contains a higher proanthocyanidin content compared to the black and purple rice varieties, which makes red rice an excellent source of these bioactive compounds. In terms of skincare and sun protection, the proanthocyanidins in red rice are considered promising due to their ability to protect the skin from UV-induced damage. Studies suggest that these compounds can neutralize the free radicals generated by UV exposure, thereby reducing oxidative stress and skin damage [38].

Carotenoids are another class of lipid-soluble natural pigments responsible for the yellow to orange hues in pigmented rice bran. These compounds are known for their powerful antioxidant properties, playing a crucial role in both plant defense mechanisms and human health [39]. The major carotenoids present in pigmented rice bran include β-carotene, lutein, and zeaxanthin, which can effectively scavenge free radicals and mitigate oxidative stress [40]. Melini et al. [41] determined the carotenoid content of two Thai rice varieties and a wild rice sample, both in raw and cooked samples. They identified that the main carotenoids detected in all samples were all-trans lutein and all-trans zeaxanthin; determined by high-temperature processing, which may induce metabolic transformation, further enhancing their antioxidant activity. Moreover, the former was the main carotenoid detected. This study reported that red unpolished parboiled rice was richest in β-carotene. At the same time, black whole-grain rice contained higher levels of α-carotene [42].

Carotenoids can absorb UV radiation and blue light, reducing direct DNA damage and collagen degradation [43], and can also neutralize ROS induced by UV exposure, thereby inhibiting lipid peroxidation and matrix metalloproteinase (MMP) activation [44,45]. Although direct evidence for rice bran is scarce, spectroscopic analyses confirm higher carotenoid levels in pigmented rice bran compared to non-pigmented varieties [19,46].

3.3.2. Phenolic Compounds

Phenolic compounds are a diverse group of secondary metabolites widely recognized for their antioxidant properties, and they represent a significant class of bioactive compounds in pigmented rice bran. These include phenolic acids, and tannins, which contribute to the rich coloration and high antioxidant capacity of red, purple, and black rice brans [47]. The predominant phenolic acids identified in pigmented rice bran are ferulic acid, p-coumaric acid, and caffeic acid, with ferulic acid often dominating in all rice varieties due to its cell wall-bound nature. The main bound phenolic acids were ferulic and p-coumaric, as well as 2,5-dihydroxybenzoic in red rice and protocatechuic and vanillic acids in black rice [48].

Recent studies comparing the phenolic content and bioactivity of red and black rice have revealed the unique strengths of red rice’s polyphenolic compounds. While black rice typically exhibits higher anthocyanin levels, red rice is distinguished by its elevated proanthocyanidin concentrations, which contribute to its superior free radical scavenging activity in certain assays. For instance, research has demonstrated that red rice varieties often contain higher levels of bound phenolic acids compared to their black rice counterparts, enhancing their antioxidative stability and functional efficacy in diverse applications. This distinct phenolic profile positions red rice as a valuable candidate for nutraceutical and cosmeceutical developments, particularly in formulations targeting oxidative stress mitigation and skin health improvement [49].

The stability and bioavailability of phenolic compounds are significantly affected by various processing techniques. Thermal treatments, including infrared radiation and extrusion, have been shown to facilitate the release of bound phenolics from the rice bran matrix, thereby enhancing their bio-accessibility [50]. These findings suggest that processing not only preserves but also amplifies the functional properties of rice bran. Although rice bran also has some nutritional limitations, such as its high dietary fiber and low protein and non-nutritive phytic acid content, fermentation has positive effects on these limitations. For instance, fermented red brown rice could protect against oxidative and stress-induced DNA damage [51]. Furthermore, for red rice, it has also been reported that fermentation could significantly increase the protein and total phenolic content by 1.7 and 1.4 times [52].

3.3.3. Flavonoids

Flavonoids are abundant in pigmented rice bran and contribute significantly to its functional properties. These compounds are chemically characterized by their hydroxylated aromatic rings and are categorized into flavonols (e.g., quercetin, kaempferol), flavones, and flavan-3-ols (e.g., catechins). Research has shown that red and black rice brans possess markedly higher flavonoid concentrations compared to white or brown rice, correlating with their darker pigmentation and superior antioxidative capacity [47]. The total flavonoid content of glutinous highland purple rice varieties was higher than those of lowland rice varieties [26].

Flavonoids in rice bran are predominantly sourced from the outer layers of the grain, where they serve as a defense mechanism against environmental stressors. These compounds exhibit remarkable bioactivities, including radical scavenging, metal ion chelation, and the inhibition of lipid peroxidation. The bioavailability of flavonoids in rice bran is subject to alteration by various processing techniques. Specifically, thermal treatments such as infrared radiation and extrusion cooking have been demonstrated to facilitate the release of bound flavonoids from the rice bran matrix, thereby augmenting their antioxidant capacity and bioaccessibility [53].

3.3.4. Functional Lipids

Rice bran is a rich source of lipids, comprising around 15–23% of its composition, with unsaturated fatty acids dominating the profile. The major fatty acids include oleic acid (35–40%), linoleic acid (30–40%), and palmitic acid (20–25%), which contribute to the stability and bioactivity of rice bran lipids [54,55]. One of the distinguishing features of rice bran lipids is their content of γ-oryzanol, a mixture of ferulic acid esters and sterols, which exhibits antioxidant and cholesterol-lowering properties. γ-oryzanol content ranges from 226.40 to 411.80 µg/g in non-colored rice and from 295.80 to 459.80 µg/g in colored rice, with black rice having the highest levels. Khao Jao Dam Sa-Nit, a black rice, has the most γ-oryzanol, 1.55 to 2.03 times more than the red rice Khao Man Bpoo and non-colored Khao Gor Kor 57 [56]. In red rice bran, γ-oryzanol accounts for 51.8% of the total antioxidants and is more effective than α-tocopherol in reducing cholesterol oxidation [6,57]. A study by Kim et al. [58] examined γ-oryzanol content in seven Korean rice varieties from the International Rice Research Institute: three white (Chucheongbyeo, Kunnunbyeo, Baekjinjubyeo), three red (Hanyangjo, Chosundo, Jeokjinjubyeo), and one purple (Heugjinjubyeo). The γ-oryzanol levels were 3.5, 8.8, and 6.1 mg/100 g in white rice; 14.3, 13.6, and 19.1 mg/100 g in red rice; and 21.4 mg/100 g in purple rice [6]. The interplay of these bioactive compounds with unsaturated fatty acids enhances the functional value of rice bran [59].

Processing methods can significantly influence the lipid content in rice bran. Techniques such as cold pressing, solvent extraction, and enzymatic extraction are commonly used to preserve the quality and functionality of these lipids. Notably, aqueous enzymatic extraction has been shown to retain a high proportion of unsaturated fatty acids while minimizing oxidation and color degradation [60].

3.3.5. Vitamins and Minerals

Pigmented rice bran contains an array of vitamins and minerals, particularly abundant in B-complex vitamins (such as thiamine, riboflavin, and niacin) and vitamin E, predominantly in the form of tocopherols and tocotrienols, which are well-known for their antioxidant properties [61]. Additionally, the mineral profile of pigmented rice bran includes significant levels of iron, zinc, magnesium, and phosphorus, with black and red rice varieties showing the highest concentrations due to their pigmented bran layers [15,62]. Studies have highlighted that traditional red rice varieties contain higher levels of tocopherols (vitamin E) and essential minerals like iron and zinc, while for purple rice, lower amounts of tocopherols and tocotrienols were detected [63], but these levels are still higher than for white rice [64], making them effective in combating oxidative stress [4].

3.3.6. Bioactive Peptides

Rice-derived bioactive peptides have emerged as promising functional ingredients in treating various diseases [65], as well as in skincare and photoprotection due to their potent antioxidant properties. One study [66] demonstrated the ability of peptides isolated from rice fermentation to mitigate oxidative stress induced by UVA exposure. These peptides act by neutralizing ROS and enhancing cellular antioxidant defense mechanisms, thereby reducing oxidative damage to skin cells. Another study [67] reported the effects of hydrolyzed peptides from germinated black rice (BRP) on HaCaT keratinocytes by analyzing the expression of about 20,000 transcripts. BRP treatment resulted in a more than 2-fold differential expression; 745 transcripts were activated and 1011 were repressed. Notably, BRP doubled the expression of the hyaluronan synthase 2 (HAS2) gene. Semiquantitative RT-PCR confirmed a dose-dependent increase in HAS2 mRNA, and ELISA demonstrated that BRP significantly boosted hyaluronan (HA) production in the cells. Such properties highlight their potential in preventing photoaging and supporting skin health, making them valuable candidates for inclusion in sunscreen formulations and anti-aging skincare products. Their natural origin and multifunctional benefits further enhance their appeal in the development of cosmeceuticals targeting UV-induced skin damage.

3.4. Mechanisms of Sun Protection and Antiphotoaging of Pigmented Rice

3.4.1. UV Absorption Capacity

Anthocyanins and polyphenols, key bioactive compounds in pigmented rice, provide effective UV protection by absorbing UVA (315~400 nm) and UVB (280~315 nm) rays. A typical ultraviolet–visible (UV–vis) spectrum of anthocyanins exhibits two primary absorbance clusters; the first occurs within the 260–280 nm range, corresponding to the UV region, and the second is observed between 490 and 550 nm, within the visible region. In addition to these, an additional peak is detected in the 310–340 nm wavelength range when the sugar moiety is acylated; this peak is either absent or manifests as a minor hump in non-acylated anthocyanins. Moreover, a hump is also recorded in the 400–450 nm range, the magnitude of which is contingent upon the number of sugar moieties attached to the anthocyanidin core. Generally, the anthocyanin structure comprises a fully delocalized conjugated system, which imparts stability to the molecule [68]. Their conjugated molecular structures, rich in hydroxyl groups, enable strong UV absorption and antioxidative activity. For instance, cyanidin-3-glucoside, a predominant anthocyanin in black rice, has demonstrated high UVB absorption efficiency, reducing UV-induced oxidative stress in skin cells [69,70].

Anthocyanins in red and black rice absorb UV rays by dissipating the energy as heat or harmless light, thereby preventing damage to cellular DNA and proteins. Polyphenols such as ferulic acid (which exhibits strong absorption in UVB and UVAII (280–340 nm) with a peak around 300 nm) [71] further enhance UV protection through their antioxidant activity, neutralizing reactive oxygen species generated by UV exposure [72,73]. Additionally, these compounds have been shown to regulate UV-induced gene expression, modulating stress-related pathways and enhancing skin protection in cosmetic applications [69].

Studies highlight the potential of anthocyanin-rich extracts from pigmented rice in formulating UV-protective cosmetics and functional foods. For instance, black rice extracts demonstrated high efficacy in absorbing UVB and UVA rays, with an SPF equivalent in emulsion formulations [74,75,76].

3.4.2. Antioxidant Effects

The conjugated double-bond structure of anthocyanins allows them to directly quench ROS, while phenolic compounds such as ferulic acid stabilize radicals by donating electrons. Furthermore, γ-oryzanol, another bioactive in rice bran, has demonstrated significant potential in reducing UV-induced skin inflammation and oxidative damage by neutralizing free radicals [77].

Free radicals (e.g., superoxide anions and hydroxyl radicals) and ROS such as hydrogen peroxide are primarily generated during UV exposure through the excitation of chromophores in skin cells. This process leads to the disruption of cellular homeostasis, inducing lipid peroxidation, DNA damage, and protein oxidation. Chronic exposure can exacerbate oxidative stress, contributing to photoaging and skin carcinogenesis [78,79]. Pigmented rice varieties, particularly red and black rice, are rich in bioactive compounds such as anthocyanins, polyphenols, γ-oryzanol, and vitamin E derivatives. These compounds exert their protective effects through multiple mechanisms: (1) inhibiting ROS formation—γ-oryzanol and tocopherols in rice bran act as physical and chemical quenchers of singlet oxygen and other ROS, thereby mitigating oxidative stress at the molecular level [77]; and (2) neutralizing free radicals—anthocyanins and phenolic acids donate electrons to stabilize free radicals, effectively preventing chain reactions of oxidative damage [69].

The antioxidant activities of 40% acetone extracts of different types of pigmented rice bran were measured in the range of 0 to 1500 μg/mL. At a 500 μg/mL concentration, red rice bran showed the highest antioxidant activity and had the highest total phenolic (259.5 μg/mg) and total flavonoid (187.4 μg/mg) contents [80]. Studies demonstrate that extracts from black rice reduce UV-induced oxidative damage in skin cells by decreasing malondialdehyde (MDA) levels, a biomarker of lipid peroxidation, while increasing antioxidant activity as measured by DPPH and ABTS assays. In addition, γ-oryzanol was also found to be a nuclear factor erythroid 2-related factor 2 (Nrf2) inducer, resulting in nucleophilic tone regulation [8]. Red rice extract demonstrates stronger antioxidant capacity in animal disease models, suggesting its potential for enhanced antioxidant efficacy in skincare applications [41,81].

UV radiation induces the formation of cyclobutane pyrimidine dimers (CPDs) and oxidative stress, leading to mutations and skin photoaging. The anthocyanins, polyphenols, and many other bioactive compounds in pigmented rice can offer natural protection against such damage by mitigating oxidative stress and enhancing DNA repair mechanisms. The anthocyanins in pigmented rice absorb UVA and UVB rays, effectively reducing ROS production, which can lead to DNA strand breaks and mutagenesis [69]. These compounds also exhibit strong antioxidant activity, scavenging free radicals that contribute to DNA damage. In addition, γ-oryzanol and ferulic acid, have been shown to upregulate nucleotide excision repair (NER) mechanisms. These mechanisms recognize and excise UV-induced DNA lesions, maintaining genomic stability [77]. UV-induced inflammation exacerbates DNA damage through oxidative stress. Ingredients in rice bran, such as tocotrienols and phenolic acids, suppress the overexpression of pro-inflammatory markers like interleukins, thereby indirectly reducing DNA damage [74].

Studies have shown that extracts from pigmented rice bran can enhance DNA protection when formulated into topical products. For instance, black rice extracts incorporated into emulsions significantly reduced CPD formation and prevented DNA fragmentation in UV-exposed skin cells [79,82]. These highlight pigmented rice’s potential as a functional ingredient in photoprotective formulations [79,83].

3.4.3. Anti-Inflammatory Effect

These pigmented rice varieties enhance their capacity to mitigate damage induced by UV radiation. UV radiation results in the accumulation of ROS in the skin, which is consistently associated with inflammation, as it stimulates keratinocytes and fibroblasts to secrete pro-inflammatory cytokines [84]. Exposure to UV radiation triggers the upregulation and release of interleukins IL-1, IL-3, IL-6, IL-7, IL-10, and IL-12 [20]. Furthermore, the overproduction of ROS mediated by UV exposure activates cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2). The inflammatory cytokines promote vasodilation and increase vascular permeability, leading to erythema and edema of the skin. An excess of cytokines, particularly IL-1 and tumor necrosis factor-alpha (TNF-α) in the stratum corneum, facilitates the recruitment of neutrophils and monocytes into the interstitial space through dilated capillaries, ultimately resulting in inflammation. In addition, keratinocytes synthesize and secrete TNF-α in response to UV radiation, which induces both local and systemic inflammatory responses in the skin [85].

Previous studies also demonstrate that the anti-inflammatory properties of red rice’s polar extract fraction may stem from the inhibition of pro-inflammatory mediators via the suppression of the AP-1, NF-κB, and MAPKs pathways [86]. Such actions may impede the progression of skin aging and photodamage, suggesting that colored rice presents a natural and sustainable strategy for skin photoprotection and inflammation management. By harnessing these properties, there is potential to develop novel skincare products that integrate effectiveness with the advantages of bioactive plant compounds.

3.4.4. Inhibition of Matrix Metalloproteinases (MMPs)

UV radiation-induced senescent fibroblasts demonstrate elevated levels of MMPs [87]. Consequently, MMPs are regarded as a primary target for the prevention of photoaging. The activation of AP-1, a transcription factor composed of c-Jun and c-Fos, by ROS can lead to collagen degradation and inhibit the transforming growth factor-beta (TGF-β) signaling pathway, thereby reducing procollagen synthesis [88]. Chronic photoaging due to UV radiation exposure results from the disruption of the balance between the production and degradation of the extracellular matrix (ECM). ROS can interact with polyunsaturated fatty acids on the cell membrane surface, leading to the formation of MDA and 4-hydroxynonenal (4-HNE) [89]. These oxidative products are capable of forming cross-links with macromolecules, including proteins and nucleic acids, leading to the generation of insoluble substances that may compromise cellular membrane functionality. Furthermore, MDA and 4-HNE are recognized as major contributors to the degradation of collagen and elastin fibers within the dermal layer [90].

MMPs, particularly MMP-1, MMP-3, and MMP-9, play a critical role in UV-induced skin aging by degrading collagen and elastin, leading to the loss of skin elasticity and the formation of wrinkles. Pigmented rice exhibits significant potential in inhibiting MMP activity, thereby mitigating photoaging. Exposure to UV radiation results in the breakdown of the ECM in the dermis, due to an increase in MMP levels in both the epidermis and dermis, and a decline in type I collagen expression. Anthocyanin suppresses MMP expression through the modulation of the MAPK/NF-κB signaling pathways, which are activated by UV radiation. These compounds reduce oxidative stress and inflammation, key drivers of MMP production [69]. Red rice extract (RRE) can significantly increase collagen and HA synthesis in UVB-irradiated human fibroblasts. Moreover, RRE significantly inhibits UVB-induced MMP-1 expression and MMP-2 and collagenase activity. Upon UVB irradiation, mitogen-activated protein kinases (MAPKs) are activated and this pathway stimulates the expression of interleukin-6 and -8 (IL-6 and -8) [24]. In vitro studies have shown that black rice extract (BRE) reduces both baseline and UV-stimulated MMP-1 levels in HaCaT cells. Additionally, BRE notably enhances type I procollagen levels and lowers MMP-1 and MMP-3 levels in human dermal fibroblasts exposed to UV [23]. The hydroglycolic crude extract of Thai red Hom–Kularb–Drice (20 µg/mL) exhibited a protective effect in UVB-irradiated primary skin fibroblast, reducing MMP-1 expression and increasing the production of type I procollagen [91].

Recent findings underscore the role of specific bioactive compounds in pigmented rice, such as cyanidin-3-glucoside, which has been shown to increase MMP production, a key factor in UV-induced collagen degradation [62]. This effect is complemented by the suppression of nuclear factor kappa B (NF-κB) and the activation of the Nrf2 pathways critical for the regulation of oxidative stress responses [92].

Moreover, the incorporation of pigmented rice extracts into topical formulations or dietary supplements has demonstrated significant improvements in skin elasticity and moisture retention, while reducing photoaging markers such as wrinkle formation and hyperpigmentation [69]. These findings point to the potential of pigmented rice as a multifunctional ingredient in anti-aging skincare and nutraceutical products.

3.4.5. Inhibition of Tyrosinase Activity

Tyrosinase is a key rate-limiting enzyme in the melanin biosynthesis process [93]. It catalyzes the oxidation of L-tyrosine to L-DOPA (L-dihydroxyphenylalanine) and subsequently converts L-DOPA to DOPA quinone. This series of chemical reactions initiates the production of melanin, which determines skin, hair, and eye color while providing photoprotection against UV radiation [94]. Tyrosinase activity and expression levels directly influence melanin content and are critical targets for managing hyperpigmentation [95]. Furthermore, tyrosinase inhibitors are widely studied in the cosmetic industry to develop skin-lightening agents.

Active ingredients in pigmented rice have shown significant tyrosinase inhibitory activity, making them promising candidates for skin-lightening and anti-aging products. Anthocyanins act as competitive inhibitors of tyrosinase. Studies have shown that anthocyanin contents from red rice bran demonstrated significant tyrosinase inhibition. The IC₅₀ values of the tyrosinase inhibition activities of the anthocyanin contents from red rice bran and Vc were 4.26 and 2.18 μg/mL, respectively [11]. Also, anthocyanin-rich extracts from black rice can significantly reduce tyrosinase activity, with effects comparable to kojic acid, a well-known skin-lightening agent [96]. Ferulic acid and protocatechuic acid also exhibit strong inhibitory effects on tyrosinase. These compounds bind to the enzyme’s active site, reducing melanin production and protecting against UV-induced pigmentation [97]. γ-oryzanol not only inhibits tyrosinase but also reduces oxidative stress, which exacerbates melanin synthesis. It acts by modulating melanogenesis-related pathways [98].

I Batubara et al. [99] reported that, for tyrosinase inhibition, the n-hexane extract of red rice was the most active extract, with the IC₅₀ = 3156 μg/mL. Protocatechuic acid methyl ester isolated from the ethyl acetate extract of black rice bran showed dose-dependent inhibition against tyrosinase activity [100]. Fermented black rice bran extracts enhanced the skin-lightening effects of formulations by improving tyrosinase inhibition, making them suitable for anti-pigmentation products [101].

3.4.6. Enhancement of Skin Barrier Function

Enhancing the skin barrier is crucial for both preventing UV-induced damage and mitigating the effects of photoaging. Pigmented rice and its compounds are pivotal in maintaining skin barrier integrity and reducing transepidermal water loss. Anthocyanins reduce oxidative damage to the skin barrier and promote lipid organization in the stratum corneum, ensuring proper moisture retention [20]. In vitro studies have demonstrated that fermented black rice and blueberry (FBBBR) with Lactobacillus plantarum enhances the expression of the collagen type 1 alpha 1 (COL1A1) gene, as well as genes related to natural moisturizing factors, including filaggrin (FLG) and transglutaminase-1 (TGM-1). Furthermore, oral administration of FBBBR in UVB-irradiated hairless mice resulted in increased serum catalase activity and reduced serum IgE levels. This treatment also improved stratum corneum hydration and epidermal thickness, while augmenting the mRNA expression of FLG, TGM-1, involucrin, and COL1A1 in dorsal skin [102].

In summary, the studies detailing the effects and mechanisms of action of pigmented rice are compiled in

Table 2. The studies report the effects and mechanisms of action of pigmented rice.

Pigmented Rice Varieties	Preparation	Experiment Type	Methods	Animal/Cell	Target/Gene Regulation	Various Key Points	Ref.
Red jasmine rice bran	Extraction	In vitro	ROS detection, melanin inhibition test, collagen gene expression	HaCaT, HFF, and B16	COL1A1 ↑	The extract from red jasmine rice bran demonstrated the ability to mitigate ROS accumulation in keratinocytes induced by blue light exposure, as well as to inhibit melanin production triggered by blue light.	[75]
Red rice	Extraction	In vitro	Collagen synthesis, collagenase activity assay, MMP-2 activity assay, hyaluronic acid (HA) synthesis assay, melanin content detection, mushroom tyrosinase activity, cellular tyrosinase activity, DPPH free radical scavenging capacity	Primary human skin fibroblasts, B16-F10	——	Proanthocyanidin and catechin effectively inhibited collagenase and MMP-2, promoted collagen and hyaluronic acid synthesis in human fibroblasts, and reduced melanin content and tyrosinase activity in B16-F10 melanoma cells. They also showed strong DPPH radical scavenging activity. Oryzanol reduced melanin but did not affect tyrosinase activity and had a minimal impact on DPPH scavenging. Hydroxybenzoic acid, vanillic acid, and oryzanol did not influence collagenase or MMP-2, and compounds from red rice extract did not affect mushroom tyrosinase.	[26]
Red rice	Extraction	In vitro	DPPH, superoxide anion scavenging activity, tyrosinase inhibitory activity	RAW264.7, HGF, HaCaT	——	The extract had good antioxidant and tyrosinase inhibition activities.	[11]
Red rice	Fermentation	In vitro	qPCR, ROS detection assay, 3D epidermal model moisture content test, melanin content test	HaCaT, 3D epidermal model, human primary melanocytes (MCs), human dermal fibroblasts (FB)	mRNA: Aquaporin 3 (AQP3) ↑, Filaggrin (FLG) ↑, Hyaluronan Synthase 1 (HAS1) ↑, Claudin 1 (CLDN1) ↑, Involucrin (IVL) ↑, Zonula Occludens-1 (ZO-1) ↑	Anthocyanins inhibit collagen degradation and scavenge free radicals.	[3]
Thai red Hom–Kularb–Drice (HKD) rice bran	Extraction	In vitro	DPPH assay, ELISA	Primary Human skin fibroblasts	MMP-1 ↓, type I procollagen protein ↑	The HKD extract at a concentration of 20 µg/mL exhibited protective effects in UVB-irradiated primary skin fibroblasts, evidenced by a reduction in MMP-1 expression and an enhancement in type I procollagen production.	[91]
Purple rice	Extraction	In clinic	qPCR, Bioinstrumentation measurements were taken, including corneometer, tewameter, ultrasound, and standardized digital imaging	——	hyaluronan synthase 2 ↑, collagen type 1a1 ↑	The skin showed a marked increase in HA content following 4 weeks of treatment.	[103]
Purple Glutinous Rice (Oryza sativa L. cv. Pieisu 1 CMU) (PES1CMU-DFRB)	Extraction	In vitro	Tyrosinase activity, melanin content test, DPPH, ABTS, collagen-stimulating effect, MDA	B16 melanoma, fibroblast cells	MMP-2 ↓	Diminishes the activity of the tyrosinase enzyme responsible for a melanogenesis inhibitor as a skin-whitening agent. PES1CMU-DFRB illustrated impressive antioxidant capacities against DPPH, ABTS radicals, and malondialdehyde production. Reduces melanin production, protects the lipid membrane of fibroblasts, and decreases the destruction of collagen.	[101]
Purple rice (riceberry rice), rice bran oil (RBO)	Extraction	In vitro	DPPH, NO radical scavenging activity, anti-elastase enzyme, anti-tyrosinase activity, wound healing, antimicrobial activity	RAW264.7, human skin fibroblast cells	——	RBO demonstrated antioxidant properties through the scavenging of DPPH and NO radicals, as well as anti-inflammatory effects by reducing NO radical production in LPS-induced macrophage cells. RBO marginally stimulated skin cell proliferation without exhibiting toxicity at concentrations ranging from 0.0001 to 0.1 mg/mL; however, a concentration of 1 mg/mL was found to be cytotoxic. RBO did not inhibit tyrosinase or elastase enzyme activities. Furthermore, no wound healing was observed following the incubation of RBO with scratched human skin fibroblast cells.	[104]
Purple rice and ferulic acid	Extraction	In vitro	Ferric reducing antioxidant potential (FRAP), inhibiting collagenase and tyrosinase activity, tyrosinase inhibitory activity	——	——	IPR demonstrated potent reducing power, anti-collagenase, and anti-tyrosinase activity.	[97]
Fermented black rice and blueberry with Lactobacillusplantarum	Fermentation	In vitro	DPPH and ABTS radical scavenging activity, ferric-reducing antioxidant power, prevention of oxidative DNA damage, measurement of intracellular ROS production, Western blot, qPCR, measurement of skin moisture, serum biochemical analysis, histological analysis	HaCaT, hairless mice	FLG ↑, TGM ↑, MMP-9 ↓, COL1A1 ↑, INV ↑, TGM ↑	The fermented mixture significantly reduced DPPH and ABTS radicals, FBBBR inhibited both extracellular and intracellular free radicals, and the declining presence of these two enzymes (caspase-3 and PARP) indicated that FBBBR protected cells from apoptosis by regulating the caspase pathway; FBBBR enhances skin barrier function by modulating the expression of FLG, TGM, MMP-9, and COL1A1, thereby preventing UVB-induced collagen breakdown and moisture depletion in HaCaT cells.	[102]
Black rice bran (BRB)	fermentation	In vitro	DPPH radical scavenging activity, Tyrosinase inhibitory activity	——	——	Fungal fermentation was effective in enhancing the antioxidant activity of BRB	[25]
Black rice (Oryza sativa L.)	Extraction	In vitro	Western, qPCR, ROS detection	HaCaT, primary HDF	MMP-1 ↓, AP-1 (c-Jun/c-Fos) ↓, ERK ↓, JNK ↓, and p38 ↓	BRE mitigates indicators of photoaging, such as the reduction in collagen and the elevation of MMPs in skin cells. The underlying mechanism contributing to these advantageous effects may involve the inhibition of ROS generation and AP-1 activation in vitro.	[23]
Black Rice Bran (Oryza sativa L. indica)	Extraction	In clinic	Measurement of Skin Brightness and Erythema Level	——	——	It effectively reduced skin melanin production	[105]
Pigmented rice (four red rice and one black rice)	Extraction	In vitro	DPPH, ABTS	——	——	The results confirmed that the content of total phenolics and the flavonoid content, as well as the antioxidant capacity (DPPH and ABTS assays) of pigmented rice, was several-fold greater than non-pigmented ones (4, 4, 3, and 5 times, respectively).	[19]
Anthocyanins (ANT) from Black rice (Oryza sativa L.)	Extraction	In vitro	Copper ion reduction activity, qPCR, cell migration assay, total collagen estimation, Western blot, immunofluorescence staining, ELISA	Rat primary dermal fibroblasts (RDFs)	mRNA expression of COL1A2 ↑ and type I collagen protein levels ↑	ANT enhanced the migration of rat RDFs and showed antioxidant effects. It boosted the mRNA expression of collagen type I alpha 2 (COL1A2) and increased type I collagen protein levels in H2O2-stimulated RDFs without causing cytotoxicity. Compared to untreated cells, ANT treatment in the presence of H2O2 activated ERK1/2 and Akt signaling pathways, while significantly inhibiting IκBα phosphorylation and suppressing the activation of NF-κB subunits p50 and p65, which are linked to inflammation.	[106]
Black glutinous rice (Oryza sativa var. glutinosa)	Extraction	In vitro	Sun protection factor (SPF) assay	——	——	Anti-UV activity is demonstrated by the SPF value, with higher doses producing higher SPF values.	[74]
Fermented unpolished black rice (Oryza sativa L.) (FUBR)	Fermentation	In vitro	DPPH, melanin content test, qPCR, intracellular tyrosinase activity, Western blot	B16F10, Hs68	mRNA and protein expression levels of tyrosinase, tyrosinase-related protein 1 (TYRP-1) ↓, TYRP-2 ↓, and microphthalmia-associated transcription factor ↓, phosphorylated ERK ↑, p38 ↑, and Akt ↑	Decreased cellular tyrosinase activity by FUBRS, decreased the expression level of melanogenesis-related proteins by FUBRS, and induced the phosphorylation of the Erk1/2, p38, and Akt signaling pathways by FUBRS.	[107]

↑ denotes the expression of the gene/protein is up-regulated; ↓ denotes the expression of the gene/protein is down-regulated; —— denotes no significant change detected or no relevant information reported in the cited literature.

, presented below. These findings indicate that pigmented rice may serve as a protective agent against UV-induced damage, with the molecular mechanisms of action illustrated in Figure 4.

4. Discussion

The exploration of pigmented rice as a source of bioactive compounds offers promising applications in the photoprotection and skincare industries. Its rich composition of antioxidants, including anthocyanins, flavonoids, and phenolic acids, highlights its potential to combat oxidative stress and UV-induced skin damage effectively. However, despite these encouraging findings, challenges remain in translating these properties into practical applications. Factors such as the stability of bioactive compounds during extraction and formulation, the scalability of production, and ensuring efficacy in diverse skin types present significant hurdles. This section discusses the practical applications of pigmented rice in skincare formulations, addressing these challenges while proposing strategies for future innovation.

4.1. Applications in Functional Skincare and Challenges

With the increasing demand for natural, sustainable, and multifunctional skincare solutions, extracts of pigmented rice bran provide an eco-friendly source of bioactive compounds. Their use supports the sustainability goals of clean beauty brands that are being incorporated into various formulations to address UV-induced aging. In particular, anthocyanins and phenolic acids make them ideal candidates for natural sunscreens.

4.2. Technological Challenges

Advanced technologies, such as high-throughput sequencing (HTS), molecular dynamics (MD) simulations, or other computational approaches, and nanoparticle encapsulation, such as liposomal and polymeric systems, are being utilized to unravel the sun protection and antiphotoaging properties of pigmented rice bran.

In addition, though pigmented rice holds significant promise in skincare applications, its integration into commercial skincare products faces several technological challenges. Particularly, achieving the optimal delivery of pigmented rice compounds to the skin requires advanced technologies such as encapsulation or controlled release systems, which increase production costs. These challenges highlight the need for innovative research and collaborative efforts between academia and industry to harness the full potential of pigmented rice in the skincare sector. Despite the verified biological benefits of colored rice and its significant effects in the treatment of various diseases, the mechanisms behind these benefits, particularly in the areas of sun protection and skincare, remain largely unexplored. More targeted research is needed to uncover the detailed mechanisms through which its bioactive compounds influence skin health, especially in preventing UV-induced damage, aging, and hyperpigmentation.

5. Conclusions

In conclusion, colored rice holds great promise in the realm of dermatology, particularly in sun protection and skincare. The key mechanisms underlying its effectiveness include its UV absorbing capacity, antioxidant properties, inhibition of tyrosinase activity, ability to inhibit MMPs, and enhancement of skin barrier function. These mechanisms collectively reduce oxidative stress, prevent collagen degradation, and improve hydration, making pigmented rice an excellent candidate for multifunctional skincare products. The advantages of pigmented rice lie in its natural origin, sustainability, and multifunctionality, catering to the increasing demand for clean, eco-friendly beauty solutions. Its incorporation into sunscreen formulations, anti-aging creams, and hydration products demonstrates its versatility and effectiveness across various skincare applications. Additionally, advancements in formulation technologies, such as nanotechnology and controlled release systems, further enhance the stability and efficacy of pigmented rice ingredients.

Further studies are needed to isolate and characterize individual compounds in different types of pigmented rice. This includes exploring variations in bioactive content across cultivars and their specific contributions to skin health. An important research direction is to explore whether a streamlined selection of these bioactive components can achieve or even exceed the efficacy of the more complex extracts currently in use. Pigmented rice holds substantial potential as a sustainable and efficacious ingredient in contemporary skincare formulations. Ongoing research, along with interdisciplinary collaboration, will be crucial in optimizing its applications and addressing the increasing consumer demand for natural, scientifically validated beauty solutions.