Melanin is a skin pigment that plays an important role in protection from the harmful effects caused by ultraviolet (UV) light. Overproduction and accumulation of melanin can result in pigmented patches and skin discolorations, such as chloasma, solar lentigo and freckles, that lead to perceived esthetic problems [1, 2]. The production of melanin pigment, also called "melanogenesis, " is a complicated process regulated by various melanogenesis enzymes, such as tyrosinase, and tyrosinase-related protein 1 (TYRP1) and TYRP2. Among these enzymes, tyrosinase is the essential enzyme in melanogenesis. It catalyzes two initial steps in this process; namely hydroxylation of L-tyrosine into 3,4-dihydroxyphenylalanine (L-DOPA) and the oxidation of L-DOPA into dopaquinone. These melanogenesis enzymes are regulated by microphthalmia-associated transcription factor (MITF) [3-5]. In addition, melanogenesis is modulated by mitogen-activated protein kinase (MAPK) signaling via extracellular signal-regulated kinases (ERK) and p38 MAPK. The phosphorylation of ERK (Thr202/Tyr204) and p38 (Thr180/Tyr182) leads to MITF degradation, which plays a pivotal role in suppressing melanin production [6-8]. The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway is also known to be involved in the regulation of melanogenesis, where the phosphorylation of Akt leads to negative regulation of melanogenesis [9, 10]. Additionally, UV light radiation causes the synthesis of reactive oxygen species (ROS) that are also involved in the regulation of melanin synthesis. Hence, ROS scavengers and inhibitors of ROS generation may down-regulate melanogenesis [11]. Currently, known depigmenting agents, such as kojic acid, arbutin and linoleic acid, are used as cosmetic agents Melanin is a major factor that darkens skin color as one of the defense systems to prevent the harmful effects of UV light. However, darkened skin from the localized or systemic accumulation of melanin is viewed in many cultures as an esthetic problem. Consequentially, searching for antimelanogenic agents from natural sources is very popular worldwide. Previous screening of fermented rice products, obtained from various rice cultivars fermented with different sources of loog-pang (Thai traditional fermentation starter), revealed that the highest ability to reduce the melanin content in B16F10 melanoma cells was from unpolished black rice fermented with a defined starter mixture of microbes isolated from loog-pang E11. The aim of this study was to investigate the mechanism of the fermented unpolished black rice (FUBR) on the inhibition of melanogenesis in B16F10 melanoma cells. The strongest reduction of cellular melanin content was found in the FUBR sap (FUBRS). The melanin reduction activity was consistent with the significant decrease in the intracellular tyrosinase activity. The FUBRS showed no cytotoxic effect to B16F10 melanoma or Hs68 human fibroblast cell lines. It also significantly reduced the transcript and protein expression levels of tyrosinase, tyrosinase-related pr...

Fermentation of rice grains requires diverse metabolic enzymes to be synchronously synthesized by the microbial community. Although many studies have used a metaproteomic approach to investigate the roles of microorganisms in improving the flavor of fermented foods, their roles in producing compounds with biological activity have not yet been reported. In a previous study the ferment obtained from unpolished black rice (UBR) fermented with a defined microbial starter (De-E11), comprised of Rhizopus oryzae , Saccharomycopsis fibuligera , Saccharomyces cerevisiae , and Pediococcus pentosaceus , (fermented UBR; FUBR) showed a strong melanogenesis inhibition activity in B16F10 melanoma cells. Hence, in this study, the roles of these microorganisms in producing the melanogenesis inhibitor(s) in FUBR was investigated using a metaproteomic approach. The melanogenesis inhibition activity of the FUBR liquid (FR-Liq) was found to increase with longer fermentation times. R . oryzae and S . cerevisiae were the major hosts of proteins related to the biosynthesis of melanogenesis inhibitor(s) in the FUBR. During fermentation, the enzymes involved in the degradation of UBR and in the carbohydrate metabolic process were identified. These enzymes were associated with the process of releasing of bioactive compound(s) from UBR and the synthesis of organic acids from the microorganisms, respectively. In addition, enzymes involved in the synthesis of some known melanogenesis inhibitor(s) and in the degradation of the melanogenesis stimulator (arsenate) were detected. Varying the combination of microorganisms in the De-E11 starter to produce the FR-Liq revealed that all four microorganisms were required to produce the most potent melanogenesis inhibition activity. Taken together with the metaproteomics results, this suggested that the microorganisms in De-E11 synchronously synthesize the FR-Liq with melanogenesis inhibition activity. In conclusion, this information on the metaproteome in FUBR will increase our understanding of the microbial metabolic modes and could lead to knowledge-based improvements in the fermented rice process to produce melanogenesis inhibitor(s).

Fermentation of food is a metabolic process through the action of enzymes from certain microorganisms. Although roles of the microbial community in the fermented food were investigated using metatranscriptomic approach in terms of flavors, but no study has been reported so far on the function of the microorganisms on producing compounds with a melanogenesis inhibition activity.

Rice contains numerous nutrients and biologically active compounds. The phytochemical composition of rice varies among cultivars that leads to diversities in biological activities. Fermentation is an efficient way for improving nutrient bioavailability and functional properties of raw materials. It enhances and/or synthesizes the compounds with health promoting or decreased antinutritive compounds during fermentation process. Rice-based fermented products have been reported for enhancing various biological activities including antioxidant, anti-cancer, anti-diabetes anti-wrinkle and anti-melanogenesis activities. Melanogenesis, melanin biosynthesis, is the cause of human skin pigmentation, however the accumulation of melanin leads to skin hyper-pigmentary disorders, such as freckles and melasma. In this review, the information on rice-based fermented products have been assembled to illustrate the fermented rice properties especially melanogenesis inhibition activity including functional roles of the microorganisms in the fermented rice products.