## 1 Introduction  
Melanin biosynthesis is an important metabolic process in the body. It has been demonstrated that melanocytes generate melanin that determines the color of skin, hair, and eyes in humans [1, 2]. Melanogenesis is a complex, multi-step procedure. Under physiological conditions, melanin production is advantageous because of the protective effects of melanin against pernicious ultraviolet radiation. However, excessive melanin biosynthesis causes hyperpigmentation, which results in various dermatological conditions such as freckles, age spots, melasma, and even skin cancer [3, 4]. Several studies have indicated that tyrosinase, a copper-containing enzyme, is extensively found in living organisms and is the pivotal rate-limiting enzyme in melanin biosynthesis. The hydroxylation of L-tyrosine to L-dihydroxyphenylalanine (DOPA) and the oxidation of DOPA to dopquinone are catalyzed by tyrosinase [5, 6, 7]. Further, an increase in tyrosinase activity promotes melanin biosynthesis, as do excessive UV irradiation and oxidative stress. [PERSON] al. demonstrated that melanogenesis could be inhibited by reducing intracellular oxidative stress [8]. Several animal models are used to study the inhibition of melanogenesis, such as zebrafish, mice, rats, guinea pigs, or humans. Recently, because melanin is present on the surface of zebrafish embryos and the process of pigmentation can be easily observed without complicated experimental steps, numerous studies have used zebrafish embryos for melanin-related experiments [9]. Detection of important indicators that affect melanogenesis, such as tyrosinase activity, in the zebrafish embryo model is also feasible [10]. In addition, the appearance of zebrafish embryos and heart rate can also be used to evaluate the toxicity of samples [9]. Because of these advantages, this study used the zebrafish embryo model in in vivo experiments. Black soybeans are rich in bioactive compounds such as isoflav, anthocyanins, and saponins, which are beneficial to human health [11]. Several studies have indicated that black soybeans can prevent low-density lipoprotein oxidation, lower cholesterol levels, scavenge free radicals, and enhance gastrointestinal function [12; 13]. During germination, the metabolism, structure, and gene expression of black soybean undergo changes [14]. The enzymes in black soybeans are activated by germination to enhance the nutritional value and promote the bioavailability of functional components [15; 16]. [PERSON] et al. established that germination not only significantly increased the anti-oxidant activities of black soybeans, but also enhanced the production of phenols and other anti-oxidant components such as peptides without aromatic amino acids [17]. In addition, fermentation could also improve the nutritional value and beneficial bioactivities of black soybean products [18]. [PERSON] and [PERSON] indicated that the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and Fe\({}^{2+}\) chelating activities of fermented black soybeans extract were significantly better than those of unfrenmented black soybeans extract [19]. Moreover, the inhibitory effect of black soybeans on tyrosinase activity in vitro were also significantly improved after fermentation [20]. Studies have indicated that glycosyl isoflavenes in soy milk are hydrolyzed to deglycosylated isoflavenes by \(\beta\)-glucosidase from lactic acid bacteria (LAB). Therefore, the content of bioactive ingredients in soy milk is increased by fermentation with LAB, which could significantly reduce the carbohydrates that cannot be absorbed by humans. _Lactobacillus plantarum_ TWK10 (TWK10) was isolated from Taiwanese pickled cabbage in our lab [21]. TWK10 fermented soy milk has been shown to display many beneficial bioactivities including anti-hypertension [22], anti-oxidation, promotion of wound healing [23] and improvement of hypertension- or diabetes-associated dementia [24; 25]. [PERSON] et al.