Abstract
Fermented soybean products have attracted great attention due to their health benefits. In the present study, the hypoxia-injured PC12 cells induced by cobalt chloride (CoCl2) were used to evaluate the neuroprotective potency of tofu fermented by Actinomucor elegans (FT). Results indicated that FT exhibited higher phenolic content and antioxidant activity than tofu. Moreover, most soybean isoflavone glycosides were hydrolyzed into their corresponding aglycones during fermentation. FT demonstrated a significant protective effect on PC12 cells against hypoxic injury by maintaining cell viability, reducing lactic dehydrogenase leakage, and inhibiting oxidative stress. The cell apoptosis was significantly attenuated by the FT through down-regulation of caspase-3, caspases-8, caspase-9, and Bax, and up-regulation of Bcl-2 and Bcl-xL. S-phase cell arrest was significantly inhibited by the FT through increasing cyclin A and decreasing the p21 protein level. Furthermore, treatment with the FT activated autophagy, indicating that autophagy possibly acted as a survival mechanism against CoCl2-induced injury. Overall, FT offered a potential protective effect on nerve cells in vitro against hypoxic damage.
Highlights
Soybean is a crucial crop and has been consumed for thousands of years in Asia.Wide varieties of soy products are available in everyday life, including tofu, soymilk, soy mayonnaise, boiled soybeans, roasted soybean, and textured soy protein, which are popular all over the world due to their high amount of protein, unsaturated fatty acid, minerals, vitamins, and especially isoflavones [1,2,3]
The insoluble phenolics can be released by enzymes generated from microorganisms, which could break down the bond between phenolics and cellular components [15]
The increased total phenolic content (TPC) in the fermented tofu observed in our study might be due to the enzymes such as α-amylase, β-glucosidase, endoglucanase, exoglucanase, esterase, and protease released by A. elegans during fermentation [18]
Summary
Soybean is a crucial crop and has been consumed for thousands of years in Asia.Wide varieties of soy products are available in everyday life, including tofu, soymilk, soy mayonnaise, boiled soybeans, roasted soybean, and textured soy protein, which are popular all over the world due to their high amount of protein, unsaturated fatty acid, minerals, vitamins, and especially isoflavones [1,2,3]. Fermentation has been an efficient approach to improving the nutrition and bioactivity of soybean foods, and their application plays a crucial role in producing biomolecules such as organic acids, phenolic compounds, flavor, and pigments [5]. Shahzad et al (2020) indicated that soybean fermented with Bacillus amyloliquefaciens RWL-1 has a higher content of total amino acids, antioxidants, total phenolic, and isoflavones than that of soybean [6]. Xiao et al (2014) reported a significant increase in the total phenolics, saponins, protective effects against DNA damage, and antioxidant capacity of chickpeas after fermentation with Cordyceps militaris SN-18 [7]. Ali et al (2017) found that the total amino acids, isoflavone aglycone, and antioxidant activity of soybean significantly increases after fermentation with probiotic Bacillus subtilis [8]. Little attention is paid to studying the neuroprotective effects of tofu fermented with A. elegans
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