Abstract
Okara is a major by-product of soymilk and tofu production. Despite retaining abundant nutrients after the process, okara is often under-utilized. In this study, solid-state fermentation (SSF) of okara was carried out using a koji starter (containing both Aspergillus oryzae and Aspergillus sojae) with the intention of releasing its untapped nutrients. Its effects on lipid metabolism in diet-induced obesity (DIO) were observed. The nutritional profile of fermented okara was elucidated using the following parameters: total phenolic content (TPC), pH, protein content, dietary fiber, amino acid content, and free sugar content. In vivo experiments were conducted using high-fat diets supplemented with unfermented okara and fermented okara over three weeks. Supplementation with fermented okara reduced body weight gain, adipose tissue weight, the serum triglyceride profile, and lipid accumulation in the liver, and altered the mRNA expression levels related to lipid metabolism; however, it did not affect pH and short-chain fatty acid (SCFA) production in this study. In conclusion, high-fat diets supplemented using okara fermented with Aspergillus spp. improved the lipid metabolism in mice, due to their high nutritional value, such as TPC, soy protein, and amino acids, and their synergistic effects without altering the gut microbiota.
Highlights
Okara is the insoluble residual components of ground soybean (Glycine max), obtained as a by-product of the soymilk and tofu production process
Previous research on the solid-state fermentation (SSF) of okara using various food-grade microorganisms such as A. oryzae, Rhizopus oligosporus, Lactiplantibacillus plantarum, and Saccharomyces cerevisiae has shown a significant enhancement of its nutritional profile [10,11,12,13]
This study was designed to quantify the effect of SSF okara on diet-induced obesity (DIO) in a rodent model
Summary
Okara is the insoluble residual components of ground soybean (Glycine max), obtained as a by-product of the soymilk and tofu production process. Incorporating okara in gluten-free cookies increases the protein and fiber content [6], demonstrating the potential of okara as a functional and beneficial ingredient in the human diet. In Japan, fermentation starter cultures are called koji starters, which typically consist of steamed rice inoculated with the filamentous fungus Aspergillus oryzae Other fungi such as A. sojae, A. luchuensis, and A. awamori are used in the food industry, not as frequently [9]. Previous research on the SSF of okara using various food-grade microorganisms such as A. oryzae, Rhizopus oligosporus, Lactiplantibacillus plantarum, and Saccharomyces cerevisiae has shown a significant enhancement of its nutritional profile [10,11,12,13]. This study was designed to quantify the effect of SSF okara (fermented with a mixture of A. oryzae and A. sojae) on DIO in a rodent model. To determine the functionality of fermented okara in managing DIO, in vivo tests were conducted, in which changes in body profiles (body weight gain and tissue weight), lipid profiles (cholesterol and triglyceride) in the serum and liver, histological analysis in the liver, and the hepatic lipid metabolism gene expression were evaluated
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