Production of β-Glucans from Rhizopus oryzae M10A1 by Optimizing Culture Conditions Using Liquid Potato Starch Waste

β-glucans from filamentous fungi are important for human health. There is limited research on polysaccharides from filamentous fungi, and no reports have been published regarding the optimization of culture media to produce β-glucans from <i>Rhizopus oryzae</i> using liquid waste from potato starch processing. In this regard, the fermentation conditions to produce β-glucans from <i>Rhizopus oryzae</i> M10A1 were optimized using the one variable at a time (OVAT) and response surface methodology (RSM). The β-glucans were chemically characterized by determining moisture, nitrogen, protein, fat, ash, and total carbohydrates. The color, molecular weight, β-glucan content, monosaccharide composition, and structural and conformational characteristics were assessed by colorimetry, gel permeation chromatography, high-performance liquid chromatography, and Fourier transform infrared spectroscopy, respectively. The microbial indicators, mesophilic aerobes, molds, yeasts, and <i>Escherichia coli</i> were quantified following ISO standard protocols. Optimization indicated that supplementation with 0.8% (<i>w</i>/<i>v</i>) glucose and ammonium sulfate enhanced heteroglycan production (3254.56 mg/100 g of biomass). The β-glucans exhibited high purity, a light brown color, a molecular weight of 450 kDa, and a composition predominantly consisting of glucose and galactose. These findings suggest that β-glucans from <i>Rhizopus oryzae</i> M10A1 could be used for food and health applications.