Document Type

Thesis - Open Access

Award Date

2025

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

Bishnu Karki

Abstract

Globally, soybean is the most widely cultivated oilseed crops, and serve as the primary source of cooking oil, contributing to around 50% of global oilseed production. During the industrial processing of soybean oil, a significant amount of soybean hull (SH) is produced, which makes up about 8% of the grain yield, resulting in approximately 18–20 million tons of hulls, one of the largest by-products in the soybean industry. The hulls have limited commercial value and are primarily used as fiber additives in dairy cattle feed, but a large portion is still discarded as agricultural waste. Similarly, cheese whey (CW), a liquid waste byproduct from cheese production, constitutes about 85-95% of the milk's volume and contains approximately 55% of the nutrients found in milk. It is a complex mixture made up of lipids, proteins, carbohydrates, vitamins, and minerals. Around 50% of the CW produced is used for making fresh products, animal feed, and extracting valuable compounds such as whey protein and β-galactosidase. However, due to the high processing costs involved in utilizing CW for these purposes, a significant portion (about half of the total production) is discarded and directed to industrial effluent treatment plants. Thus, this research was designed to evaluate the feasibility of fungal bioprocessing technologies (such as submerged fermentation, solid-state fermentation) for the potential industrial use of by-products like SH and CW. The study presents the results of fermenting SH and CW under submerged and solid-state conditions using three GRAS (generally regarded as safe) fungal strains: Aureobasidium pullulans (Ap), Aspergillus niger (An), and Trichoderma reesei (Tr). The objectives of this study are: (1) to assess the feasibility of fermenting SH and CW using three microbes (Ap, Tr, and An) under submerged and solid- state fermentation; (2) to evaluate the most effective fungal culture for enhancing microbial fermentation of SH and recovering the CW nutrients; (3) to examine the effects of fungal fermentation of SH by assessing the protein content, total solid recovery, fibers (crude fiber, acid detergent fiber, neutral detergent fiber), total soluble sugars, structural components, total phenolics, antioxidant activity, and cellulase activities; and (4) to determine if CW can replace freshwater in fermentation processes of SH, achieving similar or improved results. The submerged fermentation of 5-day in SH with either water (W) or CW using Tr resulted in the most significant enhancement in SHs nutritional profile, increasing the crude protein (CP), total phenolic content (TPC) and antioxidant activity. Also, fermentation with Tr resulted in a highest significant reduction in crude fiber (CF) and neutral detergent fiber (NDF) along with highest mass loss, with a significant portion of the starting material becoming unrecoverable in the pellets. Whereas structural carbohydrate analysis revealed that Ap was particularly effective in breaking down hemicellulose components such as xylan and arabinan. Overall, these findings demonstrate the potential of microbial fermentation in using both W and CW, as a viable method for enhancing the value of SH. These findings also highlight the crucial role of microbial strain selection and fermentation medium in optimizing SH bioconversion. The solid-state fermentation of SH for 7 days showed that solid-state fermentation positively influenced the nutrient profile of SH; the fungus An performed better when inoculated alone or in combination with other fungi. Particularly, An and tri-culture (Ap+An+Tr) showed the highest activities of β- glucosidase and endoglucanase enzymes. These treatments also significantly boosted bioactivity by increasing TPC and antioxidant activity. CW supplementation further boosted protein and phenolic levels compared to water, highlighting its potential as a nutrient-rich fermentation medium. Furthermore, fermentation led to a significant reduction in CF, acid detergent fiber (ADF), NDF, as well as hemicelluloses like xylan and arabinan, thereby effectively upgrading SHs into nutritionally enriched products. Overall, these findings highlight the promising potential of fungal fermentation in valorizing SH and CW, offering a cost-effective approach for utilizing these oftenunderutilized byproducts. Fungal fermentation can generate nutrient-dense biomass, offering a valuable source that can be utilized for various industrial applications, such as enriched animal feed or functional food ingredients.

Library of Congress Subject Headings

Soybean -- Processing.
Whey.
Fermentation.
Fungi -- Cultures and culture media.

Publisher

South Dakota State University

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Rights Statement

In Copyright