Brewers’ spent grains as potential novel functional food ingredients for food security

• Main Author: Tan, Yong Xing
• Other Authors: Chen Wei Ning, William
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Chemical engineering
• Online Access: https://hdl.handle.net/10356/146367
• Institution: Nanyang Technological University

With a growing population and increasing amount of food losses generated, food security is becoming a challenging issue. Facing the impending threat of food security, technology innovations are required to enhance food security. Strategies to enhance food security can be categorized into three main areas, urban farming, processing technology and alternative food sources. This thesis aims to explore the area of food waste processing technology, particularly development of feasible methodologies to sustainably manage brewers’ spent grains (BSG). BSG are residues generated as side streams from beer production. Currently, BSG are used as animal feed or disposed in landfills and these massive amount of BSG generated annually are causing significant environmental, economic, and climatic issues. These disposed BSG are still of high nutritive value, containing compounds such as dietary fibres, fatty acids, proteins, amino acids, polyphenols. Despite previous studies performed on the usage of BSG, there lies an issue of remaining residual waste materials after utilization. Hence, there is an urgent need to utilize BSG and sustainably manage these residues. In this work, bacterial fermentation was employed to harvest the remaining nutrients in BSG and enhance its nutritional profile. BSG were fermented using a generally recognized as safe (GRAS) bacteria, Bacillus subtilis WX-17. The first work seeks to investigate the changes which occurred during fermentation using untargeted metabolomics and pathway analysis. Based on the findings, bacterial fermentation gave a 2-fold increase in the total amount of amino acid from 0.859 ± 0.05 to 1.894 ± 0.1 mg per g of BSG. Also, the total amount of unsaturated fatty acid increased by 1.7 times and the total antioxidant quantity remarkably increased by 5.8 times after fermentation. The increase in various compounds enhanced BSG nutritional profile. In order to assess the potential of fermented BSG as functional food ingredients, an in vitro digestion-fermentation setup was employed. According to the findings, in vitro digestion of fermented BSG had higher amounts of various nutritional components. Vitamin K2 MK7 was detected with concentration of 1.2 x 10-4 ± 5 x 10-6 mg/ mL. Probiotics, Bacillus subtilis WX-17 were observed to be available for absorption. Various short chain fatty acids namely acetic acid, propionic acid and butyric acid were produced at higher amounts for fermented BSG. The concentrations obtained were 124.11 ± 18.72 mM, 13.18 ± 1.38 mM and 46.25 ± 7.57 mM respectively. Lastly, differential genera such as Bacteroides, Odoribacter were detected and correlates to beneficial effects on the intestinal microbiota. This study evaluated the potential of fermented BSG to serve as novel functional food ingredients. The last study explored the possibility of submerged stage fermentation using Bacillus subtilis WX-17 on BSG as the sole substrate to produce a potential novel nutritional beverage as its application. Bacillus subtilis WX-17 was still viable after a period of 6 weeks with a final cell count of 9.86 log CFU/ mL. The other nutritional property such as phenolic content, increased from 125.7 ± 0.74 μg/ mL to 446.74 ± 1.26 μg/ mL. In conclusion, this thesis demonstrates sustainable, zero waste food processing methods to enrich and harvest the nutrients present in underutilized BSG through fermentation using Bacillus subtilis WX-17.