Protein content in Brewer’s spent grain and its characteristics : upcycling spent grain from food waste to protein source

Sammanfattning: The United Nations have adopted sustainable development goals (SDGs). Within these SDGs, food waste management and waste valorization, an increase in value, is found. For these reasons, it was of interest to study Brewers’ spent grain, a residual product from beer production. In 2020 beer was one of the largest categories among the production of alcoholic beverages and Brewers’ Spent grain (BSG) was one of the largest sources of waste in beer production. This study aimed to extract protein from two variants of BSG, dried at different temperatures, and to study some of the protein characteristics. The protein extraction was an alkali-soluble and acid precipitation and was performed in variations. The extraction was most successful when using an alkaline concentration of 55 mM (NaOH) and a pH of 3.8 when isoelectric precipitation was performed. Concentration measurements of the proteins in the precipitates were made through Bradford analysis and for two samples using Kjeldahl analysis. At the most, the concentrations of protein showed to be 53.50% for the BSG dried at 50-60°C, results obtained from a Kjeldahl analysis. For the characterization, SDS-gels, gel filtration, foaming, gelation, and protein nanofibrilation (PNF) was carried out. The results from the SDS-gel and gel filtration showed indications of protein (or complex) of sizes > 200 kDa. The obtained proteins showed abilities to form gel and foam, but the stability and ability were questionable as the precipitates were not only pure protein. For the same reason, the results of the ability to form PNFs were difficult to draw any conclusions from. In conclusion protein from the BSG in question was able to be extracted. The precipitates showed the ability to form gel and foams, with varying desirable characteristics. Judging by the protein concentrations obtained in the precipitates and total protein content in the BSG, the use of protein as a valorization may not be the answer.