Sustainable extraction of antioxidant and antimicrobial proteins and peptides from brewer’s spent grain (BSG).

JOHANA SILVA; MAXIMILIANO VILLEGAS; BERLI, ANABELA; TONON, C.V.; TITO, FLORENCIA ROCÍO; PEPE, ALFONSO; MARÍA G. GUEVARA.

Mendoza

Congreso; Reunión Anual de la Sociedad de Bioquímica y Biología Molecular Argentina; 2022

Brewer’s spent grain (BSG) is the main by-product of brewing production since it constitutes 85% of the total waste generated in this process. BSG is a lignocellulosic material with a high content of sugars, proteins, and minerals. Additionally, BSG has been reported as a source of bioactive compounds, with antioxidant and antihypertensive activities. A common practice is to dispose of this by-product in landfills or use it as animal feed. Therefore, the environmental perspective is necessary to generate new sustainable products that increase BSG's economic value. This work aims to standardize and optimize the extraction conditions of water-soluble proteins and peptides with antimicrobial and antioxidant activities, using environmentally sustainable extraction conditions. Total protein extraction conditions were optimized using four factors with three possible values, following a Box- Behnken experimental design. These factors were pH (5, 7, and 9), temperature (30°C, 45°C, and 60°C), homogenization time (1 min, 2 min, and 3 min), and CaCl2 concentration (0, 5, and 10 mM). The amount of protein extracted varied between 0.5 and 6 g per 100 g of BSG (dry weight). SDS- PAGE analysis of the protein profiles showed that all BSG extracts obtained contain a majority protein with a molecular weight (MW) of 55 kDa., approximately. This molecular weight value would correspond to proteins like hordeins type C. Proteins bands with a molecular weight estimated between 20 and 24 kDa., were detected in extracts obtained at pH 5 and 9, and 60 °C. These molecular weight values correspond to proteins like barley glutelins. The antioxidant activity was analyzed by reducing power, DPPH (2,2-diphenyl-1-picrylhydrazyl) free radicals scavenging activity, and superoxide radical scavenging assay by the antioxidant enzyme superoxide dismutase (SOD). Results show that the maximum value of DPPH radical scavenging, 70 %, was obtained in the extracts with the highest protein content. On the other hand, no antioxidant activity was detected when the BSG was incubated at 37 °C overnight. However, SOD activity was detected in BGS extract after 37 °C overnight incubation. Antimicrobial activity was detected in BSG extracts toward E. coli culture, in a protein content-dependent manner. The results herein obtained optimize a new protocol to obtain antioxidant and antimicrobial proteins and peptides from BSG in a sustainable way.