Extraction of brewers’ spent grain in near subcritical conditions: A method to obtain high protein contents extracts

Abstract

Listen

Translate article

Accelerated solvent extractor (ASE) was used in extraction of proteins from brewers’ spent grain (BSG) using water as solvent in near subcritical conditions (<100 °C, ∼100 bar). Variables in the study were extraction time (20, 60 and 120 min) and NaOH concentration (0.01, 0.05 and 0.1 N) in the extraction solvent. Extractions were performed so that sample in aforementioned conditions was extracted in four different temperatures (21 (RT), 40, 60 and 80 °C). In between each extraction temperature extraction solvent was changed to fresh solvent. Ultrasonic and mild H 2 SO 4 pretreatments of BSG prior alkaline extraction (0.1 N NaOH, 60 min) were also experimented. Dissolved proteins were precipitated from the extracts by adjusting pH to 3, centrifuged and dried. Protein contents in dried precipitates, and in dried residual BSG after the extractions was determined using Kjeldahl method. The combined amount of precipitated proteins from four extractions varied from 21.3 to 65.3% (db) from the total amount of proteins in fresh BSG. Alkaline extraction of H 2 SO 4 pretreated BSG provided the highest, and 0.01 N NaOH as the extraction solvent the lowest proteins yields. Protein contents in the precipitated and dried extracts was more than three times the protein contents in BSG (18.6%) in 16 of the 41 analyzed extracts. Highest protein contents (69.7%) in dried extract was obtained when dried BSG was extracted with 0.05 N NaOH for 60 min at 40 °C. Water-extraction near subcritical conditions was shown to be a promising method to concentrate proteins from BSG with high protein contents and with low chemicals load. • Near subcritical conditions applied in alkaline extraction of proteins from BSG. • pH shift method affords high protein contents extracts from BSG. • Extractions of proteins from preserved six-month-old BSG samples. • Drying and grinding of BSG not required in extraction of proteins.