Influence of Hydrothermal Treatment of Brewer's Spent Grain on the Concentration and Molecular Weight Distribution of 1,3-1,4-β-D-Glucan and Arabinoxylan

Brewer's spent grain (BSG) is the most abundant residual in the brewing process. Non-starch polysaccharides such as 1,3-1,4-beta-D-glucan (beta-glucan) and arabinoxylan (AX) with proven beneficial effects on human health remain in this by-product in high amounts. Incorporating the valuable dietary fiber into the food industry could contribute to a healthy diet. However, a major challenge is extracting these dietary fibers (i.e., beta-glucan and AX) from the solid residue. In this study, hydrothermal treatment (HT) was applied to dissolve the remaining water-insoluble carbohydrates from BSG with the aim to extract high amounts of beta-glucan and AX. Particular focus was placed on the molecular weight (MW) range above 50 kDa and 20 kDa, respectively, as these are considered to have health-promoting effects. Different treatment temperatures, reaction times, and internal reactor pressures were tested to determine the best process settings to achieve high yields of beta-glucan and AX and to examine the influence on their molecular weight distribution (MWD). Overall, 85.1% beta-glucan and 77.3% AX were extracted corresponding to 6.3 g per kg BSG at 160 degrees C and 178.3 g kg(-1) at 170 degrees C, respectively. However, less than 20% of both fiber substances were in the desirable MW range above 50 kDa and 20 kDa, respectively. When lower temperatures of 140 and 150 degrees C were applied, yields of only 3.0 g kg(-1) beta-glucan and 128.8 g kg(-1) AX were obtained, whereby the proportion of desirable fiber fractions increased up to 45%. Further investigations focused on the heat-induced degradation of monosaccharides and the formation of undesirable by-products (i.e., HMF and furfural) that might pose a health risk.

Automated summary

This study focuses on extracting beta-glucan and arabinoxylan from brewer's spent grain using hydrothermal treatment. The results show that high yields of fiber can be obtained with the right process settings, and a larger proportion of desirable fiber fractions can be achieved at lower temperatures.