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

Abstract

Brewer’s spent grain (BSG) is the most abundant residual in the brewing process. Non-starch polysaccharides such as 1,3-1,4-β-D-glucan (β-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., β-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 β-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 β-glucan and AX and to examine the influence on their molecular weight distribution (MWD). Overall, 85.1% β-glucan and 77.3% AX were extracted corresponding to 6.3 g per kg BSG at 160 °C and 178.3 g kg−1 at 170 °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 °C were applied, yields of only 3.0 g kg−1 β-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.

Valorization of Spent Grains from Beer Production through β-Glucan Extraction

“…However, at the higher product purity obtained in this study, the extraction yield (0.057%, w/w) was significantly lower than that reported in [8] (13%, w/w). A much higher extraction yield and recovery yield of β-glucan of 0.63% (w/w) and 85.1% (w/w), respectively were obtained by hydrothermal treatment of BSG at 160 • C, 2 min, and a pressure of 20 bar [4]. However, most of the extracted β-glucan (more than 80%) was degraded to smaller molecules with a molecular weight of less than 50 kDa, which is undesirable as it has less health-promoting effect [18].…”

“…In addition, our study showed that the extraction of β-glucan using hot water resulted in higher β-glucan purity (59.8%, w/w) compared to the hydrothermal extraction (0.63%, w/w). The low product purity could be due to the fact that the β-glucan was not purified from the BSG hydrolysates [4]. Steiner et al [4] illustrated that the arabinoxylan in the extract from hydrothermal treatment of BSG was nearly 30 times higher than that of β-glucan.…”

“…These non-starchy polysaccharides consist of mixed (1→3) and (1→4) β-linkages. β-glucan from brewers' spent grains (BSG) can be used as a hydrocolloid [4]. Barley β-glucan shows great potential as a thickener or stabilizer in food products [5].…”

“…The BSG β-glucan has a lower average molecular mass than the barley β-glucan, which is most likely due to the degradation of the β-glucan during malting and mashing [8]. Currently, there are some reports in the literature on the extraction and characterization of β-glucan from BSG [4,8,9], but there are no reports on the potential applications of the β-glucan from BSG as a functional ingredient in the real food system. In the extraction of β-glucan from BSG by hydrothermal treatment, the treatment temperature and reaction time have an important effect on the extraction and properties of β-glucan [4].…”

“…Currently, there are some reports in the literature on the extraction and characterization of β-glucan from BSG [4,8,9], but there are no reports on the potential applications of the β-glucan from BSG as a functional ingredient in the real food system. In the extraction of β-glucan from BSG by hydrothermal treatment, the treatment temperature and reaction time have an important effect on the extraction and properties of β-glucan [4]. The physical, chemical, and functional properties of β-glucan can be influenced by the extraction conditions [10].…”