Influence of Brewer's Spent Grain Compounds on Glucose Metabolism Enzymes

Characterization of brewer's spent grain extracts by tandem mass spectrometry and HPLC-DAD: Ferulic acid dehydrodimers, phenolamides, and oxylipins

Brewer's spent grain (BSG) is a major by-product of the brewing industry which is generated in high amounts. In recent years, sustainable food production has become more and more important. BSG mainly used as cattle feed has gained high interest due to not only its valuable ingredients such as fiber and proteins but also secondary metabolites remaining in BSG after the brewing process and known for many biological effects. In the present study, various methods were applied, such as acetone extraction (A), alkaline hydrolysis followed by ethyl acetate extraction (HE), and acetone extraction of alkaline hydrolysis residue (HA). Compounds present in the respective bioactive extracts were characterized by mass spectrometry to identify the active compounds. Various hydroxycinnamic acid derivatives as well as oxylipins and some dicarboxylic acids, such as azelaic acid, were present in HE and HA extracts. In contrast, some catechins and phenolamides, such as numerous hordatines, as well as oxylipins and phospholipids were detected in A extracts. Quantification using HPLC-DAD revealed hordatine contents up to 172.2 ± 2.1 μg p-coumaric acid equivalents/mg extract. Hydroxycinnamic acid derivatives content accounted for up to 48% of the total extract (HE extracts) but only around 3% of the total HA extracts. In summary, all extracts contained secondary plant metabolites belonging to different classes, ranging from hydroxycinnamic acids to phenolamides, such as not only hordatines but also oxylipins, which were identified for the first time in BSG.

In Vitro Digestibility and Bioaccessibility of Nutrients and Non-Nutrients Composing Extruded Brewers' Spent Grain

This study aimed to evaluate the effect of the extrusion process on the bioaccessibility of brewers’ spent grain (BSG) nutrients (carbohydrates and proteins) and non-nutrients (bioactive compounds). BSG and extruded BSG (EBSG) were digested in vitro simulating human oral-gastro-intestinal digestion and colonic fermentation. The duodenal bioaccessibility of glucose, amino acids and phenolic compounds was analyzed. The fermentability of the dietary fiber was assessed by analysis of short-chain fatty acids. Additionally, assessment of the bioaccessibility of phenolic compounds after colonic fermentation was undertaken. The antioxidant, anti-inflammatory and antidiabetic properties of the bioaccessible compounds were studied. Extrusion caused no change in the digestibility of gluten and glucose bioaccessibility (p > 0.05). Moreover, the bioaccessibility of amino acids and phenolic compounds significantly increased (p < 0.05) due to extrusion. However, higher short-chain fatty acid content was formed in colonic fermentation of BSG (p < 0.05) compared to EBSG. The latter inhibited intracellular ROS formation in IEC-6 cells and showed anti-inflammatory properties in RAW264.7 cells. With respect to antidiabetic properties, glucose absorption was lower, and the inhibition of carbohydrases higher (p < 0.05), in the presence of EBSG compared to BSG. The effects of EBSG and BSG digests on glucose transporters were not significantly different (p > 0.05). In conclusion, extrusion positively affected the nutritional value and health-promoting properties of BSG.

Isolation and Characterisation of Hordatine-Rich Fractions from Brewer’s Spent Grain and Their Biological Activity on α-Glucosidase and Glycogen Phosphorylase α

Hordatines are a characteristic class of secondary metabolites found in barley which have been reported to be present in barley malt, beer and, recently, brewer´s spent grain (BSG). However, little is known about their biological activities such as antioxidative effects in beer or antifungal activity as their main task within the plants. We conducted an in vitro investigation of the activity of hordatines isolated from BSG towards enzymes of glucose metabolism. Hordatine-rich fractions from BSG were prepared by solid-liquid extraction (SLE) with 60% acetone followed by purification and fractionation. The fractions were characterised and investigated for their in vitro inhibitory potential on α-glucosidase and glycogen phosphorylase α (GPα). Both enzymes are relevant within the human glucose metabolism regarding the digestion of carbohydrates as well as the liberation of glucose from the liver. In total, 10 hordatine-rich fractions varying in the composition of different hordatines were separated and analysed by mass spectrometry. Hordatine A, B and C, as well as hydroxylated aglycons and many glycosides, were detected in the fractions. The total hordatine content was analysed by HPLC-DAD using a semi-quantitative approach and ranged from 60.7 ± 3.1 to 259.6 ± 6.1 µg p-coumaric acid equivalents/mg fraction. Regarding the biological activity of fractions, no inhibitory effect on GPα was observed, whereas an inhibitory effect on α-glucosidase was detected (IC50 values: 77.5 ± 6.5–194.1 ± 2.6 µg/mL). Overall, the results confirmed that hordatines are present in BSG in relatively high amounts and provided evidence that they are potent inhibitors of α-glucosidase. Further research is needed to confirm these results and identify the active hordatine structure.

Dietary Brewer Grain Meal with Multienzymes Supplementation Affects Growth Performance, Gut Health, and Antioxidative Status of Weaning Pigs

We conducted a 28-day feeding study on 80 weaning pigs [(Landrace × Large White) × Duroc] to determine the effects of dietary inclusion with brewer’s grain meal (BGM) and multienzymes on their growth, intestinal health, and antioxidative status. Piglets were grouped by sex and initial BW and assigned to 20 pens with four pigs each. Treatments were a corn–soybean meal-based diet with either 0.1% multienzyme addition (PC) or without (NC), and two BGM compositions fortified with 0.1% multienzyme: 10% (BGM10) and 20% (BGM20). The overall body weight, average daily weight gain, and weight gain:feed ratio were significantly greater in pigs fed BGM20 than those fed the NC diet (p < 0.05). Moreover, the BGM diets significantly increased the digestibility of total ash and ether extract, glucose, total protein, immunoglobulin A, total antioxidant capacity, superoxide dismutase, heart and small intestine weights, villus height: crypt depth ratio (VH/CD), and Lactobacillus spp. count compared with the NC diet (p < 0.05). The diarrheal rate, blood urea nitrogen, malondialdehyde, duodenal crypt depth, and Salmonella spp. count were reduced in pigs fed the BGM-supplemented diet than those fed the NC diet (p < 0.05). The diarrheal rate (p = 0.010), ether extract digestibility (p = 0.044), total protein (p = 0.044), and duodenal villus height and VH/CD (p = 0.003 and p = 0.002, respectively) decreased quadratically with the increase in BGM supplementation. Overall, diets containing up to 20% BGM with multienzyme addition improved the nutrient utilization and intestinal health in weaning pigs by suppressing pathogenic bacterial growth without compromising the overall growth of the pigs.