Barley malt products for improved intestinal health

Doktorsavhandling, 2016

Barley is a good source of dietary fibre, particularly β-glucan and arabinoxylan, to increase formation of short-chain fatty acids (SCFAs). Butyric and propionic acid are involved in the preservation of colonic barrier function, thus decreasing the risk of inflammation. Previous studies have shown that malting barley increased formation of butyric acid in caecum of rats and had abundance of butyrate-producing bacteria than unmalted barley. However, this differed between malts, probably due to the differences in fibre functional characteristics. The aim of this work was to investigate the impact of barley variety and malting conditions on the functional properties of the dietary fibre in barley malt products, with the overall aim of improving intestinal health. Focus was given to β-glucan functional properties, but also arabinoxylan. The influence of these fibres on substrate delivery to the colon, SCFAs formation, microbiota composition and gene expression was investigated. In the first study, rats fed commercial barley malts had a higher level of butyric and propionic acids in the caecum and portal serum than those fed control diets (cellulose). β-glucan with broader molecular weight seemed to better increase the caecal SCFA formation. In addition, the malts contributed to improved mucosal barrier function and inflammatory state by decreasing mRNA expression of tight junction protein and toll-like receptors in the small intestine and distal colon. However, malt with high amounts of advanced glycation end-products seemed to attenuate the effect on occludin (tight junction protein) in the small intestine. To evaluate the possibility of using malting to tailor functional characteristics of the fibre, three barley varieties were malted using different temperatures and levels of lactic acid in the steeping water. The extent to which barley components changed depended on the variety. Steeping at 35°C with 0.4% lactic acid preserved soluble fibre and β-glucan content better, but not the soluble arabinoxylan, compared with steeping at 15°C and without lactic acid. However, no changes in β-glucan molecular weight (> 10 kDa) were observed. β-glucan molecular weight analysed with AF4 at a wider molecular weight range (> 2 kDa), was shown to be affected by both variety and processing (steeping or mashing) to different extents. Addition of proteolytic enzymes shifted the β-glucan of high molecular weight to a lower molecular weight range, suggesting that proteins are involved in the structure of β-glucan, which might result in an apparently higher molecular weight. After passage through a dynamic gastrointestinal in vitro model (TIM-1), it was observed that β-glucan molecular weight gradually decreased in the different barley products investigated. The longer in vitro transit time of soluble fibre and β-glucan was related to their high content and/or molecular weight, which also seemed to be linked to a higher degree of fermentation in an in vivo model (rats). In the last study it was investigated the differences of microbiota composition in rats fed barley malt products. Rats fed malt products had higher microbiota diversity (negatively associated with ulcerative colitis and obesity) than those fed barley extracts rich in arabinoxylan or β-glucan, and control. Malts contributing with a higher content of β-glucan increased the abundance of Lactobacillus and Blautia and tended to increase butyric acid, whereas soluble arabinoxylan increased Akkermansia and propionic acid in the caecum. By mixing barley products (brewers’ spent grain and malt) it was possible to modulate the microbiota into an intermediary abundance of taxa, with slight increase of butyric acid compared with malt alone. In conclusion, malting seems to be a potential processing method for tailoring barley composition to promote intestinal health. Both the selection of barley variety and the processing conditions affected the composition of malt products. The resulting barley products with a high content of soluble fibre, β-glucan and soluble arabinoxylan, enhanced colon fermentation, microbiota composition and, to some extent, the SCFA formation.