Nutritional effects of barley products — Mechanisms of action in the intestinal tract

Author

Summary, in English

Barley is one of the most important crops in the world. Although it is mainly used as the raw material for the production of beer and animal feed, it has recently attracted interest from nutritionists and consumers, due to its high content of dietary fibre, especially β-glucan, and its relation to various positive health effects. The proposed mechanisms behind the health effects are the formation of short-chain fatty acids (SCFA), especially butyric acid, and the modification of the microbiota in the colon.

The work described in this thesis was focused on how the barley variety, malting, fat content and addition of probiotics to the diet affected the formation of SCFA and the composition of the microbiota in the hindgut of rats. The risk factors associated with low-grade inflammation were also studied, as well as levels of amino acids and cholesterol in the portal plasma. For this purpose, two barley varieties (whole-grain barley SW 49427 and Hadm 12011-06, referred to as SW and Hadm, respectively), high and low in dietary fibre and β-glucan content, respectively, four barley malts (caramelized and coloured malt, 50-malt and 350-malt) with different β-glucan contents and colours, and five probiotic strains (Lactobacillus paracasei 87002, Lactobacillus plantarum HEAL 9 and HEAL 19, Bifidobacterium infantis CURE 21 and Lactobacillus rhamnosus 271) were evaluated. The effect of the different probiotic strains was investigated together with malted barley. A conventional rat model, which has been shown to reflect the results concerning dietary fibre fermentation in humans, was used.

All the barley products generally increased the amount of SCFA in the hindgut and portal vein serum of rats, compared with the control groups. SW induced a higher caecal content of acetic acid and propionic acid in rats than Hadm, and in rats fed high-fat diets a higher caecal content of butyric acid was also seen when incorporated in the diet at the same flour level. However, when whole-grain barleys were consumed at the same dietary fibre level, similar profiles of SCFA were found in the rats. This was most probably due to the rather similar dietary fibre compositions of the diets. The increase in SCFA induced by whole-grain barleys was further enhanced by a high-fat content, apart from butyric acid and minor SCFA (iso-butyric acid, iso-valeric acid and valeric acid), which generally decreased to levels similar to those in rats consuming control diets. The effect was more pronounced when the dietary fibre intake was low. Interestingly, barley malts counteracted those effects. Furthermore, rats fed barley malts had lower caecal amounts of succinic acid, an intermediate acid and precursor of butyric acid, than rats given the two whole-grain barley varieties.

A high-fat diet decreased the abundance of total bacteria and Lactobacillus in the caecum, while whole-grain barleys increased the abundance of Lactobacillus. Furthermore, a high-fat diet increased the population of Akkermansia in rats fed whole-grain barleys. The caecal microbiota composition was different in rats fed whole-grain barley, barley malt and the control diet. Barley malt considerably increased the relative abundance of Roseburia, a butyrate-producer, while that of Akkermansia decreased.

A high-fat diet increased the concentration of lipopolysaccharide-binding protein and amino acids in the portal vein plasma and the mRNA expression of toll-like receptor 4 in the distal colon, and tight junction proteins (zonula occludens-1 and occludin) in the small intestine and distal colon, while barley products not only inhibited the increase in the plasma concentration of lipopolysaccharide-binding protein (whole-grain barleys), amino acids and mRNA expression (barley malts) to some extent, but also decreased the plasma concentration of mono¬cyte chemoattractant protein-1 (whole-grain barleys). However, high amount of advanced glycation end-products in the diet impaired the positive effect of barley malts on small intestinal occludin and portal vein amino acids.

Supplementation of the diet with probiotics had no effect on dietary fibre fermentation or SCFA formation, but increased the portal vein concentration of amino acids, and changed the composition of dominant Lactobacillus strains. A cholesterol-lowering effect was only seen with SW, which contributed to the highest amount of β-glucan in the diet.

In conclusion, barley products increased the caecal formation of SCFA, modulated microbiota composition, reduced low-grade inflammation-associated risk factors and lowered plasma cholesterol. The effects were dependent on variety, malting conditions and fat content of the diet, suggesting that the dietary fibre composition and fat content are of the greatest importance. Furthermore, malting could provide a means of changing the characteristics of dietary fibre in order to optimize the positive health effects of barley.

Topic

  • Engineering and Technology

Keywords

  • dietary fibre
  • malting
  • probiotics
  • high-fat diets
  • short-chain fatty acids
  • gut microbiota
  • low-grade inflammation
  • gene expression
  • Barley

Status

Published

Project

  • ANTIDIABETIC FOOD CENTRE

Research group

  • Department of Food Technology, Engineering and Nutrition-lup-obsolete

Supervisor

ISBN/ISSN/Other

  • ISBN: 978-91-7422-402-3

Defence date

15 June 2015

Defence time

09:15

Defence place

Lecture hall F, Kemicentrum, Getingevägen 60, Lund University, Faculty of Engineering LTH, Lund