Lactic acid bacteria fermentations in oat-based suspensions
Sammanfattning: This thesis deals with the fermentation characteristics of lactic acid bacteria (LAB) in oat-based suspensions, with formulation work of fermented products based on oat and with nutritional studies of these products. Changes in structure in terms of viscosity and ropiness were studied when exopolysaccharide (EPS)-producing LAB strains, namely, Lactobacillus delbrueckii subsp. bulgaricus NCFB 2772, Lactobacillus brevis G-77 and Pediococcus damnosus 2.6 were grown in these oat-based suspensions. Differences in structure were seen after growth of EPS-producing bacteria, resulting in higher viscosity and ropiness in these products. The formulation work of fermented products was carried out by using commercial yoghurt cultures with and without the presence of an EPS-producing strain. The products developed were found to have sensory acceptance and good bacterial survival during storage. The bacterial survival of three probiotic strains, Lactobacillus reuteri ATCC 55730, Lactobacillus acidophilus DSM 20079 and Bifidobacterium bifidum DSM 20456, was also studied in different oat-based suspensions with and without the influence of a yoghurt culture during 30 days of storage. The highest survival was seen for the Lactobacillus reuteri strain. The co-fermentation in the presence of a yoghurt culture gave a lower pH in the final products and decreased the survival rates for all strains. The nutritional effects of fermented, oat-based products were investigated by using germfree and conventional rats and by performing a clinical study on 56 healthy subjects. Physiological parameters such as changes in serum cholesterol, faecal excretion of cholesterol, and amount of faecal short chain fatty acids (SCFA) were studied. In addition, changes in the faecal flora were investigated in the human subjects. No changes in the serum cholesterol levels or faecal excretion of cholesterol were seen in the rat models when the animals were fed on different, fermented oat-based products. A diffeent feacal SCFA pattern was seen in the conventional rats fed on the oat-based diets than in the group fed on rice. A lipid lowering effect was seen in the human subjects eating a fermented, ropy, oat-based product for five weeks, which gave a dietary intake of 3.5 g native beta-glucans from oat per day. An increase in total bacterial count and Bifidobacterium subsp. was also seen in faecal samples from these subjects. In conclusion, there is a potential for the development of fermented, non-dairy, oat-based products with a "ropy" structure containing soluble fibres of both native and microbial origin and with the lipid lowering effect that is generally associated with an intake of oat.
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