Browsing by Subject "beta-glucan"

The present literature was reviewed to understand the recent indications of lipid degradation affecting β glucan molecular weight in aqueous solutions, the main topics being oat lipid reactions, oat β glucan, and oat bran/β glucan fortified yogurts, as well as the possible interplay of these three. A non-heat treated, a heat treated, and a heat treated and defatted oat bran concentrate (OBC) were produced, all with ~20% β glucan. OBCs were subjected to a storage trial in dark for 0–12 weeks at 4, 22 and 40 °C. Lipid degradation was followed during storage by assessing volatile compounds (HS-SPME-GC-MS), neutral lipid classes (NP-HPLC-ELSD) and tocopherol and tocotrienol levels (NP-HPLC-FLD) as well as β glucan molecular weights (HP-SEC). Acid milk gels were prepared as a model system for yogurts with added OBCs, and analysed for spontaneous and forced syneresis and textural changes. Lipid oxidation was observed in all OBCs, and hydrolysis in the non-heat treated OBC, but no changes in β glucan molecular weight were observed in the dry stored OBCs. OBC addition caused structural changes in an acid milk gels, the water retaining properties were improved, and the gels were softer and smoother than without added OBCs. Time and temperature affected OBC lipid oxidation and hydrolysis behaviours. Adding OBCs to gels changed gel textures compared to both without vs. with OBCs and adding fresh vs. stored OBCs.

Plant-based milks can be unstable during storage due to the colloidal structure of these drinks. In general, e-coded additives are used to increase the viscosity of the drinks and hence, improve stability. Oat beta-glucan, microbially or enzymatically produced exopolysaccharides, such as dextran, and flaxseed mucilage are natural hydrocolloids that are known to have the ability to increase viscosity. These hydrocolloids could potentially be used to replace e-coded additives. The aim of this thesis was to study the stabilizing potential of oat beta-glucan, exopolysaccharides, and flaxseed mucilage in oat drinks. Oat drinks with added hydrocolloids were compared to control samples that were oat drink without added hydrocolloids and oat drinks with pectin at concentrations of 0.2% and 0.4%. Oat beta-glucan, exopolysaccharides, and flaxseed mucilage were added to the prepared drinks by replacing 10% of water with the extracts. Additionally, stabilizing properties of isolated and freeze-dried microbially produced dextran was studied by adding it to the drinks at concentrations of 1.5%, 1.0% and 0.5%. Stability of the oat drinks was assessed during a 14−day storage period by measuring the viscosity, pH, and phase separation. Results of this study demonstrated the stabilizing potential of the natural hydrocolloids. The addition of hydrocolloids increased the viscosity in all samples. The inclusion of natural hydrocolloids led to a similar stability, and in some cases also significantly lower viscosity, compared to pectin added drinks. Oat beta-glucan had a remarkable positive impact on the stability of oat drinks. This was most likely due to the network formation of oat beta-glucan molecules, which decreased the sedimentation of colloidal particles. Enzymatically produced dextran also improved the stability of oat drinks, which might be attributed to the viscosity-increasing -capacity of dextran. However, the stabilizing role of microbially produced exopolysaccharides was not shown. For future study, the molecular interactions of natural hydrocolloids in the colloidal solution should be investigated.

Oat β-glucan is well known for its health benefits, which are related to its rheological behavior in the gut. The objective of this thesis was to investigate the extractability and viscosity of β-glucan from oat bread under physiological conditions and to see whether there were varietal differences. Oat flours of twenty different cultivars were used to bake breads which were subjected to in vitro digestion. The resulting extracts were studied for viscosity using a rheometer, and the β-glucan contents of the breads and the extracts were determined to evaluate the extractability. In addition, the effect of flour particle size on extractability was investigated. Variance in the in vitro extractability of β-glucan was seen between cultivars, which was not explained by flour particle size. All samples produced highly viscous extracts, and the viscosities increased sharply with increasing β-glucan concentration, which suggests that the β-glucan was not extensively degraded during the breadmaking process. The viscosities also varied between cultivars, as some exhibited considerably higher viscosities at similar concentrations. The results indicate that the β-glucan from the oat breads would have good capacity to increase viscosity in the intestine, although varietal differences were observed.

Most barley is used for animal feed or malting. However, barley contains technologically and nutritionally valuable components. The compositions of different barley cultivars as well as the factors affecting the concentrations of different nutrients (beta-glucan, protein, starch and ash) were surveyed in the literature part of this Master’s thesis. Special attention was paid to beta-glucan as it has attained significant interest in the food industry due to its positive health effects. In addition, the effect of grain composition on the pearling, milling and air classification properties of barley were surveyed. The nutrient composition and milling properties of ten different barley varieties were examined in the experimental part of the thesis. The varieties were divided into four subgroups based on their potential end usage: 1) speciality barley, 2) feed barley, and 3) starch barley, and 4) malting barley. The milling properties were analysed by sieve analysis and volumetric particle size distribution from the whole grain barley flours. In addition, coarse fractions were separated from the whole grain flour by air classification. These fractions were also analysed by the abovementioned particle analyses. Beta-glucan, protein and ash concentrations were usually higher in the speciality barley varieties and their coarse fractions. Starch concentrations were lower in these varieties and fractions. Feed and starch barleys had somewhat higher beta-glucan concentration compared to malting barleys, which respectively had the highest starch concentrations. Zero to 25 % of the grain’s outer layers was removed by pearling. Compositional analyses revealed that pearling decreased the amount of ash and increased the concentration of starch and betaglucan until about 15 % of the grain was pearled off. Starch and beta-glucan concentrations did not change significantly after this pearling level. Pearled barley flour was manufactured by pearling off 15–20 % of the grain’s outer layers, and milling the remaining pearled grains with a fine impact mill. Flour was then air classified to give fine and coarse fractions. The coarse fractions contained enriched concentrations of beta-glucan, protein and ash. However, their concentrations and yields were dependent on the speed of the classifier wheel. By contrast, starch was enriched in the fine fractions. The highest beta-glucan concentration was obtained with the beta-glucan-rich speciality variety D, which initially had 9.4 % beta-glucan. The beta-glucan concentration was enriched up to 11.4 % by pearling. Air classification of whole grain flour resulted maximally in 13.5 % and air classification of pearled grain flour in 15.5 % beta-glucan concentration. Based on the results, the beta-glucan concentration of the raw material seems to play the most important role in the enrichment. However, proper milling technology and air classifier settings are of utmost importance.