Extraction of β-glucan from oat bran : effect of extraction method and particle size

Sammanfattning: An increasing number of people are suffering from lifestyle related diseases due to poor dietary habits. The recommendation of a fibre intake of 25-35g per day is not achieved by many. There is a need for an optimization of already existing products in order to provide greater variety and making it easier for people to maintain healthy dietary habits. Oat bran is a by-product in the production of oat products although it is full of nutrients. It is rich in dietary fibre and β-glucan constitutes approximately 5-20% of the bran. A daily intake of β-glucan is known to reduce the risk of cardiovascular diseases and to lower the blood glucose levels and the LDL-cholesterol. The purpose of this study was to investigate how different particle sizes of oat bran and different extraction methods affect the yield and molecular weight of β-glucan. The extraction methods used were wet extraction at 95°C and subcritical water extraction at 95°C, 150°C and 170°C. To evaluate this, particle size of milled oat bran, β-glucan concentration and viscosity, as well as the molecular weight as an estimate of those, were determined. For the wet extraction both time of extraction and particle size had significant effects on the viscosity, and the statistical analysis showed an interaction between the two factors. The viscosity was increasing with decreasing particle size, and for all samples with a longer extraction time. The same conclusion was drawn for the concentration of β-glucan; a higher concentration was obtained with decreasing particle size and longer extraction time. Individually, time and particle size had significant effects on the concentration. For the molecular weight, only time had a significant effect and for all particle sizes a medium-molecular weight between 550-750 kg/mol was obtained. With subcritical water extraction there was a significant effect of temperature as well as an interaction effect between temperature and particle size on viscosity. A lower temperature used gave a higher viscosity. The yield of β-glucan was almost two-fold higher with higher temperatures at 150-170°C compared to a lower temperature at 95°C. Both temperature and particle size had significant effects on the yield. With subcritical water extraction a high yield can be obtained with high temperatures, but the molecular weight decreases dramatically to a low-molecular weight around 70-200 kg/mol.The subcritical water extraction has some advantages in time, cost-efficiency and β-glucan yield compared to the wet extraction. However, further research is needed to investigate how a high yield of β-glucan can be obtained, but still with a high or medium-molecular weight. The combination of time and temperature needs to be optimized in order to get high molecular weight.