INFLUENCE OF HEAT PRETREATMENTS OF OAT GRAIN ON THE VISCOSITY OF FLOUR SLURRIES

Heat treatment of oat grain had significant effects on the viscosity o f flour slurries. Steamed oats produced highly viscous flour slurries, whose viscosity increased with time, whereas the viscosity of hour sl urries produced from raw or roasted (104 degrees C for 120 min) oats w as much lower and degraded rapidly. Slurry viscosity was correlated wi th (1 --> 3), (1 --> 4)-beta-D-glucan concentration in the flours and treatment of slurries with lichinase lowered viscosity significantly. Effects of steaming were partially reversed by roasting treatment and vice versa. Mixtures of equal amounts of raw and steamed flour resulte d in slurries more viscous than either flour alone, but that viscosity degraded after 3 h to less than the mean viscosity of the steamed and raw controls. Water-soluble extracts from steamed flour had about twi ce the viscosity of raw or roasted flour extracts, but contained only 80% of the (1 --> 3), (1 --> 4)-beta-D-glucan present in those extract s. Molecular weight analysis of soluble carbohydrates from raw, roaste d and steamed soluble extracts indicated the molecular weight of beta- glucans in these extracts was similar. However, if extracts were made from slurries that had incubated for 3 h, extensive degradation of bet a-glucans was evident in raw and roasted samples. It is likely that en zymic degradation of (1 --> 3),(1 --> 4)-beta-D-glucans is responsible for much of the decreased raw and roasted flour slurry viscosity over extended time periods, but different heat treatments appear to also a ffect (1 --> 3), (1 --> 4)-beta-D-glucan polymer interaction.