Composition, microstructure, water imbibition, and thermal properties of abraded barley

Barley, nonwaxy hull (cvs. Crystal and Meltan) and waxy hull-less (cvs. Merlin and Waxbar), was abraded at 10, 20, and 40% of kernel weight on a laboratory scale and commercially abraded at two levels: fine and coarse. In 40% abraded kernels of Crystal, protein, ash, and free lipids contents decreased by 1.6, 1.4, and 1.4%, respectively, and starch and P-glucans contents increased by 16 and 1.2%, respectively, compared to nonabraded kernels. Merlin showed smaller changes in the levels of these components, except for proteins. Changes in starch and protein in laboratory abraded barley were used to estimate the level of barley abrasion on a commercial scale. Scanning electron microscope pictures revealed that in nonwaxy barley at 10% abrasion the hull and part of the seed coat were absent, whereas waxy barley lost all of the seed coat and most of the aleurone layer. Maximum water imbibition of 40% abraded waxy barley was reached after 5 hr of soaking, whereas nonwaxy barley needed 8 hr to level off. Nonwaxy barley kernels at 20% abrasion and cooked for 10 min required 52 N to compress to 50% thickness, whereas waxy barley needed only 28 N. Changes in chemical composition and microstructure due to abrasion had a strong effect on the thermal properties of kernels during cooking. The extent to which barley starch was gelatinized during cooking was evaluated by differential scanning calorimetry. Crystal and Merlin showed significant decreases in enthalpy value for 40% compared to 10% abraded barley. These results indicate that when a large portion of the outer layer of barley is removed, water and heat penetrate more quickly into kernels during cooking, causing more starch to be gelatinized. The results obtained in this study indicate that changes in composition and microstructure due to abrasion affect the rate of water imbibition, hardness of cooked kernels, and enthalpy value of starch. Composition and properties of laboratory abraded barley could be used to predict the level of abrasion and properties of barley abraded on a commercial scale within the same cultivar.