COMPOSITION, MICROSTRUCTURE, WATER IMBIBITION, AND THERMAL-PROPERTIESOF 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 lip ids contents decreased by 1.6, 1.4, and 1.4%, respectively, and starch and P-glucans contents increased by 16 and 1.2%, respectively, compar ed to nonabraded kernels. Merlin showed smaller changes in the levels of these components, except for proteins. Changes in starch and protei n in laboratory abraded barley were used to estimate the level of barl ey abrasion on a commercial scale. Scanning electron microscope pictur es revealed that in nonwaxy barley at 10% abrasion the hull and part o f 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% a braded waxy barley was reached after 5 hr of soaking, whereas nonwaxy barley needed 8 hr to level off. Nonwaxy barley kernels at 20% abrasio n and cooked for 10 min required 52 N to compress to 50% thickness, wh ereas waxy barley needed only 28 N. Changes in chemical composition an d microstructure due to abrasion had a strong effect on the thermal pr operties 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 enthal py value for 40% compared to 10% abraded barley. These results indicat e that when a large portion of the outer layer of barley is removed, w ater and heat penetrate more quickly into kernels during cooking, caus ing more starch to be gelatinized. The results obtained in this study indicate that changes in composition and microstructure due to abrasio n affect the rate of water imbibition, hardness of cooked kernels, and enthalpy value of starch. Composition and properties of laboratory ab raded barley could be used to predict the level of abrasion and proper ties of barley abraded on a commercial scale within the same cultivar.