RELATIONSHIP OF BREAD BAKING QUALITY TO LEVELS OF VISIBLE WHEAT-BUG DAMAGE AND INSECT PROTEINASE ACTIVITY IN WHEAT

‘Bug-damaged’ wheat is defined as wheat that produces poor bread with unusual crust and crumb characteristics, caused by the action of a proteinase secreted by a wheat-bug (Nysius huttoni). Lines of wheat (141) from the 1989 harvest season in New Zealand were analysed for the levels of visible damage and insect proteinase that were associated with bug-damaged wheat as determined by a bake test. Proteinase activity was estimated by a simple new proteinase microassay using wheat gluten as substrate. An SDS-sedimentation test was also used to estimate proteinase activity by measuring the difference in SDS-flour sediment volumes before and after incubation of flour in buffer. There were good relationships among the visible damage test, SDS-sedimentation test and proteinase assay. Thresholds (defining values for bugdamaged wheat) of visible damage, SDS-sediment volume difference and proteinase activity were determined. Different defining values were used for high-bread-quality wheat cultivars and low-bread-quality wheat cultivars. Of the wheat showing apparent bug-damage characteristics in the bake test, 85-93% of the high-quality wheats and 93% of the low-quality wheats exceeded these defining values. Explanations for anomalously assigned wheats are discussed. © 1992, Academic Press Limited. All rights reserved.