Wheat damage by Aelia spp. and Erygaster spp.:: effects on gluten and water-soluble compounds released by gluten hydrolysis

Wheat damage by heteropterous insects produces gluten hydrolysis giving different degradation products. Gluten content and gluten quality were assessed as a gluten index after incubation of the wet gluten for different intervals (0, 1, 2, 3, 7 and 24 h). Simultaneously, the water soluble products released by gluten hydrolysis during incubation were analysed by size-exclusion high performance liquid chromatography and SDS-PAGE. The results indicated that the amount of wet gluten remained constant even in the case of gluten isolated from damaged wheat, whereas the gluten index of damaged gluten showed a steady decrease with the incubation time suggesting an intense protein hydrolysis. A large amount of water soluble compounds were released from damaged gluten, increasing the relative proportion of compounds with molecular weights between 15,000 and 30,000 during the first 3 h of incubation. The SDS-PAGE studies under non-reducing conditions revealed presence of six new bands from Mr 42,000-27,000 at 3 h of incubation and they showed a progressive increase in their intensity with incubation that progressively increased in intensity. The presence of some protein aggregates with Mr higher than 200,000 suggested the endoproteolytic activity of the insect proteases, and the analysis of the aggregates under reducing conditions indicated that they were linked by disulphide bonds. The gluten index is proposed as a parameter for objectively determining the insect attack. (C) 2003 Elsevier Ltd. All rights reserved.