Storage influences the protein and carbohydrate composition of wheat.

Abstract

34A Storage influences the protein and carbohydrate composition of wheat Jae_Cheol Kim1, B.P. Mullan2 and J.R. Pluske 1 1 2 Division of Veterinary and Biomedical Sciences, Murdoch University, Murdoch WA 6150 Agriculture Western Australia, Locked Bag No. 4, Bentley Delivery Centre WA 6983 j.kim@student.murdoch.edu.au A significant increase in the AME value of some wheats for chickens following storage for 4 months has been reported (Choct and Hughes 1997), and the activation of endogenous glycanases in these wheats was suspected as a possible mechanism for the improvement. Examination of changes in the protein and fibre composition associated with wheat storage may provide an explanation for the observed change in nutritive value. Eleven wheat samples harvested in 1999/2000 from south_western Australia were used in the study. Chemical composition of the wheats was determined one month after harvest and again seven months later. The grain was stored in sealed, metal_sided bins in a grain storage shed during this time. One_way ANOVA was used to assess the effects of storage on selected chemical components of the wheats. The major changes in chemical composition of wheat during storage were decreased starch (29%, NS) and soluble non_starch polysaccharide (NSP; 27%, P<0.01) contents, and increased contents of crude protein (13%, NS) and free sugars (63%, P<0.001). Among the free sugars, mannose and glucose were the major monomers that increased during storage (35% and 62%, respectively). Jood et al. (1993) also reported increased free sugars and decreased starch contents in wheat following four months of storage. The decrease in soluble fibre and starch contents and the increased content of free sugars suggest that endogenous enzymes were degrading starch and soluble fibre during storage. A significantly decreased soluble NSP content during storage may partly explain the improved AME value seen with stored wheat in some chicken studies, since the chick is more sensitive to gut viscosity than other monogastrics. The increased protein content might be a reflection of increased levels of the endogenous enzymes required for germination (Evers et al. 1999) and (or) changes in the ratio of soluble: insoluble proteins found in wheat. Choct, M. and Hughes, R.J. (1997). The nutritive value of new season grains for poultry. In: Recent Advances Animal Nutrition in Australia 1997, pp. 146_150 (eds. J.L. Corbett, M. Choct, J.V. Nolan and J.B. Rowe). University of New England, Armidale NSW. Evers, A.D., Blakeney, A.B. and O'Brien, L. (1999). Cereal structure and composition. Australian Journal of Agricultural Research 50, 629_650. Jood, S., Kapoor, A.C., and Singh, R. (1993). Available carbohydrates of cereal grains as affected by storage and insect infestation. Plant Foods for Human Nutrition 43, 45_54. Table 1 Change in chemical composition of wheat (mean percent in DM; n = 11) during storage at room temperature. CP* 1 month 7 months Significance # TS 67.7 65.3 NS Am 21.7 19.6 ** Ap 46.0 45.7 NS TNSP 9.4 9.5 NS INSP 8.1 8.4 NS SNSP 1.3 1.1 ** FS 1.4 2.0 *** 10.8 11.7 NS * CP, crude protein; TS, total starch; Amy, amylose; Ap, amylopectin; TNSP; total NSP; INSP, insoluble NSP; SNSP, soluble NSP; FS, free sugars # Significance level: NS, non_significant; ** P<0.01; *** P<0.001 Recent Advances in Animal Nutrition in Australia, Volume 13 (2001)