Quality Changes During the Storage of Wheat Grown in the

Abstract

Wheat has been grown and utilized in northern Sudan for decades, it is grown under irrigation during the dry and comparatively cold winter period which extends from November to March. Recently the local production of wheat has greatly increased as a result of the introduction of the crop in the irrigated Schemes of central and eastern Sudan. Maintaining quality of large amount produced in safe storage is considered to be of great importance The changes in quality of one of the main wheat cultivars (Debeira) grown in the Sudan and the flour extracted from it (72% extraction) was studied during nine months of storage. The grain and flour were stored under various storage conditions namely, temperature, (low (5-8°C) and high (21-37°C), grain moisture content (m.c), (6.9% and 12.6%) and forced insect infestation (insects species used were Tribolium castaneum and Trogaderma granarium). Samples from both grain and flour were taken initially and periodically every 1.5 months , and the different quality parameters, biological ( insects count and germination) , physical ( weight loss, frass content , insect damaged kernels, 1000 kernel weight and hectolitre weight) , chemical (moisture, protein, ash, fat, free fatty acids (F.F.A) , alpha-amylase activity , sedimentation values gluten content ) and functional ( baking and organoleptic quality) were determined. The results clearly showed that grain samples stored in initial high grain m.c. (12.6%) combined with high temperature in the presence of insects decreased significantly.(p≤ 0.05) in all quality parameters studied after only 1.5 months, and as storage time increased the amount of damage also increased. Whereas the infested grain sample stored at low m.c (6.9%) and high temperature showed a decreasing trend in all quality parameters with progress of infestation and storage time. After 9 months storage , insects count increased from 20 to 467 and 3074 insect/kg grain for the two samples stored at low and high grain m.c. respectively. Weight loss, frass content and insect damaged kernels for the sample stored at low grain m.c. increased from zero to 1.52, 0.1, and 9.0 % respectively. For the high m.c. grain it increased rapidly from zero up to 13.87, 4.4 and 56% respectively. F.F.A increased from 12.4 to 42.8 and 125.1 mg KOH/100g grain for the two samples respectively. Grain viability decreased from 97 to 75% and zero for the two samples respectively. Fat content from 2.50 to 1.8 and 1.7% , gluten content from 29.6 to 21.7 and 16.3%. Storage has detrimental effect on bread quality in terms of bread specific volume and acceptability values in two samples. Bread specific volume decreased from 4.1 to 3.0 and 2.5 ml/g and the overall acceptability values of bread from 5 to 2.7 and 1.7 scores for the 2 samples. Grain sample stored at normal grain m.c. (6.9%) at high temperature, though dry and protected from insects revealed significant changes in chemical and functional parameters. After 9 months a significant (p<0.05) increase in F.F.A from 12.2 to 35.9 mg/KOH/100g grains, a significant (p<0.05) decrease in fat and gluten content from 2.05 and 29.6% to 1.9 and 24.7 for the two parameters respectively. A significant (p<0.05) decrease in bread specific volume from 4.1 to 3.5 ml/g and in the over all acceptability of bread from 5 to 3. Grain sample stored at normal grain m.c. at low temperature (control sample) maintained most of its quality parameters over the period of the storage. Although it showed a significant (p<0.05) increase in F. F. A from 12.4 to 16.8mg KOH/100g, and asignificant (p<0.05) decrease in grain germinability from 97 to 61%, gluten from 29.6 to 26.3%, and bread specific volume from 4.1 to 3.8 ml/g and it had an insignificant (p<0.05) changes in ash, fat, α-amylase activity and over all acceptability of bread. Forced infested flour stored at high temperature revealed significant (p<0.05) changes in all quality parameters studied after only 1.5 month storage. Insects count increased from 20 to 629 insect /kg after 9 months. Uninfested flour sample stored at high temperature also resulted in significant (p<0.05) changes in all parameters after 3 months storage except F.F.A. and gluten content which showed significant (p<0.05) changes after only 1.5 month. Flour sample stored at low temperature showed nearly same changes as in grain sample stored under similar conditions except that it has a significant reduction in organoleptic qualities after 4.5 months, though the over all acceptability of bread remained satisfactory.