Safe storage conditions and infestation potential of canola meal by fungi and insects

Abstract

Canola (rapeseed, Brassica napus L., B. campestris L.) meal can be stored with negligible loss in quality for more than 12 months at temperatures below 30°C and moisture contents (m.c.) of 7%, or below 25°C and 9.5% m.c. The meal was stored for 12 months at temperatures of 10, 20, 30, 40, and 50°C and four moisture contents, ranging from 6.3 to 11.5% at each temperature. Discoloration of the meal from yellow-green to brown occurred at 50°C, 10% m.c. in 1 month; by 3 months all samples at 50°C and those at 10.4 or 11.5% m.c. at 40°C were discolored. Deterioration gradually increased at lower m.c. with time and was generally related to fat acidity values above 88 mg KOH/100 g meal, a 100% increase from initial levels. Microfloral infection of the meal, reflected in fungal and bacterial incidence and fungal propagule counts, indicated that Penicillium spp predominated at 10 and 20°C during the study, but the Aspergillus glaucus group was more common at 40 and 50°C. Bacterial contamination increased most rapidly at the higher temperatures affecting all samples by 5 months. Fifteen species of stored-product insects and two species of stored-product mites were placed on canola meal for 3 months; only beetles of the genus Tribolium survived and multiplied under optimal environmental conditions. Known numbers of male and female T. castaneum (Herbst), T. confusum J. du Val, T. audax Halstead, and two strains of T. madens (Charp.) were then placed on ground wheat, wheat flour and yeast, or canola meal. Among the species tested, T. madens (Canadian strain) multiplied most successfully on canola meal, producing about 25% as many larvae as on cereal foods. Sex ratios were determined for the insect developmental stages on all of the foods and were slightly affected by different foods, especially canola meal.