Inhibition of Fungal Colonization of Stored Peanut Kernels with Products from Some Medicinal/Culinary Plants

Abstract

Abstract Products from five medicinal/culinary plants—Citrus aurantifolia fruit peel oil, Cymbopogon nardus leaf oil, Ocimum gratissimum leaf powder, Xylopia aethiopica fruit powder, and Syzigium aromaticum clove powder—were tested for activity against fungal colonization of stored peanut. The natural microflora of kernels were supplemented with a norsolorinic acid (NOR) mutant of Aspergillus parasiticus before treatment with the various plant products. Treated kernels were stored at 5.7% moisture content in mini-polyethylene bags for 11 mo. Of the five plant products, the Syzigium clove powder proved to be most efficacious. After 4 mo storage, a low colony-forming unit (CFU) value of 0.601 log units of NOR A. parasiticus was recorded per gram of kernels treated with the powder. Significantly higher CFU values (P ≤ 0.05) were associated with kernels that received no plant product (3.099 log units) and kernels treated with the other plant products(1.459–2.930 log units). CFU of total fungi, superficial fungal growth, internal kernel discoloration, and fungal growth/sporulation on the internal surfaces of the cotyledons also were suppressed by the Syzigium powder after 11 mo. The Citrus oil and the Ocimum leaf powder were moderately effective, being similar to each other in several storage parameters. The Cymbopogon leaf oil was the least effective of the plant materials tested. In a test tube experiment, the Syzigium and Ocimum powders were more efficacious when mixed with stored peanut kernels than when separated from kernels with a piece of mosquito-proof screen. The optimum rates of the two powders for preventing superficial fungal growth on kernels at 8% moisture in mini-polyethylene bags at 28 C were 150 and 100 g/kg of kernels, respectively, for Syzigium and Ocimum. At these rates, 93 and 56% of kernels treated with the Syzigium and Ocimum powders, respectively, were free from superficial fungal growth after 4 mo. These results point to the potential of the two powders, especially Syzigium, for preventing mold growth and possibly aflatoxin production in stored peanut.