CHEMICAL PROPERTIES OF TREATED NEEM (Azadirachta indica A. Juss) SEED AND PRESERVATIVE POTENTIALS OF ITS OIL ON ONIONS, SELECTED GRAINS AND FERMENTED LOCUST BEANS

Abstract

Neem seed is known to serve as antimicrobial agent on agricultural commodities. However, the consumption of its high dosage pose a health risk due to presence of other antinutritional factors. There is limited information on appropriate treatments for reduction of the antinutrients in neem seed to safe consumption level. There is need to further determine effects of some treatments on neem seed chemical properties to ensure safety for consumption. Thus, this study was designed to investigate the effects of steeping in water, alkaline solution and roasting on neem seed and toxicity of using its oil as a food preservative. Neem seeds were subjected to three treatments based on preliminary studies such as; steeping in water, and 40% NaOH solution for 24 h, and roasting for 10 min at 60oC. Proximate (crude protein, oil, crude fibre, ash, moisture and carbohydrate contents), minerals (Ca, Na, Mg, P, K, Cu, Zn, Fe, Mn and Se) and anti-nutrients contents (cyanide, nitrate, oxalate, phytate, tannin and azadirachtin) ofun-treated and treated seeds were determined using AOAC methods. Oil was extracted from raw and roasted seeds using hydraulic press.Fatty acid profile and bioactive compounds of the oil were determined using standard method. Weevil infested grains (maize, beans and rice), Fermented Locust Beans (FLB), and mouldy onions were treated with different concentrations (0.6. 0.7, 0.8, 1.0, 2.0 and 3.0 mL/200g) of oil extracted from roasted seed. The samples were stored at ambient conditions (26.0±2.0oC, RH 70%) for 45 days.Weevils population in grains and microbial growth on FLB and onions were determined weekly, using established procedure. Toxicity of roasted seed oilwas conducted using male and female rats (100.0±5.0g) in a group of three (n = 5), fed with FLB (control, 1.0, 2.0 and 3.0µL/100g) for 13 days. Haematology and histopathology of kidney, liver, heart, testes and ovaries for rats were done. Data were analysed usingANOVA at α0.05. Crude protein, oil, crude fibre, ash, moisture and carbohydrate contents of untreated seed were 18.6±0.07, 41.2±0.03, 3.6±0.04, 2.6±0.05, 6.0±0.02 and 28.1±0.02%; while treated were 16.9- 19.1, 40.4-41.8, 3.5-3.6, 2.4-2.6, 5.9-12.1 and 24.4-28.1%, respectively. The seeds had high contents (mg/100g) of Fe (16364.0-16482.0), Zn (2463.0-2398.0) and Mn (1164.3-1182.0). Steeping in water significantly reduced cyanide (45.0%), nitrate (12.5%), tannin (50.0%) and Azadirachtin (16.7%) contents. Major fatty acids in neem oil were oleic (39.10±0.03), linoleic (18.60±0.03), stearic (17.70±0.02) and palmitic (14.5±0.01%) acids. Roasting significantly affected the oil profiles. Fourteen bioactive compounds were detected with dominants being nHexadecanoic acid (28.62%), 9,12, 15-Octadecatrienoic acid (17.1%), Neophytadiene (13.7%), Hexadecanoic acid (10.0) and 9,12-Octadecadienoic (8.3%). Highest percentage weevils’ mortality of 59.2% in maize, 41.25% in beans and 36.67% in rice were recorded at 0.6, 0.7 and 0.8 mL/200g, respectively. E-coli, Pseudomonas, Staphylococcusaureusand Bacillus sp were the organisms detected in stored FLB. The microbe populations were significantly reduced by the oil. No spoilage was recorded from treated onions. Reduced erythrocytes and degradation of hepatocyte were observed in rat tissues fed with 3 µL/100g dose, an indication that the concentration was outside the safe limit for rat. The treatments reduced antinutritional factors in neem seed. Oil from roasted neem seed reduced weevils in grains and retarded microbial multiplication on fermented locust beans and onion. Low oil dosage is recommended.