Effect of Processing on Microbial Load, Physicochemical Properties and Nutritional Composition of Plukenetia conophora (Africa Walnut)

Abstract

This research was carried out to determine the effect(s) of different processing methods on the nutritional composition of Plukenetia conophora (Africa walnut) seeds. The dried walnut seeds were sorted, cleaned, cracked and dehulled by abrasion to get the cotyledons. The raw sample and processed (boiled and fermented) seeds were analyzed for microbial load, physicochemical properties (pH, total titratable acidity and moisture contents), proximate composition, vitamin contents and antioxidant level. The boiled sample had the least microbial load (7.55 Cfu/ml) followed by the raw sample 8.50 (Cfu/ml). There was a progressive increase in the microbial load with an increase in fermentation time from 8.18 Cfu/ml to 8.40 Cfu/g in FW24 and FW120, respectively. The raw sample had least pH and moisture content of 5.78 and 9.50%, respectively. Boiling and increase in fermentation time led to significant increase in pH and moisture content of the samples. The raw sample had the highest TTA (2.88N) while there was a significant decrease in (Total Titerable Acidity) TTA with an increase in fermentation time. The raw sample had the least protein (26.78%), fat (30.11%) and ash (4.43%) contents while the fermented sample had the highest percentage of protein (29.01%), fat (32.67%) and ash (6.23%). The antioxidant properties of the fermented samples, i.e. total phenolics (17.67 mg/g) and DPPH (24.57 mg/g) were significantly higher than the boiled and raw samples. The fermented sample had highest vitamin A (33.71 mg/g), vitamin B1 (0.16 mg/g) and B2 (01.2 mg/g) vitamin C (22.67 mg/g). The vitamin B2 (0.02 mg/g) and vitamin E (23.91 mg/g) of the boiled sample were significantly higher than the fermented and raw sample. From the study, it was observed that walnut is better consumed fermented for its important roles in health and nutrition than boiling and raw consumption.