Physicochemical and Microbiological Effect of Citric Acid Produced from Yam Peels and Aspergillus niger

Abstract

This work was aimed to study the physicochemical and preservative effects of citric acid produced from yam peels using Aspergillus niger. Fresh yam peels were washed, sundried and milled into flour, after which it was inoculated with Aspergillus niger in a nutrient medium and fermented for 6 days at 30℃. Citric acid was extracted from the fermented substrate (1200 mL) and total yield was 418 g of citric acid. Physico-chemical properties of the extracted and commercial citric acid were compared and the results were; pH (2.80 and 2.66), TTA (0.77% and 0.75%) and moisture content (2.40% and 1.8%) respectively. Appearance of both samples were crystalline with the extracted citric acid having a more off white colour. The preservative effects of commercial citric acid and extracted citric acid from yam peels were compared using face centered composite design. A 15 samples of fresh pasteurized watermelon juice were analyzed over a period of 7 days at room temperature with concentrations of 0.2– 0.5% per 100 mL of juice. Microbial analysis (TBC, TCC, and TFC) of citric acid was carried out. For extracted citric acid the results ranged from TBC (4.40c× 105  005 CFU/mL to 9.70 × 105  0.100 CFU/mL), TCC (no growth to 3.90 × 106  0.05 CFU/mL) and TFC (no growth to 9.70 × 105  0.100 CFU/mL).While for samples made with commercial citric acid the results ranged from; TBC (5.30 b × 105  0.001 to 2.65b × 106  005), TCC (no growth to 8.10 × 106  0.05 CFU/mL) and TFC (no growth to 2.21 × 106  0.105 CFU/mL). This implies that citric acid extracted from yam peels had better preservative effects compared to the commercially produced citric acid.