PHYSICOCHEMICAL AND MICROBIOLOGICAL FEATURES OF THE STORED CITRIC ACID TREATED ORANGES IN NIGERIA |

Poor post-harvest management of agricultural products in Nigeria adds to increased spoiling of oranges, necessitating the current policy to extend their shelf life. The physicochemical and microbiological characteristics of peeled and unpeeled oranges treated with various doses of citric acid and stored at room (hawking) and refrigeration temperatures for 16 days are evaluated in this study. The acidity and enterobacterial count of oranges were significantly changed by citric acid treatment (P0.05), but the pH, brix, total bacterial, yeasts, and enterobacterial counts were significantly affected by the nature of the samples. In addition, the storage temperature had a considerable impact on all of the characteristics. Aspergillus niger, Macrophomina species, Bacillus subtilis, and Chryseomonas luteola were identified as spoilage microbes. At hawking temperature, citric acid extended the shelf life of oranges sold in Nigerian open markets from 10 to 15 days (unpeeled) and 2 to 3 days (peeled). From spoiled oranges, two strains of Aspergillus niger and one species of Macrophomina were isolated, and both showed the potential to manufacture pectinase, but the A. niger strains were superior. Pectinases from A. niger strains had an optimal temperature of 50°C and a pH range of 4-5, but those from Macrophomina species had an optimal temperature of 40°C and pH range of 9. Ag3+ and Na+ activated crude pectinases from Aspergillus niger strains and Macrophomina species, whereas Fe3+ inhibited enzymes from all three fungal sources. For extending the shelf life of oranges sold at room temperature in open marketplaces, a 2-minute infusion in citric acid solution is recommended. Furthermore, pectinases from A. niger will be an excellent raw material in the industrial production of wine, vegetables, purees, and pastes because of their perfect pH, whereas alkaline pectinases from Macrophomina sp. will be effective in waste treatment because of their optimal pH.

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