Asian Journal of Microbiology and Biotechnology

In Nigeria, poor post-harvest handling of agricultural products contributes to increasing spoilage of oranges; hence, the need for the present strategy to enhance its shelf-life. The study evaluates, the physicochemical and microbiological features of peeled and unpeeled oranges, treated with different concentrations of citric acid and stored under room (hawking) and refrigeration temperatures for 16 days. Citric acid treatment of oranges showed significant effect (P≤0.05) on the acidity and enterobacterial count while the nature of samples significantly affected the pH, brix, total bacterial, yeasts and enterobacterial counts. Furthermore, the storage temperature significantly affected all the parameters. The spoilage organisms were identified as Aspergillus niger, Macrophomina species, Bacillus subtilis and Chryseomonas luteola. The citric acid improved the shelf-life of oranges sold in Nigerian open markets, from 10 to 15 days (unpeeled) and from 2 to 3 days (peeled) at hawking temperature. Two strains of Aspergillus niger and one species of Macrophomina were isolated from spoilt oranges and both demonstrated ability to produce pectinase, but the A. niger strains were better. The optimal temperature of pectinases from the A. niger strains was 50^oC and optimum pH range of 4-5, while that from Macrophomina species was 40^oC and pH 9 respectively. The crude pectinases from the Aspergillus niger strains and Macrophomina species were activated by Ag³⁺ and Na⁺, whereas Fe³⁺ inhibited the enzymes from all three fungal sources. A 2-minute infusion of oranges in citric acid solution is recommended for shelf life elongation of oranges hawked at ambient temperature in open markets. Moreover, based on their optimal pH, pectinases from A. niger will be a good raw material in the industrial production of wine, vegetables, purees and pastes, while the alkaline pectinases from Macrophomina sp. will be useful in waste treatment.