Changes in the Population of Schizosaccharomyces japonicus in Carissa edulis Vahl (Simple-spined Carissa) Juice Treated with Extracts of Citrus aurantifolia Christm. (lime) and Citrus limon Burm F. (lemon) Peels as Natural Preservatives during Storage

Abstract

Aim: This study was aimed at evaluating the changes in the population of Schizosaccharomyces japonicus in locally produced simple-spine Carissa juice and the effects of lemon peel, lime peel and combination of lime and lemon peels extract as preservatives on the juice samples.
 Methodology: Fruit juice produced was treated with different concentrations of citrus peels extracts (lemon, lime and lime+lemon) and their shelf lives were determined at room temperature for 30 days. The effects of the different preservatives on the pH of the juices were assessed and the Yeast count of the juice samples treated with the various concentrations of the citrus peels and the untreated samples were assessed using standard microbiological methods. The sugar fermentation and assimilation test of the isolate was also determined.
 Results: Yeast population increased in the juice samples that were without treatments (control) from 5.6×103±200 to 1.52×104±200 cfuml-1 indicating significant increase (p≥0.05). Treated juice samples showed significant decrease (p≤0.05) in yeast population in the order of 300>200>100 mg/ml of the natural preservatives. Juice samples treated with highest concentration (300 mg/ml) of combined lime+lemon peels recorded the least colony forming units of 2.0×103±100 ml-1 during the storage period. This showed that the highest concentration (300 mg/ml) of combined lime+lemon peels had more effects on yeast load reduction in the Carissa juice. The results of the preservative properties of the citrus peels revealed the combined preservative (lime+lemon) as the best among the individual preservatives of lime and lemon. The sugar fermentation and assimilation tests showed that Schizosaccharomyces japonicus is a good fermenter of most sugars and can also assimilate sugars for its growth. The pH (3.40±0.01 and 4.09±0.01) of the treated fruit juices were within the acidic ranges that support the growth of yeast cells in culture.
 Conclusion: From the findings, organic extracts of citrus peels can be used to extend the shelf-life of Carissa juice for up to three weeks.