Improvement in shelf life and safety of pasteurized palm sap (Borassus flabelliferLinn.) by the addition of nisin

Abstract

The objective of this study was to improve the quality and safety of pasteurized palm sap by the addition of various concentrations of nisin. The pasteurization condition was 75C for 10min as considered from no growth of pathogens was detected while the concentrations of nisin in the range of 0-40IU/mL were selected for addition in palm sap as considered from sensory evaluation. The initial pH of pasteurized palm sap was 6.6 and the addition of nisin caused a decrease in the pH to 6.2, 6.0, 5.8 and 5.6 for the samples added 10, 20, 30 and 40IU/mL, respectively. The initial polyphenol oxidase activity decreased by approximately 55 and 76% for the sample without nisin added and the sample added 40IU/mL nisin, respectively, from the original value measured in fresh palm sap while the initial invertase activity was not affected by nisin. During storage, the loss of sucrose, polyphenol content, DPPH-RSA and the increment in browning intensity were minimized by nisin treatment, particularly at 30-40IU/mL. The combination of pasteurization with the addition of nisin (30IU/mL) and low temperature storage could preserve palm sap for 10 weeks whereas the control sample was spoiled within 2 weeks. Practical Applications: The sale of pasteurized palm sap is a common practice in Thailand and its consumption has increased over the past years. However, pasteurized palm sap has a short shelf life (approximately 1-2 weeks). In order to control the growth of spoilage microorganisms, the use of natural antimicrobial preservatives has been preferred in the food industry. For this purpose, nisin was preferred in this study. Although there are many reports on the use of nisin to prolong the shelf life of food, research on the utilization of nisin in palm sap is limited. According to the results, the addition of nisin could reduce the pasteurization temperature and time. In addition, the use of nisin (30IU/mL) significantly reduced spoilage microorganism counts and extended the refrigerated shelf life of pasteurized palm sap for at least 10 weeks. Therefore, the safety of pasteurized palm sap during storage could be improved by the addition of nisin. This result may be a practical application for the producer because of the short shelf life of this product. © 2013 Wiley Periodicals, Inc.