Summary The effects of clarifying agents, including bentonite, polyvinylpolypyrrolidone (PVPP), gelatin and chitosan, on the quality attributes of pasteurised palmyra palm sap were evaluated. After clarification and pasteurisation, the lowest polyphenol oxidase (PPO) and invertase activities were detected in the sample clarified with bentonite. PVPP and gelatine were found to be the most effective for removing polyphenol content. In addition, the sample treated with chitosan had the highest transmittance values. However, the sucrose, glucose and fructose contents were not affected by clarification. During storage, the PPO activity, invertase activity, polyphenol content and sucrose level decreased, while the fructose and glucose levels increased with the storage times. According to the Thai Community Product Standard, all pasteurised samples treated with a clarifying agent were acceptable for up to 25 days, whereas the nonclarified sample was spoiled because of the microbial loads. Thus, the clarification process prior to pasteurisation was able to improve the quality and microbiological shelf life of the pasteurised palmyra palm sap for at least 25 days.
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 10 min as considered from no growth of pathogens was detected while the concentrations of nisin in the range of 0-40 IU/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 40 IU/mL, respectively. The initial polyphenol oxidase activity decreased by approximately 55 and 76% for the sample without nisin added and the sample added 40 IU/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 30-40 IU/ mL. The combination of pasteurization with the addition of nisin (30 IU/mL) and low temperature storage could preserve palm sap for 10 weeks whereas the control sample was spoiled within 2 weeks. PRACTICAL APPLICATIONSThe 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 (30 IU/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.Office 2010). In addition, palm sap has also been produced in many Asian countries such as India, Thailand, Myanmar, Sri Lanka and Cambodia. In Sri Lanka, the palm sap or palm sugar cottage industry is a major household income source among palm tree tappers. It provided more than 101,500 and 188,500 Rs which accounted for 53 and 62% of bs_bs_banner Journal of Food Safety
The objective of this research was to assess the potential of chitosan for improvement the quality of pasteurized palm sap during storage. First, the effect of chitosan content on sensory attributes was investigated to select suitable concentration of chitosan for further study. Fresh palm sap was enriched with chitosan at various concentrations (0-2 g/L) and pasteurized at 80 °C for 10 min, consequently evaluated by consumers. It was found that samples added chitosan in the range of 0-1.00 g/L were considered acceptable. Thus, the addition chitosan in the concentration of 0-1.00 g/L was chosen for further study. The sample without chitosan addition was used as a control sample. Each selected sample was determined for their qualities during storage at 1 week interval. It was found that lightness and transmittance values of all samples tended to increase during storage. Lower PPO and invertase activity were observed in all chitosan-treated samples compared to control sample. Chitosan could minimize the loss of sucrose and the increase in glucose and fructose content during storage. In addition, an increase in chitosan concentration resulted in the increase in DPPH radical scavenging activity. Furthermore, the addition of chitosan could retard the development of microorganism during storage as demonstrated by lower microbial loads compared to control sample. It can be concluded that a combination of pasteurization with chitosan addition (0.50 g/L) and low temperature storage could preserve palm sap for approximately 6 weeks. Thus, the incorporation of chitosan in palm sap could be used as an alternative way to extend shelf life of pasteurized palm sap.
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