Effects of sonication duration on the physicochemical properties, bioactive characters, and the shelf-stability of noni juice stored at different temperatures

Choo, Yi Xuan (2023) Effects of sonication duration on the physicochemical properties, bioactive characters, and the shelf-stability of noni juice stored at different temperatures. Master dissertation/thesis, UTAR.

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Abstract

Morinda citrifolia is a plant belonging to the Rubiaceae family, widely known as noni. Noni fruit is rich in antioxidant and has been used to treat remedies such as skin allergies, warts, hemorrhoids, diabetes, etc. Those health benefits are associated by the presence of bioactive compounds in noni fruit. Noni fruit is commonly produced into fruit juice through fermentation or freshly extracted using mechanical apparatus. The fresh noni juice is perishable. It must store under refrigerated condition to preserve the flavour and extend shelf-life, otherwise, it must be consumed immediately. Prior to consumption, either fresh or fermented noni juice is usually pasteurised to kill harmful microbes in addition to prolong the shelf-life. However, the heating process might negatively affect the flavour and nutritional values of noni juice. Sonication has emerged as a promising green technology in the food industry to overcome the limitation of pasteurisation. Besides, sonication has been perceived to fulfill the Food and Drug Administration requirement of a 5-log reduction in relevant microorganisms in fruits and vegetable products. Hence, this study aimed to investigate the effects of sonication duration on the physicochemical properties, bioactive characters, and the shelf-stability of noni juice. In brief, noni juice was sonicated at different duration intervals (20, 40, and 60 min) under constant frequency and temperature of 37 kHz and 30°C, respectively. Pasteurisation was adopted as positive control, while fresh noni juice served as negative control. Results showed that S60 significantly improved (p < 0.05) and retained the highest amounts of bioactive compounds (TPC and TFC), phenolic compounds (scopoletin, rutin, vanillic acid, and quercetin), organic acids (ascorbic, malic, fumaric, and citric acids), and antioxidant capacity (FRAP and TEAC) of noni juice compared to the fresh noni juice. Therefore, S60 noni juice was selected for 56 days of shelf-stability study at room temperature (25℃) and refrigerated temperature (4℃) together with the fresh and pasteurised noni juices. The microbial load (aerobic mesophilic bacteria, yeast, and mold counts) of noni juice samples during 56 days of storage were also evaluated. Results demonstrated that S60 retained higher phenolics, organic acids, and antioxidant capacity of noni juice than fresh and pasteurised samples after 56 days of storage at both temperatures. Refrigerated temperature showed better preservation of noni juice nutrients than room temperature storage. No yeast and mold growth observed throughout the storage study. Irrespective of the storage temperatures, the total aerobic mesophilic bacteria count (<2 log CFU/mL) of noni juice samples stored for 56 days fell within the satisfactory level of microbiological standard for ready-to-eat food (<4 log CFU/mL). Overall, this study highlights the feasibility of using sonication processing to enhance the quality of noni juice.

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