Date of Award
Master of Science
Plant and Soil Science
The natural water inside green coconuts is regarded as a healthy drink due to the elements of nutritional and therapeutic value. Since there is chance of contamination of tender coconut water (TCW) with psychrophilic microbes during extraction from its hard shell if stored at 4 ºC, thermal pasteurization is currently practiced. However, the thermal treatment of TCW causes a rise in off flavors and loss of the vital nutrients. To solve this problem, a non-thermal pasteurization technology is desirable. The goal of this research was to assess the antimicrobial effectiveness of ultraviolet light C (UVC) as non-thermal pasteurization of TCW and evaluation of physico-chemical and sensory quality of the treated TCW in comparison to the fresh TCW. A dean flow ultraviolet reactor was used with wavelength of 254 nm at the residence time of 14.0 seconds. The independent variables were three Reynold numbers (Re1 = 198.8, Re2 = 397.7 and Re3 =596.4) and two different diameters of transparent PFA tubes (3.2 mm and 1.6 mm). TCW was inoculated with cultures of Escherichia coli and Listeria monocytogenes separately up to 8 log10 CFU/mL and inactivation by cold pasteurization was evaluated with number of log reduction of each bacteria. Physico-chemical properties like total solid content (TSS) and pH were analyzed throughout the storage period of four weeks. The sensorial quality, flavor and color of the coconut water was also evaluated by a panel of 30 people to compare the organoleptic characteristics of UVC treated samples with untreated fresh coconut water. In case of Escherichia coli W1485, UVC treatment gave the log reduction of 5.27 and 4.74 log10 CFU/mL in coconut water for 1.6 mm and 3.2 mm ID reactors, respectively. Whereas the reduction of Listeria monocytogenes were 4.18 and 2.96 log10 CFU/mL for 1.6 mm and 3.2 mm ID reactors, respectively. In case of both the bacteria, as the tube size increased, microbial reduction decreased; and as the Reynold number increased, microbial reduction also increased except where there was an interaction effect. The change of tube diameters gave significantly different inactivation for both test bacteria at all Reynolds number except at Re2 and Re3 in case of Escherichia coli. The different levels of Reynolds number were not significantly variant when compared with consecutive levels, but Re1 to Re3 were significantly different for both test bacteria. The physico-chemical and sensorial changes of cold pasteurized TCW weres not significantly different compared to the fresh TCW, providing the conformity of retention of natural and organoleptic characteristics of TCW.
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