| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 99 === In the domestic beverage market, the consumption of vegetable and fruit juice is second place to the consumption of tea and as the health conception and living behavior of consumers change, people consider the nature and functions of juice. Avocado juice is high in nutrition, and not only contains essential amino acids and unsaturated fatty acids but also vitamins and minerals. The appearance of avocado juice is well-distributed and bright yellow, nevertheless the composition of avocado juice is complicated, including pulp, pigment, fiber, lipid, pectin, which causs unstable phenomenon during the process, such as browning reaction, separation or coagulation. The aim of this study is to simulate an avocado juice model and estimate the turbidity stability of avocado juice with the treatment of pH and heat, followed by additive treatments to modify the stability of avocado juice.
Under different pH treatments, the appearance of avocado juice treated with pH2, 3, 4 and 5 gets brighter with the decrease in browning index (76.12, 82.63, 81.00, and 80.86, respectively) and looks smoother but the turbidity stability decreases along with the increase in acidity. The appearance of avocado juice treated with pH6, 7, 8, 9 and 10 gets darker and the browning index increases (83.33, 83.50, 82.95, 84.29, and 86.64, respectively) while the viscosity and turbidity stability increase. According to the results, contents of soluble protein and pectin are one of the reasons to maintain viscosity and turbidity stability. The turbidity stability decreases while heating temperature increases, L* value also decreases while treating with heat, but the higher the heating temperature the higher is the L* value. The avocado juice treated with 95℃and 5 min gets a better L* value (56.72).The browning value increases as the heating temperature increases. The heat treatments denature the soluble protein which cause the coagulation and increase the degree of polymerization of pectin and increase the viscosity of avocado juice in the end. The ability to increase the turbidity stability is better with CMC treatment. The turbidity stability of avocado juice with 71 % pectin reaches to 90.1 % by adding 0.1 % CMC. The turbidity stability of avocado juice with additives treatment is maintained for extended periods of storage under 4 and 25 ℃, but it tends to present an unpleasant favor under 25℃ and decreases the quality of avocado juice.
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