Effects of Different Processing Methods on the Bitterness and Quality of Grapefruit Juice and Buntan Shaddock Juice

• Main Authors: Yi-Ting Wang, 王逸婷
• Other Authors: Yuan-Tay Shyu
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/73670553263650016665

碩士 === 國立臺灣大學 === 園藝暨景觀學系 === 103 === The grapefruit (Citrus paradis Macfad) and the buntan shaddock (Citrus grandis (L.) Osbeck) are evergreen perennials of the family Rutaceae, they also called pumelo, is one of the four original citrus species. They have some limitations on commercial processing due to their inherent bitterness. The major component causing the bitterness of pumelo is naringin, and one of the research areas of citrus processing industry is to investigate how to reduce the bitterness during food processing. The key enzyme to reducing bitterness in pumelo is the naringinase that has the most efficiency of debittering when the temperature is between 45 to 55℃. In the methods of horticulture production postharvest handling, the working temperature of the hot water dip method matches to the optimal temperature of naringinase. The combination of the hot water dip method and the naringinase at optimal temperatures is an innovative method. Moreover, the high pressure processing has been found to have the ability to modify the catalytic behavior of the enzyme and inactivate microorganisms during food processing. This study evaluated the effects of the hot water dip (HWD), the high pressure processing (HPP), and the thermo processing (TP) on the quality, the flavor, the naringin content and the microorganisms of grapefruit juices and buntan shaddock juices. The naringin content in grapefruit juice after HWD was 937.0-1233.6 mg/L, and it was higher than the non-processed control (CON) (825.0 ± 16.6 mg/L). Although the temperature of HWD matches to the optimal temperature of the naringinase, the process of HWD cannot reduce the concentration of naringin. Similarly, the TP had no effects to reduce the concentration of naringin in grapefruit juice that is 802.1 ± 0.9 mg/L after TP. On the other hand, the HPP at 100 MPa, 200 MPa, 300 MPa and 400 MPa significant reduced the concentration of naringin in grapefruit juice, from 851.09 ± 17.00 mg/L to 475.64 ± 42.10 mg/L, 468.77 ± 36.88 mg/L, 539.43 ± 69.21 mg/L and 458.34 ± 39.24 mg/L, respectively. The naringin concentration below 500 mg/L that is the bitter taste threshold. The results suggested that HPP can efficiently reduce the naringin content of grapefruit juice. Another test material is buntan shaddock juice, the naringin content in buntan shaddock juice after TP and HPP was 804.3-863.4 mg/L, and it was similar to the non-processed CON (820.64 ± 19.00 mg/L). Then, some physicochemical properties of juices has changed through TP and HHP. Comparison of TP and HHP, it has a great influence on the appearance and quality of juice after TP. However, there was no significant change in pH, soluble solids and titratable acidity of grapefruit juice and buntan shaddock juice after the TP and the HPP. In such a context, TP and HHP mild affect on physicochemical properties of juices, but the HHP maintained the physicochemical properties of the original juice well. Finally, the microbiological tests shows that thermally treating the grapefruit juice and buntan shaddock juice to 85 ℃ for 45 s reduced the bacteria population from 3.25 log CFU/mL and 3.78 log CFU/mL to 1.34 log CFU/mL and 0.85 log CFU/mL. Pressurization at 200, 300, 400, 500 MPa, 30℃ for 30 min reduced the population levels below 2.3 log CFU/mL, it conforms with the microbiological criteria of beverages in Taiwan. In conclusion, HPP not only promote activity of debittering enzyme but also inactivate bacterial cells. This processing maintain the original juice appearance, flavor and quality. It can be used in the future to reduce the bitterness of citrus juice in the food industry, and the potential applications of HPP is unlimit.