Polyphenol oxidase activity in tea, apple and potato 英语论文.doc
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1、Polyphenol oxidase activity in tea, apple and potatoMao YuLinCollege of Agriculture & Biotechnology, Zhejiang University, Hangzhou 310058, ChinaCorrespondence: Words: 1278; Figures: 4Abstractl Background Polyphenol oxidase exists in most of plants, changes plants colors, and thus decreases food qual
2、ity. Therefore, finding the main factors that impacts the PPO is benefit to store food from plants.l Methods The content of enzyme in tea leaves, apple fruits, and potato tubers was measured by Folin- phenol method. The main influence factor of PPO activity was determined by orthogonal method. l Res
3、ults The protein yields of the crude enzymes extracted from tea, apple, and potato were 44.318 mg/g, 38.626 mg/g, and 52.114 mg/g, respectively. Tea leaves showed the highest PPO activity at 8 mM catechol, 20C, and pH 6.5. Apple fruits showed the highest PPO activity at 8 mM catechol, 20C, and pH 5.
4、 Potato tubers showed the highest PPO activity at 20 mM catechol, 30C, and pH 6.l Conclusion The activator and inhibitor are the main factors that are in control of PPO.Temperature is the second important factor and is easy to control. Therefore, we should inhibit PPO activity by controlling storing
5、 temperature. Tea and potato could be stored at 40, and apple should be stored below 20 C.Key words: Polyphenol oxidase; Orthogonal method; Activator and inhibitor; TemperatureIntroductionPolyphenol oxidase (PPO) catalyzes polyphenols to quinones. PPO widely exists in various plants, and plays roles
6、 in plant growth and development, and plant adaptability to the environment. Importantly, PPO activity results in brown reactions in plant tissues, and affect the color and quality of the food derived from plants (Kong et al., 2011). Tea, apple, potato are common food and easily available, and conta
7、in abundant PPO. A recent study compared PPO activities in fresh tea, apple and potato (L.J.Song et al., 2009). This study used the same methods to extract crude PPO enzymes and measure PPO activities and used an orthogonal method to find the main factor controlling PPO activities in tea, apple and
8、potato.Materials and MethodsPlant materials Leaves of green tea grown at ChangBai Mountain were harvested in March. Local apple fruits and potato tubers were purchased from market. Crude enzyme extractionApple fruits and potato tubers were peeled and cut into small pieces; tea leaves were cut into s
9、mall pieces; 150 g of each material were homogenized in a NaF buffer (pH 7) with a ZZ homogenizer (HanNuo, Shanghai, China). After adding 150 ml 0.1 M NaCl, the homogenates were filtered with 4 layers of gauze. Fifty milliliters of the filtrate were centrifuged at 4000 rpm for 10 min at 4C. The supe
10、rnatant was mixed with 50 ml ethanol and put at 4C for 30 min, and then centrifuged at 4000 rpm for 10 min at 4C. The precipitation was dissolved in a phosphate buffer (pH 6.8) and used as the crude PPO solution.Protein determination by Folin-phenol method Protein was determined by the Folin-phenol
11、method as the protocol described by the manufacturer of the Folin-phenol regents (Sangon Biotech, Shanghai, China).Standard protein solutions were prepared from a 500 g.ml-1 invertase protein solution. After adding 10 l, 20 l, 40 l, 60 l, 80 l, and 100 l of the 500 g.ml-1 protein solution in tubes,
12、distilled water was added to make the solution volume to 1.0 ml; 1.0 ml distilled water was the blank control. The blank and standard protein solutions (5, 10, 20, 40, and 50 g.ml-1) were mixed with 5.0 ml Folin-phenol regent A and put at room temperature for 25 min, and then mixed with 0.5 ml Folin
13、-phenol regent B and put at room temperature for 20 min. The optical density of the reaction solutions were measured at 500 nm with an ultraviolet spectrometer (Shanghai Yuanxi Instruments Co. Ltd, Shanghai,China).The protein concentrations of the crude PPO solutions were then determined by the Foli
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