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Mulberry Leaves Harvested before and after Frost: Correlation between Phenylalanine Ammonia Lyase Activity and Total Flavonoid Content as well as Air Temperature

YU Xiaofeng1,2, LI Yunzhu3, ZHANG Weiwanqi2, WANG Dujun2, WEI Yuan2, OUYANG Zhen2,*   

  1. 1. School of Food and Biological Engineering, Jiangsu University, Zhenjiang 212013, China; 2. School of Pharmacy,
    Jiangsu University, Zhenjiang 212013, China; 3. Jingjiang College, Jiangsu University, Zhenjiang 212013, China
  • Online:2016-11-15 Published:2016-11-18

Abstract:

In order to explore the mechanism underlying the influence of frost on the total flavonoid content in mulberry
leaves, the dynamic changes in phenylalnine ammonia lyase (PAL) activity as a key enzyme in the biosynthesis of flavonoids
was analyzed in mulberry leaves harvested before and after frost as well as the correlation between PAL activity and total
flavonoid content or air temperature. For the determination of PAL activity in mulberry leaves, 0.2 g mulberry leaf powder
was homogenized with 0.1 mol/L borax hydrochloric acid buffer (6 mL, pH 8.8) added with 0.2 g of polyethylene (PVP) and
centrifuged, and the supernatant was allowed to react with 0.04 mol/L L-phenylalanine as substrate at 40 ℃for 40 min. At
the same time, the total flavonoid content of mulberry leaves was measured by UV spectrophotometry. The results showed
that PAL activity in mulberry leaves harvested after frost was higher than in those harvested before frost. PAL activity
showed a very significantly negative correlation with temperature, whereas it was significantly positively correlated with
total flavonoid content. Lower temperature had a significant positive effect on the accumulation of total flavonoids.

Key words: mulberry leaves, phenylalanine ammonialyase, frost, temperature, total flavonoids content

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