Mechanism Of Ultrasound Inhibiting Enzymatic Browning Of Fresh-cut Potato

Fresh-cut fruits and vegetables are favored by more and more consumers, which are one of the development directions in fruit and vegetable industry. However, enzymatic browning is extremely easy to occur in fresh-cut fruits and vegetables, leading to the decrease of nutrition, quality deterioration and shortness of shelf- life. Enzymatic browning has become the most important factor which limits the development of fresh- cut fruits and vegetables industry. In recent years, as a new and developing technology, ultrasound has been widely used in food industry, especially shows a great advantage in fruits and vegetables industry for food preservation. On the base of current situation of fresh-cut fruits and vegetables industry, the effects of ultrasonic treatment on enzymatic browning substrates, products and related enzymes of fresh-cut potato were investigated. The mainly results were as follows:1. The effects of different ultrasonic treatment conditions on enzymatic browning substrates of fresh-cut potato were investigated by UV absorption spectra, infrared spectra, mass spectra and simulation of reaction system. The results found the character of UV absorption spectra of L-Tyrosine and L-Dopa were not changed, infrared spectra and mass spectra of enzymatic browning substrates were not influenced by ultrasonic treatment, also the reaction process curve of simulation of reaction system were same with the before.2. The effects of ultrasonic treatment on enzymatic browning products and simulation of reaction system were investigated. The results indicated that the curve of simulation of reaction system showed no difference before and after ultrasonic treatments.3. The related enzymes of enzymatic browning treated by different ultrasonic treatment conditions and the change of structure and relative expression of PPO were investigated by far-UV circular dichroism, fluorescence spectra and RT-PCR. The results indicated that the secondary structure of potato PPO was obviously changed by ultrasonic treatment. Ultrasonic treatment reduced the content of α- helix and β-turn and enhanced the content of random coil of potato PPO, which leading to the decrease of enzyme activity. The break of residues of Trp and Tyr led to the drop of fluoresce nce intensity of potato PPO after ultrasonic treatment, along with the red-shift, also the relative expression of potato PPO was reduced, and the fall was added as ultrasonic power increased. The optimum temperature and pH for related enzyme were not changed, but enzyme activity could be inhibitted. As the ultrasonic power increased, ultrasonic treatment time prolonged, the activity of PPO showed a downward trend.4. The changes of PAL activity, total phenol content and browning degree of fresh-cut potato were investigated. The results indicated that all of the three indicators were higher than control group. The activity of PAL showed the tendency of increase firstly and then decrease. The change of total phenol content was consistent with the trend of PAL activity, but lagged behind the change of PAL activity.