Effects of different storage temperatures on browning-related enzymes and substrates of fresh-cut tubers of Hemsleya chinensis

【Objective】 To investigate the factors that affected the browning of tuber of Hemsleya chinensis under storage temperature， and to study the mechanism and change law of the browning process， to provide theoretical support for controlling browning and improving the stability of tuber of H. chinensis.【Method】The fresh-cut tubers of H. chinensis were placed at three different storage temperatures （-20， 4 and 25 ℃） ， and samples were taken on the 0， 2^nd， 4^th， 8^th， and 10^th d of storage respectively， to study the degree of browning， changes in peroxidase（POD） activity， malondialdehyde （MDA）， total polyphenols，cucurbitacin IIa and cucurbitacin IIb contents， and the correlation analysis between the degree of browning and measured indexes was carried out.【Result】 With the prolongation of storage time， the browning degree of fresh-cut tubers of H. chinensis increased. At the 10^th d，the browning degree of fresh-cut tuber of H. chinensis stored at 25 ℃ was significantly higher than that at -20 and 4 ℃（P＜0.05，the same below）. At this time， the POD activities of H. chinensis tubers at three temperatures showed a trend of first increasing and then decreasing， and the POD activities during the whole storage period were significantly higher than those under -20 and 4 ℃. The higher the storage temperature， the greater the MDA content of fresh-cut tubers of H. chinensis，stored at 4-10 d，the MDA content at 25 ℃ was significantly higher than -20 and 4 ℃， but there was no significant difference in MDA content between -20 and 4 ℃（P＞0.05，the same below）；the total phenolic content of resh-cut tubers of H. chinensis stored at 25 ℃ after 4 d was always significantly higher than-20 and 4 ℃. At 25 ℃， the content of cucurbitacin IIa in fresh-cut tubers of H. chinensis increased sharply after 4 d and reached the maximum value on day 6（1.1410 mg/g），significantly higher than at -20 and 4 ℃，the content of cucurbitacin IIb began to increase sharply after 2 d of storage，and on day 8，the content of cucurbitacin IIb reached 0.01143 mg/g，which was significantly higher than at -20 and 4 ℃. The results of correlation analysis showed that the BD at the three storage temperatures had an extremely significant positive correlation with the storage period（P＜0.01，the same below）， but no significant correlation with total polyphenols，cucurbitacin IIa and cucurbitacin IIb contents. BD had extremely significant and significant correlation with POD activity at -20 and 4 ℃ respectively，BD at -25 ℃ had no significant correlation with POD activity，BD at -20 ℃ had significant negative correlation with MDA content.【Conclusion】 Storage at low temperatures（-20 and 4 ℃）can inhibit the activity of POD，a key enzyme in browning，or reduce the production of browning substrate phenolic substances to effectively control the browning of fresh-cut tubers of H. chinensis. The browning control effect is better at -20 ℃.