CHARACTERISTICS AND DIFFERENCES OF POLYPHENOL OXIDASE, PEROXIDASE ACTIVITIES AND POLYPHENOL CONTENT IN DIFFERENT POTATO (SOLANUM TUBEROSUM) TUBERS
L. WANG, W. X. Wang, Lanting Zeng, Haicui Suo, C.C. LI, Jialuo Shan, J.T. LIU, Huiting Luo, X.B. Li, Xiao-ping Xiong
Abstract
Potato enzymatic browning is a serious issue during processing. It not only affects the appearance of potato products but also reduces the nutritional value of potato tubers. In the present study, seven different potato cultivars' tubers were evaluated by measuring the browning index (BI) at different times after cutting. Initial PPO and POD activity and total phenol content, which related to enzymatic browning of plant tissues, were also determined. Results showed significant differences in these factors between the different cultivars. There was significant correlation between BI and PPO, POD activities, but no significant correlation with total phenol content. The activities of PPO and POD and the total phenolic content were higher in the epidermis and perimedullary tissues than pith tissues, which is consistent with their phenotypes. Further, qRT-PCR analysis revealed that the PPO genes were induced by wounding and were more highly expressed in browning-susceptible tubers than browning-resistant tubers, suggesting that browning-susceptible cultivars have higher StuPPO gene expression levels than browning-resistant cultivars. In addition, StuPPO1 and StuPPO2 were the most highly expressed PPO genes in both browning-susceptible/resistant cultivar' tubers, indicating that StuPPO1 and StuPPO2 were the major contributors to the increase in PPO activity and the browning degree in potato tubers. This work suggests that the enzymatic browning of potato tubers is positively correlated with PPO and POD activity. StuPPO1 and StuPPO2 were the main genes responsible for enzymatic browning in potato tubers.