Research On The Mechanism Of Short-term Warming Inhibiting The Fresh-cut Potato Browning

Fresh-cut potatoes are well accepted by the consumers by its convenience,safety and nutrition,and have great market prospects.Browning is the main factor which reduces the products quality and shortens the shelf-life,leading to great waste and economic losses.In order to meet the long-term supply,potatoes are usually stored at low temperature after harvest.Previous studies showed that low temperature storage could enhance fresh-cut browning of potatoes even the storage temperature is appropriate.This effect could be reduced by warming after storage.But the time of warming treatment is too long to be used in practice.In this paper,the browning inhibition effect of fresh-cut potato(Netherlands #15)by short-term warming was studied firstly.The conditions of warming treatment were further optimized.On the basis of the treatment,polyphenol oxidase activity(PPO),total phenolic content,antioxidant enzyme activity,malondialdehyde(MDA)content,gene expression and activity of serine protease inhibitor(SPI),serine protease(SP)activity,contents of soluble protein and free amino acid,activity and gene expression of key enzymes of tyrosine synthesis and catabolism were measured to reveal the mechanism of fresh-cut potato browning.The experimental results are as follows:1.Short-term warming effectively inhibited the browning of fresh-cut potatoes.The browning degree,overall visual quality and L* value of fresh-cut potato were evaluated under different the treatment temperature(15,20,25 and 30 ?)and time(8,12,16 and 20 h).The results showed that warming at 25 ? for12 h had the best inhibition effect on browning with an extension of shelf-life for 3 d at 2~4 ?.Short-term warming could be considered as an efficient technique to control potato browning by short treatment time,easy operation and high security.2.Effects of short-term warming on PPO activity,total phenol content,antioxidant enzyme activities,antioxidant capacity and MDA content of potatoes were evaluated.During the treatment and after fresh-cut,short-term warming significantly reduced PPO activity and total phenol content,increased superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD)activities,enhanced ABTS scavenging rate and DPPH free radical scavenging rate,and reduced MDA accumulation.Therefore,short-term warming treatment could inhibit thebrowning of fresh-cut potatoes by inhibiting PPO activity and reducing total phenol accumulation,improving antioxidant enzymes activities and antioxidant capacity,and protecting the integrity of cell membrane to isolate PPO and the substrate.3.Short-term warming had little effect on StSPI gene expression at the transcription level.But it increasesd the activity of SPI,reduced SP activity,increased the content of soluble protein and reduced the generation of the total free amino acid.Short-term warming lead to the significant decrease of the contents of free tyrosine,lysine and aspartic acid,and the increase of the free glutamic acid content.The results of in vitro addition of amino acid difference showed that the decrease of free tyrosine and lysine contents played an important role in reducing browning level,while the increase of glutamic acid content significantly inhibited browning as well.Therefore,short-term warming could reduce fresh-cut browning by reducing the contents of free tyrosine and lysine and increasing the content of glutamic acid.4.The results of activity and genes expression of key enzyme chorismate mutase(CM,StCM1 and StCM2)in the synthesis pathway and 4-hydroxyphenylpyruvate dioxidase gene(StHPPD)in the catabolism pathway showed that the short-term warming inhibited the expression of the key enzyme of tyrosine synthesis,StCM1 and StCM2,and reduced CM acticity,while it has no significant effect on the expression of the key enzyme,StHPPD.This indicated that short-term warming could inhibit the browning by affecting the synthesis of potato tyrosine and reducing the content of tyrosine.