Study On Technique And Mechanism Of NaCl Solution Treatment On Potato Tuber To Inhibit Fresh-cut Browning

Fresh-cut potatoes are widely accepted by consumers for their freshness,hygiene and convenience,and have a promising market prospect.However,its commodity quality and shelf-life are limited by browning during processing and storage.As a safe and commonly used food additive,NaCl solution has been used to control browning of fresh-cut fruits and vegetables.However,treating fresh-cut potatoes post-cut with NaCl solution not only has insufficient effect on inhibiting browning,but also affect product flavor.Previous studies showed that NaCl solution treatment enable plant cells to activate the antioxidant system.Therefore,there is a possibility that the browning of fresh-cut potatoes can be inhibited by soaking potato tubers in NaCl solution before cutting.But this hypothesis has not been verified.In this paper,the inhibiting effect of pre-cutting NaCl solution treatment on browning of fresh-cut potatoes was studied,and the optimal conditions of NaCl solution treatment were then determined.To reveal the browning inhibition mechanism of pre-cutting NaCl solution treatment on potatoes,the concentration of browning substrate,the activity and genes expression of polyphenol oxidase（PPO）,the activity of peroxidase（POD）,antioxidant system,and the contents amino acids were determined.The main results are as follows:1.Pre-cutting NaCl solution treatment under appropriate conditions could significantly inhibit the browning of fresh-cut potatoes.The optimal concentration and treatment time for NaCl treatment before cutting are 5%and 3 hours,respectively.Under these conditions,treated fresh-cut potatoes were not browning within 4 day,while control and water treated potatoes were browning after 8 hours of cutting.The pre-cutting NaCl solution treatment extended the shelf-life of fresh-cut potatoes for 3 days,with significantly reduced the surface water loss of slices and no negative effect on the flavor.2.The browning inhibition of fresh-cut potatoes by pre-cutting NaCl solution treatment of tubers is related to the decreases in total phenol and tyrosine contents,the inhibition of PPO and POD activity and the influence of PPO genes expression.Soaking potato tubers in NaCl solution before cutting resulted in significantly lower total phenol content,PPO activity and POD activity during and after cutting than those in water control and untreated control.The expression of PPO genes（POT32,POT33,POT72 and POTP1/P2）are significantly higher than untreated controlin the soaking process,while the expression of POT32,POT72and POTP1/P2 was significantly lower than water and untreated control after cutting.3.Pre-cutting NaCl solution treatment on potato tubers may inhibit fresh-cut browning by accumulating reactive oxygen species（ROS）and hydrogen peroxide（H₂O₂）to activate antioxidant system to increasethe superoxide dismutase（SOD）and catalase（CAT）activities andreduce the lipid membrane peroxidation.Thus the regionalized distribution of enzyme and browning substrate is maintained,and thereby inhibited the browning.Comparing the differences of the contents of ROS and H₂O₂,the activities of SOD and CAT,the free radical scavenging capacity of 1,1-diphenyl-2-trinitrophenylhydrazine （DPPH） and2,2’-diazo-bis-3-ethylbenzothiazoline-6-sulfonic acid（ABTS）,the activites of lipoxygenase（LOX）and the content of malondialdehyde（MDA）among NaCl solution treated groups and two types of control groups during treatment and after cutting,the pre-cutting NaCl solution treatment results in a significant increase in ROS and H₂O₂ contents before cutting,while a significant decrease after cutting.The treatment also significantly increased the activity of SOD and CAT,enhanced the DPPH and ABTS free radical scavenging activity,and significantly inhibited the activity of LOX,and reduced the accumulation of MDA.4.The pre-cutting NaCl solution treatment alleviated the browning of fresh-cut potatoes by reducing thecontent of free tyrosine and increasing the contents free glutamic acid and proline.Determination of free amino acid content by high performance liquid chromatography revealed that pre-cutting NaCl solution treatment resulted in significant increases in glutamate and proline contents and significant decreases in tyrosine and arginine contents.The results of in vitro addition of amino acid difference experiments shows that the addition of tyrosine difference significantly promoted browning of the pulp of NaCl solution treated potatoes before cutting.Meanwhile,the addition of glutamate difference significantly inhibited browning of the pulp of untreated potato.The addition of proline and arginine showed insignificant effect on the browning of potato pulp.In addition,it was found that pre-cutting proline treatment could significantly inhibit the browning of fresh-cut potatoes,which means proline could reduce browning by inducing other metabolic pathways rather than directly inhibiting.