Study On The Inhibition Technology And Mechanism Of Isoleucine On Browning Of Fresh-cut Potatoes

Fresh-cut potato is one of the most important fresh-cut vegetables with huge market demand and broad development prospects.However,potatoes are prone to enzymatic browning after cutting,leading to the decrease of commodity values.As an essential amino acid and food additive,isoleucine has the advantages of high safety and low cost,and is easily accepted by consumers.Previous studies of our laboratory have shown that 11 amino acids could inhibit the browning of potato mashes,among which isoleucine had the best effect.In this study,with Netherlands No.15 as raw material,the inhibitory effect of isoleucine on browning of fresh-cut potato sticks was first tested,the treatment conditions were further optimized,and the mechanism of isoleucine inhibiting enzymatic browning was preliminarily explored.The comprehensive effect of browning control was further improved by the combination of isoleucine and modified atmosphere packaging.The results are as follows:(1)The appropriate concentration of isoleucine can significantly inhibit the browning of fresh-cut potato chips.Firstly,fresh-cut potato chips were treated with different concentrations of isoleucine,and the inhibitory effect of isoleucine on the browning of fresh-cut potato chips was determined.Through the evaluation of overall sensory quality and the browning degree,the optimum treatment concentration of isoleucine was determined to be1.0%.Subsequently,the fresh-cut potato chips were soaked in 1.0%isoleucine for different time,and the optimum treatment time was determined to be 20 min.The fresh-cut potato chips treated under this condition(1.0%,20 min)still had commercial value on day 4 at 2–4°C,while the control chips had serious browning and lost commercial value on day 1.(2)Isoleucine reduces the conversion of tyrosine to quinone by inhibiting PPO activity and improving antioxidant capacity,and then inhibits the browning of fresh-cut potato.(1)Isoleucine treatment reduced the conversion of tyrosine to quinone,and the formation of brown substances,then inhibited the browning of potato mashes.Through adding isoleucine to potato mashes with different browning degrees and the determination of tyrosine and quinone contents of the mashes,we found that isoleucine alleviated potato browning by reducing the conversion of tyrosine to quinone rather than by fading the brown substances.(2)Isoleucine treatment suppressed the PPO activity of potato mashes.PPO activity was significantly decreased when isoleucine was added to potato mashes.The PPO activity partially recovered after adding copper acetate to the mashes treated with isoleucine,indicating that isoleucine inhibited PPO activity by chelating Cu²⁺of PPO active center;In addition,the results of enzyme inhibition kinetics and molecular docking showed that isoleucine was a mixed PPO inhibitor,which further inhibited PPO activity by interacting with amino acid residues of free PPO through hydrogen bond,van der waals force and hydrophobic force.(3)Isoleucine treatment significantly improved the antioxidant capacity of potato mashes.Through the determination of the antioxidant capacity of potato mashes,we found that isoleucine treatment increased the POD and CAT activities,DPPH and ABTS radical scavenging rate and phenol content,and reduced MDA content,and thus improved the antioxidant capacity of potato.(4)Isoleucine treatment may further alleviate potato browning by inducing the formation of some anti-browning free amino acids in potato.The content of free amino acids in potato mashes was determined by high performance liquid chromatography(HPLC).Results showed that isoleucine treatment significantly increased the content of free proline,methionine,valine,leucine,phenylalanine and lysine,which have been reported to have browning inhibition effect.(3)Isoleucine treatment combined with modified atmosphere packaging further improved the browning control effect.Based on the previous research results of our laboratory,the area of modified atmosphere window and the appropriate gas proportion in the packaging bag were studied.It was finally determined that the appropriate modified atmosphere window area of fresh-cut potato was 0.004 cm~2/kg,and the suitable flushing gas proportion in the bag was 4%O₂+10%CO₂.At 4°C,compared with individual isoleucine treatment,isoleucine+MAP+gas flushing treatment prolonged the shelf life of fresh-cut potato sticks for 1 d,which better prevented the occurrence of the off-odours in regular MA bags without MA window.