| Potato（Solanum tuberosum）is popular among consumers as it can be used as both vegetable and staple food.There is a great need in domestic market in recent years of fresh-cut potato as it is convenient,fresh and hygiene.However,cutting procesoften results in enzymatic browning,and it is the main reason for shortening the shelf-life of fresh-cut potatoes.At present,it is urgent to find a simple,safe and effective method to inhibit browning in fresh-cut potato processing and storage.In this research,the effects of five safe sulfur compounds on inhibiting browning arecompared byusing the potato of Netherlands 15.The results shows that the the effect of 3-mercapto-2-butanol,an approved edible flavor in China and abroad,on inhibiting browning of potato is best.In order to explain the mechanism of 3-mercapto-2-butanol inhibiting browning of fresh-cut potatoes,we tested browning-related enzymes activities,browning substrates and products,PPOs gene expression and the contents of free amino acids.The results are as follows:（1）Five kinds of safe sulfur compounds,allicin,sulforaphane,3-mercapto-2-butanol,3-mercapto-2-butanone and 2-methyl-mercaptofuran,were used to fumigate potato shreds,and 3-mercapto-2-butanol was found inhibited browning of fresh-cut potatoes best.The conditions of fumigation of 3-mercapto-2-butanol were further optimized.It was found that when the fumigation concentration of 3-mercapto-2-butanol was 19.2μL/L(1.81×10-4 mol/L)and the fumigation time was 3 h,the browning of the treated group was delayed by 4 days compared with the control group at 5℃.In optimizing soakingexperiment,it was found that when the soaking concentration of 3-mercapto-2-butanol was 25μL/L(2.35×10-4 mol/L),the treatment potato shreds delayed browning for 5 days than the control group at 5℃,and the inhibition effect was similar to that of 0.5%sodium bisulfite(4.8×10-2 mol/L).In addition,the browning inhibition effect of 3-mercapto-2-butanol was slightly better than its isomer 2-mercapto-3-butanol.（2）3-mercapto-2-butanol significantly inhibites PPO enzyme activity and the expression of PPO regulatory genes POT 32 and POT 33.The results of enzyme kinetic experiments showed that PPO enzyme activity decreased with the increase of 3-mercapto-2-butanol concentration.In addition,the relation curve between the reciprocal of the substrate concentration and the eciprocal of the PPO enzymatic browning reaction rate is close to the intersection of Y-axis with significant different slope,which means the effect of 3-mercapto-2-butanol on PPO appears to be reversible competitive inhibition.（3）The tyrosine content in the potato shreds was significantly higher than that in the ethanol control and the water control after treatment with 3-mercapto-2-butanolfor 3 days.The results showed that 3-mercapto-2-butanol reduced total phenolic content only in 0 d,1 d,and 5d;chlorogenic acid content was only decreased in 0 d and 1 d after treatment.After treatment with 3-mercapto-2-butanol,the POD activity of potato shreds was lower than that of ethanol control at 8 h,1 d and 5 d;DPPH inhibition rate of treated group was significantly higher than that of ethanol control at 2 d,3 d and 5 d,butthe difference between two groups is not significant in other time.As a result,the effect of 3-mercapto-2-butanol in inhibiting browning may relate to the reduction of tyrosine content.Decreased total phenolicand chlorogenic acid content,increased antioxidant capacity and decreased POD activity may also relate to the inhibition of browning,but not the main factors.The above results indicate that 3-mercapto-2-butanol can be used as a safe and effective chemical for browning control of fresh-cut potato shreds.3-Mercapto-2-butanol inhibits browning of fresh-cut potato shreds by competitively inhibiting and affecting the expression of PPO regulatory genes to reduce PPO enzyme activity,and increasing the content of substrate tyrosine. |
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