Effect Of Microwave、Ethanol Treatment On Enzymatic Browning Of Fresh-cut Potatoes

Fresh-cut potatoes are increasingly being used in the processing industry of potatoes.However,fresh-cut potatoes are prone to enzymatic browning.Potatoes are prone to enzymatic browning during processing such as peeling,resulting in a blackened appearance and affecting the quality of their products.Enzymatic browning of fresh-cut potatoes has become an important factor limiting the development of fresh-cut fruits and vegetables.Therefore,potatoes are increasingly being used in the food processing industry.However,fresh-cut potatoes were prone to enzymatic browning during the cutting process,which greatly reduces their appearance quality and nutritional value.In response to this problem,potatoes were used as raw material to study the inhibitory effect of ethanol and microwave on the enzymatic browning of fresh-cut potatoes.In addition,the single factor test and response surface design were used to optimize the process conditions for the inhibition of enzymatic browning of fresh-cut potato by microwave combined with ethanol treatment,and the UV and IR spectra of enzymatic browning substrate were measured to determine the inhibition mechanism of ethanol,microwave and microwave combined with ethanol treatments on the enzymatic browning of fresh-cut potatoes.Main findings are the follows:1.The inhibitory effect of ethanol and microwave treatment on enzymatic browning of fresh-cut potatoes:In this article,different ethanol volume fraction and microwave treatments of different power were used to inhibit enzymatic browning of fresh-cut potatoes and enzymatic browning index(BI),polyphenol oxidase(PPO),peroxidase(POD),and malondialdehyde content(MDA)were determined.Results:The 5%volume fraction of ethanol soaked fresh-cut potatoes for 15 min(ethanol treated group)significantly inhibited the degree of enzymatic browning.After 9 days of storage,the BI value of the control group increased from 46.90 to 67.37,while the BI value of ethanol treated group increased from the initial value of 46.81 to 54.08,which was significantly decreased;At the end of the storage period,PPO and its POD activity were also significantly reduced,the PPO and POD activities of the control group were 18.25 U and 2.9 U,respectively,while the PPO and POD activities in ethanol treated group were 14.23 U and 2.18 U respectively;The MDA content of the control group increased from 0.68μmol/g to 1.16μmol/g,and the MDA content of ethanol treated group increased from 0.66μmol/g to 0.91μmol/g;Fresh-cut potatoes were treated with390 W microwave power for 5 s(microwave treated group)had a good effect on inhibiting enzymatic browning.On the 9~thh day of storage,the BI value of the control group increased from the initial 47.51 to 67.47,while the BI value in microwave treated group was increased from 39.21 to 53.75.At the 9~thh day of the storage period,PPO and its POD activity were also significantly reduced,the PPO and POD activities of the control group were 17.52 U and 2.25U,respectively,while the PPO and POD activities in microwave treated group were 13.25 U and 1.95 U respectively;The MDA content of the control group increased from 0.68μmol/g to 1.21μmol/g,and the MDA content in microwave treated group changed from the initial value of 0.31μmol/g to 0.61μmol/g.Therefore,the method for determining the effective inhibition of the enzymatic browning of fresh-cut potatoes were:5%volume fraction ethanol soaked for 15 min and 390 W microwave treatment for 5 s.2.Optimization of process conditions for inhibition of enzymatic browning of fresh-cut potatoes by microwave combined with ethanol treatment:the effects of ethanol volume fraction,ethanol soaking time,microwave power and microwave heating time on the enzymatic browning of fresh-cut potatoes were obtained by single factor experiment and response surface analysis.Conclusion:The 390 W treatment for 5 s combined with 5%volume fraction of ethanol for 15 min has the best inhibitory effect on the enzymatic browning of fresh-cut potatoes.After the whole storage period,the BI value was 29.94,PPO and POD activities are reduced which were 12.93 U and 1.4 U respectively.The MDA content was 0.50μmol/g.3.Effect of microwave and ethanol treatment on the ultraviolet spectrum of enzymatic browning substrate:It was concluded that there was no significant difference in the UV absorption of L-tyrosine and L-dopa between control group and ethanol and microwave treatment groups.Therefore,the ultraviolet absorption spectrum of L-tyrosine and L-dopa did not be changed by ethanol and microwave treatments.4.The effect of microwave and ethanol treatment on the infrared spectrum of enzymatic browning substrate:the IR of L-tyrosine and L-dopa was measured.It was concluded that there was no significant difference in the IR absorption of L-tyrosine and L-dopa between control group and ethanol and microwave treatment groups.Therefore,the infrared absorption spectrum of L-tyrosine and L-dopa did not be changed by ethanol and microwave treatments.5.Determination of PPO circular dichroism by microwave treatment:Studies showed that compared with the control group,the PPO molecular structure of microwave treated potatoes changed significantly.The content ofα-helix and random coil were reduced and turned intoβ-sheet,this change in secondary structure may be the main reason that microwave treated PPO activity and enzymatic browning of fresh-cut potatoes was inhibited.