Effects Of Enzyme Activity And Cell Structure On The Browning Of Two Fresh-cut Potato Cultivars

Fresh-cut potato products are favored by consumers.It has the advantages of convenient to eat,healthful and fresh,high nutritional value,cost saving and reducing environmental pollution.In recent years,fresh-cut potato is in great demand in the food industry at home and abroad.However,the fresh-cut potato surface occurred enzymatic browning,which seriously reduces products quality and visual quality,shortens shelf life,reduces desire to buy.“Minshu”and“Huangjin”cultivars with different resistance to browning were used as materials in this research.The browning phenotype of these two fresh-cut potato cultivars were studied at room temperature.And then we detected browning related enzyme activities.The effect of polyphenol metabolism,antioxidant system,and membrane lipid metabolism to fresh-cut potato browning in different cultivars were analyzed.And the cells ultrastructure of different cultivars during the process of browning were also observed.In this research,the effect mechanism of membrane lipid metabolism on fresh-cut potato browning was discussed.The main results are as follows:(1)The browning phenotype analysis showed that serious browning of fresh-cut“Huangjin”potato occurred at 3 h,while the“Minshu”occurred slight browning at 7 h.So,the browning speed and degree of“Huangjin”is significantly higher than“Minshu”and it is more sensitive to browning,while“Minshu”has better browning resistance.(2)The activities of browning related enzymes(PPO,TYR,POD and PAL)and the contents of total phenol and soluble quinone in fresh-cut“Minshu”were significantly lower than“Huangjin”at room temperature(P<0.05).The results were consistent with the anti-browning phenotype of fresh-cut“Minshu”.However,the activities of antioxidant enzymes(CAT,SOD and APX)of fresh-cut“Minshu”were lower than“Huangjin”.It indicated that antioxidant enzymes were not the key factor causing the difference of browning sensitivity between“Minshu”and“Huangjin”cultivars.(3)The activities of PPO,POD,TYR,PLD,LOX,the contents of soluble quinone,H₂O₂and MDA in fresh-cut potato were extremely significant positive correlation with BI(P?0.001),and PALactivity was significant positive correlation with BI(P?0.01).These results indicated that higher activities of PPO,POD,TYR,PAL,PLD,LOX,contents of soluble quinone,H₂O₂ and MDA were the main factors leading to browning.(4)The enzymes activities and transcript levels of PLD and LOX in fresh-cut“Minshu”were lower than“Huangjin”.And the contents of H₂O₂ and MDA in fresh-cut“Minshu”were also significantly lower than“Huangjin”(P<0.05).It indicated that the membrane lipid peroxidation degree of fresh-cut“Minshu”was lower.We speculated that complete cell structure of fresh-cut“Minshu”was one of the important reasons for the resistance to browning.(5)The structure of intercellular layer and plasma membrane of fresh-cut“Minshu”still maintained better integrity.The plasma membrane was close to the cell wall without obvious incipient plasmolysis.The organelles such as mitochondria,vacuoles,nucleus and plastids remained intact without obvious changes.The most of bilayer membrane structure of mitochondria and nuclear membrane,and cristae are still clear.The more Golgi complexes,plastoglobules and black protein particles were found in“Minshu”.Therefore,we speculated that the more Golgi complexes,plastoglobules,black protein particles around the cell wall,complete mitochondria and vacuoles may be the important reasons to maintain the ultrastructural integrity of plasma membrane and delay the browning occurrence.On the contrary,many intercellular layers and plasma membranes of fresh-cut“Huangjin”were severely damaged.The cell wall was white,and the plasma membranes boundary was unclear.The cytoplasmic content spilled out,and the incipient plasmolysis was serious.The membrane structures of vacuoles,mitochondria and cell nucleolus were severely disintegrated.The cristae structure was blurred,the mitochondrial matrix flowed out.PPO enzyme in the cytoplasm contacted with phenolic substrates in vacuoles to form black flocculent deposits.The plasma membrane of“Huangjin”dissolved seriously,and a large number of multivesicular bodies were formed.There aggravated the degree of browning.The browning resistance of fresh-cut“Minshu”is stronger than“Huangjin”due to the key browning enzyme(PPO,TYR,POD and PAL)activities,membrane lipid peroxidation and plasma membrane stability.The higher activities of PPO,POD,TYR,PAL,PLD,LOX,contents of soluble quinone,H₂O₂ and MDA were the main factors leading to browning.In addition,the integrity of mitochondria,vacuoles and plasma membranes,and a large number of Golgi complexes and a large number of black protein particles,played an important role in improving the resistance to fresh-cut potato browning.