Application Of Highly-nuclear Molybdenum Cluster On Food Perservation

Tyrosianase?EC 1.14.18.1?,also called polyphenoloxidase?PPO?,has monophenolase activity and diphenolase activity.It can lead to the production of melanin by hydroxylation of L-tyrosine and oxidation of L-dopa.Tyrosianase widely distributed in fruits,vegetables and aquatic products,which is key enzyme that catalytic generated melanin to cause a decline of food quality.Therefore,it is great significance to development of tyrosinase inhibitor that used to cut-off the melanin synthesis pathway for delaying the decline of food quality.Highly-nuclear molybdenum cluster,with discrete cluster structure and nanoscale size,is one of the hotspot in research of polyoxometalates chemistry.There have researches show that polyoxometalates exhibited strongly inhibitory effects on the activity of tyrosinase.Hence,six kinds of highly-nuclear molybdenum cluster with different structures were synthesized.And,their inhibitory mechanisms on tyrosinase,the effect of preventing enzymatic browning on fruits and vegetables and inhibitory effect on melanosis of aquatic product were investigated.The paper will provide a new idea to discover novel tyrosinase inhibitors,and expand the application fields of high-nuclear molybdenum cluster.The results showed as follows:?1?Highly-nuclear wheel molybdenum cluster Mo₅₇Mn₆ was synthesized and characterized.Inhibitory effect of Mo₅₇Mn₆ on diphenolase activity of tyrosianse and enzymatic browing of apple slices were studied.The results showed that Mo₅₇Mn₆ can effectively reduce diphenolase activity of tyrosinase,and the IC₅₀ value was 0.0455 mmol/L.Mo₅₇Mn₆ was a reversible and competitive type inhibitor on tyrosinase,and the inhibition constant?K_I?was 0.0157 mmol/L.During the low temperature storage,Mo₅₇Mn₆ can inhibit the activity of PPO,regulate the activity of POD and reduce the browing degree of apple slices.Meanwhile,Mo₅₇Mn₆ can significantly reduce the weight loss rate and the amount of MDA production to delay the aging of tissue,which has fresh-keeping effect on apple slices.?2?Inorganic and organic–inorganic molybdenum cluster polyoxometalates Mo₃₆6 and Mo₃₆-bipy were synthesized and characterized.Inhibition mechanisms on monophenolase activity and diphenolase activity of tyrosianase and effects on shrimp anti-melanosis and preservation of Mo₃₆6 and Mo₃₆-bipy were investigated.Results showed that both Mo₃₆6 and Mo₃₆-bipy can inhibit the activity of tyrosinase,and Mo₃₆ was better than Mo₃₆-bipy.For monophenolase of tyrosinase,Mo₃₆6 and Mo₃₆-bipy can extend the lag time and decrease the steady-state activity.For diphenolase of tyrosinase,Mo₃₆ was a reversible and competitive type inhibitor,and Mo₃₆-bipy was a reversible and mixed type inhibitor.Effect on shrimp anti-melanosis and preservation of Mo₃₆-bipy was stronger than that of corresponding Mo₃₆.During the period of storage of shrimp,both Mo₃₆6 and Mo₃₆-bipy can significantly improve the value of sensory score and L*,and reduce the pH value and the total number of colonies.Besides,Mo₃₆-bipy can significantly decrease the content of TVB-N,but the effect of Mo₃₆6 was not obvious.?3?Highly-nuclear molybdenum clusters,which were wheel-type Mo₅₇V₆ and Mo₁₅₄,and keplerate-type Mo₁₃₂,were synthesized and characterized.And,their inhibitory mechanisms on diphenolase activity of tyrosianase were investigated.Based on this,inhibition kinetic parameters of polyoxometalates on diphenolase activity of tyrosianase were analyzed.Results showed that Mo₅₇V₆,Mo₁₃₂ and Mo₁₅₄ have strong inhibitory effects on diphenolase activity of tyrosianase,which the inhibition mechanisms were reversible and the inhibition types were competitive.Compared with lowly-nuclear polyoxometalates,the effect of highly-nuclear molybdenum cluster polyoxometalates on diphenolase activity of tyrosianase is stronger.Among them,the inhibition effect of keplerate-type molybdenum clusters is better than that of the wheel-type molybdenum clusters.