Effects And Application Of Synergetic Bacteriostasis Of Myricetin And Phloretin In Food Preservation

Food is susceptible to microbial infection and spoilage in the production and processing.About one third of the food in the world is wasted due to spoilage every year.With the improvement of living standards,the demand for the higher quality of food is increasing.Developing green preservatives to meet the needs of human for the food of natural origin has attracted much attention.The utilization natural food raw materials and by-products of food with nutritional fortification as well as preservation has become highlighted.Myricetin(MYR)is the major polyphenol from the leaves of Ampelopsis grossedentata,which was admitted as a new food raw material in 2016.Phloretin(PH)widely exists in apple fruit and peel.Both of them have effects in regulating bactericidal activity activity and biological redox states,they have been used to inhibit microorganism proliferation and scavenge reactive oxygen free radicals.At present,PH has been approved to be added to food as food additives without limited doses.MYR has been used as nutrition supplements in USA and Europe.To our knowledge to date there is no report about the synergistic effects of MYR and PH in regards to the food preservation.In this study,the synergistic effects on microorganisms and antioxidant effects against Escherichia coli(E.coli)and Staphylococcus aureus(S.aureus)of MYR and PH were explored.The ratio of bacteriostatic concentration was optimized via mixing design test.The impacts of MYR and PH at the ratio of synergistic combination were applied in the preservation of beef at 4℃,20℃and 30℃as well as fresh noodles at 20℃and 30℃.The accomplishment of the project would provide a technique support for the formulation and development of a nutritious preservatives of natural origin for the food.The main research results are as follows:1.The minimal inhibitory concentration(MIC)of MYR,PH and potassium sorbate was explored by microdilution method.The results showed that the MIC values of MYR,PH and potassium sorbate against S.aureus were 0.246 mmol/L,0.171 mmol/L and 53.2mmol/L,respectively.The MIC values of MYR,PH and potassium sorbate against E.coli were 3.93 mmol/L,0.685 mmol/L and 6.65 mmol/L,respectively.The results showed that MYR and PH had stronger inhibitory effect on S.aureus and E.coli than potassium sorbate.he synergistic antibacterial index fractional inhibitory concentration(FIC)of MYR and PH was determined via chessboard experiment.The combination of MYR and PH in DMSO at the ratio of 1/1 had synergistic effect.The experimental design of mixture was carried out with Design Expert software to investigate the ratio of the synergistic effect.The results showed that MYR and PH at the ratio of 7.729/2.271 on the bacterial cell wall as well as cell membrane was investigated.Adsorbtion of substances in MRY and PH formulation treated group were lower than those in the control group,and the relative conductivity as well as protein content of bacteria in the formulation group were significantly higher than those in the control group.It demonstrated the formulation of MYR and PH destroyed the cell wall and increases the permeability of bacterial cell membrane.In addition,the antioxidant effect of MYR and PH was investigated via comparing the scavengering rates of DPPH~+,ABTS~+and superoxide anion free radicals as well as inhibition of lipid oxidation.The results showed that MYR and PH formulation had synergistic antioxidant effect in the ratio of7.729/2.271.2.The mixture of MYR and PH was applied in the preservation of fresh beef.After the fresh beef was soaked in MYR and PH formulated solution for 1 minute,the weight loss rate,total bacterial count,total volatile base nitrogen,thiobarbituric acid value,chromaticity,p H and sensory evaluation of beef stored at 4℃,20℃and 30℃were quantified at different intervals.The beef stored at 4℃was spoiled in the control group on the 4th day,while the preservation solution prolong the shelf life of beef to 9 days.The p H of the fresh-keeping solution group was always maintained at about 5.85,which was the first-order freshness and was better than that of the control group.In addition,the TBARS value of the preservative solution group maintained below 0.1 mg/kg in the first8 days,and increased rapidly to 0.47 mg/kg on the 9th day,which was still lower than the national standard value.The beef stored at 20℃was spoiled in the control group at 32hours,and the shelf life of beef extended to 44 hours by the preservation solution.The p H of the preservation solution group was always maintained at about 5.60,which was the first-order freshness,and the color change was better than that of the control group.The beef stored at 30℃was spoiled in the control group at 20 hours,and the shelf life of the fresh-keeping beef was extended to 32 hours.3.The formulation of MYR and PH was added to fresh noodles.The water loss rate,p H,chromaticity value,cooking loss,total number of colonies and sensory scoring indexes of fresh noodles at different time points were investigated at 20℃and 30℃to comprehensively evaluate the shelf life of fresh noodles.Finally,according to the shelf-life model,the shelf-life of the control group and polyphenol noodles at 4℃was predicted.Fresh noodles stored at 20℃were spoiled in the control group at 22 h.The shelf life was extended to 58 hours after adding polyphenols.And p H value decreased less than the control group,cooking loss and total bacterial count were significantly lower than the control group.The fresh noodles stored at 30℃were spoiled at 14 hours in the control group,and the shelf life extended to 22 hours after the fresh-keeping solution was added.Water absorption and dry matter loss rate indicators were significantly better than the control group.Finally,according to the shelf life model,the shelf life of fresh noodles stored at 4°C in the control group was about 2 days,and the shelf life of fresh noodles was extended to 11 days after the addition of polyphenols.According to shelf life estimation via accelerated shelf-life testing experiment,fresh noods with polyphenol formulation at 4℃was extended to 11 days from less than 2 days in the control group.