Investigation On The Oxidative Regulation And Simulated Digestion Characteristics Of Mulberry Polyphenols On Pork Myofibrillar Protein

Oxidation is one of the most important reasons for the quality deterioration of meat products.Studies have shown that plant polyphenols,as a natural antioxidant,can effectively delay protein oxidation during meat processing,which is of great significance to improve the quality of meat products.However,it is still not clear about the regulation of phenolic substances on the quality of meat products,the change of phenolic substances during the processing of meat products,the interaction mechanism between phenolic substances and muscle proteins,and the digestion and absorption characteristics after the interaction of phenolics and proteins.In this study,mulberry polyphenols were taken as the representative of plant polyphenols to study the oxidative regulation characteristics of mulberry polyphenols on minced meat products,and to explore the change of phenolic compounds during the processing of minced meat products.Subsequenctly,the effects of mulberry polyphenols on the conformation and functional properties of myofibrillar protein(MP)were studied,and the oxidative regulation mechanism of mulberry polyphenols on MP in different oxidation systems was explored.Finally,the mulberry polyphenol-MP adduct was digested in vitro,and the effects of mulberry polyphenols on the digestion and fermentation characteristics of MP were investigated.Specific experimental contents and results are as follows:(1)Taking sausage as an example,the oxidative regulation characteristics of mulberry polyphenol extract(MPE)on minced meat products were studied.The results showed that the prohibition effect of MPE on protein and lipid oxidation of sausge was more significant than that of other antioxidants(sodium nitrite(SN),Flammulina velutipes polysaccharide(FVP)and starter culture(SC)).Meanwhile,the sausage supplemented with MPE showed higher antioxidant activity than traditional sausage(supplemented with SN).(2)Taking the dried minced pork as an example,the effects of heat treatment time-temperature combinations and?-cyclodextrin addition on the polyphenols stability in MPE enriched minced meat products were studied.Phenolic compounds underwent the greatest when drying at high temperature followed by long time baking at low temperature.A procedure of drying for 10 h at 40°C followed by baking for 3 min at150°C was recommended for slice preparation on the basis of the highest retention rates of phenolic compounds(54.84%polyphenols,39.1%flavonoids,and 59.62%anthocyanins).Four phenolic acids(neochlorogenic acid,chlorogenic acids,cryptochlorogenic acid and caffeic acid),three flavonoids(catechin,rutin and quercetin),and two anthocyanins(cyaniding-3-O-glucoside,cyanidin-3-O-rutinoside)were detected in the products.Retention rate of most phenolic compounds,except for caffeic acid and quercetin,and antioxidant capacity of the product could be further enhanced by adding 1%?-cyclodextrin.(3)The conformational and functional properties of MP modified by five phenolic compounds,including cyanidin 3-O-glucoside,cyanidin 3-O-rutinoside,caffeic acid,quercetin and rutin,dominantly presented in MPE-enriched sausage were investigated.These phenolic compounds significantly affected the structure of MP as indicated by the remarkable losses of carbonyl and?-NH₂ and the obvious fluorescence quenching(P<0.05).Modification by phenilic compounds increased antioxidative activity but decreased thermal stability of MP.Rutin improved the MP emulsifying properties of MP.Quercetin showed little effect on secondary structure of MP.Caffeic acid triggered the conversion of?-helix to?-sheet in MP,and the resulted protein exhibited the strongest fluorescence quenching,solubility,and antioxidant activity among all samples.(4)Gelation behaviors of MP modified by five phenolic compounds,including quercetin,rutin,caffeic acid,cyanidin-3-O-glucoside,and cyanidin-3-O-rutinoside,were investigated with a hydroxyl radical-generating system.Results showed that oxidation could decrease the content of sulphydryland ?-NH₂ group,and increase the content of carbonyl,thus altering the gelation behavior of MP.Caffeic acid jeopardized the gel quality of MP considering the decreased gel strength,water-holding capacity(WHC)and elastic modulus(G?),and the collapse of microstructure.Other phenolic compounds,especially quercetin,weakened the sensitivity of MP to hydroxyl radicals by interacting with the amino acid side chain groups of MP,thus enhancing the strength and WHC of the heat-induced gel.After oxidation,the quercetin-modified MP gel exhibited a dense and uniform microstructure,which was even better than the non-oxidized MP gel.(5)The dose-dependent effects of polyphenols(0,0.5%,1%,2.5%,and 10%)and malondialdehyde(MDA)(0,5,10,20,and 40 m M)on the emulsifying and gel properties of MP emulsion were studied.Addition of mulberry polyphenols enhanced the antioxidant ability of MP emulsion,enlarged its particle size,and reduced its Zeta potential(P<0.05).MDA played an important role on the gelling behavior of MP emulsion modified with 2.5%polyphenols.Due to the enhanced protein-protein cross-linking,the emulsion gels showed improved elasticity,strength,and WHC at intermediate MDA concentrations(5–20 m M).However,high MDA concentration(40m M)could destroy protein-protein interactions,resulting in"oil leakage"and gel structure collapse.Polyphenols is not conducive to the gelation but weaken the oxidative damage of MDA to protein.The gel structure of MP emulsion collapsed after high dose of polyphenols or MDA treated.Thus,to maintain uniform textural and antioxidant activity of meat product,both polyphenols addition and oxidation intensity should be controlled simultaneously.(6)In vitro simulated digestion and fermentation of MP and MP-mulberry polyphenol adduct were carried out,respectively,and the antioxidant activity of digestive liquid,the degradation and transformation of protein and phenolic substances,and the effects of digestion products on intestinal microbial metabolism were analyzed.Results showed that both MP and polyphenols underwent degradation and transformation during simulated digestion,which directly affect the antioxidant activity of the digestive liquid.In general,mulberry polyphenols improved the antioxidant activity of the digestive liquid during MP simulated digestion and promoted the hydrolysis of MP.With mulberry polyphenols modified,the MP hydrolysis degree increased to 81.76%,and the ABTS and DPPH scavenging rates of the final simulated digestive liquid reached 350.10?mol Trolox/mg protein and 33.96%,which were 34%and 47%higher than those of the control group,respectively.Furthermore,the polyphenols that reach the colon after gastrointestinal digestion can be extensively biotransformed by fecal bacteria to accumulation of short-chain fatty acids(SCFAs)and the enrichment of Enterococcus and Lactobacillus,which was beneficial to the microbial balance.