Preparation Of Roast-beef Characteristic Flavor Precursors And Regulation Of Their Process Flavor Formation

At present,the main components of the commercially available process meat flavorings are formed by the complete Maillard reaction of reducing sugar,amino acid/peptide and hightemperature oxidized animal fats.Most of them show strong volatile and unstable physicochemical properties.Especially during high-temperature thermal processing,they extremely tend to escape,and difficult to maintain a stable and sustained aroma enhancing effect in the food systems.The Maillard reaction intermediate Amadori rearrangement products(ARP)are able to complete the subsequent Maillard reaction to form characteristic flavor compounds during thermal processing,and achieved controlled formation of fresh process flavor.Therefore,in this study,the intermediate ARP and oxidized tallow were prepared,and they were combined to construct a roast-beef characteristic flavor precursor base stock.They were applied to strengthen the flavor of thermal processed food.ARP was able to form characteristic flavor with roast aroma and meat flavor through Maillard reaction,and oxidized tallow was able to form beef characteristic aroma,with achievement of controlled formation of roast-beef characteristic flavor with rich and vivid aroma.Firstly,the flavor characteristics of the complete Maillard reaction products from six systems were evaluated through a descriptive sensory analysis method.Furthermore,a complex substrate of cysteine/glycine/ribose was determined to prepare an intermediate thermalprocessing flavor precursor that enhanced the characteristic flavor of roast beef.The glycineribose Maillard intermediate(GR-ARP)was prepared via the reaction at atmospheric pressure coupling with vacuum dehydration,and purified by ion exchange chromatography to reach a purity of 96.27%.The GR-ARP/Cys,as characteristic flavor intermediate and flavor precursor for roast beef,was constructed by mixing GR-ARP with cysteine(Cys).The formation of volatile flavor compounds in the GR-ARP/Cys after thermal processing was further investigated.It was found that the total content of 2-acetylthiazole with both beef flavor and roasted aroma remained high,while the content of pyrazines with roasted fruit aroma was low.Further study on the mechanism and control methods for flavor formation of GRARP/Cys during thermal processing was focused on.The results revealed that after thermal degradation of GR-ARP to form methylglyoxal and glyoxal,cysteine preferentially reacted with methylglyoxal,and the formation of 2-acetylthiazole was the main and specific reaction pathway.When the concentration of 2-acetylthiazole raised to the plateau stage,the remaining cysteine intensely reacted with glyoxal to form pyrazine.However,the reaction pathway for glyoxal regeneration was more reactive than the Strecker degradation reaction pathway for pyrazine formation.A regulation method for the formation of thermal-process characteristic flavor compounds in the GR-ARP/Cys was accordingly proposed.The effective mechanism of cysteine increase for promoting the formation of pyrazines,and cysteine reducing for increasing2-acetylthiazole was clarified.It was determined that when GR-ARP and Cys were mixed at a concentration of 1:1,the thermal processed roast-aroma was the most enhanced.Beef flavor precursors with low acid value(AV)and high peroxide value(PV)were prepared by enzymatic hydrolysis and mild oxidation of beef fat.Lipase was applied for tallow hydrolysis,and the optimal conditions for enzymatic hydrolysis of tallow were determined as follows: enzyme addition 70 U/g,enzymatic hydrolysis time 6 h,enzymatic hydrolysis temperature 47°C,substrate concentration 60%,p H 8.0;the optimal mild oxidation conditions for enzymatic hydrolysis of tallow were determined as follows: temperature 110℃,ventilation rate 50 L/h,and oxidation reaction time 3 h.Through partial least square regression(PLSR)analysis,it was clarified that mild oxidation temperature was a key indicator for regulating the oxidation degree of enzymolyzed tallow.Through sensory analysis,it was determined that the thermal processing products of GRARP/Cys with addition of 20% enzymolyzed and mild oxidized product showed the best meat aroma,baking aroma,aroma coordination,and overall acceptance.A complex flavor precursor as GR-ARP/Cys/enzymolysis mild oxidation products with the characteristic aroma of roasted beef was constructed,and the mechanism of its thermal process flavor formation was analyzed.By comparing the species and contents of volatile flavor compounds in the products of enzymolyzed and mild-oxidized tallow,GR-ARP/Cys,and GR-ARP/Cys/enzymolyzed and mild-oxidized tallow,it was clarified that 13 compounds in the roast-beef characteristic thermal processing flavor components of complex flavor precursors were formed through thermal reaction of enzymolyzed and mild-oxidized tallow;9 compounds were formed by the Maillard reaction of GR-ARP/Cys;1 compound was produced by the interaction between the enzymolyzed and mild-oxidized tallow and GR-ARP/Cys in the thermal reaction.It was confirmed that enzymolyzed and mild-oxidized tallow modified each other with intermediates during the thermal processing with the formation of fresh flavor characteristics,and they jointly constructed a full and realistic flavor profile of roast beef characteristics.The complex flavor precursor base stock of GR-ARP/Cys/enzymolyzed and mild-oxidized tallow was applied to the production of baked potato slices.Compared with the application effect of flavor products yielded through complete Maillard reaction,it was found that the complex flavor precursor base stock could rapidly produce 2-acetylthiazole with a significant baking aroma,and make the formation of pyrazines faster at higher yields,and with more diverse species.It had significant advantages in enhancing the roast aroma and roasted-fruit aroma of baked potato slices,achieving the goal of controlled thermal processing flavor formation,while reducing the content of nonanal,caproic acid,nonanoic acid and 2-pentylfuran which contributed significantly to the off-flavor.It significantly improved the flavor profiles of baked potatoes and showed broad application prospects.