Influence Of Phospholipid Molecules And Processing Technology On Characteristic Flavor Formation Of Water-boiled Salted Duck

In 2018,the total output of meat in China was 86.24 million tons,including 1994 million tons of poultry.In recent years,the consumption of poultry increased at a rate of over 19% every year.Water-boiled salted duck(WSD),which originated from Nanjing,Jiangsu Province,China,is one of the few traditional Chinese meat products processed at low temperatures.The traditional WSD requires “rubbing with cooked salt,stewing in old brine,drying thoroughly,and cooking well”.It is famous for its large quantity and wide range in traditional Chinese food,but the traditional technology is complex and mostly manual operation,the product flavor is not stable and the characteristic flavor is not obvious,so it is difficult to meet the people's demand for food,which has become an obstacle to industrial development.It is an urgent problem to explore the formation mechanism of WSD's characteristic flavor and to maintain the traditional flavor to realize the modernization of product processing.Research shown that lipid is very important to the formation of meat flavor.However,there are many kinds of lipid,and the change rule of lipid during processing is not very clear,and the relationship between key precursor lipids and meat characteristic flavor substances is also not clear.Therefore,on the basis of defining the characteristic flavor of salted duck,starting from food processing,this study systematically and accurately studies the " phospholipid fingerprint" of Nanjing WSD and its change rule in the processing of dry-curing,marinating,dry-ripening and boiling,the relationship between phospholipid molecules and characteristic flavor substances,and the flavor precursor phospholipid molecules and key factors(dry salt content,spices)based on lipidomics.The research results can provide scientific theoretical support for the key technologies of flavor maintenance and regulation in salted duck processing,and have great application value.In this study,SPME-GC-MS/IMS-O,electronic nose,amino acid analysis and electronic tongue were used to analyze the odor and taste of 4 brands of WSD.The results showed that 27 volatile components were identified by GC-IMS,including 9 aldehydes,10 alcohols,4 ketones,2 esters,1 ether and 1 furan;31 volatile components were identified by SPME-GC-MS-O,including 10 aldehydes,5 alcohols,2 esters,2 ketones,7 hydrocarbons and 5 other compounds.ROAV and olfactory technology were used to identify the characteristic flavor compounds of WSD,including hexanal,heptanal,octanal,1-octyl-3-ol and 2-pentylfuran.Although there are differences in flavor of WSD samples,the characteristic flavor substances of WSD are mainly aldehydes.E-nose and GC-MS combined with PCA were used to identify WSD samples,and the results were basically the same.E-tongue and amino acid analysis showed that there was no difference in taste of WSD samples.In this study,on the basis of optimizing the detection parameters of shotgun-MS/MS,and combining with SPME-GC-MS/IMS method,the change rules of phospholipid(PL)molecular species and volatile flavor substances during processing were studied.The key PL molecular species and processing were identified by partial least squares discriminant analysis(PLS-DA),principal component analysis(PCA),partial least squares regression(PLSR)and Pearson correlation analysis,and the PL molecular species and volatile flavor substances related model were established.The results showed that the contents of PC,PE,PG,PI and PS were 31481.30,27640.03,4870.07,1531.64 and 3331.54 ng/mg,respectively.PC and PE are the main phospholipids.Only 110 PL molecules were identified in raw meat,while 119 PL molecules were identified during processing,most of which were rich in unsaturated fatty chain.During processing,the molecular content of PLs decreased gradually,while the content of lysophospholipids(LPLs)increased.PCA analysis showed that the changes of PLs were mainly concentrated in S1-S5 stage,and a lot of degradation occurred in the S6-S7 stage.The key processing to affect the change in PL molecules is the 3 d of dry-ripening and boiling.10 PL molecules were identified by PLS-DA model as potential markers to distinguish each processing point.A total of 22 volatile flavor compounds were identified by GC-MS and 25 by GC-IMS.The content of volatile flavor compounds,especially aldehydes,increased gradually during WSD processing.From PLSR and Pearson correlation analysis,it can be seen that 40-55% of PL molecules are low or not involved in the formation of volatile substances during processing;most of the LPLs have low correlation with the formation of volatile substances;PC and PE contribute a lot to the formation of volatile substances in the whole processing.In S7 stage,although some PL molecules are completely degraded,more than 60% of PL molecules are involved in the formation of volatile substances.Shotgun-MS/MS method and SPME-GC-MS method were used to study the effect of different amount of the dry-cured salt on the changes in PL molecular species and volatile flavor substances during processing.NMR technique was used to analyze the effect of different amount of dry-cured salt on the change of water content.The PLS-DA,PCA and PLSR models were used to reveal the effect of dry-cured salt content on PL molecular species and volatile flavor compounds.The results showed that 12 PL molecules(VIP > 1.0)could be used as a marker to distinguish low salt group(LS,4%),medium salt group(MS,6%)and high salt group(HS,8%),including PC 34:1(16:0/18:1),PC 34:2(16:0/18:2),PC 34:3(16:2/18:1),PC 36:1(18:0/18:1),PC 36:2(16:0/20:2),PC 36:3(16:0/20:3),LPE 18:0,PE 36:2(16:0/20:2),PE 38:4(18:0/20:4),LPG 18:0,PG 38:4(18:0/20:4)and PS 36:2(18:0/18:2),The changes in LPE 18:0,LPG 18:0,PC 34:3(16:2 / 18:1)and PC 36:3(16:0 / 20:3)were positively correlated with the amount of dry-cured salt.PCA analysis showed that the degradation rate of PL molecules in the LS group was similar,and the degradation rate of PL molecules in the HS group was inhibited due to the high dry-cured salt content,and the sample points in the HS group were more concentrated.While,in the MS group,the amount of dry-cured salt was more effective to promote the degradation of PL.30 kinds of volatile compounds were identified in the treatment groups with different dry-cured salt amount during processing.NMR showed that in the S4-S6 stage,the bound water and free water in the 3 treatment groups were basically the same as those in the S2-S3 stage,but the change in immobilized water was significant,especially in the HS group.The salt content in the LS group was lower and the water activity was relatively higher.PLSR analysis showed that low concentration of dry-cured salt could promote the degradation of PL molecular species,and the degradation products were mainly volatile substances of lipid source.With the increase of dry-cured salt content,the promotion gradually changed to inhibit the degradation of PL molecular species,and promote the formation of non-lipid source volatile substances.With the development of processing technology,this kind of non-lipid source volatile substances is more obvious in PLSR model.40-55% of PL molecular species did not participate or participate in the formation of volatile substances during processing,LPLs had a low or no correlation with volatile substances,and the result had a low correlation with dry-cured salt content.Based on shotgun-MS/MS and SPME-GC-MS method,the effect of spices on the changes in PL molecular species and volatile flavor substances during processing was studied.PLS-DA,PCA and PLSR models were used to reveal the effect of spices on PL molecular species and volatile flavor substances during processing.The results showed that spices contributed to the flavor of WSD in two aspects: one was to directly give flavor to WSD,such as limonene,anethole and cineole;the other was antioxidant effect.The results showed that 118 kinds of PL molecular species were identified during processing,and 7 kinds of PL molecular species markers were identified by PLS-DA method.PCA analysis showed that the effect of spices on PL molecular species was not significant,but the effect of spices on PL molecular species might be to improve its stability.There are 26 kinds of volatile substances identified during processing.PLSR analysis showed that the correlation between the volatile substances and PL molecules in the same processing point is similar,some of the volatile substances may be introduced by the spice,and the spice does not show strong antioxidant.During processing,40-55% of PL molecular species did not participate or low participate in the formation of volatile substances,and the correlation between LPLs and volatile substances was low or no.When the amount of spices used is high(0.5-1.0%),the antioxidant components in spices show better antioxidant effect,but the amount of spices used in this study is between 0.025-0.075%(w / W),which is not enough to achieve significant effect.Based on the shotgun-MS/MS and SPME-GC-MS method,the changes in PL molecular species and volatile flavor substances during WSD processing of traditional technology and quantitative halogenation were studied.NMR technology was used to analyze the changes in water content during processing.The optimized processing parameters of quantitative halogenation are medium speed and intermittent rolling,and the rolling mileage is 3600 m,that is,the total running time is 7h,the running time is 50 min,and the stopping time is 10 min.A total of 100 PL molecular species were identified during processing,and 8 key PL molecular species(VIP > 1.0)identified by PLS-DA had high discrimination ability.There was no significant difference in the change of PL molecular species during processing of quantitative halogenation.A total of 23 volatile compounds were identified during processing.Compared with the traditional technology,rolling technology can effectively promote the production of WSD aroma substances.After rolling,the combined water content in the muscle tissue is the same as that before rolling.The rolling processing changes the structure of duck meat,and absorbs a lot of water,resulting in obvious changes in the flow of water and free water.Boiling is the most obvious stage of water change in meat except for bond water.The two processing methods have no effect on the water change in muscle tissue during boiling.The yield of the product can be increased by the quantitative halogenation.Compared with the traditional technology,this method can effectively reduce lipid oxidation and improve product quality.