Effects Of Freshness And Pickling Temperature Of Raw Eggs On Gel Properties And Flavor Quality Of Preserved Eggs

The preserved eggs,also called Pidan,as a traditional egg product in China,have the concomitant function of both medicine and foodstuff,and are loved by the public.However,due to the lack of standards for the key processing such as the freshness of raw eggs,pickling and ripening temperature of preserved egg,the quality of preserved eggs is uneven.Therefore,it is of great theoretical significance and application value to reveal the correlation between the freshness of raw eggs and the gel properties of preserved eggs,and to establish the effect of temperature-controlled mode and ripening temperature on the texture properties and flavor of preserved eggs.Therefore,in this study,Gaoyou duck eggs were used as the research objects to explore the effects and correlation of the freshness of the raw eggs on the gelling properties of alkaline-induced egg white,to study the temperature-controlled modes and ripening temperature on the quality of preserved egg white and yolk were studied.The main research contents and conclusions are listed as follows:(1)To study the effect of the freshness of raw eggs on the gelling properties of alkali-induced egg white at different storage temperatures,and to establish the correlation between the freshness of raw eggs and gelling properties of alkaliinduced egg white.The results showed that the comprehensive freshness evaluation index Y gradually decreased with the extension of the storage time of raw eggs at 25 °C and 4 °C storage condition.However,the hardness of alkali-induced egg white gel increased with the decrease of freshness of raw eggs(P<0.05)within 12 days at 25 °C and 20 days at 4 °C.And the texture properties of alkali-induced egg white gels decreased with the decrease of the comprehensive evaluation index Y of raw eggs after12 days at 25 °C and 20 days at 4 °C(P<0.05).The correlation between the molecular structure of egg white protein and the properties of alkali-induced gel showed the hardness of alkaline-induced egg white gel was significantly negatively correlated with the comprehensive freshness evaluation index Y,ionic bonds,S-S bonds,and α-helix(P<0.05)within 12 days at 25 °C and 20 days at 4 °C.and the texture properties of alkaline-induced egg white gels were positively correlated with the comprehensive freshness evaluation index Y,ionic bond,S-S bond and β-turn after 12 days at 25 °C and 20 days at 4 °C(P<0.05).In summary,the comprehensive freshness evaluation index can be used to predict the gel properties of preserved egg white gel,and this study provides a theoretical basis for the establishment of freshness evaluation standards for raw egg for pickling preserved eggs.(2)To study the evolution of preserved egg gel and volatile flavor substances under different ripening temperatures(18 °C,25 °C and 32 °C),and to explore the influence of ripening temperature on the properties and flavor substances of preserved egg.The results showed the color of the preserved egg white and yolk gradually darkened during ripening process,and the intermediate and end products of the Maillard reaction increased.Moreover,the color of the egg white and yolk was the best at 25 ℃,as excessively high or low temperatures could affect the color evolution.Additionally,the texture properties of both the egg white and egg yolk gel increased first and then decreased under these three ripening temperatures,with the best quality obtained at 25 ℃,which was further verified by the results of LF-NMR analysis.Furthermore,the texture properties of the egg white and yolk gel were significantly positively correlated(P<0.05)with the content of β-sheet,α-helix,and SS bonds.In addition,PCA and LDA analysis of electronic nose data showed that there were significant differences in the volatile flavor of egg white and yolk in the early stage of ripening(within 3 days)at different ripening temperatures,but the flavor of preserved eggs tended to be consistent with the extension of ripening time.In summary,the color and gel properties of preserved eggs were the best at a ripening temperature of 25 ℃,which provided the theoretical guidance and data support for the industrial production of preserved eggs.(3)To study the effects of temperature-controlled pickling modes on the physicochemical properties and characteristic flavor substances of preserved eggs,and to reveal the regulation of alkalinity,gel properties,and flavor substances of preserved eggs by temperature-controlled pickling modes.The results showed that compared with the thermostatic curing and two-stage temperature-controlled pickling,the texture properties of the egg white gel from P-12-18-30 °C group were significantly increased,and the LF-NMR and SEM analysis results further verified that the P-12-18-30 °C pickling mode could promote the duck egg white to form a highly ordered and dense three-dimensional gel network structure.Additionally,the TAV of FAAs from the P-12-18-30 ℃ group is also significantly increased(P<0.05),especially the increase of umami amino acids.At the same time,the egg yolk from P-12-18-30 ℃ group had higher gel strength and lower adhesiveness properties.Moreover,the volatile components of preserved eggs under different temperature-controlled pickling modes were similar,mainly including short-chain hydrocarbons,alcohols,aldehydes and ketones,some aromatic compounds,long-chain hydrocarbon lipids,and inorganic sulfides,and there was no significant difference in the content of each flavor substance.In summary,compared with the thermostatic curing and two-stage temperaturecontrolled pickling,the three-stage controlled-temperature pickling of P-12-18-30 °C can significantly improve the gel properties of preserved eggs and achieve the controllable preparation of high-gel preserved eggs.