Optimization Of Fry Technology Of Ready-to-eat Loach And Changes Of Volatile Odor Substances

As a freshwater fish with high protein and low fat,loach is known as“ginseng in water”,because it is rich in amino acids and minerals.Its proportion of monounsaturated fat（MUFA）and polyunsaturated fatty acid（PUFA）is reasonable.With the breakthrough of loach culture technology,its output is increasing year by year,and the output in 2020is 2.96%higher than that in 2019.As the main processing form of ready-to-eat loach,deep frying gives it fragrance,good taste and attractive color,but the complex chemical reactions（excessive lipid oxidation）are difficult to control.Therefore,by analyzing the nutritional quality of loach in pond and paddy field,the Paramisgurnus dabryanus ssp.in pond-cultivated mode（PPOC）is selected as the processing raw material,and then the quality change and process optimization of ready-to-eat loach during deep frying are studied.Finally,the changes of volatile flavor compounds in the process of processing and storage are analyzed from the point of view of lipid oxidation.（1）To explore the effects of different culture patterns on the nutritional quality of P.dabryanus ssp.and Misgurnus anguillicaudatus.In this experiment,the body characteristics,nutritional compositions,and qualities of PPOC,P.dabryanus ssp.in paddy-cultivated mode（PPAC）,M.anguillicaudatus in pond-cultivated mode（MPOC）and M.anguillicaudatus in paddy-cultivated mode（MPAC）were evaluated,and the correlation between their indexes was discussed.The results showed that the fatness of P.dabryanus ssp.was significantly higher than that of M.anguillicaudatus（P<0.05）.Compared with P.dabryanus ssp.,M.anguillicaudatus had higher crude protein content（19.0-21.0%）and lower crude fat content（0.8-1.2%）.Under the pond culture mode,the IA and IT of the two kinds of loach were significantly lower than those of the same species cultured in paddy-cultivated mode.It is indicated that PPOC and MPOC had higher unsaturated fatty acids（UFA）,which is beneficial to human body.The hardness of PPOC was 2.24 times that of MPOC,and the springiness of PPOC was 4.85 times that of MPOC.The muscle of loach in paddy-cultivated mode had more flavor characteristics than that of loach in pond-cultivated mode,and the contents of each free amino acid showed MPAC>PPAC>MPOC>PPOC,which is related to its ecological environment and living habits.The results of principal component analysis showed that there was a close relationship between body characteristics and nutritional qualities.Fatness was negatively correlated with the ratio of body length to height（-0.996）,positively correlated with TPA characteristics and crude fat content,and negatively correlated with moisture content,ash content,and crude protein content.Based on the indexes of fatness and texture properties,PPOC is the most suitable raw material for loach processing.（2）To optimize the deep frying technology of ready-to-eat loach.Taking PPOC as the research object,the quality of PPOC was studied according to its deep frying time,deep frying temperature and oil types,and the L₉（3⁴）orthogonal experiment was designed to evaluate the rationality of the processing technology after holding the product at 36℃±1℃for 10 days,and the best frying process was obtained.The results showed that in the process of deep frying（0-180 s）,the water content decreased significantly（P<0.05）,from 52.33±0.41%to 41.31±0.27%,the oil content increased.It is indicated that water evaporate rapidly and pores are formed on the surface of loach during frying.The body shrinks,and then the oil enters the pores,resulting in the decrease of water content and the increase of oil content.The ready-to-eat loach after deep frying is light yellow,which was related to the L*value increase first and then decrease,and increased of b*value.With the extension of frying time,the water distribution of ready-to-eat loach is a process of moving from free water to immobilized water,which is related to the decrease of water content in ready-to-eat loach.Deep Frying temperature law of the physical and chemical indexes,colour and water distribution is consistent with the deep frying time.According to the score of sensory evaluation,the deep frying time is 120 s,150 s,180 s,the deep frying temperature is 170℃,180℃,190℃,and the oil types are soybean oil,sunflower oil,peanut oil.Through the range analysis method,the primary and secondary order affecting the sensory score of ready-to-eat loach is obtained,oil types>deep frying time>deep frying temperature,and the best frying process is soybean oil frying at 190℃for120 s.（3）The eight key ring points of P.dabryanus ssp.,such as raw materials,deep frying（120 s,190℃,soybean oil）and storage,were selected to measure their odor acceptance and odor substances,and then the relationship between odor substances and lipid oxidation was explored by peroxide value（POV）,thiobarbituric acid value（TBARS）and fatty acids.The results showed that the sensory score of ready-to-eat loach increased significantly from 1.36±0.81 of raw material to 7.79±0.91 on 0 d,which increased by5.7 times.A total of 109 kinds of volatile substances are identified in ready-to-eat loach,mainly alcohols,ketones and amines et al,with a total content of more than 60%.POV is increased continuously during processing.POV is increased first and then decreased during storage,in which POV at 4 days was the highest,reaching 16.64±1.47 mg/100g.The TBARS of ready-to-eat loach is increasing during processing and storage,and the growth rate of TBARS during storage was faster than that during processing,from 0.51±0.01 mg MDA/kg of 0 d to 1.45±0.01 mg MDA/kg on 10 d.It is due to the high temperature and relatively long storage time at 36℃±1℃,which accelerated the oxidation of UFA and produced more malondialdehyde.The main fatty acids are different in different stages.C17:0 was the main component of SFA during processing,while C20:0was the main component of SFA during storage.The correlation analysis between 34 main flavor substances and 21 fatty acids showed that the same fatty acid is related to many kinds of volatile compounds,among which C18:ln9c was related to 26 kinds of substances,such as aldehydes,heterocyclic compounds and amides.