| Sour meat is a natural lactic acid fermented pork product with local characteristics in Southwest China.Fermentation is not only the basis of the formation of sour meat flavor quality,but also the method of preservation of sour meat.Traditional sour meat is mainly cured in winter.It is eaten from about 15 days after fermentation and preserved by the way of fermentation.Sometimes it may last more than half a year.With the influence of their own enzymes and microbial extracellular enzymes,the protein and lipid in sour meat will be degraded and oxidized,and the nutrition,safety and edible quality will inevitably be affected,or even food safety problems may arise due to long-term microbial acid production and salt stress.In order to find the best and longest edible period of sour meat,it is necessary to systematically study the nutrition,flavor and edible safety of sour meat preserved by fermentation for a long time,so as to provide support for the rational consumption of traditional fermented sour meat.In view of this,based on the traditional processing methods of sour meat in Guizhou and Chongqing,this paper studied the changes of nutrition,flavor quality and safe eating period of sour meat during long-term(180 days)fermentation and preservation,determined the best and longest edible period of sour meat preservation by fermentation,in order to effectively utilize fermentation preservation measures,develop food flavor and control safety risks.(1)The changes of nutritional quality and safety quality of sour meat during 180 days fermentation and the growth and decline of microorganisms were studied.The results showed that the macronutrient moisture and protein content in sour meat decreased gradually,the fat content increased slightly in the first 30 days of fermentation,then decreased.The NPN in sour meat increased,and the trend became gentle after 150 days of fermentation and the polypeptide nitrogen and amino acid nitrogen increased first and then decreased,with the peaks appearing at 90 days and 120 days respectively.Fatty acid species decreased,and the number of fatty acid species was the smallest at 90 days of fermentation,indicating that the oxidation of fat was more intense during this period.The content of TVB-N in the first 120 days of fermentation was 2.19-13.24 mg/100 g,which was lower than the national standard of TVB-N in fresh(frozen)livestock and poultry products(<15 mg/100g),and after 150 days of fermentation,the value exceeded 20 mg/100 g,but in the range of standard limit(<45 mg/100g)of pickled pork secondary products;the peroxide value showed an upward trend and it reached 0.525 g/100 g on the 120 th day of fermentation,which exceeded the safety limit of peroxide value of cured meat stipulated by the national standard.The TBA value increased first,then decreased and then increased.The first peak value reached at 90 days of fermentation,the higher the value,the higher the degree of lipid oxidation.In addition,the number of lactic acid bacteria in sour meat reached a peak at 90 days,which became the most dominant bacteria in sour meat and had a significant inhibitory effect on the growth of Escherichia coli.According to this chapter,the edible period of sour meat should not exceed 120 days.(2)The changes of physicochemical indexes during the fermentation of sour meat were studied to evaluate the edible quality of sour meat.The results showed that during 180 days of fermentation,the surface color of Sour Meat changed obviously,the red color of fat meat disappeared rapidly in the early stage of fermentation,and became Milky white,and the surface yellowed seriously in the late stage of fermentation(150 days later).The a* value of lean meat had an obvious upward trend in the early stage of fermentation(P < 0.05).After 30 days of fermentation,the red color gradually became lighter,while the b* value changed insignificantly.From the texture characteristics,the hardness of lean meat increased while that of fat meat decreased.The chewiness of lean meat was always higher than that of lean meat,and the overall trend of chewiness increased first and then decreased.The highest value appeared in 30-60 days.The elasticity of lean meat and fat meat both decreased.After 60 days of fermentation,the elasticity of lean meat began to be higher than that of fat meat,indicating that the elasticity of lean meat was higher than that of fat meat during fermentation.Although the cohesion of sour meat showed no significant fluctuation(P > 0.05),the cohesion of fat meat was always greater than that of lean meat,indicating that the ability of fat meat to resist fermentation damage was higher than that of lean meat,so that fat meat could better maintain its integrity.The pH value decreased during fermentation,and there was a significant decline in the initial stage of fermentation and about 60 days of fermentation respectively.After 90 days of fermentation,there was a slow upward trend.Fermentation increased the content of organic acids.The main organic acids were lactic acid and succinic acid.After 60 days of fermentation,these two acids dominated the sour taste of sour meat.Microorganisms use carbohydrates in sour meat to decrease soluble sugar content and increase the content of aldehydes,ketones and organic acids.And chlorides show an increasing trend,reaching 4.35 g/100 g after 60 days of fermentation,while the growth trend slows down,and osmotic pressure between sour meat and the external environment tends to balance.The content of FAA reached the peak in 60-120 days,which would affect the taste quality of sour meat to a certain extent.Based on the above conclusions,it is preliminarily inferred that the optimal eating period of sour meat is 60-90 days,and should not exceed 120 days.(3)Sensory evaluation of sour meat at different fermentation stages was carried out by means of fuzzy mathematics.Volatile flavor substances in sour meat were determined qualitatively and quantitatively.The results of sensory evaluation showed that the comprehensive sensory score of 60-day fermented sour meat was the highest,while that of 120-day fermented sour meat was lower than 5 points,which indicated that 120-day fermented sour meat was difficult to accept.Through the correlation analysis of sensory score and other indicators,the change of texture characteristics of Sour Meat and safety indicators such as TVB-N,POV,TBA had a significant impact on sensory score.The results of volatile flavor substance analysis showed that 114 flavor substances were produced during the whole fermentation process,including 37 esters,11 acids,13 alcohols,23 carbonyls and 27 hydrocarbons.The quantity and content of esters,carbonyls and acids increased during the fermentation process,which dominated the characteristic flavor of sour meat,alcohols and acids.The change of analogous substances was not obvious.And the OAV analysis showed that there were 26 kinds of characteristic flavor substances in sour meat.Fatty flavor,grass flavor and melon and fruit flavor together constituted the characteristic flavor of sour meat.In summary,the best eating period of sour meat is 60-90 days,and the longest fermentation period should not exceed 120 days. |
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