Effect Of Nisin Addition And Storage Temperature On The Quality Change Of Sour Meat

Sour meat is a traditional fermented meat product with fine quality,rich nutrition and unique flavor.It has a long eating history and strong national characteristics.The effects of different concentrations of Nisin on the nutritional,flavor and volatile flavor quality of Sour Meat with vacuum packed stored at room temperature(20?±2?),4?,and-20? were studied in this paper.The shelf life of sour meat under different storage conditions was judged by sensory evaluation,which provided theoretical reference for industrialized development of sour meat.The main research contents and results are as follows:(1)Using sour meat processed by traditional processing methods in Guizhou and Chongqing as raw materials,vacuum-packed sour meat with 0,0.15,0.30 and 0.45g/kg of Nisin were respectively named CK,?,? and ?.The changes of nutritional quality and safety of sour meat stored at room temperature,4? and-20? were studied.The results showed that with the prolongation of storage time,the contents of water,protein and fat in sour meat decreased continuously,while the contents of non-protein nitrogen,free fatty acid,volatile base nitrogen and thiobarbituric acid increased continuously.The changes of these indices can be effectively inhibited and delayed at room temperature and 4? after adding Nisin.The higher the concentration of Nisin,the more significant the effect was at 4 ?.There was no significant difference between different concentrations of Nisin and CK at-20?.The color difference of sour meat increased with the storage time.The color difference of fat meat was smaller than that of lean meat at room temperature and 4 ?.There was no significant difference between the color difference of fat meat and that of lean meat at-20?.The total number of bacterial colonies of sour meat increased with the prolongation of storage time.The addition of Nisin effectively inhibited the growth of total bacterial colonies at room temperature and 4 ?,while the addition of Nisin did not significantly inhibit the growth of total bacterial colonies at-20 ?.Based on the national TVB-N secondary freshness limit(?20 mg/100g),TBA decay odor threshold(0.5 mg MDA/100g),and the maximum acceptable range of the total number of colonies prescribed by the International Commission on Microbiological Spectifications for Foods(ICMSF)7.0 lgCFU/g,the sensory evaluation results showed that the optimum eating period of CK,?,? and ? groups stored at room temperature was 20,30,30 and 30 days,respectively.The optimum eating period of CK,?,? and ? groups stored at 4 ? was 30,60,60 and 60 days,respectively.The optimum eating period of CK,?,? and ? groups stored at-20? was 60,90,90 and 90 days,respectively.(2)The changes of taste quality of sour meat during storage were studied by analyzing soluble sugar,free amino acid,organic acid and pH.The results showed that the soluble sugar content in sour meat decreased with the storage time at room temperature and 4 ?.The total free amino acid content increased at first and then slowly decreased.The pH value decreased significantly at first and then slowly increased slightly.The change range of Nisin group was smaller than CK group.It indicated that Nisin could effectively delay the change of taste quality.With the storage time prolonged,the soluble sugar content in sour meat decreased,the total free amino content increased,the pH decreased slowly.There was no significant difference between Nisin group and CK group.The organic acids in sour meat are mainly tartaric acid,lactic acid,succinic acid,oxalic acid and citric acid.The content of oxalic acid and citric acid were low and had no significant change during the whole storage period.Lactic acid,tartaric acid and succinic acid were the higher organic acids in sour meat,which provide unique sour taste characteristics for sour meat.Based on the comprehensive indexes of sweet,fresh and sour taste,and the results of sensory evaluation,the optimum eating period of CK,?,? and ? groups stored at room temperature was 30,45,45 and 45-60 days,respectively.The optimum eating period of CK,?,? and ? groups stored at 4 ? was 90-120,120,120 and 120 days,respectively.The optimum eating period of CK,?,? and ? groups stored at-20? was 120,120-150,150 and 150 days,respectively.According to the changes of nutrition,safety and taste quality indexes in sour meat storage and sensory evaluation,Nisin was recommended to be added 0.45g/kg at room temperature for 45 days,0.15g/kg at 4 ? for 120 days,and to be frozen at-20? for 150 days.(3)The results of comprehensive nutritional safety and taste quality analysis were used to determine the volatile flavor compounds in the samples stored for the longest time.The samples were stored for 45 days at room temperature,120 days at 4 °C,and 150 days at-20 °C for volatile flavor determination.Volatile flavor substances in sour meat were detected by HS-SPME-GC-MS method.The content of volatile flavor substances was quantitatively analyzed by internal standard method.The odor activity value was determined by OAV method and the relative odor contribution rate was determined by ROC method.The results showed that 70,73 and 72 volatile flavor compounds,mainly esters,aldehydes,acids,alcohols and hydrocarbons,were detected at room temperature,4?,and-20?.Hydrocarbons were the most,but the content of hydrocarbons is the least,which had little effect on the overall flavor of sour meat.Alcohols and acids were less but more,because of the higher flavor thresholds of alcohols and acids,their contribution to the overall flavor of sour meat was small.14,15 and 12 flavor active substances were detected,and 10,12 and 9 kinds of OAV > 1 were detected,including octanaldehyde,n-hexanal,nonanal,1-octene-3-ol,2-heptanal,heptanal,2-n-pentanyl furan,trans-2-octenal,2,3-octanedione,n-heptanol,decanal and ethyl octanate.The substances with high relative odor contribution(ROC)in sour meat storage were n-hexanal,furfural,1-octene-3-ol,and new high relative odor contribution rate appears in cryogenic refrigeration and frozen storage.The substance octanal brings fat and grassy taste to the acid meat;there were 4 kinds of ester substances in the storage of acid meat at room temperature,and there were 2 kinds and 1 kind of low temperature refrigerated and frozen storage,indicating that the storage at room temperature was more conducive to the ester substance in the sour meat.The formation of rich and sour flavour.The alcohols detected in sour meat are saturated alcohols such as ethanol,which can promote the esterification of fatty acids and give the product alcoholic fragrance;unsaturated alcohols such as 1-octene-3-alcohol,which had a lower odor threshold,had a higher contribution to the flavor of the product,and had mushroom and fermentation aroma.The esters detected in sour meat were mostly ethyl esters,such as ethyl octanoate,ethyl acetate,ethyl lactate,etc.Generally,esters formed by short-chain fatty acids have fruit flavor,and esters composed of long-chain fatty acids had fat flavor.Aldehydes detected in sour meat mainly include n-hexanal,nonanal and anti-2-octenal.Aldehydes have very low odor threshold and high contribution to the flavor of products.They were the main flavor substances in sour meat.2-n-pentyl furan detected in sour meat has the flavor of baking and malt.It was an oxidized product of n-6 fatty acids such as linoleic acid.Because of its low odor threshold,it contributes more to the flavor of sour meat.