Development Of Lactic Acid Bacteria Fermentation Broth-assisted Marinated Beef Products And Study Of Quality Changes During Freezing

Recently,research on the application of lactic acid bacteria（LAB）in meat products has achieved great progress.However,most research have found that excessive inoculation,long fermentation time or high fermentation temperature can cause excessive fermentation,resulting in a heavily acidic meat product,which can seriously affect the taste and require the addition of sugar or other seasonings that can mask the acidity to improve the acceptability of the product.This not only increases the cost of processing,but also goes against the consumer’s idea of a healthy diet that is low in sugar and light.In order to make effective use of LAB while avoiding the undesirable consequences of over fermentation.This study attempts to combine the application of conventional seasonings and LAB fermentation broth in the key curing process of marinated beef,and apply solid-phase microextraction-gas chromateography-mass spectrometry（SPME-GC-MS）to clarify the quality and flavor substance changes in the marinated beef,study the quality changes of marinated beef under storage conditions at-18℃,reveal the influence of LAB fermentation broth on the quality and flavor of marinated beef.To provide a theoretical basis and technical support for the optimisation of flavor quality and product improvement of LAB fermentation broth-assisted marinated beef.The major findings are as follows.（1）The LAB for marinated beef were specified by comparing the fermentation characteristics of Lactobacillus rhamnosus LR1,Lactobacillus plantarum LP5,Lactobacillus fermentum LF20-1,Pediococcus acidilactici PA45 and Lactobacillus helveticus LH 32-1 in terms of salt tolerance,nitrite tolerance and acid production rate,protein degradation,fat degradation,etc.It was found that Lactobacillus rhamnosus LR1,Lactobacillus plantarum LP5 and Pediococcus acidilactici PA45 can produce acid rapidly and have a certain tolerance to NaCl and NaNO₂.The three strains of LAB have no obvious ability to decompose protein and fat,and do not produce viscous and gas,which meet the basic requirements of meat product fermenters,and can be used as fermenting strains for marinated beef.（2）The curing process parameters of the LAB fermentation broth-assisted marinated beef were optimized.Lactobacillus rhamnosus LR1,Lactobacillus plantarum LP5 and Pediococcus acidilactici PA45 were cultured in food-grade medium to obtain fermentation broth,which was applied to marinated beef.The best curing process was obtained by single-factor and orthogonal test using sensory,texture and color as evaluation indicators:LAB fermentation broth is Lactobacillus rhamnosus LR1:Lactobacillus plantarum LP5:Pediococcus acidilactici PA45=1:2:1,the amount of the LAB fermentation broth is added at 15%,the curing time is 8 h,the curing temperature is 15℃.Under these optimal curing conditions,the flavor and texture of the LAB fermentation broth-assisted marinated beef were significantly improved.（3）The key flavor substance substances of the LAB fermentation broth-assisted marinated beef were clearly identified.Comparative analysis of the differences in quality and flavor components of marinated beef seasoned with fermentation broth-assisted seasoning（LAB broth group）,marinated beef seasoned with seasoning（control group）and uncured beef（blank group）by SPME-GC-MS,revealed that in the blank,control and LAB broth groups,23,32 and 42 volatile flavor substances were detected respectively,and the type and content of volatile flavor substances in the LAB broth group increased significantly compared with the control and blank groups.The result of principal component analysis（PCA）showed that 2,4-di-tert-pentylphenol,acetic acid,2-Ethyl-6-methylpyrazine,2-Ethyl-3-methylpyrazine,2-Ethyl-3,5-methylpyrazine,heptanoic acid are the key flavor substances in the LAB broth group,imparting chars and a distinctive roasted aroma to the marinated beef.Studies have shown that LAB fermentation broth-assisted curing can enrich the flavor of marinated beef and give it a higher quality.（4）The pattern of quality changes in the LAB fermentation broth-assisted marinated beef under frozen storage conditions was clarified.With extended freezing time,the pH,total bacterial colony count,TVB-N and TBARS of the marinated beef in the control and LAB broth groups showed a continuous increase,and these values were consistently lower in the LAB broth groups than in the control group throughout the storage e period.After 63 d,the pH,total bacterial colony count,TVB-N and TBARS of beef in the LAB broth group were 6.53±0.09,5.10±0.03 lg CFU/g,14±1.4 mg/100g,0.83±0.01 mg/kg respectively,and were in the secondary fresh.During freezing,the hardness and chewiness of the marinated beef were significantly lower in both groups（P<0.05）,and there was also a decreasing trend in cohesiveness and recovery,but hardness,chewiness and their rate of decrease were always lower in the LAB broth group than in the control group.The trend in the color of the two groups is more consistent,the L*shows a gradual increase in general and the a*show a significant decrease.The results showed that the addition of LAB fermentation broth can slow down the textural changes during storage,and stabilise the quality of the marinated beef,but did not have a significant effect on the color.