Screening Of Degrading Astringence Strains And Their Application In Prepared Lamb Products

Lamb is a nutritious,medicated food.The meat is tender and easy to digest.Its crude protein content is lower than that of beef and higher than pork.The crude fat content is lower than that of pork and higher than beef.The main amino acid species and quantity contained in the protein meet the nutritional needs of the human body.Because of the unique astringency of mutton,theacceptability of lamb is reduced.It hinders people’s consumption of lamb,and is not conducive to the development of lamb market.The astringency of lamb is mainly derived from adipose tissue,4-methyloctanoic acid and 4-ethyloctanoic acid are the main fatty acids that cause the astringency of lamb.At present,the microorganism method is relatively good one of domestic degradingastringence technologies,but it is difficult to select a suitable strain.This experiment methylated4-methyloctanoic acid and 4-ethyloctanoic acid in 6 different methods.The appropriate method was selected to methylate and determine the content of astringent fatty acids in four varieties of lamb in Guizhou by GC-MS analysis.The soils and hams were used as screening samples,and the strains capable of hydrolyzing lamb fat and degrading astringent fatty acids were isolated,screened and identified.The selected strains were subjected to functional analysis experiments to further screen out strains that did not produce H₂S and biogenic amines,has good salt and nitrite tolerance,strong antibacterial ability.And determine the optimal compounding ratio of the strains.The strain was applied to the frozen prepared lamb for fermentation.Combining sensory score,pH value,color difference and cooking loss rate,the effects of inoculum size,soy protein addition,fermentation time and fermentation temperature on frozen prepared lamb were investigated.On this basis,the response surface optimization test was used to further analyze various factors to obtain the optimum process conditions for processing frozen prepared lamb.The results show:（1）The methylation methods of two astringent fatty acids were studied,the acid-base method and the boron trifluoride-methanol were screened out from 6 methyl esterification methods.（2）Traditional lipase-producing bacterias screening use olive oil medium with indicator.In this experiment,the olive oil in medium was replaced with lamb fat,and the emulsified lamb fat and fluorescent indicator were added to plates to screen the 11 strains,which accurately acting on lamb fat.The 11 strains were identified by morphological,biochemical experiments and 16s rRNA gene sequences and ITS gene sequences.Through liquid fermentation experiments,it was found that all the 11 strains could degrade 4-methyloctanoic acid and 4-ethyloctanoic acid.（3）Considering food safety,4 strains were selected from the 11 strains,were Rhizopus microsporus,Rhizopus oryzae,Aspergillus oryzae and Lichtheimia ramosa.Screened out Rhizopus oryzae and Aspergillus oryzae which did not produce H₂S and biogenic amines,had strong antibacterial ability,and salt and nitrite tolerance were better.When the ratio of the two strains was 1:1,the growth was better.（4）Combining sensory evaluation,pH value,color difference and cooking loss rate,theeffects of inoculum size,soy protein addition,fermentation time and fermentation temperature on frozen prepared lamb were investigated.Based on the single factor experiment,the responsesurface optimization test was carried out.Taking sensory score and pH value of prepared lamb as the response value,the optimal process parameters were:1.7%inoculum,3.0%soy protein,20h fermentation time and 30℃fermentation temperature.Under this condition,the sensory score of prepared lamb was（30.35±0.69）,the pH was 5.46±0.05.When the pH value was between 5.15and 5.55,the sensory score was higher.The aroma,taste and taste of prepared lamb wew more suitable.