Isolation And Identification Of L.helveticus SMN2-1 And Its Effect On The Quality Of Cheddar Cheese

Traditional fermented dairy products are rich in lactic acid bacteria,among which Lactobacillus helveticus is widely used in food industry because of its many functional characteristics.Lactobacillus helveticus,as a non-starter lactobacillus,is generally thought to have the ability to reduce the bitter taste of cheese and accelerate the formation of flavor,as the cheese matures.The low hydrolysis degree casein and a special hydrophobic polypeptide formed by Lactobacillus helveticus are related to the structure of cheese,so the non-starter lactic acid bacteria were screened out and applied to the production of Cheddar cheese.It can not only shorten the ripening time of cheddar cheese,but also improve the flavor and texture of cheddar cheese,accelerate the ripening of cheese,which has economic significance and technical prospect.In this study,a strain of Lactobacillus SMN2-1 was isolated from traditional fermented dairy products in Inner Mongolia.On the basis of observing the morphological characteristics of the strain,the taxonomic status of SMN2-1 was preliminarily determined by physiological and biochemical characteristics,and the homology was analyzed by 16 s rRNA method.The strain sequence was submitted to the nucleic acid sequence database of GEN BANK website to obtain the accession number KP408151,and the phylogenetic tree was constructed,which belongs to Lactobacillus helveticus SMN2-1.Lactobacillus helveticus SMN2-1 was added to the production of cheddar cheese as a non-fermentative agent.The physical and chemical indexes were tested during the ripening period,and the hardness,elasticity,cohesion,chewiness and sensory evaluation were tested by physical property analyzer.The physical and chemical indexes showed that the change trend of water,protein,fat and salt content of the three kinds of cheese was about the same during the period of 6 months’ maturity: after 90 days of maturity,the water content was lower than 39%,and the protein content was between 24% and 25%.The fat content was stable at about 32%,and the salt changed little during maturation,ranging from 1.6% to 1.7%.However,the pH value of cheese increased slightly to about 5.45 in the experiment 1 group supplemented with Lactobacillus Switzerland(main starter: SMN2-1=1: 1).After 45 days,the pH value of cheeses decreased rapidly and pH was lower than 4.5.The physical properties analyzer showed that the hardness of group 1 cheese with the main fermentation agent: 1: 1 SMN2-1: 1 was the lowest in 90 days,and the hardness of group 1 was not different from that of the control group at 180 days after inoculation with Lactobacillus helveticus(main starter: 1 SMN2-1=1: 1).The chewiness of cheese added with Lactobacillus Switzerland was always higher than that of cheese without Lactobacillus helveticus,but the chewiness of cheese added with Lactobacillus helveticus had no significant change during the ripening period,which kept the original taste of the cheese.The chewiness of cheeses in the control group without Lactobacillus helveticus was significantly lower than that in the control group,in terms of elasticity.The cheeses of group 1 with Lactobacillus helveticus(main starter: SMN2-1=1: 1)were significantly better than those of control group and experimental group 2 without and without Lactobacillus helveticus.After 45 days,the elasticity of cheeses decreased obviously,the hardness of cheese increased,the tissue of cheese lost adhesion,and the cheese hardened.Finally,the formation of similar tofu residue-like organizational state,the late cannot continue to detect.Sensory evaluation showed that the sensory score of cheeses in group 1 was significantly higher than that in control group during 30 days of maturation,but after 30 days,the sensory score of cheddar cheese added with Lactobacillus helveticus decreased sharply.The tissue was so loose that it deteriorated completely at 90 days,and the value of detection was lost.The cheese tissue and flavor evaluation of group 1 with Lactobacillus helveticus was always better than that of control group without Lactobacillus helveticus.Based on the electronic nose technique,the flavor changes during the ripening of the cheese were detected.The flavor of Cheddar cheese after 90 days was mainly composed of hydrogen sulfide,nitrogen oxide,organic aromatic sulfides,alcohols and methane.By PCA and LDA analysis,electronic nose can not only distinguish the different maturity of Cheddar cheese,but do not affect the composition of smell.And the smell of Cheddar cheese added to different proportions of Lactobacillus helveticus can be distinguished.