The Development Of Fermented Milk

There are variety of flavored fermented milk products on the market and consumers love them,but the fermented milk products of aquatic fruit and vegetable are rare.Eleocharis dulcis is a shallow fruit and vegetable ingredients,and has a broad development prospect because it is not only nutritious but also has medicinal value.The strains which produce exopolysaccharides(EPS)can make fermented dairy products with good viscosity,water holding capacity and stability,so this study aimed to prepare a new fermented milk of eleocharis dulcis with good texture and flavor,and enrich the products of fermented milk by using the lactic acid bacteria(LAB)with the characteristics of high production of EPS and producing aroma.The main results were as follows:1.Screening of fermentation strains for the fermented milk of eleocharis dulcis.5 LAB strains with high production of EPS were selected from 50 Streptococcus thermophilus of our own laboratory,which are 822-1,YBA980-2,975-1 and XPL-1-4.Their production of EPS was 320.43mg/L,311.98mg/L,294.09mg/L,273.26mg/L and 269.40mg/L.5 strains with high production of EPS were combined with commercial strain Y430A(S.thermophilus,Lactobacillus delbrueckii subsp.bulgaricus)with good aroma-producing ability.The results showed that H(937),I(822-1),B3 and Cl were the most effective combinations of high production of EPS.The volatile flavor components,the characteristics of curd and sensory and the storage stability of the fermented milk prepared by 6 strains were studied.The results showed that the relative content of the aroma flavor substances of fermented milk prepared by strain combination with Y430A was significantly increased,including octanoic acid,3-hydroxy-2-butanone,2-tridecanone,2-nonanone,8-dodecalactone,8-decalactone and ?-dodecalactone.The fermented milk produced by C1 produced acid rapidly,curded in 4h,and had high scores of sensory evaluation,besides the viscosity is 3288cP,the acidity of curd is 68.740T,the water holding capacity is 71.44%.The fermented milk was stored at 4?C for 15 days,and its acidification degree was the weakest and the storage stability was good.Therefore,the LAB combination C1 was selected as the fermentation strains for the fermented milk of eleocharis dulcis.,which prepared by S.thermophilus 937 and S.thermophilus,Lactobacillus delbrueckii subsp.Bulgaricus Y430A at a ratio of 1:1(v/v).2.Study on the preparation condition of fermented milk added eleocharis dulcis.The preparation conditions of eleocharis dulcis jam were optimized by single factor and orthogonal test.The results showed that the best processing conditions of the jam was as follows:added 20%(m/m)amount of lemon pulp,20%(m/m)amount of sucrose,60%(m/m)amount of eleocharis dulcisandconcentrated for 5 minutesat 100? and40min for at 80?.The analysis of volatile flavor components of ordinary fermented milk and fermented milk added eleocharis dulcis showd that,the proportion of esters is the highest in the ordinary fermented milk and the relative content was 28.83%,followed by acid 8.08%,ketones 3.58%,alcohols 1.82%and olefins 0.4%.In the fermented milk added eleocharis dulcis,the olefins had the highest relative content,which were between 29.92%and 40.18%,and the esters were between17.97%and 22.3%,acids were between 4.77%and 6.89%,ketones were between 0.84%and 1.51%,Alcohols were between 1.04%and 1.39%.The relative content of acids,ketones and esters in fermented milk decreased and the ethylenes increased significantly(P<0.05)with the addition of jam.the newly detected compounds of fermented milk added jam can be classified into three classes according to their fragrance characteristics:?The substances offruit aroma,including 2-tridecanone,dextrorpene diene,terpinene and terpinolene;?The compounds of floral aroma,including neryl acetate,geranyl acetate,1-caryophyllene and farnesene;?The substances of pine oil flavor,including?-terpineol,a-pinene and ?-pinene.The relative content of dextrorpene dienes is the highest,which were 29.92%,40.18%and 36.55%in fermented milk with 4%,6%and 8%eleocharis dulcis jam,respectively.The correlation analysis between the sensory evaluation of fermented milk prepared by adding different amount of jam and the newly detected volatile flavor components showed that the sensory evaluation had positive correlation with alkenes,esters and alcohols,and the sensory evaluation of fermented milk was significant positive correlated with geranyl acetate and 1-nonanol(P<0.05).Based on the apparent viscosity and thixotropy,the amount of sucrose in ordinary fermented milk was determined to 10%(m/m),in this condition,the apparent viscosity of ordinary fermented milk was 5.066Pa s and the area of hysteresis loop was 628.0 Pa s-1,and the stickiness ratio was 0.26.Besides,the sensory and rheological properties of the fermented milk added eleocharis dulcis were studied and the amount of jam was determined to be 7%(m/m),in this condition,the sensory evaluation score of the fermented milk added eleocharis dulcis was 9.3,the apparent viscosity was 6.604Pa s,the area of the hysteresis loop is 881.8 Pa s-1,and the viscosity ratio is 0.30.3.Study on the quality and storage characteristics of the fermented milk added eleocharis dulcisa.The jam of eleocharis dulcisprepared under the optimum conditions was suitable for sweet and sour,which had the fragrance of eleocharis dulcis and lemon.The total sugar content of jam was about 46.35g/100g and the content of dry matter was about 54.87g/100g.The fermented milk of eleocharis dulcisa prepared under optimum condition not only had the unique taste and aroma of ordinary fermented milk,but also had the fragrance of eleocharis dulcis and lemon.Besides,it had uniform tissue and taste fine.The protein content of fermented milk added eleocharis dulcisa was greater than 2.3%,the acidity greater than 70°T,the content of total solids is about 18.70%,the total colonies is up to 5.61×108 CFU/mL,the pathogens were not detected,and all indicators are in line with the national standard of flavor fermented milk requirements.The water content of eleocharis dulcis was increased from 45.13%to 80.48%,and the fermented milk decreased by 2.57%after stored at 4? for 15 days.The water content of eleocharis dulcis and fermented milk was almost the same in the later storage period.The water content was extremely significant positive correlated with hardness,significant positive correlated with chewiness,extremely significant negative correlated withadhesion,and significant negative correlated with elasticity.The acidity increased from 76.00°T to 89.20°T after stored at 4? for 15 days.The total colonies reached 8.971gCFU/mL at the 11th day and decreased to 8.7221gCFU/mL at the 15th day.During the storage period,the total sugar content of the eleocharis dulcis particles decreased gradually,the total sugar of the fermented milk increased gradually and reached the equilibrium state after 7 days.The total sugar of the eleocharis dulcis was 9.01g/100g and the fermented milk was 2.72mg/g at the 7th day.In this optimized preparation process,the quality of fermented milk added eleocharis dulcis was good,and it did not change obviously after stored at 4? for 15 days.