Study On Production Technology Of Probiotics Fermented Medlar Powder

This study aims to develop a vacuum freeze drying method of preparing medlar powder with active Lactobacillus plantarum.Differential scanning calorimetry(DSC)and freeze drying microscope were used to analyze the physical properties of fermented medlar slurry.The type and concentration of protective agents for fermented medlar slurry was optimized by orthogonal test,meanwhile,the freeze-drying curves were obtained.the color and the rehydration were good,indicating the high quality of product.The result as follows:(1)Quality analysis of probiotic fermentation broth: The dynamic change of growth process of Lactobacillus plantarum NCU137 in mash was in accordance with the logarithmic curve.The logarithmic phase was 2-12 h,and the highest viable amount reached 9.1log/ml.The physical and chemical indicators of acidity change in the fermentation process is on the rise,and the value is gradually increasing.The p H gradually decreased from the initial 5.3 to the end of the fermentation 3.8.The sucrose content of nutrients did not change significantly,and the content of glucose and fructose decreased.During the whole fermentation process,fructose decreased by5.1 mg/ml,glucose decreased by 8.4 mg/ml,and organic acid lactic acid content increased continuously,increasing by 8.6 ug/ml.The free amino acids detected 11 kinds of amino acids before sterilization.The type of amino acids decreased after fermentation,and the total amount decreased slightly to 3.46 mg/g.The content of flavonoids increased to 6.6 mg/g after sterilization and rose to 7.2 after fermentation.mg/g.(2)The physical property parameters of the fermented medlar were as follows:co-melting point was-5.28℃,eutectic point was-19.59℃,glass transition temperature was-31.82℃ with the method of annealing continuous scanning at heating rate of 5 k/min and annealing temperature of-5℃,disintegration temperature was-36℃,so the pre-freezing temperature was-40℃,pre-freezing time was 4 h,sublimation drying temperature was-45℃.The optimal protective agent combination was: 20% maltodextrin,14% lactose and 6% trehalose,and the sublimation drying temperature was-30℃ after mixing with protective agents.The freeze drying curves of the samples were separately drawn.(3)Probiotic fermentation of lyophilized powder: effects of pre-freezing temperature,four different pre-freezing temperature gradients of liquid nitrogen(-196 ℃),-80 ℃,-40 ℃,-20℃,with pre-freezing temperature Elevated,the number of viable bacteria contained in the pulp showed a downward trend;the effect of pre-freezing time,three different pre-freezing temperatures,the lower the temperature,the faster the cooling rate,considering the pre-freezing temperature-40℃for the experiment The pre-freezing temperature determines that the freezing time of the fermented pulp at the pre-freezing temperature of-40℃ is 4 h.At this time,the fermented mash has been completely frozen;the effect of lyophilization thickness,the temperature tends to be stable with the increase of the material thickness The longer it takes.The number of viable bacteria contained after lyophilization showed a tendency to rise first and then decrease.Overall,10 mm thickness is the best choice.When the temperature of the heating plate in the sublimation stage is changed,and the temperature of the sublimation dried heating plate is changed,the lyophilization curve shows a significant difference in sublimation drying.When the temperature of the heating plate is raised to-45℃,-40℃,-30 ℃,the temperature balance is 27 h,15 h,12 h,respectively.The choice of freeze-drying method,the two freeze-drying methods,the lyophilization state of the plate loading and granulation are very good,but the liquid nitrogen is pre-frozen,the operation is cumbersome,and finally the platooning method is adopted for lyophilization.(4)Characteristics of fermented medlar powder: The water content of lyophilized powder is less than 3%,and the reconstituted glutinous powder is a pseudoplastic fluid.The particle size distribution of medlar beverage has three peaks,between 100-1000 nm,It is more stable;the potential value is negative,the absolute value is within 30 mv,unstable,and the lyophilized powder in the environment of 4°C keeps the number of viable bacteria longer,and the powder is more stable.Determination of volatile components: A total of 71 volatile components were detected.The most important substances before sterilization were ketones and aldehydes.The number of species after sterilization was basically unchanged,and the ketones and aldehydes were still composed of skeleton aroma components.After fermentation,the species decreased,the dominant aroma changed into esters and phenols,and the number of reconstituted species of lyophilized powder decreased sharply.The dominant component was p-ethylphenol,which accounted for 76.67%.