Abstract Lactic acid bacteria are a type of typical probiotics that promote human health. For this type of bacteria to achieve its beneficial effects, the number of viable bacteria should reach at least 1 million CFU/g. Due to the adverse effects of the outside world and the human stomach environment, the naked bacteria are not easy to survive. Microencapsulation of probiotics is considered to be the most effective and promising method of protection. In this study, based on the single factor study, the response surface method was used to optimize the process parameters of microcapsules prepared by vacuum mini spray dryer. The test results show that, under the condition of -0.05 ~ -0.06 MPa, the best process conditions are the inlet air temperature of 79.07 ℃, the feed rate of 727.54 mL/h, and the ratio of bacterial wall 1:4 55. The amount of protection carrier (skimmed milk powder) is 9. 80%, and the number of viable cells under this condition is 2. 81 × 108 CFU/g.
Equipment: YC-2000 vacuum mini spray dryer
Lactic acid bacteria are probiotics that have important physiological and health care functions to the human body, but they do not form spores, so they have poor resistance to stress and are easily inactivated and cannot perform their probiotic functions well. It is of great significance to study the protection technology of lactic acid bacteria to reduce its loss in food processing and storage, human digestive tract and other processes. At present, microencapsulation of probiotics is considered to be the most effective and promising method. Microcapsule preparation methods include: spray molding method, emulsification method, extrusion method, co-aggregation/phase separation method and electrostatic method, etc.Among them, the spray molding method to prepare lactic acid bacteria microcapsules has high drying rate, short time, product dispersibility and The advantages of good solubility, simple production process and suitable for continuous production have become the focus of industrialized application technology research. This experiment focuses on researching the technology of preparing lactic acid bacteria microcapsules with a low-temperature vacuum mini spray dryer, optimizing its process parameters, and providing a low-energy, high-activity product technical solution for the production of lactic acid bacteria microcapsules.
1) Preparation of bacterial suspension. After activating the stored lactic acid bacteria in MRS solid medium twice, inoculate it in fresh MRS liquid medium and cultivate it at 37 ℃ to the end of the logarithmic phase and before the stable phase. Collect the bacterial liquid in the early stage of the stable phase and centrifuge at 3 500 r/min for 10 min. Remove the supernatant, wash the collected bacteria with sterile saline, centrifuge again, and repeat 3 times. Resuspend the bacteria with 20mL sterile normal saline for use.
2) Process flow: Dissolve gum arabic powder and maltodextrin in the corresponding amount of deionized water at a ratio of 1:8, the solid content is 15% → 40 ℃ heating, 4 000 r / min high-speed dispersion for 10 min, stir to complete Dissolve → let stand until the foam disappears, add 20 mL bacterial suspension containing inoculum (1:1 ), heat at 40 ℃, stir for 5 min at 500 r/min → add corresponding amount of skimmed milk powder and stir evenly → set the feeding speed and Inlet air temperature, spray dryer.
3) The influence of feed rate on the number of viable bacteria In the vacuum mini spray dryer process, the faster the feed rate, that is, the more materials that will be atomized into small droplets by the atomizer per unit time, and the material liquid will be dried and converted The more heat is required for powder. Therefore, under certain conditions of other factors, that is, when the heat provided by the hot air to the material per unit time is constant, the higher the feed rate, the worse the drying effect. On the other hand, the core material in this study is a biologically active substance, the longer the drying time, the greater the degree of inactivation. When the feed rate is 200 ~ 600 mL/h, the contact time between the material and the hot air is too long. As the feed rate increases, the number of viable bacteria increases. The feeding speed is 600 ~ 1 000 mL/h, and the feeding speed is too fast. As the feeding speed increases, the drying effect becomes worse and the number of viable bacteria decreases. Therefore, the feed rate is selected as 600 mL/h.
The influence of inlet air temperature on the number of viable bacteria In the vacuum mini spray dryer process, the air inlet temperature is one of the main considerations. With the increase of the inlet air temperature, the number of viable bacteria generally shows a downward trend, and the decline is slow at 60 ~ 80 ℃. It drops sharply after 80 ℃. The moisture content of the powder sprayed at 60 ~ 70 ℃ is close to 5%, which is not conducive to later storage; when the temperature rises to 80 ℃, the moisture content of the powder drops to 3.9%, which is in line with GB/T 5410-2008. If the temperature exceeds 80 ℃, the number of viable bacteria will drop sharply, so the optimal temperature of the inlet air is around 80 ℃ of vacuum mini spray dryer.
Based on the single-factor experiment, the study optimized the process of preparing lactic acid bacteria microcapsules by low-temperature vacuum mini spray dryer through response surface experiment design. The optimization results show that the influence of the four factors of bacterial wall ratio, inlet air temperature, feeding speed, and carrier amount on the preparation of lactic acid bacteria microcapsules by spray dryer is as follows: feeding rate> inlet air temperature> bacterial wall ratio> carrier amount, the most The best process conditions are bacterial wall ratio 1:4.55, inlet air temperature 79.07 ℃, feed rate 727.54 mL/h, carrier amount 9.80%, and the number of viable microcapsules obtained under these conditions is 2 . 81 × 108 CFU / g, meeting general product processing requirements.