Research on the Process of Yogurt Powder by Lab Spray Dryer

Research on the Process of Yogurt Powder by Lab Spray Dryer

Abstract: This study optimizes the preparation, fermentation parameters and spray parameters of single-bacterial starter culture to obtain the best production process of yogurt powder. The ratio of strains (Lactobacillus bulgaricus: Lactobacillus acidophilus: Streptococcus thermophilus) is 2:2:3, and the inoculation amount is 5% of the milk volume (Lactobacillus bulgaricus: 6.85×106 cfu/mL. Lactobacillus acidophilus: 7.71×106 cfu/mL, Streptococcus thermophilus: 1.35×10 7 cfu/mL), the fermentation time is 8h, which is the best condition for yogurt fermentation. At this time, the number of bacteria in the yogurt is 6.0×108cfu/mL; the inlet temperature of the spray dryer is 150°C. The feed flow rate is 300mL/h, and the cyclodextrin content is 0.0159/ml. , is the best condition for spray drying of yogurt powder. The viable bacteria rate in the yogurt powder is 78.4%, and the finished product is milky white and slightly yellowish.

Yogurt has a special flavor and high nutritional value, is easily absorbed by the human body, and can help intestinal digestion and is beneficial to human health. Therefore, how to preserve yogurt cheaply and effectively is a huge problem facing the yogurt industry today. The yogurt powder produced by spray drying the yogurt through spray drying technology can ensure the number of viable bacteria in it, and on the other hand, it can extend the storage period of the yogurt product. This experiment uses commercially available strains to ferment and produce yogurt, and spray-dries them to study the process of spray-drying to produce yogurt powder. The use of spray drying technology to produce yogurt powder that is easy to transport and store has good development prospects.

Materials and Methods

1 Raw materials and reagents Yoghurt, whole milk powder, skim milk, MRS culture medium, cyclodextrin, sucrose, etc.

2 Process flow

Strain screening and isolation and purification – preparation of single bacterial starter – yogurt production – yogurt powder production – packaging – finished product

Preparation method of bacterial starter 1:4:1 Isolation, purification and screening of bacterial strains.

Dilute the yogurt and culture it at 37°C for 48 hours. Pick a single colony and streak it on the solid lactic acid bacteria medium for purification 3 to 4 times. The single bacterial colony is large, transparent and gray-white. The strain with a rod-shaped shape under microscopy is Bulgarian milk. bacilli; individual bacterial colonies are small, smooth, moist, slightly whitish, with neat edges, and the bacterial cells are oval when examined under the microscope. Those that form pairs or form long chains are identified as Streptococcus thermophilus; larger colonies are milky white. The slightly yellowed strain is Lactobacillus acidophilus. Take Lactobacillus bulgaricus, Lactobacillus acidophilus and Streptococcus thermophilus, add them to the skim milk liquid culture medium, and culture them at 37°C for 12 hours to obtain a pure culture of the bacteria. Take 300mL of skim milk and put it in a dry Erlenmeyer flask, sterilize it, take 3% of the skim milk and put the bacteria into the Erlenmeyer flask for culture (12~14h), until the clotted state is uniform and dense. The mother starter can be obtained when there is a small amount of whey or no whey is precipitated, and can be used to make starter. Sterilization parameters of skim milk used in the production of starter (80°C, 30~60min), methods and preparation of mother starter The same, prepare the starter culture box at 4°C for later use.

Orthogonal experiment on yogurt fermentation process

On the basis of single-factor experiments, it was determined that the proportion of bacteria (A) fermentation time (B) and inoculum amount (C) are important factors affecting the number of viable bacteria in fermented milk. L, (3) orthogonal experimental design was carried out to determine the fermentation The optimal fermentation conditions for milk are listed in Table

Lab Spray dryer parameter research method

1.1 The influence of different cyclodextrin concentrations on drying results. The fan frequency of the spray dryer is set to 50Hz (the outlet temperature is about 70°C and the inlet temperature is set to 150°C. The feed flow rate is 240mLh, and the cyclodextrin agent concentration is 0005g/mL, respectively. Spray drying was carried out under the conditions of 0.01g/mL, 0.015g/mL, 0.020g/mL, and 0.025g/mL to study the effect of B-cyclodextrin concentration on the number of viable bacteria in yogurt powder.

1.1 The influence of different feed flow rates on drying results. The fan frequency of the spray dryer is set to 50Hz (the outlet temperature is about 70°C). The inlet temperature is set to 150°C, the B-cyclodextrin concentration is 0015g/mL, and the feed flow rate is at Spray drying was performed under the conditions of 120mL/h, 180mL/h, 240mL/h, 300mL/h, and 360mL/h to study the effect of feed flow on the number of viable bacteria in yogurt powder.

1.3 The influence of different inlet temperatures on drying results. The fan frequency of the spray dryer is set to 50Hz (the outlet temperature is about 70°C), the feed flow rate is 240mL/h, the B-cyclodextrin concentration is 0.015g/mL, and the inlet temperature is 130 respectively. Spray drying was carried out under the conditions of °C, 140°C, 150°C, 160°C and 170°C to study the effect of inlet temperature on the number of viable bacteria in yogurt powder.

1.4 Orthogonal test of spray drying process parameters. Based on the single factor test, the factors that affect the viable bacteria rate of yogurt powder are inlet temperature (A) feed flow (B) and B-cyclodextrin concentration (C). For these three Carry out L, (3) orthogonal experimental design with three factors to determine the optimal spray parameters. See Table 3.

Measurement and calculation methods

Starter viability assay

(1) The reduction indicator principle of C12 H17NO4 is used to react with the acid produced by the lactic acid bacteria in yogurt during the reproduction process. In an oxygen-free environment, the C12 H17NO4 solution will fade from pink to colorless, that is, when containing 1mL of starter culture and 9mL Add 1mL of 0.005% C12 H17NO4 solution to the skim milk, and then place it in a constant temperature incubator at 36.7C for more than 35 minutes. The activity of the starter is judged based on the color change.

(2) Determination of the number of bacteria in a single-bacteria starter culture: Take a single-bacteria starter culture that is diluted a certain number of times, then spread it on a lactic acid bacteria solid medium and culture it in a constant temperature incubator for 48 hours, and then record and calculate the number of bacteria in each starter culture. Concentration of bacteria [8] 1.7.2 Determination of bacterial count Use a pipette to measure 1.0mL of the yogurt to be tested, dilute it 10 times with sterilized physiological saline, take 0ml and inject it onto the culture medium, spread evenly, and keep at a constant temperature of 37C Cultivate for 48 hours [9. Take the petri dishes without bacterial contamination and count the number of colonies between 30 and below 300.

results and analysis

Orthogonal test results of yogurt fermentation process

The data in Table 4 shows that the strain ratio has the largest difference, and the inoculum amount has the smallest difference. The order of their influence on fermentation conditions is strain ratio > fermentation time > inoculum amount. From the data in the table, we can get the best fermentation The conditions are A3B1C1 (Lactobacillus bulgaricus: Lactobacillus acidophilus: Streptococcus thermophilus 2:3:3, fermentation time 8h, inoculum volume 5%). Because this experimental combination is not included in the orthogonal experimental results, it needs to be corrected. The optimal fermentation conditions were verified. The experimental results show that when the optimal conditions are used for yogurt fermentation, the number of viable bacteria can reach 6.0X10cfu/mL. This result is significantly higher than the results in the orthogonal experiment, so it can be proved that the optimal fermentation conditions are A3B1C1。

Spray drying condition results and analysis

Results and analysis of the effects of different cyclodextrin concentrations on viable bacteria rate

It can be clearly seen from Figure 2 that when spray drying is used to produce yogurt powder, the viable bacterial rate in the yogurt powder is the highest when the cyclodextrin concentration is 0.015g/mL. At this time, the bacterial survival rate is 73.2%, because with the increase of B-cyclodextrin As the concentration increases, the survival rate of the bacteria in the yogurt powder will continue to increase, but gradually stabilize in the later period. Therefore, on the premise of ensuring the rate of viable bacteria in the yogurt powder, the concentration of the protective agent is selected to be 0015g/mL for the taste and flavor of the yogurt powder.

Results and analysis of the impact of different feed flow rates on viable bacteria rate

As shown in Figure 3, when the process parameter feed flow rate is 300mL/h when spray drying is used to produce yogurt powder, the viable bacteria rate of the produced yogurt powder is the highest 76.6%. This is because when spray drying is used to produce yogurt powder, the feed flow rate continuously changes with the material feed flow rate. With the increase, the viable bacteria rate gradually increases. After the feed flow reaches 300mL/h, the viable bacteria rate in yogurt powder decreases.

Results and analysis of the effects of different inlet temperatures on the viable bacteria rate

It is obvious from Figure 4 that when spray drying is used to produce yogurt powder, the inlet air temperature is 150°C, and the survival rate of bacteria in the yogurt powder is the highest. At this time, the viable rate of bacteria is 75.6%. The spray drying temperature is low, and the spray Incomplete drying results in poor powder extraction, resulting in a low viable bacteria rate in yogurt powder. As the temperature gradually rises, the powder extraction effect becomes better and the viable bacteria rate gradually increases. When the temperature rises to 150°C, as the temperature As the temperature increases, the viable bacteria rate in yogurt powder gradually decreases. The reason may be that excessive temperature causes inactivation of bacteria.

Results and analysis of orthogonal tests on spray parameters

The data in Table 4 shows that the order of influence of spray parameters on powdered yogurt is: inlet temperature, feed flow rate > protective agent concentration. From the data in Table 4, it can be obtained that the optimal fermentation conditions are A1B2C2. After verification, it was found and the results obtained from the orthogonal test Consistent, so when the spray dryer inlet temperature is 150°C, the feed flow is 300mL/h, and the cyclodextrin concentration is 0015g/mL, it is the best drying parameter for producing yogurt powder. At this time, the activity in the powdered yogurt The bacterial rate is 78.4%.

Conclusion and Outlook

This article studies the production process of spray-dried yogurt powder. Under the combined conditions of cyclodextrin content of 15g/mL, spray dryer inlet temperature of 150°C, and feed flow of 300mL/h, it is the optimal spray drying parameter. At this time, the viable bacteria rate in the yogurt powder is 78.4%. The yogurt powder is milky white with a slight yellowish color, and the powder is fine. The yogurt powder does not require low-temperature storage, is easy to carry, and has a long shelf life; the yogurt powder still has fermentation activity. , nutrition and flavor, it can be used as a fermentation agent for yogurt and does not require further activation and amplification; the research and development of yogurt powder can play a balancing role in the production of yogurt throughout the year and can adjust the demand relationship in the market. Therefore, yogurt powder There are good development prospects in the future. However, there is still a certain gap between the yogurt powder produced in the trial and commercially available milk powder, instant coffee and other products. Therefore, the mature production process of yogurt powder needs further research.

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