There are different types of fermented dairy products and each product is produced with the help of lactic starter culture bacteria. Dairy starter cultures are microorganisms used in the production of various dairy products, including butter, cheese, yogurt, and fermented milk. All dairy starter cultures produce acid. The most important group of microorganisms are lactic acid bacteria (LAB), which are present in almost all dairy starter cultures.

Factors Affecting Starter Culture

A number of factors may negatively affect starter culture activity, leading to poor-quality fermentation products and financial loss. When lactic acid is not produced by the starter culture at the desired rate, the fermentation is called "slow". The slowness in acid production can be due to the genetic structure of the strains or external factors. Others include bacteriophage (the most common cause of slow fermentation), antibiotics residuals and disinfectants, inhibitory compounds in milk, changes in milk composition due to mastitis or seasonal factors, and metabolites of spoilage bacteria. Lower acid production rates can also be caused by improper shipping conditions, fluctuating incubation temperatures, and excessive acidification.

Heat treatment

Heat treatment is the most widely used production technology in the dairy industry. Its main purpose is to destroy microorganisms, both pathogenic and spoilage, to ensure the milk is safe and increase its shelf life. Each microorganism has a specific temperature for optimal growth and production rate (g/L/h). Generally, the temperature 65-72°C kills 60-60% of bacteria.

Fermentation time

The time required for fermentation is 2.5 hours for the classic yogurt starter culture. As can be expected based on the acidification chemical reaction that underlies the fermentation process, the pH decreases to 4.6 during 3-5 hours. In addition, based on studies, samples produced by strains with low proteolytic activity have an irreversible pH reduction, and samples containing starter culture with high proteolytic activity have different acid profiles and longer fermentation times. 

Quantity of additives and sanitizing chemicals

Many disinfectant chemicals, such as quaternary ammonium compounds, iodine, and chlorine compounds, delay acid development by starter cultures. Colostrum and late lactation milk contain non-specific agglutinins that inactivate and precipitate sensitive starter strains. Agglutinins may delay the rate of acid production by interfering with the transport of lactose and other nutrients. Seasonal changes in milk solid fraction affect the growth and balance of strains. Another reason for the delay in fermentation may be attributed to the antibiotics present in the milk, so that even low concentrations of 0.05-0.005 (IU) of antibiotic per milliliter of milk can lead to partial or complete inhibition of the starter culture. Proper use of disinfectants including exact disinfectant concentrations and removing residual disinfectants from pipes and containers before use, is essential for processing fermented dairy products.

Storage conditions

Starter cultures are perishable and have a limited shelf life! Freeze-dried starter cultures can be stored at 4°C for more than 12 months. Since the successful production of fermented products depends on healthy and active starter bacteria, it is important to transport and store them properly to ensure their effective functioning.

Source:

Bezie, Assefa. “The Role of Starter Culture and Enzymes/ Rennet for Fermented Dairy Products Manufacture-A Review.” NFSIJ, 2019. doi:10.19080.