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Measuring the pH of yogurt has a major limitation due to an inadequate interaction between the reference electrolyte and the sample. This is due to the semi-solid consistency of yogurt that makes it difficult for a conventional sensor to pierce through the sample. The delicate sensing membranes of the pH sensor has a spherical shape and may suffer damage during the measurement process. Another factor, which contributes towards the limited interaction between the reference electrolyte and the sample, is low miscibility due to high fat and protein content of the samples. This along with a few other factors described below cause unstable readings and longer response times.
METTLER TOLEDO's InLab Solids Pro-ISM is a specialized sensor for measuring the pH of yogurt with accuracy and precision. The sensor has a spear shaped tip made of toughened glass that allows direct insertion into the samples and is resistant to damage. The low maintenance solid XEROLYT®EXTRA polymer reference system offers two benefits: it has a clog-free open junction which eliminates the risk of protein fouling; and the sensor interacts with the sample through diffusing ions, eliminating the difficulties associated with immiscibility of aqueous reference electrolyte with the sample. The specialized design and overall sensor technology of the InLab Solids Pro-ISM ensures direct sample measurement of yogurt samples, which is critical for ensuring reliability and consistency in manufacturing and quality control.
For more information on this sensor, its advantages and pH measurements of yogurt, download our application note.
In the following section, we cover more information about yogurt manufacturing and the role of pH for consistent quality.
What is Yogurt?
It is a type of food that is produced by the bacterial fermentation of milk. It acts as a probiotic carrier due to the presence of live bacteria strains.
What happens during the fermentation process?
The sugars in milk i.e. lactose are converted into lactic acid with the help of bacterial cultures, which gives the desired tartness and texture to the product. The pH of milk drops from 6.7 to less than or equal to 4.6 pH units and is an important step in the yogurt manufacturing process.
What are different stages in yogurt manufacturing?
- Typically, the processing steps involve homogenization, pasteurization, and cooling of milk to an incubation temperature before starter culture is added
- The fermentation process begins with the addition of the live bacterial strains at optimum temperature
- The reduction in pH due to lactic acid formation is monitored and controlled until the desired pH is achieved as pre-determined by the manufacturer (below 4.6 pH units)
- It is then partially cooled (below 20 °C) and then fruit or flavoring ingredients as per requirement are added
- The product is then transferred to cold storage, which reduces further acid development
Why is monitoring pH of yogurt important?
A correlation between the pH of post storage yogurt and the survival of probiotic bacterial strains serves as an indicator of the shelf life of the yogurt products. The probiotic benefits, taste and shelf stability of yogurt samples, all depend on accurate pH measurements throughout manufacturing and quality control processes. Therefore, measuring the pH of yogurt becomes an important parameter during manufacturing and also while assessing the quality of the desired product.
For more information about the advantages of using right sensor and good measuring practices, download our application note for the pH measurement of yogurt.
