pH measurement in food is one of the most important analytical variables for quality control. It numerically expresses the acidity or alkalinity of the medium and is directly associated with texture, flavor, preservation, and food safety.
The most common method for measuring pH is using electrochemical sensors – more specifically, combined electrodes. These sensors are based on the potential difference generated between an internal reference electrode and a measuring electrode, which has a glass membrane sensitive to pH.
In food measurement, there are 3 critical elements in pH sensors, whose functioning is directly affected by the characteristics of the samples. Therefore, in addition to being specifically designed for the application, the operation and maintenance of pH sensors must take these particularities into account. Let's look at them!
- Glass membrane – This is the most critical element of the sensor. It is responsible for detecting the pH of the sample, and its accuracy and speed of response depend directly on, among other factors, its composition and preservation. In the analysis of semi-solid foods such as meats, cheeses, fruits, and breads, this element needs to be robust enough to withstand friction, but have low enough impedance to prevent static electricity effects. Furthermore, it needs to be adapted to the type of sample being measured. For example, for measurements on surfaces like leather and gelatin, flat membranes are more suitable, while for meats and cheeses, the membrane should offer minimal resistance to insertion.
- Junction – It separates the reference electrolyte (internal medium) from the sample (external medium). It needs to balance the need for ionic conduction between the reference and measuring electrodes, and the protection of the reference electrolyte from contamination by compounds from the sample. In samples prone to adhesion of substances such as proteins and fats, porous point junctions can be blocked very easily, interrupting contact between the electrodes and leading to erroneous measurements. To overcome this problem, sensors used in food analysis should have wider, open junctions, or multiple junctions.
- Electrolyte of reference – The chloride concentration in the internal reference solution must remain unchanged for the generated potential to be constant. In food samples, however, the migration of compounds that react with chlorides from the sample, such as sulfides and proteins, can contaminate the reference by migrating through the junction. To prevent this type of error, specific gel or semi-solid electrolytes, internal pressurization, and/or the use of "ion traps" can be employed.ion trap).
How can Alutal help with pH measurement in food in a laboratory setting?
A Apera instruments It is a manufacturer dedicated to the development of instruments and sensors for water analysis, which throughout its more than 30-year history has specialized in pH measurement for diverse applications.
In addition to the 8500 series portable and 9500 series benchtop analyzers for field and laboratory use, respectively, the LabSen® series pH electrodes are designed with the necessary requirements for greater accuracy and durability in food analysis. Check out the main sensor models applied to this segment below!
With a PVC body, flat glass membrane, and PTFE ring junction, this sensor is suitable for measurements on flat surfaces such as hides, leather, and others.
The LabSen lance-type electrode has two junctions – an open junction and a ceramic junction – with different characteristics and are difficult to clog, significantly extending the electrode's lifespan. Designed to penetrate soft samples such as soils and pulps, and to perform direct pH measurements, the sensor membrane features advanced technology. sturdy-layerThis makes it strong enough for measurements requiring penetration into food. The food-grade titanium alloy body effectively protects the glass rod, does not corrode, and is best suited for testing solid and semi-solid foods such as cheese, pasta, meat, fruit, and others.
Based on the same construction principle as the 751 puncture membrane model, this sensor features an external titanium blade that easily cuts through frozen or raw meat, fish, and other solid samples to directly measure pH. For electrode cleaning, the blade can be unscrewed, facilitating maintenance.
When using conventional pH electrodes to test dairy products and other liquid foods containing proteins, these proteins react with the reference electrolyte, clogging the ceramic junction and contaminating it. For these applications, a gel electrolyte is used, which inhibits the reaction with proteins. Furthermore, the sensor is equipped with 3 ceramic junctions, further reducing the chance of clogging, making it suitable for products such as yogurt, whey, milk, creams, jams, etc.
But not only that…
Alutal represents renowned manufacturers of analytical instrumentation and can offer other instruments for the food industry. Consult usLearn more about our laboratory portfolio!
