Predict pH in complex foods.

Knowing the pH of foods is important for several reasons. It not only impacts flavor, physical structure and color, but also is an important determinant of a product's microbiological stability. Acidic foods--those with low a low pH--are less hospitable for the growth of microorganisms, especially food poisoning bacteria. Many preservatives used to extend product shelf life work much better against bacteria when at low pH. But it is often difficult to predict the pH of complex systems such as food.

The pH of a food is related to the concentration of protons or hydrogen ions. The protons come from acid ingredients that release them in the presence of water. It is difficult to predict pH because most of the protons in foods come from weak acids, such as citric acid, that don't always release the same amount of protons. The number of protons they release depends on the total number of protons in the system, i.e., on the pH itself.

Food systems often contain many different acid ingredients that compete with one another to release their protons. Moreover, the oils and fats in many foods cause complications by possibly absorbing the acids and removing them from solution.

Researchers at the Institute of Food Research (IFR, Norwich Research Park, Colney, Norwich NR4 7UA, England, U.K.) have developed a buffering technique that considers all of the ingredients of the system that are too complicated or whose composition is uncertain. It characterizes them by measuring strong acid titration and other characteristics. These data can be married with the behavior of those parts of the system that are well-characterized--the organic acids and lipids--to predict the whole system's pH and its response to varying the formulation.

One possible application: biotechnology. Many processes involve fermentation that requires the careful control and monitoring of evolving pH. Application of the buffering technique could, in principle, lead to better process control by allowing the back-calculation of acid concentrations from easily measured values of pH.

The IFR buffering technique involves several procedures. These include a process for solving a series of coupled equilibrium equations; a series of modified equations that account for partitioning into nonaqueous phases, incorporating meat and vegetable tissues and the like; and a process for dealing with components too complicated to account for by using simple equilibrium constants and partition coefficients.

Control of pH is significant when acidity is the key to the shelf life of a product. Manufacturers often formulate new products, or reformulate existing ones, to meet the needs of consumers. The ability to model and predict the pH of a future product at its design stage would allow microbiologists to assess likely shelf life at an early stage.

IFR researchers are developing the technique to allow them to predict the pH of the mixtures of buffering components. They're developing software tools needed to demonstrate the buffering theory and would like to collaborate with industry to commercially utilize their technique on products.

Further information. Peter Wilson; phone: [phone]; fax: [phone]; email: [e-mail].