Prediction of pH during food formulation

As part of a study into the effect of food structure on microbial growth, a need for accurate prediction of the chemistry of the food environment was identified. The project described here aimed to develop tools to predict the local pH and concentration of organic acids in products from the agri-food industry and related sectors.

pH is a key property of foods. It affects flavour, physical structure, colour and can be one of the key determinants of microbiological stability. Acidic products are intrinsically less hospitable for the growth of food poisoning bacteria and low pH also promotes the action of weak acid preservatives such as potassium sorbate. Despite this pivotal role, predicting the pH of a product from knowledge of its recipe is far from straightforward and therefore products are frequently formulated entirely by trial and error.

Scientists at the Institute of Food Research have been developing tools that can help food scientists and technologists manipulate the pH of their products at the recipe stage. Though developed initially with food applications in mind, it is possible that these tools may be applied to any problem where pH prediction in complex systems is required, thus providing a significantly wider scope for the technology.

Why is predicting pH in complex foods so difficult?

The pH of a system is a measure of the concentration of hydrogen ions (protons) within it. These protons come from ‘acid’ ingredients that release them (dissociate) in the presence of water. In foods, many of these protons come from so-called ‘weak acids’. Weak acids, such as acetic acid and citric acid, release different numbers of protons depending upon the pH. Whilst this simple equilibrium behaviour is well understood by chemists, foods usually contain many different weak acids, hence calculations rapidly become complicated. In addition to a range of acid ingredients all competing with one another to release their protons, real foods frequently also contain alkaline ingredients (both weak and strong). These ingredients adsorb protons, acid or alkaline salts that interact with their corresponding acids or alkalis, and fats & oils into which some ingredients preferentially partition. This sort of problem is difficult to solve owing to the following:

• Some of the major pH-determining components of food, such as proteins or whole tissues, are too complicated to be described by an equilibrium constant
• Often the composition of a food product is not known with sufficient accuracy

By solving these two major problems, IFR’s Buffering Theory makes the prediction of the pH of real food systems possible. The trick is to take the ingredients within the system that are either too complicated or whose composition is uncertain and perform a simple characterisation of them (a Strong Acid Titration, SAT). This data can then be married with the behaviour of those parts of the system that can be well characterised (e.g. the organic acids and lipids) to predict the whole system’s pH as a function of recipe.

Theory calculator

To demonstrate the application of IFR’s Buffering Theory, in either a new or existing product development environment, we have developed an easy-to-use Windows based application. This allows users to build a recipe from a database of SATs derived from relevant ingredient materials. The software then calculates the mixture’s strong acid titration behaviour and predicts its initial pH.

To this mixture the user may choose to simulate the addition of further components: acids, alkalis, salts thereof and an oil phase, into which the components may partition. The software predicts the final pH of the overall mixture and provides the user with a graphical display indicating the amounts of each component that are dissociated, undissociated or partitioned into the oil phase.

Alternatively, if the user has a target pH in mind the software will calculate the amount of a given component or its salt that is required to achieve that specification.

Towards on-screen product development

We are evaluating exploitation routes for IFR’s Buffering Theory and the software tools we have developed around it. The software technology has been licensed to PBL (www.pbltechnology.com), the technology management company who are commercialising the product with evaluation and development partners. Currently the emphasis is on development of new product development tools for the food industry.