Predict acidification of vegetable slurries to target pH levels.

Reducing pH levels is critical for creating safe, flavorful and properly textured acidified foods. Currently, it is difficult to predict the amount of acid required to reach a target pH.

A semi-mechanistic partial buffer (SMPB) approach to modeling the complex buffering situations that occur in biological materials has been implemented in MATLAB[TM], a vector language with extensive built-in libraries, as a program called pHTools. The pHTools toolbox is a collection of MATLAB files which make it possible to mathematically model buffer systems.

This program can be used to predict pH adjustments, distributions of acid species, buffer capacity and ionic strength in foods. pHTools numerically models vegetable slurries as a mixture of simple and complex buffers so that you can predict the acid concentrations required to reach a target pH.

The goal of Ohio State University scientists was to validate the SMPB modeling approach by comparing experimental pH adjustments of fresh cucumber slurries with predictions made by the pHTools program. In experiments, fresh cucumber slurries were titrated with HCl from pH 6 to a final pH of less than 3.0. The titration curves were used to predict the amount of acetic, malic, citric and phosphoric acids required to acidify fresh cucumber slurries with and without 0.3 M NaCl to pH 4.5, pH 4.0, pH 3.7 and pH 3.3.

In cucumber slurries without NaCl, the modeled and experimental amounts required to reach the target pHs were not significantly different for acetic, malic and citric acids. In the presence of 0.3 M NaCl, predicted and experimental amounts were also not significantly different for acetic, malic and citric acids. However, phosphoric acid predictions were underestimated from 9.1% at pH 4.5 to 15.3% at pH 3.3. Phosphoric acid predictions made using pHTools were overestimated by 33% at pH 4.5, but only by 0.6% at pH 3.3.

Still, the researchers believe that the SMPB modeling approach gives reasonable estimates of the amounts of common food acidulants required to reach a range of target pH values in vegetable slurries. With pHTools, the core software routines make it possible to predict buffer capacity, ionic strength and titration curves. These routines are then used in other routines to achieve various goals. For example, the software allows one to compute the amount of a primary buffer required to achieve a desired pH in a secondary buffer. There are also routines that can be incorporated into systems of differential equations for predicting pH, buffer capacity and species concentration in dynamical systems.

Further information. Roger McFeeters, USDA-ARS and North Carolina State University, Department of Food Science, Box 7624, Raleigh, NC 27695; phone: [phone]; email: [e-mail].