MICROBIAL STABILIZATION OF INTERMEDIATE MOISTURE FOOD SURFACES II. CONTROL OF SURFACE pH

Abstract

This paper explores the possibility of reducing surface pH to solve intermediate moisture foods microbial stability problems associated with localized surface condensations caused by temperature fluctuations. Surface pH reduction increases surface availability of the most active form of sorbic acid and other lipophilic acids used as preservatives. A negatively charged macromolecule was immobilized in the form of a food surface coating component while other molecules, particularly electrolytes, move freely. The effect on surface pH was described using a Donnan equilibrium model that predicted a permanent pH difference between surface and food bulk. The key parameters were electrolyte concentration and the concentration of charged groups on the macromolecule. An IMF model with low total electrolyte concentration was coated with a deionized mixture of λ-carrageenan and agarose. Measured pH differential was 0.3 to 0.5 pH units. Such a pH reduction resulted in a calculated 2.5 fold increase in the surface availability of the active form of sorbic acid as compared to food bulk conditions.