Inhibitory activity of phosphates on moulds isolated from foods and food processing plants

Abstract

Inhibition by six commercial phosphates on the growth of 17 molds isolated from food sources was investigated. The assays were performed at neutral and natural (without pH adjustment) pH values, streaking the molds on PCA-phosphate (Plate Count Agar with added phosphates). Concentrations of 0.1%, 0.3%, 0.5%, 1.0% and 1.5% (w/v) of phosphates were used and the Minimal Inhibitory Concentration (MIC) values were determined. The resistance of molds to phosphates depended on the species. At a neutral pH, Aspergillus ochraceus and Fusarium proliferatum were resistant to all phosphates and concentrations assayed, while Byssochlamys nivea, Aureobasidium pullulans and Penicillium glabrum were most sensitive. The most inhibitory phosphates were those with chain lengths greater than 15 phosphate units and the highest sequestering power. At natural pH values (resulting from dissolving the phosphate in the medium), inhibitory activity changed dramatically for phosphates that produced alkaline or acidic pH values in the medium. Phosphates with alkaline pH values (sodium tripolyphosphate–high solubility, sodium tripolyphosphate and sodium neutral pyrophosphate) showed greatly increased inhibition compared with that observed at a neutral pH, while sodium acid pyrophosphate (acidic pH) showed decreased activity. Our results demonstrated that some phosphates could be used in the food industry to inhibit molds linked to food spoilage.