Stability of biocontrol products carrying Candida sake CPA-1 in starch derivatives as a function of water activity

Abstract

ABSTRACTThe preservation and shelf-life of formulations of the biocontrol agent Candida sake CPA-1 and starch derivatives as a function of water activity (aW) were studied in terms of the physical stability of the products and cell viability. Formulations of biocontrol products (BCPs), based on combinations of potato starch and pre-gelatinised potato starch (F1 and F2) or maltodextrines (MD) (F3) containing cell protectants, were obtained by fluidised-bed drying. The carriers and the formulated products were stored at 20°C under different aW conditions. The water sorption and water plasticization behaviour of the different products were analysed through the water sorption isotherms and glass transition temperatures (Tg). Likewise, the viability of C. sake over time was determined as a function of the aW. The solubility of the products was also assessed. Although formulations stored at 20°C and low aW (≤ 0.33) exhibited a better shelf-life, a significant decrease in cell survival ratio after 180 storage days was observed. Cold storage (5°C) was required to better maintain the cell viability, thus prolonging the shelf-life of BCPs. Formulations containing MD were the most effective at preserving cell viability and also exhibited the highest water solubility. All the formulations were physically stable at ambient temperature; therefore, the cell stability is the critical point at which to establish both the aW levels and temperature during storage. Packaging the product using high water vapour barrier material and under cold storage would be necessary to ensure a high number of viable cells and an effective and competitive BCP.