Carob pulp as raw material for production of the biocontrol agent P. agglomerans PBC-1

Abstract

Large-scale production has been the major obstacle to the success of many biopesticides. The spreading of microbial biocontrol agents against postharvest disease, as a safe and environmentally friendly alternative to synthetic fungicides, is quite dependent on their industrial mass production from low-cost raw materials. Considerable interest has been shown in using agricultural waste products and by-products from food industry as nitrogen and carbon sources. In this work, carob pulp aqueous extracts were used as carbon source in the production of the biocontrol agent Pantoea agglomerans PBC-1. Optimal sugar extraction was achieved at a solid/liquid ratio of 1:10 (w/v), at 25°C, for 1 h. Batch experiments were performed in shake flasks, at different concentrations and in stirred reactors at two initial inoculums concentrations, 10⁶ and 10⁷ cfu ml⁻¹. The initial sugar concentration of 5 g l⁻¹ allowed rapid growth (0.16 h⁻¹) and high biomass productivity (0.28 g l⁻¹ h⁻¹) and was chosen as the value for use in stirred reactor experiments. After 22 and 32 h of fermentation the viable population reached was 3.2 × 10⁹ and 6.2 × 10⁹ cfu ml⁻¹ in the fermenter inoculated at 10⁶ cfu ml⁻¹ and 2.7 × 10⁹ and 6.7 × 10⁹ cfu ml⁻¹ in the bioreactor inoculated at 10⁷ cfu ml⁻¹. A 78% reduction of the pathogen incidence was achieved with PBC-1 at 1 × 10⁸ cfu ml⁻¹, grown in medium with carob extracts, on artificially wounded apples stored after 7 days at 25°C against P. expansum.