Statistical media optimization using cheese whey powder for production of Vishniacozyma victoriae postharvest biocontrol yeast in pears

Vishniacozyma victoriae NPCC 1263 was selected for this work because of the active antagonistic effect over several fungi. A cheese whey powder (CWP) based medium for the maximum biomass production of biocontrol agent was statistically optimized using a central composite design based on response surface methodology (RSM). The optimization condition was found to be in g/L: CWP 80, KH2PO4 10, (NH4)2SO4 1.2 and, under optimum conditions, the biomass production in a 15-L fermenter was about 15 g/L after 74/78 h cultivation. The efficacy of V. victoriae NPCC 1263 for controlling postharvest decay of pear fruits was evaluated in semi-commercial packing-house conditions with the application of 108 CFU mL-1 yeast cells, with CaCl2 (2 % w/v) addition in two treatments, fresh and lyophilized-rehydrated biomass on Packham's Triumph pear cultivars. After 150 days of storage, lyophilized-rehydrated biomass treatment reduced the incidence caused by B. cinerea, P. expansum and Cladosporium spp., reaching 36 %, 71 % and 55 % of control respectively. The fresh biomass treatment reached 47 % and 58 % of control for B. cinerea and P. expansum, but no control for Cladosporium spp. was observed. The two treatment yeasts were able to control decay and colonize the surface of the fruits during the postharvest period, with an estimated increase in the population density of approximately-three log units independently of the treatment applied.