A Box-Behnken design for predicting the combined effects of relative humidity and temperature on antagonistic yeast population density at the surface of apples

Abstract

The objective of this work was to develop models predicting the combined effects of relative humidity (RH, 75-98%), temperature (5-25°C), and initial applied yeast concentration (10 4 -10 8 CFU/ml) on the apple-surface population densities of two biocontrol agents fused against postharvest diseases; the antagonistic yeasts Pichia anomala strain K and Candida oleophila strain O. Experiments were carried out according to a Box-Behnken matrix. Multiple regression analyses showed that both models yielded a good prediction of yeast density. The effect of relative humidity appeared greater than that of temperature. The number of yeast colony-forming units per square centimeter of apple fruit surface increased with increasing relative humidity, temperature, and initial applied yeast concentration. The models predict that under optimal growth conditions (25°C, 98%), strains O and K should reach a density of 10 4 CFU/cm 2 when applied initially at 2 × 10 7 (strain O) or 10 7 CFU/ml (strain K). The model results suggest that rainfall was likely the principal cause of the variability of yeast efficacy reported for previous preharvest orchard trials spanning two successive years. Temperature may also contribute to this variation. The models developed here are important tools for predicting population densities of both strains on the apple surface within the experimental limits. The use of these results should contribute to achieving yeast densities of 10 4 CFU/cm 2 on apples by controlling yeast application and environmental factors such as relative humidity and temperature. The results of this study also confirm our previous in vitro findings that water activity has a greater effect than temperature on yeast population density.

A new semi-selective agar medium for recovery and enumeration of antagonistic yeast, Pichia guilliermondii strain Z1 from orange fruit surface

“…Jijakli et al (1999) underlined that the development of a monitoring method for tracking the population dynamic of BCA on the fruit surface is of particular interest because the efficiency of the yeast is closely related to its colonization. Such findings have been confirmed by Lahlali et al (2008) who reported that a yeast density of 1 × 10 4 CFU/cm 2 of apple fruit surface is required to reach a higher protection against P. expansum during storage. Therefore, a semi-selective medium allowed growers to determine which concentration of BCA could be used to obtain complete reduction of the rot incidence on fruit rot.…”

“…Therefore, a semi-selective medium allowed growers to determine which concentration of BCA could be used to obtain complete reduction of the rot incidence on fruit rot. Lahlali et al (2008) demonstrated that the initial concentration of application is a crucial factor limiting the effectiveness of antagonistic yeast when applied at preharvest and the density of yeast on apple surface was significantly dependant on environmental factors and with its initial concentration of application. Different wash buffers have been used in literature to recover the population of antagonistic yeast on fruit surface (Beuchat and Pitt, 1990;Chand-Goyal et al, 1998;Leibniger et al, 1997;Lima et al, 1999;Johnson et al, 2000;Usall et al, 2001).…”

“…In this work, we have used KBTP as a wash buffer. This wash buffer has been largely cited for higher recovery efficiency with more than 99% of yeast cells from the treated apple surface (De Clerq et al, 2004;Lahlali et al, 2008;Pujol et al, 2004). Having selected the semi-selective medium for the strain Z1, we conducted a study on the impact of temperature on growth of strain Z1 in in vivo conditions.…”

Biological control of crown rot of bananas with Pichia anomala strain K and Candida oleophila strain O

“…The characterization of these strains include also the development of a monitoring method (Massart et al, 2005) and the study of their ecological behavior (Lahlali et al, 2008). As strain K and strain O were already extensively characterized, it is easier to asses their efficacy against crown rot disease of banana than to select novel uncharacterized micro-organisms.…”

Multivariate optimization of microwave-assisted digestion of copper and zinc from powder milk

“…7 The sequence analysis time can be reduced by using a microwave oven, thus leading to greater in analytical sampling rate. 8 The response surface methodology (RSM) is a good tool for determining experimental factor settings 9 and assesses the relationship between experimental and observed results. 10 It is a mathematical tool that can aid to find the optimum conditions for a reaction with the minimum number of experiments to obtain statistically acceptable results.…”