Apple disinfection: preventing or inducing bias?

Fruit material used in postharvest phytopathology research is generally disinfected prior to subjecting it to treatments. Although this is common practice, many different protocols exist, most of them with ethanol or sodium hypochlorite (NaOCl). A targeted investigation into the effects these treatments might have on the fruit and, hence, on the research outcome, is lacking. Therefore, the aim of this research was to investigate the effect of ethanol (70 %, 2 min), NaOCl (2.5 %, 2 min), and hot water (55 °C, 4 min) treatments on macroscopic quality parameters of apple fruit (Malus ×domestica ‘Jonagold’) in order to select a disinfection protocol suitable for research purposes. Treated apples were stored at 18 °C for 15 days during which respiration was measured regularly. On day 15, firmness, brix, color, and weight loss were measured. All treated apples exhibited a significantly (p < 0.05) higher respiration rate compared to the control. Ethanol had a significant effect on the apple fruit color attributes and NaOCl treatment caused an increase in brix. No significant changes were detected for firmness or weight loss. The same setup was then used to test different NaOCl concentrations ranging from 0.095 to 4.75 % (2 min) in order to find an optimum at which no changes occur for the measured variables. Although respiration rates and brix values were correlated with NaOCl concentration, no significant changes were found in contrast to previous results. Treatment with 4.75 % NaOCl did exhibit a significantly higher weight loss, indicating changes in the apple’s cuticle. This study demonstrated that prevalent disinfection methods used in postharvest phytopathology studies induce changes in macroscopic fruit quality parameters. Therefore, they can possibly introduce a bias on the research outcome. No significant effects were detected for NaOCl concentrations of 1.58 % or lower.

Publication year:2016