Apple disinfection: Preventing or introducing 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. 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), sodium hypochlorite (8°Cl, 2 min), and hot water (55°C, 4 min) treatments on macroscopic quality parameters of apple fruit (cv. Jonagold) in order to select a disinfection protocol suited 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 sodium hypochlorite 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 sodium hypochlorite concentrations ranging from 0.3 to 15°Cl (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 sodium hypochlorite concentration, no significant changes were found in contrast to previous results. Treatment with 15°Cl 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 or apparent effects were detected for sodium hypochlorite concentrations of 1°Cl.status: accepte