Pursuit of sanitiser products for potential use in the apple and pear industry

Few fruit sanitation products are registered and currently available to the South African pome fruit industry. Alternatives to chlorine (Cl) are needed. This study aims to identify and test the efficacy of potential new sanitisers against Penicillium expansum and Botrytis cinerea for use in the pome fruit industry of South Africa.

An in vitro test was used to test the efficacy of seven sanitiser products against P. expansum and B. cinerea. Four of the most effective sanitisers were included in packhouse water sanitation trials. The efficacy of the sanitisers was tested on tap / dam (source) and flume water from five packhouses. The efficacy of the three most effective sanitisers was tested on apples and pears (in vivo).

Glutaraldehyde, fulvic acid, persulfate salts + organic acids + bioflavonoids (Salts+Mix), ascorbic acid + bioflavonoids (AA+Bioflav), peracetic acid + hydrogen peroxide (PPA1+H2O2), peracetic acid (PPA2) and potassium sorbate were selected as sanitisers. Initial results indicate continuing trials with AA+Bioflav, PPA1+H2O2, PPA2 and fulvic acid. Results differed for P. expansum and B. cinerea. PPA1+H2O2 was as effective as Cl. AA+Bioflav was effective against B. cinerea but not P. expansum. Fulvic acid and PPA2 required a 2X concentration to kill B. cinerea spores but was ineffective against P. expansum. PPA1+H2O2 showed improved efficacy when combined with 30 ppm Cl. Packhouse trials confirmed the efficacy of PPA1+H2O2 and Cl (150 ppm) to sanitise source and flume water from packhouses, even when B. cinerea and P. expansum spores were added (spiking of water). AA+Bioflav, and to a lesser extent fulvic acid, was effective against B. cinerea. In vivo trials on apples and pears again revealed PPA1+H2O2 as the most effective sanitiser and a possible alternative to Cl. The short contact time between spores and sanitisers prior to dipping of fruit can be considered as too short for sanitising water but close to maximum for sanitising fruit surfaces based on industry practices.

PPA1+H2O2 was identified as a possible alternative to Cl. AA+Bioflav is an organic fungicide exhibiting efficacy towards B. cinerea but less effective against P. expansum. Fulvic acid showed potential against B. cinerea but only at high dose rates. Products with low efficacy, especially green alternatives such as the Salts+Mix hold potential but require further optimisation. It should be clear whether a sanitiser is used to sanitise water or fruit surfaces. Long contact periods are available to sanitise water in flume tanks but a fast kill rate will be necessary to sanitise fruit surfaces or water handling large amounts of heavily contaminated fruit loads. Not all sanitisers will be able to achieve the latter. Optimising and combining sanitation practices can lead to improved sanitation of water and potentially fruit surfaces.