Sanitation of Apple Storages

The two most important postharvest diseases of apples are blue mold (caused by Penicillium expansum) and gray mold (caused by Botrytis cinerea). Both Penicillium and Botrytis are wound pathogens and spores can be found in any apple storage facility. Therefore, sanitation is critical for the control of these fungi. In addition to sanitizing apple bins and packing line equipment, sanitation of all parts of storage rooms is required each season. These include: 1) floors, walls, ceilings, doors, and structural beams; 2) refrigeration system components; 3) electrical wires and light fixtures; and 4) air and water pipes, ducts, channels, grates and drains.

The following summary is modified from the Agriculture and Agri-Food technical bulletin: Hygiene Measures in Fruit and Vegetable Storage Warehouses. 1999 E. V. Toussaint, A. Ouimet, O. Carisse, J. DeEll, and C. Vigneault.

Cleaning - Debris on the floor can generally be removed by sweeping. However, vigorous brushing may be required for debris that is on the walls and ceiling. Any remaining dirt and organic matter should be removed with water and detergent. It is important to scour surfaces well enough to dislodge any ground-in dirt. High-pressure washing with a non-foaming industrial detergent is often the easiest method. For safety reasons, electrical systems and motors that are not waterproof should be covered. Cleaning is important because organic matter impedes and/or neutralizes the action of disinfectants. In addition, cleaning removes the substrates that can promote the growth of pathogens in the storage rooms. However, many pathogens will not be removed by simple cleaning and thus disinfectants are required.

Disinfecting - Information on the disinfectants approved for use in Canada is presented in Table 1. Special care should be taken if there is a high rate of contamination, as disinfectants destroy only pathogens on the surfaces. The conditions of application and contact time must be followed exactly in order for any disinfectant to be effective. It is also important to follow the recommended time between disinfectant use, airing of storage rooms, and entry of apples. To give storage rooms a good airing, the doors should be opened and outside air forced in. Storage rooms must be thoroughly ventilated for several days after the use of disinfectants and precautions should be taken to avoid anyone coming into contact with these products by mistake. Disinfectants are often irritating and thus to avoid discomfort and health problems, protective equipment and clothing should be worn when using them, e.g. safety glasses, breathing mask, and waterproof garments. Activated-carbon air filter prevent odors from developing in the storage rooms. It has been suggested that fungicide-based paint be applied to walls for additional protection (Phillips et al., 1979; Lidster et al., 1988). Ozone and UV radiation are not effective at disinfecting storage rooms. Leaving bins, pallets, and other equipment out in the sun and/or strong wind will partially disinfect them. Fumigants can be used to reach the small hidden corners that cannot be reached by conventional methods. However, this method is only effective when used with wet surfaces.

Rinsing - The use of some disinfectants results in off-odors, which may result in unpleasant tasting fruit after storage. In addition, the long-acting effect of certain disinfectants can corrode materials within the storage structure, as well as equipment. Therefore, proper rinsing is essential when disinfectants are used. Rinsing involves thoroughly spraying all surfaces treated with disinfectants, starting with high areas so that the residues run down to the floor. Any stagnant water must be removed and it is essential to use water of drinking quality so that the storage will not be re-contaminated.

Drying - The goal of drying is to eliminate humidity, which provides ideal conditions for the development of molds and storage rots. If the disinfectant used does not require rinsing, then drying takes place immediately after disinfecting. Drying involves removing any surplus water and giving the storage rooms a good airing. If outside conditions are hot and dry, then outside air can be forced inside. Maintaining a high temperature and low humidity in the off-season can help to reduce the growth of pathogens in the storage.