The first step in household or commercial food processing is the preparation of food using various mechanical processes, such as removing damaged or soiled items or parts of crops, washing, peeling, trimming or hulling. This often leads to significant declines in the amount of pesticide residues in the remaining edible portions (Petersen et al., 1996; Celik et al., 1995; Schattenberg et al., 1996).

WASHING

Household washing procedures are normally carried out with running or standing water at moderate temperatures. Detergents, chlorine or ozone can be added to the wash water to improve the effectiveness of the washing procedure (Ong et al., 1996). If necessary, several washing steps can be conducted consequently. The effects depend on the physiochemical properties of the pesticides, such as water solubility, hydrolytic rate constant, volatility and octanol-water partition coefficient (Pow), in conjunction with the actual physical location of the residues; washing processes lead to reduction of hydrophilic residues which are located on the surface of the crops. In addition, the temperature of the washing water and the type of washing has an influence on the residue level. As pointed out by Holland et al. (1994), hot washing and the addition of detergents are more effective than cold water washing. Washing coupled with gentle rubbing by hand under tap water for 1 min dislodges pesticide residues significantly (Barooah and Yein, 1996). Systemic and lipophilic pesticide residues are not removed significantly by washing. Table (1) shows examples of the effects of washing on the residue levels of different pesticides applied to fruits and vegetables.

PEELING

The outer leaves of vegetables often contain residues of pesticides applied during the growing season. Therefore, peeling or trimming procedures reduce the residues levels in leafy vegetables. Peeling of root, tuber and bulb vegetables with a knife is common household practice. Many examples show that most of the residues concentration is located in or on the peel. Peeling of the RACs may remove more than 50% of the pesticide residues present in the commodity. Thus, removal of the peel achieves almost complete removal of residues, so leaving little in the edible portions. This is especially important for fruits which are not eaten with their peels, such as bananas or citrus fruits. Reynolds (1996) showed that peeling or trimming of carrot reduced the residues of chlorfenvinphos, primiphos-methyl, quinalphos, triazophos resulting a transfer factor of 0.2. However, the peel from commercial peeling processes can be used as animal feed or for the production of essential oils (citrus) or pectin (citrus, apple etc.). For such industrial processes, it is important to realize that especially non-systemic surface residues are often concentrated in the peel. For systemic pesticides, peeling may not be as effective as shown by Sheikhorgan et al (1994). After application of thiometon on cucumbers, no reduction of residue levels could be detected in the peeled cucumbers. Under the Codex Alimentarius, as in other international standards, MRLs refer to the whole fruits, which is appropriate for assessing compliance with GAP. These MRLs are of limited significance, however, in assessing dietary exposure to pesticides from fresh fruits, which are peeled (Holland et al.,1994).