Removal of soil and chemical spray contaminants from tomatoes during industrial washing

Abstract

Chemical spray residues on unprocessed tomatoes are known to be above limits recommended by World Health Organization (WHO) and Food and drug Act (FDA) at Kenya. Soil contamination on tomatoes delivered for processing is substantial and water shortages are a problem in tomato processing. A study was undertaken to investigate the effectiveness of a commercial tomato washing system on removal of contaminants, water usage and rate of washing with an aim of Identifying areas of improvement. samples of tomatoes were analyzed for chemical and soil contaminants before and after washing through the system. The effect of soil concentration in the wash water on the effectiveness of the water to remove soil from tomatoes was also investigated. Water usage and the rate of washing tomatoes by the system were also determined. Chemical residues as dithiocarbamates on unwashed tomatoes ranged from 0.02ppm to 2.00 ppm. Washing reduced the chemicals to between 0.45 and 0.00 ppm. Amounts of chemical residues remaining on washed tomatoes were negatively correlated to initial chemical concentration on dirty tomatoes. Amount at soil on dirty tomatoes ranged tram 58.6 ppm to I,115.6 ppm. Washing reduced the soil to between 9.6 ppm and 191.3 ppm. Amount of soil removed from tomatoes was negatively correrated to initial amount of soil on unwashed tomatoes. Soil removed from tomatoes showed an exponential decrease with increase of soil concentration in the wash water and an exponential increase with initial soil load on tomatoes. overall batch washing rate averaged 5.2 ton/h while mean batch washing rate averaged 11.8 ton/h. Water used for all operations of processing averaged 5000 litres /ton of tomatoes. with about 66 percent going to the washing operation. Analysis of data on water consumption and tomato flow rate through the system revealed a potential of reducing water usage by at least 400 litres/ton of tomatoes processed and increase. batch washing rate by at least 7'i if the system is modified to include water recirculation.