An assessment of methods to clean citrus fruit surfaces

A move away from harsh chemicals towards more natural or organic postharvest treatments for sanitizing fruit surfaces has prompted interest in alternate sanitizers for cleaning fruit in packinghouses. In this study a comparison was made of some sanitizing methods presently used (e.g. warm water and sodium hypochlorite solutions) with the sanitizing activity of peroxyacetic acid. To assess the initial microflora population on the surfaces of unwashed fruit, oranges were collected from the field and their surfaces washed in sterile buffer solutions. The buffer was analyzed for numbers of microbial organisms, and populations were found to be between approximately log(10) 4.0 and log(10) 6.0 cfu/cm(2) of fruit surface. Organisms from these analyses were isolated for later use. To assess the effectiveness of sanitizers on microbial populations on the fruit surfaces, oranges were picked from the field and surface sterilized in a circulating hot water bath (2 minutes at 85 degrees C). A cocktail of microorganisms previously isolated from the surfaces of oranges was made. These included the pathogens Penicillium digitatum, Geotrichum citri-aurantii and Colletotrichum gloeosporioides. In addition, 2 non-pathogenic yeasts and a bacterium were included to obtain a log(10) 6.0 total concentration of suspended spores and cells. The sterilized oranges were inoculated by dipping them into this spore mix for 30 seconds. The fruit were allowed to air dry for 24 hours and were then sanitized with warm water, sodium hypochlorite (200 ppm, pH 6.5) or peroxyacetic acid (100 ppm). Averaged microflora populations remaining on orange surfaces after treatments were; warm water log(10) 4.1 cfg/cm(2), sodium hypochlorite log(10) 3.3 cfu/cm(2) and peroxyacetic acid log(10) 2.4 cfu/cm(2).