Articles
THE ROLE OF POSTHARVEST HANDLING AND PEACH SKIN DISCOLORATION
Research conducted at various packing houses in southern New Jersey has shown that this disorder originates in the hydrocooler and the percent of fruit that becomes discolored increases throughout the packing house operation.
Water analysis indicated that the pH was 4.8 with iron levels of 80 ppm.
The use of calcium hypochlorite, at a chlorine concentration of 120 ppm total chlorine, significantly reduced this disorder.
Analysis of the hydrocooler water, after the addition of calcium hypochlorite, indicated that the pH had risen from 4.8 to 6.4 and the iron levels had dropped from 80 to 3 ppm.
Two laboratory experiments were designed to evaluate the affect of iron on discoloration.
The first experiment consisted of keeping the iron concentration constant at 100 ppm and decreasing pH from 7.0 to 4.5. In this experiment discoloration did not appear until pH 5.5 and increased in severity to pH 4.5. At pH 4.5 all fruit became black within 15 minutes of treatment.
The other experiment involved keeping the pH at 6.5 and increasing the iron concentration from 0 to 100 ppm.
Discoloration started to appear at 30 ppm iron and increased until all fruit became discolored at 75 ppm iron.
The form of iron seems to be the important factor in discoloration.
Above pH 6.0 iron exists as Fe+3 or ferric iron, at pH’s below this iron exists as Fe+2 or ferrous iron.
It is ferrous iron that seems to trigger discoloration in peaches and nectarines.