Mealiness and pectolytic activity in peaches and nectarines in response toheat treatment and cold storage

'Elegant Lady', 'O'Henry' and 'September Sun' peaches [(Prunus persica (L.) Batsch (Peach Croup)] and 'Summer Bright' and 'Summer Grand' nectarines [( Prunus persica (L.) Batsch f. nucipersica (Nectarine Group)] heated to a se ed surface temperature of 47.2 degreesC over a period of 4 hours developed mealy flesh sooner and to a much greater extent than nonheated fruit follow ing cold storage at 5 degreesC for 1 to 3 weeks. Exo- and endopolygalacturo nas activities were reduced following 3 to 4 hours of heating and may have been responsible for the increased mealiness, Mealiness often developed in defined regions rather than throughout the entire fruit. Comparison of juic y and mealy regions within individual fruit revealed that mealy regions con tained 65% and 86% less exo- and endopolygalacturonase activity, respective ly, than juicy regions, whereas pectinmethylesterase activity was unchanged . Extractable protein was reduced by >50% in the mealy regions of the fruit . Intermittent warming periods of 24 hours at 20 degreesC at weekly interva ls during storage at 5 degreesC were less effective in reducing mealiness i n heat-treated than in control fruit. It is important that future work with heat treatments and stone fruit closely monitor potential effects on this disorder to avoid loss of market quality following treatment.