IICAT TREATMENTS TO REDUCE POST-HARVEST DECAY OF FRUITS 



W;illiam J. Bramlage 

 Departnic?nt of P]ant and Soil Sciences 



It has Inns been known that exposure of fruits to a brief period 

 of high tempera txn^e can reduce decay from certain organisms. Until the 

 recent controversies over cliemical residues focused attention on non- 

 chemical disease-control measures, little practical consideration was 

 given this knowledge. But during the past few years, the U.S. Depart- 

 ment of Agriculture has been conducting numerous tests with heat treat- 

 ments, and some of these tests have been quite successful. 



Peaches r'cspond very well to heat treatments. In an early report 

 by V\/.L. Smith, e_t al . (U„S.D.A. Mktg. Res. Rept. No. 643), it was sliown 

 that the organisms Monilinia fructicola and Rlilzopus stolonifer , which 

 cause most of the post-Jiarvest rot of peaches, are very susceptible to 

 heat inactlvation. Most of the ungerminated spores on the fruit surface, 

 as well as the vegetative growth of established infections under the 

 skin of the fruit, were killed by a 3 -minute dip in 130 F water, and 

 subsequent decay was greatly reduced and market life extended. However, 

 the 3-minute dip sometimes Injured the peaches, causing a tan mottling 

 on the skin, and although this injury was not severe, it was objection- 

 able. This report emphasized that a heat treatment must be followed by 

 rapid cooling of the fruit or storage life wou.ld be reduced and hydro- 

 cooling was recommended. 



A recent report by Smith (Proc . Va . State Hort. Soc . 54:95-97.) i-iw 

 recommends the use of a 2\ minute dip in water at 125-128 F. This ex- 

 posure avoids the injury to the fruit and still produces substantia] re- 

 ductions of decay. The time and temperature of the dip are critical; 

 too short an exposiu:-e or too low a temperature does not provide disease 

 control, and too long an exposure or too high a temperature results in 

 injury. Bulk dips of the fruit are practical and effective, and the 

 treatment can readily be applied along the packing line. A hot water 

 dip should be followed by hydrocooling, and it is essential that the hy- 

 drocooling be done sanitarily, that is, the water must contain sufficient 

 chlorine to prevent re-inncul atlon with fungal spores. 



Hot water treatments have been used commercially for 3 years in the 

 Southeast on peaches. . Some earJy results were discouraging, but the 

 problem proved to be uusairitary hydrocooling, not the hot water treatment 

 itself. Witli careful control of time and temperature of dip and of san- 

 itation, decay of peaches is usually markedly rcnhu-'cd by the heat treat- 

 ment. 



Another expej'imental approacli to lieat treatments involves the use 

 of hot air instead of hoL wn tcrr . Holding strawberries at 110° F at 98% 

 relative Juiinidity for 30 iniiuit'cs 1ms greatly rcducet) decay. Such a 

 treatment iniglil pi'ovc coiniiKM'c iu Tl y feasible, h\\\ tliis lias yet to be es- 

 tablished . 



