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THE STARCH TEST GUIDE FOR APPLE MATURITY 



William J. Bramlage 

 Department of Plant and Soil Sciences 



Once apples begin to ripen, a large portion of the potential 

 benefit from CA storage is lost, since CA has the capability of 

 suppressing the beginning of ripening. It is therefore very help- 

 ful in harvest management to know which apples are and which are 

 not yet ripening. The most precise measure of the onset of ripen- 

 ing is through ethylene analyses since ripening is accompanied by 

 a huge burst of ethylene production. Unfortunately, methods for 

 measuring ethylene production during commercial harvesting have 

 been hampered by many technical difficulties and few observers 

 feel that ethylene measurements are commercially feasible today. 



It has long been known that as apples ripen, their starch is 

 rapidly converted to sugar. Starch concentrations, starch pat- 

 terns, and starch conversion rates vary among varieties and are 

 influenced by environmental conditions, yet for some varieties 

 the changes can be very clear and dramatic. Mcintosh is such a 

 variety. At the University of Guelph, in Ontario, extensive stu- 

 dies led to the development of a very simple procedure for 

 measuring the progress of ripening in Mcintosh by following the 

 loss of starch from the fruit. 



The test is based on the fact that starch, but not sugar, 

 will react with iodine to form a blue-black color. To perform 

 the test, a random sample of 10 to 20 fruit are cut open and half 

 of each apple is immersed briefly in a shallow dish containing an 

 iodine solution. The apples are allowed to sit a minute or 2 to 

 allow the color to develop, and the color is then matched to a 

 chart which tells whether the apples were "immature," "mature," 

 or "overmature." For "finer tuning," each of these classes is 

 subdivided into 3 numerical classes. 



This very simple, rapid test allows growers to see for them- 

 selves the stage of development of their fruit. Periodic sampling 

 of fruit from different blocks can give them an ongoing view of 

 where ripening is occurring fastest, and help in determining when 

 and where to pick. The test also can be a very important guide 

 in deciding which fruit should be directed into Ck storage. Cer- 

 tainly, batches of fruit in which a large percentage of the 

 apples are scoring as "overmature" should not be placed in CA, as 

 they are too ripe to hold up during and following storage. 



