July 15. 1919 Carbohydrate Metabolism in Green Sweet Corn 151 



SUMMARY 



The data recorded in this paper apply to Stowell's Evergreen corn, 

 picked in the typical milk or best eatable stage and having a water 

 content of approximately 80 per cent. 



A method was devised by which the rate of sugar loss from green 

 sweet com could be determined for consecutive 24-hour periods of storage 

 by comparing analyses of corn from the same ear. 



The depletion of sugar in green sweet corn after it is separated from 

 the stalk does not proceed at a uniform rate but becomes slower and 

 slower until finally the loss of sugar ceases when the initial total sugar 

 has decreased about 62 per cent and the sucrose about 70 per cent. 

 Calculated on the basis of original moisture, the corn contained, 

 when the depletion of sugar ceased, approximately 1.5 per cent total 

 sugar as invert sugar, 0.7 per cent sucrose, and 0.8 per cent free-reducing 

 substances. The actual percentage of sugars would depend upon the 

 amount of water in the corn after storage. Under the experimental 

 conditions there was very little change in the percentage of water 

 in the com employed in this work. 



Reversibility of the chief processes involved in the sugar depletion, 

 resulting in an equilibrium between the rate of sugar loss and the rate 

 of sugar formation, would account for the cessation of actual sugar loss. 



During the early periods of storage, the falling off in the rate of 

 actual sugar loss is due to mass action. When the equilibrium is nearly 

 reached the counter reaction, that is the formation of sugar, also tends 

 to slow up the rate of sugar loss. Any destruction or decrease in the 

 quantity of enzymes present would produce a falling off in the value 

 of the velocity constant, with a consequent decrease in the rate of 

 actual sugar loss. There is no evidence that this occurs up to 30° C. 

 At 40° there is actual destruction of the enzymes or other altera- 

 tion on the system. The rate of actual sugar loss must not be con- 

 fused with the velocity constant. 



Raising the temperature simply hastens the attainment of the equilib- 

 rium positions, which seem to be about the same for all temperatures. 

 At 30° C, 50 per cent or most of the total sugar loss occurs during the 

 first 24 hours of storage. At 20°, 25 per cent, and at 10°, or good 

 refrigerator temperature, only about 15 per cent is depleted during the 

 same period. 



Relative rates at different temperatures, of processes that become 

 slower and slower until an equilibrium is reached, can be accurately 

 determined throughout this entire course only by comparing the times 

 required to bring the process to the same stage at all temperatures. 

 In order to make this comparison possible the experimental results 

 were interpolated by a simple ■ graphic method. The temperature 

 coefficient was then obtained by comparing the reciprocals of the times 



