gap'' reflected a definite physiological state of the fruit, which could prove 
to be a guide to "absolute" maturity in relation to picking for maximum storage 
life. He found that the "point minimal gap'' occurred earliest in the season 
with earliest date of petal fall and latest in season with latest date of petal 
fall. 
Ting (80) reported that, in general, as Rome Beauty apples developed on 
the tree during the period between 140 days (lst pick) and 175 days after full 
bloom (last pick of 6), respiration rate increased slowly, ground color values, 
reducing sugars, and nonreducing sugars increased, and total acidity, alcohol 
insoluble solids, and firmness of fruit decreased. 
Wilkinson (91) described a simple method for following the climacteric 
in apples. His procedure depended on measuring the gas conditions in a closed 
system. He found that production of CO) or ethylene or decrease in 05 could be 
used to indicate state of fruit maturity. Of the three he concluded that the 
measure of 09 with the Beckman Oxygen meter was probably the simplest method. 
Martin (52), working with light and heavy crop trees picked at succes- 
sive maturities, showed that although other criteria of maturation, such as 
diameter, acidity, color change, etc., showed significant differences, the 
respiration per unit fresh weight of fruit was the same for different crop 
levels. 
Sullivan and Enzie (79), trying a technique of correlating expressible 
juice of composite apple samples with various other criteria of maturity, found 
a direct correlation with rate of respiration. They found that at harvest and 
after being stored at 35° F. large Richared and Jonared apples had greater 
respiration rate and higher expressible juice content than small ones. 
(See also section on Ripening and Composition for a discussion of re- 
lation of respiration to maturity and ripening.) 
Acidity and Soluble Solids Determination 
Determination of total acid, pH and soluble solids in apples has been 
found valuable in assessing stage of maturation (43, 10, 44, 51, 53, 94, 92, 
46, 84, 80). 
Martin (53) noted that acid concentration declined continuously during 
maturation, There appeared to be a relation between firmness and acid level. 
Wiley and Thompson (90) pointed out that early harvested apples exhi- 
bited highest amount of total acid and water soluble pectic constituents. They 
found a 0.80 correlation coefficient between shear press reading on raw apple 
slices when harvested and when removed from storage and total pectins of Stay- 
man, York and Jonathan varieties. Of the single tests, titratable acidity, 
shear press, soluble solids, and soluble solids/acid ratio appeared to be most 
important. They found that combinations of these factors gave the best estimate 
of overall grade. 
LaBelle et al. (37) found a high correlation between soluble solids/acid 
ratio and heat unit accumulation in Rhode Island Greening and Baldwin apple 
varieties, The soluble solids/acid ratio changed rapidly prior to and at har- 
vest and had a direct bearing on quality of applesauce, 
Sullivan and Enzie (79) found that expressible juice was directly corre- 
lated with respiration rate and percent soluble solids of Richared and Jonared 
varieties, 
Robertson and Turner (67) present the relationship of total organic acid, 
and malic and citric acids with varying days from full bloom for Granny Smith 
apple. 
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