Lawrence and Groves (40) pointed out that available methods for deter- 
mination of pectin in apples are not particularly satisfactory for routine use. 
They presented a modified calcium pectate method and a new photometric method 
based on the absorption at 295 nm of a pectin sample heated in a boiling water 
bath with nine volumes of 84 percent sulfuric acid. 
Gee, Reeve, and McCready (22) introduced a new direct method for follow- 
ing the esterification of pectic substances in fruits at different stages of 
their development. They showed that the degree of esterification increased to 
nearly 100 percent with the onset of optimum maturity but decreased markedly as 
both Gravenstein and Golden Delicious apple varieties became overmature and 
softer. 
Griffin and Kertesz (23) after a 5-year study with Webster apple variety 
found no conclusive evidence that protopectinase and pectin - polygalacturonase 
(pectinase) actually occur in the apple. Their results indicated that during 
maturation and softening of apples the tensile strength of the tissue and pro- 
portion of total pectic constituents decrease and the proportion of water- 
soluble pectic materials increases. They concluded that while it appears that 
both protopectinase and polygalacturonase are absent in apples, the functions 
attributed to both enzymes may be performed by nonenzymatic agents. 
Woodmansee, McClendon, and Somers (92) found in the Stayman variety a 
significant decrease in total pectin (on a fresh weight basis) from the unripe 
to overripe stage while for "soluble" pectins, crude fiber, and protein no 
consistent trends could be observed. A characterization of total and "soluble" 
pectins showed that ripening of fruits was associated with decrease in apparent 
equivalent weight and in degree of esterification. 
Wiley and Thompson (90) found the pectic contents of raw apples of vari- 
ous maturity levels were significantly different, with early maturity apples 
exhibiting the highest amounts of total, acid soluble, and water soluble pectic 
constituents. Total pectins were more closely related to raw apple texture, 
and acid soluble pectins were more closely related to firmness and wholeness of 
canned slices. 
Kertesz, Eucare, and Fox (32), studying apple cellulose, found that 
apples that were originally firm softened more in storage than those that were 
less firm. -Their results indicated that cellulose concentration is a factor in 
apple firmness at time of picking but that neither changes in amount nor in 
quality of the cellulose are involved in softening that occurs in storage. 
Truscott and Wickson (82) and Simpson (72) found considerable changes 
in viscosity of fruit juice measured at intervals before commercial harvest. 
They suggested juice viscosity as a useful indicator of proper picking maturity. 
Working with Duchess variety, Truscott and Wickson observed that changes in 
viscosity of harvested fruit ripened in the laboratory essentially paralleled 
those in similar fruit maturing on the tree. 
(See also section on Ripening and Composition.) 
Literature Cited for Harvest Maturity 
iy Aubert. Pe 
1950. The Relation Between Fruit Quality and Time of Picking (Apples) 
Rev. Romande Agr. Vitic. and Arbor. 6:54-56 and 61-63. 
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