CHEMICAL CHANGES ASSOCIATED WITH THE RIPENING OF APPLES AND TOMATOES^a

Abstract

The ripening and eventual softening of fruits is a natural phenomenon. More knowledge concerning the chemical changes associated with ripening is necessary to improve the present handling techniques for maintaining the quality of fruits in fresh market channels. In this study, the chemical changes of several constituents in whole apples and tomatoes were ascertained at the unripe, ripe, and overripe stages of maturity to help explain the softening process.Objective measurements of fruit quality have as their goal the establishment of precise specifications to characterize any given lot of material. For example, measurements such as alcohol-insoluble solids, crude fiber, protein, acid content, and fruit pressure tests have been used by many workers for quantitative evaluation of the nutrition and quality levels of fruits and vegetables (3,5,10, If, 12,18,20,21,26). For many years, changes in the quantity and type (16) of pectic substances have been considered to play a role in ripening and firmness of fruits (7,13,15,19,22,25,27,28). Some evidence suggests that the pectic components of fruits may be hydrolyzed to soluble forms, with accompanying demethylation, and finally to smaller, less complex, units ( 4 ) . The mechanism involved in the transformation of these pectic substances as fruits mature, as well as their function in providing firmness to plant tissues, has not been clearly demonstrated. Older methods for extracting and analyzing pectic substances from plant material have been not entirely free from criticism (15). Recent methods (24) use less drastic extractions with little or no degradation, possibly yielding a product comparable to pectin in situ.This study seeks to provide fundamental information, using reliable methods, for a quantitative evaluation of some chemical changes associated with the maturation process of apples (Red Delicious and Stayman) and tomatoes (Brookston and Valiant). Especial attention is given to the determination and characterization of the pectic constituents. EXPERIMENTAL MATERIALS AND METHODSApple and tomato fruits. The fruits were obtained from orchards and plots at the University Farm during the 1953 and 1954 seasons. They were carefully harvested at the unripe and ripe stages of maturity with the ripe stage allowed to become overripe in the laboratory. Extremely large and small specimens were excluded as well as those with cracks or blemishes. The selection of fruits for analyses at the 3 stages of maturity was on the basis of skin color and firmness. Unripe fruits were full size but essentially green and were hard. Ripe fruits had full color change and were firm. Overripe fruits were similar to ripe, except senescence and softening had taken place, hence special care was required in handling them.

The Extraction of Pectins from Apple Marc Preparations

“…It is interesting too that the degree of esterification is higher in the latter case. Doesburg (1959b) and Woodmansee et al (1959) recently reported that, contrary to previously published observations, neither the degree of polymerization nor the degree of esterification of apple pectins changes materially during ripening and storage.…”

“…This variety was selected because it was investigated fairly extensively by Eggenberger (1949) and used by Schlubach and Hoffmann-Walbeck (1949). Apples as a fruit have been investigated more thoroughly than other fruits (Hulme, 1955;Smock and Neubert, 1950 ;Wiley and Stembridge, 1961 ;and Woodmansee et al, 1959).…”

Role of Pectin Methylesterase in Firmness of Canned Tomatoes

“…Protopectin is the insoluble parent pectic compound of natural occurrence. In the ripening of fruits, the insoluble protopectin is changed gradually to soluble r 583 1 584 PECTIN METHYLESTERASE IN CANNED TOMATO FIRMNESS pectin by hydrolysis and depolymerization (Woodmansee and McClendon, 1959). Appleman and Conrad (1927) studied transformations in pectic substances during maturation and during canning.…”

Irradiation‐induced Textural Change in Fruits and Its Relation to Pectin Metabolisma

“…of fruits during normal development (Postlmayr et al, 1956;Woodmansee et al, 1959;Esau et al, 1962). It was found that fruit development is accompanied by an increase in water-soluble pectin substances and a decrease in protopectin content.…”