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  • Author or Editor: Ruth Ben-Arie x
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Abstract

The compositional changes occurring in the cell wall of maturing and ripening pear fruits (Pyrus communis L. cv. Spadona) were examined in relation to the activity of pectolytic enzymes and cellulase. Fruit softening was accompanied by a rise in water and EDTA-soluble pectic fractions, and in free galacturonic acid. The latter reached peak levels after 15 weeks of cold storage and thereafter declined. Simultaneously with the degradation of pectin there was a 4 to 5 fold increase in polygalacturonase activity, but pectin-methyl-esterase activity declined as it did throughout the harvest and storage seasons. Cellulase activity which was present also in immature fruit increased 2 to 3 fold as the fruit softened, but in the last stages of softening it decreased. Treatment of the firm fruit with partially purified preparations of cellulase and polygalacturonase both caused a dissolution of insoluble pectin material.

Open Access

Abstract

Pomegranate (Punica granatum L. ‘Wonderful’) fruit reached horticultural maturity for commercial harvest when the soluble solids content (SSC) attained a fairly constant level of 15%. The level of titratable acidity (TA) varied from one location to another and from one year to the next but also generally remained stable at the same time that the SSC reached 15%. After harvest, there was no further change in either SSC or TA at 20°C, but redness of the juice continued to increase in intensity up to and after harvest. The respiration pattern of the mature fruit was of the nonclimacteric type, with only traces of ethylene evolved on occasion. Ethylene treatment of the fruit caused a rapid transient rise in CO2 evolution but no changes in SSC, TA, and fruit or juice color. A pseudo-climacteric pattern of respiration was found in very young immature fruit. The respiration rate of dehisced arils paralleled that of the intact fruit, but there was no response to exogenous ethylene treatment. Ethylene evidently stimulated the CO2 output only of the fruit rind.

Open Access

`Anna' and `Granny Smith' apples (Malus domestics Borkh.) that were held at 38C for 4 days before storage at 0C not only were firmer than controls upon removal from storage, but also softened more slowly during shelf life at 17C. Skin yellowing and loss of acidity attendant upon the heat treatment were not prevented by dipping fruit in 2% CaCl2 before heating. Both heat-treated and control fruit softened at the same rate upon exposure to ethylene at 100 μl·liter-1 upon removal from storage. The insoluble pectin content of cortical tissues was higher in heat-treated fruit than in controls after 10 days at 17C, while soluble pectin levels were lower. Arabinose and xylose levels were lower in cell walls from heat-treated cortical tissue, but the treatment had no effect on loss of galactose residues during shelf life.

Free access

In `Jonathan' apples grown in Israel, the incidence of senescent breakdown after 5 months of storage at 0C was not correlated with total or water-soluble Ca content at harvest. Likewise, no other assayed component of the water-soluble or total mineral content (P, Mg, K) of the fruit pulp at harvest correlated with the disorder after storage. After storage, a general decrease in the solubility of Ca was observed. However, this decrease was not uniform in all fruit and, as a result, the correlation between water-soluble and total Ca content, which was high at harvest, diminished after storage. Water-extractable Ca from stored fruit was negatively correlated and water-soluble K/Ca was positively correlated with the incidence of senescent breakdown, whereas total Ca was not correlated.

Free access

A prestorage heat treatment of 38C for 4 days applied to `Granny Smith' apples (Malus domestics Borkh.) before regular air storage at 0C inhibited the development of superficial scald. Heat-treated apples stored for 3 months had superficial scald levels similar to diphenylamine (DPA)-dipped apples, while all nontreated control apples had scald. After 5 or 6 months of storage, this inhibition of scald development by prestorage heat treatment declined. The prestorage heat treatment inhibited the accumulation of α-farnesene and conjugated trienes in apple cuticle during storage, while DPA inhibited only α-farnesene oxidation. This treatment may be a substitute for chemical treatments against scald not only for short-term storage of `Granny Smith' but possibly also for other scald-susceptible apple cultivars.

Free access

Harvested nectarine fruit [Prunus persica (L.) Batsch `Flavortop'] were held for 5 days at 20 °C, or stored at 0 °C either immediately (control), or after 2 days at 20 °C (delayed-cooling). Observations were conducted after removal from storage for 1, 3, or 5 weeks and a shelf life of 5 additional days at 20 °C. After 5 weeks storage, 87% of control fruit developed woolliness (mealiness in texture accompanied by dry tasting fruit as a result of reduced juice content), while only 7% of delayed-cooling fruit showed signs of woolliness. Firmness of fruit in the delayed-cooling treatment was less at the beginning of ripening than control fruit, but after shelf life in both treatments, fruit reached the same final softness. Expressible juice was lower in woolly fruit (46%) than in healthy fruit (65%). Along with woolliness, viscosity of the resuspended alcohol insoluble residue (cell wall material) of expressed juice increased, implying accumulation of large molecular-weight polymers. The high performance liquid chromatography profile confirmed there were more large pectin polymers (2000 to 76 Ku) in the cell wall components of juice from woolly fruit and a lower arabinose content in these polymers reflected greater side chain removal from pectins in the juice of woolly fruit. Accumulation of larger sized pectin polymers along with high viscosity correlated with lower polygalacturonase activity in woolly fruit. Degradation of soluble pectin released into the juice of woolly fruit may have been impeded by repressed polygalacturonase activity.

Free access

Most `Flavortop' nectarines [Prunus persica (L.) Batsch (Nectarine Group)] that were placed directly into 0 °C storage developed chilling injury after removal, while preconditioning fruit for 2 days at 20 °C (delayed storage) reduced chilling injury substantially. Chilling injury was expressed as the development of a dry, woolly flesh texture during ripening. Delayed-storage fruit were as firm as control fruit when placed in storage, but softened more during storage. Analysis of cell wall components showed that in woolly fruit a higher percentage of pectin was retained in the sodium carbonate fraction, although during ripening polymers in this fraction decreased in molecular mass (Mr). In the guanidine thiocyanate hemicellulose fraction of woolly fruit, the associated pectin and hemicellulose remained as large polymers, while in delayed-storage fruit they decreased in Mr during ripening. Endo-polygalacturonase (PG), pectin esterase (PE), and endo-glucanase (EGase) activities of delayed-storage fruit were the same as control fruit at the beginning of storage, although exo-PG was higher. However, differences were observed at the end of storage. Endo-PG activity was lower in control than delayed-storage fruit at the end of storage while PE activity was higher, and exo-PG and EGase activities were similar. These differences in activity were not reflected in the mRNA abundance of the respective enzymes. Endo-PG and PE message was similar in all fruit at the end of storage and increased during ripening, while EGase message was low at all times except in control fruit after storage and development of woolliness. Prevention of chilling injury by delayed storage appears to be due to the ability of the fruit to continue a progressive, slow cell wall degradation in storage which allows normal ripening to proceed when the fruit are rewarmed. Regulation of the softening process did not appear to be by enzyme synthesis, since mRNA levels of the enzymes did not correspond with enzyme activity.

Free access