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B. Fils-Lycaon and M. Buret

Pectic fractions soluble in water, oxalate, or hydrochloric acid were prepared from an alcohol-insoluble residue of cherry (Prunus avium L., `Bigarreau Napoléon') tissue. Galacturonic acid and neutral sugar contents were measured during the ripening and overripening of fruit. Fruit firmness was also determined. The changes occurring during fruit development gave prominence to three physiological stages and suggested the progressive degradation of the middle lamella and primary cell wall. The firmness measurement was related to the equilibrium between the relative parts of these pectic fractions.

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Joshua D. Klein, Susan Lurie, and Ruth Ben-Arie

Contribution 2605-E from the Volcani Center-ARO. We thank Ken Gross and Norman Livsey of the U.S. Dept. of Agriculture Horticultural Crops Market Quality Laboratory, Beltaville, Md., for generous assistance in measuring neutral sugars. J.D. Klein

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Elizabeth J. Mitcham and Roy E. McDonald

`Keitt' and `Tommy Atkins' mango (Mangifera indica L.) fruit were evaluated for selected ripening criteria at six ripening stages, from mature green to overripe. `Tommy Atkins' mangos developed more red and yellow pigmentation (CIE a* and b*) in peel and mesocarp tissues than `Keitt'. The outer mesocarp of `Keitt' remained firm longer than `Tommy Atkins', and the inner mesocarp was softer than the outer at each stage in both cultivars. Cell wall neutral sugars, particularly arabinosyl, rhamnosyl, and galactosyl residues, decreased with ripening in both cultivars. `Keitt' had more loosely associated, chelator-soluble pectin, accumulated more soluble polyuronides, and retained more total pectin at the ripe stage than `Tommy Atkins'. Both cultivars had similar polygalacturonase (EC 3.2.1.15) activity which increased with ripening. The amount and molecular weight of cell wall hemicellulose decreased with ripening in both cultivars. These data indicate that enzymatic and/or nonenzymatic processes, in addition to polygalacturonase activity, are involved in the extensive softening of mango fruit.

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W.R. Miller, E.J. Mitcham, R.E. McDonald, and J.R. King

Postharvest quality of `Climax' rabbiteye blueberries (Vaccinium ashei Read) was evaluated after exposure to dosages of 0, 0.75, 1.5, 2.25, or 3.0 kGy gamma irradiation (0.118 kGy·min-1) and after subsequent storage. Irradiation did not affect weight loss, but irradiated berries were softer than nontreated berries. There was also a trend toward increased decay as dose increased. Irradiation had no effect on powdery bloom or surface color; total soluble solids concentration, acidity, and pH were affected slightly. Flavor preference was highest for nonirradiated berries and generally declined as dosage increased. Irradiation at 2.25 and 3.0 kGy resulted in increased levels of xylosyl residues in cell walls, and xylosyl residues were the most abundant cell-wall neutral sugar detected in blueberries. There was no evidence of cell wall pectin loss in irradiated berries. Irradiation at 21.5 kGy lowered the quality of fresh-market `Climax' blueberries.

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Noboru Muramatsu, Toshio Takahara, Kiyohide Kojima, and Tatsushi Ogata

Various species and cultivars of citrus were studied to determine the relationship between texture and cell wall polysaccharide content of fruit flesh. Among those tested cultivars, navel orange (Citrus sinensis Osbeck) and hassaku (C. hassaku Hort. ex Tanaka) were firmest, `Fukuhara orange' (C. sinensis Osbeck) was intermediate, and satsuma mandarin (C. unshiu Marc.) was softest. There was a 3-fold difference in firmness among the 12 citrus cultigens measured. Cohesiveness values ranged from 0.30 to 0.49 and were not correlated with fruit firmness. Sugar content in each cell wall fraction was highest in the water and EDTA fractions, followed by the hemicellulose fraction, and was lowest in the cellulose fraction. Correlation coefficients between firmness and sugar content ranged from 0.69 to 0.88 and were highest in the cellulose fraction. This study suggests that firmness of fruit flesh among the cultigens is influenced by cell wall polysaccharide composition. Chemical name used: ethylenediaminetetraacetic acid (EDTA).

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Jaroslav Ďurkovič, František Kačík, Miroslava Mamoňová, Monika Kardošová, Roman Longauer, and Jana Krajňáková

(A 1371 /A 2884 )] according to Nelson and O’Connor (1964b) . Determinations of polysaccharide content and neutral sugar composition. Total content of polysaccharides (i.e., holocellulose) was determined using the method of Wise et al. (1946

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Guiwen W. Cheng and Donald J. Huber

Softening and liquefaction of `Solar Set' locules was studied by examining cell wall polysaccharides during fruit developmental stages (FDS) of immature green, mature green and breaker. Ethanol insoluble solids (EIS) were sequentially extracted by H2O, CDTA, and Na2CO3 solutions. The chromatograms of gel filtration among the same-solution extracts of EISs from three FDS were similar. Gradient DEAE also yielded similar patterns among FDS in each extraction solvent, even though the patterns of Na2CO3 extracts differed from those of H2O and CDTA extracts. The mole ratio of total polyuronides decreased for Gal, Ara, and Xyl at later FDS in both EIS and in all extracted polymers. Gal had the highest mole percentage of total neutral sugars, followed by Ara, Xyl, and Rha. While the mole percentage of neutral sugars for Gal, Rha, Ara, and Xyl were relatively similar among FDS in H2O extracts, those in CDTA and Na2CO3 extracts either increased or decreased, depending on individual neutral sugar. SDS-PAGE showed increased density in locule-tissue proteins, especially one with a molecular weight of less than 20 kDa, during later FDS. Results indicate that pectin depolymerization was limited and major neutral sugars commonly composing side chains showed a net decrease.

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Supreetha Hegde and Niels Maness

Peach fruit softening appears to be associated with changes in cell wall polymers, particularly pectins and hemicelluloses. To determine changes of cell wall polymers associated with peach fruit softening, we conducted sequential extractions of pectin and hemicellulose from softening fruit. A more tightly bound hemicellulose fraction contained considerable amounts of pectin associated sugars. This fraction was separated into charged and neutral fractions, using anion exchange chromatography, and then fractionated into two apparent molecular weight classes by size exclusion chromatography. Virtually all of the charged fraction eluted in the higher apparent molecular weight fraction. The neutral sugar fraction segregated into both apparent molecular weight size classes, with a redistribution from the large to the small size class during softening. This redistribution was accompanied by changes in neutral sugar composition. A possible relationship between changes in this fraction and fruit softening will be discussed. Supported by USDA grant 92-34150-7190 and the Oklahoma Agricultural Experiment Station.

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JD Klein, J Hanzon, PL Irwin, S Lurie, and N Ben Shalom

Prestorage heating of apples lead to enhanced retention of fruit firmness of as much as 10 N upon removal from storage, compared to unheated fruit. Further enhancement of firmness retention was obtained by dipping fruit in 2-3% calcium chloride after heating prior to storage. Cortical tissue of heated fruit had more insoluble and less water soluble pectin than unheated fruit, although the total pectin content was similar in both treatmenats. During the heat treatment neutral sugars were lost from the pectic fractions, with no accompanying decrease in galacturonic acid. No effect of heat treatment on degree of methyl esterification was observed in pectic fractions or in critical-dried whole tissues, using colorimetric and NMR techniques, respectively. Treatment differences in dissolution of the middle lamella were not observable in electron micrographs. We suggest that loss of neutral sugar side chains during the heat treatment may have lead to closer packing of the pectin strands and in turn hindered enzymatic cleavage during and after storage.

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Y. Liu, B.S. Patil, H. Ahmad, and D.T. Gardiner

Pectin is a class of complex polysaccharides that function as hydrating agents and cementing materials for the cellulose network. Pectin has various health benefits, such as decreasing serum cholesterol levels, alleviating diabetes mellitus, and preventing cancer. It has been reported that the cancer prevention effect is closely related to the structure of pectin (galactose-rich, molecular weight <10,000, and methylation degree 50% to 70%). This study was conducted to investigate the variation of grapefruit pectin content due to harvest time. `Rio Red' grapefruit on sour orange rootstock grown at Texas A&M Univ.-Kingsville Citrus Center were harvested every 2 months and analyzed for pectin content, galacturonic acid concentration, methylation degree, and neutral sugar composition. Results showed that lamella contains more pectin than flavedo and albedo. In the lamella, the edible section, the uronic acid content ranged from 85% to 90% from August to April the following year. Methylation degree increased from August (31.89%) to April (46.99%). Total neutral sugar content of lamella pectin decreased from 110.54 to 61.77% mg·g -1. Galactose, arabinose, and rhamnose are the major sugar contents of pectin (85%), and glucose content increased with the season from 3.14 to 13.34 mg·g-1. Molecular weight of pectin was also determined.