Pectic substances in the cell wall have long thought to
be responsible for the textural changes in fruit during
ripening and senescence. Compositional variation within
the pectic macromolecules could affect the external
characteristics of the fruit. Strawberries undergo adverse
quality changes such as softening and juice loss after
freezing and subsequent thawing. To obtain a desirable
cultivar that retains sound textural qualities after
processing has long been an objective of both strawberry
breeders and food processors.
The fruit of Selva is exceptionally firm and some may
consider it to be too firm. The purpose of this study was
to investigate the compositional factors that would account
for the unusual textural qualities of the Selva
strawberry. Two major Oregon-grown commercial cultivars,
Totem and Benton, were also included to facilitate
comparisons between pectic substances and textural profiles
of strawberry fruits.
Fruit firmness was measured by the resistance of berry
halves to shear and the amount of juice released after
thawing. Very firm characteristic of Selva fruit was
documented in that the shear value of thawed Selva was
equal to fresh Totems and even greater than that of fresh
Bentons. Juice-release after thawing was lowest in Selva
samples. The quantity of acetone-insoluble solids obtained
from freeze-dried powders of strawberry fruits was high for
Selva and Benton, and low for Totem. Selva contained
higher amounts of total soluble polyuronides and lower
quantities of hemicellulose fraction as compared to Totem
and Benton. Elution profiles of water-soluble polyuronides
and chelator-soluble polyuronides from DEAE ion-exchange
chromatography showed that Selva samples had a longer
retention time and wider peak distribution, suggesting that
its pectin species were of higher molecular weight and/or
charge than Totem or Benton samples. The elution profile
of ripe Selva was similar to that of underripe Totem and
Benton. Ratios of uronic acid to rhamnose, indicating the
extent of kinking and branching, were high for Selva and
Totem in the water-soluble fraction and for Selva in the
chelator-soluble fraction. Arabinose and galactose levels
were relatively high in Selva base soluble polysaccharides,
indicating that an arabinogalactan may be present in the
hemicellulose fraction. This arabinogalactan may play a
role in connecting the rhamnogalactan to the glycoprotein in the cell wall. / Graduation date: 1987
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27214 |
| Date | 22 May 1986 |
| Creators | Lin, Ben-lin |
| Contributors | Wrolstad, Ronald E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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