Thesis (Ph. D.)--Northeastern University, 2008. / Title from title page (viewed March 26, 2009). Graduate School of Arts and Sciences, Dept. of Mathematics. Includes bibliographical references (p.80-82).

Digitized by Kansas State University Libraries / End of abstract missing.

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Maintaining the structural integrity of cell walls largely determines the texture of fruit products during freezing processes. Strawberries undergo major textural changes when frozen, and varietal differences in quality after thawing are not readily predicted from mechanical and sensory testing of the fresh fruit. The objectives of this study were to develop a quantitative sensory texture profile of three strawberry varieties, individually quick frozen (IQF), to determine differences in cell wall composition and structure, and to relate the sensory and compositional profiles to differences in instrumental values of firmness. Intervarietal differences in IQF strawberries of Benton, Totem, and Selva varieties were examined and a summary of major findings follows. Drip-loss measurements, and work-of-compression on thawed berries were correlated to sensory ratings. Puree viscosity was highest in Selva samples, lowest in Bentons and shows potential as a screening test for strawberry cultivars. Firmness of thawed, whole Selva berries was rated 4x and 2x as compared to Bentons and Totems, respectively, via sensory profile evaluation with magnitude estimation scaling. Fractionation of fruit cell walls showed Selva had the highest percentages of acetone-insoluble solids. Total pectin content and absolute weight percentages of uronic acids and neutral sugars did not show major differences. Ratios of: 1) uronic acids to neutral sugars, 2) uronic acids to rhamnose, and 3) neutral sugars to rhamnose followed trends of increasing with varietal firmness in water-soluble polysaccharides (WSP) and decreasing in chelator-soluble polysaccharides (CSP). Ratios of galactose to arabinose decreased with increasing firmness scores in WSP and increased in CSP. Selva had the highest amount of high molecular-weight polymers in water-soluble and chelator-soluble polysaccharides. / Graduation date: 1986

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

published_or_final_version / Mathematics / Master / Master of Philosophy

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This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

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