Thesis (Ph.D.) - University of Queensland, 2002. / Includes bibliography.

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

The need to replace the present methods of rating the acceptability of a manufacturer's lot of strawberries is indicated. Work has been done towards adapting and developing laboratory techniques for this purpose. The quality factors checked upon were the state of maturity, the effectiveness of processing work, and the freedom from adulteration. In connection with the maturity of the strawberries a color technique is outlined, some factors of the growing conditions are introduced, and a relationship is shown between these and the aroma. The residues of dirt and insects are checked against a classification of the processing plants in showing the quality of preparation. Mold and included water are considered under adulteration. New methods are outlined for preparing the sample, counting the insects, estimating dirt, and evaluating maturity by color. / Graduation date: 1954

Enzymic systems able to hydrolyze the compounds forming the supporting structure of plant tissues have a major effect upon the texture of fruit products. The objective of this thesis was the development of a theory to explain the textural changes in fresh and processed strawberries. The presence of pectinolytic enzymes and the substrates upon which they act were studied. In addition the activity of cellulase was investigated. The following conclusions were made: 1. An endopolymethylgalacturonase exists in Northwest strawberries which catalyzes the hydrolysis of pectins, pectates and protopectins. 2. The strawberry endopolymethylgalacturonase indicated a maximum activity at pH values between 4.5 and 5.5. 3. The degree of methylation of the substrate did not appear to have an influence upon the activity of the enzymes. This enzyme demonstrated the same rate of action upon Na pectate and citrus pectin. 4. Sodium chloride solutions at concentrations up to 0.50 M and calcium ion at concentration 0.01 M did not show any effect on the activity of the strawberry endopolymethylgalacturonase in citrate buffer at pH 5.0. 5. The strawberry endopolymethylgalacturonase was inactivated after heating at 212°F for approximately 35 minutes in citrate buffer at pH 5.0. 6. Non-enzymic hydrolysis of the strawberry pectic substances occurs and hydrolysis is more pronounced at lower pH values. 7. The pectinesterase activity in Northwest strawberry is low in comparison with tomato fruits. The optimum activity of strawberry P.E. occurred at pH 7.5. 8. While cellulase activity existed in Northwest strawberries, the strawberry cellulase did not hydrolyze the insoluble strawberry cellulose. / Graduation date: 1964

Thesis (doctoral)--Gothoburg, 1716. / At head of title: Q.F.F.Q.S. Tail-pieces. Signatures: A-C⁸ D¹. Includes bibliographical references.

Graduation date: 1981

Thesis (M.S.)--Oregon State College, 1942. / Typescript. Includes bibliographical references (leaves [69-71]). Also available online.

Total strawberry production in both Canada and the United States has been steadily declining for the past decade. This trend can, to a large extent, be attributed to the increasing cost and difficulty of getting this crop manually harvested. This research, therefore, is directed toward development of a mechanical harvesting system for strawberries. During initial development of any new concept, a system analysis should be undertaken to ensure that excessively complicated problems will not arise unexpectedly and to ensure that redundant research is not undertaken. Such an analysis indicated that the development of a once-over harvesting system is more feasible than the development of a selective harvesting system. The analysis also indicated that system development will require input from engineers, fruit growers, fruit processors and horticulturalists. An attempt is made to allocate appropriate areas of investigation and research to each of these groups. Group interactions are also investigated. To successfully develop the proposed system, one essential step is development of a mechanical picking machine. A design, based on the physical and mechanical properties of the strawberry fruit and plant, was used to build a picking -machine model. This model was field tested and evaluated. Limited field tests indicated that some field preparation for mechanical harvesting is essential and that a vacuum fruit pick up device should be considered to assist machine feeding. Tests indicated, however, that the proposed concept can be used to remove berries from the plant with very little fruit damage. / Land and Food Systems, Faculty of / Graduate

Using strawberry as a test plant, captan has been shown to inhibit pollen germination when included in or sprayed on the germination medium, or when sprayed on anthers after pollen dehiscence. Toxic effects did not disappear during prolonged germination. However, pollen germination was slightly affected by captan sprayed on the undehisced anthers. When open flowers were sprayed before anther dehiscence, berry set was reduced in the variety Siletz but not in the variety Northwest. When sprayed after anther dehiscence, achene set, and berry development were decreased. The proportion of mishappen fruits increased with captan concentration. Pollination from sprayed anthers was not as effective in fruit setting as control pollination of sprayed pistils. Sprays applied to pistils either just before or just after pollination decreased fruit set. Fruit set was not affected by sprays one day after pollination. Captan therefore seemed to act directly upon pollen germination and not upon the receptivity of the stigma or upon pollen tube growth in the style or upon fertilization. / Land and Food Systems, Faculty of / Graduate