An effort was made to determine what factors are responsible for differences in color quality between preserves commercially manufactured from Hood and Tioga strawberry varieties. Color analyses made on Hood and Tioga preserves, during a 26 week storage period, included spectral measurements of aqueous extracts from the preserve samples. In addition, Hunter color coordinates were determined for both the insoluble residues (remaining after extraction) and the intact preserve samples. Color analyses revealed that color deterioration occurred at a much faster rate in Tioga preserves than in Hood preserves, and that this deterioration was due to a faster rate of browning in Tioga preserves. Complete chemical analyses of fruit revealed striking compositional differences between Hood and Tioga varieties. The concentrations of free amino acids and metal ions were found to be similar in both varieties. Ascorbic acid, which is believed by many to contribute significantly to color deterioration, was actually present in lower concentration in the Tioga variety. Anthocyanins were present in greater amounts in the Hood variety, while leucoanthocyanins, flavanols and total phenolics were higher in Tiogas. Recent work, primarily with wine and model wine systems, has shown that leucoanthocyanins, catechins, and possibly other reactive phenolics, will react with anthocyanins to form polymeric pigments. The results of this study are supportive of the hypothesis that a similar reaction in preserves (between anthocyanins and other phenolics) is responsible for color deterioration during storage. / Graduation date: 1978

Polyphenol oxidase (PPO) from strawberries was purified, partially characterized, and used to study its role in the degradation of anthocyanin pigments. The extraction method included the use of a buffered solution containing the phenolic binders Polyclar AT and Amberlite XAD-4. Addition of Triton X-100 resulted in an increase of the extracted activity. Higher levels of PPO activity were obtained using citrate rather than acetate in the buffer. This was possibly due to the capacity of citrate to chelate calcium ions, and, therefore, to inhibit crosslinking of the pectic polymers which would trap the enzyme. Using a Phenyl Sepharose CL-4B (PS) hydrophobic column two fractions of the enzyme, Fl and F2, were separated from the pectic material and the bulk of the 280 nm absorbing material. PP0-F1 obtained from the PS column was less hydrophobic than F2, and showed a molecular weight of 111,000 by gel filtration on Sephacryl S-300. Form Fl eluted in the void volume of an anion exchange column and did not penetrate into the running gel during electrophoresis. The binding of PP0-F1 to a Concanavalin-Agarose (ConA) column demonstrated the presence of carbohydrate associated with the enzyme. PP0-F2 showed a molecular weight of 34,500 and could be resolved by anion exchange chromatography into one large peak and a smaller one at its shoulder. Fraction F2 of the enzyme resolved into two bands during electrophoresis, and did not bind to the ConA column, Both fractions of the enzyme showed multiple banding on lithium dodecyl sulfate -- polyacrylamide gradient gels. Both fractions of the enzyme obtained from the PS column showed very high activity in the presence of D-catechin. The Michaelis constants for D-catechin for PPO fractions Fl and F2 were 0.50mM and O.4lmM respectively, and the maximum velocity 82,700 and 18,800 nmoles 0₂ per min per ml respectively. D-catechin in the presence of PP0-F1 was rapidly oxidized and the resulting solution had a maximum absorption at 390 nm. When D-catechin and PP0-F1 were combined in model systems with either pure cyanin or pelargonin, an absorbance peak at 390 nm was noticed with increased absorbance in the region of the anthocyanin pigments. After 24 hr, 50% of the pelargonidin and 60% of the cyanin was destroyed and a brown precipitate was formed. PPO-Fl seemed to oxidize cyanin at a very slow rate but did not oxidize pelargonin. It was suggested that the anthocyanin pigments were destroyed by either the direct oxidation by the quinones formed from D-catechin by PPO, or that the anthocyanin pigments were co-polymerized into the brown polymeric pigment, tannin, formed from D-catechin-quinone polymerization. / Graduation date: 1984

Thesis (M.S.)--Oregon State University, 1984. / Typescript (photocopy). Includes bibliographical references (leaves 55-62). Also available online.

Thesis (MSc)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Graduation date: 1912

Thesis (M.S.)--Oregon State College, 1955. / Typescript. Includes bibliographical references (leaves 41-42). Also available online.

Thesis (PH. D.)--Michigan State College of Agriculture and Applied Science, 1937. / Technical bulletin no. 162, February 1939, of the Michigan Agricultural Experiment Station, Lansing, with cover having thesis note. eContent provider-neutral record in process. Description based on print version record.

Thesis (M.S.)--Wisconsin. / Includes bibliographical references (leaves 69-80).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 99-103).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1962. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 41-45).