Thesis (doctoral)--Bordeaux III, 1978. / Includes bibliographical references (p. 1101-1158) and index.

A dissertation of published papers submitted by the author for the degree of Doctor in AgricSciences / Thesis (DSc)--Stellenbosch University, 1983. / ENGLISH ABSTRACT: No abstract available / AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar

Thesis (MSc)--Stellenbosch University, 1980. / Een kopie is mikrofiche. / ENGLISH ABSTRACT: No abstract available / AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar

Improved sensitive techniques were developed for the determination of soluble proteins in grape, juice and wine. These techniques which permitted direct sample analysis without prior dialysis or concentration, were used for: 1) characterization of heat unstable proteins, 2) evaluating the effect of bentonite fining and ultrafiltration (UF) on the soluble proteins and heat unstable proteins in Gewurztraminer and Riesling juices and wines. Protein molecular weights (MW), isoelectric points (pI) and glycoproteins were determined by using LDS-polyacrylamide gel electrophoresis and 2-dimensional isoelectric focusing (IF)-LDS electrophoretic techniques with silver staining as well as protein blotting for glycoprotein detection. Relative concentrations of proteins in stained gels were determined by laser scanning densitometry. Bentonite fining tends to remove higher pi (5.8-8.0), intermediate MW (32,000-45,000) protein fractions first. In general, it is necessary to remove the lower pI (4.1-5.8), lower MW (12,600 and 20,000-30,000) fractions and glycoproteins to "protein stabilize" wines to heat testing. Unstable proteins precipitated by heat test were recovered and analyzed. These proteins were mainly of low MW (<30,000) and primarily glycoproteins. Protein fractions with MW of greater than 14,000 were more heat sensitive than lower MW fractions. Wines and juice were ultrafiltered with Romicon and Millipore systems operated with membranes of "nominal MW cut-off (MWCO)" of 10,000-100,000 daltons. A progressive increase in membrane retention of soluble protein was observed with decreasing MWCO, up to 99% of wine protein being retained with membranes of 10,000 dalton MWCO. However, certain high MW protein fractions also remained in permeates even with 10,000 MWCO membranes. In the order of 3-2 0 mg protein/L frequently remained in UF wine permeates, this correlated with the periodic detection of heat instability and of a low bentonite requirement for "protein stability" as determined by sensitive heat testing. "Protein stability" could be obtained with MWCO of 10,000 and 3 0,000; however, when not obtained, reductions in the order of 80-95% in "bentonite demand" were achieved. Protein stabilization of wines by UF is similar to that by bentonite fining in that it is necessary to remove the lower MW (12,600 and 20,000-30,000), lower pI (4.1-5.8) fractions, and glycoproteins to stabilize wines to heat testing. UF membranes were more effective at retaining wine proteins than juice proteins. UF juices were more susceptible to heat induced haze formation than UF wines. / Graduation date: 1986

It has long been recognized that fermented food products possess a characteristic but pleasant flavor. The use of such foods, however, has been limited by the presence of ethanol. Thus the objective of this research was to investigate the possibility of producing non-alcoholic fermented juice concentrates. Three varieties of juices, Concord grape, apple, and blackberry, were ameliorated as needed and fermented to five to seven percent alcohol by volume. The fermented flavor was extracted with ethyl chloride and concentrated by distillation. These extracts were analyzed by gas chromatography using two different column temperatures. Low column temperature was 100°C while high column temperature was 170°C. Four peaks were found to contribute from 93 to 97 percent of the flavor compounds chromatographically separated from the three juices at low temperature. By use of the enrichment technique, these peaks appeared to be propyl alcohol, isobutyl alcohol, butyl alcohol, and a mixture of isoamyl and active amyl alcohol. At high temperature separation, four peaks were observed to comprise 56 to 64 percent of the flavor components fractionated. These four peaks appeared to be a mixture of acetic acid and ethyl octanoate, caproic acid, phenethyl alcohol and caprylic acid. Other components were tentatively identified to be acetone, ethyl acetate, ethanol, n-amyl alcohol, ethyl hexanoate, n-hexanol, propionic acid, 2, 3-butylene glycole, butyric acid, isovaleric acid, diethyl succinate, 4-butyrolactone, valeric acid and capric acid. Freeze drying and a combined method of distillation and freeze centrifugation were the two methods employed to remove ethanol and water from the fermented juices. A fivefold concentration of the original juices was obtained. From 91 to 95 percent of the alcohol and 80 percent of the water were removed from the juices by freeze drying while the combined technique removed only 79 percent of the ethanol and 80 percent of the water. Total acids, color and total soluble solids were not affected by the freeze drying procedure whereas the combined technique for removal of the alcohol resulted in some loss of these constituents. The fermented dealcoholized juices were analyzed by gas chromatography using only high temperature columns. These data indicate that dealcoholization resulted in a decrease in the peak heights of the first ten peaks to be separated. The remainder of the peaks generally showed an increase although a few exceptions were noted. The dealcoholized fermented juice concentrates were reconstituted and evaluated by a flavor panel. The panel data indicated that the rank order of preference for the three juices was blackberry, apple and Concord grape. The flavor panel also preferred the juices served at the higher levels of sweetness. The total average panel score for these three juices was observed to be about a neutral rating of "neither like nor dislike". / Graduation date: 1966

To provide a possible alternative for the antimicrobial action of sulfur dioxide in winemaking, and address the issue of stuck fermentations, I studied the efficacy of chicken lysozyme (EC 3.2.1.17) as an antimicrobial in grape juice. Two different forms of lysozyme were used: native lysozyme (NL), that is known to be an effective inhibitor of lactic acid bacteria in wine, and partially unfolded lysozyme (PUL), that has been reported to have antimicrobial activity against both Gram-positive and Gram-negative bacteria. Lactobacillus kunkeei and Acetobacter pasteurianus, two bacteria associated with the induction of stuck fermentations were used in the experiments. Chardonnay and Pinot Noir juices were inoculated with L. kunkeei and two days later with yeast strain EC1118 and then incubated for 10 days. The addition of 250ppm of either NL or PUL reduced populations of L. kunkeei to less than 10 CFU/mL in 24 hours while in inoculated grape juice that did not contain any lysozyme, the bacteria grew to 10⁹ CFU/mL within two days. Grape juices supporting the growth of L. kunkeei developed up to 14 times more volatile acidity (VA) than the control or either of the lysozyme treatments. No differences were observed in the antimicrobial action of NL and PUL or in their effects on the composition of the wine. / Graduation date: 2002

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on December 29, 2009). Thesis advisor: Dr. Ingolf Gruen. Includes bibliographical references.

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

Graduation date: 1955

Graduation date: 1949