'Marion' and 'Thornless Evergreen' blackberry volatiles were analyzed by capillary gas chromatography-flame ionization detection (GC-FED) and GC-mass spectrometry (GC-MS). Based on total percentage of FID area 'Thornless Evergreen' contains significantly more alcohols, hydrocarbons, and phenols than the 'Marion'; 'Marion' contains more acids and esters. Both cultivars contained comparable amounts of aldehydes and ketones; alcohols were most abundant. The six most abundant volatiles in 'Marion' were ethanol, acetic acid, hexanoic acid, ethyl acetate, linalool, and 2-heptanol; they totaled 52% of total peak area. In 'Thornless Evergreen' the six most abundant volatiles were 2-heptanol, ethanol, 2,3-butanediol, hexanol, α-pinene, and ethyl acetate; they totaled 43% of total peak area. 'Marion' and 'Thornless Evergreen' blackberry aromas were compared using a pair of extraction and gas chromatography-olfactometry-mass spectrometry (GC-O-MS) methods. One method is based on purge-and-trap (P&T, dynamic headspace) extraction and aroma intensity rating by detection frequency (DetF) and a numeric scale, and the other based on solvent assisted flavor extraction (SAFE) and aroma threshold dilution analysis (AEDA). The parallel use of P&T-DetF GC-0 and SAFE-AEDA provided more representative blackberry volatile compositional data than either alone. Eighty-four compounds were identified; seventy-seven were in 'Marion', and sixty-eight in 'Thornless Evergreen'. Thirty-seven have not been previously reported in blackberry. Fourteen volatiles out of eighty-four were described with aroma descriptors specific to bramble fruit (berry, blackberry, bramble, raspberry); no single compound was unanimously described as "characteristically blackberry". Fresh 'Marion' blackberry aroma has been described as floral, fruity, sweet, caramel-fruity, and woody, while fresh 'Thornless Evergreen' aroma is spicy, green, herbaceous, fruity, and sweet. Except for esters, the cultivars contain comparable numbers of acids, alcohols, aldehydes, furanones, hydrocarbons, ketones, phenolics, sulfur, and Theaspirane compounds. Research data implies some portion of the more floral, fruity, and sweet aroma of the 'Marion' blackberry may be the result of additional esters not shared with the 'Thornless Evergreen' blackberry, yet both cultivars apparently contain five furanones, which are powerful sources of sweet, fruity, and spicy aromas. Aroma reconstitution studies will be the key to resolving the significant aroma profile differences between 'Marion' and 'Thornless Evergreen' blackberries, as characteristic blackberry aroma is apparently a complex formulation of volatiles. / Graduation date: 2004

A method for the assessment of volatile compounds in dairy products was developed using solvent desorption dynamic headspace sampling. The method was first applied to assay for diacetyl and acetoin in buttermilk. Major buttermilk volatiles recovered included diacetyl, acetic acid, and acetoin. Normalized detector responses were linear over the range of concentrations tested for diacetyl and acetoin. The method enabled quantitative estimation of diacetyl and acetoin in <30 min, including sample preparation time. Next, the ability of stabilizing and emulsifying agents to inhibit the release of diacetyl from a model dairy matrix was examined using modified purge parameters. Stabilizers (guar, xanthan, and carrageenan) and emulsifiers (lecithin, carboxymethyl cellulose, and Tween 80) were examined for their effects on headspace available diacetyl at 0.05, 0.10, and 0.20% (wt/wt) in a 5% milkfat model system. Guar gum and carrageenan exhibited similar diacetyl release inhibition when corrected for viscosity. Xanthan gum exhibited the greatest decrease in headspace available diacetyl after correction for viscosity at increasing gum levels. Tween 80 imparted no significant viscosity and had no effect on recoverable diacetyl. Lecithin had no effect on viscosity, however it did inhibit the release of diacetyl as a function of lecithin level. Carboxymethyl cellulose increased viscosity and inhibited diacetyl release. Finally, a rapid dynamic headspace sampling technique was evaluated for its ability to differentiate between Cheddar cheese samples for volatile aroma compounds. Seven samples of Cheddar cheese were examined ranging in flavor from mild to extra sharp. A total of 14 volatile compounds were tentatively identified with published retention indices and retention times of known standards. Major volatiles recovered were 2-butanol, acetoin, propanoic acid, butyric acid, and caproic acid. Other identified compounds were 2-butanone, diacetyl, ethyl butyrate, 1-butanol, ethyl caproate, hexanol, acetic acid, 2,3-butanediol, and octanoic acid. The application of solvent desorption dynamic headspace sampling of dairy volatiles is a simple, rapid method for the determination of volatile compounds previously shown to influence flavor and aroma of dairy products. This research was conducted to demonstrate the optimized application of this technology to tracking dairy products aroma compounds. / Graduation date: 1996

Graduation date: 2000

Graduation date: 1994

Graduation date: 1992

Copies of author's previously published articles inserted. / Bibliography: leaves 121-144. / xiii, 150 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study investigates the site of biosynthesis of flavour compounds in the grapevine. Most of the secondary metabolites, including flavour compounds, are glycosylated and stored in plant tissues as glycosides. The chemical properties of these compounds, especially their water solubility, suggests that glycosides might be forms of translocated secondary metabolites in plants. / Thesis (Ph.D.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, 1996?

No description available.

No description available.

Thesis (PhD)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: A number of relevant brewing industry issues associated with malt quality were examined. These included beer foam quality, premature flocculation of yeast during fermentation and antimicrobial factors in malt. The cause of poor foam at a brewery relative to other similar breweries was identified as being related to the boiling temperature during wort preparation and the associated conformational changes of the abundant foam protein lipid transfer protein 1 (LTPl). The temperature range of 96 to 102°C was revealed to be critical. At the higher temperature the denaturation of LTP 1 was more extensive and its effectiveness as a foam protein was reduced. In addition, it was shown that the prominent role of LTPI with respect to foam was as a lipid binding protein, forming a lipid sink and protecting foam from lipid damage. The occurrence of malt associated premature yeast flocculation (PYF) during fermentation was induced in malt by the addition of extra-cellular fungal enzymes to the malt husk or by micro-malting barley in the presence of fungi. In addition, treating malt husk with commercial xylanase or adding commercial arabinoxylan to the fermentation also impacted on yeast flocculation. It was proposed that a range of molecular weight arabinoxylans formed by the enzymatic breakdown of the major barley husk component (arabinoxylan) resulted in PYF. Antimicrobial activity against brewing yeast (Saccharomyces cerevisiae), other fungi and bacteria was found in barley, malt and malt derived wort trub. Wort trub is the non-specific precipitate of protein, polyphenols and lipids formed during wort boiling and which is, to some extend, carried over in the wort to the fermentation. Antimicrobial activity appeared to increase during malting. The growth of brewery collected yeast was inhibited in the presence of brewery production wort when compared to the same wort filtered to remove the trub. Brewery yeast was found to be more sensitive to inhibition than laboratory propagated yeast of the same strain. Different strains of S. cerevisiae were also found to differ in their sensitivity to inhibition. Investigation revealed that the activity originated from the inside of the barley grain and impacted on yeast sugar uptake. However, there was no direct correlation detected between levels of antimicrobial activity in malt and fermentation performance. At high concentrations the factors were microcidal causing cell lysis. Partial characterisation of an antimicrobial extract from malt revealed the presence of a factor between 5 and 14 kDa, containing a cationic peptide component. The optimum pH stability was ±5 when it was also most cationic. The factor easily and irreversibly lost activity at extreme pH and when exposed to certain reagents but was heat resistant in accordance with its survival in wort trub. Preliminary results showed the presence of LTP1 associated with other peptides in the active cationic fraction from the one malt tested. The occurrence of malt related PYF and malt antimicrobial factors are associated with microbial contamination of the grain. The fungi generating the PYF factors from the barley husk while the barley's defence mechanism generates antimicrobial factors to cope with the pathogenic effect of the fungi. In addition there is a potential link between the foam protein LTP 1 and malt antimicrobial activity as LTP 1 or LTP 1 in association with another component(s) is potentially antimicrobial. / AFRIKAANSE OPSOMMING: 'n Aantal problematiese areas in die broubedryf, wat met mout geassosieer word, is ondersoek, naamlik bierskuimkwaliteit, voortydige flokkulering van gis tydens fermentasie en die invloed van antimikrobiese faktore in mout. Die oorsaak van swak bierskuim by 'n spesifieke brouery relatief tot ander soortgelyke brouerye was geidentifiseer as die moutekstrakkookpunt tydens moutekstrakbereiding. Tydens hierdie proses ondergaan dieskuimprotein, lipiedoordrag proteien 1 (lipid transfer protein 1, LTPI), 'n konformasieverandering. Die temperature tussen 96 to 102°C was kritiek t.o.v. ideale konformasieverandering vir skuimaktiwiteit. Denaturering van LTPI het by hoër temperature plaasgevind wat die skuimproteien se aktiwitiet verminder het. Daar is ook bewys dat LTPI 'n verdere rol in bierskuim speel aangesien dit 'n lipiedbindingsproteien is wat die skuimnegatiewe lipiede verwyder. Die voorkoms van moutgeassosieerde voortydige flokkulering van gis (PYF) tydens fermentasie is op twee maniere in mout geinduseer, naamlik: • deur die toevoeging van ekstrasellulêre swamensieme tot die moutdop • deur mikrovermouting van gars in die teenwoordigheid van swamme. Die behandeling van die moutdop met kommersiele xilanase of die toevoeging van kommersiele arabinoxilaan by fermentasies het ook die flokkulering van gis beinvloed. Die hipotese was dat PYF veroorsaak is deur 'n reeks arabinoxilane met verskillende molekulêre massas wat gevorm het tydens die ensimatiese afbraakproses van die primere moutdopkomponent (arabinoxilaan). Antimikrobiese aktiwiteit teenoor brouersgis (Saccharomyces cerevisiae), ander swamme en bakterie was teenwoordig in gars, mout en moutekstrakpresipitaat. Die presipitaat bestaan uit nie-spesifieke presipitate van proteien, polifenole en lipiede wat gedeeltelik in die gekookte moutekstrak agterbly. Daar is gevind dat antimikrobiese aktiwiteit tydens vermouting toe geneem het. Die groeiproses van brouersgis, gekollekteer by 'n brouery, was geinhibeer deur die teenwoordigheid van brouery-geproduseerde moutekstrak in vergelyking met dieselfde moutekstrak wat gefiltreer was om die presipitaat te verwyder. Die brouersgis was meer sensitief heens inhibisie in vergeleke met dieselfde gisstam wat opgegroei is in die laboratorium. Verskillende S. cerevisiae stamme het ook verskille in sensitiwiteit getoon t.o.v. the antimikrobiese komponente in die moutekstrakte. 'n Verdere ondersoek het getoon dat die oorprong van die inhiberende aktiwiteit die interne dele van die gars is, asook dat dit die gissuikeropname beinvloed. Daar was egter geen direkte verband tussen antimikrobiese aktiwiteit in mout en fermentasie effektiwiteit, soos gemeet onder laboratorium toestande, nie. Hoë konsentrasies van die faktore het egter gelei tot seldood weens sellise. 'n Kationiese peptiedbevattende fraksie tussen 5 en 14 kDa en 'n optimale pH stabliliteit van 5 is gevind deur gedeeltelike karakterisering van 'n antimikrobiese moutekstrak. Die aktiewe fraksie se aktiwiteit is onomkeerbaar vernietig by ekstreme pH en blootstelling aan sekere reagense. Die aktiewe verbinding(s) is egter hittebestand en resultate het getoon dat hierdie aktiwiteit die brouproses oorleef as deel van die moutektrakpresipitaat. Voorlopige resultate van die een mout wat getoets is het die teenwoordigheid van LTP 1 getoon, asook die moontlike assosiasie met ander peptiede of kleiner komponente in die aktiewe kationiese fraksie. Die voorkoms van moutgeassosieerde PYF en antimikrobiese faktore in mout word met die mikrobiologiese kontaminasie van gars verbind. Swamme produseer die PYF faktore vanuit die moutdopkomponente, terwyl die plant weer antimikrobiese faktore produseer as deel van 'n beskermingsmeganisme teen die patogene effek van die swamme. Daar is ook 'n potensieele verwantskap tussen bierskuimproteien LTP 1 en antimikrobiese faktore in mout, aangesien LTPI ofLTPl tesame met 'n ander verbinding(s) moontlik antimikrobies is.

Heat treated orange juice, both pasteurized and concentrate, are being increasingly consumed in the U.S. Orange juice is primarily heat treated to increase its shelf life, by curbing the growth of microorganisms; and to inactivate pectin methylesterase, which demethylates pectin and leads to cloud loss in the juice. However, because of heat processing, orange juice undergoes undesirable flavor changes that decrease its acceptability to consumers. The objectives of this study were to differentiate between fresh frozen and heat treated orange juice employing descriptive analysis, and to determine by Osme, a gas chromatography-olfactometry (GCO) method, odor active volatiles that were either lacking or created in the heat treated juice. The second objective was to determine how changes in the odor-active volatile profile of heat treated orange juice, relates to changes in the aroma and flavor intensities of the samples as assessed by descriptive analysis. Through descriptive analysis, the panel was successful in significantly (p<0.05) separating the fresh, pasteurized, and concentrate samples. Orange, orange peel, sweet, and grassy descriptors were found to be important for fresh aroma and flavor, while cooked, yam, metallic, tamarind, green bean and artificial orange descriptors were higher in heat treated samples. Using Osme, it was possible to separate fresh frozen from heat treated orange juice, on the basis of their aroma profiles. Fresh frozen samples show a higher concentration of peaks tentatively identified as gamma-butyrolactone, citral, nonanal, carvone, perillaldehyde, carvyl propinate, valencene, and other unidentified peaks possessing descriptors such as floral, lime, citrus, pine, bamboo leaf, metallic, and vinyl. Pasteurized samples show a larger concentration of peaks tentatively identified as hexanol, octanol, nerol / carveol, myrcene, 2-octanone, p-cymene, terpenen-4-ol, betacitronellol, and other unidentified peaks with descriptors such as cilantro, vinyl, melon, mushroom, and metallic. Descriptors such as orange, orange peel, sweet, grapefruit, and grassy are more pronounced in the fresh samples and are similar to the odor descriptors of Osme peaks higher in the fresh samples. Descriptors such as cooked, artificial orange, yam, metallic, tamarind, and green bean are higher in the pasteurized samples, and are similar to the odor descriptors of peaks higher in these samples. / Graduation date: 1999