Thesis (Ph. D.)--Colorado State University, 2004. / Includes bibliographical references.

The study presented here consists in an original piece of work to better understand complex food packaging interactions. The majority of investigations on food polymer interactions related to orange juice and this provided a good base to our study (Literature reviews: cf. Chapters 1a and b). Additionally a rather remarkable finding in 1994 was that limonin, a trace bitter material found in some varieties of orange juice was rapidly absorbed by highly plasticised polyvinyl chloride (PVC plastisol) (Chapter 2). Several commercial absorbants are available for debittering, relying on limonin absorption on the large surface area of the highly porous absorbant pellets. However, the absorptive properties of the smooth plastisols apparently relied on a different mechanism. Limonin is a very large (470.5 g/mol) compound, but some preliminary experiments with another much smaller orange juice constituent d- of absorbates in plastisols, methods used earlier (Moisan 1980, Holland and Santangelo 1988) to measure solubilities and diffusion constants in packaging films could be advantageously used to survey these properties in a wide range of materials, including model compounds of various types, and a number of compounds which may be found in citrus juices (Chapters 3, 4 and 5). Experimentally, the method found most suitable was to use a ‘test film’ of pure plastisol which was wrapped tightly on both sides by a similar ‘supply film’ blended with 1 Molar test material (also called ‘absorbate’), setting up a concentration gradient. The inner test film was removed at regular intervals (minutes to hours) to measure (mainly by weighing) the uptake of the test reagent with time. Rather unexpectedly, it was found in a number of cases that the test film lost weight, either from the beginning, or after a period of time. Three main types of behaviour were identified: Type A lost weight from the beginning and over a long period of time, Type B gained weight initially and then lost weight, and Type C gained weight until a steady state was reached. Often the maximum, or near maximum, mass increase occurred within around 100 minutes, indicating a very rapid, liquid-like diffusion mechanism, in harmony with the rapid uptake of d-limonene and limonin. The major parameters of interest with these compounds are their diffusion rates and their solubilities, and in the presence of aqueous media (orange juice and other foodstuffs) the partition coefficient between the plastisol and water, which is related to the hydrophobicity function LogP for the compound. The major complicating factor in these measurements is the observation that the plasticiser materials themselves also migrate, in the reverse direction, because of the lower effective concentration in the supply film. This effect tends to be small, but is one explanation for the mass loss observed above, and cannot be ignored over the long term, nor in its practical applications to contamination in foods. There are many possible applications for the techniques described above. The removal or addition of compounds in food packaging itself is one. Upgrading foods, such as orange juice, commercially, is another. In many cases ‘scalping’ off-flavours or other minor components takes place exclusively through solid or liquid contact with the packaging. The removal from the headspace measured by the current gas permeation methods is irrelevant for the vast numbers of involatile, but easily diffusable compounds. For such compounds these novel applications are simple and rapid, require little specialised equipment, and fill a niche in the armoury of food and packaging chemists. / Doctor of Philosophy (PhD)

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 175-187). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 175-187). Also available on the Internet.

Thesis (Ph.D.) -- University of Western Sydney, 2004. / A thesis presented to the University of Western Sydney, Centre for Advanced Food Research, in fulfilment of the requirements for the degree of Doctor of Philosophy in Advanced Food Science (& Food Packaging Science). Includes bibliography.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 80-84). Also available on the World Wide Web.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Spoilage, be it due to microbial actions, chemical reactions or both, poses a serious threat to the food and beverage industries. Not only can spoilage lead to great economic losses, but it can also cause industries to lose their competitive edge in the economic and consumer market. Considering all the modern technologies and the range of preservation techniques that are available, it is surprising that spoilage is still an economic problem. Wine spoilage due to unpalatable bitterness, and the role of lactic acid bacteria (LAB) in causing this bitterness, have received much attention over the years, but no definite understanding has yet emerged. The first objective of this study was to isolate, enumerate and identify the LAB from three red grape varieties, viz. Pinotage, Merlot and Cabernet Sauvignon. The LAB populations on the grapes of all three varieties ranged from 102 to 104 cfu/ml during the 2001 and 2002 harvest seasons. The Cabernet Sauvignon grapes had slightly higher numbers than the Pinotage and Merlot. The LAB population in the Cabernet Sauvignon, Pinotage and Merlot wines after completion of the alcoholic fermentation ranged from 102 to 105 cfu/ml, while during 2002 the numbers in wine undergoing malolactic fermentation (MLF) ranged from 104 to 108 cfu/ml. The isolated LAB were divided into the three metabolic groups, with 59% belonging to the facultatively heterofermentative group, 26% to the obligately heterofermentative group and 15% to the obligately homofermentative group. The isolates were identified by means of species-specific primers as Leuconostoc mesenteroides (4), Oenococcus oeni (28), Lactobacillus brevis (15), Lb. hilgardii (15), Lb. plantarum (98), Lb. pentosus (12), Lb. paraplantarum (3), Lb. paracasei (28), Pediococcus acidilactici (2) and Pediococcus spp. (35). The most predominant species isolated was Lb. plantarum, followed by Pediococcus spp. The results suggest that Pinotage carries a more diverse LAB population in comparison to Merlot and Cabernet Sauvignon. The second objective of this study was to determine the presence of the glycerol dehydratase gene in the LAB strains by using the G01 and G02 primers. Twenty-six strains tested positive, namely Lb. plantarum (15), Lb. pentosus (1), Lb. hilgardii (5), Lb. paracasei (2), Lb. brevis (2) and a Pediococcus spp. (1). Interestingly, 62% of these strains were isolated from Pinotage. The strains all had the ability to degrade glycerol by more than 90%, and no significant differences were observed between the species. The GO-possessing strains exhibited varying degrees of inhibition towards Gram-positive and Gram-negative bacteria, and the results suggest that this inhibition activity may be similar to that of reuterin, which is produced by Lb. reuteri. This study can form the foundation for unravelling the causes of bitterness in red wines. Combining the results of this study with analytical, sensory and molecular data may very well provide the industry with valuable tools with which to combat the occurrence of bitterness. / AFRIKAANSE OPSOMMING: Bederf as gevolg van mikrobiese aksies, chemiese reaksies of beide, hou 'n groot bedreiging vir die voedsel- en drankbedrywe in. Nie net kan bederf lei tot groot ekonomiese verliese nie, maar dit kan ook veroorsaak dat bedrywe hul kompeterende voordeel in die ekonomiese en verbruikersmarkte verloor. As die moderne tegnologie en die reeks preserveringstegnieke wat beskikbaar is, in ag geneem word, is dit verbasend dat bederf steeds 'n ekonomiese probleem is. Wynbederf as gevolg van oormatige bitterheid en die rol van melksuurbakterieë (MSB) in die ontwikkeling van hierdie bitterheid het oor die jare heen baie aandag geniet, maar geen definitiewe verklaring is nog daarvoor gevind nie. Die eerste doelwit van hierdie studie was om MSB vanaf drie rooidruifvariëteite, nl. Pinotage, Merlot en Cabernet Sauvignon, te isoleer, te kwantifiseer en te identifiseer. Die MSB-populasies op die druiwe van al drie variëteite het gedurende die 2001- en 2002-parsseisoene tussen 102 en 104 kvu/ml gevarieer. Die Cabernet Sauvignon-druiwe het effens hoër getalle as die Pinotage- en Merlot-druiwe gehad. Die MSB-populasies in die Cabernet Sauvignon-, Pinotage- en Merlot-wyne aan die einde van die alkoholiese fermentasie het tussen 102 en 1055 kvu/ml gevarieer. Gedurende 2002 het die MSB-getalle in die wyne waarin appelmelksuurgisting (AMG) aan die gang was tussen 104 en 108 kvu/ml gevarieer. Die geïsoleerde MSB was onderverdeel in die drie metaboliese groepe, met 59% wat behoort aan die fakultatiewe, heterofermentatiewe groep, 26% aan die obligate, heterofermentatiewe groep en 15% aan die obligate, homofermentatiewe groep. Die isolate is geïdentifiseer as Leuconostoc mesenteroides (4), Oenococcus oeni (28), Lactobacillus brevis (15), Lactobacillus hi/gardii (15, Lactobacillus p/antarum (98), Lactobacillus pentosus (12), Lactobacillus parap/antarum (3), Lactobacillus paracasei (28), Pediococcus acidi/actici (2) en Pediococcus spp. (35) deur middel van spes iespesifieke inleiers. Die mees algemeen geïsoleerde spesies was Lb. p/antarum, gevolg deur Pediococcus spp. Die resultate impliseer dat Pinotage 'n meer uiteenlopende MSB-populasie in vergelyking met Merlot en Cabernet Sauvignon dra. Die tweede doelwit van hierdie studie was om die teenwoordigheid van die gliseroldehidratase-geen in die MSB-isolate deur middel van die GD1- en GD2- inleiers te bepaal. Ses-en-twintig isolate was positief, nl. Lb. p/antarum (15), Lb. pentosus (1), Lb. hi/gard;; (5), Lb. paracasei (2), Lb. brevis (2) en 'n Pediococcus spp. (1). 'n Interessante resultaat was dat 62% van hierdie isolate vanaf Pinotage geïsoleer is. Die isolate was almal in staat om meer as 90% van die gliserol te gebruik en geen noemenswaardige verskille is tussen die isolate waargeneem nie. Die GD-bevattende isolate het verskillende grade van inhibisie teenoor Grampositiewe en Gram-negatiewe bakterieë getoon, en die resultate impliseer dat hierdie inhiberende aktiwiteit dieselfde is as dié van reuterin wat deur Lb. reuteri geproduseer word. Hierdie studie kan dus die basis vorm vir die ontrafeling van die oorsake van bitterheid in rooiwyne. Deur die resultate van hierdie studie met analitiese, sensoriese en molekulêre data te kombineer, kan die wynbedryf voorsien word van waardevolle metodes om die voorkoms van bitterheid mee te bekamp.

Characterizing the cortical representation of sweet and bitter tastes in awake behaving mice has been challenging due to the sheltered location of the gustatory cortex in the insula, which restricts optical and electrophysiological recordings, and the various functions of the insula, complicating conclusions about taste representation. To overcome these obstacles, we developed a brain-wide imaging paradigm that combines functional magnetic resonance imaging (fMRI) with optogenetic and taste receptor knock-out manipulations in mice. This approach allowed us the study the gustatopic map in awake, behaving mice, showing that sweet and bitter tastes are topographically segregated along the rostro-caudal axis of the gustatory cortex, with sweet represented rostrally and bitter caudally. Notably, this map is subject to plasticity following conditioned taste aversion (CTA) for sweet stimuli, resulting in a posterior shift of the sweet taste field—a phenomenon reversible after CTA extinction.