Master of Science / Food Science Program / Thomas J. Herald / For the last decade in the U.S., consumers have demanded fresh, healthier convenience-type foods namely, fresh-cut vegetables. Globalization has played a major role in rapid growth of the fresh-cut industry sector. Thus, consumers may purchase their favorite seasonal vegetables in local grocery stores year-round. However, the convenience of year-round produce availability brings the potential of foodborne outbreaks. Thirty-two states reported 190 produce-associated outbreaks, 16,058 reported illnesses, 598 hospitalizations, and eight deaths from 1973 to 1997. Pathogenic bacteria contaminate raw agricultural commodities through various pathways such as irrigation with untreated water, use of noncomposted animal manure as fertilizer, and wash water systems. The increasing number of produce-related outbreaks has raised awareness to interventions that remove human pathogens on fresh produce. Washing solely with tap water cannot be relied upon to completely remove pathogens. Chlorinated water is the most frequently used sanitizer, however, reductions are less than 2.63-log CFU/g on leafy and salad vegetables. Such reductions, although significant, are not sufficient to assure the microbial safety of minimally processed vegetables. The efficacy of several other chemical agents such as chlorine dioxide, ozone, electrolyzed water, hydrogen peroxide, organic acids, and other commercial products have been evaluated as potential alternatives to chlorine.

Doctor of Philosophy / Food Science Program / Edgar Chambers IV / Three studies, using descriptive sensory analysis with highly trained panelists, were conducted to better understand the sensory characteristics of fresh and processed tomatoes. A “green” note often has been described as part of tomato flavor and is noted in many fruits, vegetables, grains and processed products. Thus, the first study developed a sensory lexicon for green characteristics in foods. The lexicon, consisting of 17 sensory attributes, was used to characterize sensory properties of 22 chemicals potentially associated with green odor. Green characteristics can be differentiated as green-unripe, green-peapod, green-grassy/leafy, green-viney and green-fruity. Additional attributes that are important in various green characteristics included musty/earthy, pungent, bitter, sweet and floral. Various chemicals were described as green at different concentrations. Green-grassy/leafy was the most common characterizing green attribute of many of the chemicals studied. Changing the concentrations of the chemicals resulted not only in changing the intensity of the attributes, but it also altered the sensory profile of many of the chemicals. A sensory lexicon for describing tomatoes also was developed. A variety of fresh tomatoes, processed tomatoes, and tomato-based products such as ketchup and pasta sauce were used to create the lexicon. The characteristics of tomatoes can be described using 33 aroma, flavor and texture attributes. Some characteristics were common across all or most fresh and processed tomatoes. However, reducing the number of attributes may be possible for certain studies because some attributes were appropriate only for fresh or processed tomatoes, not both. A third study determined the sensory characteristics of five tomato types, including newer and older cultivars that varied in their physical traits and primary use. The impacts of processing on the sensory quality of tomato products were investigated, with juice (minimal processing) and paste (higher level of processing) being made from the cultivars. Fresh tomatoes differed significantly because of cultivar and ripening stage differences. Fresh tomatoes differed considerably from processed tomatoes. A low processing level intensified some key aroma and flavor attributes, but differences in flavor attributed to cultivar became minimal after a higher degree of processing. Textural differences among cultivars after processing were more pronounced than flavor differences.

A demanda por frutas e hortaliças frescas, associada à necessidade de maior praticidade da vida atual, está causando um aumento no interesse, por parte dos consumidores, nos produtos minimamente processados (MP). Processamento mínimo inclui as operações de lavagem, corte, descascamento e embalagem do produto. Entre os microrganismos patogênicos que, potencialmente, podem ser transmitidos por vegetais MP citam-se: Listeria monocytogenes, Escherichia coli O157:H7 e Salmonella sp. A pesquisa destes microrganismos é usualmente demorada mas, a cada dia, novos métodos para detecção rápida de patógenos em alimentos são lançados no mercado. Dentre estes métodos, aqueles que empregam ferramentas moleculares têm se tornado mais populares, cabendo destacar os que empregam a reação de polimerização em cadeia (PCR). Para a pesquisa de Listeria monocytogenes existe no mercado o sistema automatizado BAX®System que permite a detecção de L. monocytogenes em, no máximo, 54 h. Neste estudo, buscou-se avaliar a microbiota de vegetais folhosos MP além do emprego do sistema BAX® para a detecção de L. monocytogenes nestes produtos. Foram examinadas, no período de março a julho de 2003, 181 amostras de saladas MP coletadas em diferentes estabelecimentos comerciais no município de São Paulo, SP. Em 133 amostras foram feitas determinações das populações de coliformes totais e fecais, Enterobacteriaceae, microrganismos psicrotróficos aeróbios e pesquisa de Salmonella sp. L. monocytogenes foi pesquisada nas 181 amostras empregando-se o sistema BAX® e, paralelamente, a semeadura do caldo de enriquecimento em placas contendo ágar Palcam e Oxford, com a identificação das colônias suspeitas através de testes bioquímicos tradicionais. Das 133 amostras, 51% apresentaram populações de microrganismos psicrotróficos aeróbios > 106 UFC/g e 42% apresentaram populações de Enterobacteriaceae entre 105 – 106 UFC/g. Coliformes fecais estiveram presente em populações superiores a 102 UFC/g em 97 amostras (73%) e Salmonella foi detectada em 4 amostras (3%). L. monocytogenes estava presente em 1 (0.6%) amostra de espinafre das 181 amostras examinadas, tendo sido detectada, simultaneamente, por ambos os métodos empregados. As outras espécies de Listeria encontradas, empregando-se a semeadura em placa foram: L. welshimeri (1 amostra de alface mimosa) e L. innocua (2 amostras de agrião). Os resultados indicam que grande parte dos vegetais MP examinados, apresentaram qualidade microbiológica deficiente e podem ser veículos de patógenos como a Salmonella. O BAX®System é de grande utilidade para as análises de vegetais MP, que permite a obtenção de resultados mais rapidamente que o método tradicional, sem perda na sensibilidade e na especificidade. / The increasing demand for fresh fruits and vegetables, associated with the desire of convenient goodies, is causing an expansion on the market share of minimally processed products (MP). Minimal processing includes operations such as washing, cutting, peeling and packaging of the product. Amongst pathogenic microorganisms that can be transmitted by MP vegetables are: Listeria monocytogenes (Lm), Escherichia coli O157:H7 and Salmonella sp. Searching for these microorganisms is labor intense and time-consuming, however new methods for fast detection of pathogens are commercially available. Methods employing molecular technology are becoming more popular and the polymerase chain reaction (PCR) is now a good choice. There is an automatized PCR system (BAX®System) that can be used for Lm detection in up to 54 h. The aims of this study was to evaluate the microflora of MP vegetables and to evaluate the effectiveness of the BAX®System for screening Lm on those products. From March to July 2003, 181 samples of MP salads were collected at retail level in the city of São Paulo, SP. Total and faecal coliforms, Enterobacteriaceae, psychrotrophic microorganisms enumeration and Salmonella evaluation were conducted in 133 samples. L. monocytogenes was assessed in 181 samples using the BAX®System and also by plating the enrichment broth onto palcam and Oxford agars. Suspected colonies of Listeria were submited to classical biochemical tests. Population of psychrotrophic microorganisms >106 CFU/g was observed in 51% of the 133 samples and Enterobacteriaceae population between 105 - 106 CFU/g was in 42%. 97 samples (73%) showed population of faecal coliforms >102 CFU/g (Brazilian standard) and Salmonella was detected in 4 samples (3%). L. monocytogenes was detected in 1 spinach sample (0,6%) out of the 181 examined MP vegetables. This positive sample was simultaneously detected by both methods. The other Listeria species identified by plating were L. welshimeri (1 sample of curly lettuce) and L. innocua (2 watercress samples). The results indicate that the MP vegetables had poor microbiological quality and could be vehicle of pathogens such as Salmonella. BAX®System showed good specificity and sensitivity when used for vegetable analysis and was easier to perform and faster than the classical method.

In today’s electronics, transistors are the main building blocks of the vast majority of electronic devices and integrated circuits. Types of transistors vary depending on the device structure and operation principle. Metal-oxide-based thin film transistors (MO TFTs), in particular, are an emerging technology that has a promising future in many applications, such as large-area display and wearable electronics. It exhibits unique features that make it superior to the existing Si-based technology, such as optical transparency and mechanical flexibility. However, some technical challenges in MO TFTs limit their emplyoment in today’s applications, such as low carrier mobility and high processing temperature. Solution-processed MO TFT based on spray pyrolysis combined with a carefully engineered TFT structure offers a dramatically enhance carrier mobility at low processing temperature. In this work, we are utilizing spray pyrolysis to grow In2O3 and ZnO based TFTs at low processing temperature. The structural effects of the channel layer on the electrical performance is investigated in two parts. The first part highlights the impact of thickness of the channel layer on the device performance of both In2O3 and ZnO, while the second part explores In2O3/ZnO heterojunction-based active layer. The results showed that increasing the channel thickness of both In2O3 and ZnO based TFTs enhanced the carrier mobility due to a reduced surface-roughness scattering effect. In addition, evidence showed that the electron transport mechanism in In2O3/ZnO heterojunction transitioned from trap-limited conduction (TLC) to percolation conduction (PC) process. Thanks to the existence of a 2D-confined electron sheet at the atomically sharp In2O3/ZnO heterointerface, the electron mobility was dramatically enhanced.

The thesis has been focused on testing of micromethod of DNA isolation from leaves, fruits and fruit products. Jams were selected for the analysis of plant DNA in technologically processed foods. Plant leaves, fruits, and jams were homogenized using plastic copist in a lysis buffer containing 2% cetyltrimethylammonium bromide (CTAB) with 2.5M sodium chloride (NaCl). Microisolation of plant DNA was performed using poly(hydroxyethylmethacrylate-co-glycidylmethacrylate) – P(HEMA-co-GMA)microparticles. Isolated the DNA concentration and purity were assessed by UV light aborbance using a spectrophotometer. After that, amplification of the DNA was tested in PCR. Primers specific for plant ribosomal DNA: 18S_for a 5,8S_rev (PCR product - 700bp), 26S_for a 26S_rev (PCR product - 220 bp), 18S_for a 18¬S_rev (PCR product - 263 bp) were used. The PCR conditions were optimized and the effect of the amplicon length on its detection was followed. PCR products were detected by agarose gel electrophoresis. It was shown that DNA isolated from almost all of leaves using magnetic particles was in PCR-ready quality in contrary to the fruits. DNA amplified in PCR with primers giving short PCR products was isolated from almost all tested jams. The method must be optimalised, yet.

The aim of this diploma thesis was to monitor influence of storage conditions (temperature and time) on content of aroma substances in sterilized processed cheeses and also on their flavour. The part of cheeses was stored at 6°C, second part at room temperature 23 °C and third part at 40 °C. Processed cheeses were produced by Madeta, a. s., sterilized at 117 °C 20 min. The analysis was made at regular intervals, cheeses stored 16 and 23 months were analysed in this work. The aroma compounds were isolated by SPME and subsequently identified and quantified by gas chromatography. In total 37 aroma compounds were identified and quantified, 7 aldehydes, 7 ketones, 6 acids, 12 alcohols and 5 esters. Total content of aroma compounds increases with higher storage temperature. The time of storage has also influence on content of aroma compounds, we may say, that content is increasing, although sharp growth was registered only after 23 months, namely in the thermostat. Simultaneously sensory analysis of cheeses was made. Ranking test and evaluation using scale were used. Cheeses from a fridge were always evaluated as the best in all categories. Cheeses stored at room temperature were evaluated worse and cheeses from thermostat were the worst. So it is apparent, that high temperature supports undesirable chemical changes in cheeses and certainly is related to their flavour.

This thesis is focused on determination of fatty acids in processed and/or processed cheese analogues using gas chromatography with FID detection. Characterization of fatty acids, various methods for lipid extraction and the possibilities of determination of fatty acids are described in the theoretical part. Simple and rapid method for the determination of fatty acids in natural and/or processed cheese was optimized and validated in the experimental part. The modified Folch method (by mixture of chloroform - methanol) was selected for lipid extraction from the samples. The standard method (ISO 5509), using a methanol solution of potassium hydroxide, was selected for lipid esterification. Type of the stationary phase and parameters of the column, flow of carrier gas, temperature of the injector, injection technique, temperature of the detector and temperature program were optimized. Calibration curves were constructed from five calibration points (in the concentration range of 0.01 - 60 g.ml-1), all correlation coefficients R2 were higher than 0,99. The limits of detection and quantification of individual fatty acids ranged from 0.002 - 6 g.ml-1. The repeatability of the method was good, all the relative standard deviations of the peaks were below 9 %. The optimized and validated method was applied to selected samples of processed cheese analogues. In total five types of analogues containing different kinds of fat (butter, apricot, linseed, black currant and grape seed oils) were analyzed. In samples 34 fatty acids were identified based on a comparison of retention times of standards.

Milch und daraus hergestellte Erzeugnisse spielen eine zentrale Rolle in der Ernährung des Menschen. Infolge einer Optimierung der molkereitechnologischen Produktionsprozesse ist eine gesteigerte Qualität sowie eine verlängerte Haltbarkeit dieser Produkte erzielt worden, wobei dies das Fundament des bis heute beständig wachsenden, vielfältigen Produktspektrums an Milch und der daraus hergestellten Erzeugnisse bildet. Die Globalisierung der Märkte sowie die in den letzten Jahren stark ansteigenden Rohstoff- und Energiekosten haben dabei zu einer erheblichen Verschärfung des Konkurrenzdrucks auch zwischen Lebensmittelproduzenten geführt. Um kostensenkend zu produzieren werden zahlreiche Massnahmen ergriffen, welche vorwiegend auf dem Ersatz von Fett- und Proteinanteilen, der Mischung von Milchsorten unterschiedlicher Spezies, dem Zusatz billiger Füllstoffe auf Milchbasis zur Ausbeuteerhöhung sowie einer falschen Deklaration von Produkten geschützter geografischer Herkunft beruhen (De la Fuente et al. 2005). Der Einfluss des globalisierten Milchmarktes macht dabei auch vor Schmelzkäseerzeugnissen und Schmelzkäsen keinen Halt. Produzenten dieser Produkte wurden infolgedessen mehr und mehr dazu verleitet, die in diesen Erzeugnissen wertgebende Rohware Käse anteilig durch günstigere Füllstoffe auf Milchbasis zu ersetzen. Neben ernährungs-physiologischen und technologischen Aspekten spielen in diesem Zusammenhang vor allem ökonomische Interessen eine entscheidende Rolle. Dem Endprodukt Schmelzkäse ist dieser Qualitätsverlust, welcher durch den Austausch von Käse-Protein durch Nicht-Käse-Protein resultiert, dabei auf den ersten Blick nicht unbedingt anzusehen. Bislang existieren auch keine einfachen analytischen Marker zur qualitativen Unterscheidung, geschweige denn quantitativen Bestimmung, dieser Rohwaren in Schmelzkäsen. Die analytischen Herausforderungen welche sich aus der vorliegenden Problemstellung ergeben, sind dabei sehr vielfältig. Nicht nur, dass alle wertgebenden Zutaten von Schmelzkäsen einem gemeinsamen Ausgangsrohstoff Milch entstammen, welcher zudem noch natürlichen Schwankungen in der Zusammensetzung unterliegt, sondern auch die in der wertgebenden Rohware Käse sorten-, reifungs- und lagerungsabhängig ablaufenden Prozesse führen zu starken Schwankungen der Zusammensetzung dieser Produkte. Wie genau die große Gruppe der Käsesorten basierend darauf chemisch charakterisiert werden kann, erscheint aus analytischer Sicht äußerst anspruchsvoll. Darüber hinaus kann eine Beeinflussung der chemischen Zusammensetzung der fertigen Schmelzkäseprodukte auch durch die während des Herstellungsprozesses herrschenden Bedingungen hervorgerufen werden. Das Ausmaß einer solchen Veränderung in handelsüblichen Schmelzkäsen ist jedoch nur schwer abschätzbar und bislang wenig erforscht worden. Einer Irreführung und Täuschung der Verbraucher sowie einer Verzerrung des Wettbewerbs zwischen den einzelnen Schmelzkäseproduzenten ist somit Tür und Tor geöffnet. Dies wird letztlich auch durch den Gesetzgeber nicht unterbunden, da dieser die Deklaration der eingesetzten Menge und Sorte an Käse sowie der Menge an zugesetztem Proteinzusatz zur Herstellung von Schmelzkäsen und Schmelzkäseerzeugnissen nicht zwingend fordert. Das Ziel der vorliegenden wissenschaftlichen Arbeit besteht somit darin, ein Analysenportfolio verschiedenster, analytischer Parameter zur Bestimmung der kompositionellen Zusammensetzung von Schmelzkäseerzeugnissen zu erarbeiten, mit deren Hilfe eine Unterscheidung der am Markt erhältlichen Produktqualitäten möglich ist. Weiterhin soll anhand der Kombination dieser analytischen Messgrößen sowie deren mathematischer Auswertung mittels multivariater Datenanalyseverfahren eine Bewertung und Priorisierung hinsichtlich deren Aussagekraft vorgenommen werden. Neben der Analyse handelsüblicher Schmelzkäse werden im Rahmen dieser Aufgabenstellung auch verstärkt die Schmelzrohwaren und Proteinzusätze sowie Modell-Schmelzkäse hinsichtlich deren chemischer Zusammensetzung charakterisiert. Das Hauptaugenmerk liegt dabei auf der Unterscheidung der Rohwaren Käse und den zum Schmelzkäseprodukt weiterhin zugesetzten Proteinpulvern auf Milchbasis. Zu diesen zählen neben den Trockenmilch- und Trockenmolkeerzeugnissen (Magermilchpulver, Milchpulverkonzentrat, Molkepulver) auch Milcheiweiß-erzeugnisse (Säure- und Labcasein). Zusammen stellen diese mengenmäßig den größten Anteil in Schmelzkäsen dar und bestimmen somit maßgeblich deren technologische und sensorische Eigenschaften und damit verbunden die Qualität und den Preis der fertigen Schmelzkäseprodukte.

The effect of ultra-high temperature processing by direct steam injection and room temperature storage of pH-adjusted and unadjusted 3X (volume reduction) skim milk retentate and the effect of storage at various temperatures of 3X skim milk retentate without pH adjustment on their ζ-potential, viscosity, and pH were determined. Pasteurized skim milk was concentrated to 3X by ultrafiltration. In the pH study portions of skim milk retentate were adjusted to pH 6.38 ± .02 with HCl and 6.85 ± .01 and 7.32 ± .02 with NaOH between ultrafiltration and ultra-high temperature processing. In the storage temperature study, storage temperatures used for pH-unadjusted retentate samples were 11°C, 23°C (room temperature), and 37°C. Although pH 6.38 samples had the lowest viscosity in the pH study before ultra-high temperature processing, these samples precipitated during ultra-high temperature processing. For non-acidified samples, increasing pH of retentate resulted in higher viscosities and quicker age gelation times. Destabilization occurred more rapidly at 37°C than at 23°C or 11°C. The pH drop tended to be greater for samples stored at a higher temperature or adjusted to a higher pH. During 28 weeks of 37°C storage the pH decreased from 6.54 to 6.06. During 32 weeks of 23°C storage pH of samples initially adjusted to pH 7.32 dropped to 7.06. ζ-Potentials of casein micelles were calculated from electrophoretic mobility obtained by measuring Doppler frequency shifts of scattered laser light in samples that had been diluted 300 fold with their own ultra.filtrate. Absolute values of ζ-potential of samples stored at 37°C decreased from -23.4 millivolts immediately after ultra-high temperature processing to -18.5 millivolts after 28 weeks of storage. For samples stored at 11°C and 23°C in the storage temperature study and control samples in the pH study, absolute values of ζ-potential decreased approximately 1.5 to 2.0 millivolts during 28 or 32 weeks of storage.

Mechanically deboned rainbow trout (Oncorhynchus mykiss) was analyzed and then used in texture studies. The meat contained a moderately low amount of fat (10% ± 2%, x ± SD). Pre-deboned meat had more calcium than deboned meat (PIF/=0.37). A combined response model predicted formulations for fish sausage that would closely duplicate the texture of commercially available processed meats. A thermal model was developed that helped verify the thermal properties of rainbow trout. Thermal conductivity was measured (k == 0.48 W/m·K) and specific heat was calculated (Cp= 3200 J/kg·K).