Dissertations / Theses on the topic 'Antibiotics in food preservation'

Thesis (MScVoedselwet)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: Red meat has a limited shelf-life at refrigerated temperatures, where spoilage is mainly due to the proliferation of bacteria, yeast and moulds, acquired during the dressing process. In addition, almost a fifth of food-borne disease outbreaks, caused by microorganisms such as Escherichia coli 0157:H7, Listeria monocytogenes and Staphylococcus aureus are associated with red meat. To improve the microbiological quality of red meat, systems such as HACCP, GHP and GMP are currently practiced; however, these practices are not able to extend the shelf-life of these products. At present suitable food-grade preservatives are recommended, but the use of some of these preservatives is increasingly being questioned with regard to their impact on human health. Additionally, food service customers demand high quality products that have a relatively long shelf-life, but still prefer the appearance of minimally processed food. All these factors challenge the food manufacturing industry to consider more natural means of preservation. Antimicrobial metabolites of food grade bacteria, especially lactic acid bacteria, are attracting increasing attention as food preservatives. Bacteriocins are antimicrobial peptides (3 to 10 kDa) with variable activity spectra, mode of action, molecular weight, genetic origin and biochemical properties that are bacteriostatic or bactericidal to bacteria closely related and bacteria confined within the same ecological niche. Micro-organisms were isolated from beef, lamb and pork, obtained from four commercial retailers. The number of viable cells three days after the sell-by date at 4ºC ranged from 80 cfu.g-1 to 1.4 × 108 cfu.g-1. Fifty-three percent were Gram-negative bacteria, 35% Gram-positive and 12% yeast. The microbial population of the meat was greatly influenced by the origin, i.e. the retailer. Bacteriocins produced by Enterococcus faecalis BFE 1071, Lactobacillus curvatus DF 38, Lb. plantarum 423, Lb. casei LHS, Lb. salivarius 241 and Pediococcus pentosaceus ATCC 43201 were screened for activity against bacteria isolated from the different meat samples. Sixteen to 21% of the isolates, identified as members of Klebsiella, Shigella, Staphylococcus, Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Pediococcus, Streptococcus and Bacillus were sensitive to the bacteriocins. Curvacin DF 38, plantaricin 423 and caseicin LHS (2.35 to 3.4 kDa) had the broadest activity range and inhibited species of Lactobacillus, Pediococcus, Enterococcus, Listeria, Bacillus, Clostridium and Propionibacterium. The bacteriocins remained stable at 121ºC for 20 min, in buffers with a pH ranging from 2 to 10 and in NaCl concentrations of between 0.1 and 10% (m/v). Like most peptides, they were sensitive to proteolytic enzymes. Curvacin DF 38 is sensitive to amylase, suggesting that the bacteriocin might be glycosylated. To assess the efficiency of curvacin DF 38, plantaricin 423 and caseicin LHS as meat preservatives, they were partially purified by ammonium sulphate precipitation and separation in a Sep Pak C18 cartridge. The shelf-life of pork may be extended by up to two days. Meat samples treated with bacteriocins were darker than the control (untreated) sample. Descriptive sensory evaluation by a seven-member panel indicated that there were significant differences (P ≤ 0.05) regarding the aroma, sustained juiciness, first bite and metallic taste attributes of the control and the 4 day-treated samples. The control and 2 day-treated samples and the 2 day- and 4 day treated samples did not differ significantly regarding these attributes. There were no significant differences regarding the initial juiciness, residue and pork flavour attributes. Concluded from the results obtained in this study, bacteriocins produced by Lb. curvatus DF 38, Lb. plantarum 423 and Lb. casei LHS effectively extended the shelf-life of pork loins by up to 2 d at refrigerated temperatures with no drastic changes on sensory characteristics. In edition, the stability of these bacteriocins broadens their application as preservatives in many foods.
AFRIKAANSE OPSOMMING: Die rakleeftyd van rooivleis by yskastemperature is beperk, waar bederf hoofsaaklik deur die vermenigvuldiging van bakterieë, giste en swamme veroorsaak word. Die meeste van hierdie kontaminante is afkomstig van die slagtingsproses. Byna ’n vyfde van alle uitbrake van voedselvergiftigings wat deur organismes soos Escherichia coli 0157:H7, Listeria monocytogenes en Staphylococcus aureus veroorsaak word, word met rooivleis geassosieër. Die praktyke HACCP, GMP en GHP word tans toegepas om die mikrobiologies kwaliteit van vleis te handhaaf, maar is egter nie voldoende om die rakleeftyd van rooivleis the verleng nie. Die preserveermiddels wat huidiglik aanbeveel word vir dié doel, word toenemend bevraagteken aangaande die invloed daarvan op die menslike gesondheid. Hierby is daar ’n aanvraag na hoë kwaliteit, ongeprosesseerde produkte met ’n verlengde rakleeftyd. Gevolglik word die voedsel vervaardigings industries aangemoedig om meer natuurlike vorms van preservering the oorweeg. Die aandag word tans op die anti-mikrobiese metaboliete van voedselgraad microbes, veral melksuurbakterieë, gevestig. Bakteriosiene is anti-mikrobiese peptiede (3 tot 10 kDa) met verskeie aktiwiteitsspektra, werkswyse, molekulêre massa, genetiese oorsprong en biochemiese eienskappe. Bakteriosiene is meestal bakterie-dodend of - staties teen taksonomies naby geleë organismes en organismes vanuit dieselfde ekologiese nis. Mikroörganismes is geïsoleer vanuit bees-, skaap- en varkvleis, verkry vanaf vier supermarkte. Die aantal lewensvatbare selle per gram (cfu.g-1) het drie dae na die “verkoop”-datum by 4ºC vanaf 80 cfu.g-1 tot 1.4 × 108 cfu.g-1 gevarieër. Drie en vyftig persent van die isolate is as Gram-negatief, 35% as Gram-positief en 12% as giste geïdentifiseer. Die sensitiwiteit van hierdie isolate teen bakteriosiene wat deur Enterococcus faecalis BFE 1071, Lactobacillus curvatus DF 38, Lb. plantarum 423, Lb. casei LHS, Lb. salivarius 241 en Pediococcus pentosaceus ATCC 43201 geproduseer is, is vervolgens getoets. Tussen 16% en 21% van die isolate was sensitief teen die bacteriosiene en is onder andere as Klebsiella, Shigella, Staphylococcus, Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Pediococcus, Streptococcus en Bacillus geïdentifiseer. Die bakteriosiene met die wydste aktiwiteitsspektrum, naamlik, curvacin DF 38, plantaricin 423 en caseicin LHS is verder ondersoek. Hierdie antimikrobiese peptiede (2.35 tot 3.4 kDa) toon aktiwiteit teen spesies van Lactobacillus, Pediococcus, Enterococcus, Listeria, Bacillus, Clostridium and Propionibacterium. Die bakteriosiene is stabiel by 121ºC vir 20 min, in buffers met ‘n pH-reeks van tussen 2 en 10 en soutkonsentrasies vanaf 0.1% tot 10%. Soos die geval by meeste peptiede is hierdie bakteriosiene sensitief vir proteolitiese ensieme. Curvacin DF 38 is ook sensitief vir amylase, wat daarop dui dat hierdie bakteriosien moontlik geglikosileer is. Die effektiwiteit van curvacin DF 38, plantaricin 423 en caseicin LHS as preserveermiddel in voedselsisteme is getoets deur dit te suiwer (ammonium sulfaat presipitasie en Sep Pak C18 kolom) en op vark lendestukke aan te wend. Mikrobiese analise het bewys dat die rakleeftyd van vark met sowat 2 dae verleng kan word. Volgens die vleiskleurevaluering was die bakteriosien behandelde vark donkerder as die kontrole. Die aroma-, sappigheid-, tekstuur- en metaalgeur-eienskappe van die kontrole en die 4-dag behandelde monster het volgens ‘n opgeleide sensoriese paneel betekenisvol verskil (P ≤ 0.05). Die kontrole en die 2-dag behandelde en die 2-dag behandelde en die 4-dag behandelde monsters het nie betekenisvol verskil nie. Daar was geen betekenisvolle verskil aangaande die aanvanklike sappigheid-, residu- en varkgeur-eienskappe nie. Hierdie sensoriese eienskappe is belangrik ten opsigte van die verbruiker se aanvaarding van die produk. Vervolgens kan uit hierdie resultate afgelei word dat die bakteriosiene wat deur Lb. curvatus DF 38, Lb. plantarum 423 en Lb. casei LHS geproduseer word voldoende is om die rakleeftyd van vark lendestuk by 4ºC met 2 dae te verleng met min of geen effek op die sensoriese persepsie van die vleis. Hierdie bakteriosiene is ook stabiel onder verskeie kondisies wat die toepassing as preserveermiddel aansienlik verbreed.

The application of ionizing radiation as a preservation method for food is described and examined. The prospects and problems of introducing radiation technology for food preservation are discussed under the following aspects: (1) technical feasibilities; (2) irradiator design requirements; (3) facilities' cost analysis, and (4) legislation. Within the specified limits, ionizing radiation provides an efficacious food preservation treatment which will not lead to radioactivity induction or prejudice the safety and wholesomeness of the food. A brief introduction and description of the design approach of an industrial scale irradiator is given with an illustrative example. Assessments of the cost of radiation treatment of food of some commercially available irradiators are cited and analyzed. The international regulatory efforts and the present status of clearance, standardization and legislation of food irradiation is reviewed and discussed. It is concluded that food irradiation is ready for commercial applications and could be effectively regulated by pertinent health and safety authorities.

As foodstuffs are being produced, transported and stored in greater quantities than ever before in human history and with an alarming amount of food products being lost to spoilage every year, new, environmentally friendly ways of preserving food products are being actively researched and developed in today’s world. Oxygen is a key pathway towards food decay and destruction, due to its dual roles as a source of respiration for the multitude of microorganisms that can cause food spoilage and through direct destruction through oxidation reactions within food products that cause oxidative deterioration. Fuel cells have the theoretical potential to be an energy efficient and environmentally friendly way of preserving food, such as fish, fruit and vegetables.  Because of their nature to consume oxygen through the electrochemical reactions that produces their electrical power, they have the potential to be used to reduce localised oxygen content for the storage and transportation of foods, minimising their spoilage, as well as potentially providing electrical energy for other components in potential control systems for the fuel cell. The purpose of this project is to design and build a PEM fuel cell and examine its potential for lowering of oxygen concentrations at the gas output at the cathode.  The outcome of these experiments are designed to validate the  theoretical capacity of fuel cells to reduce output oxygen concentrations to levels that are able to aid in the preservation of foodstuffs.  It is hoped that this study, in conjunction with the researched literature, can be used as a guide for future food shipping and storage methods. The experimental stage of this diploma work was unsatisfactory. The fuel cell was unable to produce a voltage and the reactant gases were unable to flow through the fuel cell due to a design flaw. Therefore the effectiveness of a fuel cell for depletion of oxygen to levels able to preserve food is based on the theoretical basis of the internal PEM fuel cell reactions, as well as studying past literature and patents. If the theoretical ability of the fuel cell is proven, it can be asserted that PEM fuel cells have the potential to be a real contender in the field of food preservation in shipping and storage, as well as offering greater levels of control for supplies for how and when they can ship their product. However this will require more independent research development work on the effects of low oxygen concentrations on a fuel cell operation as well as the preservation effects on a greater variety of foodstuffs. Furthermore, more research is required for more efficient and cheaper fuel cell catalysts or innovative designs are required to avoid concentration losses that arise from oxygen reduction at low oxygen levels.

Recent reports detail a rise in the practice of home food preservation in the United States due to economic woes, nutritional concerns, and increasing devotion to local food production.Home food preservation is the processing of foods in order to extend its shelf-life. Current common approaches to preserving foods at home include pressure canning, freezing, drying, water bath canning, and cellaring/storing. Local food production in four Kentucky counties were examined through in-depth qualitative interviews with home food preservation practitioners to yield a rural/urban comparison. Forty home food preservation practitioners were interviewed between Fall 2009 and Fall 2013. The primary question driving this project is what motivates those who grow gardens and practice home food preservation in an era of readily available, relatively cheap foodstuffs? Secondary questions include, how do the motivations of home food preservation practitioners compare in rural and urban areas? What are the links, if any, between home food preservation and environmental sustainability concerns in rural and urban areas? Each of these questions will be examined through a mixture of qualitative methods and a grounded theoretical approach. In-depth field interviews with 40 preservers, documentary filmmaking, and participant observation were conducted in two rural and two urban Kentucky counties. Interview transcripts were coded by themes, interpreted using hermeneutic analysis, and analyzed by grounded theory. Policy institutes could make gains from this research by building upon already existing community food practices. Agriculture extension agent could use these findings to inform their food preservation programs and improve safety recommendations.

The overall objective of the doctoral thesis was the development of starch-based (S) biodegradable active films for food packaging applications, by applying both casting method and thermoprocessing. Different blends of S with protein material have been studied in order to improve the functional properties of the films or confer antimicrobial/antioxidant activity. The following protein materials were used: powder buttermilk (BM); lactoferrin (LF) and/or lysozyme (LZ), and bovine gelatin (BG). Ethyl lauroyl arginate (LAE, E243) was also incorporated as antimicrobial compound. Likewise, S:BG blend films, either with or without LAE, with previously oxidized S, have been studied to enhance the crosslinking of polymer chains and to improve the film properties. The films have been characterized as to their functional properties as packaging material, their antioxidant and/or antimicrobial properties, as well as their capacity for preserving different food systems, in terms of lipid oxidation and microbial spoilage. Blends of S with BM gave rise to films with a heterogeneous structure, in which the formation of a protein gel was observed when BM dispersion was heated with S at 90 ºC for 30 min. The heat treatment promoted an increase in the resistance to break and stretchability of films, together with a decrease in water vapour permeability. Only those films subjected to heat treatment exhibited antioxidant activity, probably due to the release of active peptides as a result of high temperatures. However, no antilisterial activity was observed for any film containing BM. The incorporation of LF and/or LZ into S films, obtained by the casting method, led to a partial compatibility between polymers, thus affecting the microstructure of S films, as well as leading to an rise in the glass transition temperature. Films with proteins were less extensible, especially when LF was incorporated. All of the films tested were effective at controlling the progress of lipid oxidation in pork lard, whereas only films with LF/LZ blend reduced the growth of coliforms in minced pork meat, as a result of their synergistic action. Films based on S and BG blends (1:1) were obtained by both casting method and thermo-processing. Phase separation of both polymers (stratified structure or separated domains of both polymers, respectively) was observed in both cases. The incorporation of LZ, but mainly LAE, into films, enhanced the compatibility between polymers. Thermo-processed films were more permeable to water vapour and oxygen, less rigid and resistant and more stretchable, in comparison with those films obtained by casting. While LAE incorporation improved the water vapour barrier capacity, it worsened the oxygen barrier properties, contrary to the effect produced by LZ. All films with LAE exhibited high antilisterial activity. Films based on oxidized S and BG (1:1), obtained by casting, showed a high polymer compatibility, and crosslinking between the polymer chains occurred due to the carbonyl-amino condensation reaction. As a result, the water uptake ability of the films decreased and the mechanical and barrier properties improved, although film browning was induced due to the formation of Maillard compounds. LAE incorporation implied its involvement in condensation reactions, due to its bi-functional character (carbonyl-amino), thus affecting crosslinking and the film properties. These reactive processes progressed throughout storage time, leading to an increase in the mechanical resistance and browning of the films. The obtained Maillard compounds conferred antimicrobial capacity on the films, which increased as the storage time progressed. The application of blend films of native or oxidized S and BG with LAE, for the purposes of preserving vacuum packaged chicken breast fillets, extended the shelf-life through the inhibition of bacterial growth (total viable counts; psicrotrophic, anaerobic,lactic acid bacteria and coliforms). Samples packaged i
El objetivo general de la presente tesis doctoral se basa en el desarrollo de films activos biodegradables a base de almidón (S) para su aplicación en sistemas de envasado de alimentos, por medio de dos métodos diferentes de obtención, método en húmedo por extensión y secado (casting) y método en seco (termoprocesado). Se estudiaron mezclas de S con diferentes materiales proteicos, con fin de disminuir la alta higroscopicidad de los films de S y su retrogradación a lo largo del tiempo de almacenamiento y mejorar sus propiedades funcionales, así como conferirles actividad antimicrobiana/antioxidante. Los materiales proteicos utilizados fueron los siguientes: suero de mantequilla en polvo (BM); lactoferrina (LF) y/o lisozima (LZ), y gelatina bovina (BG). El etil lauroil arginato (LAE, E243) fue también incorporado como compuesto antimicrobiano. Asimismo, se estudiaron los films mezcla de S con BG, con y sin LAE incorporado, habiendo oxidado previamente el S, para así potenciar el entrecruzado de las cadenas poliméricas y mejorar las propiedades de los films. Estos fueron caracterizados en sus propiedades funcionales como material de envase, sus propiedades antioxidantes y/o antimicrobianas, así como por su capacidad de conservación de diferentes sistemas alimentarios, en términos de su oxidación lipídica y deterioro microbiológico. Las mezclas de S con BM dieron lugar a películas con una estructura heterogénea, en las que se observó la formación de un gel proteico como resultado del calentamiento de la dispersión BM con S a 90 ºC durante 30 min. El tratamiento térmico promovió un aumento de la resistencia a la rotura y extensibilidad de los films, junto con una disminución en la permeabilidad al vapor de agua. Sólo las películas sometidas a tratamiento térmico y homogeneización con cizalla mostraron actividad antioxidante, probablemente debido a la liberación de péptidos activos en consecuencia de la alta temperatura y fuerza de cizalla aplicada Sin embargo, no se observó actividad antilisteria para ninguno de los films con BM. La incorporación de LF y/o LZ en films de S condujo a una compatibilidad parcial entre polímeros, afectando así a la microestructura de los films de S, y produciendo un aumento de la temperatura de transición vítrea y disminución de la capacidad de alargamiento de los films, especialmente cuando se incorporó LF. Todos los films resultaron eficaces en el control del progreso de la oxidación lipídica de la manteca de cerdo, mientras que sólo las películas con mezcla LF/LZ redujeron el crecimiento de coliformes en carne picada de cerdo, como resultado de su acción sinérgica. Los films basados en la mezcla S y BG (1: 1) fueron obtenidos por casting y termo-moldeado y compresión, llevando a la separación de fases entre ambos polímeros (estructura esratificada o separación de dominios de ambos polímeros, respectivamente). La incorporación de LZ, y principalmente de LAE, en los films, aumentó la compatibilidad entre ambos polímeros. Los films termoprensados fueron más permeables al vapor de agua y al oxígeno, menos rígidos y resistentes y más extensibles, en comparación con aquellos obtenidos por casting. La incorporación de LAE mejoró la capacidad de barrera contra el vapor de agua, mientras que incurrió en un empeoramiento de la barrera frente al oxígeno, contrariamente al efecto producido por la LZ. Los films con LAE, moldeados o termoprensados, mostraron una alta eficacia antilisteria. Los films basados en S oxidado y BG (1: 1), fueron obtenidos por casting y mostraron una alta compatibilidad polimérica, lo cual condujo al entrecruzado de las cadenas como resultado de la reacción de condensación carbonilo-amino producida entre ambos polímeros. En consecuencia, la capacidad de absorción de agua de los films disminuyó y se mejoraron las propiedades mecánicas y de barrera, aunque también se indujo a un pardeamiento de los films, indicando
L'objectiu general de la tesi doctoral és el desenvolupament de films actius biodegradables a base de midó (S) per a la seua aplicació en sistemes d'envasat d'aliments, amb l'utitització del mètode d'extensió i assecat (casting) i termoprocessat (barrejat en fos i termo-compressió). Es van estudiar barreges de S amb diferents materials proteics, per millorar les propietats funcionals dels films o conferir activitat antimicrobiana. Els materials protèics utilitzats van ser: sèrum de mantega en pols (BM); lactoferrina (LF) i/o lisozima (LZ), i gelatina bovina (BG). L'ètil lauroil arginat (LAE, E243) va ser també incorporat com a compost antimicrobià. Així mateix, es van estudiar els films barreja de S amb BG, amb i sense LAE, havent oxidat prèviament el S, per potenciar l'entrecreuat de les cadenes polimèriques i millorar les propietats dels films. Aquests van ser caracteritzats en les seues propietats funcionals com a material d'envàs, les seues propietats antioxidants i/o antimicrobianes, així com en la seua capacitat de conservació en diferents sistemes alimentaris, en termes de la seua oxidació lipídica i deteriorament microbià. Les barreges de S amb BM van donar lloc a films amb una estructura heterogènia, en què es va observar la formació d'un gel protèic com a resultat del calfament de la dispersió BM amb S a 90 ºC durant 30 min. El tractament tèrmic va promoure un augment de la resistència al trencament i extensibilitat dels films, juntament amb una disminució en la permeabilitat al vapor d'aigua. Només el films sotmesos a tractament tèrmic van mostrar activitat antioxidant, probablement a causa de l'alliberament de pèptids actius com a conseqüència de l'alta temperatura. No obstant això, no es va observar activitat antilisteria per cap dels films amb BM. La incorporació de LF i/o LZ en films de S obtinguts per casting va donar lloc a una compatibilitat parcial entre polímers, afectant a la microestructura dels films de S, i produint un augment de la temperatura de transició vítria. Els films amb les proteïnes van ser menys extensibles, especialment quan es va incorporar LF. Tots els films van resultar eficaços en el control de l'oxidació lipídica de la mantega de porc, mentre que només el films amb barreja LF/LZ van reduir el creixement de coliforms en carn picada de porc, com a resultat de la seua acció sinèrgica. Els films amb barreges S i BG (1: 1) van ser obtinguts per casting i termo-processat. En tots dos casos es va observar separació de fases entre els dos polímers (estructura estratificada o separació de dominis d'ambdós polímers, respectivament). La incorporació de LZ, i principalment de LAE, en els films, va augmentar la compatibilitat entre tots dos polímers. Els films termo-processats van ser més permeables al vapor d'aigua i l'oxigen, menys rígids i resistents i més extensibles, en comparació amb els obtinguts per càsting. La incorporació de LAE va millorar la capacitat de barrera al vapor d'aigua, a l'hora que va disminuir la capacitat de barrera davant l'oxigen, contràriament a l'efecte produït per la LZ. Tots els films amb LAE, van mostrar una alta capacitat antilisteria. Els films amb S oxidat i BG (1: 1), van ser obtinguts per casting i van mostrar una alta compatibilitat dels polímers, tot produint entrecreuat de les cadenes com a resultat de la reacció de condensació carbonil-amino. En conseqüència, va disminuir la capacitat d'absorció d'aigua dels films i es van millorar les propietats mecàniques i de barrera, encara que es va promoure l'enfosquiment dels films, cosa que indica la formació de compostos de Maillard. La incorporació de LAE va implicar la seua participació en les reaccions de condensació, a causa del seu caràcter bi-funcional (carbonil-amino), el que va afectar a l'entrecreuat i les propietats dels films. Aquests processos reactius van progressar al llarg del temps d'emmagatzematge, donant lloc a un augment de l
Moreno Marro, O. (2017). Starch-protein active films for food preservation [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/80616
TESIS

Lactic acid fermented fruit and vegetables are normally obtained following a natural spontaneous fermentation in which no starter cultures are added. It could be expected that a suitable starter culture would help standardise production. Several lactic acid bacteria were selected for a series of physiological studies, in a defined medium (MRS broth) and in carrot juices, under varying conditions of growth temperature, salt concentration and carbohydrate source. Based on these, the homofermenter Lactobacillus pentosus and the heterofermenter Leuconostoc mesenteroides were tested as potential starters, in single and mixed cultures, for the fermentation of carrots (Daucus carota), as a novel fermentable substrate, and cabbage (Brassica oleracea) into sauerkraut. Fermentations were performed in the presence of the natural microflora. Sugar catabolism and acid production were monitored through H.P.L.C. In the fermentation of carrots Leuconostoc mesenteroides played a major role, with no homofermenters present. For sauerkraut, the mixed starter culture composed of Leuconostoc mesenteroides and Lactobacillus pentosus gave the closest resemblance to the product normally obtained following a natural commercial fermentation. The inclusion of the heterofermenter provided the required acid balance for correct product flavour and aroma by enhancing production of acetic acid. Acetate is also a better antimicrobial than lactate. A shorter fermentation time was also obtained, reducing the time from 3-4 weeks in the natural fermentation to only 7 days with the use of the mixed starter. When reduced salt concentrations were tried, 1% NaCl (w/w) resembled the spontaneous fermentation more closely, in regard to microbial sequence, pH and total acidity. Different ratios of the two lactic acid bacteria in combination were tried, the best being that in which L, mesenteroides and L. pentosus were initially present in the same proportions. Survival of Listeria monocytogenes in fermenting sauerkraut was shorter when starter cultures were used, but no difference was detectable between mixed and single cultures.

This dissertation addresses the history of antibiotic use in British and US food production between 1950 and 2013. Introduced to agriculture in the 1950s, antibiotics underpinned the 20th-century revolution in Western food production. However, from the late 1950s onwards, controversies over antibiotic resistance, residues and animal welfare began to tarnish antibiotics' image. By mapping both the enthusiasm and the controversies surrounding antibiotic use, this dissertation shows how distinct civic epistemologies of risk influenced consumers', producers' and officials' attitudes towards antibiotics. These differing risk perceptions did not emerge by chance: in Britain, popular animal welfare concerns fused with new scenarios of antibiotic resistance and drove reform. Following 1969, Britain pioneered antibiotic resistance regulation by banning certain feed antibiotics. However, subsequent reforms were only partially implemented, and total antibiotic consumption failed to sink. Meanwhile, scandals and public pressure forced the American FDA to install the first comprehensive monitoring program for antibiotic residues. However, differing public priorities and industrial opposition meant that the FDA failed to convince Congress of resistance-inspired bans. The transatlantic regulatory gap has since widened: following the BSE crisis, the EU phased out growth-promoting antibiotic feeds in 2006. The US proclaimed only a voluntary and partial ban of antibiotic feeds in December 2013. In the face of contemporary warnings about failing antibiotics, the dissertation shows how one group of substances acquired different meanings for different communities. It also reveals that the dilemma of antibiotic regulation is hardly new. Despite knowing about antibiotic allergies and resistance since the 1940s, no country has managed to solve the dilemma of preserving antibiotics' economic benefits whilst containing their medical risks. Historically, effective antibiotic regulation emerged only when differing perceptions of antibiotics were broken down either by sustained regulatory reform or large crises.

Thesis (PhD) -- University of Western Sydney, 2003.
"A thesis submitted for degree of Doctor of Philosophy, Centre for Advanced Food Research, School of Science, Food & Horticulture, University of Western Sydney, Hawkesbury campus, Richmond, Australia, January 2003" Bibliography: leaves 199-227.

Weak acids are commonly used in the food industry as food preservatives however a complete understanding of their mode of action is not available. This study aimed to gain an understanding of the inhibitory mechanisms of two weak acids: sodium acetate and sodium benzoate. The ability of these weak acids to perturb the internal pH of cells was determined, a phenomenon previously shown as a mode of action of weak acids. However, changes in pHi alone were not sufficient in explaining the growth inhibition observed with sodium acetate, suggesting that the weak acid anion may also contribute to growth inhibition. The effect of the accumulation of was weak acid anions was found to be a reduction of cellular amino acid pools, mainly glutamate. When cells were transferred from medium containing weak acid to acid-free medium, recovery of internal pH was shown to be dependent on glutamate synthesis. The relieving effects of methionine on weak acid inhibition were also investigated. The aim of this section of the study was to identify the mechanism by which methionine resulted in relief of weak acid inhibition. It was found that addition of weak acid resulted in a 16-fold increase of the intracellular concentrations of homocysteine. This methionine precursor has been shown to act as a competitive inhibitor of methionine for methyl-tRNA-synthetase. Addition of methionine is therefore proposed to reduce weak acid inhibition by reducing homocysteine pools by feedback inhibition and by out-competing the intermediate.

Thesis (Masters Diploma (Food Technology)) -- Cape Technikon, Cape Town, 1992
Kakamas peaches and Bulida apricots were heat processed in transparent and aluminium laminated plastic bags and compared with fruit heat processed in standard cans. Heat processing conditions were optimized to produce acceptable processed products. Appropriate chemical and microbiological properties of all treatments as well as sensory quality of peaches were investigated. Although rectifiable disadvantages such as texture softening and fading of colour appeared during storage, peaches and apricots were successfully heat processed in aluminium laminated pouches. Heat processed peaches had a maximum storage life of 12 months and apricots 6 months when stored at ambient temperature in aluminium laminated pouches.

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第19779号
農博第2175号
新制||農||1041(附属図書館)
学位論文||H28||N4995(農学部図書室)
32815
京都大学大学院農学研究科応用生命科学専攻
(主査)教授 小川 順, 教授 阪井 康能, 教授 栗原 達夫
学位規則第4条第1項該当

Dissertação para obtenção do Grau de Doutor em Química Sustentável
Antimicrobial agents have revolutionized medicine and promoted an increase in average life expectancy of human populations worldwide. These drugs are used not only in human medicine but also in veterinary practice, in the treatment and prevention of infections, and in some regions in the world, as well as growth promoters, ensuring a greater and better animal production. The use of antimicrobial agents in animal production causes contamination of the final product with drug residues that are eventually distributed in human food chain. Residues of antimicrobial agents provenient from human and animal consumption are also present in sewage, surface water or ground water. It is still unknown all the consequences of this contamination, but there are indications of changes in indigenous microbiota. The use of these drugs was quickly followed by the emergence of resistance, which led to decreased efficacy and compounds available. Therefore, the spread of antimicrobial agents in the environment is also associated with increased resistance to such drugs. The presented work intended to establish methods for monitoring the presence of antibiotics in animal foods, evaluate if the presence of antimicrobial agents in the environment at sub-inhibitory concentrations can contribute to the selection of resistant bacteria and characterize the biological activity of a number of compounds of the quinoxaline family as potential new antimicrobial agents. In order to achieve these objectives, chromatographic techniques were used for detection and quantification of antimicrobial agents, methods of microbiology and molecular biology to evaluate the behavior of bacteria under selective pressure. Various strains of prokaryotes and eukaryotes microorganisms were also used to evaluate the antimicrobial activity of N-oxide derivatives of quinoxaline. We used, also, cell cultures to assess the potential toxicity of these new antibiotics. A new chromatographic method was developed to quantify the reduced and oxidized forms of glutathione, in order to infer the cellular oxidative stress induced by exposure to the quinoxaline derivative compounds with proven antimicrobial activity. The results confirm that the chromatographic HPLC-DAD methods are powerful tools in monitoring food quality. They also indicate that the presence of subinhibitory amounts of ciprofloxacin in water may influence the dynamic of susceptible and resistant to ciprofloxacin Escherichia coli population. An assessment of the biological activity of quinoxaline derivatives indicated the compounds studied as potential new antimicrobial agents who have shown low toxicity in cell lines and oxidative cell damage in small extent.
Fundação para a Ciência e Tecnologia - bolsa de doutoramento SFRH / BD /48116 / 2008

Nisin is a bacteriocin produced by Lactococcus lactis subsp. lactis, which is active against Gram-positive organisms including bacterial spores. It is not generally active against Gram-negative bacteria, yeasts and fungi. Gram negatives show nisin-sensitivity when their outer membrane permeability is altered by various means, such as treatments with chelators, e.g. EDTA, osmotic shock, heating, freezing, freeze-drying, high- pressure etc. Application of chelators and nisin is effective against Gram-negatives when exogenous nisin is added. Nisin produced in situ and chelators are not an effective combination, since nisin production follows the pH drop caused by sugar fermentation, and this interferes with the sequestering ability of the chelators. Presence of nisin during thermal inactivation of Gram-negatives though is effective. Bacteria become structurally injured during heating showing sensitivity to agents like SDS and deoxycholate and extended detection times by impedimetry. These injured bacteria are inactivated by nisin, with a concomitant reduction of the measured D-values. Low pH and the presence of small amount of chelators enhance the injury and inactivation and reduce D-values further. Gram-negative bacteria injured by chilling and freezing are also sensitive to nisin. The effectiveness of nisin is reduced in a food environment mostly of nisin binding to fat, and food particles. D-values were decreased less or not at all in egg white and liquid whole egg, respectively, and rapid chilling of bacteria attached to chicken skin in presence of nisin did not give the effect seen in laboratory media. Nisin is active against heat-, chill-, and freezing-stressed Gram-negatives only if it is present during the treatments. When the stress factor is removed, the bacteria recover their nisin resistance, implying transient susceptibility to nisin, but not to smaller molecules. This is probably due to rapid reorganisation and restoration of OM permeability damage, rather than biochemical repair. The LPS chain length influences the sensitisation of Gram-negatives to nisin, only in the case of freezing, where the strain with the shorter LPS chain was more sensitive than the wild type. Heat-, and freezing-stressed bacteria lost lipopolysaccharides and increased their cell surface hydrophobicity. This was not seen with chill-stressed bacteria, which were sensitive to nisin though. This indicates that release of LPS is not a prerequisite for nisin sensitivity in Gram-negatives.

The application of pulsed electric fields (PEF) in food processing is a novel technique that requires careful study. In addition, improved understanding of the effect of PEF parameters on both physical and qualitative attributes of agrifood products is a requirement for the application and control of this emerging technology. PEF parameters investigated were pulse widths of 100, 200, and 300 mus, with electric field strengths of 0.75 and 1.5 kV/cm. The amount of pulses used for apples was up to 60, whereas up to 120 pulses were used for potatoes. Initially, apple and potato slices were exposed to various combinations of PEF parameters in order to evaluate the change in their electrical conductivities as an indicator of the disruption of the cell membrane. Subsequently, the impact of PEF on color and texture attributes was studied. In the final set of experiments, PEF was applied as a pre-treatment in order to accelerate the diffusion of moisture in a convective air-drying process at 70°C.
Results regarding the electrical conductivity and the changes in color revealed the similar effect of applying pulses with 100, 200 and 300 mus of duration. Increasing the number of pulses and/or the electric field strength resulted in increased electrical conductivity and discoloration rates of samples. PEF reduced the compressive strength of apple tissues between 21 to 47%. However, the compressive strength of potato tissues did not seem to be affected by the application of PEF. When PEF was applied as a pre-treatment, it caused an increase of up to 30% in the moisture diffusion coefficients of potatoes. In the case of apples, PEF pre-treated samples did not show any increase in drying rates.

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xvi, 231 p.; also includes graphics (some col.) Includes bibliographical references (p. 212-224). Available online via OhioLINK's ETD Center

The refrigeration energy load in a modern day supermarket makes up a large proportion of the total energy bill. Better design of refrigerated display cases would reduce this load and also have a corresponding effect on the running costs of the refrigeration plant. Further enhancements such as the reduction of air overspill from the case would also influence the aisle temperatures and therefore the comfort levels in the store. This research project uses the technique of computational fluid dynamics (CFD) to investigate the contemporary design of a vertical multideck refrigerated display case. From a two dimensional computational model conclusions were drawn as to the principles of operation of the case. During the course of the project, a custom designed experimental facility was constructed, capable of testing the display case according to the relevant test standards. Using this facility, experimental validation was carried on a number of the design modifications to assess the actual refrigeration load against that predicted by the CFD model. The success of this validation allowed further work into the feasibility of certain design changes by making modifications to the CFD model. The work presented in this thesis makes a contribution to the global effort towards the reduction of the energy consumption by retail refrigeration systems. It does this by showing that possibilities do exist for an improvement in the energy efficiency of multideck refrigerated display cases and that CFD provides a useful tool towards this goal. It also demonstrates the design modifications which proved to yield a saving in energy. These were a reduction in the mass flow rate of air around the case, the inclusion of a honeycomb section on the air curtain outlet of the case the addition of a front upstand and the introduction of a second air curtain thus applying a velocity gradient across the curtain.

The effect of acids on the growth, survival and detection of Salmonella enteritidis PT4 is particularly important in view of the number of outbreaks in which mayonnaise has been implicated as a vehicle. Capacitance measurement was compared with colony counting procedures for the enumeration and determination of sub-lethal injury of Salmonella enteritidis during storage under varied conditions of pH, acidulant and temperature. Capacitance monitoring was shown to offer an improved technique for the measurement of sub-lethal injury in cell populations. Higher levels of sub-lethal injury were detected by the extension of capacitance detection time than were indicated by differential colony counts on selective and non-selective media. The extension of detection time noted with sub-lethally injured cell populations was shown to be due to an extended lag phase when cells were placed in the capacitance growth medium and not the result of delayed detection of the growth of a small, uninjured sub-population. Plots of percentage survival and extension of detection time in survivors gave similar curves for acetic and lactic acid. These acids showed both greater lethality and greater ability to inflict sub-lethal injury than the stronger citric or hydrochloric acid. Sub-lethal injury and lethality were not simply related, as little sub-lethal injury was observed with the stronger acids even under conditions that were ultimately highly lethal. The results indicate that weak organic acids cause more reversible damage to cellular sites prior to death: an observation that has implications for choice of resuscitation procedures when examining acidified foods. Injured cells were found to contain lower levels of ATP than healthy unstressed cells. Inhibition with chloramphenicol did not appear to increase injury and total protein patterns for injured and uninjured cells were similar, suggesting that protection afforded by the synthesis of stress proteins is not a significant factor in this case. The recovery of sub-lethally injured cells in various pre-enrichment and selective enrichment media using capacitance detection times and colony counts on selective and non selective media was determined. Buffered peptone water appeared more effective in recovering injured Salmonella compared to Lactose broth. Additionally, selenite cystine was shown to recover cells faster than the other two selective broths tested; the Muller-Kauffmann Tetrathionate broth and the Rappaport Vassiliadis enrichment broth. In this study, different injury conditions were applied; these included acid stress, heating and freezing. According to the lag phases of injured cell populations, short pre-enrichment is not recommended in the present study.

Sodium phosphite was evaluated for inhibition of growth of spoilage yeasts in laboratory media and in two commercial carbonated beverages. In addition, the effects of pH and atmosphere in combination with sodium phosphite were also examined in laboratory media. Inhibition studies in laboratory media were performed with optimal or near optimal growth conditions for each yeast. Growth was monitored by measuring optical density at 600 nm. A time to significant growth was determined for experiments in laboratory media and was used to evaluate the effect that sodium phosphite and other test variables had on growth. A time to detectable growth was determined for experiments in commercial carbonated beverages and post incubation counts on observations with undetectable growth were used to evaluate the effects of sodium phosphite on yeast growth. Sodium phosphite was most effective in inhibiting growth of Zygosaccharomyces bailii, and less effective against Saccharomyces cerevisiae, and Saccharomyces uvarum respectively. Results from this investigation show the potential use of sodium phosphite as an antimicrobial food preservative has potential.
Master of Science

CAPES
A quitosana é um polímero abundante e oriundo principalmente de crustáceos a qual vem sendo amplamente estudada em vários segmentos inclusive como coberturas comestíveis de frutas. Frutas e hortaliças sofrem com a ação do clima, insetos e injurias do pós colheita; atentos a isto, pesquisadores vem estudando e desenvolvendo coberturas comestíveis que protejam a integridade dos vegetais. As coberturas de quitosana podem ser funcionalizadas com outros compostos que melhorem as suas características bem como a sua resistência pode ser aumentada com o uso de agentes reticulantes.
Chitosan is an abundant polymer and derived mainly on crustaceans which has been widely studied in various segments including as edible fruit toppings. Fruits and vegetables suffer from climate action, insects and injuries of post harvest; aware of this research has been developing and studying edible coatings that protect the integrity of the plants. The chitosan covers can be functionalized with other compounds that improve its characteristics and its strength can be increased by the use of crosslinking agents.
5000

Thesis (MSc)--Stellenbosch University, 2001.
ENGLISH ABSTRACT: Kepi is a refreshing, fermented dairy beverage that has been consumed for centuries and is traditionally made by incubating Kepi grains in milk. The Kepi grain is a complex starter culture consisting of a variety of lactic acid bacteria and yeasts. The successful marketing of the grains requires the effective preservation of the microbes present in the grains as well as an appropriate packaging that will retain the acidification activity of the preserved grains over an extended period of time. The aim of this study was to evaluate different preservation techniques and packaging materials in terms of their respective abilities to retain grain viability and activity over an extended storage period. Four different preservation techniques (freezing at -18°C, refrigeration at 4°C, air-drying and Iyophilisation) and three packaging materials including a low density polyethylene film (LOPE), an oriented polyester film (OPET) and a metallised oriented polyester film (MOPET), were evaluated. Activity tests were used to evaluate the impact of the preservation techniques in terms of the retainment of the acidification activity of the preserved grains, and the storage potential of the preserved and packaged grains. The activity tests included changes in pH, %TA, lactic acid production and lactose and volatile compound content over an 18 h fermentation period. In addition, the microbial viability of the packaged Iyophilised grains after two months of storage, was also investigated. Frozen and refrigerated grains showed the best retainment of the acidification activity over a 10-month storage period. Air-drying and Iyophilisation showed a good retention of the activity up to three months of storage, but the application of these techniques both resulted in a retarded initial acidification activity. After 10 months of storage, the air-dried and Iyophilised grains showed only a low acidification activity. No volatile compounds could be detected during the course of the fermentation period, due to the relative short fermentation period of 18 h. Overall, the best retainment of the fermentation activity was given by the LOPE and the OPET packaging films. However, the storage period had a considerable influence on the retention of the activity of the packaged Iyophilised grains. The viability study of the Iyophilised packaged Kepi grains after two months of storage showed leuconostocs and lactobacilli to be the prevalent microbes in the grains. Low microbial counts were obtained from the lactococciselecting medium for all three of the differently packaged Kepi grains, whereas no growth was observed on the media that selected for the propionibacteria and yeasts. The OPET packaging film provided the best preservation of the microbial composition. It was, therefore, concluded that all four preservation techniques would be suitable for the preservation of Kepi grains and the subsequent storage at room temperature for three months. However, for storage periods of 10 months or longer the use of freezing and refrigeration are recommended as most suitable preservation techniques. All three of the packaging materials proved to be suitable for the packaging and storage of the Iyophilised Kepi grains for periods of up to one month. However, for storage periods of two months or longer, the use of the OPET film for the packaging and retainment of the acidification activity of the Iyophilised grains, can be recommended.
AFRIKAANSE OPSOMMING: Kepi is 'n eeu-oue verfrissende, gefermenteerde suiweldrankie wat tradisioneel vervaardig word deur Kepikorrels in melk te inkubeer. Hierdie Kepikorrels bestaan uit 'n komplekse samestelling van hoofsaaklik melksuurbakteriee en giste. Die effektiewe preservering en verpakking van die korrels is belangrike voorvereistes vir die suksesvolle bemarking daarvan. Dis belangrik dat die preserverinq en die verpakking van die korrels 'n positiewe bydrae sal lewer tot die behoud van die fermentasie-aktiwiteit van die mikrobes in die korrels oar 'n verlengde opbergingsperiode. Die doel van hierdie studie was om die opbergingspotensiaal van verskillend gepreserveerde en -verpakte Kepikorrels te evalueer in terme van die behoud van die lewensvatbaarheid en fermentasie-aktiwiteit van die samestellende mikrobes. Vier verskillende preserveringstegnieke (bevriesing by -18°C, verkoeling by 4°C, lugdroging en vriesdroging) en drie verskillende tipes verpakkingsmateriale, nl. 'n "low density polyethylene film" (LOPE), 'n "oriented polyester film" (OPET) en 'n "metallised oriented polyester film" (MOPET) was qeevalueer. Aktiwiteitstoetsing was gebruik om die impak van die verskillende preserveringstegnieke en die verpakkingsmateriale op die behoud van die fermentasie-aktiwiteit van die Kepikorrels te ondersoek. Die verskillende aktiwitieitstoetse wat gedoen is, het die meting van die verandering in pH, %TA, melksuur- en laktosekonsentrasie oor 'n fermentasieperiode van 18 h ingesluit. Tesame met die aktiwitietstoetsing IS die lewensvatbaarheid van die gevriesdroogde, verpakte Kepikorrels na twee maande van opberging ook ondersoek. Die bevrore en verkoelde Kepikorrels het die beste behoud van aktiwitiet na 'n 10-maande opbergingsperiode getoon. Die gelugdroogde en gevriesdroogde korrels het 'n goeie behoud van aktiwiteit getoon vir 'n opbergingstydperk van tot drie maande, maar beide die lugdroging- en vriesdrogingstegnieke het 'n aanvanklik vertraagde fermentasie-aktiwitieit getoon. Na 'n : opbergingsperiode van 10 maande het beide die gelugdroogde en gevriesdroogde korrels egter 'n lae fermentasie-aktiwiteit getoon. As gevolg van 'n relatiewe kort fermentasieperiode van 18 h kon geen vlugtige komponente in die Kepimonsters gevind word nie. Die LDPE- en OPET-verpakkingsmateriale het die beste behoud van die fermentasie-aktiwiteit van die gevriesdroogde korrels getoon. Die opbergingsperiode het egter 'n aansienlike impak op die aktiwitietsbehoud van die korrels gehad. Die lewensvatbaarheidstudie het aangetoon dat Leuconostoc- en Lactobacillus-spesies die oorheersende mikrobes in die verpakte, gevriesdroogde Kepikorrels na 'n opbergingsperiode van twee maande was. Lae mikrobiese tellings vir al drie van die verpakkingsmateriale was gevind op die Lactococcusselekterende medium, en geen mikrobegroei kon op die giste- en propionibakteriee-selekteringsmedium waargeneem word nie. Die beste behoud van die mikrobiese samestelling in die verpakte, gevriesdroogde Kepikorrels was gevind vir die OPET-verpakkingsmateriaal. Die gevolgtrekking kan gemaak word dat al vier die preserveringstegnieke geskik is vir die preservering van die Kepikorrels en die daaropvolgende opberging van drie maande by kamertemperatuur. Vir opbergingsperiodes van 10 maande en langer word die gebruik van bevriesing en verkoeling aanbeveel as die mees geskikte preserveringstegnieke. AI drie verpakkingsmateriale kan gebruik word vir die verpakking en opberging van gevriesdroogde Kepikorrels vir 'n tydperk van een maand. Indien 'n opbergingsperiode van twee maande of langer verlang word, word die OPET-verpakkingsmateriaal aanbeveel vir die suksesvolle behoud van die fermentasie-aktiwiteit van die Kepikorrels.

The performance of a new horizontal retort (Steriflow Standard 1-Basket Model, Barriquand, Paris, France) was evaluated on the basis of temperature, heat and lethality distribution. Time-temperature data for these studies were obtained from bare thermocouples (type T), and rectangular bricks fabricated from Teflon$ sp{ rm TM}$ and Lexan$ sp{ rm TM}$ with thermocouples positioned at their geometrical centres.
The effect of entrapped air on processing parameters for bricks packaged in retort pouches was determined using silicone rubber bricks (10 x 14.5 x 2 cm), containing 5 thermocouples with their junctions positioned from the geometrical centre to near the top surface. The processing media employed were steam/air at two temperatures (121.1$ sp circ$C and 115.6$ sp circ$C) and two levels of superimposed air over-pressure, corresponding to 65% and 75% steam content.
With the exception of the highest level of over-pressure (116 kPa), 60 ml of entrapped air caused the heating rate index (f$ sb{ rm h}$) to double. At low levels of air over-pressures, the slowest heating region (often assumed to be the geometrical centre) in the brick was shifted to a height equivalent to 3/4 of the brick thickness from the centre when the entrapped air volume was 60 ml. For similar conditions, the location receiving the least combined lethality during heating and cooling was near the top surface of the brick.

Thesis (M.S.)--West Virginia University, 2005.
Title from document title page. Document formatted into pages; contains vii, 59 p. : ill. Includes abstract. Includes bibliographical references (p. 56-58).