Résumé : Le poly(acide lactique) ou PLA est une famille de polyester thermoplastique linéaire qui a connu un essor commercial important durant la dernière décennie. L'enthousiasme pour le PLA vient de sa nature biosourcée, de ses bonnes propriétés mécaniques comme un module élastique élevé et de la possibilité de le biodégrader. Toutefois, certaines carences comme une faible résistance thermique et une faible élasticité à l’état fondu limitent son champ d’application. Fait à noter, le monomère d’acide lactique possède deux stéréo-isomères (L et D). Il est possible de polymériser les isomères L ou D pour former respectivement le PLLA ou le PDLA mais de façon surprenante, le mélange de PLLA et de PDLA permet la formation d’une structure cristalline distincte appelée le stéréocomplexe. Cette forme cristalline a un point de fusion 50[degré]C plus élevé par rapport aux formes cristallines du PLLA ou de PDLA d’où un premier intérêt pour augmenter la résistance thermique du matériau. Dans ce travail, l’usage de petites quantités (0-5 % massique) de PDLA comme additif dans une phase majeure de PLLA sera analysé. L’effet du stéréocomplexe formé à haute température sur la nucléation du PLLA et sur les propriétés rhéologiques du mélange sera plus particulièrement étudié. La présente thèse comprend une revue de littérature sur la cristallisation des PLA suivie de quatre parties expérimentales, conclusions et recommandations. La revue de littérature a pour objectif de réinterpréter l’ensemble des données disponibles sur la cristallisation du PLA afin d’en tirer des conclusions claires. La première partie expérimentale porte sur la cinétique de formation du stéréocomplexe à l'état fondu. Il a été constaté que la formation du stéréocomplexe est lente aux températures usuelles de mise en forme du PLLA ( 180[degré]C). De plus, la coexistence d’une morphologie baptisée dans ce travail « structure en réseau » et d’une morphologie sphérulitique a été révélée pour la première fois. Il a été démontré que la structure de réseau a une température de fusion moins élevée que la structure sphérulitique. Dans la seconde partie du travail, la cinétique de stéréocomplexation a été améliorée significativement pour adapter celle-ci aux cycles de refroidissement courts typiques des méthodes de mise en forme à l’état fondu. Ceci a été réalisé en ajoutant des agents nucléants qui initient la cristallisation à plus haute température et des agents plastifiants qui viennent augmenter la mobilité des polymères. Cette stratégie a permis de réduire le temps de cristallisation d’un ordre de grandeur. Dans un troisième temps, l'effet du stéréocomplexe sur les propriétés rhéologiques d’un mélange PDLA/PLLA a été investigué. En raison de son point de fusion élevé, le stéréocomplexe peut être préservé dans une matrice PLLA fondue et ainsi changer significativement les propriétés rhéologiques. La présence du stéréocomplexe a mené à une augmentation significative de la viscosité et de l'élasticité du PLA expliqué par la formation de points de « réticulation physique » dans la matrice amorphe. Enfin, dans la dernière partie expérimentale, le stéréocomplexe a été utilisé pour améliorer le comportement en moussage du PLA. Des expériences de visualisation et de moussage en mode discontinu ont montré que la présence de stéréocomplexe augmente la densité de nucléation de bulles et améliore significativement la morphologie de la mousse finale grâce à un effet de nucléation et à l’augmentation de l’élasticité du fluide. La revue de littérature et les trois premières parties expérimentales sont présentées sous forme d’articles scientifiques. La dernière partie expérimentale est à titre prospectif pour la suite du projet et ne sera pas soumise pour publication. // Abstract : Poly(lactic acid), or PLA, is a family of linear thermoplastic polyesters that has experienced strong market growth over the past decade. The enthusiasm for PLA originates from its bio-based nature, its good properties and its biodegradability. However, some of PLA deficiencies such as low thermal resistance and low melt elasticity have limited the development of this polymer. It is noteworthy that the lactic acid monomer has two stereo-isomers (L and D) that can be polymerized respectively into PLLA and PDLA but surprisingly, blending of PLLA and PDLA can lead to the formation of a “stereocomplex” which has a distinct crystalline structure from that of the homopolymers. This crystalline form has a melting point 50 oC greater than the crystalline PDLA or PLLA forms, thus it has by itself an interest in terms of heat resistance. In this work, the use of small amounts of PDLA (0-5%) in a matrix of PLLA will be explored. Particular emphasis will be on the nucleating ability of the stereocomplex (formed at high temperature) on PLLA crystallization and on its effect on the blends rheological properties. The current thesis comprises a literature review on PLA crystallization followed by four experimental sections. The objective of the literature review was to reinterpret the large body of data available on PLA in order to draw clear conclusions on PLA crystallization. The first experimental part of the work focused on the kinetics and conditions of stereocomplex formation in the melt state. It was found that stereocomplex formation is slow in the melt processing temperature range of PLLA (180 oC). Co-existence of a so-called “network structure” with a spherulitic structure was revealed for the first time. It was shown that the network structure has a lower melting point than the spherulitic one. In the second part of the work, stereocomplexation kinetics was improved significantly to match it with the fast cooling cycles typical of melt processing techniques. This was achieved by adding nucleating agents that initiated crystallization at higher temperatures and plasticizers that enabled more polymer fluidity. This strategy enabled an order of magnitude decrease in crystallization time. The third part of the work was the investigation of rheological properties upon formation of the stereocomplex structure in 0-5% PDLA in PLLA blends. Due to its higher melting point, the stereocomplex can be preserved in molten PLLA and alter significantly the blend melt rheology. Stereocomplex formation was monitored through rheological measurements and compared to classical calorimetry data. The presence of the stereocomplex lead to a significant increase in viscosity and in melt elasticity explained through the presence of physical crosslink points in the amorphous matrix. Finally, in the last experimental part of the work, the stereocomplex was employed to enhance PLA foaming behavior. Foaming visualization experiments as well as batch foaming tests showed that the presence of the stereocomplex can increase bubble nucleation density and led to a finer and more uniform foam morphology due to its nucleating effect and to the increased melt elasticity. The literature review and the three first experimental sections are presented in Peer-reviewed journal format. The last experimental section is meant as an exploratory and prospective part for the project and will not be submitted for publication.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Lactic acid bacteria (LAB) are common inhabitants of the human gastro-intestinal tract (GIT). Some LAB, especially lactobacilli, are well known for their application in fermented foods and probiotic properties. These microorganisms exert many beneficial effects on human health, such as digestion and assimilation of food and preventing pathogens colonising the GIT. Furthermore, some selected probiotic strains are believed to perform a critical role in the treatment of gastro-intestinal disorders, lactose intolerance and in the stimulation of the immune system. Despite the ever increasing consumer interest in probiotic LAB, the mechanisms by which they exert their beneficial effects and the activities of probiotics in the GIT often remain poorly understood. Understanding survival mechanisms of LAB in the GIT, especially the interaction between LAB and pathogens, would be facilitated by the direct in vivo monitoring of these processes. Using the mCherry fluorescence gene, we successfully constructed Lactobacillus plantarum 423 and Enterococcus mundtii ST4SA reporter strains. With this study we showed that fluorescence imaging can be used to detect Lb. plantarum 423 and Ent. mundtii ST4SA in the GIT of mice. The two species colonized the cecum and colon for at least 24 h after one oral administration. To our knowledge, this is the first report on fluorescence imaging of LAB expressing mCherry in a mouse model. Using a bioluminescence marker system, we evaluated the impact of Lb. plantarum 423 and Ent. mundtii ST4SA on orally acquired Listeria monocytogenes infection and the ability of the probiotics to compete with the pathogen in the GIT of mice. Challenging Lb. plantarum 423 and Ent. mundtii ST4SA that were already established in the GIT of mice with L. monocytogenes EGDe had no effect on the survival and persistence of the probiotic strains. We demonstrated that the colonization of mice with Lb. plantarum 423 and Ent. mundtii ST4SA, or a combination of the strains, protected the animals against colonization of the GIT by L. monocytogenes EGDe. Enterococcus mundtii proved more effective than Lb. plantarum 423 in reducing the number of L. monocytogenes EGDe in the mouse model. / AFRIKAANSE OPSOMMING: Melksuurbakterieë (MSB) kom algemeen in die mens se spysverteringkanaal (SVK) voor. Verskeie MSB, veral lactobacilli, is bekend vir hul gebruik in gefermenteerde voedsel en as probiotika. Die bakterieë het baie eienskappe wat die mens se gesondheid kan bevoordeel, insluitend vertering en assimilasie van voedsel en voorkoming van kolonisering van die SVK deur patogeniese bakterieë. Sekere probiotiese rasse speel ook ʼn belangrike rol in die behandeling van SVK versteurings, laktose intoleransie en die stimulering van die immuun stelsel. Alhoewel die belangstelling in probiotiese bakterieë toeneem, is daar min inligting bekend oor die meganismes wat MSB gebruik om hulle voordelige eienskappe in die SVK uit te voer. Die oorlewing van MSB in die SVK, veral die interaksies tussen MSB en patogene, kan met behulp van ʼn in vivo moniteringsisteem bestudeer word. Deur die mCherry fluorisensie geen in Lactobacillus plantarum 423 en Enterococcus mundtii ST4SA te kloneer, het ons daarin geslaag om ʼn effektiewe verklikker sisteem te ontwikkel en kon die voorkoms en migrasie van die twee spesies in die SVK van muise bestudeer word. Lactobacillus plantarum 423 en Ent. mundtii ST4SA het veral die blindederm en kolon gekoloniseer. Beide rasse het na ʼn enkele mondelingse toediening vir ten minste 24 h in die SVK oorleef. Sover ons kennis strek, is hierdie die eerste verslag van fluoriserende MSB wat met behulp van die mCherry geenproduk in die SVK bestudeer is. Deur gebruik te maak van ʼn bioliggewende verklikker sisteem, het ons die vermoë van Lb. plantarum 423 en Ent. mundtii ST4SA om met Listeria monocytogenes in die SVK te kompeteer, bestudeer. Listeria monocytogenes het geen invloed gehad op die kolonisering van Lb. plantarum 423 en Ent. mundtii ST4SA nie. Deur die muise vooraf met Lb. plantarum 423 en Ent. mundtii ST4SA te koloniseer (in kombinasie of met net een van die twee rasse), kon ons daarin slaag om kolonisering van die SVK met L. monocytogenes te voorkom. In die muis model wat in hierdie studie gebruik is, was Ent. mundtii ST4SA meer effektief as Lb. plantarum 423 in die verlaging van Listeria selgetalle.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2007. / Lactic acid bacteria (LAB) are producers of bacteriocins, ribosomally synthesized antimicrobial peptides. Bacteriocins are secreted into the surrounding environment where they inhibit growth of other bacteria competing for the same nutrients in a particular environment, usually closely related strains. Some of the bacteriocin-sensitive bacteria include food spoilers and - pathogens, which makes bacteriocins potential natural food preservatives. The need for more natural preservation techniques in the food industry is high: Consumers prefer ready-toeat, minimally processed foods containing no chemical preservatives, but at the same time food spoilage and food-related illnesses are areas of big concern. The antibacterial and antiviral properties of some bacteriocins have also made them suitable for controlling bacterial infections, e.g. as part of pharmaceutical ointments. The increasing rate of resistance against antibiotics by micro-organisms has created a market for alternative treatments for infections. Commercial bacteriocin manufacturing proceeds in controlled fermentations or by extraction from plant material. Enterococcus mundtii ST4SA produces a bacteriocin, bacST4SA, with properties giving it potential for use as a food preservative or as part of a pharmaceutical product. In this study, production of bacST4SA by fermentation of low-cost food-grade growth media, sugarcane molasses, corn steep liquor (CSL) and cheese whey, was considered to increase the economic viability of production for food application. Furthermore, individual de Man Rogosa and Sharpe (MRS) medium components, pH and fed-batch fermentation were evaluated to improve bacST4SA activity...

Thesis (PhD)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Research on probiotics has increased over the past years, which led to commercialization of a number of probiotic supplements and functional foods. In vitro assays such as tolerance to acid and bile, adhesion to mucus and epithelial cells, antimicrobial activity and antibiotic resistance tests are performed to screen lactic acid bacteria for probiotic properties. Enterococcus mundtii ST4SA produces an antimicrobial peptide (peptide ST4SA) with activity against Gram-positive and Gram-negative bacteria. Lactobacillus plantarum 423 produces plantaricin 423, a typical class II bacteriocin, active against a number of Gram-positive bacteria. A gastro-intestinal model (GIM) simulating the gastro-intestinal tract (GIT) of infants, was developed to study the survival of E. mundtii ST4SA and L. plantarum 423 and evaluate them as possible probiotics. Growth of the two strains in the GIM was compared to the growth of commercially available probiotics. Infant milk formulations were used as growth medium. Changes in pH, the addition of bile salt and pancreatic juice, and intestinal flow rates were controlled by peristaltic pumps linked to a computer with specifically designed software. Strain ST4SA was sensitive to low pH and high concentrations of bile salts. Growth of strain ST4SA was repressed in the first part of the GIM, however, the cells recovered in the ileum. Strain 423 was also sensitive to acidic conditions. However, the cells withstood the presence of bile and pancreatin in the first part of the GIT. Neither of the two strains displayed bile salt hydrolase (BSH) activity. Both strains were resistant to amoxicillin, ampicillin, chloramphenicol, cefadroxil, roxithromycin, meloxicam, doxycycline, erythromycin, novobiocin, rifampicin, tetracyclin, bacitracin, oflaxacin and cephazolin, anti-inflammatory drugs Na+- diklofenak and ibuprofen, and painkillers codeine terprim hydrate aminobenzoic acid, metamizole aspirin and paracetamol. Strain 423 was resistant to ciprofloxacin. Genes encoding cytolysin, non-cytolysin β-hemolysin and cell aggregation substances were detected on the genome of strain ST4SA but they were not expressed. L. plantarum 423 does not contain genes encoding gelatinase, cell aggregation, enterococcus surface protein, hemolysin, non-cytolysin β- hemolysin and enterococcus endocarditis antigen. Both strains inhibited the growth of Listeria monocytogenes ScottA in the GIM. Survival of the strains improved when used in combination and compared well with the survival of commercially available probiotics. Adhesion to epithelial cells is an important prerequisite for bacterial colonization in the GIT. The adhesion of E. mundtii ST4SA and L. plantarum 423 was studied using Caco-2 (human colon carcinoma epithelial) cells. Both strains revealed good adhesion compared to other probiotic strains. No correlation was found between hydrophobicity, auto-aggregation and adhesion to Caco-2 cells. Antibiotics and anti-inflammatory medicaments had a negative effect on adhesion. Different combinations of proteins were involved in the adhesion of E. mundtii ST4SA and L. plantarum 423 to Caco-2 cells. E. mundtii ST4SA, L. plantarum 423 and L. monocytogenes ScottA were stained with fluorescent dyes to visualize adhesion to Caco-2 cells. Adhesion of L. monocytogenes ScottA to Caco-2 cells was not reduced in the presence of strains ST4SA and 423. Cell-free culture supernatants of both strains inhibited the invasion of L. monocytogenes ScottA. The cell structure of Caco-2 cells changed in the presence of L. monocytogenes ScottA. Strains ST4SA and 423 protected Caco-2 cells from deforming. / AFRIKAANSE OPSOMMING: Navorsing op probiotika het die afgelope tyd drasties toegeneem en aanleiding gegee tot die kommersialisering van ‘n groot hoeveelheid probiotiese supplemente en funksionele voedselsoorte. In vitro studies, soos bv. weerstand teen suur en gal, vashegting aan mukus en epiteelselle, antimikrobiese aktiwiteit en weerstand teen antibiotika word uitgevoer om te bepaal of melksuurbakteriëe aan probiotiese standaarde voldoen. Enterococcus mundtii ST4SA produseer ’n peptied met antimikrobiese werking teen Grampositiewe en Gram-negatiewe bakteriëe. Lactobacillus plantarum 423 produseer ‘n tipiese klas II bakteriosien, plantarisien 423, met aktiwiteit teen sekere Gram-positiewe bakteriëe. ’n Gastro-intestinale model (GIM) wat die spysverteringskanaal (SVK) van babas simuleer, is ontwikkel om die oorlewing van E. mundtii ST4SA en L. plantarum 423 te bepaal en hul eienskappe met dié van kommersiële probiotiese stamme te vergelyk. Babamelk formules is as groeimedium gebruik. Verandering in pH, byvoeging van galsoute en pankreassappe, en intestinale vloei is met behulp van peristaltiese pompe gereguleer wat seine vanaf ‘n spesiaal ontwikkelde rekenaarprogram ontvang. E. mundtii ST4SA was sensitief vir lae pH en hoë galsoutkonsentrasies en groei is in die eerste deel van die GIM onderdruk. Selgetalle het wel in die ileum herstel. Stam 423 was ook sensitief vir lae pH, maar het die galsout- en pankreatienvlakke in die laer deel van die SVK weerstaan. Geen galsout-hidrolase aktiwiteit is by enige van die twee stamme gevind nie. Beide stamme het weerstand getoon teen amoksillien, ampisillien, chloramfenikol, cefadroksiel, roksitromisien, meloksikam, doksisiklien, eritromisien, novobiosien, rifampisien, tetrasiklien, basitrasien, oflaksasien, kefazolien, die anti-inflammatoriese medikamente Na+-diklofenak en ibuprofen, en die pynstillers kodeïenterprimhidraataminobensoësuur, metamisoolaspirien en parasetamol. L. plantarum 423 was bestand teen ciprofloksasien. Gene wat kodeer vir sitolisien, nie-sitolisien β-hemolisien III en sel-aggregasie is op die genoom van E. mundtii ST4SA gevind, maar word nie uitgedruk nie. L. plantarum 423 besit nie die gene wat vir gelatinase, selaggregasie substansies, enterokokkus selwandproteïen, hemolise, nie-sitolisien β-hemolisien en enterokokkus endokarditis antigeen kodeer nie. Albei stamme inhibeer die groei van Listeria monocytogenes ScottA in die GIM. Die twee stamme in kombinasie het tot beter oorlewing in die GIM gelei. Stamme ST4SA en 423 vergelyk goed met kommersieël beskikbare probiotika. Vashegting van probiotiese stamme aan epiteelselle is belangrik vir kolonisering in die SVK. Vashegting van E. mundtii ST4SA en L. plantarum 423 is bestudeer deur van Caco-2 (kolon epiteel) selle van die mens gebruik te maak. Die aanhegting van beide stamme aan Caco-2 selle het goed vergelyk met kommersieël beskikbare probiotiese stamme. Geen korrelasie is gevind tussen hidrofobisiteit, aggregasie en vashegting aan Caco-2 selle nie. Antibiotika en antiinflammatoriese medikamente het ‘n negatiewe effek op vashegting gehad. Verskillende kombinasies van proteïene is betrokke in die vashegting van E. mundtii ST4SA en L. plantarum 423 aan Caco-2 selle. E. mundtii ST4SA, L. plantarum 423 en L. monocytogenes ScottA is met fluoreserende kleurstowwe gemerk om vashegting aan Caco-2 selle te monitor. Vashegting van L. monocytogenes ScottA aan Caco-2 selle is nie deur die teenwoordigheid van stamme ST4SA en 423 beïnvloed nie. Sel-vrye kultuursupernatante van beide stamme het die binnedring van L. monocytogenes ScottA verhoed. Die selstruktuur van Caco-2 selle het in die teenwoordigheid van L. monocytogenes ScottA van vorm verander. E. mundtii ST4SA en L. plantarum 423 het die Caco-2 selle teen vervorming beskerm.

Several lactic acid bacteria (LAB) of the Lactococcus, Lactobacillus, Leuconostoc and Pediococcus genera were screened for inhibition of food-borne pathogens and spoilage microorganisms in raw milk and dairy products. Listeria monocytogenes was killed by Lactococcus lactis subsp. lactis and Pediococcus pentosaceus due to their production of bacteriocin-type inhibitors. Staphylococcus aureus was not able to grow in raw milk at temperatures below 5°C even without LAB being present. Gram negative Salmonella enteritidis. Salmonella typhimurium and Escherichia coli, along with spoilage bacteria of the genus Pseudomonas were dramatically inhibited by a Lactobacillus species, designated AS-1, in raw and pasteurized milk as well as in cottage cheese. However, other LAB were not able to inhibit these organisms. Lactobacillus AS-1, did not produce hydrogen peroxide but carbon dioxide was produced. The AS-1 strain was a gram positive coccobacillus, catalase and oxidase negative and produced DL-lactic acid. It deaminated arginine and grew over a temperature range of 5°C to 45°C. It was also able to ferment glucose, galactose, fructose and lactose in addition to 17 other carbohydrates. High numbers (107 CFU/ml) of AS-1 were required to obtain complete inhibition of gram negative bacteria. A selective medium (ASLM) for Listeria monocytogenes was developed to follow the fate of this particular pathogen in association with LAB in raw milk; other selective media were not able to inhibit the growth of background flora of raw milk. ASLM was superior to four other media in allowing only the growth of the target pathogen. For the Lactococcus genus, a selective and differential agar medium (Alsan) was formulated to selectively allow growth of Lactococcus spp. and to differentiate between Lactococcus lactis subsp. lactis and the biovariety diacetylactis, based on citrate utilization. / Graduation date: 1993

An attempt was made to evaluate the applicability of a theorized model concerning plasma lactic acid kinetics to running performance assessment. This model incorporated two distinct lactate thresholds identified as the aerobic threshold (AerT) and the anaerobic threshold (AT). Two groups of males with different levels of fitness were tested. Group 1 (n = 5) consisted of recreational athletes (͞X VO₂ max = 49.3 ml/kg•min⁻¹) who ran less than 20 miles per week, while Group 2 (n = 6) were highly trained runners (͞X VO₂ max = 65.5 ml/kg•min⁻¹) who all ran at least 40 miles per week. All subjects participated in two incremental work load (IWL) and four constant work load (CWL) tests that consisted of horizontal treadmill running at different speeds. The IWL tests elicited linear increases in VO₂ and were highly correlated for both Group 1 (r = .986) and Group 2 (r = .999). However, three unbiased observers found the identification of both AerT and AT, using independent lactate and respiratory gas exchange "breakpoints," very subjective in nature. The test-retest reliablity was generally poor and varied considerably among both the observers and the individual predictor variables. The validity of the respiratory gas exchange predictors was then evaluated against the criterion lactate thresholds using the estimates of a fourth, more experienced observer. The resultant correlation coefficients were generally not high, while t-test evaluation demonstrated significant (p < .05) differences in fifty percent of the cases. This same observer then pooled all of the ventilatory predictors in an effort to better estimate both AerT and AT indirectly. These indirect ventilatory estimates consistently underpredicted the criterion lactate thresholds. This finding suggests that increases in running speeds may confound the normal associate between plasma lactate and ventilation at increasing work levels. Arbitrary lactate concentrations of 2mmol/2 and 4 mmol/L were further evaluated as threshold predictors. This methodology consistently overpredicted the criterion lactate thresholds in terms of VO₂. When any of these AerT and AT threshold estimates were compared to the lactate responses during the appropriate CWL test, no meaningful relationship were found. These observations question the physiological significance of both AerT and AT evaluation during treadmill running, as well as pointing out the difficulty in reliably detecting both plasma lactate thresholds regardless of the methodology.

No description available.

The purpose of the study was to evaluate the generalisability of the heart rate-blood lactate relationship determined in laboratory testing in comparison to running over ground. This plays a crucial role to prescribe exercise intensity from laboratory results. Ten well trained runners performed a maximal oxygen uptake (VO2max) pre-test and an incremental submaximal test performed at a two degrees inclined treadmill and a running track. Statistical analysis included student’s t-test of heart rate at interpolated blood lactate levels and comparison of second order polynomial regression lines. VO2max was 60,4 ± 6 ml/kg/min for men and 56,3 ± 4,3 ml/kg/min for women. There was no significant difference in heart rate at interpolated blood lactate of 3 and 4 mmol/L. There was no significant difference between heart rate values at any running velocity. A significant difference between blood lactate values was observed 14km/h (p=0,04). When considering blood lactate values up to 6mmol/L, heart rate-blood lactate relationships were similar. In conclusion, lactate threshold testing on treadmill through incremental test protocols on a two degrees incline gives similar heart rate- blood lactate relationship as running over ground and may be used to prescribe intensity in training performed over ground.

Master of Science / Department of Animal Sciences and Industry / J.S. Drouillard / Three studies were conducted to investigate alternative ingredients and processing methods for manufacturing low-moisture blocks. Study 1 was designed to determine if ruminal lactate could be transiently increased by feeding fructose-based blocks to heifers fed prairie hay, thus providing substrate for establishment of lactate utilizing microbes. Low-moisture blocks comprised of 96% fructose and 4% vegetable oil (DM basis) were manufactured and dosed via ruminal fistulas. Administration of fructose blocks resulted in transient increases in ruminal lactate (P < 0.05), accompanied by transient decreases in pH (P < 0.05). Ruminal fluid incubated with semi-defined lactate medium became more turbid (P < 0.05) as a result of prior exposure to fructose blocks suggesting greater capacity for lactate metabolism. In study 2 a portion of the molasses was replaced by corn steep liquor (CSL) or condensed corn distiller’s solubles (CCDS). Heifers were fed a forage-based diet and supplemented with 1 of 4 supplement blocks. Supplements were a 30% CP molasses block manufactured at ambient pressure and high temperatures (Mol-30). The remaining treatments were manufactured at reduced pressure and temperature and were a 30% CP block with 36% CSL (CSL-30); a 40% CP block with 40% CSL (CSL-40); or a 40% CP block with 25% CCDS (CCDS-40). Supplementing with Mol-30 and CSL-40 resulted in greater DMI (%BW) than with CCDS-40 (P < 0.05). Supplementing with CSL-30 improved efficiency and ADG compared to Mol-30 (P < 0.01). Study 3 evaluated the affect of cooking temperature on blocks containing CSL fed to heifers receiving a forage-based diet. Heifers were offered no supplement (Control) or a 15% CSL block manufactured at ambient pressure and high temperature (HT-15). The remaining treatments were manufactured at reduced pressure and temperature and were a 15% CSL block (LT-15); or 40% CSL block (LT-40). Control heifers had the lowest DMI and LT-40 had the greatest (P < 0.05). Feeding heifers LT-15 or LT-40 improved ADG compared to heifers fed HT-15 or no supplement (P < 0.05). Heifers fed LT-40 tended to be more efficient than those fed HT-15 and Control (P = 0.07).

Thesis advisor: Jeffery A. Byers / This dissertation focuses on the development of iron-based polymerization catalysts for use in the production of high commodity polymers, polyethylene and poly(lactic acid). Chapter one establishes the current landscape of the plastic market and outlines the advantages to developing iron-based catalysts. Chapter two then explores the use of bis(pyridinylimino)isoindolate-ligated iron complexes as a family of ethylene polymerization catalysts possessing distinctive mechanistic behavior. Chapter three moves to focus on the polymerization of stereoregular poly(lactic acid) from an achiral bis(imino)pyridine-ligated iron precatalyst. The mechanism for the desymmetrization of the catalyst is further detailed, and new avenues for enhancing the behavior of the reaction are discussed. Chapter four details the development of conditions for the rapid chain transfer polymerization of lactide and cyclohexene oxide, offering another tool by which value and complexity may be added to polymerization reactions carried out by this family of bis(imino)pyridine-ligated iron complexes. Finally, chapter five leverages the known redox-switchable features of bis(imino)pyridine-ligated iron complexes to develop reaction conditions for the controlled branching of poly(lactic acid) in a one-pot polymerization reaction. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.