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Nisin, an antimicrobial peptide used in food preservation was evaluated for thermal stability. Nisin retained antimicrobial activity after having been heated at 121��C for seven hours. Anhydrous nisin and concentrated nisin solutions (5-10 mg/ml) were still active after having been heated up to 190��C or 230��C. When exposed to high temperatures of 200 or 250��C for up to one hour, nisin lost all antimicrobial activity. After 3.5 hours of heating at 121��C an inactive nisin degradation product, designated nisin L, was isolated. In comparison to native nisin, nisin L had reduced activity against Pediococcus pentosaceus FBB-61 and no activity against Bacillus cereus T vegetative cells or spores. Structural changes to nisin L were studied by high performance liquid chromatography (HPLC), ion spray mass spectroscopy (MS), ��H nuclear magnetic resonance spectroscopy (NMR) and circular dichroism (CD) spectroscopy and compared to original nisin. There was no difference in molecular weight between nisin and nisin L. Both MS spectra contained nisin, with average molecular weight (MW) of 3354 daltons (D), and hydrated nisin with average molecular weight of 3372 D. Nisin L had higher proportion of hydrated molecules, and it had molecules with more then one water addition. Proton NMR analysis of nisin L indicated that dehydrobutyrine 2 and dehydroalanine 5 residues had been altered, and that several new hydrogen resonances appeared. Water additions in nisin L are likely to have occurred at dehydroresidues, making them inactive. Nisin L was found to be more polar, as would be expected for a more hydrated peptide. Analysis of CD spectra indicated that nisin L had smaller content of a helix and therefore lesser membrane spanning capability. Tandem mass spectroscopy of original nisin revealed that it was hydrated at lysine 34 residue. / Graduation date: 1996

Eight foodborne pathogenic and spoilage Gram-positive bacteria were evaluated for their spontaneous resistance frequencies to the peptide antimicrobial nisin. In brain heart infusion (BHI) medium, nisin resistance frequencies were in the range of l06 to l08 when exposed to nisin at concentrations 2 to 4 times the minimal inhibitory concentrations. A stable nisin resistant mutant of Listeria monocytogenes Scott A was obtained by increasing stepwise exposure to nisin and subsequently characterized. Phospholipid content, fatty acid composition, phase transition temperature (Tc), and specific growth rates of the resistant mutant and parent were determined. The Tc of the resistant mutant (44.4°C) in comparison of the parent (37.4°C) indicated that significant changes occurred in the lipid composition of the mutant. Gas chromatographic analysis of fatty acids of mutant and parent revealed significant differences (P<0.05) in the proportional ratios of fatty acids; 14:0, 15:0 iso, 15:0 anteiso and 17:0 iso. cells and the concentration of nisin required for reaching a 50% maximum killing rate was five times that of sensitive cells. The bactericidal activity of nisin was more effective at 37°C than 4°C for both resistant and sensitive cells, but there was always higher survival of resistant cell than sensitive cells for both temperatures. Nisin degradation and plasmid involvement were demonstrated to not be the responsible resistance mechanism to nisin in L. monocytogenes. No cross-resistance was observed to therapeutically important antibiotics (rifampicin, chloramphenicol, vancomycin, erythromycin) and to metabolic inhibitors (CCCp, DCCD) by the nisin-resistant mutant. / Graduation date: 1993

Thesis (M.S. in biological and agricultural engineering)--Washington State University, May 2010. / Title from PDF title page (viewed on June 14, 2010). "Department of Biological Systems Engineering." Includes bibliographical references.

This thesis is compromised of two distinct formulation sections, which are described below: New compression-coated tablet formulations were developed for amoxicillin/clavulanate. Amoxicillin in an outer coat was separated from clavulanic acid in a core tablet by inactive ingredients in a middle coat. A chewable compression-coated tablet formulation with 50% stearic acid in the middle coat showed high clavulanic acid stability in comparison to the marketed traditional tablet formulation. Stearic acid acted as a hydrophobic barrier that prevents passage of moisture through the outer coats into the core and it helped in the bonding of the outer coats to the core because it softens upon compression. The bioavailability of clavulanic acid, however, was reduced which was attributed to the effect of stearic acid. Stearic acid was removed from the formulation of swallow tablets and replaced with Avicel��, consequently, the outer coat did not adhere tightly to the core and tended to cap off, which resulted in low stability of clavulanic acid. In bioavailability studies of the swallow tablets, the two formulations were equivalent to the marketed formulation for amoxicillin, but not for clavulanic acid, which is most likely due to the small sample size studied and high intersubject variation. Nisin, an antimicrobial protein, was evaluated for ability to emulsify oil-in-water using conductivity measurements. In comparison to Tween�� 80 and ��-casein, nisin showed substantial emulsifying activity. The emulsifying activity was found to be highly concentration- and pH-dependent. Nisin was found to form a gel-like structure at the oil water interface which retarded release of the drug sulfasalazine. Interfacial tension kinetics exhibited by nisin at an oil-water interface were monitored with DuNoy tensiometry. Interfacial pressure kinetics were interpreted with reference to a simple model that allows for a protein to be adsorbed in structurally dissimilar states. The model suggested that nisin's tendency to adapt a more unfolded structure at the oil-water interface increases with decreasing concentration. The effects of nisin on drug release from oil-in-water emulsions, and on erythrocytes were evaluated as well. It was found that nisin retards drug release in emulsions and lyses red blood cells. / Graduation date: 1999

Varying concentrations of the food preservatives nisin and lysozyme were adsorbed onto glass surfaces chemically modified to exhibit different degrees of hydrophobicity. The antimicrobial activity of the adsorbed preservatives was evaluated by documenting the ability of Listeria monocytogenes to adhere and grow on the glass surfaces. A bioluminescence protocol was developed to effectively enumerate bacterial cells adhered to glass. Lysozyme adsorption onto glass surfaces was monitored by labeling with ¹²⁵I. Results indicated that synergy was present for 0.9/0.1 molecular ratio of nisin/lysozyme. Synergistic effect was increasing gradually with the increase of nisin in the ratios tested. This trend was observed on both surface types. However, the magnitude of synergy was more pronounced on hydrophobic surfaces than on hydrophilic ones. Results from protein radiolabeling showed that lysozyme was adsorbed with higher mass to hydrophilic surfaces than to hydrophobic ones. / Graduation date: 1999

Nisin is an antibacterial peptide, which when adsorbed on a surface can inhibit bacterial adhesion and viability. The ability of noncovalently immobilized nisin to withstand exchange by the milk proteins bovine serum albumin, ��-lactoglobulin, ��-lactalbumin, and ��-casein on surfaces that had been silanized with dichlorodiethylsilane to exhibit high and low hydrophobicities was examined using in situ ellipsometry. Kinetic behavior was recorded for nisin adsorption for 1h and 8h, followed in each case by rinsing in protein-free buffer solution, and sequential contact with a single milk protein for 4h. Concerning nisin adsorption to each surface, a higher adsorbed mass was consistently recorded on the hydrophilic relative to the hydrophobic surface, independent of adsorption time. While desorption was greater from the hydrophilic surface in the 1h test, the amount desorbed was quite similar on each surface in the 8h tests. The sequential data were consistent with the assumptions that nisin organization at the interface involved adsorption in at least two different states, possibly existing in more than one layer, and that in the absence of exchange, upon addition of the second protein adsorbed mass would increase by an amount equivalent to its experimentally observed monolayer coverage. The Mass of nisin exchanged was generally higher on the hydrophobic compared to the hydrophilic surface presumably because of the presence of a more diffuse outer layer in the former case. ��-casein was the most effective eluting agent among the proteins studied, while ��-lactalbumin was the least effective, apparently adsorbing onto the nisin layers with little exchange. Both bovine serum albumin and ��-lactoglobulin were moderately effective in exchanging with adsorbed nisin, with the amount of nisin removed by bovine serum albumin being more substantial, possibly due to its greater flexibility. / Graduation date: 1995

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Haiqiang Chen, Animal & Food Sciences. Includes bibliographical references.

Techn. University, Diss., 2002--Berlin.

Amido nativo (AN) extraído das sementes de pinhão foi modificado por duas metodologias: hidrólise ácida (AHA) e ultrassom (AUS). As três amostras – AN, AHA e AUS - foram submetidas à secagem em spray dryer. Efetuaram-se análises de composição centesimal, características reológicas e morfologia por microscopia eletrônica de varredura. As moléculas de amido modificado por ondas ultrassônicas e por hidrólise ácida atingiram tamanho nanométrico, representando redução de aproximadamente 97% e 99,85%, respectivamente. As três amostras foram significativamente diferentes em relação ao teor de amido e amilose, ao percentual de sinérese e a colorimetria. A amostra AHA diferiu das demais em termos de solubilidade (mais solúvel), higroscopicidade (mais higroscópica) e claridade de pasta (mais translúcida). As amostras AN e AUS tiveram suas cargas aparentes modificadas com adição de anidrido succínico para a incorporação de nisina através da atração eletrostática. Alíquotas dessas amostras foram dispostas em placas com ágar BHI previamente inoculadas com Listeria monocytogenes. Estas foram mantidas em diferentes temperaturas, 4 e 37ºC. A avaliação da atividade antimicrobiana foi medida através do halo de inibição. As placas armazenadas a temperatura mais baixa apresentaram maior atividade no decorrer dos 21 dias quando comparadas as mantidas a 37ᵒC. Neste estudo pode-se observar que as modificações realizadas nas moléculas de amido pinhão atingiram escala nanométrica e que a incorporação de nisina na superfície destas foi eficaz, resultando na inibição da L. monocytogenes através da formação de halos de inibição. / Native starch (AN) extracted from the seeds of pinhão was modified by two methods: acid hydrolysis (AHA) and ultrasound (AUS). The three samples - AN, AHA and AUS - were subjected to spray drying. We carried out analyzes of chemical composition, rheological characteristics and morphology by scanning electron microscopy. The modified starch molecules by ultrasonic waves and by acid hydrolysis achieved nanosize, representing a reduction of approximately 97% and 99.85% respectively. The three samples were significantly different in four items: starch and amylose content, the percentage of syneresis and colorimetry. The AHA sample differed from the others in terms of solubility (more soluble), hygroscopicity (more hygroscopic) and paste clarity (more translucent). The samples of AN and AUS had their aparent charge modified with addition of succinic anhydride to incorporation of microspheres of nisin by electrostatic attraction. Aliquots of these samples were placed in Petri dishes containing BHI agar inoculated with Listeria monocytogenes. These were kept at different temperatures, 4 and 37 ° C. The antimicrobial activity was measured by the inhibition zone. The plates stored at lower temperature showed greater activity during the 21 days when compared with those maintained at 37 ᵒ C. In this study it can be seen that the nanomolecules with microspheres nisin showed antimicrobial activity lower than the molecules of pinhão native starch microspheres nisin, suggesting that they have low stability.