The objectives of this study were (l) to screen out active proline-specific peptidases from Lactobacillus casei subspecies, (2) to study growth kinetic and enzyme production from enriched medium (MRS) and cheese whey medium, (3) to purify and characterize two active proline-specific enzymes, and (4) to investigate the action of purified enzyme on bitter tryptic digests of $ beta$-casein as well as bitter enzyme-modified cheese. Lactobacillus casei subsp. casei LLG and Lactobacillus casei subsp. rhamnosus S93 were examined for extra- and intra-cellular proline-specific peptidase activities. Both strains showed strong activity for x-prolyl dipeptidyl peptidase and proline iminopeptidase but had weak activities for prolidase, prolinase, and post proline endopeptidase. Histochemical staining of crude enzyme extract from Lactobacillus casei ssp. casei LLG with different substrates revealed a distinct protein band for x-prolyl dipeptidyl peptidase as well as for proline iminopeptidase. The growth kinetics showed that the intracellular proline-specific peptidases increased gradually at the beginning of the exponential phase and reached a maximum at the beginning of stationary phase. / Storage stability of x-prolyl dipeptidyl peptidase and proline iminopeptidase in crude extract, with and without stabilizers showed no significant loss in activity of these two enzymes at 4$ sp circ$C for 9 days without adding any stabilizers. The levels of x-prolyl dipeptidyl peptidase, proline iminopeptidase, and post proline endopeptidase activities of cells grown in whey did not vary markedly from cells grown in MRS broth. X-prolyl dipeptidyl peptidase and proline iminopeptidase were purified from crude cell-free extract of Lactobacillus casei ssp. casei LLG by Fast Protein Liquid Chromatography (FPLC) equipped with ion-exchange and gel-filtration columns. X-prolyl dipeptidyl peptidase was found to be a serine-dependent enzyme with molecular mass of 79 kDa. The pH and the temperature optima by the purified enzyme were 7.0 and 50$ sp circ$C, respectively. Proline iminopeptidase was sulfhydryl enzyme with molecular mass of 46 kDa. The maximum enzyme activity was observed at pH 7.5 and 40$ sp circ$C. This is the first report describing the purification and characterization of x-prolyl dipeptidyl peptidase and proline iminopeptidase from Lactobacillus casei to homogeneity. / The debittering of tryptic digests from $ beta$-casein by x-prolyl dipeptidyl peptidase was studied by reversed phase high performance liquid chromatography (RP-HPLC) and liquid chromatography/mass spectrometry. The results showed that two bitter peptides (f53-97 and f03-209) containing X-Pro-Y-Pro in their amino acid residues were completely hydrolyzed and many other peptides with high hydrophobicity were decreased in peak area. The addition of purified x-prolyl dipeptidyl peptidase on bitter enzyme-modified cheese (EMC) also showed that at least one bitter peptide with X-Pro-Y derived from $ alpha$-casein hydrolysis was removed.

Thesis (Ph.D. in food science)--Washington State University. / Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1944. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1951. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 50-53).

Thesis (M.S.)--University of Wisconsin--Madison, 1994. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 48-50).

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xiv, 107 p.; also includes graphics. Includes bibliographical references (p. 90-97). Available online via OhioLINK's ETD Center

The effect of monolaurin (0.35 mM) and lauric acid (5.0 mM) alone and in combination has been tested on growth of three cheesebome strains of Listeria monocytogenes and two strains of L. innocna. The Listeria spp. were grown in Tryptose Soya Yeast Glucose Broth (TSGYB) in shake culture at 10 °C and an initial pH of 7.0. The additives were dissolved in butter oil 10 % (w/v). Lauric acid (5.0 mM) increased the doubling time of the five Listeria spp. by 3 - 8 h at 10 °C. Monolaurin by itself was found to slightly increase or decrease the doubling time depending on the microbial strain. Monolaurin had an augmentative effect when combined with lauric acid in the presence of butter oil, where the doubling time increased between 10 to 15 h depending on the strain. Inhibition of Listeria spp. was seen in the model bi-phasic broth system. A model food system was developed to test the antimicrobial properties of lauric acid and monolaurin, where the fat soluble additives were dissolved in cream and milk with 3.6% (w/v) fat. The milk was reconstituted from skim milk and cream 40 % (w/v) fat containing lauric acid or monolaurin. This milk was used to make a soft-ripened cheese of the Brie Camembert type. Two strains of L. innocna were added to the reconstituted milk. During production of the soft-ripened cheese, a draining table was designed to comply with COSHH regulations so that the whey containing L. innocua could be removed and disposed of by heating for 30 min at 121 °C.In cheeses without lauric acid or monolaurin the population of L. innocua increased from 10[3] g[-1] to 10[7] cfu g[-1] on the surface of the cheese. The counts in the centre of the cheese were less at 10[5] cfu g[-1] after ripening for 28 d at 10 °C. Addition of 0.9 mM monolaurin reduced the count to 10[5] cfu g[-1] after 28 d ripening at 10 °C on the surface of the cheese. The effect of increasing the initial draining time at ambient temperature from 24 h to 48 h reduced the population to 0 after 28 d ripening at 10 °C. Unlike experiments in broth culture, addition of lauric acid changed the aroma of the Camembert-type cheese to give a blue cheese aroma. This was due to the conversion of lauric acid to a methyl ketone (2-undecanone) by the starter fungus Penicillium camembertii. Due to lack of stability of lauric acid in this system, lauric acid was omitted from the reconstituted milk in further experiments. During production of cheese, lactose was converted to mainly lactic acid by metabolism of the lactic acid starter. The presence of lactic acid combined with the added monolaurin resulted in a significant reduction in the population of L. innocua particularly when the draining time was increased from 24 h to 48 h. The unusual approach in this study was to dissolve the biocide in the non-aqueous phase, butter oil in the experiments in broth culture and in cream in the model cheese experiments. An untrained taste panel detected monolaurin (0.9 mM) in soft-ripened cheese. Some respondents liked the 'mature' taste whilst others described it as 'farmyard like'. In food systems the use of antimicrobials which result in an increase in the lag phase or a reduction in the overall population of pathogens, has a significant role in promoting the microbiological safety of a product which is eaten without further heat treatment.

Orientador: Mirna Lucia Gigante / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-03T19:15:17Z (GMT). No. of bitstreams: 1 Salles_AntonioSergio_M.pdf: 233527 bytes, checksum: 23062b9d3bdc093e7873c5ea4165382b (MD5) Previous issue date: 2003 / Resumo: O Cream Cheese é um queijo obtido por coagulação ácida de alto teor de umidade que apresenta como principal defeito a sinérese, ou exudação do soro durante o período de armazenamento. O objetivo deste trabalho foi avaliar o efeito da adição do sorbato de potássio, sobre a estabilidade do Cream Cheese e da solução de goma locusta. Os queijos foram fabricados a partir de leite padronizado, homogeneizado, tratado termicamente e fermentado com cultura tipo ¿O¿, composta de Lactococcus lactis subsp. lactis e Lactococcus lactis subsp. cremoris. A massa obtida após fermentação foi dividida em duas porções para fabricação de queijos com e sem adição de sorbato de potássio. Os queijos de cada processo foram divididos em dois lotes e armazenados a 4°C ou a 20°C. Amostras de Cream Cheese foram randomicamente escolhidas após 4, 10, 17, 24, 31, 38, 45, 52 e 59 dias de armazenamento e analisadas quanto ao pH, quantidade de fase aquosa obtida por centrifugação, contagem total de microrganismos e de bolores e leveduras. A fase aquosa foi avaliada quanto ao teor de sólidos totais e parâmetros reológicos. O delineamento experimental utilizado foi Split-Split-Plot em blocos com três repetições. O efeito dos tratamentos, da temperatura e do tempo de armazenamento sobre as características estudadas foi avaliado por análise de variância. Para avaliar o efeito da adição de sorbato sobre o comportamento reológico da solução de goma locusta esta foi dissolvida em água destilada a 80°C, adicionada ou não de sorbato de potássio, tendo sido o pH ajustado para 4,60 ± 0,05. Soluções com e sem sorbato de potássio foram armazenadas a 4°C ou a 20°C. Amostras foram escolhidas após 4, 11, 18, 25, 32, 39, 46, 53, 60 e 67 dias de armazenamento e avaliadas quanto ao pH, contagem total de microrganismos, bolores e leveduras e parâmetros reológicos. A adição de sorbato de potássio não afetou a composição dos queijos, exceto o pH que foi mais alto no queijo com sorbato. A capacidade de retenção de água do Cream Cheese diminuiu significativamente durante o período de armazenamento e diminuiu mais rapidamente quando o queijo foi armazenado a 20°C. As contagens total e de bolores e leveduras aumentaram linearmente e significativamente durante o período de armazenamento e foram maiores para os queijos fabricados sem adição de sorbato e armazenados a 20°C. À medida que a contagem microbiológica aumentou, ocorreu a redução da viscosidade aparente da fase aquosa e, à medida que a viscosidade diminuiu, observou-se a redução da capacidade de retenção de água do Cream Cheese. A avaliação do efeito da adição de sorbato de potássio sobre o comportamento reológico da solução de goma locusta mostrou que durante o período de armazenamento não houve crescimento expressivo de microrganismos e nem alteração da viscosidade das soluções, o que indica que a capacidade de retenção de água da goma não foi alterada. Estes resultados sugerem que a manutenção da viscosidade da fase aquosa do Cream Cheese é consequência do retardamento do crescimento microbiano e contribui para minimizar a sinérese melhorando a capacidade de retenção de água e a qualidade do produto final / Abstract: Cream cheese is a product of high moisture content obtained by acid coagulation, the main defect being syneresis or whey exudation during the storage period. The objective of this study was to evaluate the effects of the addition of potassium sorbate on the stability of cream cheese and on a solution of locust bean gum. The cheeses were prepared from standardized homogenized milk, heat treated and fermented with an ¿O¿ type culture. The mass obtained after fermentation was divided into two parts to manufacture the cheeses with and without potassium sorbate. The cheeses from each process were divided into two batches and stored at 4 or 20°C. Samples of cream cheese were taken at random after 4, 10, 17, 24, 31, 38, 45, 52 and 59 days of storage and analyzed for pH, amount of aqueous phase obtained by centrifugation, total microbial count and yeast and mold count. The aqueous phase was evaluated for total solids and rheological parameters. A Split-Split-Plot block experimental design was used with three repetitions. The effect of the treatments, the temperature and time of storage on the characteristics under study was evaluated by the analysis of variance. To evaluate the effect of the addition of sorbate on the rheological behavior of a solution of locust bean gum, the latter was dissolved in distilled water at 80°C, with or without the addition of potassium sorbate, the pH having been previously adjusted to 4.60 ± 0.05. Solutions with and without potassium sorbate were stored at 4 or 20°C. Samples were taken after 4, 11, 18, 25, 32, 39, 46, 53, 60 and 67 days of storage and evaluated for pH, total microbial count, yeast and mold count and the rheological parameters. The addition of potassium sorbate did not affect the composition of the cheeses, with the exception of the pH, which was higher in the cheese with sorbate. The water holding capacity of the cream cheese decreased significantly during the storage period, decreasing quicker when stored at 20°C. The total and yeast and mold counts increased linearly and significantly during the storage period and were higher in the cheeses manufactured without the addition of potassium sorbate and stored at 20°C. As the microbial count increased so the apparent viscosity of the aqueous phase reduced, and as the viscosity reduced there was a reduction in the water holding capacity of the cream cheese. The evaluation of the effect of the addition of potassium sorbate on the rheological behavior of the locust bean gum solution showed that during the storage period there was no expressive growth of microorganisms nor alterations in the viscosity of the solutions, indicating that the water holding capacity of the gum was unaltered. These results suggest that the maintenance of the viscosity of the aqueous phase of the cream cheese is a consequence of retarding microbial growth and contributes to minimize syneresis, improving the water holding capacity and quality of the final product / Mestrado / Mestre em Tecnologia de Alimentos

Please read the abstract in the front section of this document / Dissertation (M Inst Agrar ( Food Processing))--University of Pretoria, 2006. / Food Science / unrestricted