Thesis (Ph.D.)--University of Massachusetts Amherst, 2008. / Adviser: Kalidas Shetty. Includes bibliographical references.

M.Tech.

[No abstract available] / Land and Food Systems, Faculty of / Graduate

[No abstract available] / Land and Food Systems, Faculty of / Graduate

[No abstract submitted] / Land and Food Systems, Faculty of / Graduate

No description available.

No description available.

Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Medicine, 1998. / During graded exercise, an intensity is reached where a subjects ability to remove lactate lags behind the rate of lactace production. The influence of body fluid shifts, during exercise of increasing intensity, on the pattern of the blood lactate response was studied. The maximal oxygen uptake (V02 max) was measured using a treadmill, on eleven subjects. Subsequently, lactate accumulation in venous blood was measured, in triplicate, up to an oxygen consumption greater than 90% V02max. During all exercise, oxygen consumption was measured using an online system. In addition, the blood samples at each workload were used to determine haematocrit (Hct) and haemoglobin (Hb) levels. The Hct and Hb values were used to calculate lactate accumulation (corrected for body fluid shifts) as opposed to the absolute or total lactate levels. The correction for body fluid shifts was done using two techniques. The one using haematocrit only and the other using both haematocrit and haemoglobin. The total and accumulated lactate levels were related to %V02max using two different models. Firstly, a lactate threshold (LT) was determined using the classic lactate turning point (LTP) concept, (ie. two straight lines fitted to the data points) . These Tines iii were computer generated. The intercept of the two lines (LT) was compared for total lactate against accumulated lactate (calculated using Hct alone and secondly Hct in combination with Hb. In the latter cases, both the LT intercepts were shifted slightly to the right (ie. to a higher % of V02max) . The average difference in LT when adjusting with Hb and Hct was 0,519 of %V02max (0,72% change) and when adjusting with Hct only was 1,17 of %V02 max (1,65% change). Secondly, an exponential curve was fitted by regression to the data (r=0.989+/-0.018). A substantial shift in the curve, both down and to the right, was obtained when adjusting total lactate to accumulated lactate. The %V02 max at a lactate concentration of 4 mmol/I was used to define the position of the curve. The difference when using Hct alone to calculate accumulated lactate corrected for fluid shift was - 9,20% of V02max (p<0.05), and when using Hb and Hct in combination, -8,71% of V02max (p<0,05) . It is concluded that expressing the lactate curve as an accumulated curve (corrected for body fluid shifts), rather than in absolute terms, significantly alters the construction of the curve during the exercise protocol used in this study. This is especially relevant when using the exponential model,

I declare that this is my own, unaided work. It is being submitted for the degree of Master of Science in the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination in any other University. / Heat resistance and inactivation of processed meat spoilage lactic acid bacteria was investigated in vitro and by in-package pasteurization of South African vacuum-packaged vienna sausages. In vitro heat resistance of four lactic acid bacteria strains was low, since reductions of at least one log cycle in bacterial numbers occurred upon heating at 57, 60 and 63°C in quarter-strength Ringers solution for one minute. In vitro heat resistance data were used to calculate three in-package pasteurization treatments of increasing severity for vacuum-packaged vienna sausages. Depending on treatment, pasteurization in a water cooker at 67°C increased microbiological shelf life of sausages 10, 14 and 17 times that of control samples, during storage at 8'C. Although in-package pasteurization successfully decreased growth of spoilage lactic acid bacteria and increased product shelf life fit did not entirely prevent spoilage by pediococci. Since pasteurization also promoted growth of potentially pathogenic Bacillus and Clostridium, safety of pasteurized vacuum-packaged vienna sausages was compromised. / Andrew Chakane 2018

<i>Lactobacillus plantarum</i> (<i>Lb. plantarum</i>) NRRL B4496 and <i>Lactococcus lactis</i> (<i>Lc. lactis</i>) NRRL B1821 prolidase genes were isolated, cloned, and sequenced. The sequence-confirmed genes were subcloned into the expression systems. The recombinant prolidases from the pKK223-3 systems were purified through ammonium sulphate precipitation and anion-exchange column chromatography. Recombinant <i>Lb. plantarum prolidase</i>, however, demonstrated a loss of activity during the purification. The following characterization work was performed on purified recombinant <i>Lc. lactis prolidase</i>. <p>The mass spectroscopic result and the molecular modelling suggested a 80 kDa homodimer with two metal cations at the catalytic centre of the prolidase. The optimum temperature was 50 ºC and showed more than 50% activities between 40 and 55 ºC. The enzyme was most stable at 30 ºC and withstood 20 min of heat-treatment up to 60 ºC, however, lost activity over 70 ºC. Circular dichroism indicated a denaturation temperature of 67 ºC. The optimum pH was 6.5 for hydrolyzing Leu-Pro and the enzyme did not display any activity below pH 5.5 nor above pH 7 with this peptide. However, Phe-Pro was hydrolyzed the fastest at pH 7 and Arg-Pro had a maximum rate at pH 9. This metallopeptidase exhibited a broad range of metal cation preference, hydrolyzing Leu-Pro with Mn++, Co++, Zn++, Ca++, and Mg++. Further kinetic analysis showed unusual allostery of the enzyme (Hill coefficient: 1.3). The unique substrate intakes onGlu-Pro and tripeptides were observed while Val-Pro was not hydrolyzed. The molecular modelling of this prolidase suggested a difference in the substrate specificity resulting from a loop structure, L33 to R40, near the substrate binding site.