Preliminary experiments by API ZYM enzyme system showed that Lactobacillus casei (Lb. casei) subspecies contained low proteinase and high aminopeptidase and esterase-lipase activities, which are the desirable traits of microorganisms to be used as starter adjuncts in Cheddar cheese-making. Six strains of Lb. casei (ssp. casei, ssp. rhamnosus, and ssp. pseudoplantarum), selected from superior peptidase and esterase-lipase profiles, were further studied for their amino-, di-, and carboxy-peptidase activities using thirty synthetic substrates. This study revealed useful information towards improving our understanding of the peptidase profiles and probable role of Lb. casei in Cheddar cheese ripening. Although individual strains varied in their specific activities against different substrates, Lactobacillus subspecies generally exhibited high amino- and di-peptidase, relatively weak tripeptidase, but no carboxypeptidase activities. The knowledge gained from these studies helped us selecting two strains (Lb. casei ssp. casei LLG and Lb. casei ssp. rhamnosus S93) with highest amino- and di-peptidase activities for further research. In order to study their enzymatic characteristics and kinetics, aminopeptidase of these two strains were purified to homogeneity by Fast Protein Liquid Chromatography (FPLC). A single monomeric enzyme was shown to be responsible for the entire aminopeptidase activity of the cell-free extracts. This investigation provided new insights and revealed fundamental knowledge about the peptidases of Lb. casei group. In addition, new methodologies were developed for rapid enzyme purification using FPLC system, and evaluation of peptidases by API ZYM enzyme system.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.70186 |
| Date | January 1990 |
| Creators | Arora, Gulshan |
| Contributors | Lee, Byong H. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Food Science and Agricultural Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001171944, proquestno: AAINN67599, Theses scanned by UMI/ProQuest. |
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