Semester of Graduation

Fall 2017

Degree

Master of Science (MS)

Department

Animal, Dairy and Poultry

Document Type

Thesis

Abstract

The importance of Leuconostoc mesenteroides is recognized for its contribution to taste in cultured dairy products. It has been cited for its potential role as a probiotic. Consumer demand exists for new dairy products with health benefits. In the manufacture of probiotic-products survival of Leuconostoc mesenteroides would depend on its ability to tolerate challenging processing and storage conditions. Improved viability by prior exposure to mild stresses can increase stress tolerance toward a more severe stress. Furthermore, it can result in cross-protection due to connection of several proteins in response to stresses. Objective was to evaluate the effect of prior exposure to various mild stress conditions on the survival of Leuconostoc mesenteroides in challenging conditions. Leuconostoc mesenteroides spp. cremoris Vivolac Cremosa CIT/FPC Series cells were subjected to four mild stresses (acid, heat, ethanol and oxidative). Each mild stress had three levels of intensity; low, medium and high. Then culture was subjected to challenging acid, heat or osmotic conditions. MRS Agar was used for plating. Plates were incubated aerobically (30°C 48 h). The experiments were repeated three times with duplicate readings. Data were analyzed as a RBD using the Glimmix procedure and Tukey mean separation with a level of significance of 0.05. Heat tolerance of Leuconostoc mesenteroides at 60 °C was significantly enhanced by subjecting the bacteria to acid mild treatments of pH 5.0, 4.5 and 4.0 and heat mild treatments of 30, 35 and 45 °C (P<0.05). Acid tolerance of Leuconostoc mesenteroides was not enhanced by application of any of the mild stresses studied when compared to their respective controls (P>0.05). However good survivability was achieved with the application of the acid mild stress having cell counts ranging from 9.36 -8.77 log CFU/mL. Leuconostoc mesenteroides survivability was not affected with the exposure to osmotic challenge (P>0.05). Furthermore, osmotic conditions promoted the growth Leuconostoc mesenteroides when compared to their initial cell counts (P<0.05). The enhancement of its heat tolerance and the robustness displayed to the acid and osmotic challenging conditions has possible applications of Leuconostoc mesenteroides spp. cremoris in food products in which such challenging conditions are encountered.

Date

11-4-2017

Committee Chair

Aryana, Kayanush

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