Listeria monocytogenes leads to severe health problems and is the third leading cause of death among the major 5 pathogens. A synthesized novel sugar ester, lactose monolaurate (LML), has antimicrobial properties against Listeria monocytogenes. The minimum bactericidal concentration (MBC) of LML is less than 5 mg/mL (9.5 mM) in growth media. To determine which moiety of LML dominates in its bacteriostatic activities, the antibacterial effect of lactose, lauric acid and Tween 20 were tested. Lactose has no inhibition effect on Listeria. Lauric acid and Tween 20 had some antimicrobial effect (3.48 and 1.59 log reduction respectively), but did not have a bactericidal effect as LML did. To determine the antibacterial effect of LML on L. monocytogenes a 5-strain cocktail of L. monocytogenes with an initial concentration of approximately 5 log CFU/mL was incubated in milk, yogurt and cottage cheese. The effects were determined via plate counts after 24-hour incubation at 37°C. LML had at least a 4 log reduction and killed all the bacteria at 5 mg/mL in fat-free milk, fat-free drinkable yogurt, 1% fat drinkable yogurt, and fat-free cottage cheese. LML also showed bacteriostatic effect in low-fat milk, whole milk, 1.5% fat drinkable yogurt, and 2% fat cottage cheese with a log reduction varying from 3.54 to 4.35. These tests showed that the antibacterial effect of LML was related to the fat content of the dairy products as well as temperature. LML only inhibited Listeria at room temperature (37°C) and showed no inhibitive effects at refrigeration temperature (4°C). LML can inhibit the viable but nonculturable state of Listeria monocytogenes for up to 6 weeks at room temperature.

There is a constant need of new synthetic emulsifiers in the food industry. Sugar esters are widely used as food grade synthetic emulsifiers, amongst which sucrose esters are the most common. Although sucrose esters are used very frequently, little is known about the use of lactose esters in food. There is a need for characterization of lactose esters before they can be used in foods. The objective of this study was to characterize a lactose ester, lactose monolaurate (LML) as an antimicrobial agent on food pathogens, evaluate its effect on 20 % oil-in-water emulsions as an emulsifier, and to explore its effect on crystallization behavior of anhydrous milk fat. In the first study (Chapter 3), the effect of LML was evaluated on survival of some Gram-positive and Gram-negative bacteria. For Listeria monocytogenes, a concentration of 1 mg/ml showed some inhibition in growth media whereas the cells were completely killed at 5 mg/ml. For Mycobacteria, an LML concentration between 0.1-1mg/ml was lethal. Scanning electron microscopy was also conducted to examine any changes in the morphology of cells. Listeria exhibited a change in morphology and a wrinkling effect was shown in Mycobacteria. In the second study (Chapter 4), the effect of LML as an emulsifier was evaluated in 20 % oil-in-water emulsions. The use level of LML was comparable to commercially available emulsifier polysorbate 20, and produced comparable stabilization in the emulsions upon use. In this study, an attempt was also made to optimize the synthesis of LML with respect to the immobilized enzyme and solvent combination. It was concluded that for 20 % oil-in-water emulsions, LML is a promising emulsifier at 0.5%. In the third study (Chapter 5), the effect of LML was evaluated at two concentrations on the crystallization behavior of anhydrous milk fat at two temperatures with high and low supercooling. On application of high intensity ultrasound (HIU) to anhydrous milk fat (AMF) at 31°C and 0.05 % LML the effect on viscosity of sample and crystallization behavior was evaluated. It was concluded that the viscosity of AMF decreased with the addition of 0.05% LML. The lower viscosity of anhydrous milk fat on addition of LML could be restored with the application of HIU.

There is a constant need of new synthetic emulsifiers in the food industry. Sugar esters are widely used as food grade synthetic emulsifiers, amongst which sucrose esters are the most common. Although sucrose esters are used very frequently, little is known about the use of lactose esters in food. There is a need for characterization of lactose esters before they can be used in foods. The objective of this study was to characterize a lactose ester, lactose monolaurate (LML) as an antimicrobial agent on food pathogens, evaluate its effect on 20 % oil-in-water emulsions as an emulsifier, and to explore its effect on crystallization behavior of anhydrous milk fat. In the first study (Chapter 3), the effect of LML was evaluated on survival of some Gram-positive and Gram-negative bacteria. For Listeria monocytogenes, a concentration of 1 mg/ml showed some inhibition in growth media whereas the cells were completely killed at 5 mg/ml. For Mycobacteria, an LML concentration between 0.1-1mg/ml was lethal. Scanning electron microscopy was also conducted to examine any changes in the morphology of cells. Listeria exhibited a change in morphology and a wrinkling effect was shown in Mycobacteria. In the second study (Chapter 4), the effect of LML as an emulsifier was evaluated in 20 % oil-in-water emulsions. The use level of LML was comparable to commercially available emulsifier polysorbate 20, and produced comparable stabilization in the emulsions upon use. In this study, an attempt was also made to optimize the synthesis of LML with respect to the immobilized enzyme and solvent combination. It was concluded that for 20 % oil-in-water emulsions, LML is a promising emulsifier at 0.5%. In the third study (Chapter 5), the effect of LML was evaluated at two concentrations on the crystallization behavior of anhydrous milk fat at two temperatures with high and low supercooling. On application of high intensity ultrasound (HIU) to anhydrous milk fat (AMF) at 31°C and 0.05 % LML the effect on viscosity of sample and crystallization behavior was evaluated. It was concluded that the viscosity of AMF decreased with the addition of 0.05% LML. The lower viscosity of anhydrous milk fat on addition of LML could be restored with the application of HIU.