Doctor of Philosophy (PhD)


Dairy Science (Animal, Dairy, and Poultry Sciences)

Document Type



There is a pronounced public awareness about herbal remedies. Garlic and ginger have antibacterial properties and prevent cardiovascular diseases. Onion and turmeric decrease the risk of diabetes and like garlic, they have anticancer properties. Streptococcus thermophilus, Lactobacillus bulgaricus and Lactobacillus acidophilus are lactic acid bacteria that produce lactase and reduce the symptoms of malabsorption. Earlier work has shown the influence of spice extracts but the influence of pure spice juice on yogurt culture bacteria is not known. Characteristics of yogurt culture bacteria were measured by suspending freshly thawed cultures in 0.1% peptone water (growth), acidified MRS broth (acid tolerance), MRS-Thio broth with oxgall (bile tolerance) and skim milk (protease activity) with 1% (v/v) of freshly extracted spice juice. Control samples had no spice juice. A probiotic blueberry yogurt was made with 0.05% of individual spice juice. Physico-chemical characteristics of the three bacterial cultures used were determined and a consumer acceptability test was conducted. Results show that these 4 spices did not have an inhibitory effect on the growth of the three culture bacteria. Turmeric improved the protease activity of L. bulgaricus and alongside with ginger, it also improved the protease activity of L. acidophilus. All four spices decreased the pH of the spicy yogurt. Coliform bacterial growth was significant on turmeric yogurt at day 1 of storage when compared to control and the other spices. Streptococcus thermophilus grew better in garlic and ginger yogurt, while L. bulgaricus grew better in onion and turmeric yogurt. Color measurements showed a decreased lightness (L*) from all spices, red color space values for the red-green axis (a*), turmeric in the yellow color space and the rest of the spices in the blue color space for the blue-yellow axis (b*). Apparent viscosity was higher in onion and ginger yogurt. The consumer testing showed a well acceptance of the control and ginger yogurt. Ginger had the highest intent of purchase by consumers. Ginger can be used in yogurts for direct consumption while all 4 spices have potential for a new product line of yogurts for cooking and dips, enabling potential health benefits from both sources.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Aryana, Kayanush



Included in

Dairy Science Commons