Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Environmental Science

First Advisor

Ibrahim, Salam A.


Bifidobacteria and Lactobacilli are purportedly beneficial to human health and are called probiotics which are live microorganisms, when administered in adequate amounts conferring a health benefit on the host. It is believed that the maximum probiotics effect can be achieved if the organisms adhere to intestinal mucosal cells. Probiotics, perhaps in combination with prebiotics, may become an important means of preventing and treating disease. In fact, several types of diarrhea have been successfully treated with probiotics. The mechanisms behind favorable clinical outcome are still largely unknown, however, the potential benefits of probiotic therapy promise to be almost limitless. Organic acids offer therapeutic/health benefits, such as increasing of pancreatic secretion. Prebiotics, such as oligosaccharides and polysaccharides, are defined as nondigestible food ingredients that beneficially affect host health by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon. Shiitake mushroom (Lentinus edodes) is an edible and medicinal mushroom popular in Japan, with a prominent activity in very small dosages. Shiitake mushroom extract contains many of oligosaccharides and polysaccharides for this reason it is considered as prebiotics. Lactobacillus and bifidobacteria are thought to stimulate the immune system, produce B vitamins, inhibit pathogen growth, reduce blood ammonia and blood cholesterol levels, and help to restore the normal flora after antibiotic therapy. The probiotics are encouraged to grow by oligosaccharides and polysaccharides. The overall goal of this project is to develop a new technique that could be applied in the food industry to ensure food-grade probiotics that extend the viability longer, express α-galactosidase/ β-galactosidase, and overall to enhance the quality of dairy products. Specific objectives to be accomplished are as follows: 1) to investigate the effect of mushroom extract on growth of bifidobacteria and lactobacillus in vitro; 2) to determine the effect of shiitake mushroom extract on the pH, titratable acidity, viability and α-galactosidase/ β-galactosidase of probiotics in milk during refrigerated storage; 3) to study the impact of mushroom extract on viability and αgalactosidase/β-galactosidase activities of probiotics in yogurt products during refrigerated storage. The proposed research will build and extend our knowledge to develop food-grade probiotics, which can extend probiotics viability, produce higher α-galactosidase/β-galactosidase activity and enhance the quality of the dairy products. Information obtained from this study will be valuable in developing strategies for the industrial application of this food grade bacteria and enzymes in dairy products.