Addis Ababa Institute of Technology School of Graduate Study Department of Chemical Engineering Effect of Oat Flour Addition on the Physico-chemical and Microbiological Quality of Probiotic Bio-yoghurt A Thesis Submitted to the School of Graduate Studies of Addis Ababa Institute of Technology, in Partial Fulfillment of the Requirements for the Degree of Masters of Science in Chemical Engineering (Food Engineering Stream) By: Yared Tesfaye Advisor: Professor Yogesh Kumar Jha (PhD) Addis Ababa, Ethiopia July, 2013