Site and time of experiment: The experiment was carried out at the Dairy Chemistry and Technology Laboratory of the Department of Dairy Science, Bangladesh Agricultural University, Mymensingh, during the period of July to October, 2008.
Collection of soybean seeds and buffalo milk: The soybean seed was collected from Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh and the buffalo milk was collected from local buffalo farm, Senbari of Trisal Thana, Mymensingh.
Preparation of soy milk from whole soybean powder: Whole soybean (1000 gm) free from immature field damage and black spot were grinded in a soy flour mill. Grained powder (125g) was dissolved with 1000 ml of water by stirring. The milk was strained through a fine cloth to separate the residue. Soy milk was then boiled at 100°C for 10-15 minutes with constant stirring.
Preparation of different types of dahi: Four types of dahi were prepared in this experiment. Out of four samples, one was prepared only from whole buffalo milk (control) and other three were prepared by replacing whole buffalo milk with soy milk at the rate of 25, 50 and 75% , respectively .
Preparation of dahi from buffalo milk (control): The collected (1250 ml) buffalo milk was heated to boiling temperature until reduced up to 20% of the original volume of milk. At the time of boiling , sugar was added to the milk at the rate of 12%. During heating, milk was stirred thoroughly with the help of the spoon. After heating milk pan was taken out from the heater and allowed to cool down to 40°C. The mixed bacteria containing starter culture was added to the milk at the rate of 2% and dissolved properly by stirring it and then milk was poured in several pre-boiled water washed plastic cups of about 100 ml size and kept at an incubation temperature of 37°C until complete coagulation of the samples (6 - 8hrs). After complete coagulation, the dahi samples were taken out from the incubator and were stored 2 hours in a refrigerator at 5°C for evaluation. This type of dahi was identified as 'A' type (control) dahi for experimental purpose.
Preparation of dahi from buffalo milk with the addition of different levels of soy milk: For the preparation of these types of dahi from buffalo milk, milk s were divided into three portions (937.5 , 625 and 312.5 ml) and taken in three different beakers. Previously collected soy milk was added with the buffalo milk (312.5, 625 and 937.5 ml) in different levels like 25, 50 and 75% in different beakers. The buffalo and soy milk samples were mixed properly with the help of the spoon. After mixing the different mixtures were boiled in different suspans and then dahi was prepared by using the same procedure used for making buffalo milk dahi. These different types of dahi were identified as 'B', 'C' and 'D' types of dahi for the experimental purpose, respectively. Evaluation of different types of Dahi Organoleptic parameters measured by a panel of expert judges included smell and taste score (50) ; body and consistency score (30); color and texture score (20); overall score (100).
Chemical tests and analysis of Dahi: For certifying the nutritional status the samples were evaluated in various ways. After organoleptic evaluation; all dahi samples were chemically analyzed in the laboratory in terms of acidity percentage, moisture content (g/kg), total solids (TS) content (g/kg), fat content (g/kg), protein content (g/kg), carbohydrate content (g/kg), ash content (g/kg).
Statistical analysis: Analysis of variance test (ANOVA) was done to find out the statistical differences between different treatments. As all experimental materials were completely homogenous and for this reason data were analyzed by using one way analysis of variance test (Completely Randomized Design, CRD ) as per MSTAT statistical program. The differences among sample means were compared by calculating LSD value with the help of a Least Significant Difference (LSD) test (Go mez and Gomez, 1984).