3 rd International Symposium on Food Rheology and Structure 559 ABSTRACT The TA XT 2 Texture Analyzer was used to measure the texture characteristics of mango soy fortified yoghurt (MSFY) prepared from blends of buffalo milk of varying fat content, soy milk (7.5° B) and mango pulp (18° B). Texture profile data were used to develop regression models for dependant variables like hardness (HD), cohesiveness (CO), adhesiveness (AD), springiness (SP), gumminess (GU) and chewiness (CH), which were used to optimize ingredients. The optimized MSFY had HD (107.913 - 112.273 g), CO (0.410 - 0.416), AD (-70.32 to - 72.90 g.s), SP (0.930 - 0.953), GU (44.978 - 46.397 g) and CH (41.67 - 43.89 g) The optimized value are 2.95 % fat content in buffalo milk, 14.7 % soymilk and 7.2 % mango pulp in the blend for obtaining MSFY having similar textural charac- teristics that of yoghurt having 6 % fat. 1 INTRODUCTION Yoghurt is a cultured product, fermented with L. bul- garicus and S. thermophilus bacteria. Soymilk is characterized by beany flavor, which can be modified by lactic acid fermentation [1]. Soymilk based yoghurt would offer several distinct nutritional advan- tages over milk yoghurt including reduced level of cholesterol, saturated fat and lactose. Mango pulp is added to enhance vitamin A, vitamin C and mineral contents as well as it provides sweetness and masks the some beany flavor of soymilk. The texture of yoghurt varies widely due to milk composition, the microorganism used, presence of stabilizer, fruits etc. [2, 3]. The aim of this study was to find out opti- mum fat content in buffalo milk and optimum propor- tions of soy milk and mango pulp in the blend to pro- duce MSFY which has textural profile similar to that of the control yoghurt made from buffalo milk of 6 % fat content. 2 MATERIALS AND METHODS Standardized buffalo milk, soymilk (7.5° B [4]) and canned mango pulp (18° B) were used for prepara- tion of MSFY samples. Culture of S. thermophilus NCDC 075 and L. bulgaricus NCDC 008 were used. MSFY were prepared by using method described by Tamime and Robinson [2] and Calvo et al. [5]. TPA tests of set MSFY were carried out at 10 ± 0.5° C in 100 ml cup using a TA.XT2 Texture Analyzer with 5- kg load cell and 25 mm diameter perplex cylindrical probe. From the force – time curve, values for texture attributes were obtained which were shown to corre- late well with sensory characteristics of these param- eters [6]. 2.1 Experimental design A central composite design (CCD) was used to eval- uate the combined effect of independent variables, viz fat content in buffalo milk, proportion of soy milk and mango pulp content in blend on textural param- eters of MSFY samples. Levels were selected based on the literature survey and preliminary experiments. Twenty experiments were conducted. Response sur- face methodology (RSM) was used to study the sys- tem followed by optimization of blend proportion uti- lizing prediction models obtained [7]. A second order polynomial equation was assumed to relate the response. The data were analyzed by Systat 8.0 software. Optimization of the fat content in buffalo milk and the proportions of soy milk and mango pulp in blend was done by solving the developed equa- tions for specific value of each textural profile param- eter. Values for which the equations were solved were those of the laboratory made standard yoghurt sample (control). 3 RESULTS AND DISCUSSION Textural profile data of MSFY (average of 5 meas- urements) were correlated as second order polyno- mial models by using coded level of independent variables and the dependent variables. The regres- sion models had satisfactory value of correlation coefficient (R). 3.1 Effect on textural parameters of MSFY Textural characteristics of coagulated dairy products are affected by their structural characteristics. Microstructure of these products consists of a con- tinuous protein matrix with a loose and open struc- ture with space occupied by the fat globules dis- persed through the protein network. Changes in the textural profile parameters of the MSFY, which is classified as yoghurt, can be explained in similar manner. Hardness of the MSFY decreased with TEXTURAL CHARACTERISTICS OF MANGO SOYMILK FORTIFIED YOGHURT AND ITS OPTIMIZATION Pradyuman Kumar and H. N. Mishra Post Harvest Technology Centre, Agricultural and Food Engineering Department, Indian Institute of Technology, Kharagpur - 721 302, India