S S Zamal
BADC Matijil, Dhaka
M S Huda
Farm Div., BARI, Gazipur
M M Rahman
T&C Wing, BARI, Gazipur
M A Haque
FMP Engineering Div., BARI, Gazipur
M N Kabir
Supreme Seed Co. Ltd, Bangladesh
Soy Tofu, Preservatives, Self Life
Department of Food Technology and Rural Industries, Bangladesh Agricultural University, Mymensingh
Postharvest and Agro-processing
Fortified food
The study was conducted in the laboratories of the Department of Food Technology and Rural Industries, Bangladesh Agricultural University, Mymensingh, Bangladesh during July, 2005 to December 2005. The soybean variety sohag was used in the study. Aluminium foil was used for package and storage of samples. The potassium meta bi sulphite (KSM), sodium benzoate and potassium sorbate and their mixture were as used preservatives. Procedure for preparation of tofu: The previously prepared soymilk was cooked in an electric cooker for 20 min at 85-900c and it was cooled to specific coagulants temperature, and then coagulants CaSO4 and MgSO4 were added slowly, stirring until soy protein starting to coagulate. Allowed the curd to set without disturbing for 20 min. The curd transferred to a cheese cloth-lined wooden box (16.5×16.6×3.5 cm2) and pressed by placing weighted (16 g.cm2) on the top for 20-25 in by adding four types of preservatives. The whole tofu block then immersed into cold water in order to remove it from the block easily without sticking to the cloth. Thus prepared tofu were packed in 10 aluminium foil. The sample of tofu was treated with five types treatments such as Without preservatives (control), With preservative Potassium meta bi sulphite ( KMS ) @ 300 mg/kg, With preservative sodium benzoate @ 350 mg/kg, With preservative potassium sorbate @350 mg/kg and Mixed preservative i.e. the mixture of (KMS (250 mg/kg)+ sodium benzoate (250 mg/kg) + potassium sorbate (200 mg/kg). Then stored in a refrigerator and at room temperature. Shelf-life studiesconducted at room temperature (28-35°C) and refrigerated temperature (5±1°C) and sensory evaluation conducted. The media for total plate count of micro-organism was prepared. Composition of 1 litre nutrient Agar was as 5 g Tryptone (peptone), 2.5 g Yeast extracts, 1.0 g Glucose, 15.0 g Agar, 5.0 g NaCl and 1000 ml Distilled water. The ingredients tryptone, yeast extract, glucose and agar were weighed. The ingredients were dissolved in 1000 ml of distilled water. The mixture was boiled for dissolving completely and was sterilized in an autoclave at 121°C temperature; 15 psi pressure for 15 min. the media was then cooled at 40°C and distributed to Petri dishes. Total plate count of micro-organisms - An amount of 10g collected sample was diluted with sterile distilled water and homogenized and used as stock solution. An amount of 1 ml sample stock solution was further dilated with 9 ml phosphate buffer saline (PBS) in a taste tube. From this diluted stock solution, a series of subsequent 10 fold dilution ranging from 10-1 to 10-6 was prepared for the microbial examination of food. The changes of colour, flavour, texture and taste of soymilk and tofu sample were observed at different intervals at room temperature (28-35°C) and refrigerated (5±1°C) storage condition in aluminium foil package. Storage samples were observed in every 12 hours for colour, flavour, texture and taste and visual fungal growth. Sensory evaluation, Hedonic rating test - The sensory evaluation of five types of tofu containing various proportions of preservatives were evaluated for colour, flavour, taste, texture and overall acceptability by a panel of 10 panelists. The panelists were selected from the teachers, students and staff, Department of Food Technology and Rural Industries, Bangladesh Agricultural University, Mymensingh and were briefed before evaluating sensory quality of the tofu on soup. For statistical analysis of sensory data, a 9-point hedonic rating test was performed to assess the degree of acceptability to tofu containing different coagulants. One cup of tofu soup from each coagulant was presented to 16 panelists as randomly coded samples. The taste panelists were asked to rate the sample on a 9 point hedonic scale for colour, flavour, texture and overall acceptability with the ratings of: 9= like extremly, 8 = like very much, 7 = like moderately, 6 = like slightly, 5 = neither like nor dislike, 4 = dislike slightly, 3 = dislike moderately, 2 = dislike very much, 1 = dislike extremely. The results were evaluated by Analysis of Variance and Duncan’s Multiple Range Test (DMRT) procedures of the MSTAT system. Studies on the storage stability of tofu - The changes of colour, flavour, body and texture and taste of tofu sample were observed at different intervals under room temperature (28±35°C) and refrigerated (5±1°C) storage condition in aluminium foil package. Storage samples were observed in every 12 hours for colour, body and texture, flavour taste and visual fungal growth. Water was change daily to keep it fresh.
Eco-friendly Agril. J. 6(07): 124-127, 2013 (July); ISSN 1999-7957
Journal