The experiment was conducted in the Department of Food Engineering and Tea Technology, Shahjalal University of Science and Technology, Sylhet, Bangladesh, 2013.
2.1. Materials Fresh green bananas (Musa sapientum) were collected from local market. Then the sample was dried by using a hot air drier and freeze drier. The dried sample was turned into flour by using a blender. Other materials like refined wheat flour, sugar, fat etc. required for biscuit making were purchased from local markets. 2.2. Biscuit Formulation The basic formulations used for preparation of biscuits are outlined in Table 1. The biscuits were prepared with the incorporation of hot air dried and freeze dried banana flour in 0, 5, 10, 15 and 20% concentration with wheat flour. The pre-weighed ingredients were mixed properly. The baking chemicals and sugar were dissolved in water. A mixture of raw materials was added to obtain a uniform dough and the dough was allowed to relax for 15 minutes before rolling out. The dough was then kneaded and rolled to a uniform thickness of 3 mm.
The rolled out dough was allowed to relax for 5 minutes. Then the biscuits were cut out with round biscuit cutter of 3.5 cm diameter. The cut out biscuits were placed on either greased pans or paper lined pans about 0.5 inches apart and the biscuits were allowed to rest in the pan about 10 minutes and baked at 220°C for 10-15 minutes, cooled to ambient temperature and packed in high density polyethylene bags. 2.3. Proximate Composition Banana flours were analyzed for their physicochemical and functional properties. Particularly, the functional properties are required for the formulation of value-added composite bakery products. 2.4. Physicochemical Properties Protein (micro- Kjeldahl, × 6.25), fat (Folch method), moisture, ash and crude fiber were determined by the AOAC (2004) [6] methods. The carbohydrate content was calculated by the subtraction method. Calcium (Ca), Phosphorus (P), Iron (Fe) and Zinc (Zn) were determined by using Atomic Absorption Spectrophotometer (Thermo scientific iCE 3000) and the calorific value was calculated. 2.5. Functional Properties 2.5.1. Water and Oil Absorption Capacity The water and oil absorption capacities were determined by the method of Sosulski et al., 1986. The sample (1.0 g) was mixed with 10 ml distilled water or refined soybean oil, kept at ambient temperature for 30 min and centrifuged for 10 min at 2000×g. Water or oil absorption capacity was expressed as percent water or oil bound per gram of the sample.
2.5.2. Bulk Density The bulk density was determined according to the method described by Okaka and Potter [8]. The sample (50 g) was put into a 100 ml graduated cylinder and tapped 20-30 times. The bulk density was calculated as weight per unit volume of sample. 2.5.3. Swelling Capacity The method of Okaka and Potter with some modifications was used for determining the swelling capacity. The sample filled up to 10 ml mark in a 100 ml graduated cylinder was added with water to adjust the total volume to 50 ml. The top of the graduated cylinder was tightly covered and mixed by inverting the cylinder. The suspension was inverted again after 2 min and allowed to stand for further 30 min. The volume occupied by the sample was taken after 30 min. 2.5.4. Foaming Capacity Foaming capacity and foaming stability were determined as described by Narayana and Narasinga Rao (1982) with slight modifications. Sample (1.0 g) was added to 50 ml distilled water at 30± 20 ºC in a graduated cylinder. The suspension was mixed and shaken for 5 min to foam. The volume of the foam after whipping for 30 Sec was expressed as foaming capacity.
2.5.5. Emulsifying Activity: Emulsifying activity was determined as described by Okaka and Potter. The sample (0.5 g) was added to 10 ml distilled water and shaking the mixture for 3 min in a centrifuge tube. The mixture was made up to 12.5 ml by adding oil and homogenized for 3 min. The resulting emulsion was centrifuged at 2000 RPM for 5 min and then the emulsion volume was measured.
2.6. Physical Analysis of Biscuits Diameter of biscuits was measured by laying three biscuit edge to edge with the help of a scale rotating them 90° and again measuring the diameter of three biscuits (cm) and then taking an average value. Thickness as measured by stacking three biscuits on top of each other and taking average thickness (cm). Weight of biscuits was measured as average of values of three individual biscuits with the help of digital weighing balance. Spread ratio was calculated by dividing the average value of the diameter by average value of thickness of biscuits. Percent spread was calculated by dividing the spread ratio of supplemented biscuits with a spread ratio of control biscuits and multiplying by 100.
2.7. Sensory Analysis of Biscuits Biscuit samples were analyzed for sensory characteristics. Sensory quality characteristics were evaluated by a panel of 10 semi-trained members using a 9-point Hedonic scale where 9 = like extremely; 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 biscuits were evaluated for their color, flavor, texture and overall acceptability.
2.8. Statistical Analysis Data was analyzed using analysis of variance (ANOVA) to determine significant differences among the various samples in triplicate using the software, statistical package for social science (SPSS) version 11.00 SPSS inc., Chicago, IL, USA at the 0.05 level.