Place of experiment The sample analyses were conducted in the laboratory of Food Technology and Nutritional Science (FTNS) Department, Mawlana Bhashani Science and Technology University (MBSTU), Santosh, Tangail-1902, Bangladesh. Collection of raw materials The banana (Musa sapientam L), which local name is “Sagor kola” was purchased from local market of Santosh, Tangail, Bangladesh. The other ingredients which were used in cookies production i.e. refined wheat flour, hydrogenated vegetable oil, sugar powder, vegetable oil (soybean), egg, whole milk, iodized salt, baking powder and required chemicals were used from the laboratory of FTNS department, MBSTU and some of them procured from the local market.
Preparation of banana (unripe) peel flour At first the bananas were collected and washed with water to remove all harmful ingredients. After peeling, the peels were sliced and dipped for ten minutes in 0.5% (w/v) citric acid solution to reduce enzymatic reaction. After drained out, the sliced were then dried in oven at 500C for 16-20 hrs. The dried banana peels were then amalgamated by using a commercial blender and passes through 60 mesh screen to obtain fine banana peel flour. The dried banana peels powder were then stored in airtight packet at ambient temperature.
Hydrogenated vegetable oil (80g) and sugar (200g) were uniformly mixed together for 3 minutes at a speed of 10 and 8 rpm by rotary mixture machine. Then other ingredients such as milk, egg, salt and baking powder were mixed together at a speed of 6 rpm. After mixing above ingredients then added vegetable oil and uniformly mixed for 3 minutes at a speed of 8 rpm. Finally wheat flour, mashed banana and banana peel flour were added and uniformly mixed well together. The batter were rolled out and cut uniformly and send it to baking chamber and baked at 1500 C temperatures for 15-16 minutes. When the color of cookies turned to light brown color it indicates the finished baked cookies. After baking, cookies were then cooled and packed in plastic packets. The ready to eat cookies were than stored at room temperature for further analysis.
Analysis of functional properties of banana peel and wheat flour Functional qualities such as water and oil holding capacity, swelling capacity, emulsion activity and stability and also flour dispersibility of banana peel flour and wheat flour were analyzed. Water holding capacity (WHC) About 1g of flour sample and 25ml of water were taken in a 30 ml capacity test tube and allowed for 15 minutes at room temperature. The tube was then centrifuge for 20 min at 3000 rpm and drained off the supernatant. The weight of the residue after drained off the excess water was the water holding capacity of flour and determined as g of water/g dry sample (Rodriguez-Ambriz et al., 2008). Oil holding capacity (OHC) About 1g of flour sample and 25 ml of commercially olive oil were taken in a 30 ml capacity test tube and centrifuged the mixture at 3000 rpm for 20 minutes. The weight of the residue was recorded after decanted the free oil. OHC was calculated as gram of water per gram of dry sample (Rodriguez-Ambriz et al., 2008). Swelling capacity (SC) The swelling capacity of flour sample was evaluated by Okaka and Potter (1977) method. Emulsion activity (EA) and emulsion stability (ES) The emulsion activity and emulsion stability of sample were evaluated by Yasumatsu et al., (1972) method. Flour dispersibility (FD) About 10 g of sample were mixed with distilled water in a cylinder to make a final volume of 100ml, stir vigorously and then allowed it to settle. After 3 hours, settled particles volume was recorded. And finally percentage of flour dispersibility (Kulkarni et al., 1991)was calculated by subtracted it from 100.
Sensory evaluation of cookies The sensory evaluation of prepared cookies was carried out by 15 panel members (trained on sensory evaluation) from different food industries in Bangladesh. The panel members evaluated each sample of the cookies for color and appearance, texture & consistency, taste, aroma and overall acceptability. The samples were rated by 9 point hedonic scale (9-like extremely, 8- like very much, 7-like moderately, 6- like slightly, 5-neither like or dislike, 4-dislike, 3-dislike moderately, 2-dislike very much, 1-dislike extremely). Score were collected and analyzed statistically. The score 6 or more were considered as acceptable for the consumer acceptability. Proximate analyses of composite flour and cookies Proximate analyses such as moisture, ash, fat, protein and crude fiber of the sample were analyzed by using AOAC- 2000 method (AOAC, 2000). Energy value of the sample was calculated by using factor method described by by Chinma and Igyor and the Atwater factor method is [(9xfat) + (4xcarbohydrate) + (4x protein)] (Chinma and Igyor, 2007) Physical characteristics of cookies Physical property of cookies is an important attributes which plays an important role to determine the consumer acceptability. AACC method was used to determine the diameter and thickness of the cookies (AACC, 2000). The Spread Factor (SF) of the cookies was determined according to the following formula: SF = (Diameter/Thickness × Correction Factor) × 10, where correction factor was 1.0 in this study at constant atmospheric pressure.
Statistical analysis All the sample analyses were performed in triplicate and descriptive statistics were analyzed by using SPSS (Statistical Package for the Social Science) software package version 16.0 (SPSS Inc., Chicago, IL, USA) for all variables. All of the values are expressed as the mean of three individual replicates ± Standard Error Mean (SEM). All data were subjected statistically to ANOVA test (analysis of variance) and mean value were separated using Tukey’s test (Steele Torrie, 1980). Differences between mean values were considered to be significant at p < 0.05.