Raw ingredients: Ingredients for biscuits formulation such as wheat flour, sugar, baking powder, milk were purchased from the local market. Raw mature, ripen banana (Musa sapientum), carrot (Daucus carota), apple (Malus domestica) were also procured from the local market of Chattogram, Bangladesh.
Preparation of mixed peel powder (MPP): Whole banana, apple and carrot were washed with tap water for cleaning and removal of extraneous dirt. Then clean fruits and vegetables were peeled using Peeler and chopped. The slices of peel were dipped into the Potassium metabisulfite solution (0.02%) for 5 minutes to prevent from discoloration. Then they were blanched separately for 5 minutes. Collected peels were then spread on trays and dried in Cabinet Dryer at 60°C for 12 hr. Dried peels were ground separately in grinder to fine powders. Equal amount of each powder were mixed together and packed in polythene bags and stored in air tight food grade plastic containers until used.
Biscuit formulation and preparation: Sweet biscuits were prepared using the traditional creamery method. Biscuits were prepared from blend of whole wheat flour, MPP using the proportions. Refined flour/ blends, sugar powder, vegetable oil, milk, common salt, baking powder and water as required for proper consistency were used as the recipe for preparing biscuits. Sugar and fat were creamed in a mixer. To do this, a well-mixed blend of white flour/blends, MPP, milk and baking powder were added along with water containing common salt. The contents were mixed further for 5 minutes to make the dough. Using a wooden rolling pin, the dough was sheeted on a platform to a uniform thickness. Circular star shape biscuits were cut and baked for 15 minutes at 220°C in a baking oven.
Then the biscuits were cooled, packed in air-tight boxes and stored at room temperature. Control biscuits were also prepared from refined flour along with other ingredients using the above proportions.
Proximate analysis of MPP and biscuit: MPP and prepared biscuit samples were analyzed for their moisture, ash, crude protein, lipids and crude fiber contents according to the methods described in AOAC, (2007). The moisture content was determined by moisture analyzer. Nitrogen content was estimated by Kjeldahl method and converted to protein by multiplying with the factor 6.25 for MPP and biscuit samples, the lipids were estimated by extracting known weight of samples with petroleum ether as solvent, using a Soxhlet apparatus. Ash content was determined by igniting the samples in muffled furnace at 550ºC (dull red) until grayish white ash were obtained. Crude fiber was determined by acid-alkali digestion method. All the analyses were carried out in triplicates. Total carbohydrates were calculated by the difference % carbohydrate = 100-(% moisture + % ash + % crude protein + % fat +% crude fiber)
Determination of mineral contents: Iron (Fe), Calcium (Ca), Potassium (K), Manganese (Mn) and Magnesium (Mg) contents were determined by using atomic absorption spectrophotometer according to AOAC, (2007).
Evaluation of sensory attributes: Sensory evaluation was carried out using a trained panel of ten members consisting equal men and women. Samples of both control and MPP fortified biscuits were presented to each of the panelist and were asked to assess the taste, color, texture, aroma, flavor, sweetness, and overall acceptability using nine point hedonic scale with 1 representing the least score (dislike extremely) and 9 the highest score (like extremely).
Proximate composition of the biscuits: The incorporation of flour from fruits and vegetable residue in bakery products improve dietary fiber and functional properties (Ajila et al., 2008). Moisture content of the control biscuit was found to be 10.85% while incorporation of MPP decreased the moisture content to 7.51%. Lower moisture content will prolong the storage time of MPP fortified biscuit and contributes to the textural quality and the inhibition of chemical and biochemical reactions. Furthermore, fortification of biscuit
Statistical analysis: Obtained data were subjected to one-way analysis of variance (ANOVA) using Minitab Version 18.1 Statistical Software followed by Fisher’s LSD test to distinguish statistical differences among them to test the level of significance (p<0.05).