2.1 Materials Procurement Ginger (Zingiber officinale) rhizome were collected from local market for this study. All chemicals and reagent used in this study were procured from sigma aldrich, Bangladesh.
2.1.1 Dehydrated GP preparation Ginger rhizome were cleaned with tap water. For extending shelf life and color cleaned ginger were soaked in boiling water for 25 sec. Then immersed in 0.3% Potassium metabisulphite (KMS) solution for 15 minutes at room temperature. Treated ginger were cut into 3-5 mm slices and dehydrated in four different drying methods. i. Sun drying – Gingers were dehydrated in open hot sunlight. ii. Oven drying - Gingers were dehydrated at (50 ±5) 0 C for 6-8 hours. iii. Mechanical drying - Gingers were dehydrated in hot air mechanical dryer. iv. Microwave drying - Gingers were dehydrated in Microwave of 800W for 5-10 minutes. Dehydrated ginger slices were ground using a grinder for making fine powder. Prepared GP was stored at 4°C in airtight polyethylene bag for further analysis.
2.2 Methods of Analysis All experimental parameters were conducted at ambient temperature and carried out in three replications.
2.2.1 Moisture estimation Moisture content was estimated following AOAC,2005 method [10]. 5 g GP was taken in pre-weighed petri dish and dried in oven maintaining temperature (105±5)°C until a constant weight was obtained. Moisture content was calculated following this formula.
Moisture (%)= [{(Initial wt. of sample – Dried wt. of sample) ÷ Initial wt. of sample} ×100]
2.2.2 Ash content estimation Ash content was estimated following AOAC,2005 method [10]. 5g sample was taken into preweighed crucible and heated over a bunsen burner until the sample completely burnt. Then the crucible was taken into muffle furnace and burnt for 5 hours at 550°C. The crucible was kept into a desiccator for cool. The ash content was calculated following this formula. Ash (%) = [(Wt. of ash ÷ Wt. of sample taken) ×100]
2.2.3 Protein content estimation Protein content of GP was estimated following Kjeldahl Method. This method was involved in digestion, distillation and titration. 0.5 g sample and 0.2 g digestion mixture was taken in Kjeldahl tube then 20 ml 98% sulfuric acid added in tube. The mixture was digested with speed digester at 420°C for 4 hours. Digested solution entered into distillation chamber. After distillation the solution was titrated with 0.1N hydrochloric acid. After estimating the nitrogen content then that was multiply with 6.25 as factor. Protein content was estimated following this formula.
Nitrogen (%) = [(Burette reading × Normality of acid × 1.4007) ÷ Sample weight] Protein (%) = [Nitrogen content (%) × 6.25]
2.2.4 Fat estimation Crude fat was estimated following soxlet method approved by AOAC, 2005. 5 g sample was taken in cellulose extraction thimble. Thimble was taken into soxlet extraction column of the fat analyzer. Boiling flask (250 ml) was filled with 150 ml (60-40) petroleum ether and placed under extraction column according to the corresponding thimble. Thimble was dipped into solvent for 3 hours at 90°C. Then the thimble was raised above from the solvent and set for 30 minutes. The thimble was removed carefully and petroleum ether solvent was collected from the top of the container and preserve for reuse. Boiling flask was taken in oven for blowing out extra petroleum ether solvent. Then the crude fat was weighed. The fat content was calculated using this formula.
Fat (%) = [(Wt. of fat ÷ Wt. of sample) × 100]
2.2.5 Crude fiber estimation Crude fiber content of defatted dry sample was estimated by using AOAC,2005 method [10]. About 2.5 g defatted dry sample was taken for fiber analysis. The sample is allowed to boil with 1.25% dilute H2SO4, washed with water, further boiled with 1.25% dilute NaOH and the remaining residue after digestion was taken as crude fibrate residue was taken in a furnace and digest at 600 0 C. Crude fiber was estimated following formula.
Crude fiber (%) = [(Loss in weight on ignition ÷ Weight of the sample) × 100]
2.2.6 Carbohydrate estimation Carbohydrate content was estimated by calculation using the difference method. The constituents of food i.e. protein, fat, moisture and ash were determined individually and summed, then the sum was subtracted from the total proximate percentage of food. This is referred to as total carbohydrate by difference.
Total Carbohydrate (%) = [100 − %(Protein + Fat + Moisture + Ash + Fiber)]
2.2.7 Energy value calculation The energy value of the samples was determined by multiplying the protein content by 4, carbohydrate content by 4 and fat content by 9.
Food energy (Kcal/100g) = [(%Crude protein × 4) + (%Fat content × 9) + (%Carbohydrate × 4)]
2.2.8 Estimation of minerals content Mineral contents of dehydrated ginger powder were estimated following Flame photometric method and Atomic absorption spectrophotometric method. About 2.0 g dry sample was taken in muffle furnace and burnt to ash at 600°C. Ash sample was taken in into a volumetric flask. It was digested with 7 ml Nitric acid and 2 ml H2O2 two times for 15 minutes at 180°C in 1200-Watt radiation. Sonication was done by the ultra sound system for mixing and to remove bubbles from the digested sample and then it was filtered with filter paper. The solution was made up-to a certain volume. The sample was then placed into the flame mode of Atomic absorption spectrophotometer at about 2300°C to 2600°C temperature. The flame mode includes dissolving, vaporization, Atomization and ionization. This method typically used for determinations of minerals in mg/100g. The concentrations of minerals were determined by their calibration curves.
Amount per 100 g = [(Concertation × Dilutions × 100) / weight of sample]
2.3 Sensory Quality The sensory quality of the produced dehydrated ginger powder in respect of color, flavor, appearance and texture was judged by panelists using 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.
2.4 Statistical Analysis All the statistical analyses for this study were done by SPSS 22.0 version. Data values were expressed as a percentage and mean± SD. Oneway ANOVA with suitable Post hoc analysis was done to figure out the significant/non-significant difference of the mean value. The findings were considered as statistically significant, if p < 0.05.