2. Preliminary Research & Experimentation
2.4 Preliminary Experimental Work
2.4.4 Machine Modification and Results
The determination of the moisture content was carried out by the oven method in accordance with AOAC (2000) at a temperature of 103oC for 10 hours at the Department of Chemical
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Engineering laboratory, Nnamdi Azikiwe University Awka. Equation 3.1 was employed for moisture content determination of both water yam and aerial yam.
χ
= 𝑀1− 𝑀2𝑀1 𝑥 100=𝑀𝑑𝑏 (3.1)
Where;
χ
is the moisture content of the sample after drying.M1 is the initial mass before drying and M2 is the mass after oven drying.For any weight of the sample at any time, the moisture content at that weight was determined from eqn. (3.2), (Onu, et al., 2017).
𝑀𝑡 𝑑𝑏 = 𝑀𝑜(𝑑𝑏) − 100 𝑊𝑜−𝑊𝑡
1−𝑀𝑜 𝑤𝑏 𝑊𝑜 (3.2)
Where; Mt(db) = Moisture content at any time %(db), Mo (db) = initial moisture content % (db), Mo(wb) = initial moisture content % (wb), Wt = weight of sample at any time, g and Wo
= initial weight of sample, g 3.3.1Convective hot-air drying
The convective hot air dryer (Fig 3.2) is made up of an oven-like body consisting of blower (for air circulation), heating element (for heat supply), airspeed regulator, thermocouple, temperature control knob and trays. Hot air is forced through the material with the help of fan or blower and which aid the moisture diffusion process that results in the drying. This experiment was carried out at the Chemical Engineering laboratory, Nnamdi Azikiwe University Awka. The method employed in convective hot air drying was according to Daniel et al., (2017). The two samples (Water yam and Aerial yam) were dried with convective hot-air dryer (Fig. 3.2) at the following conditions: temperature (40, 50, 60 and 70oC), air speed (2.0, 2.5, 3.0, 3.5 and 4.0 m/s ) and
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sample thickness (2.0, 4.0 and 6.0mm). 2.0 mm of the samples was cut and 100g each of the samples weighed with an electronic weighing scale (Model TDUB-63V09, from Netzgerat) into the dryer tray. The temperature and air speed of the dryer was set at 40oC and 2.0 m/s, respectively. The losses in weight of the samples were taken at an interval of 5, 10, 20, 30, 60, 90 mins. and so on, until there was no significant change in the weight of the sample. The experiments were repeated for various temperatures while keeping air speed and thickness constant and thereafter repeated for various air speeds with temperature and slice thickness kept constant. Also, the thicknesses of the samples were varied with temperature and air speed kept constant. The moisture contents of the sample at time t, was calculated using equation (3.1).
Fig 3.2: A Schematic diagram of convective hot air dryer used
Chamber
Sample tray
Chamber Door
Blower switch Temperature knob
Hinges Hinges
vent
90 3.3.2 Solar Drying
The solar dryer (Fig 3.3) is made up of drying chamber, trays, concentrator, fan or blower, vents, and metal supports. The airflow into the dryer can be generated by forcing preheated air into the drying chamber with the help of the attached fan or blower. This experiment was carried out at the Chemical Engineering laboratory, Nnamdi Azikiwe University Awka. Following Fauziah et al., (2013) methods, the experiments were conducted at five different airspeed (0.5, 1.0, 1.5, 2.0 and 2.5m/s), and three different sample thickness (2, 4 and 6mm). The samples (water yam and Aerial yam) were cut to different sizes (2, 4 and 6mm), and 100g each of the samples weighed with electronic weighing scale (Model TDUB-63V09, from Netzgerat) and placed into the drying tray. The airspeed was set at 0.5m/s using anemometer. The loss in weight was recorded at an interval of 5, 10, 20, 30, 60, and 90 mins. until there was no significant change in weight of the samples. Hygro-thermometer (Model TH029) was used to measure the wet and dry bulb temperatures of the surrounding as well as the relative humidity of the surrounding. The experiments were repeated for different speed of fan and sizes of samples. The solar radiation of the surroundings at the department of Chemical Engineering laboeratory, Nnamdi Azikiwe University, Awka, was taken using a radiometer (Model QED-100 )between the hours of 8AM-4PM on 1st, 10th, 15th, 20th and 28th of the months examined.The moisture contents of the sample at time, t was calculated usingequation(3. 2).
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Fig 3.3: A Schematic diagram of solar dryer used 3.3.3 Blanching of the Samples
This experiment was carried out at the Chemical Engineering laboratory, Nnamdi Azikiwe University Awka. In blanching for both convective hot air dryer and solar dryer, 2.0 mm of the sample was cut and 100g of the sample weighed into a bowel containing boiled water at 80oC.
The sample was left in the hot water for 10 minutes. The water was removed and the new weight of the sample taken. The samplewas put in the dryer (convective and solar) and allowed to dry to constant weight with the weight taken at interval as done with unblanched samples.
3.3.4 Determination of drying rate (Dr)
The drying rate of the yam species was determined using equation (3.3) (Akpinar et al., 2003);
Dr=Mt+dt − Mt
dt (3.3)
Where;Dr is the drying rate (qwater/qdry matter ), Mt and Mt+dt are the moisture contentsat t and t+dt, respectively, and t is the drying time.
92 3.4 Phytochemical analysis
3.4.1 Preparation of sample of water yam and aerial yam extract
All the phytochemical analyses were carried out at the Material, Energy and Techonology Laboratory, Project Development Institute, Enugu state. The two different species of yam samples were prepared for qualitative phytochemical analysis as described by Harbone, (1998).
The crude extracts of the samples were prepared using standard procedure (Falope etal.. 1999).
The fresh yam samples were peeled with a sharp stainless knife. The yams were cut into 5mm diameter and pounded with a ceramic mortar and pestle. This was done to increase the surface area and reduce the size. About 5 g of each sample was weighed into four different 250ml conical flasks. 100ml of four different solvents was added to the samples (ethanol, water, butanol and hexane). The mixture was agitated at room temperature with a vibrator shaker at 500rpm.
Each of the mixtures was filtered with a Whatman filter paper I at room temperature. Then, the extract was collected into sample bottles and kept in the refrigerator for further analysis.
(i) Test for alkaloids:
1mL of 1% HCl(V/V) was pipetted into a test tube containing 3mL of the extract. The mixture was heated gently for 10 minutes in a water bath at 600C. Itwas then cooled and filtered. 1mL of the filtrate was pipetted into a test tube, 0.5mL of Wagner's reagent was added immediately.
Reddish brown colouration confirmed the presence of alkaloid.
(ii) Test for flavonoids:
3mL of the extract was pipetted into a test tube, then 10mL of distilled water was added. The solution was shaken and 1mL of 10% Na0H solution was added. A yellow (pale yellow) coloration confirmed the presence of flavonoids.
93 (iii) Test for tannin:
2mL of extract was pipette into a test tube and boiled gently. 2mL of 10% ferric chloride was added. The presence of tannin was confirmed by green colour, green precipitation or bluish green colouration.
(iv) Test for glycosides:
1mL of extract was pipetted into a test tube, 1mL of 2% 3,5-dinitrosalicyclic acid (DNS) in methanol was added. This was followed by 5% aqueous sodium hydroxide.Bright orange coloration indicated the presence of cyanogenic glycoside. The mixture was heated in boiling water to obtain a brick red coloration. This indicates cardiac glycoside.
(v) Test for Saponin:
(a) Frothing Test: 2mL of extract was pipetted into a test tube, 2mL of distilled water was introduced. The solution was shaken vigorously. A persistent mass of bubbles movement indicated the presence of saponin.
(b) Emulsion Test: 2mL of extract was pipetted into a test tube and 5 drops of olive oil were added. Emulsification was observed. These are thick liquid drops which are very distributed.
(vi) Test for steroid:
In a test tube, 2mL of extract was treated with 0.5mL of acetic acid, 0.5mL of chloroform and 1mL of concentrated sulphuric acid were added. A reddish-brown ring indicated the presence of steroid.
(vii) Test for Phenol/Polyphenol:
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In a test tube containing 2mL of extract, 5mL of distilled water was added and heated gently in a water bath at 600C for 10 minutes. Then, 1mL of 10% potassium ferricyanide was added tothe mixture. The formationof a green-blue coloration indicated the presence of polyphenol.
3.4.2 Proximate analysis