Effects of drying process parameters on the quality attributes of hot air dried okra and its statistical optimization

Figures & data

Figure 1. A cabinet-tray dryer for the drying of okra slices.

Table 1. Experimental range and levels of the variables using RCCD for okra drying

Dependable Variable	−2	−1	0	+1	+2
Air Velocity (AV), (m/s)	0.0	0.5	1.0	1.5	2.0
Relative Humidity (RH),(%)	60	65	70	75	80
Drying Temperature (DT), x(^oC)	40	50	60	70	80
Drying Time (DRT), x(min)	90	180	270	360	450
Run	AV (m/s) x	RH (%) x	DT (^o C) x	DRT (min) x
1	0.5	65	50	180
2	1.5	65	50	180
3	0.5	75	50	180
4	1.5	75	50	180
5	0.5	65	70	180
6	1.5	65	70	180
7	0.5	75	70	180
8	1.5	75	70	180
9	0.5	65	50	360
10	1.5	65	50	360
11	0.5	75	50	360
12	1.5	75	50	360
13	0.5	65	70	360
14	1.5	65	70	360
15	0.5	75	70	360
16	1.5	75	70	360
17	0.0	70	60	270
18	2.0	70	60	270
19	1.0	60	60	270
20	1.0	80	60	270
21	1.0	70	40	270
22	1.0	70	80	270
23	1.0	70	60	90
24	1.0	70	60	450
25	1.0	70	60	270
26	1.0	70	60	270
27	1.0	70	60	270
28	1.0	70	60	270
29	1.0	70	60	270
30	1.0	70	60	270

Each of the experimental run was done in triplicate (n = 3) of which the mean value of the response variable was utilized.

Figure 2. Plots for (a) PMC (b) TPC (c) PTC (d) CHC results obtained from different experimental runs carried out at different drying process parameters (AV, DT, RH and DRT).

Table 2. Model coefficient estimate and ANOVA for the dried okra’s PMC, PTC, CHC and TPC

Source	Product Moisture Content (PMC)				Protein Content (PTC)
	C. Estimate	MS	F-value	P-value	C. Estimate	MS	F-value	P-value
Model (β0)	28.2	180.6	82.2	<0.0001*	6.61	1.65	134.5	<0.0001*
Χ1(β1)	-2.41	139.5	63.52	<0.0001*	0.24	1.44	117.2	<0.0001*
Χ2((β2)	1.85	82.03	37.34	<0.0001*	-0.14	0.49	40.1	0.0448*
Χ3(β3)	-4.69	527.1	240	<0.0001*	0.46	5.10	414.4	<0.0001*
Χ4(β4)	-7.79	1455	662.3	<0.0001*	0.77	14.3	1164	<0.0001*
Χ1^2(β11)	1.12	34.54	15.72	0.0012*	-0.14	0.56	45.6	<0.0001*
Χ2^2(β22)	-1.60	70.46	32.07	<0.0001*	0.076	0.16	12.8	0.0027*
Χ3^2(β33)	-0.63	10.81	4.92	0.0424*	0.052	0.074	6.05	0.0265*
Χ4^2(β44)	0.76	15.83	7.21	0.0170*	-0.054	0.080	6.54	0.0219*
Χ1Χ2(β12)	-0.81	10.61	4.83	0.0441*	0.064	0.065	5.29	0.0363*
Χ1Χ3(β13)	-0.99	15.74	7.17	0.0172*	0.11	0.21	16.8	0.0009 *
Χ1Χ4(β14)	-1.23	24.18	11.01	0.0047*	0.085	0.12	9.40	0.0078*
Χ2Χ3(β23)	-0.40	2.58	1.18	0.2953	0.043	0.029	2.35	0.1461
Χ2Χ4(β24)	0.96	14.76	6.72	0.0204*	-0.076	0.093	7.56	0.0149*
Χ3Χ4(β34)	-2.54	103.4	47.06	<0.0001*	0.14	0.30	24.2	0.0002*
R^2= 0.9871; Adj. R^2= 0.9751; Pred. R^2= 0.9259; Adeq. Pre = 38.356					R^2= 0.9921; Adj. R^2= 0.9847; Pred. R^2= 0.9545; Adeq. Pre = 46.150
Source	Carbohydrate Content (CHC)				Total Plate Count (TPC)
	C. Estimate	MS	F-value	P-value	C. Estimate	MS	F-value	P-value
Model (β0)	30.20	1.75	91.8	<0.0001*	39.70	142.3	52.2	<0.0001*
Χ1(β1)	0.25	1.50	78.4	<0.0001*	- 1.74	72.9	26.7	0.0001*
Χ2((β2)	-0.19	0.86	44.8	<0.0001*	2.16	111.5	40.9	<0.0001*
Χ3(β3)	0.46	5.01	262.8	<0.0001*	-4.00	384.6	141.0	<0.0001*
Χ4(β4)	0.79	15.0	784.3	<0.0001*	-6.85	1125	412.4	0.0204*
Χ1^2(β11)	-0.11	0.36	18.7	0.0006*	0.82	18.3	6.72	<0.0001*
Χ2^2(β22)	0.12	0.38	20.2	0.0004*	-1.40	53.4	19.6	0.0005*
Χ3^2(β33)	0.091	0.23	11.9	0.0036*	-1.52	63.4	23.2	0.0002*
Χ4^2(β44)	-0.058	0.092	4.81	0.0446*	-0.96	25.2	9.22	0.0083*
Χ1Χ2(β12)	0.079	0.10	5.28	0.0363*	-0.89	12.5	4.59	0.0489*
Χ1Χ3(β13)	0.11	0.18	9.36	0.0080*	-0.97	15.1	5.55	0.0325*
Χ1Χ4(β14)	0.078	0.098	5.12	0.0389*	-0.97	14.9	5.46	0.0337*
Χ2Χ3(β23)	0.008	0.001	0.055	0.8172	-0.58	5.43	1.99	0.1787
Χ2Χ4(β24)	-0.092	0.14	7.08	0.0178*	1.32	27.9	10.2	0.0060*
Χ3Χ4(β34)	0.17	0.46	24.1	0.0002*	-2.02	65.1	23.9	0.0002*
R^2= 0.9885; Adj. R^2= 0.9777; Pred. R^2= 0.9336; Adeq. Pre = 39.833					R^2= 0.9799; Adj. R^2= 0.8841; Pred. R^2= 0.9037; Adeq. Pre = 26.950

Note: C. Estimate = Coefficient Estimate; MS = Mean Square; Adj. = Adjusted; Pred. = Predicted; Adeq. Pre. = Adequate Precision; * Significant at p < 0.05.

Figure 3. Three dimensional (3D) response surface plot indicating the interaction effect of RH and AV on (a) PMC (b) TPC (c) PTC (d) CHC during the okra drying process.

Figure 4. Three dimensional (3D) response surface plot indicating the interaction effect of DT and AV on: (a) PMC (b) TPC (c) PTC (d) CHC during okra drying process.

Figure 5. Three dimensional (3D) response surface plot indicating the interaction effect of DRT and AV on: (a) PMC (b) TPC (c) PTC (d) CHC during okra drying process.

Figure 6. Three dimensional (3D) response surface plot indicating the interaction effect of DRT and RH on: (a) PMC (b) TPC (c) PTC (d) CHC during the okra drying process.

Figure 7. Three dimensional (3D) response surface plot indicating the interaction effect of DRT and DT on: (a) PMC, (b) TPC, (c) PTC and (d) CHC during okra drying process.

Table 3. Optimization and verification of PMC, TPC, PTC and CHC

	Drying Process Conditions				Response
	AV (m/s)	RH (%)	DT (°C)	DRT (min)	PMC (%)	TPC (CFU/g)	PTC (%)	CHC (%)
Predicted Value	1.64	60	55	450	5	10.30	8.54	32.41
Experimental Value	1.64	60	55	450	5.2	11.00	8.64	32.52
Percent Error (%E)	-	-	-	-	−4.00	−6.80	−1.17	−0.34