Effect of High Pressure Processing on Rheological Properties, Pectinmethylesterase Activity and Microbiological Characteristics of Aloe Vera (Aloe barbadensis Miller) Juice

Figures & data

TABLE 1 Independent variables and levels of a rotatable central composite design (RCCD) used in the present study for aloe vera juice

		Coded-variable levels
Independent variables	Symbol	−1.682	−1	0	+1	+1.682
Pressure (MPa)	X1	63.64	200	400	600	736.36
Dwell time (min)	X2	3.16	10	20	30	36.82
pH	X3	2.32	3	4	5	5.68

TABLE 2 The matrix of RCCD followed in this study and experimental data obtained of rheological properties and PME activity of aloe vera juice

Independent variables			Rheological model parameters*
Pressure (MPa)	Dwell time (min)	pH	K, Pa.s^n	n	σo, Pa	PME Enzyme activity (PE units/ml)
200	10	3	0.0701 ± 0.0002	0.672 ± 0.001	0.160 ± 0.002	0.056 ± 0.002
600	10	3	0.0734 ± 0.0003	0.664 ± 0.002	0.160 ± 0.010	0.040 ± 0.003
200	30	3	0.0699 ± 0.0002	0.675 ± 0.001	0.150 ± 0.003	0.058 ± 0.002
600	30	3	0.0789 ± 0.0001	0.673 ± 0.005	0.180 ± 0.008	0.036 ± 0.001
200	10	5	0.0661 ± 0.0004	0.685 ± 0.003	0.142 ± 0.005	0.060 ± 0.003
600	10	5	0.0763 ± 0.0006	0.652 ± 0.002	0.182 ± 0.010	0.044 ± 0.001
200	30	5	0.0653 ± 0.0011	0.662 ± 0.004	0.121 ± 0.005	0.058 ± 0.002
600	30	5	0.0751 ± 0.0002	0.660 ± 0.005	0.172 ± 0.010	0.047 ± 0.001
63.64	20	4	0.0590 ± 0.0006	0.659 ± 0.006	0.135 ± 0.002	0.058 ± 0.002
736.36	20	4	0.0784 ± 0.0007	0.644 ± 0.010	0.192 ± 0.006	0.037 ± 0.001
400	3.18	4	0.0696 ± 0.0002	0.673 ± 0.001	0.162 ± 0.007	0.050 ± 0.002
400	36.82	4	0.0688 ± 0.0010	0.684 ± 0.002	0.130 ± 0.006	0.039 ± 0.001
400	20	2.32	0.0600 ± 0.0010	0.705 ± 0.002	0.131 ± 0.001	0.038 ± 0.003
400	20	5.68	0.0628 ± 0.0003	0.697 ± 0.003	0.134 ± 0.002	0.048 ± 0.003
400	20	4	0.0642 ± 0.0004	0.686 ± 0.004	0.144 ± 0.007	0.047 ± 0.002
400	20	4	0.0638 ± 0.0003	0.691 ± 0.003	0.145 ± 0.005	0.040 ± 0.003
400	20	4	0.0632 ± 0.0004	0.693 ± 0.005	0.131 ± 0.006	0.046 ± 0.002
400	20	4	0.0645 ± 0.0005	0.682 ± 0.004	0.142 ± 0.006	0.042 ± 0.003
400	20	4	0.0648 ± 0.0002	0.685 ± 0.007	0.153 ± 0.006	0.040 ± 0.002
400	20	4	0.0655 ± 0.0001	0.684 ± 0.002	0.144 ± 0.006	0.043 ± 0.003
LSD value^c			0.00647	0.0121	0.0179	0.0080

*Rheological properties’ values given as mean ± standard deviation (N = 4);

K: consistency index (Power law); n: flow behavior index (Power law); σ_o: yield stress (Casson);

^cDepicts the least significant difference (LSD) values obtained from Fisher’s LSD test, estimated at 95% confidence interval.

FIGURE 1 Experimental flow curves for aloe vera juice at 25°C processed under different conditions of pressure, dwell time, and pH. (Mean values plotted, N = 4, SD < ±10% for shear stress; SD < ±5 for apparent viscosity, SS = shear stress, and AV = Apparent viscosity.)

FIGURE 2 Response surface plots showing the effect of pressure level, dwell time, and pH on consistency index (a and b), flow behavior index (c and d), and yield stress (e and f) of aloe vera juice.

FIGURE 3 Cloud loss and settling in aloe vera juice.

FIGURE 4 Effect of pressure level, dwell time, and pH on % residual activity of in situ PME enzyme in aloe vera juice.

FIGURE 5 Contour plots of pressure-pH (a) and pressure-dwell time (b) showing iso --- (%) inactivation lines for in situ PME enzyme of aloe vera juice within the studied domain of pressure, dwell time, and pH.

TABLE 3 Experimental data for microbiological characteristics of aloe vera juice

Independent variables			Microbiological counts (Log cfu ml^−1)^a
Pressure (MPa)	Dwell time (min)	pH	AMC	Y&M	LAB	TC
200	10	3	2.30 ± 0.05	2.78 ± 0.05	ND	ND
600	10	3	0.60 ± 0.01	ND^b	ND	ND
200	30	3	3.03 ± 0.08	3.84 ± 0.04	1.3 ± 0.02	ND
600	30	3	ND	ND	ND	ND
200	10	5	3.42 ± 0.06	3.91 ± 0.10	3.31 ± 0.06	3.48 ± 0.12
600	10	5	0.78 ± 0.01	0.6 ± 0.01	ND	ND
200	30	5	3.59 ± 0.12	3.51 ± 0.04	ND	3.65 ± 0.06
600	30	5	0.78 ± 0.02	0.48 ± 0.03	ND	ND
63.64	20	4	5.77 ± 0.16	5.71 ± 0.06	5.69 ± 0.04	5.73 ± 0.10
736.36	20	4	ND	ND	ND	ND
400	3.18	4	1.32 ± 0.06	0.60 ± 0.01	ND	ND
400	36.82	4	0.60 ± 0.02	ND	ND	ND
400	20	2.32	0.70 ± 0.00	ND	ND	ND
400	20	5.68	0.95 ± 0.01	0.48 ± 0.01	ND	ND
400	20	4	0.90 ± 0.01	ND	ND	ND
400	20	4	0.90 ± 0.02	0.3 ± 0.02	ND	ND
400	20	4	0.85 ± 0.01	0.48 ± 0.02	ND	ND
400	20	4	1.00 ± 0.01	ND	ND	ND
400	20	4	0.95 ± 0.01	ND	ND	ND
400	20	4	1.04 ± 0.02	ND	ND	ND
LSD value^c			0.72	0.90	1.68	1.33

^aMicrobiological counts’ values given as mean±standard deviation (N = 4);

^bND denotes count not detected as count was below detection limit of the present study (<1 cfu ml⁻¹);

^cDepicts the least significant difference (LSD) values obtained from Fisher’s LSD test, estimated at 95% confidence interval.

FIGURE 6 P-t and P-pH contour plots showing iso --- (%) reduction lines for AMC (a and b), Y&M (c and d), LAB (e and f) and TC (g and h) counts in aloe vera juice within the studied domain of pressure, dwell time, and pH.