Combined treatments of benzoic acid and pasteurization factors for controlling microbiological and physico-chemical quality in asparagus stalk juice using response surface methodology

Figures & data

Table 1. Factors and levels applied in Box-Behnken design to produce pasteurized asparagus stalk juice.

		Experimental levels
Factors	Code	Low (-1)	Intermediate (0)	High (+1)
Temperature (^oC)	X1	65	75	85
Time (min)	X2	15	20	25
Benzoic acid (mg/mL)	X3	0	0.5	1

Where Y is the response, $x_1$, $x_2$ and $x_3$ represent independent variables, ${\beta }_0$ is the constant, ${\beta }_1$, ${\beta }_2$, ${\beta }_3$ are linear coefficients, ${\beta }_{11}$, ${\beta }_{22}$, ${\beta }_{33}$ are quadratic coefficients, and ${\beta }_{12}$, ${\beta }_{13}$, ${\beta }_{23}$ are interaction coefficients.

Figure 1. Response surface plot of total viable count as a function of temperature and time for asparagus stalk juice.

Table 3. F values and their statistical significance for different response variables of asparagus stalk juice.

Source of variable	F values
	Total viable count	L*	a*	b*	pH	Total phenolic content	DPPH scavenging rate
Model	1.87	26.49***	41.79***	82.38***	885.21***	885.21*	3.21**
$x_1$	1.52	71.39***	22.07***	0.22^ns	14.64***	14.64*	0.05^ns
$x_2$	0.01	0.00^ns	1.27^ns	76.22***	0.30^ns	0.30*	1.59^ns
$x_3$	4.08*	8.39**	104.73***	70.32***	6050.31***	–	3.03^ns
$x_1{x}_2$	–	1.04^ns	4.12*	119.70***	2.33^ns	–	0.38^ns
$x_1{x}_3$	–	18.59***	0.88^ns	4.16*	0.94^ns	–	0.54^ns
$x_2{x}_3$	–	5.66*	0.54^ns	7.71**	0.97^ns	–	7.39**
$x_1^2$	–	8.44**	29.65***	13.41***	6.44*	–	2.76^ns
$x_2^2$	–	91.92***	201.73***	333.01***	59.59***	–	9.49**
$x_3^2$	–	22.54***	0.19^ns	84.19***	1798.04***	–	4.09*
Predicted R^2	0.0322	0.7394	0.8368	0.9083	0.9909	0.0972	0.0811
Adjusted R^2	0.0498	0.8211	0.8801	0.9361	0.9983	0.1402	0.2849

*p < 0.05; **p < 0.01; ***p < 0.001; ns: non-significant.

Figure 2. Response surface plot of L* as a function of (A) temperature and time, (B) temperature and benzoic acid, and (C) time and benzoic acid for asparagus stalk juice.

Figure 3. Response surface plot of a* as a function of (A) temperature and time, (B) temperature and benzoic acid, and (C) time and benzoic acid for asparagus stalk juice.

Figure 4. Response surface plot of b* as a function of (A) temperature and time, (B) temperature and benzoic acid, and (C) time and benzoic acid for asparagus stalk juice.

Figure 5. Response surface plot of pH as a function of (A) temperature and time, (B) temperature and benzoic acid, and (C) time and benzoic acid for asparagus stalk juice.

Table 2. Experimental results of quality parameters of asparagus stalk juice.

Experiments	Coded values			Quality parameters
	X1	X2	X3	Total viable count (CFU/ml)	L*	a*	b*	pH	Total phenolic content (mgGAE/ml)	DPPH scavenging rate (%)
1	75	25	1	17	92.51	4.56	4.12	3.83	2.68	7.61
2	75	20	0.5	10	86.17	3.54	8.74	4.07	2.67	5.11
3	75	20	0.5	43	86.22	3.33	8.79	4.05	2.60	2.83
4	75	20	0.5	17	86.11	3.34	8.79	4.07	2.65	3.36
5	85	25	0.5	0	87.89	4.97	8.65	4.18	2.62	5.55
6	65	20	0	37	91.19	3.16	8.11	6.64	2.68	2.74
7	85	20	0	27	82.48	3.17	7.74	6.40	2.54	3.91
8	75	20	0.5	7	86.26	3.32	8.60	4.07	2.59	3.95
9	85	20	1	0	90.28	4.41	6.34	3.65	2.69	3.56
10	85	15	0.5	20	90.07	4.81	2.65	4.12	2.70	5.49
11	65	15	0.5	13	93.12	4.37	5.81	4.30	2.84	6.84
12	75	20	0.5	47	86.22	3.35	8.71	4.07	2.91	3.12
13	75	15	0	13	92.51	4.02	4.87	7.00	2.55	3.34
14	65	20	1	10	92.34	4.17	5.54	3.78	2.89	3.81
15	65	25	0.5	23	92.51	4.03	5.54	4.20	2.70	5.71
16	75	25	0	17	91.99	3.83	6.34	6.92	2.58	2.98
17	75	15	1	7	89.35	4.58	4.24	3.80	2.63	2.74

Figure 6. Response surface plot of total phenolic content as a function of temperature and time for asparagus stalk juice.

Figure 7. Response surface plot of percentage of DPPH scavenging rate as a function of (A) temperature and time, (B) temperature and benzoic acid, and (C) time and benzoic acid for asparagus stalk juice.

Figure 8. Normal % probability and externally studentized residuals of the (A) total viable count, (B) L*, (C) a*, (D) b*, (E) pH, (F) total phenolic content, and (G) % DPPH scavenging rate.

Data availability statement

The data that supports the findings of the study are available within the manuscript.