Optimization of extraction conditions for functional compounds from thinned unripe apple using β-cyclodextrin-based ultrasound-assisted extraction

Figures & data

Figure 1. Sample image of unripe apple.

Table 1. Box–Behnken experimental values for the TPC, CAC, and DPPH RSA of unripe apples under different extraction conditions.

Run	Independent variables			Dependent variables
	β-CD concentration (mg/mL)	Extraction time (min)	Extraction temperature (°C)	TPC (mg GAE/g DW),	CAC (mg/100 g DW)	DPPH RSA (%)
1	30	45	50	3.76 ± 0.08	215.18 ± 2.17	84.72 ± 3.77
2	40	30	50	3.65 ± 0.05	207.15 ± 1.48	82.44 ± 4.67
3	20	30	50	3.30 ± 0.05	182.29 ± 3.49	85.66 ± 1.15
4	30	45	50	3.78 ± 0.06	197.86 ± 1.93	82.33 ± 1.94
5	30	30	40	3.40 ± 0.03	182.66 ± 0.18	86.93 ± 1.51
6	40	45	40	3.55 ± 0.05	202.63 ± 0.41	85.20 ± 1.06
7	30	60	60	3.74 ± 0.05	202.09 ± 0.84	82.19 ± 1.27
8	30	60	40	3.51 ± 0.01	204.18 ± 0.97	83.99 ± 2.81
9	20	60	50	3.30 ± 0.03	190.67 ± 0.16	82.19 ± 1.15
10	30	45	50	3.63 ± 0.04	208.88 ± 0.38	84.19 ± 2.13
11	20	45	40	3.75 ± 0.04	194.17 ± 0.64	82.29 ± 2.48
12	40	60	50	4.22 ± 0.05	223.23 ± 0.91	87.28 ± 2.07
13	20	45	60	3.47 ± 0.06	180.83 ± 2.26	75.00 ± 2.00
14	30	30	60	3.76 ± 0.02	206.10 ± 0.19	77.93 ± 3.10
15	40	45	60	4.66 ± 0.02	222.34 ± 0.18	81.65 ± 1.90

β-CD, β-cyclodextrin; CAC, chlorogenic acid content; DPPH, 1,1-diphenyl-2-picrylhydrazyl; DW, dry weight; GAE, gallic acid equivalent; RSA, radical scavenging activity; TPC, total polyphenol content.

Values are mean ± standard deviation (n = 3).

Table 2. Regression coefficient, R², and F-test values of the predicted second-order polynomial models for the TPC, CAC, and DPPH RSA of unripe apples.

	TPC		CAC		DPPH RSA
Term	Coefficient	P-value	Coefficient	P-value	Coefficient	P-value
Intercept	3.7233	.000	207.31	.000	83.747	.000
Linear
X1	0.2825	.001	13.42	.002	1.429	.039
X2	0.0825	.085	5.25	.063	0.336	.541
X3	0.1775	.006	3.46	.177	−2.705	.003
Quadratic
X1*X1	0.0746	.244	−2.62	.457	−0.540	.507
X2*X2	−0.1804	.024	−3.85	.289	1.185	.178
X3*X3	0.0596	.340	−4.70	.208	−2.172	.035
Interaction
X1*X2	0.1425	.047	1.93	.564	2.078	.035
X1*X3	0.3475	.001	8.26	.046	0.935	.254
X2*X3	−0.0325	.576	−6.38	.096	1.800	.056
R^2	0.9660		0.9235		0.9273
Model		.004		.025		.022
Lack of fit		.317		.903		.413

R², coefficient of determination; TPC, total polyphenol content; CAC, chlorogenic acid content; DPPH, 1,1-diphenyl-2-picrylhydrazyl; RSA, radical scavenging activity; X₁, β-cyclodextrin concentration (mg/mL); X₂, extraction time (min); X₃, extraction temperature (°C).

Figure 2. Response surface plots depicting the effects of the β-cyclodextrin (CD) concentration, extraction time, and extraction temperature on the total polyphenol content (TPC). GAE, gallic acid equivalent; DW, dry weight.

Figure 3. Response surface plots depicting the effects of the β-cyclodextrin (CD) concentration, extraction time, and extraction temperature on the chlorogenic acid content (CAC). DW, dry weight.

Figure 4. Response surface plots depicting the effects of β-cyclodextrin (CD) concentration, extraction time, and extraction temperature on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (RSA).

Table 3. Validation of predicted and experimental values determined at optimal extraction conditions.

Response	Optimum conditions			Maximum values		%RSD
	β-CD concentration (mg/mL)	Extraction time (min)	Extraction temperature (°C)	Predicted	Experimental
TPC (mg GAE/g DW)	40.00	53.03	60.00	4.72	4.70 ± 0.09	0.65
CAC (mg/100 g DW)	40.00	46.67	60.00	225.18	224.74 ± 0.43	1.38
DPPH RSA (%)	20.00	30.00	40.00	87.97	86.49 ± 2.81	2.18

β-CD, β-cyclodextrin; RSD, relative standard deviation; TPC, total polyphenol content; CAC, chlorogenic acid content, DPPH, 1,1-diphenyl-2-picrylhydrazyl; RSA, radical scavenging activity; GAE, gallic acid equivalent; DW, dry weight.

Values are mean ± standard deviation (n = 3).

Table 4. Total polyphenol content, chlorogenic acid content, and DPPH radical scavenging activity of polyphenol-rich extract obtained by β-cyclodextrin-based ultrasound-assisted extraction and hot water extraction.

	β-CD-based UAE	HWE
Total phenol content (mg GAE/g extract)	17.68 ± 1.20*	14.19 ± 0.34
Chlorogenic acid content (mg/g extract)	5.99 ± 0.04*	3.39 ± 0.05
IC50 value for DPPH RSA (μg/mL)	198.07 ± 1.21*	566.26 ± 0.67

Values are mean ± standard deviation (n = 3).

GAE, gallic acid equivalent; CD, β-cyclodextrin; UAE, ultrasound-assisted extraction; HWE, hot water extraction.

*Significant differences between CD-based UAE and HWE extracts according to t-test (p < .05).