Major Polyphenolics in Pineapple Peels and their Antioxidant Interactions

Figures & data

Table 1  Identification of polyphenolic compounds in pineapple peels by HPLC–ESIMS

Rt/min	Molecular weight	[M-H]^−(m/z)	Other fragment ions (m/z)	Tentative identification	Molecular structure	Content^a
2.602	170	169.0	125	Gallic acid		31.76 ± 2.28^a
16.118	290	289.1	245, 205	Catechin		58.51 ± 3.59^b
24.447	290	289.1	245, 205	Epicatechin		50.00 ± 4.39^c
24.504	194	192.9	133.8	Ferulic acid		19.50 ± 1.93^d

All values are expressed as means ± standard deviation.

^aResults expressed: as mg/100 g dry peel. different letters in this column mean significant differences (p < 0.05).

Figure 1  HPLC chromatograph of pineapple peel extracts detected at (A) 280 nm and (B) 320 nm. Peak numbers refer to Table 1.

Table 2  Antioxidant capacity of PPE and the major polyphenolic compounds

Sample	PPE	Catechin	Epicatechin	Gallic acid	Ferulic acid
IC50^a	1.13 ± 0.03	107.39 ± 8.52^a	103.24 ± 9.37^a	87.07 ± 4.23^b	139.70 ± 10.57^c
TAC^b	0.037 ± 0.003	1.754 ± 0.105^a	1.930 ± 0.037^b	0.692 ± 0.014^c	0.622 ± 0.053^c

All values are expressed as means ± standard deviation.

^aResults expressed: as mg/ml for PPE; as μM for catechin, epicatechin, gallic acid, and ferulic acid measured by DPPH• scavenging assay;

^bTAC; Results expressed: as g ascorbic acid equivalents/g for PPE; as mol ascorbic acid equivalents/mol for catechin, epicatechin, gallic acid, and ferulic acid measured by phosphomolybdenum method.

^abDifferent letters in each row (except for PPE) mean significant differences (p < 0.05).

Table 3  Antioxidant activity of polyphenolics combinations measured by DPPH• scavenging assay

Combinations (1:1)	CAT + ECAT	CAT + GA	CAT + FA	EPCAT + GA	EPCAT + FA	GA + FA
IC50 (μM)	128.65 ± 3.75	121.19 ± 2.88	141.55 ± 5.72	113.08 ± 5.15	135.13 ± 6.49	127.79 ± 4.62
Difference in DPPH•Scavenging capacity (%)	−22.16 ± 5.35^a	−24.64 ± 8.72^a	−14.57 ± 8.05^a	−18.83 ± 4.58^a	−11.28 ± 5.52	−12.70 ± 6.39

Catechin (CAT), epicatechin (ECAT), gallic acid (GA), and ferulic acid (FA).

All values are expressed as means ± standard deviation.

^aWithin rows indicates significant difference was found between theoretical and real values at P < 0.05.

Table 4  Theoretical and real values of total antioxidant capacity of polyphenolics combinations measured by phosphomolybdenum method

Combinations(1:1)	CAT + ECAT	CAT + GA	CAT + FA	EPCAT + GA	EPCAT + FA	GA + FA
Theoretical value^a	1.932	1.201	1.225	1.383	1.396	0.664
Real value^a	1.842 ± 0.14	1.223 ± 0.31	1.188 ± 0.21	1.311 ± 0.35	1.276 ± 0.33	0.657 ± 0.29

Catechin (CAT), epicatechin (ECAT), gallic acid (GA), and ferulic acid (FA).All values are expressed as means ± standard deviation.

^aResults expressed: as mol ascorbic acid equivalents/mol; the statistical analysis in each column indicates there is no significant difference between the theoretical and real values at P < 0.05.

Table 5 Theoretical values (TV) and real values (RV) of total antioxidant activity^a of polyphenolics combinations measured by phosphomolybdenum method

Molar ratio^b	0.5:1.0		0.5:1.5		1.0:0.5		1.5:0.5
Combinations	TV	RV	TV	RV	TV	RV	TV	RV
CAT + ECAT	2.978	2.697 ± 0.022	4.037	4.161 ± 0.038	2.806	2.415 ± 0.177	3.682	3.269 ± 0.122
CAT + GA	2.076	2.028 ± 0.014	2.952	2.740 ± 0.086	1.524	1.585 ± 0.056	1.849	1.939 ± 0.014
CAT + FA	1.562	1.730 ± 0.029	1.849	1.771 ± 0.018	2.095	1.925 ± 0.022	2.971	2.718 ± 0.042
EPCAT + GA	2.432	2.308 ± 0.089	3.486	3.258 ± 0.170	1.702	1.903 ± 0.061	2.027	1.967 ± 0.091
EPCAT + FA	1.740	1.927 ± 0.058	2.083	2.084 ± 0.050	2.450	2.588 ± 0.058	3.504	3.859 ± 0.110
GA + FA	1.010	1.143 ± 0.009	1.352	1.509 ± 0.019	0.991	1.127 ± 0.015	1.316	1.365 ± 0.057

Catechin (CAT), epicatechin (ECAT), gallic acid (GA), and ferulic acid (FA).

^aResults expressed: as mol ascorbic acid equivalents; the statistical analysis indicates there is no significant difference between the theoretical and real values of each combination at P < 0.05.

^bPolyphenolic compounds were mixed at different molar ratios (mol:mol).