Soluble and insoluble-bound phenolics and antioxidant activity of various industrial plant wastes

Figures & data

Figure 1. Total phenolic (a) and total flavonoid (b) contents of soluble free (black) and insoluble-bound (gray) extracts of plant wastes. Means of soluble and insoluble-bound phenolics for each waste marked with different lowercase letters are significantly different (p < .05). Means of soluble or insoluble-bound phenolics of wastes marked with different uppercase letters are significantly different (p < .05)

Figure 2. Antioxidant activity of soluble free (black) and insoluble-bound (gray) extracts of plant wastes by DPPH (a) and CUPRAC (b) assays. Means of soluble and insoluble-bound phenolics for each waste marked with different lowercase letters are significantly different (p < .05). Means of soluble or insoluble-bound phenolics of wastes marked with different uppercase letters are significantly different (p < .05)

Table 1. Concentration of soluble free and insoluble-bound phenolic compounds in wastes

	Concentration (mg/100 g dm)^†‡
	Apple peel		Apple pomace		Pomegranate peel		Pomegranate seed		Chestnut shell		Black carrot pomace
Compound	Free	Bound	Free	Bound	Free	Bound	Free	Bound	Free	Bound	Free	Bound
Hydroxybenzoic acids
Gallic acid	0.09 ± 0.02		0.50 ± 0.02		19.0 ± 3.9	7.71 ± 1.25	2.81 ± 0.22	0.44 ± 0.12	7.82 ± 0.38	18.96 ± 0.27
4-hydroxybenzoic acid	0.39 ± 0.01										0.21 ± 0.03	0.62 ± 0.14
Protocatechuic acid		0.56 ± 0.05		0.28 ± 0.02						3.98 ± 0.02		0.62 ± 0.13
Ellagic acid					3697 ± 99	199 ± 7	1426 ± 118	14.62 ± 0.14	52.1 ± 1.0	52.1 ± 1.9
Hydroxycinnamic acids
Chlorogenic acid			17.69 ± 0.02								79.1 ± 3.6	2.01 ± 0.12
p-coumaric acid		0.22 ± 0.01	1.38 ± 0.03	0.51 ± 0.01								0.76 ± 0.06
Ferulic acid												4.55 ± 0.42
Sinapic acid												2.12 ± 0.21
Anthocyanins
Cyanidin-3,5-O-diglucoside					4.68 ± 0.31
Cyanidin-3-O-galactoside											18.0 ± 1.6
Cyanidin-3-O-glucoside					4.51 ± 0.26		14.73 ± 0.45				70 ± 6
Peonidin-3-O-glucoside							0.44 ± 0.03
Malvidin-3-O-glucoside											35.1 ± 2.7
Isoflavonoids
Daidzein	3.17 ± 0.38
Flavanols
Catechin		2.05 ± 0.18	6.67 ± 0.01						17.1 ± 1.7
(-)-Epicatechin			7.05 ± 0.01
Flavanones
Naringenin			9.62 ± 0.21
Flavonols
Quercetin-3-O-galactoside	10.48 ± 0.11
Quercetin-3-O-glucoside	3.96 ± 0.04
Quercetin-3-O-glucuronide	5.57 ± 0.05
Quercitrin	7.73 ± 0.01
Chalcones
Phlorizin	2.91 ± 0.10		2.81 ± 0.07
Hydrolyzable tannins
Punicalagin derivative 1					1076 ± 92		194 ± 13
Punicalagin derivative 2					698 ± 83		136 ± 28

^†Means ± standard deviation (n = 3).

^‡Blank: Not detected.