Effect of Ferulic Acid on the Formation of Pyranoanthocyanins from Purple Corn (Zea mays L.) Cob in a Model System and Their Effects on Color

Figures & data

FIGURE 1 Effect of various concentrations of ferulic acid on the visible light spectral characteristics in the model system. (1): control samples (anthocyanins without ferulic acid; λ_max = 515 nm and A_max = 0.557); (2), (3), and (4): test samples (anthocyanins with ferulic acid) with various concentrations (2, 4, and 6 mg mL^–1, respectively) of ferulic acid.

FIGURE 2 Effect of ferulic acid on the visible light spectral characteristics of the model system initially and after 90 days of storage at 25°C while protected from light. (1): control samples (anthocyanins without ferulic acid); (2): samples enhanced with ferulic acid. The concentration of ferulic acid was 6 mg mL^–1. (A): before storage; (B): after 90 days of storage.

TABLE 1 Effect of ferulic acid on the color changes of anthocyanins from purple corn cob at pH 3.0, initially and after 90 days storage at 25°C protected from light

Sample	Chroma (C*)		Hue angle (h°)
Time (days)	0*	90	0	90
Control	14.75 ± 0.18b	10.88 ± 0.11c	21.93 ± 0.18a	44.85 ± 0.16a
Test	28.66 ± 0.14a	21.11 ± 0.14b	16.67 ± 0.12c	40.95 ± 0.12b

All trials were performed in triplicate (n = 3), and control and test data are reported as means ± SD; Control: anthocyanins enhanced without ferulic acid; Test: anthocyanins enhanced with ferulic acid; For each assay, ferulic acid was added at a concentration of 6 mg/mL; Letters that are the same in the same vertical column indicate no statistically significant difference (p < 0.05).

TABLE 2 Identification of the pigment compounds of test samples by HPLC-MS before and after 90 days storage

Peak	Time (min)	Compound	M^+ (m/z)	Fragment ion (m/z)
1	13.53	Cyanidin-3-glucoside	449	287
2	15.71	Pelargonidin-3-glucoside	433	271
3	16.61	Peonidin-3-glucoside	463	301
4	18.10	Cyanidin-3-(6-malon)-glucoside	535	287
5	20.36	Pelargonidin-3-(6-malon)-glucoside	519	433
6	21.10	Peonidin-3-(6-malon)-glucoside	549	463, 301
7	21.93	Peonidin-3-(6-malon)-glucoside	575	449
8	29.1	Cyanidin-3-glucoside-vinylguaiacol	595	433
9	31.4	Pelargonidin-3-glucoside-vinylguaiacol	579	417
10	32.1	Peonidin-3-glucoside-vinylguaiacol	609	447

HPLC–MS: high-performance liquid chromatography–mass spectrometry.

FIGURE 3 Changes in HPLC profiles of test samples at the beginning and end of storage. (A): before storage; (B): after 90 days of storage. (1): cyanidin-3-glucoside; (2): pelargonidin-3-glucoside; (3): peonidin-3-glucoside; (4): cyanidin-3-(6-malon-glucoside); (5): pelargonidin-3-(6-malon-glucoside); (6) and (7): peonidin-3-(6-malon-glucoside).

FIGURE 4 Positive ion mass spectra and molecular structure of the novel co-pigmentation compounds formed in the test sample and detected after 90 days of storage. Peak 8: cyanidin-3-glucosede-vinyguaiacol; Peak 9: pelargonidin-3-glucosede-vinylguaiacol; Peak 10: peonidin-3-glucosede-vinylguaiacol; Glu: glucoside.

FIGURE 5 The proposed pathway of formation of the new pyranoanthocyanin adduct with anthocyanin-3-glucoside and ferulic acid; Glu: glucoside.

FIGURE 6 Absorption spectrum of (a) cyanidin-3-glucoside-vinylguaiacol; (b) cyanidin-3-glucoside; (c) pelargonidin-3-glucoside-vinylguaiacol; (d) pelargonidin-3-glucoside; (e) peonidin-3-glucoside-vinylguaiacol; and (f) peonidin-3-glucoside.

Francis, F.J. Food Colorants: Anthocyanins. Critical Reviews in Food Science and Nutrition 1989, 28, 273–314.

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