Stability and Antioxidant Activity of Food-Grade Phycocyanin Isolated from Spirulina platensis

Figures & data

FIGURE 1 Effect of pH on the spectra of phycocyanin in phosphate-citrate buffer at A: room temperature and B: the corresponding purity ratios (A₆₂₀/A₂₈₀). C_R values of phycocyanin in phosphate-citrate buffer at C: different pH values after incubation in a water bath at 55ºC and D: 65ºC for different durations in darkness.

TABLE 1 Degradation rate (κ) and half-life (T_1/2) of phycocyanin in phosphate-citrate buffer at pH 5.0, 6.0, and 7.0

	pH 5.0		pH 6.0		pH 7.0
Temperature (°C)	κ (min)	T1/2 (min)	κ (min)	T1/2 (min)	κ (min)	T1/2 (min)
50 ± 1	0.0022 ± 0.0000	321.3 ± 5.5	0.0014 ± 0.0000	495.0 ± 9.9	0.0028 ± 0.0001	243.6 ± 10.6
55 ± 1	0.0036 ± 0.0000	193.0 ± 0.6	0.0027 ± 0.0002	253.9 ± 17.1	0.0058 ± 0.0001	119.1 ± 2.4
60 ± 1	0.0072 ± 0.0001	96.4 ± 1.1	0.0058 ± 0.0006	120.7 ± 12.0	0.0125 ± 0.0008	55.6 ± 3.7
65 ± 1	0.0116 ± 0.0000	59.8 ± 0.1	0.0133 ± 0.0005	52.0 ± 2.0	0.0210 ± 0.0004	33.0 ± 0.7
70 ± 1	0.0146 ± 0.0000	47.5 ± 0.2	0.0178 ± 0.0001	39.0 ± 0.2	0.0235 ± 0.0004	29.4 ± 0.6
75 ± 1	0.0165 ± 0.0002	42.1 ± 0.4	0.0194 ± 0.0011	35.7 ± 2.0	0.0242 ± 0.0012	28.6 ± 1.4

FIGURE 2 C_R values of phycocyanin in phosphate-citrate buffer at pH 5.0, 6.0, and 7.0 after incubation in a water bath at various temperatures for 30 min in darkness.

TABLE 2 C_R values of phycocyanin in phosphate-citrate buffer at pH 5.0, 6.0, and 7.0 at the indicated temperatures for short-term treatment in darkness

	CR (%)
	pH 5.0			pH 6.0			pH 7.0
Temperature (°C)	1 min	2 min	4 min	1 min	2 min	4 min	1 min	2 min	4 min
60 ± 1	97.5 ± 0.6	93.9 ± 0.4	89.4 ± 0.5	98.9 ± 0.8	97.2 ± 0.6	91.6 ± 1.0	96.3 ± 0.3	91.7 ± 0.1	80.7 ± 0.7
65 ± 1	99.2 ± 0.5	92.7 ± 0.5	84.8 ± 0.5	98.3 ± 0.3	95.2 ± 0.7	87.8 ± 0.0	96.1 ± 0.5	86.8 ± 0.0	74.3 ± 0.6
60 ± 1	95.9 ± 0.3	88.0 ± 0.1	79.3 ± 0.2	94.2 ± 0.0	87.3 ± 0.2	74.8 ± 0.4	90.4 ± 0.2	76.8 ± 1.0	61.0 ± 0.2
75 ± 1	92.3 ± 2.4	77.9 ± 0.1	70.6 ± 0.1	92.8 ± 0.4	75.7 ± 0.2	65.3 ± 1.2	81.9 ± 0.6	57.9 ± 0.3	51.4 ± 0.3

FIGURE 3 C_R values of phycocyanin in phosphate-citrate buffer at pH 5.0, 6.0, and 7.0 exposed to light for 50 and 100 μmol m^–2 s^–1 at room temperature for indicated durations.

FIGURE 4 C_R values of the phycocyanin solution at pH 5.0, 6.0, 7.0, and 8.0 with 20% sucrose, glucose or NaCl (w/v) after heating at A: 65ºC for 30 min. C_R values of the phycocyanin solution at B: pH 6.0 with sucrose, glucose or NaCl at each concentration after incubation at 65ºC for 30 min.

TABLE 3 Antioxidant activity of phycocyanin as determined by TEAC and DPPH methods

	TEAC^a	ABTS (IC50)^b	DPPH (IC50)^b
Phycocyanin	0.75 ± 0.01	0.56 ± 0.02	1.86 ± 0.18

^aTEAC expressed in mmol Trolox equivalent/g phycocyanin; ^bIC₅₀ expressed in mg/mL.

FIGURE 5 Antioxidant activity of phycocyanin as determined by ABTS and DPPH methods.