Quinoa treated by an optimized method of microwave heating and their effect on antioxidant activity and phenolic compounds after in vitro gastrointestinal digestion

Figures & data

Table 1. Effects of the time and power factors of microwave cooking of quinoa on TPC, TFC, and TEAC.^a,b

Treatment	Time (T)	Power (P)	TPC	TFC	TEAC
	min	(%)	µg GAE/g ± SE	µg QE/g ± SE	µM TE/g± SE
RQ	–	–	62.74 ± 17.67	1126.30 ± 25.75	2.60 ± 0.16
1	14	60	67.17 ± 13.2	594.77 ± 14.2	2.74 ± 0.10
2	14	100	749.67 ± 16.2	803.37 ± 20.1	4.61 ± 0.10
3	18	60	471.26 ± 16.2	406.21 ± 18.6	2.28 ± 0.08
4	18	100	51.03 ± 17.3	547.47 ± 18.6	2.88 ± 0.01
5	14	80	474.91 ± 17.3	521.38 ± 18.6	2.89 ± 0.09
6	18	80	565.11 ± 13.8	475.62 ± 14.2	3.09 ± 0.08
7	16	60	466.55 ± 14.5	403.24 ± 16.4	2.98 ± 0.08
8	16	100	53.38 ± 16.2	543.66 ± 18.6	3.17 ± 0.09
9	16	80	578.47 ± 13.8	504.05 ± 14.2	2.65 ± 0.08
10	16	80	514.02 ± 16.2	509.30 ± 18.6	2.55 ± 0.10
11	16	80	509.14 ± 18.6	501.66 ± 18.6	2.36 ± 0.10
12	16	80	471.43 ± 16.2	498.48 ± 20.1	2.43 ± 0.10
13	16	80	518.08 ± 18.7	511.46 ± 17.4	2.52 ± 0.12

^aData are the mean ± standard error (n = 3). ^bRaw quinoa (RQ), total phenol content (TPC), total flavonoid content (TFC), Trolox equivalents antioxidant capacity (TEAC), gallic acid equivalents (GAE), quercetin equivalents (QE), Trolox equivalents (TE).

Figure 1. Response surfaces for the TPC (total phenol content) (a), TFC (total flavonoid content) (b), and antioxidant activity determined by TEAC assay (c) in quinoa as a function of the microwave irradiation time and power.

Table 2. Coefficients of the regression equations for TPC, TFC, and TEAC.^a

Coefficients of the equation	TPC	TFC	TEAC
	µg GAE/g	µg QE/g	µM TE/g
Intercept
β0	771.30**	810.85**	2.64**
Linear
β1	23.80**	−39.58 **	−0.09 *
β2	1.32*	3.55**	0.01**
Quadratic
β11	18.86**	118.85**	−0.06 *
β22	0.05ns2	0.09*	−0.001 **
β12 interaction	0.31ns	−0.22ns	0.005*
Lack of fit	0.0001	0.0001	0.0001
P value	0.0001	0.0001	0.0001
Prob > F	0.0001	0.0001	0.0001
R^2	0.34	0.64	0.44
R^2 adjusted	0.30	0.61	0.40

^aTotal phenol content (TPC), total flavonoid content (TFC), TEAC (Trolox equivalents antioxidant capacity), gallic acid equivalents (GAE), quercetin equivalents (QE), Trolox equivalents (TE). ²ns: not significant (p > .05); *significant (p < .05), **significant (p < .01).

Table 3. Total phenol content (TPC), total flavonoid content (TFC), antioxidant activity (TEAC), and individual phenolic compounds of methanolic extracts of microwave-optimized quinoa (MQ) and raw quinoa (RQ).^a

Component	RQ	MQ
TPC (µg GAE/g)	620.74 ± 17.67^b	749.67 ± 36.62^a
TFC (µg QE/g)	1126.30 ± 25.75^a	803.37 ± 27.0^b
TEAC (µM TE/g)	2.60 ± 0.16^b	4.61 ± 0.16^a
Phenolic acids(µg/g)
Gallic acid	25.73 ± 0.59^b	42.93 ± 1.39^a
Coumaric acid	0.94 ± 0.04^b	1.31 ± 0.04^a
Ferulic acid	0.82 ± 0.03^b	1.34 ± 0.06^a
Flavonoids(µg/g)
Routine	13.84 ± 0.48^b	17.80 ± 0.81^a
Myricetin	1.99 ± 0.06^b	2.19 ± 0.03^a
Quercetin	4.71 ± 0.01^a	4.80 ± 0.001^a
Kaempferol	ND	2.31 ± 0.01^a

^aValues correspond to the mean ± standard error (n = 3). Values with different letters between rows are significantly different at p < .05 with Tukey´s test. TEAC (Trolox equivalents antioxidant capacity); GAE (gallic acid equivalents); QE (quercetin equivalents; TE (Trolox equivalents).

Figure 2. Total phenolic content (TPC) (a,b), Total flavonoid content (TFC) (c,d) and antioxidant activity (TEAC) (e,f) (lines), after simulated gastrointestinal digestion of RQ (raw quinoa) and MQ (microwaved quinoa). Bars represent bioaccessibility of TPC, TFC and TEAC calculated from undigested extract concentrations considered as 100%.

Table 4. Phenolic acids and flavonoids (µg/g) and bioaccessibility (%) in microwaved quinoa after in vitro gastrointestinal digestion.^a

	Gastrointestinal digestion phase
Component	Oral	%B	Gastric	%B	Intestinal	%B
RQ
Gallic acid	130.37 ± 5.07^Ac	506	256.79 ± 13.11^Bb	998	449.99 ± 32.03^Aa	1748
Coumaric acid	0.54 ± 0.01^Bb	57	1.52 ± 0.05^Ba	161	0.50 ± 0.01^Bc	53
Ferulic acid	1.61 ± 0.07^Bb	196	0.88 ± 0.04^Bc	107	3.38 ± 0.18^Aa	412
Routine	3.85 ± 0.13^Bc	27	6.14 ± 0.33^Aa	44	6.99 ± 0.42^Ab	50
Myricetin	0.44 ± 0.01^Bc	22	0.93 ± 0.03^Aa	46	0.90 ± 0.02^Ab	45
Quercetin	3.74 ± 0.28^Ac	79	47.36 ± 0.76^Aa	1000	13.17 ± 0.19^Ab	279
Kaempferol	ND	NC	4.07 ± 0.19^B	NC	ND	NC
MQ
Gallic acid	72.24 ± 3.58^Bb	168	371.93 ± 44.86^Aa	866	36.88 ± 2.93^Bc	85
Coumaric acid	0.81 ± 0.02^Ab	61	2.01 ± 0.04^Aa	153	0.66 ± 0.02^Ac	50
Ferulic acid	2.20 ± 0.17^Aa	164	1.04 ± 0.04^Ab	77	1.04 ± 0.07^Bb	134
Routine	5.59 ± 0.43^Ab	31	6.80 ± 0.65^Aa	38	3.40 ± 0.17^Bc	19
Myricetin	0.51 ± 0.01^Ac	23	1.05 ± 0.03^Aa	47	0.88 ± 0.01^Ab	40
Quercetin	2.02 ± 0.10^Bc	42	22.12 ± 0.40^Ba	460	2.24 ± 0.00^Bb	46
Kaempferol	ND	NC	13.65 ± 0.95^Aa	590	1.08 ± 0.001^b	46

^aValues correspond to the mean ± standard error (n = 3). Values denoted with different capital letter within the same column for the same phenolic compound are significantly (p < .05). Values with different small letter within the same row are significantly (p < .05). ²RQ (raw quinoa); MQ (microwaved quinoa); % Bioaccessibility (%B); ND not detectable; NC not calculable.