Effects of drying on the bioactive compounds in organic sweet potatoes (<i>Ipomoea batatas</i>)

Pacheco, Okelynton Ayres; Silva, Luciana Alves da; Stafussa, Ana Paula; Marques, Amábile Mariano; Bergamasco, Rita de Cássia; Scapim, Mônica Regina da Silva

doi:10.4025/actasciagron.v48i1.74917

Sweet potato (Ipomoea batatas L.) is a source of vitamin A, carbohydrates, organic acids, and minerals. It is rich in bioactive compounds, making it a very healthy food. Indeed, it helps in the prevention of various diseases such as cardiovascular diseases, certain types of cancer, and in controlling the glycemic index of people with diabetes. Additionally, it provides nutrients for at-risk groups, such as children and pregnant women with deficiencies in magnesium and vitamin A. In its natural form, sweet potatoes have high water activity, making them highly perishable and reducing their shelf life. This study aimed to evaluate the influence of the drying process at different temperatures (50, 60, and 70°C) and thicknesses (1, 2, and 3 mm) on the antioxidant content and phenolic compounds of two sweet potato cultivars: BDI (Brasilândia) and BDII (not cataloged). The drying process was evaluated based on 10 mathematical models, comparing the coefficient of determination (R²), chi-square (χ²) value, and root mean squared error (RMSE). The Page model stood out for the BDI cultivar and the diffusion approximation and Page models were significant for the BDII cultivar. The total phenolic content ranged from 71.67 to 99.33 mg gallic acid equivalents 100 g^-1. The 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and ferric reducing antioxidant power (FRAP) methods were used to quantify antioxidant activity, with values ranging from 21.93 to 51.53 µmol Trolox 100 g^-1 and 656.34 to 1021 µM ferrous sulfate 100 g^-1, respectively. A drying temperature of 70°C combined with a thickness of 1 mm required a shorter drying time to reach the equilibrium moisture content, between 2 and 3 hours.

Keywords:
Sweet potato; antioxidant activity; total phenolics; thickness; mathematical models

[TFN1] MR is the moisture ratio (dimensionless value); t is the drying time (minutes); k, k₀, and k₁ are drying constants (s^-1); and a, b, c, and n are coefficients of the models.

Model	Equation	Number MMM
Newton	MR = exp (-k.t)	2
Page	MR = exp (-k. tn)	3
Henderson and Pabbis	MR = a. exp (-k. t)	4
EDT	MR = a. exp (-k. t) + (1- a) exp (-k. a. t)	5
Thompson	MR = exp ((-a - (a² + 4. b. t) 0.5) / 2. b)	6
Wong and Sing	MR = 1 + a. t + b. t²	7
Midilly and Kucuk	MR = a. exp (- k. t) + b. t	8
Logarithmic	MR = a. exp (- k. t) +c	9
Diffusion approximation	MR = a. exp (-k. t) + (1- a). exp (-k. b. t)	10
Two terms	MR = a. exp (-k0. t) + b. exp (-k1. t)	11

Parameters	BDI	BDII
Ash (%)	0.6^a ± 0.06	0.7^b ± 0.04
Moisture (%)	64.60^a ± 0.49	61.02^a ± 0.50
Proteins (%)	5.25^a ± 0.43	4.37^a ± 0.43
Carbohydrates*	29.15	33.51
Lipids (%)	0.4^a ± 0.00	0.3^a ± 0.01

Cultivar	Thickness (mm)	50°C	60°C	70°C	R²
BDI	1	8760.97	8762.48	8763.90	0.999
	2	34285.13	34293.91	34302.18	0.999
	3	1414.06	1414.35	1414.62	0.999
BDII	1	3.03	3.04	3.04	0.999
	2	670.08	670.24	670.39	0.999
	3	865879.89	865892.84	865905.05	0.999

BDI cultivar
Temperature (°C)	Thickness (mm)	Total phenolic content	ABTS	FRAP
50	1	58.22^c ± 7.21	50.82^a ± 22.7	627.02^c ± 11.1
50	2	68.67^abc ± 3.54	42.82^a ± 11.5	665.83^c ± 56.02
50	3	67.22^bc ± 1.50	41.40^a ± 4.1	672.73^bc ± 20.05
60	1	50.22^c ± 7.51	27.89^a ± 8.3	510.60^c ± 57.20
60	2	53.67^c ± 9.03	26.91^a ± 7.3	513.94^c ± 38.17
60	3	52.33^c ± 5.58	28.78^a ± 5.6	525.26^c ± 67.47
70	1	99.33^a ± 19.12	48.16^a ± 12.5	1021.97^a ± 21.1
70	2	91.22^ab ± 7.12	51.53^a ± 3.4	939.62^ab ± 93.67
70	3	71.67^abc ± 6.24	43.62^a ± 12.5	755.51^abc ± 40.10
BDII cultivar
Temperature (°C)	Thickness (mm)	Total phenolic content	ABTS	FRAP
50	1	50.11^d ± 5.37	13.22^a ± 7.8	386.86^e ± 10.77
50	2	47.11^cd ± 3.47	16.15^a ± 3.0	471.80^de ± 38.21
50	3	42.00^d ± 0.72	24.33^a ± 11.0	408.42^de ± 13.99
60	1	45.55^cd ± 2.35	25.84^a ± 7.3	513.19^cde ± 40.39
60	2	49.11^cd ± 5.15	19.27^a ± 8.3	497.24^cde ± 37.40
60	3	52.00^cd ± 4.58	22.82^a ± 9.0	569.67^cd ± 42.23
70	1	83.55^a ± 7.82	21.93^a ± 5.0	887.88^a ± 56.47
70	2	75.44^ab ± 3.91	31.71^a ± 13.3	802.08^ab ± 54.91
70	3	59.55^bc ± 4.63	25.13^a ± 14.3	656.34^bc ± 79.59

1 mm thickness
Cultivar	Temperature (°C)	Total phenolic content	ABTS	FRAP
BDI	50	58.22^bc ± 7.21	50.82^b ± 22.7	627.02^bc ± 11.1
BDI	60	50.22^c ± 7.51	27.89^ab ± 8.3	510.60^c ± 57.20
BDI	70	99.33^a ± 19.12	48.16^b ± 12.5	1021.97^a ± 21.1
BDII	50	50.11^c ± 5.37	13.22^a ± 7.8	386.86^c ± 10.77
BDII	60	45.55^c ± 2.35	25.84^ab ± 7.3	513.19^c ± 40.39
BDII	70	83.55^ab ± 7.82	21.93^ab ± 5.0	887.88^ab ± 56.47
2 mm thickness
Cultivar	Temperature (°C)	Total phenolic content	ABTS	FRAP
BDI	50	68.66^abc ± 3.54	42.82^ab ± 11.5	665.83^bc ± 56.02
BDI	60	53.66^bcd ± 9.03	26.91^bc ± 7.3	513.94^c ± 38.17
BDI	70	91.22^a ± 7.12	51.53^a ± 3.4	939.62^a ± 93.67
BDII	50	47.11^cd ± 3.47	16.15^c ± 3.0	471.80^c ± 38.21
BDII	60	49.11 ^d ± 5.15	19.27^c ± 8.3	497.24^c ± 37.40
BDII	70	75.44^b ± 3.91	31.71^bc ± 13.3	802.08^b ± 54.91
3 mm thickness
Cultivar	Temperature (°C)	Total phenolic content	ABTS	FRAP
BDI	50	67.22^a ± 1.50	41.40^a ± 4.1	672.72^bc ± 20.05
BDI	60	52.33^bc ± 5.58	28.78^a ± 5.6	525.26^ad ± 67.47
BDI	70	71.67^a ± 6.24	43.62^a ± 12.5	755.51^b ± 40.10
BDII	50	42.00^c ± 0.72	24.33^a ± 11.0	408.42^a ± 13.99
BDII	60	52.00^bc ± 4.58	22.82^a ± 9.0	569.67^cd ± 42.23
BDII	70	59.55^ab ± 4.63	25.13^a ± 14.3	656.34^bcd ± 79.59

	Phenolics	ABTS	FRAP
Phenolics	1	0.5032	0.8969
ABTS	0.5032	1	0.5612
FRAP	0.8969	0.5612	1

Effects of drying on the bioactive compounds in organic sweet potatoes (Ipomoea batatas)