The impact of convective drying on the color, phenolic content and antioxidant capacity of noni (<i>Morinda citrifolia</i> L.)

MIRELES-ARRIAGA, Ana Isabel; RUIZ-LÓPEZ, Irving Israel; HERNÁNDEZ-GARCÍA, Pedro Abel; ESPINOSA-AYALA, Enrique; LÓPEZ-MARTÍNEZ, Leticia Xóchitl; MÁRQUEZ-MOLINA, Ofelia

doi:10.1590/1678-457X.00415

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Research Paper • Food Sci. Technol (Campinas) 36 (4) • Oct-Dec 2016 • https://doi.org/10.1590/1678-457X.00415 copy

The impact of convective drying on the color, phenolic content and antioxidant capacity of noni (Morinda citrifolia L.)

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The effect of thin-layer drying temperature on color, phenolic content and antioxidant capacity of noni slices was investigated. Noni slices were air-dried at 50, 60 and 70 °C under natural convection conditions. Drying curves were fitted to thin-layer drying models in order to evaluate the drying characteristics of the product. In addition, an unsteady-state diffusion equation was numerically solved considering both product shrinkage and a variable mass Biot number in boundary condition to accurately estimate water diffusivity in a process with external resistance to mass transfer. Results revealed that the Aghbashlo model accurately reproduced the experimental behavior. As expected, water diffusivities, corrected for shrinkage, increased with the use of higher drying temperatures, with values in the range of 1.80-3.19 to ×10^-9 m²/s. On the other hand, while drying caused a reduction in product lightness (24-31%) and total phenolic content (20-28%), the antioxidant capacity of dried noni was high (82-93% DPPH inhibition), which is advantageous for the further storage or processing of this fruit.

Keywords:
antioxidants; natural convection; noni drying

Model	Temperature	Parameters				$R^{2}$	$R M S E \times 10^{2}$	$χ^{2} \times 10^{2}$
Model	Temperature	$k_{1} \times 10^{2}$	$k_{2} \times 10^{2}$	$a$	$b$	$R^{2}$	$R M S E \times 10^{2}$	$χ^{2} \times 10^{2}$
Newton	50	1.0400	-	-	-	0.9687	12.2141	1.5747
	60	1.5100	-	-	-	0.9826	7.8061	0.6452
	70	2.4800	-	-	-	0.9378	15.9855	2.7683
Page	50	0.1036	-	1.3999	-	0.9965	2.9648	0.0982
	60	0.3986	-	1.2386	-	0.9969	2.5284	0.0719
	70	0.1366	-	1.5443	-	0.9950	3.7219	0.1637
Modified exponential	50	0.6307	-	1.1843	-0.1170	0.9939	3.6552	0.1586
	60	0.7106	-	0.9246	-0.0798	0.9900	7.1628	0.6158
	70	0.7826	-	1.2564	-0.1800	0.9902	11.3226	1.5384
Two-term exponential	50	0.7826	-0.6770	1.0923	-0.0007	0.9870	2.8819	0.0928
	60	1.1768	-0.6832	1.0450	-0.0007	0.9949	2.1216	0.0506
	70	1.4548	-0.0863	1.0775	-0.0015	0.9880	3.0949	0.1132
Aghbashlo	50	0.4206	-0.2256	-	-	0.9988	1.7358	0.0337
	60	0.9277	-0.1369	-	-	0.9988	1.7192	0.0332
	70	0.8528	-0.3586	-	-	0.9996	1.0953	0.0148

Parameter	Value
$k_{0}$ (s^-ⁿ)	1919.27
$n$ $E_{S}$ (J/mol)	71530
(dimensionless)	2.0992
$Δ$ (dimensionless)	0.2383
$R^{2}$	0.9663

Set	$D_{0} \times 10^{5}$ (m2/s)	$E_{D}$ (J/mol)	$α$ (1/m)	$β$ (1/m)	$γ \times 10^{4}$ (1/sn)	$η$ (dimensionless)	$R^{2}$
1	3.302 (3.247/3.357)	26326.5 (25094.1/27558.9)	55.781 (29.813/81.749)	46.935 (26.701/67.168)	3.604 (1.351/5.8567)	1.034 (0.847/1.221)	0.985
2	3.276 (2.544/4.007)	26351.1 (26044.3/26657.9)	55.997 (49.295/62.699)	46.578 (38.627/54.529)	2.943 (1.715/4.1712)	Set to 1, not fitted	0.985

Variable	Fresh	Drying temperature (°C)			p
Variable	Fresh	50 °C	60 °C	70 °C	p
L*	60.42 ± 6.2^a	45.79 ± 2.5^b	45.30 ± 5.4^b	41.94 ± 4.8^b	0.0093
a*	3.98 ± 3.5^a	4.62 ± 1.1^a	3.29 ± 1.3^a	4.38 ± 0.8^a	0.6532
b*	14.12 ± 5.0^a	14.99 ± 2.1^a	12.49 ± 1.1^a	15.66 ± 1.9^a	0.2943
Hue	181.30 ± 1.1^a	181.27 ± 0.1^a	181.31 ± 0.1^a	181.30 ± 0.0^a	0.2711
Chroma	14.65 ± 4.7^a	15.68 ± 2.1^a	12.91 ± 1.3^a	16.25 ± 1.9^a	0.2185
TPC (g GAE/g dm)	31.67 ± 1.6^a	25.28 ± 1.1^b	22.76 ± 3.0^b	22.97 ± 2.3^b	0.0000
AC (% DPPH inhibition)	93.25 ± 0.5^a	93.56 ± 0.8^a	91.97 ± 1.0^a	82.52 ± 1.8^b	0.0000

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[1] *Corresponding author: ofeliammolina@yahoo.com, ofeliamarquezmolina@gmail.com