DRYING CHARACTERISTICS AND QUALITY ANALYSIS OF HOT AIR-ASSISTED RADIO FREQUENCY AND HOT-AIR DRYING OF JUJUBE ( <i>Zizyphus jujube</i> Miller cv. <i>Jinsixiaozao</i> )

Song, Shujie; Huang, Xue; Liu, Yufang; Zhang, Qingan

doi:10.1590/1809-4430-Eng.Agric.v42n1e20210112/2022

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Scientific Paper • Eng. agríc. (Online) 42 (1) • 2022 • https://doi.org/10.1590/1809-4430-Eng.Agric.v42n1e20210112/2022 copy

DRYING CHARACTERISTICS AND QUALITY ANALYSIS OF HOT AIR-ASSISTED RADIO FREQUENCY AND HOT-AIR DRYING OF JUJUBE ( Zizyphus jujube Miller cv. Jinsixiaozao )

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Radio frequency (RF) drying is a rapid dehydration technique that reduces water activity and extends the shelf life of agricultural products. In this study, the drying characteristics of jujube during HARF and hot air (HA) were investigated, and quality analyses, such as color, vitamin C (VC) and total flavonoid content (TFC), of jujube were performed. The drying curves revealed that the drying time used to reduce the moisture content from 81.7 to 6.0% on a dry basis was 360 and 1320 min using HARF drying and hot air (HA) drying, respectively. The logarithmic model was the best to describe the HARF drying process with R ², RMSE and SSE values of 0.998, 0.00508 and 0.000306, respectively. Quality analysis demonstrated significant differences in color, VC content and total flavonoid content between the HARF and HA treatments during the drying process and storage periods (P > 0.5), and the HARF-dried jujube product performed much better than that dried by HA. Compared with HA drying, HARF drying showed a shorter drying time, higher drying efficiency and better product quality, indicating that HARF drying was a more promising drying method for jujube with acceptable product quality.

KEYWORDS
kinetic models; hot air-assisted radio frequency drying; drying rate; color; hot air drying

NO.	Electrode gap (cm)	Air temperature (°C)	Average heating rate for the first 60 min (°C/min)	Sample temperature during RF heating between 60 and 120 min (°C, average±SD)
1	19	40	0.78	72.69±2.15
2	19	50	0.92	81.29±2.52
3	19	60	1.06	90.65±2.96
4	20	40	0.48	55.01±1.36
5	20	50	0.56	60.99±1.66
6	20	60	0.70	70.09±1.73
7	21	40	0.37	49.30±1.18
8	21	50	0.53	59.84±1.74
9	21	60	0.65	66.67±1.73

No.	Models	Equations	Reference
1	Wang and Singh	$M R = 1 + b t + a t^{2}$	( Ahmet & Derya BO 2020Ahmet EA, Derya BO (2020) Determination of drying behaviour in industrial type convectional dryer and mathematical modelling. Thermal Science 24(3B): 1935-1950. DOI: https://doi.org/10.2298/tsci180315244a https://doi.org/10.2298/tsci180315244a... )
2	Newton	$M R = \exp (- k t)$	( White et al., 1981White GM, Ross IJ, Poneler R (1981) Fully exposed drying of popcorn. Transactions of the American Society of Agricultural Engineers 24(2): 466-468. DOI: https://doi.org/10.13031/2013.34276 https://doi.org/10.13031/2013.34276... )
3	Page	$M R = \exp (- k t^{n})$	( Chkir et al., 2015Chkir I, Balti MA, Ayeda L, Azzouzc S, Kechaou N, Hamdi M (2015) Effects of air drying properties on drying kinetics and stability of cactus/brewer’s grains mixture fermented with lactic acid bacteria. Food and Bioproducts Processing 94: 10-19. DOI: https://doi.org/10.1016/j.fbp.2014.12.003 https://doi.org/10.1016/j.fbp.2014.12.00... )
4	Henderson and Pabis	$M R = a \exp (- k t)$	( Khodifad & Kumar, 2020Khodifad BC, Kumar N (2020) Foaming properties of custard apple pulp and mathematical modelling of foam mat drying. Journal of Food Science and Technology 57(2): 526-536. DOI: https://doi.org/10.1007/s13197-019-04082-0 https://doi.org/10.1007/s13197-019-04082... )
5	Logarithmic	$M R = a \exp (- k t) + b$	( O’callaghan et al., 1971O’callaghan JR, Menzies DJ, Bailey PH (1971) Digital simulation of agricultural dryer performance. Journal of Agricultural Engineering Research 16(3): 223-244. DOI: https://doi.org/10.1016/s0021-8634(71)80016-1 https://doi.org/10.1016/s0021-8634(71)80... )
6	Midilli	$M R = a \exp (- k t^{n}) + b t$	( Moradi et al., 2019Moradi M, Niakousari M, Khaneghah AM (2019) Kinetics and mathematical modeling of thin layer drying of osmo‐treated Aloe vera (Aloe barbadensis) gel slices. Journal of Food Process Engineering 42(6): https://doi.org/10.1111/jfpe.13180 https://doi.org/10.1111/jfpe.13180... )

Model	R ²	RMSE	SSE	k	n	a	b	c
Newton	0.981	0.0964	0.0626	0.00317
Page	0.927	0.0560	0.0407	0.0158	0.702
Modified Page	0.981	0.0694	0.0262	2.070	0.00152
Henderson and Pabis	0.991	0.0147	0.00281	0.00234		0.847
Logarithmic	0.998	0.00508	0.000336	0.000545		2.740		-1.914
Wang and Singh	0.949	0.0674	0.0589			-0.00334	4.497

Drying time (min)	Color ( ΔE )		Vitamin C (mg/100 g)		TFC (g/100 g)
Drying time (min)	HARF	HA	HARF	HA	HARF	HA
0	-	-	564.82±25.58aA	564.82±25.58aA	10.44±1.24cA	10.44±1.24aA
180	16.25±0.98bB	20.45±1.25dA	354.75±20.67bA	278.54±17.67bB	14.56±1.98bA	12.26±1.57bB
360	24.34±1.52aB	27.56±1.67cA	298.45±17.67cA	154.26±13.78cB	20.07±2.12aA	14.23±1.68cB
840	-	30.25±1.85b	-	89.56±10.84d		16.54±1.74d
1320	-	35.01±2.24a	-	-		17.54±1.97e

Storge time(d)	Color ( ΔE )		Vitamin C (mg/100 g)		TFC (g/100 g)
Storge time(d)	HARF	HA	HARF	HA	HARF	HA
0	24.34±1.52aB	35.01±2.24aA	298.45±17.67a	-	20.07±2.12aA	17.54±1.97aB
10	25.56±1.87aB	34.51±2.54aA	186.78±12.68b	-	15.54±1.61bA	12.68±1.08bB
20	25.45±2.36aB	35.47±2.68aA	91.56±8.57c	-	10.35±1.18cA	8.68±0.76cB

Associação Brasileira de Engenharia Agrícola SBEA - Associação Brasileira de Engenharia Agrícola, Departamento de Engenharia e Ciências Exatas FCAV/UNESP, Prof. Paulo Donato Castellane, km 5, 14884.900 | Jaboticabal - SP, Tel./Fax: +55 16 3209 7619 - Jaboticabal - SP - Brazil
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[1] * Corresponding author. College of Food Engineering and Nutrition Science, Shaanxi Normal University, Xi’an 710062 , China. E-mail: foodssj@snnu.edu.cn