Optimization of temperature and power density in microwave-assisted hot air oven drying and storage stability of dried apple sticks

Haneef, Nabeela; Garièpy, Yvan; Raghavan, Vijaya; Lyew, Darwin; Hanif, Tahira; Hanif, Najma

doi:10.1590/1981-6723.00623

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Brazilian Journal of Food Technology

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ORIGINAL ARTICLE • Braz. J. Food Technol. 26 • 2023 • https://doi.org/10.1590/1981-6723.00623 copy

Optimization of temperature and power density in microwave-assisted hot air oven drying and storage stability of dried apple sticks

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Apple (Malus Demestica cv. Cortland) is a perishable fruit due to its high moisture content. In this study, apple sticks were dried to increase their shelf life. Osmotic dehydration was used as pretreatment followed by microwave-assisted hot air drying (MAHD) at different temperatures (45 ºC, 55 ºC, 65 ºC) and microwave power densities (0, 0.5, 1 W/g). Optimum process parameters were estimated by the central composite design of response surface methodology (RSM). The results showed that the temperature and power density had a significant effect on response variables. Optimum conditions of moisture content (9.54%), time (100 minutes) and change in color (7.54) were found at 65 ºC and 1 W/g microwave power density (MWPD). Then the samples dried at optimum conditions were stored at ambient temperature and analyzed for color, moisture content, texture and total fungal count at regular intervals for 75 days. The results showed a non-significant change in color and fungal counts from 10.45 to 10.73 and from 0.45 to 0.69 log cfu/g respectively, and a significant decrease in moisture content from 10.11% to 5.69% was observed from 0 to 75 days. While increasing firmness resulted in increased force and energy to the breaking point and micrographs of electron microscope showed shrinkage in cell structure along with storage. The brittleness of apple sticks increased significantly during storage but remained acceptable till the end of 75 storage days.

Keywords:
Shelf life; Moisture contents; Time; Texture; Color; Fungal count

Highlights

• Quality of microwave-assisted hot air-dried apple sticks remained acceptable at ambient storage for 75 days

Symbols	Variables	Low level	Mid level	High level
A	Temperature (ºC)	45	55	65
B	MWPD (W/g)	0	0.5	1

Run	Uncoded variables		Coded variables
Run	Temperature (ºC)	MWPD (W/g)	A	B
1	65	1	1	1
2	55	0.5	0	0
3	55	0.5	0	0
4	65	0.5	1	0
5	55	0.5	0	0
6	65	0	1	-1
7	55	0	0	-1
8	45	0.5	-1	0
9	55	0.5	0	0
10	55	1	0	1
11	55	0.5	0	0
12	45	1	-1	1
13	45	0	-1	-1

Run	Temperature (ºC)	MWPD (W/g)	Time (min)	Moisture content (%)	Change in color (∆E)
1	65	1	100	9.54	7.65
2	55	0.5	152	12.83	10.69
3	55	0.5	140	13.18	11.03
4	65	0.5	132	10.97	9.08
5	55	0.5	148	12.91	10.95
6	65	0	222	15.82	14.69
7	55	0	248	16.45	15.87
8	45	0.5	168	13.97	11.93
9	55	0.5	151	12.88	10.73
10	55	1	120	11.53	9.56
11	55	0.5	155	12.69	10.61
12	45	1	150	12.65	11.59
13	45	0	270	17.79	16.67

Source	Time	MC	∆E
Intercept	12.21	3.58	3.28
A	-0.88^ Significant at < 0.0001. *Significant at < 0.05.	-0.19**	-0.22**
B	-2.31**	-0.37**	-0.44**
AB	-0.18	-0.057*	-0.097**
A²	-0.027	-0.042	-0.035*
B²	1.15**	0.16^*	0.27**
P-value	<0.0001	<0.0001	<0.0001
F-value	190.79	150.69	594.72
R²	0.9927	0.9908	0.9977
R²adj	0.9875	0.9842	0.99.60
R²pred	0.9726	0.9308	0.9930
Lack of fit	0.7145	0.0981	0.7188

	Temperature (ºC)	MWPD (W/g)	Time (min)	MC	Color
Predictive	65	1	100	9.53	7.60
Actual	65	1	100	9.54	7.64

Storage days	Color change
Storage days	L*	a*	b*	∆E
0	72.86 ± 1.91^a	0.74 ± 0.31^c	14.19 ± 1.13^f	10.45 ± 0.10^a
15	72.95 ± 1.64^a	0.89 ± 0.5a^b	14.28 ± 0.22^e	10.33 ± 0.11^a
30	72.89 ± 1.56^a	0.84 ± 0.47^bc	14.52 ± 0.56^d	10.32 ± 0.05^a
45	72.60 ± 1.11^b	0.90 ± 0.26^ab	14.83 ± 1.85^c	10.53 ± 0.13^a
60	72.41 ± 1.39^c	0.94 ± 0.17^ab	14.86 ± 1.34^b	10.71 ± 0.08^a
75	72.37 ± 2.29^c	0.98 ± 0.34^a	14.95 ± 0.95^a	10.73 ± 0.14^a

Storage days	Moisture content (%)	Texture		TFC (Log cfu/g)
Storage days	Moisture content (%)	Force (N)	Energy (J)	TFC (Log cfu/g)
0	10.11 ± 0.13^a	29.22 ± 1.21^e	0.048 ± 0.01^d	0.45 ± 0.08^a
15	7.96 ± 0.06^ab	32.15 ± 1.79^d	0.049 ± 0.02^d	0.54 ± 0.09^a
30	7.41 ± 0.09^ab	38.83 ± 1.83^c	0.055 ± 0.02^c	0.51 ± 0.21^a
45	6.49 ± 0.16^b	53.67 ± 2.49^b	0.062 ± 0.06^b	0.60 ± 0.26^a
60	5.58 ± 0.15^b	85.72 ± 1.91^a	0.082 ± 0.02^a	0.69 ± 0.32 ^a
75	5.69 ± 0.22^b	85.70 ± 2.36^a	0.084 ± 0.05^a	0.69 ± 0.47^a

Instituto de Tecnologia de Alimentos - ITAL Av. Brasil, 2880, 13070-178 Campinas - SP / Brasil, Tel 55 19 3743-1762 - Campinas - SP - Brazil
E-mail: bjftsec@ital.sp.gov.br

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[1] *Corresponding Author: Nabeela Haneef, PMAS Arid Agriculture University, Institute of Food and Nutritional Sciences (IFNS), Shamsabad, Muree Road, 46000, Rawalpindi - Pakistan, e-mail: nabeelahanif2011@gmail.com