1. Ultrasound treatment (min)
EFFECT OF MALTODEXTRIN AND ULTRASOUND ON OSMOTIC DEHYDRATION OF ORANGE PEEL
NedićTiban, Nela; Lončarić, Ante; Papac, Snježana; Piližota, Vlasta
JosipJurajStrossmayerUniversity of Osijek, Faculty of Food Technology Osijek,
F. Kuhača 20, Osijek
Osmotic dehydration (OD) is a process in which partial water is removed by immersion of water containing cellular solid in a concentrated aqueous solution of high osmotic media for a specified time and temperature. Different osmotic agents have been used namely sucrose, glucose, fructose, maltodextrin, sorbitol, etc. In order to improve the processing efficiency and the quality of the final product, the application of ultrasound is explored in combination with osmotic dehydration (Deng and Zhao, 2008; Mohebbi et al., 2011). Vacuum application for a short period of time at the beginning of the osmotic process (pulsed vacuum osmotic dehydration, PVOD) has beneficial effects on process kinetics and fruit quality in many fruits and also helps to reduce energy costs (Fito et al., 2001). OD treated products can also be used in the bakery, dairy and candy industries (Xin et al., 2013). In this work, ultrasound pretreatment of orange peel cubes using aqueous solutions of sucrose (45, 55 and 65 %) with and without addition of maltodextrins (10 and 20 %) were used to enhance mass transfer during osmotic dehydration at atmospheric pressure (OD) and pulsed vacuum osmotic dehydration (PVOD).
Introduction
Materials and Methods
Raw materials
Orange (Citrus sinensiscv. Navel Lane Late, Spain) was purchased in local market and stored in refrigerated chambers at 4 °C. Before treatments, fruit were washed and peeled. Orange peel cut into pieces (1.5x1.5 cm); sample thickness ranged between 0.4 and 0.5 cm.
Osmotic dehydration
The orange peel samples were immersed in the respective osmotic solution (sucrose, 45, 55 and 65%, and maltodextrin, MD 20, 10 and 20%) during 120 min. The product/solution ratio was about 1:5 (w/w) and at each OD treatments, the osmotic solution was changed in order to avoid changes in its concentration. The first experiment consisted of samples that were immersed in respective osmotic solution and subsequently submitted to ultrasonic waves for 5, 10 and 15 min. The experiments were carried out at 25 °C in an ultrasonic bath (Sonorex Super RK 100H, Bandelin, Germany). The ultrasound frequency was 35 kHz. The temperature increase during the treatments was lower than 2 °C. In the second experiment, pressure of 50 mbar was applied to the system for the first 5 min of the osmotic process, afterwards restoring the atmospheric pressure for 5 min more, in order to promote the previous sample impregnation with the osmotic solution (Figure 1). After OD (PVOD), the samples were removed from the osmotic medium and gently dried by rolling on four layers of clean absorbent tissue paper (1 min) to remove excess solution from the surface and then weighed.
Analysis of physicochemical properties
Total dry matter(TDM) was obtained in fresh orange peel and treated samples by vacuum drying at 70 °C until constant weight was achieved. Soluble solids (SS) were determined at 20 °C by means of a refractometer (Carl Zeiss Germany). All measurements were made in duplicate, and the mean values were reported. Mass transfer parameters and changes in the water and soluble solids (ΔMwt and ΔMst, respectively) were calculated using the following equations:
ΔMwt = [(Mot·Xwt - Moo·Xwo) / Moo] (1)
ΔMst = [(Mot· Xst- Moo·Xso) / Moo] (2)
where Motand Moo represent the sample weight at times t and 0; and Xwt, Xst,Xwoand Xso are the water (w) and soluble solid (s) mass fraction in a sample at times t and 0, respectively.
Colour of the orange peel pieces was measured before and immediately following treatment with a Minolta Chromameter (CR-300, Japan). The measurements are expressed as lightness (L*), redness (a*) and yellowness (b*). Total colour difference (E) from the untreated sample, was used to describe the colour change after treatment, bythe following equation:
E = [(L*)2 + (a*)2 + (b*)2] 1/ (3)
Firmness was measured using a texture analyser (TA.XT 2, Stable Micro Systems, UK) fitted with a 2 mm diameter probe. The penetration depth was 4 mm and the cross-head speed was 1.5 mm s-1. Measurements for colour and texture were carried out with ten replicates.
Results
Table 1 Effect of ultrasound on mass transfer parameters and changes in the water, total dry matter and soluble solids (total processing time 120 min)
Ultrasound treatment (min)
45% S +20% MD
65% S
TDM (%)
SS (%)
ΔMtw
ΔMts 5
42.25
27.8
-0.17
0.17
43.66
30.0
-0.16
0.20 10
44.10
-0.18
0.19
44.77
30.4
0.21 15
43.30
0.18
44.96
Table 2 Colour evaluation in the fresh samples and samples treated: 10 min ultrasound+5 min VI at 50 mbar, afterwards restoring the atmospheric pressure for 5 min)
Sample/Treatment
Albedo layer L a b
Δ E
fresh peel
90.74
-1.56
32.99
45% S
74.37
0.63
47.01
21.66
55% S
74.38
1.51
49.03
23.12
65% S
69.73
1.8
42.95
23.49
45%S+10%MD
70.37
1.43
45.66
24.17
45%S+20%MD
67.05
1.71
43.26
26.03
Flavedo layer
66.86
29.41
64.67
65.19
26.35
67.33
4.39
65.14
27.12
65.31
2.93
64.82
25.12
64.88
4.75
64.59
24.46
64.36
5.45
62.38
22.00
60.45
9.63
Figure 2 Effect of treatments on firmness of orange peel
min without agitation; min with agitation; 3 - ultrasound 10 min (total processing time 120 min); 4 - vacuum 50 mbar 5 min, afterwards restoring the atmospheric pressure for 5 min; 5 - ultrasound 10 min, vacuum 50 mbar 5 min, afterwards restoring the atmospheric pressure for 5 min
Conclusions
The results of this work indicate that the combination of ultrasound and vacuum accelerates mass transfer in orange peel. The combined effects of ultrasound (10 min at 35 kHz) and PVOD (5 min at 50 mbar, and afterward 5 min at atmospheric pressure) in treatments with 45 % sucrose and 20 % maltodextrinshowed the best conditions for dehydrating orange peel. Ultrasound and PVOD treatments are recommendable to develop high-quality orange peel products, taking advantage of much shorter treatment times, increasing its sweetness and improving its sensory acceptability.
ORANGE PEEL
PRETREATMENT WITH/OUT ULTRASOUND* OD
atmosphere pressure
with/out
agitation
120 min
PVOD
50 mbar (5 min) +
5-115 min
* 10min
Figure 1 Treatment procedures applied for orange peel
References
Deng, Y., Zhao, Y.: Effects of pulsed-vacuum and ultrasound on the osmodehydration kinetics and macrostructure of apples (Fuji). Journal of Food Engineering, 85 (1), 84-93, 2008.
Fito, P., Chiralt, A., Barat, J.M., Andres, A., Martinez-Monzo, J., Martinez-Navarrete, N.: Vacuum impregnation for development of new dehydrated products. Journal of Food Engineering, 49, , 2001.
Mohebbi, M., Shahidi, F., Fathi, M., Ehtiati, A., Noshad, M.: Prediction of moisture content in pre-osmosed and ultrasounded dried banana using genetic algorithm and neural network. Food and Bioproduct Processing, 89 (4), , 2011.
Xin, Y., Zhang, M., Adhikari, B.: Effect of trehalose and ultrasound-assisted osmotic dehydration on the state of water and glass transition temperature of broccoli (Brassica oleracea L. var. botrytis L.). Journal of Food Engineering, 119, , 2013.