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Journal of Food Science and Technology logoLink to Journal of Food Science and Technology
. 2019 Jul 22;56(10):4482–4491. doi: 10.1007/s13197-019-03933-0

Vacuum radio frequency drying: a novel method to improve the main qualities of chicken powders

Xin-li Ran 1, Min Zhang 1,2,✉, Yuchuan Wang 3, Yaping Liu 4
PMCID: PMC6801249  PMID: 31686680

Abstract

Vacuum radio frequency drying (VRFD) combining the advantages of RF heating with vacuum drying (VD) was applied to produce chicken powders. Drying time and some properties of VRFD the powders were compared with VD and microwave vacuum drying (MVD) (915 MHz and 2450 MHz). Results showed that the total drying time of VRFD chicken powders was the shortest (100 min) while that for VD powders was the longest (180 min). VRFD chicken powders exhibited the lowest hygroscopicity (2.17%), the highest water holding capacity (254.80%), and better color and taste. Besides, VRFD powders had maximum umami flavor among the obtained powders. Contrarily, the color and flavor of VD powders were the most undesirable. Additionally, VRFD had less effect on protein secondary structures compared with MVD. It was concluded that, VRFD possesses the necessary potential for use at industrial level in the production of chicken powders with high qualities.

Keywords: Vacuum radio frequency drying, Chicken powders, Microwave vacuum drying, Protein secondary structures, Hygroscopicity

Introduction

Drying process and its operating parameters affect the physical and chemical characters (solubleness, rehydration, etc.) and functional substances (antioxidant components, proteins, etc.) of dried samples (Zhang et al. 2018). Vacuum drying (VD) is appropriate for the drying of thermosensitive matters owing to its lower temperatures (50–80 °C) and could result in higher quality than conventional hot air drying (Balzarini et al. 2018). Nevertheless, VD is a time-consuming and energy-intensive method which resulted in low heat transfer efficiency (Mujumdar et al. 2010). Moreover, VD would also accelerate mass transfer but reduce convective heat transfer in the low-temperature chamber due to the lack of drying medium (Mujumdar and Law 2010).

Radio frequency (RF) heating has a larger depth than microwave (MW) drying because the RF wave length of free space is ranged from 20 to 360 times longer than that of normally MW applied (Wang et al. 2012a). Several researches have been reported about RF-related combination drying such as RF-assisted hot-air drying (RFHAD) in stem lettuce slices (Roknul et al. 2014) and RF-assisted heat pump drying (RFHPD) in crushed brick (Marshall and Metaxas 1999). It was found that RFHAD was the most uniform drying means and produced higher-quality products.

Vacuum radio frequency drying (VRFD), combining the advantages of RF with VD, can prevent fat oxidation, protein degradation and surface discoloration without the presence of oxygen. Publications have focused on the application of VRFD to the drying of wood (Avramidis and Liu 1994; Avramidis et al. 1996). To our knowledge, there are little studies reporting the agricultural food processing involving VRFD.

Another widely applied drying technique is microwave vacuum drying (MVD). The allowable frequency for MD is generally 2450 MHz in most European countries (Chen et al. 2013). Actually, microwave with a frequency of 915 MHz is also applicative for industrial purposes and proved to originate from electric energy with a conversion efficiency of about 50% for 2450 MHz while 85% for 915 MHz (Haque 1999).

For another thing, pure chicken powders, with rich nutrient and pleasant flavor, are mostly used as complex seasoning for cuisine, instant noodles and preprocessed food. Traditional chicken powders are primarily produced using spray drying, normally including chopping, enzymatic hydrolysis, concentrating, colloid grinding, homogenizing and so on. Apart from the complicated process, spray-dried chicken powders generally have objectionable color and odor and strongly hygroscopic ability, which need to be improved through food additives. At present, a large number of domestic researches are mainly about spray-drying conditions for chicken powders or applying products as condiments to cuisine or convenience food. Few literature centers on novel drying techniques and its impact on physico-chemical properties of chicken powders.

Therefore, the objective of this work was to provide an idea for the application of VRFD in food processing. A VRFD equipment, developed previously in our lab, was experimentally used to produce chicken powders. In this work, drying time and quality evaluation were conducted via comparison of VRFD powders with VD and MVD powders on the basis of color, sensory evaluation, protein secondary structures, hygroscopicity, solubility and water holding capacity.

Materials and methods

Materials

Frozen chicken breast (original production place: Tyson Foods, Inc., Jiangsu, China; size: 200 ± 5 g per piece) was obtained from chilled area of Auchan supermarket (Wuxi, China) followed by storing in a fridge at 4 ± 1 °C with relative humidity of 95% prior to the experiment. The main compositions were: water content: 75.97 ± 0.96% (w.b.); protein: 33.20 ± 0.09 g/100 g; fat: 1.74 ± 0.03 g/100 g.

Chilled chicken breast was chopped into nuggets (3 × 3 × 3 cm), poached (90 °C, 20 min) by an induction cooker (C21-WT 2120, Midea Electric Manufacturing Co., Ltd., Guangdong, China), and put into a meat mincer (MEAT GRINDER LV388, Foshan Shunde love to use e-commerce Co., Ltd. Guangdong, China) and made into loose granules (70 × 50 × 45 mm), the original moisture was 63.87% (w.b.).

Experimental equipment

The schematic diagram of vacuum dryer included the following parts: a vacuum drying chamber where samples were heated and dried; two heating plates (58 × 40 cm) where samples were placed; a pressure indicator for monitoring vacuum degree; a temperature indicator for temperature display; a water-ring vacuum pump and a vacuum valve for adjusting vacuum degree; a control panel for setting temperature of each heating plates in the drying chamber; a cooler which could prevent vapor generation during drying. The vacuum system and cooling system were applied to VD, MVD and VRFD. The vacuum degree and cooling temperature were set as 0.098 MPa and − 40 °C, respectively.

The machine for VRFD was previously developed in our lab based on RFD dryer (Roknul et al. 2014) to which a vacuum system was installed. There were two paralleled electrode panels top and bottom (83 × 40 cm and 99 × 59 cm, respectively). Adjusting the plate distance could alter the power of RFD. Chicken granules were heated in a special drying chamber (glass bottle) that was flatwise placed in a Teflon container (280 × 200 × 40 mm). The required vacuum pressure was achieved by a vacuum system, which was connected with drying chamber through a rubber tubing.

Except for pulse spouting installation, the MVD (2450 MHz) dryer was similar to the pulse-spouted microwave vacuum dryer (Wang et al. 2013), the MVD (2450 MHz) was composed of five essential parts: a cylindrical multimode microwave cavity (glass) (200 mm, od) distributed symmetrically with four microwave generators (at 2450 MHz); a heating supply system; a vacuum drying chamber (cylindrical pipe, Teflon) (50 mm, od); a water load system; a vacuum system with a water-ring vacuum pump and a cooler.

The MVD (915 MHz) equipment based on MD dryer (Chen et al. 2013) was consisted of such components as 915 MHz microwave source, loop device, water load, drying container, control system and vacuum system with a cooler and water-ring vacuum pump.

Drying

Same load of chicken granules (350 g) were prepared to be dried to target water content below 5% (w.b.).

For VD, chicken granules were dried on heating plate in drying chamber. The vacuum value was adjusted at 0.0098 MPa with the temperature of 75 °C; for VRFD, based on some pre-experiment, chicken granules were dehydrated with the electrode distance of 135 mm. The used vacuum degree and cool temperature was 0.0098 MPa and − 40 °C respectively for preventing generation of water vapor on the wall of drying chamber during dehydration; for MVD at 915 MHz and 2450 MHz, the microwave power density was 1.78 W/g and 1.71 W/g respectively. The vacuum level and cool temperature was the same with that of VRFD.

Chicken granules were taken out in every 20 min during drying to obtain moisture data. Steps were repeated till final moisture content. The dried granules were grinded via a pulverizer (Asahi Man 800Y, Platinum Europe Hardware Products Co. Ltd, China) to obtain chicken powders (30 mesh) for further analyses.

Analytical methods

Moisture content

Oven-drying method (National Standard of China/AOAC Method 1999) was used for measuring water content of chicken samples. Samples were dried in an oven for 5 h at 105 ± 1 °C till a constant weight. This test was repeated three times.

Low-field nuclear magnetic resonance (LF-NMR)

On the basis of different interaction of hydrogen proton of moisture with various molecular environment, NMR techniques was applied to the determination of water state in foods (Chaland et al. 2000).

The water transference of minced chicken breast was examined by a low field NMR analyzer (MicroMR20-030V-I, Niumag Technology Co., Ltd, Shanghai, China). A T2-Inverter software specialized and glass pipes (3 × 20 cm) were utilized for measurement. 3 ± 0.4 g of samples were put in the glass pipes. The Carr–Purcell–Meiboom–Gill sequence was used for detection of T2 relaxation time of samples. The repetition time of two consecutive scans was set as 3 s. Main operating conditions were as follows: NECH = 1000, TW = 4000 ms, and NS = 16.

Measuring of color

A chromatic meter (CR-400, Konica Minolta Co., Japan) was used for color measuring of samples. The observed values of color were showed as L* (brightness) value—the lower its value, the more browning, a* (red-green) value—the lower its value, the more green; b* (yellow-blue) value—the lower its value, the more blue. Besides, color difference (∆E) was calculated to understand color variation after drying (Roknul et al. 2014):

ΔE=(L0∗-L∗)2+(a0∗-a∗)2+(b0∗-b∗)2

In which L*0, a*0, b*0 stand for the readings of the device testing chicken granules before drying.

Analysis of electronic nose (E-nose)

The determination of odor constituent of samples were detected by E-nose (iNose102, Isenso, USA). The equipment was primarily composed of such units as gas injection system, array of sensors, detection curves of sensors along with knowledgeware. The sensor array of E-nose had 14 sensors responding to different flavor substances: S1—aromatic compounds, ethers and phenol ethers, with aromas of spices; S2—sulfides, mercaptans, thioethers, dipropyl disulfides, etc.; S3—hydrogen; S4—organic acid esters and terpenoids, followed by secondary alcohols, ketones, acids, etc.; S5—biosynthesis of terpenoids, esters, pyrazines; S6—mushroom essence; S7—aliphatic hydrocarbon oxygenated derivatives; S8—nitrogen oxides, ammonia, low molecular amines; S9—hydrogen compounds; S10—hydrocarbon; S11—volatile organic compounds (alkanes, aromatic hydrocarbons, alkenes, halocarbons, aldehydes, ketones, etc.; S12—alcohol, organic solvent; S13—ethylene; S14—volatile gases in food cooking.

Approximately 5 g of samples were added into 40 mL sample vials (powder samples were soaked by aqua distillate), standing for half-hour before measurement. Then two probes were implanted into the vials (1–2 cm over the surface of samples). One of the probes was connected to the instrument for detection. Another one was connected with the air to allow pressure to be equalized. When measuring, the sensors of the device was washed for 2 min before next testing and every detecting was kept for 60 s.

Analysis of electronic tongue (E-tongue)

The taste of chicken powders was evaluated by electronic tongue (TS-5000Z, INSENT, Japan), which basically consisted of taste sensor arrays for sourness, bitterness, astringency, aftertaste-B, aftertaste-A, umami, richness and saltiness.

2.5 ± 0.05 g of chicken powders were placed in a flask adding 100 mL of boiling water. After centrifuging for 10 min with 4500 rpm, supernate was poured into test cups for measuring. Every testing was performed with the test circulation as follows: test of reference solutions, detection of sample solutions, short washing and test of aftertaste.

Fourier transform infrared spectroscopy

The secondary structure of chicken powder protein was measured by Fourier infrared spectrum analyzer (IS10, ThermoNicoletCorporation, America).

The separation and purification of protein (Ma et al. 2017): the chicken powder samples were mixed with ethanol solution (85.0%, v/v) in a ratio of 1:11.8 (w/v) at 36.4 °C. The mixed solution was then continuously oscillated (210 rpm, 60 min) and centrifuged (1500 rpm, 10 min). The precipitate was taken and mixed with 97.5% ethanol in a ratio of 1:8.0 (w/v) at 38.4 °C. The solution was again oscillated for 30 min and centrifuged for 10 min. Finally, the precipitate was dried at 40 °C until its water content was below 5%.

Determination: chicken powder protein was mixed with potassium bromide in a ratio of 1:100 (w/w), which was fully ground by a mortar and then made into a sheeting. The sample sheeting was subjected to full-band scanning measurement, with potassium bromide as a blank.

The baseline correction, Fourier selfdeconvolution, second-order derivative, and curve fitting were analyzed via OMNIC 8.0 and Peak Fit v4.12 software.

Hygroscopicity

0.5 g powders weighted were put in pre-dried aluminum sample boxes and placed in a desiccator (contained saturated NaCl solution). The desiccator was then put in a constant temperature (at 30 °C) incubator for 24 h.

H(%)=m2-m1m1×100

Here, H (%) was powders hygroscopicity; m2 (g) was the mass of chicken powders after moisture absorption; m1 (g) was the mass of chicken powders before water absorption.

Solubility

The solubility measurement of samples was improved based on the statement of Gong et al. (2007). Samples weighted 1.0 ± 0.02 g were placed in a 50 mL flask in which 10 mL of aqua distillate (50 °C) was added. After dissolving for 60 s, 1 mL of each sample solution was drawn to weighing bottles (40 mm × 25 mm) and dried for 4 h at an oven (105 °C).

S(%)=10m2m1×100

Here, S (%) represented solubility of samples; m2 (g) was the mass of samples being kiln dried; m1 (g) was the mass of chicken powders before dissolving.

Water holding capacity

The measuring for water holding capacity was modified according to that of Kim et al. (2012). Chicken powders (weighted about 2 g) were placed in centrifugal tubes (50 mL) and dissolved by 20 mL of aqua distillate, standing for 60 min at a temperature of 25 °C. Next, centrifugation was done (4500 rpm, 30 min), obtaining the precipitate of powders.

W(%)=m2-m1m1×100

Here, W (%) was the water holding capacity of powders; m2 (g) was the sediment weight; m1 (g) represented the samples weight.

Data analysis

SPSS software (version 20.0 SPSS Inc., Chicago, IL) was utilized for analyzing experimental data. The difference of sample characteristics was evaluated by the method of one-way ANOVA. Three repetitions were carried out for each value. Significance was showed at a level of p < 0.05.

Results and discussion

Drying curves

Results showed that the drying time for VRFD (100 min) was less than MVD (120 min) for larger penetration depth of RF than that of MV. Furthermore, MVD at 915 MHz was a little faster than MVD at 2450 MHz for lower frequency contributed to deeper penetration (Torrealba-Meléndez et al. 2015).

Additionally, VD needed the longest time (180 min) to reach target moisture of sample, which may because superficial heat transfer of VD was slow due to poor convection (Chen et al. 2014) while VRFD and MVD can avoid heat transfer with positive vapor pressure from internal heating (Zhang et al. 2007). Moreover, water reduction was relatively faster at first and slowed down as moisture content below 10% (w.b.). This occurred because the terminal drying was concerned with the remove of bound moisture, which was more difficult than that of free water (Jiang et al. 2015). Furthermore, the less available moisture interacting with RF and MV lead to the less remove of inside water (Wang and Sheng 2006).

Low field NMR analysis

In our study, the moisture inside granule samples was classified into three status concerning T2 transverse relaxation time: 0.1–20 ms, strongly bound water (SBW) connecting closely to large molecular compounds; 20–100 ms, loosely bound water (LBW) linking to large molecular compounds via hydrogen bonds, 100–1000 ms, free water (FW). The LBW and SBW can be hard to be eliminate except intensively physical treatments or chemical methods are used.

As shown in Table 1, transverse relaxation time ranged from 0.1 to 1000 ms and three parts were observed—T21, T22, T23—suggesting the aforementioned three states of water (Qiao et al. 2005). The corresponding relative amplitude indicated the content of SBW, LBW, FW (Khan et al. 2016). Results showed that the dominating moisture state before drying was LBW (more than 90%) instead of FW (only 0.48%) as FW was easily removed during precooking. It was observed that T21 moved toward the shorter relaxation time, while T22 moved to the longer relaxation time after drying. Additionally, content of each part of water showed significantly difference. It could be found that the proportion of LBW of dried chicken powders decreased dramatically (approximately decreased by 35%) while that of SBW increased obviously (approximately increased by 37%). This may be due to the fact that the migration of LBW would result in cellular shrinkage and cytomembrane destruction of materials (Joardder et al. 2016).

Table 1.

Information about relaxation time spectrum of chicken powders by different drying methods

Chicken powders T21 T22 T23 SBW (%) LBW (%) FW (%)
Before drying 0.60 ± 0.01a 23.82 ± 0.12e 235.43 ± 0.28a 3.94 ± 0.02d 95.59 ± 0.31a 0.48 ± 0.1a
VD 0.37 ± 0.03c 77.53 ± 0.13a 0b 40.64 ± 0.17a 59.36 ± 0.09d 0b
VRFD 0.30 ± 0.02d 44.08 ± 0.22d 0b 37.75 ± 0.11c 62.25 ± 0.13b 0b
MVD (915 MHz) 0.42 ± 0.01b 72.27 ± 0.21c 0b 40.55 ± 0.05a 59.45 ± 0.08d 0b
MVD (2450 MHz) 0.34 ± 0.01c 74.80 ± 0.09b 0b 39.50 ± 0.22b 60.50 ± 0.14c 0b
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The different letters of a, b, c, d among them mean there is a significant difference, p < 0.05

Color

As seen in Table 2, VD chicken granules exhibited the lowest brightness with L* value of 49.21, followed by MVD (2450 MHz) and MVD (915 MHz) with L* value of 57.24 and 59.09 respectively. And VRFD granules showed the highest L* value of 62.84. Besides, significant difference of L* was observed, indicating that drying processes can exert effects on the brightness of final products. For a* and b*, VD granules showed higher redness (a*) of 4.70 and lower yellowness (b*) of 24.69 than those of MVD and VRFD, which was not in agreement with Huang et al. (2011), who stated that the b* value of restructured chips mixing potatoes with apples dried by VD was higher than those dried by MVD. In addition, the ∆E value of VD granules was the highest (32.54) while that of VRFD granules was lowest (20.12), indicating that VRFD created the minimum color destruction.

Table 2.

Color of chicken granules and powders dried by different drying methods

Samples L* a* b* ∆E
Chicken granules
VD 49.21 ± 0.04d 4.70 ± 0.02a 24.69 ± 0.03d 32.54 ± 0.07a
VRFD 62.84 ± 0.09a 4.01 ± 0.12b 28.23 ± 0.14a 20.12 ± 0.14d
MVD (915 MHz) 59.09 ± 0.08b 3.12 ± 0.05d 27.05 ± 0.14b 23.14 ± 0.10c
MVD (2450 MHz) 57.24 ± 0.06c 3.45 ± 0.06c 25.43 ± 0.21c 24.61 ± 0.17b
Chicken powders
VD 69.98 ± 0.05d 0.72 ± 0.03a 12.86 ± 0.04d –
VRFD 82.76 ± 0.08a 0.50 ± 0.01d 14.09 ± 0.09a –
MVD (915 MHz) 79.52 ± 0.06b 0.59 ± 0.03c 13.95 ± 0.08b –
MVD (2450 MHz) 78.59 ± 0.05c 0.67 ± 0.03b 13.63 ± 0.05c –
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The different letters of a, b, c, d among them mean there is a significant difference, p < 0.05

Concerning color of chicken powders, the L* by VRFD was the largest (82.76) while that by VD was the smallest (69.98). a* and b* values of the powders dried using different methods exhibited following order: VD > MVD (2450 MHz) > MVD (915 MHz) > RFD and VRFD > MVD (915 MHz) > MVD (2450 MHz) > D, respectively. Notably, the values of L* and b* ought to be higher while that of a* be lower to obtain chicken powders with better color. Consequently, VRFD can produce chicken powders with the best color.

E-nose evaluation

It was demonstrated that sulfur amino acid, cystinol and cysteine are basically required constituents for the generation of meaty flavor substances during thermal treatments (Wang et al. 2012b).

The radar chart is a relatively straightforward graphical comprehensive evaluation method. The radar chart of electronic nose analysis can directly reflect the response value of each sensor when the sample is detected. The responsiveness of each sensor during detection of chicken powders was shown in Fig. 1a. As could be found, the outlines of radar fingerprint for different samples were similar, probably because the flavor substances are similar in kind. The response of S5 (biosynthetic pyrazine aroma component) was the strongest, indicating that it was the most sensitive to the sample odor, probably because pyrazine was the main source of processed chicken flavor (Liu et al. 2015). Additionally, the responsive value of sensors for VRFD chicken powders was the largest among samples. Similar to microwave drying, RF drying is related to dielectric heating. Electromagnetic energy is coupled with solvent (water) in materials and moisture is heated and removed while drying, which generates volume heat and reduces heating resistance. Combining with vacuum, VRFD could also prevent fat oxidative decomposition, protein denaturation, browning of product color and other physicochemical reactions induced by oxygen. Consequently, VRFD had the least effect on the flavor compounds for its unique drying characteristics of high-efficiency and deep-penetration.

Fig. 1.

Fig. 1

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Electronic nose radar fingerprint chart (a) and PCA graph (b) of chicken powders dried by VD, VRFD, MVD (at 915 MHz and 2450 MHz)

Besides, Principal Component Analysis (PCA) is a multivariate statistical analysis that can be used to distinguish differences between different samples. The value of identification index (DI) reflects the flavor distinguishing ability of E-nose. The larger the DI value (at least 85%), the greater the discrimination. As shown in Fig. 1b, the DI value for different samples was 89.8%, showing electronic nose detection could be used to distinguish the odor among samples.

E-tongue evaluation

Dehydrating treatments could also have effects on the product taste. As seen in Table 3, umami was the uppermost taste, followed by saltiness and richness. Compounds of taste were basically produced via such physico-chemical reactions as denaturalization of proteins, oxidizing reactions, heat-degradation (Cao et al. 2017). Taste has also proved to be strongly associated with taste substances and its contents (Ghasemi-Varnamkhasti and Aghbashlo 2014). In our study, results showed that the primary taste of all chicken powders were umami, richness and saltiness. It may be that taste substances of these powders were basically identical to each other. Moreover, VRFD powders exhibited the most umami flavor (a value of 11.89), which may because VRFD impacted the taste components most mildly.

Table 3.

Taste of chicken powders (CP) using VD, VRFD, MVD (at 915 MHz and 2450 MHz)

Samples Sourness Astringency Aftertaste-A Umami Richness Saltiness
Reference 0 0 0 0 0 0
VD-CP − 42.53 ± 0.53cd − 7.20 ± 0.23b − 0.44 ± 0.09abcd 8.83 ± 0.34d 1.04 ± 0.74ab 4.90 ± 0.37b
VRFD-CP − 45.44 ± 0.23a − 10.21 ± 0.05a − 0.50 ± 0.09a 11.89 ± 0.23a 0.84 ± 0.12abcd 5.51 ± 0.07a
MVD (915 MHz)-CP − 43.66 ± 0.25b − 7.09 ± 0.06bc − 0.40 ± 0.05ab 9.84 ± 0.22b 0.85 ± 0.13abc 4.78 ± 0.07bcd
MVD (2450 MHz)-CP − 43.20 ± 0.33bc − 6.92 ± 0.09bcd − 0.36 ± 0.05abc 9.40 ± 0.18bc 1.06 ± 0.26a 4.88 ± 0.15bc
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The different letters of a, b, c, d among them mean there is a significant difference, p < 0.05

Fourier transform infrared spectroscopy (FTIR)

The same baseline was used in the amide I band and the amide II band of protein for the FTIR analysis. The peak for amide I band of protein ranging from 1600 to l700 cm−1 was generally applied to identify the secondary structures of protein (Carbonaro and Nucara 2010). Deconvolution of amide I band spectrum was performed, followed by second derivative and curve-fitting, to determine the relationship between the peak and secondary structures (Long et al. 2015). The correspondence between the peak and each secondary structure was as the following (Mitra et al. 2017): the band ranging from 1600 to 1640 cm−1 and 1660 to 1680 cm−1 was identified as β-sheet; the band ranging from 1640 to 1650 cm−1 was identified as random coil; the band ranging from 1650 to 1660 cm−1 was identified as α-helix; the band ranging from 1680 to 1700 cm−1 was identified as o β-turn. The fitting spectrum of the amide I band of chicken powder samples was shown in Fig. 2. Six characteristic peaks of amide I band were found in the FTIR spectrum of samples before drying. For VD and VRFD chicken powder, six characteristic peaks were also observed, while MVD (915 MHz and 2450 MHz) dried samples appeared five peaks.

Fig. 2.

Fig. 2

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Fourier spectrum from 1700 to 1600 cm−1 (upper) and Gaussian fitting curves (bottom) in amide I region of different chicken powder samples

As shown in Table 4, the secondary structures of sample protein before drying (pre-cooked chicken granules) were mainly α-helix (24.76%), β-sheet (70.23%) and β-turn (5.01%). The type of secondary structures for VD and VRFD dried samples was the same as samples before drying, while its content of each structure was different. Both VD and VRFD increased the α-helix and β-turn structure content, however decreased β-sheet content. Inversely, Guo et al. (2017) reported that RF treatment would increase the content of β-sheet compared with untreated soy protein isolate. It may be because VD and VRFD process enhanced the intramolecular hydrogen bonding while reduced the intermolecular interaction force (hydrogen bonding). Additionally, MVD (915 MHz and 2450 MHz) affected both the type and content of protein secondary structures. The α-helix structure in chicken powder was transformed into random coil structure after MVD drying, which may ascribe to the non-thermal effects of microwaves (such as electrical effects, magnetic effects, etc.). As a result, the hydrogen bond interaction within the protein molecule weakened or even disappeared while the irregular structure increased significantly.

Table 4.

The content of each secondary structures of samples obtained by different drying methods through deconvolution of FTIR

Drying methods β-sheet (%) Random coil (%) α-helix (%) β-turn (%)
Before drying 70.23 ± 0.99a 0c 24.76 ± 0.28c 5.01 ± 0.65d
VD 66.38 ± 0.71b 0c 28.21 ± 0.17b 5.41 ± 0.91d
RF-VD 62.18 ± 0.87c 0c 30.49 ± 0.76a 7.33 ± 0.28c
MVD (915 MHz) 60.55 ± 0.79d 26.78 ± 0.83b 0d 12.67 ± 0.61a
MVD (2450 MHz) 60.20 ± 0.96d 29.52 ± 0.68a 0d 10.28 ± 0.73b
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The different letters of a, b, c, d among them mean there is a significant difference, p < 0.05

Hygroscopicity

Hygroscopicity was recognized as a critical indicator of quality of the powder product during storage and post processing. The final moisture content of chicken powders obtained by VD, VRFD, MVD (915 MHz and 2450 MHz) was 4.91%, 4.26%, 4.92%, 5.01% respectively. It was found that VD powders showed the highest hygroscopicity (3.61 ± 0.03%), next by MVD (915 MHz and 2450 MHz) (2.55 ± 0.11%, 2.54 ± 0.09% respectively) and VRFD powders had the lowest hygroscopicity (2.17 ± 0.04%). Generally, the product showing high degree of hygroscopicity possess higher amounts of bound water while less amounts of free water. Mostly because bound water inside the positive hole in the dehydrated matters shows lower rotational degree of freedom, equilibrium vapor pressures and absorption of energy compared with free water. High degree of moisture absorption could be showed once plenty of free water occurs inside the dehydrated materials (Xie and Puri 2006). Therefore, the less level of free water inside VRFD powders contributed to lower hygroscopicity.

Solubility

Results showed that chicken powders showed inferior solubility, ranging from 20.98 to 24.01%, which was a little opposite to the solubility of onion powders (Kim et al. 2007). Solubility of VRFD powders was the minimum (20.98 ± 0.08%), followed by 915 MHz and 2450 MHz MVD (21.04 ± 0.17% and 21.12 ± 0.21%, respectively). Whereas VD powders exhibited the maximum (24.01 ± 0.12%). Different drying means could significantly influenced the solubility of chicken powders (p < 0.05), which was inconsistent with the conclusion that solubility of jujube powder was not obviously affected by drying methods (Kim et al. 2012). For fruit-vegetable powder, sugar content may be the dominant factor that affects solubility since sugar is the main soluble substance of the products (Shittu and Lawal 2007). It was resulted that all chicken powders obtained showed poor solubility, which may due to fact that powders itself contains some amount of insoluble components like protein. Different drying processes could cause various changes of protein content, which may be the main reason for different solubility.

Water holding capacity of chicken powders

It was found that the water holding capacity (WHC) of VRFD powders were higher (254.80 ± 0.24%) than those of MVD (915 MHz) (249.50 ± 0.16%), VD (243.75 ± 0.19%) and MVD (2450 MHz) (242.40 ± 0.11%) powders. Generally, the WHC depend on characteristics of surface, thickness, electric charge densities, and lyophobic/hydrophil properties of particles (Dehnad et al. 2016). The higher WHC of VRFD powders may be attributed to smaller physicochemical changes particularly protein denaturation during VRFD with more uniform heating and shorter drying time.

Conclusion

Characteristics of chicken powders obtained using vacuum drying (VD), vacuum radio frequency drying (VRFD) and microwave (915 MHz and 2450 MHz) vacuum drying (MVD) methods were compared. On the basis of the experiment research, VRFD technique could significantly reduce the drying time required for chicken powders. Overall, VRFD of chicken powders makes desirable natural food ingredient with better flavor and color, along with the lowest hygroscopicity and the best water holding capacity. It was also observed that, VRFD powders had the most desirable taste than the other three powders. Moreover, VRFD had less effect on protein secondary structures compared with MVD. We draw the conclusion that VRFD is a prospective way to obtain high-quality products of chicken powders. However, more investigation about scale-up and cost-effectiveness are suggested to be conducted before commercialization.

Acknowledgements

This work was financially supported by National Key R&D Program of China (Contract No. 2017YFD0400501), National First-class Discipline Program of Food Science and Technology (No. JUFSTR20180205), Jiangsu Province Key Laboratory Project of Advanced Food Manufacturing Equipment and Technology (No. FMZ201803).

Footnotes

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References

  1. Avramidis S, Liu F. Drying characteristics of thick lumber in a laboratory radio-frequeocy/vacuum dryer. Dry Technol. 1994;12:1963–1981. doi: 10.1080/07373939408962215. [DOI] [Google Scholar]
  2. Avramidis S, Zwick RL, Neilson JB. Commercial-scale RF/V drying of softwood lumber. 1. Basic kiln design considerations. For Prod J. 1996;46:44–51. [Google Scholar]
  3. Balzarini MF, Reinheimer MA, Ciappini MC, Scenna NJ. Comparative study of hot air and vacuum drying on the drying kinetics and physicochemical properties of chicory roots. J Food Sci Technol. 2018;55:4067–4078. doi: 10.1007/s13197-018-3333-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Cao X, Zhang M, Qian H, Mujumdar AS, Wang Z. Physicochemical and nutraceutical properties of barley grass powder microencapsulated by spray drying. Dry Technol. 2017;35:1358–1367. doi: 10.1080/07373937.2017.1332074. [DOI] [Google Scholar]
  5. Carbonaro M, Nucara A. Secondary structure of food proteins by Fourier transform spectroscopy in the mid-infrared region. Amino Acids. 2010;38:679. doi: 10.1007/s00726-009-0274-3. [DOI] [PubMed] [Google Scholar]
  6. Chaland B, Mariette F, Marchal P, Certaines JD. 1H nuclear magnetic resonance relaxometric characterization of fat and water states in soft and hard cheese. J Dairy Res. 2000;67:609. doi: 10.1017/S0022029900004398. [DOI] [PubMed] [Google Scholar]
  7. Chen H, Zhang M, Fang Z, Wang Y. Effects of different drying methods on the quality of squid cubes. Dry Technol. 2013;31:1911–1918. doi: 10.1080/07373937.2013.783592. [DOI] [Google Scholar]
  8. Chen F, Zhang M, Mujumdar AS, Jiang H, Wang L. Production of crispy granules of fish: a comparative study of alternate drying techniques. Dry Technol. 2014;32:1512–1521. doi: 10.1080/07373937.2014.903410. [DOI] [Google Scholar]
  9. Dehnad D, Jafari SM, Afrasiabi M. Influence of drying on functional properties of food biopolymers: from traditional to novel dehydration techniques. Trends Food Sci Technol. 2016;57:116–131. doi: 10.1016/j.tifs.2016.09.002. [DOI] [Google Scholar]
  10. Ghasemi-Varnamkhasti M, Aghbashlo M. Electronic nose and electronic mucosa as innovative instruments for real-time monitoring of food dryers. Trends Food Sci Technol. 2014;38:158–166. doi: 10.1016/j.tifs.2014.05.004. [DOI] [Google Scholar]
  11. Gong Z, Zhang M, Mujumdar AS, Sun J. Spray drying and agglomeration of instant bayberry powder. Dry Technol. 2007;26:116–121. doi: 10.1080/07373930701781751. [DOI] [Google Scholar]
  12. Guo C, Zhang Z, Chen J, Fu H, Subbiah J, Chen X, Wang Y. Effects of radio frequency heating treatment on structure changes of soy protein isolate for protein modification. Food Bioprocess Technol. 2017;10:1–10. doi: 10.1007/s11947-017-1923-2. [DOI] [Google Scholar]
  13. Haque KE. Microwave energy for mineral treatment processes—a brief review. Int J Miner Process. 1999;57:1–24. doi: 10.1016/S0301-7516(99)00009-5. [DOI] [Google Scholar]
  14. Huang L-l, Zhang M, Mujumdar AS, Lim R-x. Comparison of four drying methods for re-structured mixed potato with apple chips. J Food Eng. 2011;103:279–284. doi: 10.1016/j.jfoodeng.2010.10.025. [DOI] [Google Scholar]
  15. Jiang H, Zhang M, Mujumdar AS, Lim RX. Comparison of the effect of microwave freeze drying and microwave vacuum drying upon the process and quality characteristics of potato/banana re-structured chips. Int J Food Sci Technol. 2015;46:570–576. doi: 10.1111/j.1365-2621.2010.02523.x. [DOI] [Google Scholar]
  16. Joardder MUH, Karim A, Kumar C, Brown RJ. Porosity: establishing the relationship between drying parameters and dried food quality. Berlin: Springer; 2016. [Google Scholar]
  17. Khan MIH, Wellard RM, Nagy SA, Joardder MUH, Karim MA. Investigation of bound and free water in plant-based food material using NMR T 2 relaxometry. Innov Food Sci Emerg Technol. 2016;38:252–261. doi: 10.1016/j.ifset.2016.10.015. [DOI] [Google Scholar]
  18. Kim HR, Seog EJ, Lee JH, Rhim JW. Physicochemical properties of onion powder as influenced by drying methods. J Korean Soc Food Sci Nutr. 2007;36:342–347. doi: 10.3746/jkfn.2007.36.3.342. [DOI] [Google Scholar]
  19. Kim SH, Choi YJ, Lee H, Lee S-H, Ahn J-B, Noh B-S, Min SC. Physicochemical properties of jujube powder from air, vacuum, and freeze drying and their correlations. J Korean Soc Appl Biol. 2012;55:271–279. doi: 10.1007/s13765-012-1039-3. [DOI] [Google Scholar]
  20. Liu J, Liu M, He C, Song H, Feng C. Effect of thermal treatment on the flavor generation from Maillard reaction of xylose and chicken peptide: food science + technology. Science + technologie alimentaire. LWT Food Sci Technol. 2015;64:316–325. doi: 10.1016/j.lwt.2015.05.061. [DOI] [Google Scholar]
  21. Long G, Yuan J, Pan H, Sun Z, Li Y, Qin G. Characterization of thermal denaturation structure and morphology of soy glycinin by FTIR and SEM. Int J Food Prop. 2015;18:763–774. doi: 10.1080/10942912.2014.908206. [DOI] [Google Scholar]
  22. Ma T, Zhu H, Jing W, Qiang W, Yu L, Sun B. Influence of extraction and solubilizing treatments on the molecular structure and functional properties of peanut protein. LWT Food Sci Technol. 2017;79:197–204. doi: 10.1016/j.lwt.2017.01.037. [DOI] [Google Scholar]
  23. Marshall MG, Metaxas AC. Radio frequency assisted heat pump drying of crushed brick. Appl Therm Eng. 1999;19:375–388. doi: 10.1016/S1359-4311(98)00058-1. [DOI] [Google Scholar]
  24. Mitra B, Rinnan Å, Ruiz-Carrascal J. Tracking hydrophobicity state, aggregation behaviour and structural modifications of pork proteins under the influence of assorted heat treatments. Food Res Int. 2017;101:266. doi: 10.1016/j.foodres.2017.09.027. [DOI] [PubMed] [Google Scholar]
  25. Mujumdar AS, Law CL. Drying technology: trends and applications in postharvest processing. Food Bioprocess Technol. 2010;3:843–852. doi: 10.1007/s11947-010-0353-1. [DOI] [Google Scholar]
  26. Mujumdar AS, Chunglim L, Zude M, Schlüter O, Rosenthal A. Drying technology: trends and applications in postharvest processing. Food Bioprocess Technol. 2010;3:843–852. doi: 10.1007/s11947-010-0353-1. [DOI] [Google Scholar]
  27. Qiao Y, Galvosas P, Callaghan PT. Diffusion correlation NMR spectroscopic study of anisotropic diffusion of water in plant tissues. Biophys J. 2005;89:2899. doi: 10.1529/biophysj.105.064709. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Roknul ASM, Zhang M, Mujumdar AS, Wang Y. A comparative study of four drying methods on drying time and quality characteristics of stem lettuce slices (Lactuca sativa L.) Dry Technol. 2014;32:657–666. doi: 10.1080/07373937.2013.850435. [DOI] [Google Scholar]
  29. Shittu TA, Lawal MO. Factors affecting instant properties of powdered cocoa beverages. Food Chem. 2007;100:91–98. doi: 10.1016/j.foodchem.2005.09.013. [DOI] [Google Scholar]
  30. Torrealba-Meléndez R, Sosa-Morales ME, Olvera-Cervantes JL, Corona-Chávez A. Dielectric properties of beans at different temperatures and moisture content in the microwave range. Int J Food Prop. 2015;19:564–577. doi: 10.1080/10942912.2015.1038565. [DOI] [Google Scholar]
  31. Wang J, Sheng KC. Far-infrared and microwave drying of peach. LWT Food Sci Technol. 2006;39:247–255. doi: 10.1016/j.lwt.2005.02.001. [DOI] [Google Scholar]
  32. Wang J, Luechapattanaporn K, Wang Y, Tang J. Radio-frequency heating of heterogeneous food—meat lasagna. J Food Eng. 2012;108:183–193. doi: 10.1016/j.jfoodeng.2011.05.031. [DOI] [Google Scholar]
  33. Wang R, Yang C, Song H. Key meat flavour compounds formation mechanism in a glutathione–xylose Maillard reaction. Food Chem. 2012;131:280–285. doi: 10.1016/j.foodchem.2011.08.079. [DOI] [Google Scholar]
  34. Wang Y, Zhang M, Mujumdar AS, Mothibe KJ, Roknul Azam SM. Study of drying uniformity in pulsed spouted microwave-vacuum drying of stem lettuce slices with regard to product quality. Dry Technol. 2013;31:91–101. doi: 10.1080/07373937.2012.721431. [DOI] [Google Scholar]
  35. Xie X, Puri VM. Uniformity of powder die filling using a feed shoe: a review. Part Sci Technol. 2006;24:411–426. doi: 10.1080/02726350600934663. [DOI] [Google Scholar]
  36. Zhang J, Min Z, Liang S, Fang Z. Microwave-vacuum heating parameters for processing savory crisp bighead carp (Hypophthalmichthys nobilis) slices. J Food Eng. 2007;79:885–891. doi: 10.1016/j.jfoodeng.2006.03.008. [DOI] [Google Scholar]
  37. Zhang L, Wang Z, Shi G, Yang H, Wang X, Zhao H, Zhao S. Effects of drying methods on the nutritional aspects, flavor, and processing properties of Chinese chestnuts. J Food Sci Technol. 2018;55:3391–3398. doi: 10.1007/s13197-018-3227-6. [DOI] [PMC free article] [PubMed] [Google Scholar]

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