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The effects of freeze-drying process parameters on Broiler chicken breast meat
LWT - Food Science and Technology 42 (2009) 1325–1334
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The effects of freeze-drying process parameters on Broiler chicken breast meat Jelena Babic´ a, Marı´a J. Cantalejo b, *, Cristina Arroqui b a b
Faculty of Technology, University of Banja Luka, 78 000 Banja Luka, Bosnia & Herzegovina Department of Food Technology, School of Agriculture Engineering, Public University of Navarre, Campus de Arrosadia, E-31006 Pamplona, Navarre, Spain
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 August 2008 Received in revised form 27 March 2009 Accepted 30 March 2009
Freeze-dried meat can be stored for unlimited periods retaining the majority of their physical, chemical, biological and sensorial properties as in the fresh state. However, adequate process conditions must be applied to prevent quality problems in the product. The aim of this work was to study the effect of freeze-drying process parameters on the quality of Broiler chicken breast meat. Therefore, different meat thicknesses, speed of freezing, time of drying phases and pressure were assayed. Physical and sensory analyses were carried out on treated meat samples. Results showed that sample thickness was critical for the determination of process conditions. The study has demonstrated that it is possible to obtain freeze-dried poultry meat that looks and tastes similar to fresh poultry meat when the right process conditions for the sample’s thickness are applied. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Freeze-drying Chicken breast meat Rehydration Freezing
1. Introduction Poultry meat is very perishable and its stability and microbiological security is based on the combination of various factors (hurdles) in order not to be contaminated by microorganisms. In the design of new raw products, the three following barriers were considered (ozonization, freeze-drying and packaging of the product in modified atmospheres), in order to obtain a new food product from chicken by using gas ozone, first to get a very hygienic product, with a high nutritional value. Afterwards, freeze-drying would be applied to avoid cold chain, reduce sample-size and extend the lifespan of these products, which might be used in the making of soups, consomme´, sauces such as Bolognese, in stews and casseroles, etc. In this case, the energy costs would be reduced, because time for cooking products would be shorter than in the case of traditional foods. Afterwards, the products would be packaged in modified atmosphere to obtain enough safety factors for these new products to guarantee the consumption of chicken that is safer, longer lasting and accepted by consumers. To achieve this, the conditions which most affect freeze-drying were studied with the aim of optimizing each treatment separately and, afterwards, combined. Freeze-drying (lyophilization) has been extensively used to process food since the end of the nineteenth century. Freeze-drying
* Corresponding author. Tel.: þ34 948 169 135; fax: þ34 948 169 893. E-mail address: [email protected] (M.J. Cantalejo). 0023-6438/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2009.03.020
is an effective method to extend the average lifespan of food, given that it prevents the deterioration due to microbial growth or oxidations (Barbosa & Vega-Mercado, 2000). Besides, the characteristics of rehydrated freeze-dried products could be similar to those of fresh ones. The process takes place in three distinct stages: pre-freezing, sublimation or primary drying and desorption or secondary drying (Baker, 1997), in which drying continues until the desired moisture content of the product is achieved. These products do not require cold chain and only have 10–15% of original weight that makes their storage, distribution and commercialization easy. However, the deep freezing and low pressures applied along with the duration (1–3 days) of the process make freeze-drying treatments very expensive. The use of freezedrying in food industries is then restricted to high added-value products such as coffee, tea and infusions, ingredients for ready-toeat foods (vegetables, fruit powders, pasta, meat, cheese starter cultures, fish, shrimps, etc.) and several aromatic herbs (Adam, 2004; Hammami & Rene, 1997; Stawczyk, Sheng, & Romuald, 2004). The freeze-dried meat products, which have been adequately packaged, can be stored for unlimited periods retaining the majority of their physical, chemical, biological and sensorial properties as in the fresh state (Girard & Omolosho, 1983). Freeze-drying takes place at low temperatures and the drying is produced mainly by direct sublimation of ice, avoiding the translocation of salts, creating a honeycomb texture and relatively little histological change. Freeze-drying does not alter the biological value of the meat proteins and, indeed, may enhance it. Nevertheless, there is a loss of
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60
FREEZING
1,000
SECONDARY DRYING
PRIMARY DRYING
0,900
40
0,800 20
0
0,600 0,500
-20
0,400
-40
Pressure (mb)
Temperature (°C)
0,700
0,300 -60 0,200 -80
0,100 0,000 1600
-100 0
200
400
600
800
1000
1200
1400
Time (min) Fig. 1. Process scheme: evolution of temperature of chicken breasts samples and some of the process parameters during the freeze-drying in the freeze drier Lyobeta 25. Temperature of the fluid, temperature of the condenser, temperature of the product and pressure in the process chamber.
about 30% of the thiamine content of the meat during freeze-drying, but this would also occur when cooking in any case. The process causes similar loss of riboflavin in mutton, but not in beef or pork (Lawrie, 1985). A major defect of freeze-dehydrated meats is the typical deterioration of texture (Bird, 1965). The loss of textural qualities in meats and fish is often difficult to explain. In comparison with fresh or frozen meat, freeze-dried meat is somewhat lower in tenderness and juiciness (Karel, 1968). The changes in texture may be due to one or all of the following events in the actomyosin complex: aggregation or cross-linking of proteins; denaturizing of proteins, followed by aggregation; interaction of the native or denaturized proteins with lipids or carbohydrates (Connell, 1957). Harper and Tappel (1957) also reported that texture and poor rehydration were
the principal problems in freeze-dried meat. They studied the effects of time and temperature of cooking on freeze-dehydrated chicken and observed that fresh meat was significantly more tender than that obtained after freeze-dehydrated treatments. These results agree with those of Seltzer (1961), Sosebee, May, and Powers (1964), Sosebee, May, and Schmittle (1964), and Wells, May, and Powers (1962) who noted toughening effects due to freeze dehydration. Likewise, porosity of freeze-dried meat samples is much higher than the air-dried and vacuum dried samples (Maurer, Baker, & Vadehra, 1972). King, Wing, and Sandall (1968) studied the effects of freezing rate on rehydration of freeze-dried turkey meat with results ranging from 87 to 95% of rehydration. The effect of freezing rate on the structure of the samples was clearly seen, being
Table 1 Experiment design to study: (a) the effect of sample thickness; (b) freezing rate, total time of freeze-drying and pressure; (c) different time of primary drying at 0 C and 10 C. (a) Primary drying at 10 C (h)
Total primary drying (h)
Secondary drying (h)
Pressure (Pa)
8
10
18
–
25
Fast (3 h)
12
12
24
7
30
Thickness (cm)
Freezing rate
Primary drying at 0 C (h)
Primary drying at 10 C (h)
Total primary drying (h)
Secondary drying (h)
Pressure (Pa)
Treatment 3
Thin (0.7 0.2)
Slow (6 h)
12
6, 8.5, 11
18, 20.5, 23
7
25
Treatment 4
Thin (0.7 0.2)
Slow (6 h) Fast (3 h)
12
6, 8.5, 11
18, 20.5, 23
7 7
30 30
Thickness (cm)
Freezing rate
Primary drying at 0 C (h)
Primary drying at 10 C (h)
Total primary drying (h)
Secondary drying (h)
Pressure (Pa)
Thin (0.7 0.2) Thin (0.7 0.2)
Slow (6 h) Slow (6 h)
12 8
8.5 12.5
20.5 20.5
– –
30 30
Thickness (cm)
Freezing rate
Treatment 1
Thin (0.7 0.2) Thick (1.3 0.2)
Slow (6 h)
Treatment 2
Thin (0.7 0.2) Thick (1.3 0.2)
Primary drying at 0 C (h)
(b)
(c)
Treatment 5 Treatment 6
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Table 2 Analyses carried out on meat samples during the study.
Fresh meat Freeze-dried rehydrated meat Freeze-dried meat Fresh cooked meat Freeze-dried rehydrated and cooked meat
Humidity
Aw
x
x
x
x
influenced by the kind of meat studied. Luyet (1962) studied the effect of freezing on pore size in freeze-dried beef and found the average pore width to be 2 mm for fast freezing, 5–10 mm for intermediate rates and 150 mm for very slow freezing rates. Freezing rates affected both surface area and pore size distribution of freeze-dried poultry meat, although it had little effect on total porosity. Also Kuprianoff (1962) observed that the more slowly a material was frozen, the higher the freeze-drying rates, due to an increase of the pore size (an effect of growth of large ice crystals). However, slow freezing caused a decrease in the rehydration rate in meats due to toughening of the muscle tissue. Different studies demonstrated that the colour of a freeze-dried product was also directly affected by freezing conditions. Farkas and Singh (1991) found that quick frozen pieces of chicken meat maintained a whiter colour than those frozen more slowly (Stone & May, 1969). King et al. (1968) also observed that the appearance of freeze-dried turkey meat seemed to depend on freezing conditions. In addition, pressure is another factor that could influence the product quality and the duration of the process. At low pressures (below 10–20 mm Hg), the drying is rate-limited by heat conduction, but at higher pressures freeze-drying rates are limited by mass transfer (King et al., 1968). The aim of this work was to study the effect of freeze-drying process factors on the quality of Broiler chicken breast meat, one of
Rehydratation
pH
Texture
Colour
Sensory analyses
x x
x x x x x
x x
x x x
the most consumed and perishable meats. To reach this objective, different meat thickness, speed of freezing, time of freeze-drying phases and pressure were assayed. Therefore, the planned goals correspond to a type of applied research orientated to finding the process conditions to be applied to this type of food widely consumed freshly in Spain, but in fact without any treatment that would allow a longer sale period in the case of natural catastrophes (earthquakes, floods,.), export to third countries, military campaigns, mountain climbers, scarcity in electricity supply. For these reasons, the final goal is to develop new raw products from fresh chicken meat, safe from the sanitary point of view, with a high nutritional value, no additives added and with long shelf-life at room temperature. 2. Materials and methods 2.1. Raw matter and sample preparation Broiler chicken breast meat was obtained from Pollos Iriarte S.A (Orcoyen, Navarre, Spain). The age of the chicken before slaughtering was 43 2 days with 2.40 0.28 kg of weight. Chicken meat was transported from the supplier to the laboratory in less than 24 h after slaughtering and stored at 4 C until used. The samples were prepared for analyses by cutting and removing fat parts.
Fig. 2. (a) Principle of work by Kramer shear cell. (b) Maximum force peak measurement by Kramer shear cell (Fmax ¼ 172.68 N) (http://www.instron.us/wa/applications/food/ testing.aspx?ref¼http).
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Table 3 Effect of chicken breast meat thickness on humidity, water activity and rehydration of freeze-dried samples. Humidity (%)
Water activity
Thin Fresh meat Treatment 1 Treatment 2
Thick
Thin
Thick
0.987 0.002 18.83 1.59 2.83 0.36
0.291 0.010 0.055 0.007
2.2. Freeze-drying treatment, samples storage and preparation for analyses The freeze drier used for the process was a Lyobeta 25 (Telstar Industrial, S.L., Terrasa, Barcelona). The different phases of the freeze-drying process are shown in Fig. 1. Preliminary experiments were done to define process conditions to be applied for breast meat lyophilization. Firstly, different thicknesses were assayed in order to compare extreme process conditions to identify the most adequate ones for further experiments (Table 1a). Likewise, the different parameters of the freezedrying process assayed in this study were the following ones: freezing rate (time to reach 45 C in the fluid), time and pressure of drying (Table 1b), and time of primary drying at 0 C and 10 C, respectively (Table 1c). Secondary drying process, when used, was carried out at 35 C and at maximum vacuum (Fig. 1). After lyophilization process, samples were packaged in impermeable plastic trays made of PPevoPP (Ilpra Systems, Barcelona, Spain) filled with nitrogen. Samples were coded and stored in a dark place at room temperature. Freeze-dried samples had to be rehydrated and cooked in order to be analyzed. Sample rehydration was performed in tap water at room temperature. The duration of rehydration process was fixed in 3 h and 3.5 h for thin and thick samples, respectively, as after that time period there was no more absorption of water by the samples. Percentage of rehydration was calculated using the following expression:
rehydrationð%Þ ¼
Thick
72.41 0.13 9.94 1.78 3.48 0.44
Rehydratation (%)
Thin
ðWr Wl Þ 100 ðW0 Wl Þ
– 0.855 0.075 0.170 0.035
53.35 4.47 61.43 5.44
43.81 5.81 39.80 3.24
Wr: weight of rehydrated sample (g); Wl: weight of lyophilizated sample (g); W0: weight of fresh sample (g). To be cooked, samples were packaged in impermeable plastic bags and introduced in a water bath at 80 C for 4 min 30 s and 4 min for thick and thin samples, respectively.
2.3. Analyses of samples Different analyses were carried out on meat samples (Table 2). Humidity was determined by the ISO R-1442 method (AOAC, 1975), using the gravimetric method. Water activity was determined by means of a hygrometer NOVASINA RS-232 C. The pH value was measured by a pH-meter CRISON pH 25 with combined electrode which penetrates the meat sample. Colour was measured in different parts (same side) of meat samples according to the CIELab system (L*, a*, b* values). A Minolta spectrophotometer CM-508d, with white standard was employed for the measurements. The multi-blade Kramer shear cell was commonly used for measuring poultry meat tenderness (Heath & Owens, 1997). A Texture Analyzer TA-XT2i with 5 bladed Kramer shear cell was employed to measure maximum force of penetration (N) into the sample (toughness) at certain distance (mm) (Fig. 2). It simulates the force needed for chewing and gives information about hardness of sample. Sensory characteristics of meat samples (springiness, deformation, toughness, juiciness and chewiness) were evaluated by five trained people. Each of these sensory characteristics was evaluated by a scale from 0 to 5, where range 0–1 was
40
1,000 PRIMARY DRYING
0,900
20 0,800
FREEZING
0,700 0,600
-20
0,500 -40
0,400
Pressure (mb)
Temperature (°C)
0
0,300
-60
0,200 -80 0,100 -100
0,000 0
200
400
600
800
1000
1200
1400
1600
Time (min) Fig. 3. Evolution of temperature of thin and thick chicken breasts samples and some of the process parameters during treatment 1. Temperature of the fluid, temperature of the thin product, temperature of the thick product and pressure in the process chamber. of the condenser,
temperature
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1,000
60 SECONDARY DRYING
0,900
40 PRIMARY DRYING
0,700 0
0,600 0,500
-20
0,400
-40
Pressure (mb)
Temperature (°C)
0,800
FREEZING
20
0,300 -60 0,200 -80
0,100
-100 0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
0,000 2400
Time (min) Fig. 4. Evolution of temperature of thin and thick chicken breasts samples and some of the process parameters during treatment 2. Temperature of the fluid, temperature of the thin product, temperature of the thick product and pressure in the process chamber. of the condenser,
described as very low, 1–2 low, 2–3 medium, 3–4 high and 4–5 very high. Process parameters and their influence were considered for statistical analyses with 95% level of confidence. ANOVA Analyses, Multifactor Analyses of Variance and Multiple Range Tests were carried out for all data, using the Statgraphic Plus program (version 5.1, December 2001. Rockville, Maryland, USA). 3. Results and discussion The effect of the different product and process parameters assayed were analysed from the results of the physical, chemical and sensory analyses carried out in treated samples. 3.1. Effect of chicken breast meat thickness Freeze-dried (treated meat – TM) thin samples showed lower moisture content and water activity than those of thick samples (Table 3) when the less intensive freeze-drying treatment was applied (treatment 1, without secondary drying). Water activity of freeze-dried thick samples was very high (0.855 0.075) and very close to fresh meat (0.987 0.002), that means that liophilization was not completed. Contrary to thin samples, the temperature of thick ones did not reach 0 C which corresponds to the fluid
temperature
temperature at the end of the primary drying (Fig. 3). Likewise, rehydratation was not adequate, and would affect negatively the texture of samples (Tables 3 and 5). Therefore, depending on the conditions of the process, either a longer duration of primary drying or secondary drying should be included for thick samples. However, when a more intensive treatment was applied (treatment 2, Table 1a), there were no statistically significant differences in moisture content between freeze-dried thin and thick samples (Table 3), which would mean that sublimation was completely reached, and this is in accordance with what was observed in Fig. 4 (temperature of thick samples exceeded 0 C at the end of the primary drying). Despite that, the rehydration percentage of thick samples treated when treatment 2 was employed was much lower than in thin ones due mainly to the sample thickness. These results agree with those obtained by Harper and Tappel (1957), who pointed out that poor rehydration was one of the main problems in freeze-dried meat. Thickness of TM had an influence on their colour. In fact, statistically significant differences were found in L* and b* parameters from both thickness at the 95.0% confidence level. In general, L*, a* and b* values of TRCM were closer to those of FCM samples when samples were thinner (Table 4). On the one hand, texture analyses applied in samples after treatment 1 showed that cooked and rehydrated freeze-dried thin
Table 4 Colour of control and treated thin and thick samples of chicken meat. Treatment 1
Treatment 2
L*
a*
b*
L*
a*
b*
Fresh meat FCM
50.93 0.90 79.73 0.77
1.65 0.40 1.46 0.56
9.34 0.89 14.70 0.25
49.73 1.63 79.34 1.48
1.80 0.53 1.28 0.53
9.08 0.99 15.68 0.53
Thin TM TRM TRCM
73.53 5.92 62.09 3.40 76.40 2.40
2.99 0.34 4.27 0.41 1.33 0.13
14.62 1.97 14.49 2.39 15.54 0.50
78.69 1.76 67.64 1.34 70.98 4.04
1.88 0.13 3.11 0.46 0.49 0.19
17.64 0.52 16.07 1.60 14.55 0.83
Thick TM TRM TRCM
80.89 1.74 55.50 6.84 77.63 2.46
1.96 0.23 2.52 0.66 1.29 0.50
15.95 0.58 11.68 3.93 17.07 2.23
80.47 2.61 66.97 2.49 64.92 6.68
2.15 0.62 4.17 0.76 0.34 0.29
17.26 1.03 17.81 1.49 15.49 1.48
FCM: fresh cooked meat; TM: treated meat; TRM: treated rehydrated meat; TRCM: treated rehydrated cooked meat.
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Table 5 Sensory analyses of cooked chicken meat samples of different thickness. Samples
Springiness
Deformation
Hardness
Juiciness
Chewiness
Acceptability
FCM
Very high
Very low
Very low
Very high
Very high
A
Treatment 1 TRCM – thin TRCM – thick
High Low
Medium High
Medium Very high
Medium Very low
High Very low
A NA
Treatment 2 TRCM – thin TRCM – thick
Low Very low
Medium Medium
High High
Very low Very low
Very low Very low
NA NA
FCM: fresh cooked meat; TRCM: treated rehydrated and cooked meat; A: acceptable; NA: non-acceptable.
samples (27649.5 N) were tougher and harder for consumption than thick ones (17440.8 N). Moreover, both treated rehydrated and cooked meat (TRCM) showed a higher maximum strength than fresh cooked meats (FCM) (4292.1 N). Nevertheless, in treatment 1 no correlation was observed between the results of texture and those obtained by the sensory analysis (Table 5). In fact, the strength applied on thin samples was higher than on thick samples, whereas in the case of sensorial analyses thin samples were scored as juicier and less hard than thick ones, probably due to their low level of rehydration (Table 3). On the other hand, members of the sensory panel described TRCM thick samples of chicken meat obtained after the application of treatments 1 and 2 as very hard and unacceptable for consumption (Table 5). 3.2. Effect of freeze-drying parameters: freezing rate, time of drying and pressure From the results obtained in the previous section, thin samples and times of primary drying above 18 h were selected to assay the effect of freezing rate, time of drying and pressure on quality of freeze-dried chicken breast samples (Table 1b). Concerning humidity and water activity, fast-frozen samples presented, in general, lower values of humidity and water activity than slow-frozen ones that were freeze-dried under similar conditions (Table 6). For each treatment, humidity and aw were reduced as drying time increased. Multifactor analyses of variance Type III Sums of Squares showed that freezing rate and time of drying had statistically significant influence on humidity and water activity (p < 0.05). It was observed that the TM samples treated up to 20.5 h at the lowest pressure (treatment 3, 25 Pa) had higher values of
humidity and aw than those treated at 30 Pa. However, there was not a clear effect of the different pressures assayed either on humidity or on water activity of TM samples (Table 6), probably due to the fact that the differences in pressure were not so high. Regarding rehydratation, slow-frozen samples had higher values of rehydratation percentage than fast-frozen ones, although the latter presented more variability. Rehydration was better when samples were treated using the highest pressure. In the case of colour, L* and b* values of treated rehydrated meat (TRM) were much higher than those of fresh ones, showing more brightness and yellowness (Fig. 5). However, for a* parameter, only a difference was noted when the smallest pressure was applied (25 Pa). Freeze-dried, rehydrated and afterwards cooked samples (TRCM) had more similar L* and b* values to fresh cooked meat samples (FCM), especially when treated at the highest pressure (30 Pa, treatment 4) (Fig. 6). However, in the case of a* value, important differences were observed between TRCM and FCM samples. Contrary to fresh samples, a* value of treated samples when rehydrated and cooked (TRCM) was lower (less red) than the obtained in FCM. Results showed that there were no differences on a* (red), b* (yellow) and L* (lightness) values between frozen samples at different rates. Thus, in the conditions assayed of these treatments, a clear effect of the freezing rate on samples’ colour was not observed for the assayed pressures, although Stone and May (1969) found that quick frozen pieces of chicken meat maintained a whiter colour than those frozen more slowly and, when a fast freezing took place, a larger number of crystals and of a smaller size with a more luminous colour were obtained. In general, no effect of the duration of primary drying on colour was observed, except for the component a* in TRCM samples.
Table 6 Effect of freezing rate, time of drying and pressure on humidity, water activity and rehydration of freeze-dried samples. Treatment
Fresh meat
Humidity (%)
Pressure (Pa)
Slow freezing
Fast freezing
Duration of drying (h) 18 3 4
Duration of drying (h) 23
31a
18
20.5
23
31a
5.38 0.53 3.75 0.94
3.53 0.31 2.47 0.16
2.32 0.30 1.89 0.12
1.64 0.74 1.66 0.08
3.12 0.92
2.11 0.13
1.70 0.55
1.44 0.35
25 30
Water activity 3 0.981 0.003 4 0.984 0.001
0.426 0.028 0.126 0.018
0.234 0.131 0.156 0.014
0.080 0.005 0.125 0.008
0.047 0.017 0.038 0.013
0.123 0.018
0.148 0.013
0.094 0.003
0.053 0.003
25 30
Rehydratation (%) 3 4
40.38 4.20 75.35 1.17
51.17 8.10 76.87 4.23
56.80 11.14 73.48 3.65
57.47 6.18 87.79 6.07
74.21 9.75
75.66 6.03
81.15 7.66
73.30 4.64
25 30
a
72.5 0.33 73.4 0.28
20.5
Secondary drying included.
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100 90
Treatment 3
Treatment 4
slow freezing
80
fast freezing
slow freezing
70
L*
60 50 40 30 20 10 0 Fresh meat
25 mb- 25 mb- T25 mb- 25 mbSF-18h SF-20,5h SF-23h SF- sec
30 mb- 30 mb- 30 mbSF-18h SF- 20.5h SF- 23h
30 mbSF- sec
30 mb- 30 mb- 30 mbFF- 18h FF- 20.5h FF- 23h
30 mbFF- sec
7
Treatment 3 Treatment 4
slow freezing
6
fast freezing
slow freezing
5
a*
4 3 2 1 0 Fresh meat
25 mbSF-18h
25 mbSF-20,5h
25 mbSF-23h
30 mb30 mb30 mbSF-18h SF- 20.5h SF- 23h
25 mbSF- sec
30 mb30 mb30 mbFF- 18h FF- 20.5h FF- 23h
30 mbSF- sec
30 mbFF- sec
25
Treatment 3 Treatment 4
slow freezing
fast freezing
slow freezing
20
b*
15
10
5
0 Fresh meat
25 mb25 mb25 mbSF-18h SF-20,5h SF-23h
25 mbSF- sec
30 mb30 mb30 mbSF-18h SF- 20.5h SF- 23h
30 mbSF- sec
30 mb30 mb30 mbFF- 18h FF- 20.5h FF- 23h
30 mbFF- sec
Fig. 5. Effect of freezing rate, time of drying and pressure on colour of rehydratated freeze-dried samples (TRM). SF: slow freezing rate, FF: fast freezing rate, Sec: with secondary drying. Error bars are the standard deviation of means of triplicate samples.
As for texture, in this study we did not found a direct relationship between the changes in freezing rate, drying time or pressure and the maximum force of penetration for TRCM (data not shown). Sensory analyses showed that the samples having the best sensory characteristics were those slow frozen and dried during 20.5 h at a pressure of 30 Pa (Table 7), although they were not the only acceptable ones. In general, a material frozen slowly is tougher
due to the growth of large ice crystals; the smaller the pore size, the less the histological damage and the finer the honeycomb of air spaces left after sublimation will be (Kuprianoff, 1962). The results of the sensory analyses showed that, in our case, the speed of freezing is not the only ruling factor. The good results for texture in most of the slow-frozen samples could be due to the fact that they rehydrated better than fast-frozen samples (Table 6). Moreover,
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100
L*
Treatment 3
Treatment 4 fast freezing
slow freezing
slow freezing 80
60
40
20
0 Fresh cooked meat
25 mb - 25 mb - 25 mb SF- 18h SF- 20.5h SF- 23h
25 mb SF- sec
30 mb - 30 mb - 30 mb SF- 18h SF- 20.5h SF- 23h
30 mb SF- sec
30 mb - 30 mb FF- 18h FF- 20.5h
30 mb FF- 23h
30 mb FF- sec
2,00 1,80
a* Treatment 3
1,60
Treatment 4
1,40 1,20 1,00
fast freezing
slow freezing
slow freezing
0,80 0,60 0,40 0,20 0,00 Fresh cooked meat
25 mb - 25 mb - 25 mb SF- 18h SF- 20.5h SF- 23h
25 mb SF- sec
30 mb - 30 mb - 30 mb SF- 18h SF- 20.5h SF- 23h
30 mb SF- sec
30 mb - 30 mb - 30 mb FF- 18h FF- 20.5h FF- 23h
30 mb FF- sec
25,00
b*
Treatment 4
Treatment 3
20,00
fast freezing
slow freezing slow freezing 15,00
10,00
5,00
0,00 Fresh meat
25 mb - 25 mb - 25 mb SF- 18h SF- 20.5h SF- 23h
25 mb SF- sec
30 mb - 30 mb - 30 mb SF- 18h SF- 20.5h SF- 23h
30 mb SF- sec
30 mb - 30 mb - 30 mb FF- 18h FF- 20.5h FF- 23h
30 mb FF- sec
Fig. 6. Effect of freezing rate, time of drying and pressure on colour of rehydrated and cooked freeze-dried samples (TRCM). SF: slow freezing rate, FF: fast freezing rate, Sec: with secondary drying. Error bars are the standard deviation of means of triplicate samples.
better results were achieved in treatment 4 when pressure was higher (30 Pa). In this case, samples were acceptable till 23 h of primary drying, whereas the secondary drying had a negative effect, as samples turned drier, less juicy and tougher. This could be caused by microstructure changes in the samples due to process conditions during the secondary drying (Fig. 1). Regarding the data of humidity shown in Table 6, ice sublimation of samples hardly took place during secondary drying (humidity changed from 1.89% to 1.66%), due to which temperature could be increased and
affected texture negatively. On the contrary, with respect to treatment 3, the change in humidity was higher (from 2.32 to 1.64%) and, hence, samples were acceptable after secondary drying. 3.3. Effect of different time of primary drying applied at 0 C and 10 C From the results obtained in treatments 1–4, another assay was proposed to check whether changes of primary drying temperature
J. Babic´ et al. / LWT - Food Science and Technology 42 (2009) 1325–1334
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Table 7 Sensory analyses of cooked chicken meat samples of different speed of freezing, time and pressure of drying. Samples
Springiness
Deformation
Hardness
Juiciness
Chewiness
Acceptability
Treatment 3 (25 Pa) FCM TSF-18 h TSF-20.5 h TSF-23 h TSF-sec
Very high Very low High Low High
Very low Very high Low High Low
Very low Very high Low High Low
Very high Very low Medium Low High
Very high Very low High Low Medium
A NA A NA A
Treatment 4 (30 Pa) FCM TSF-18 h TFF-18 h TSF-20.5 h TFF-20.5 h TSF-23 h TFF-23 h TSF-sec TFF-sec
Very high Very high High Very high High Medium Medium Low medium Low
Very low Very low Low Very low Low Medium Very low High Medium
Very low Low Very low Very low Low Medium Low Very high Very high
Very high Very high Very high High High Medium Medium Low Low
Very high Very high High High Medium Medium Low Very low Very low
A A A A A A A NA NA
FCM: fresh cooked meat; TSF: slow freezed, rehydrated and cooked meat; TFF: fast freezed, rehydrated and cooked meat; A: acceptable; NA: non-acceptable.
Table 8 Effect of time of primary drying applied at 0 C and 10 C on humidity, water activity and rehydration of freeze-dried chicken meat samples.
Fresh sample Treatment 5 (12 h at 0 C and 8.5 h at 10 C) Treatment 6
Humidity (%)
Water activity
Rehydratation (%)
74.56 0.48 1.77 0.30
0.980 0.005 0.127 0.031
– 74.45 8.95
1.91 0.39
0.077 0.009
62.22 3.95
Table 9 Effect of different time of primary drying applied at 0 C and 10 C on colour of chicken meat samples. Colour parameters
L*
a*
Fresh meat FCM
53.17 2.51 81.72 0.82
2.19 0.44 1.09 0.10
b* 9.62 0.82 4.92 0.47
Treatment 5 TM TRM TRCM
81.54 1.42 68.17 2.07 79.29 1.11
2.49 0.42 1.64 0.68 0.58 0.66
15.76 0.29 13.23 1.58 15.70 0.44
Treatment 6 TM TRM TRCM
80.78 2.54 68.62 1.86 77.24 2.62
2.80 0.53 2.29 0.57 0.18 0.07
15.97 0.25 12.91 0.25 15.43 0.48
FCM: fresh cooked meat; TM: treated meat; TRM: treated rehydrated meat; TRCM: treated rehydrated cooked meat.
affected the quality of treated meat. Treatments 5 and 6 (Table 1c) were applied for the same time of primary drying, 20.5 h, but different duration of steps at 0 C and 10 C. Humidity of samples obtained after treatment 5 was applied was lower than those of treatment 6. However, the former (12 h at
0 C and 8.5 h at 10 C) had the highest water activity. On the other hand, samples after treatment 5 rehydrated better than those of treatment 6 (Table 8). As was observed in the previous experiments, samples of FM had lower L* values than TRM (Table 9). Contrary to this, there were no differences of L* and b* values among samples treated with different times of primary drying at 0 C and 10 C. However, the applied analyses of variance showed that the above mentioned time had statistically significant influence on a* values of TRCM. According to the texture analyses, samples with 12 h of primary drying at 0 C showed better texture characteristics (less maximum force peak and closer to that of fresh cooked meat), than the ones in which the duration of primary drying at 0 C was shorter. As was experimentally observed, after a short treatment of primary drying at 0 C, samples only reached 10 C, therefore, all ice was not totally sublimated. Moreover, it is probable that in the second part of primary drying, after exceeding the sublimation temperature, the residual ice melted and texture was affected after the rehydration. However, in treatment 5, as the primary drying at 0 C was longer, at the end of the phase, the samples practically reached the fluid temperature at 0 C which meant that sublimation was completed. This is in accordance with the results obtained in sensory analyses. The sensory panel found samples freeze-dried after 20.5 h with 12 h of primary drying at 0 C and 8.5 h at 10 C more acceptable, than the ones with 8 h of primary drying at 0 C and 12.5 h at 10 C (Table 10). The best quality of TRCM from the assayed processes applied to chicken breast meat samples of 0.7 0.2 cm of thickness was obtained when the following parameters were used: slow freezing, 20.5 h of primary drying (12 h at 0 C and 8.5 h at 10 C) at 30 Pa. Using these conditions, freeze-dried chicken meat samples when rehydrated and cooked, looked and tasted similar to the fresh ones.
Table 10 Effect of different time of primary drying applied at 0 C and 10 C on sensory characteristics of cooked meat samples. Samples
Springiness
Deformation
Hardness
Juiciness
Chewiness
Acceptability
FCM Treatment 5 Treatment 6
Very high Very high Very high
Very low Very low Very low
Very low Very low Very low
Very high Very high High
Very high Very high High
A A A
FCM: fresh cooked meat; A: acceptable; NA: non-acceptable.
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4. Conclusions
References
Related to the effect of product and process parameters on the characteristics of TM samples, the following conclusions were obtained: sample thickness was critical for the determination of conditions of freeze-drying process in order to reach an adequate rehydration, quality and shelf-life of the freeze-dried chicken meat; when thickness increased, the process had to be more intensive and it was more difficult to obtain a quality product near to that of the fresh one, due mainly to the difficulty of reaching an adequate rehydration of the product. The speed of freezing affected some aspects of the quality of freeze-dried chicken meat. Those samples that were frozen more slowly had in general a better texture, sensory characteristics and percentage of rehydration than fast-frozen samples. The small differences between the pressures used in the primary drying of the process also affected the quality of the treated samples. Drying at the highest pressure (30 Pa) gave better results than the lowest one (25 Pa), being also more economical. On the other hand, the time of primary drying at the different temperatures would be fixed and determined in each particular case depending on sample thickness, and process parameters such as pressure and temperature. To sum up, the quality of TRCM samples depends on product characteristics and on the parameters of freeze-drying process, the sample thickness and time of drying being the most significant. Thus, besides a low humidity and water activity in the meat sample for the long-term preservation of the product, a high percentage of rehydration of the freeze-dried sample is needed to obtain a TRCM of similar sensory characteristics to FCM. From the results obtained in this work, it was demonstrated that it is possible to achieve good quality and long shelf-life in freezedried chicken, but it is necessary to adjust the different parameters for each thickness. As for further research, the optimization of the conditions of ozonization and packaging in modified atmospheres is being carried out, in order to apply the barrier technology to develop a lyophilized product stable at ambient temperature and of long shelf-life.
Adam, K. L. (2004). Food dehydration options. Value-added technical note. ATTRA publication IP-147. National Sustainable Agriculture Information Service. AOAC. (1975). Official methods of analyses. Washington, DC, USA: Association of Official Agricultural Chemists. Baker, C. G. J. (1997). Industrial drying of foods. London: Blackie Academic and Professional. ´n de alimentos. Zaragoza: Barbosa, C. G. V., & Vega-Mercado, H. (2000). Deshidratacio Acribia. Bird, K. (1965). Palatability of freeze-dried meats. Food Technology, 19, 55. Hammami, C., & Rene, F. (1997). Determination of freeze-drying process variables for strawberries. Journal of Food Engineering, 32, 133–154. Connell, J. J. (1957). Some aspects of the texture of dehydrated fish. Journal of the Science of Food and Agriculture, 9, 526–537. Farkas, B. E., & Singh, R. P. (1991). Physical properties of air dried and freeze-dried chicken white meat. Journal of Food Science, 56(3), 611–615. Girard, F. P., & Omolosho, D. A. (1983). Proble`mes technologiques relatifs a` la de´shydratation de la viande. InEuropean meeting of meat research workers, Vol I (pp. 260–278), 29. Harper, J. C., & Tappel, A. L. (1957). Freeze-drying of food products. Advances in Food Research, 7, 220. Heath, J. L., & Owens, S. L. (1997). Measurement of broiler breast meat shear values. Journal of Applied Poultry Science, 6, 185–190. Karel, M. (1968). Unsolved problems in chemical stability of freeze-dried foods. InProceeding of the research conference American meat institute foundation (pp 119–137). King, J. C., Wing, K. L., & Sandall, C. O. (1968). Physical properties important for freeze-drying poultry meat. Food Technology, 22, 1302–1308. Kuprianoff, J. (1962). Some factors influencing the reversibility of freeze-drying of foodstuffs. In F. R. Fisher (Ed.), Freeze-drying of foods. National Academy of Sciences – National Research Council. Lawrie, R. A. (1985). Meat science (4th ed.). Oxford: Pergamon Press. Luyet, B. J. (1962). Effect of freezing rate on the structure of freeze-dried materials and on the mechanism of rehydration. In F. R. Fisher (Ed.), Freeze-drying of foods. National Academy of Sciences – National Research Council. Maurer, J., Baker, R. C., & Vadehra, D. V. (1972). Factors affecting the drying, stability, and rehydration of freeze-drying chicken meat. Poultry Science, 52, 784–792. Seltzer, E. (1961). Importance of selection and processing method for successful freeze-drying of chickens. Food Technology, 15, 18–22. Sosebee, M. E., May, K. N., & Powers, J. J. (1964). The effects of enzyme addition on the quality of freeze-dehydrated chicken meat. Food Technology, 18, 149–152. Sosebee, M. E., May, K. N., & Schmittle, S. C. (1964). Histological effects of proteolytic enzyme addition on freeze-dehydrated chicken meat. Poultry Science, 3, 553–559. Stawczyk, J., Sheng, L., & Romuald, Z. (2004). Freeze-drying of food products in a closed system. InProceedings of the 14th international drying symposium, Vol B (pp. 949–953). Brazil: S ao Paulo. Stone, W. E., Jr., & May, K. N. (1969). The effect of time and temperature of cooking on quality of freeze-dehydrated chicken. Poultry Science, 48(3), 813–818. Wells, G. H., May, K. N., & Powers, J. J. (1962). Taste-panel and shear-press evaluation of tenderness of freeze-dried chicken as affected by age and pre-slaughtering feeding of ions. Food Technology, 16, 137–139, Available from. http://www. instron.us/wa/applications/food/testing.aspx?ref¼http.
Acknowledgements The authors would like to thank the Public University of Navarra for financial support and Pollos Iriarte for providing the raw matter.
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
The effects of freeze-drying process parameters on Broiler chicken breast meat Jelena Babic´ a, Marı´a J. Cantalejo b, *, Cristina Arroqui b a b
Faculty of Technology, University of Banja Luka, 78 000 Banja Luka, Bosnia & Herzegovina Department of Food Technology, School of Agriculture Engineering, Public University of Navarre, Campus de Arrosadia, E-31006 Pamplona, Navarre, Spain
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 August 2008 Received in revised form 27 March 2009 Accepted 30 March 2009
Freeze-dried meat can be stored for unlimited periods retaining the majority of their physical, chemical, biological and sensorial properties as in the fresh state. However, adequate process conditions must be applied to prevent quality problems in the product. The aim of this work was to study the effect of freeze-drying process parameters on the quality of Broiler chicken breast meat. Therefore, different meat thicknesses, speed of freezing, time of drying phases and pressure were assayed. Physical and sensory analyses were carried out on treated meat samples. Results showed that sample thickness was critical for the determination of process conditions. The study has demonstrated that it is possible to obtain freeze-dried poultry meat that looks and tastes similar to fresh poultry meat when the right process conditions for the sample’s thickness are applied. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Freeze-drying Chicken breast meat Rehydration Freezing
1. Introduction Poultry meat is very perishable and its stability and microbiological security is based on the combination of various factors (hurdles) in order not to be contaminated by microorganisms. In the design of new raw products, the three following barriers were considered (ozonization, freeze-drying and packaging of the product in modified atmospheres), in order to obtain a new food product from chicken by using gas ozone, first to get a very hygienic product, with a high nutritional value. Afterwards, freeze-drying would be applied to avoid cold chain, reduce sample-size and extend the lifespan of these products, which might be used in the making of soups, consomme´, sauces such as Bolognese, in stews and casseroles, etc. In this case, the energy costs would be reduced, because time for cooking products would be shorter than in the case of traditional foods. Afterwards, the products would be packaged in modified atmosphere to obtain enough safety factors for these new products to guarantee the consumption of chicken that is safer, longer lasting and accepted by consumers. To achieve this, the conditions which most affect freeze-drying were studied with the aim of optimizing each treatment separately and, afterwards, combined. Freeze-drying (lyophilization) has been extensively used to process food since the end of the nineteenth century. Freeze-drying
* Corresponding author. Tel.: þ34 948 169 135; fax: þ34 948 169 893. E-mail address: [email protected] (M.J. Cantalejo). 0023-6438/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2009.03.020
is an effective method to extend the average lifespan of food, given that it prevents the deterioration due to microbial growth or oxidations (Barbosa & Vega-Mercado, 2000). Besides, the characteristics of rehydrated freeze-dried products could be similar to those of fresh ones. The process takes place in three distinct stages: pre-freezing, sublimation or primary drying and desorption or secondary drying (Baker, 1997), in which drying continues until the desired moisture content of the product is achieved. These products do not require cold chain and only have 10–15% of original weight that makes their storage, distribution and commercialization easy. However, the deep freezing and low pressures applied along with the duration (1–3 days) of the process make freeze-drying treatments very expensive. The use of freezedrying in food industries is then restricted to high added-value products such as coffee, tea and infusions, ingredients for ready-toeat foods (vegetables, fruit powders, pasta, meat, cheese starter cultures, fish, shrimps, etc.) and several aromatic herbs (Adam, 2004; Hammami & Rene, 1997; Stawczyk, Sheng, & Romuald, 2004). The freeze-dried meat products, which have been adequately packaged, can be stored for unlimited periods retaining the majority of their physical, chemical, biological and sensorial properties as in the fresh state (Girard & Omolosho, 1983). Freeze-drying takes place at low temperatures and the drying is produced mainly by direct sublimation of ice, avoiding the translocation of salts, creating a honeycomb texture and relatively little histological change. Freeze-drying does not alter the biological value of the meat proteins and, indeed, may enhance it. Nevertheless, there is a loss of
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1326
60
FREEZING
1,000
SECONDARY DRYING
PRIMARY DRYING
0,900
40
0,800 20
0
0,600 0,500
-20
0,400
-40
Pressure (mb)
Temperature (°C)
0,700
0,300 -60 0,200 -80
0,100 0,000 1600
-100 0
200
400
600
800
1000
1200
1400
Time (min) Fig. 1. Process scheme: evolution of temperature of chicken breasts samples and some of the process parameters during the freeze-drying in the freeze drier Lyobeta 25. Temperature of the fluid, temperature of the condenser, temperature of the product and pressure in the process chamber.
about 30% of the thiamine content of the meat during freeze-drying, but this would also occur when cooking in any case. The process causes similar loss of riboflavin in mutton, but not in beef or pork (Lawrie, 1985). A major defect of freeze-dehydrated meats is the typical deterioration of texture (Bird, 1965). The loss of textural qualities in meats and fish is often difficult to explain. In comparison with fresh or frozen meat, freeze-dried meat is somewhat lower in tenderness and juiciness (Karel, 1968). The changes in texture may be due to one or all of the following events in the actomyosin complex: aggregation or cross-linking of proteins; denaturizing of proteins, followed by aggregation; interaction of the native or denaturized proteins with lipids or carbohydrates (Connell, 1957). Harper and Tappel (1957) also reported that texture and poor rehydration were
the principal problems in freeze-dried meat. They studied the effects of time and temperature of cooking on freeze-dehydrated chicken and observed that fresh meat was significantly more tender than that obtained after freeze-dehydrated treatments. These results agree with those of Seltzer (1961), Sosebee, May, and Powers (1964), Sosebee, May, and Schmittle (1964), and Wells, May, and Powers (1962) who noted toughening effects due to freeze dehydration. Likewise, porosity of freeze-dried meat samples is much higher than the air-dried and vacuum dried samples (Maurer, Baker, & Vadehra, 1972). King, Wing, and Sandall (1968) studied the effects of freezing rate on rehydration of freeze-dried turkey meat with results ranging from 87 to 95% of rehydration. The effect of freezing rate on the structure of the samples was clearly seen, being
Table 1 Experiment design to study: (a) the effect of sample thickness; (b) freezing rate, total time of freeze-drying and pressure; (c) different time of primary drying at 0 C and 10 C. (a) Primary drying at 10 C (h)
Total primary drying (h)
Secondary drying (h)
Pressure (Pa)
8
10
18
–
25
Fast (3 h)
12
12
24
7
30
Thickness (cm)
Freezing rate
Primary drying at 0 C (h)
Primary drying at 10 C (h)
Total primary drying (h)
Secondary drying (h)
Pressure (Pa)
Treatment 3
Thin (0.7 0.2)
Slow (6 h)
12
6, 8.5, 11
18, 20.5, 23
7
25
Treatment 4
Thin (0.7 0.2)
Slow (6 h) Fast (3 h)
12
6, 8.5, 11
18, 20.5, 23
7 7
30 30
Thickness (cm)
Freezing rate
Primary drying at 0 C (h)
Primary drying at 10 C (h)
Total primary drying (h)
Secondary drying (h)
Pressure (Pa)
Thin (0.7 0.2) Thin (0.7 0.2)
Slow (6 h) Slow (6 h)
12 8
8.5 12.5
20.5 20.5
– –
30 30
Thickness (cm)
Freezing rate
Treatment 1
Thin (0.7 0.2) Thick (1.3 0.2)
Slow (6 h)
Treatment 2
Thin (0.7 0.2) Thick (1.3 0.2)
Primary drying at 0 C (h)
(b)
(c)
Treatment 5 Treatment 6
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Table 2 Analyses carried out on meat samples during the study.
Fresh meat Freeze-dried rehydrated meat Freeze-dried meat Fresh cooked meat Freeze-dried rehydrated and cooked meat
Humidity
Aw
x
x
x
x
influenced by the kind of meat studied. Luyet (1962) studied the effect of freezing on pore size in freeze-dried beef and found the average pore width to be 2 mm for fast freezing, 5–10 mm for intermediate rates and 150 mm for very slow freezing rates. Freezing rates affected both surface area and pore size distribution of freeze-dried poultry meat, although it had little effect on total porosity. Also Kuprianoff (1962) observed that the more slowly a material was frozen, the higher the freeze-drying rates, due to an increase of the pore size (an effect of growth of large ice crystals). However, slow freezing caused a decrease in the rehydration rate in meats due to toughening of the muscle tissue. Different studies demonstrated that the colour of a freeze-dried product was also directly affected by freezing conditions. Farkas and Singh (1991) found that quick frozen pieces of chicken meat maintained a whiter colour than those frozen more slowly (Stone & May, 1969). King et al. (1968) also observed that the appearance of freeze-dried turkey meat seemed to depend on freezing conditions. In addition, pressure is another factor that could influence the product quality and the duration of the process. At low pressures (below 10–20 mm Hg), the drying is rate-limited by heat conduction, but at higher pressures freeze-drying rates are limited by mass transfer (King et al., 1968). The aim of this work was to study the effect of freeze-drying process factors on the quality of Broiler chicken breast meat, one of
Rehydratation
pH
Texture
Colour
Sensory analyses
x x
x x x x x
x x
x x x
the most consumed and perishable meats. To reach this objective, different meat thickness, speed of freezing, time of freeze-drying phases and pressure were assayed. Therefore, the planned goals correspond to a type of applied research orientated to finding the process conditions to be applied to this type of food widely consumed freshly in Spain, but in fact without any treatment that would allow a longer sale period in the case of natural catastrophes (earthquakes, floods,.), export to third countries, military campaigns, mountain climbers, scarcity in electricity supply. For these reasons, the final goal is to develop new raw products from fresh chicken meat, safe from the sanitary point of view, with a high nutritional value, no additives added and with long shelf-life at room temperature. 2. Materials and methods 2.1. Raw matter and sample preparation Broiler chicken breast meat was obtained from Pollos Iriarte S.A (Orcoyen, Navarre, Spain). The age of the chicken before slaughtering was 43 2 days with 2.40 0.28 kg of weight. Chicken meat was transported from the supplier to the laboratory in less than 24 h after slaughtering and stored at 4 C until used. The samples were prepared for analyses by cutting and removing fat parts.
Fig. 2. (a) Principle of work by Kramer shear cell. (b) Maximum force peak measurement by Kramer shear cell (Fmax ¼ 172.68 N) (http://www.instron.us/wa/applications/food/ testing.aspx?ref¼http).
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Table 3 Effect of chicken breast meat thickness on humidity, water activity and rehydration of freeze-dried samples. Humidity (%)
Water activity
Thin Fresh meat Treatment 1 Treatment 2
Thick
Thin
Thick
0.987 0.002 18.83 1.59 2.83 0.36
0.291 0.010 0.055 0.007
2.2. Freeze-drying treatment, samples storage and preparation for analyses The freeze drier used for the process was a Lyobeta 25 (Telstar Industrial, S.L., Terrasa, Barcelona). The different phases of the freeze-drying process are shown in Fig. 1. Preliminary experiments were done to define process conditions to be applied for breast meat lyophilization. Firstly, different thicknesses were assayed in order to compare extreme process conditions to identify the most adequate ones for further experiments (Table 1a). Likewise, the different parameters of the freezedrying process assayed in this study were the following ones: freezing rate (time to reach 45 C in the fluid), time and pressure of drying (Table 1b), and time of primary drying at 0 C and 10 C, respectively (Table 1c). Secondary drying process, when used, was carried out at 35 C and at maximum vacuum (Fig. 1). After lyophilization process, samples were packaged in impermeable plastic trays made of PPevoPP (Ilpra Systems, Barcelona, Spain) filled with nitrogen. Samples were coded and stored in a dark place at room temperature. Freeze-dried samples had to be rehydrated and cooked in order to be analyzed. Sample rehydration was performed in tap water at room temperature. The duration of rehydration process was fixed in 3 h and 3.5 h for thin and thick samples, respectively, as after that time period there was no more absorption of water by the samples. Percentage of rehydration was calculated using the following expression:
rehydrationð%Þ ¼
Thick
72.41 0.13 9.94 1.78 3.48 0.44
Rehydratation (%)
Thin
ðWr Wl Þ 100 ðW0 Wl Þ
– 0.855 0.075 0.170 0.035
53.35 4.47 61.43 5.44
43.81 5.81 39.80 3.24
Wr: weight of rehydrated sample (g); Wl: weight of lyophilizated sample (g); W0: weight of fresh sample (g). To be cooked, samples were packaged in impermeable plastic bags and introduced in a water bath at 80 C for 4 min 30 s and 4 min for thick and thin samples, respectively.
2.3. Analyses of samples Different analyses were carried out on meat samples (Table 2). Humidity was determined by the ISO R-1442 method (AOAC, 1975), using the gravimetric method. Water activity was determined by means of a hygrometer NOVASINA RS-232 C. The pH value was measured by a pH-meter CRISON pH 25 with combined electrode which penetrates the meat sample. Colour was measured in different parts (same side) of meat samples according to the CIELab system (L*, a*, b* values). A Minolta spectrophotometer CM-508d, with white standard was employed for the measurements. The multi-blade Kramer shear cell was commonly used for measuring poultry meat tenderness (Heath & Owens, 1997). A Texture Analyzer TA-XT2i with 5 bladed Kramer shear cell was employed to measure maximum force of penetration (N) into the sample (toughness) at certain distance (mm) (Fig. 2). It simulates the force needed for chewing and gives information about hardness of sample. Sensory characteristics of meat samples (springiness, deformation, toughness, juiciness and chewiness) were evaluated by five trained people. Each of these sensory characteristics was evaluated by a scale from 0 to 5, where range 0–1 was
40
1,000 PRIMARY DRYING
0,900
20 0,800
FREEZING
0,700 0,600
-20
0,500 -40
0,400
Pressure (mb)
Temperature (°C)
0
0,300
-60
0,200 -80 0,100 -100
0,000 0
200
400
600
800
1000
1200
1400
1600
Time (min) Fig. 3. Evolution of temperature of thin and thick chicken breasts samples and some of the process parameters during treatment 1. Temperature of the fluid, temperature of the thin product, temperature of the thick product and pressure in the process chamber. of the condenser,
temperature
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1329
1,000
60 SECONDARY DRYING
0,900
40 PRIMARY DRYING
0,700 0
0,600 0,500
-20
0,400
-40
Pressure (mb)
Temperature (°C)
0,800
FREEZING
20
0,300 -60 0,200 -80
0,100
-100 0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
0,000 2400
Time (min) Fig. 4. Evolution of temperature of thin and thick chicken breasts samples and some of the process parameters during treatment 2. Temperature of the fluid, temperature of the thin product, temperature of the thick product and pressure in the process chamber. of the condenser,
described as very low, 1–2 low, 2–3 medium, 3–4 high and 4–5 very high. Process parameters and their influence were considered for statistical analyses with 95% level of confidence. ANOVA Analyses, Multifactor Analyses of Variance and Multiple Range Tests were carried out for all data, using the Statgraphic Plus program (version 5.1, December 2001. Rockville, Maryland, USA). 3. Results and discussion The effect of the different product and process parameters assayed were analysed from the results of the physical, chemical and sensory analyses carried out in treated samples. 3.1. Effect of chicken breast meat thickness Freeze-dried (treated meat – TM) thin samples showed lower moisture content and water activity than those of thick samples (Table 3) when the less intensive freeze-drying treatment was applied (treatment 1, without secondary drying). Water activity of freeze-dried thick samples was very high (0.855 0.075) and very close to fresh meat (0.987 0.002), that means that liophilization was not completed. Contrary to thin samples, the temperature of thick ones did not reach 0 C which corresponds to the fluid
temperature
temperature at the end of the primary drying (Fig. 3). Likewise, rehydratation was not adequate, and would affect negatively the texture of samples (Tables 3 and 5). Therefore, depending on the conditions of the process, either a longer duration of primary drying or secondary drying should be included for thick samples. However, when a more intensive treatment was applied (treatment 2, Table 1a), there were no statistically significant differences in moisture content between freeze-dried thin and thick samples (Table 3), which would mean that sublimation was completely reached, and this is in accordance with what was observed in Fig. 4 (temperature of thick samples exceeded 0 C at the end of the primary drying). Despite that, the rehydration percentage of thick samples treated when treatment 2 was employed was much lower than in thin ones due mainly to the sample thickness. These results agree with those obtained by Harper and Tappel (1957), who pointed out that poor rehydration was one of the main problems in freeze-dried meat. Thickness of TM had an influence on their colour. In fact, statistically significant differences were found in L* and b* parameters from both thickness at the 95.0% confidence level. In general, L*, a* and b* values of TRCM were closer to those of FCM samples when samples were thinner (Table 4). On the one hand, texture analyses applied in samples after treatment 1 showed that cooked and rehydrated freeze-dried thin
Table 4 Colour of control and treated thin and thick samples of chicken meat. Treatment 1
Treatment 2
L*
a*
b*
L*
a*
b*
Fresh meat FCM
50.93 0.90 79.73 0.77
1.65 0.40 1.46 0.56
9.34 0.89 14.70 0.25
49.73 1.63 79.34 1.48
1.80 0.53 1.28 0.53
9.08 0.99 15.68 0.53
Thin TM TRM TRCM
73.53 5.92 62.09 3.40 76.40 2.40
2.99 0.34 4.27 0.41 1.33 0.13
14.62 1.97 14.49 2.39 15.54 0.50
78.69 1.76 67.64 1.34 70.98 4.04
1.88 0.13 3.11 0.46 0.49 0.19
17.64 0.52 16.07 1.60 14.55 0.83
Thick TM TRM TRCM
80.89 1.74 55.50 6.84 77.63 2.46
1.96 0.23 2.52 0.66 1.29 0.50
15.95 0.58 11.68 3.93 17.07 2.23
80.47 2.61 66.97 2.49 64.92 6.68
2.15 0.62 4.17 0.76 0.34 0.29
17.26 1.03 17.81 1.49 15.49 1.48
FCM: fresh cooked meat; TM: treated meat; TRM: treated rehydrated meat; TRCM: treated rehydrated cooked meat.
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Table 5 Sensory analyses of cooked chicken meat samples of different thickness. Samples
Springiness
Deformation
Hardness
Juiciness
Chewiness
Acceptability
FCM
Very high
Very low
Very low
Very high
Very high
A
Treatment 1 TRCM – thin TRCM – thick
High Low
Medium High
Medium Very high
Medium Very low
High Very low
A NA
Treatment 2 TRCM – thin TRCM – thick
Low Very low
Medium Medium
High High
Very low Very low
Very low Very low
NA NA
FCM: fresh cooked meat; TRCM: treated rehydrated and cooked meat; A: acceptable; NA: non-acceptable.
samples (27649.5 N) were tougher and harder for consumption than thick ones (17440.8 N). Moreover, both treated rehydrated and cooked meat (TRCM) showed a higher maximum strength than fresh cooked meats (FCM) (4292.1 N). Nevertheless, in treatment 1 no correlation was observed between the results of texture and those obtained by the sensory analysis (Table 5). In fact, the strength applied on thin samples was higher than on thick samples, whereas in the case of sensorial analyses thin samples were scored as juicier and less hard than thick ones, probably due to their low level of rehydration (Table 3). On the other hand, members of the sensory panel described TRCM thick samples of chicken meat obtained after the application of treatments 1 and 2 as very hard and unacceptable for consumption (Table 5). 3.2. Effect of freeze-drying parameters: freezing rate, time of drying and pressure From the results obtained in the previous section, thin samples and times of primary drying above 18 h were selected to assay the effect of freezing rate, time of drying and pressure on quality of freeze-dried chicken breast samples (Table 1b). Concerning humidity and water activity, fast-frozen samples presented, in general, lower values of humidity and water activity than slow-frozen ones that were freeze-dried under similar conditions (Table 6). For each treatment, humidity and aw were reduced as drying time increased. Multifactor analyses of variance Type III Sums of Squares showed that freezing rate and time of drying had statistically significant influence on humidity and water activity (p < 0.05). It was observed that the TM samples treated up to 20.5 h at the lowest pressure (treatment 3, 25 Pa) had higher values of
humidity and aw than those treated at 30 Pa. However, there was not a clear effect of the different pressures assayed either on humidity or on water activity of TM samples (Table 6), probably due to the fact that the differences in pressure were not so high. Regarding rehydratation, slow-frozen samples had higher values of rehydratation percentage than fast-frozen ones, although the latter presented more variability. Rehydration was better when samples were treated using the highest pressure. In the case of colour, L* and b* values of treated rehydrated meat (TRM) were much higher than those of fresh ones, showing more brightness and yellowness (Fig. 5). However, for a* parameter, only a difference was noted when the smallest pressure was applied (25 Pa). Freeze-dried, rehydrated and afterwards cooked samples (TRCM) had more similar L* and b* values to fresh cooked meat samples (FCM), especially when treated at the highest pressure (30 Pa, treatment 4) (Fig. 6). However, in the case of a* value, important differences were observed between TRCM and FCM samples. Contrary to fresh samples, a* value of treated samples when rehydrated and cooked (TRCM) was lower (less red) than the obtained in FCM. Results showed that there were no differences on a* (red), b* (yellow) and L* (lightness) values between frozen samples at different rates. Thus, in the conditions assayed of these treatments, a clear effect of the freezing rate on samples’ colour was not observed for the assayed pressures, although Stone and May (1969) found that quick frozen pieces of chicken meat maintained a whiter colour than those frozen more slowly and, when a fast freezing took place, a larger number of crystals and of a smaller size with a more luminous colour were obtained. In general, no effect of the duration of primary drying on colour was observed, except for the component a* in TRCM samples.
Table 6 Effect of freezing rate, time of drying and pressure on humidity, water activity and rehydration of freeze-dried samples. Treatment
Fresh meat
Humidity (%)
Pressure (Pa)
Slow freezing
Fast freezing
Duration of drying (h) 18 3 4
Duration of drying (h) 23
31a
18
20.5
23
31a
5.38 0.53 3.75 0.94
3.53 0.31 2.47 0.16
2.32 0.30 1.89 0.12
1.64 0.74 1.66 0.08
3.12 0.92
2.11 0.13
1.70 0.55
1.44 0.35
25 30
Water activity 3 0.981 0.003 4 0.984 0.001
0.426 0.028 0.126 0.018
0.234 0.131 0.156 0.014
0.080 0.005 0.125 0.008
0.047 0.017 0.038 0.013
0.123 0.018
0.148 0.013
0.094 0.003
0.053 0.003
25 30
Rehydratation (%) 3 4
40.38 4.20 75.35 1.17
51.17 8.10 76.87 4.23
56.80 11.14 73.48 3.65
57.47 6.18 87.79 6.07
74.21 9.75
75.66 6.03
81.15 7.66
73.30 4.64
25 30
a
72.5 0.33 73.4 0.28
20.5
Secondary drying included.
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100 90
Treatment 3
Treatment 4
slow freezing
80
fast freezing
slow freezing
70
L*
60 50 40 30 20 10 0 Fresh meat
25 mb- 25 mb- T25 mb- 25 mbSF-18h SF-20,5h SF-23h SF- sec
30 mb- 30 mb- 30 mbSF-18h SF- 20.5h SF- 23h
30 mbSF- sec
30 mb- 30 mb- 30 mbFF- 18h FF- 20.5h FF- 23h
30 mbFF- sec
7
Treatment 3 Treatment 4
slow freezing
6
fast freezing
slow freezing
5
a*
4 3 2 1 0 Fresh meat
25 mbSF-18h
25 mbSF-20,5h
25 mbSF-23h
30 mb30 mb30 mbSF-18h SF- 20.5h SF- 23h
25 mbSF- sec
30 mb30 mb30 mbFF- 18h FF- 20.5h FF- 23h
30 mbSF- sec
30 mbFF- sec
25
Treatment 3 Treatment 4
slow freezing
fast freezing
slow freezing
20
b*
15
10
5
0 Fresh meat
25 mb25 mb25 mbSF-18h SF-20,5h SF-23h
25 mbSF- sec
30 mb30 mb30 mbSF-18h SF- 20.5h SF- 23h
30 mbSF- sec
30 mb30 mb30 mbFF- 18h FF- 20.5h FF- 23h
30 mbFF- sec
Fig. 5. Effect of freezing rate, time of drying and pressure on colour of rehydratated freeze-dried samples (TRM). SF: slow freezing rate, FF: fast freezing rate, Sec: with secondary drying. Error bars are the standard deviation of means of triplicate samples.
As for texture, in this study we did not found a direct relationship between the changes in freezing rate, drying time or pressure and the maximum force of penetration for TRCM (data not shown). Sensory analyses showed that the samples having the best sensory characteristics were those slow frozen and dried during 20.5 h at a pressure of 30 Pa (Table 7), although they were not the only acceptable ones. In general, a material frozen slowly is tougher
due to the growth of large ice crystals; the smaller the pore size, the less the histological damage and the finer the honeycomb of air spaces left after sublimation will be (Kuprianoff, 1962). The results of the sensory analyses showed that, in our case, the speed of freezing is not the only ruling factor. The good results for texture in most of the slow-frozen samples could be due to the fact that they rehydrated better than fast-frozen samples (Table 6). Moreover,
J. Babic´ et al. / LWT - Food Science and Technology 42 (2009) 1325–1334
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100
L*
Treatment 3
Treatment 4 fast freezing
slow freezing
slow freezing 80
60
40
20
0 Fresh cooked meat
25 mb - 25 mb - 25 mb SF- 18h SF- 20.5h SF- 23h
25 mb SF- sec
30 mb - 30 mb - 30 mb SF- 18h SF- 20.5h SF- 23h
30 mb SF- sec
30 mb - 30 mb FF- 18h FF- 20.5h
30 mb FF- 23h
30 mb FF- sec
2,00 1,80
a* Treatment 3
1,60
Treatment 4
1,40 1,20 1,00
fast freezing
slow freezing
slow freezing
0,80 0,60 0,40 0,20 0,00 Fresh cooked meat
25 mb - 25 mb - 25 mb SF- 18h SF- 20.5h SF- 23h
25 mb SF- sec
30 mb - 30 mb - 30 mb SF- 18h SF- 20.5h SF- 23h
30 mb SF- sec
30 mb - 30 mb - 30 mb FF- 18h FF- 20.5h FF- 23h
30 mb FF- sec
25,00
b*
Treatment 4
Treatment 3
20,00
fast freezing
slow freezing slow freezing 15,00
10,00
5,00
0,00 Fresh meat
25 mb - 25 mb - 25 mb SF- 18h SF- 20.5h SF- 23h
25 mb SF- sec
30 mb - 30 mb - 30 mb SF- 18h SF- 20.5h SF- 23h
30 mb SF- sec
30 mb - 30 mb - 30 mb FF- 18h FF- 20.5h FF- 23h
30 mb FF- sec
Fig. 6. Effect of freezing rate, time of drying and pressure on colour of rehydrated and cooked freeze-dried samples (TRCM). SF: slow freezing rate, FF: fast freezing rate, Sec: with secondary drying. Error bars are the standard deviation of means of triplicate samples.
better results were achieved in treatment 4 when pressure was higher (30 Pa). In this case, samples were acceptable till 23 h of primary drying, whereas the secondary drying had a negative effect, as samples turned drier, less juicy and tougher. This could be caused by microstructure changes in the samples due to process conditions during the secondary drying (Fig. 1). Regarding the data of humidity shown in Table 6, ice sublimation of samples hardly took place during secondary drying (humidity changed from 1.89% to 1.66%), due to which temperature could be increased and
affected texture negatively. On the contrary, with respect to treatment 3, the change in humidity was higher (from 2.32 to 1.64%) and, hence, samples were acceptable after secondary drying. 3.3. Effect of different time of primary drying applied at 0 C and 10 C From the results obtained in treatments 1–4, another assay was proposed to check whether changes of primary drying temperature
J. Babic´ et al. / LWT - Food Science and Technology 42 (2009) 1325–1334
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Table 7 Sensory analyses of cooked chicken meat samples of different speed of freezing, time and pressure of drying. Samples
Springiness
Deformation
Hardness
Juiciness
Chewiness
Acceptability
Treatment 3 (25 Pa) FCM TSF-18 h TSF-20.5 h TSF-23 h TSF-sec
Very high Very low High Low High
Very low Very high Low High Low
Very low Very high Low High Low
Very high Very low Medium Low High
Very high Very low High Low Medium
A NA A NA A
Treatment 4 (30 Pa) FCM TSF-18 h TFF-18 h TSF-20.5 h TFF-20.5 h TSF-23 h TFF-23 h TSF-sec TFF-sec
Very high Very high High Very high High Medium Medium Low medium Low
Very low Very low Low Very low Low Medium Very low High Medium
Very low Low Very low Very low Low Medium Low Very high Very high
Very high Very high Very high High High Medium Medium Low Low
Very high Very high High High Medium Medium Low Very low Very low
A A A A A A A NA NA
FCM: fresh cooked meat; TSF: slow freezed, rehydrated and cooked meat; TFF: fast freezed, rehydrated and cooked meat; A: acceptable; NA: non-acceptable.
Table 8 Effect of time of primary drying applied at 0 C and 10 C on humidity, water activity and rehydration of freeze-dried chicken meat samples.
Fresh sample Treatment 5 (12 h at 0 C and 8.5 h at 10 C) Treatment 6
Humidity (%)
Water activity
Rehydratation (%)
74.56 0.48 1.77 0.30
0.980 0.005 0.127 0.031
– 74.45 8.95
1.91 0.39
0.077 0.009
62.22 3.95
Table 9 Effect of different time of primary drying applied at 0 C and 10 C on colour of chicken meat samples. Colour parameters
L*
a*
Fresh meat FCM
53.17 2.51 81.72 0.82
2.19 0.44 1.09 0.10
b* 9.62 0.82 4.92 0.47
Treatment 5 TM TRM TRCM
81.54 1.42 68.17 2.07 79.29 1.11
2.49 0.42 1.64 0.68 0.58 0.66
15.76 0.29 13.23 1.58 15.70 0.44
Treatment 6 TM TRM TRCM
80.78 2.54 68.62 1.86 77.24 2.62
2.80 0.53 2.29 0.57 0.18 0.07
15.97 0.25 12.91 0.25 15.43 0.48
FCM: fresh cooked meat; TM: treated meat; TRM: treated rehydrated meat; TRCM: treated rehydrated cooked meat.
affected the quality of treated meat. Treatments 5 and 6 (Table 1c) were applied for the same time of primary drying, 20.5 h, but different duration of steps at 0 C and 10 C. Humidity of samples obtained after treatment 5 was applied was lower than those of treatment 6. However, the former (12 h at
0 C and 8.5 h at 10 C) had the highest water activity. On the other hand, samples after treatment 5 rehydrated better than those of treatment 6 (Table 8). As was observed in the previous experiments, samples of FM had lower L* values than TRM (Table 9). Contrary to this, there were no differences of L* and b* values among samples treated with different times of primary drying at 0 C and 10 C. However, the applied analyses of variance showed that the above mentioned time had statistically significant influence on a* values of TRCM. According to the texture analyses, samples with 12 h of primary drying at 0 C showed better texture characteristics (less maximum force peak and closer to that of fresh cooked meat), than the ones in which the duration of primary drying at 0 C was shorter. As was experimentally observed, after a short treatment of primary drying at 0 C, samples only reached 10 C, therefore, all ice was not totally sublimated. Moreover, it is probable that in the second part of primary drying, after exceeding the sublimation temperature, the residual ice melted and texture was affected after the rehydration. However, in treatment 5, as the primary drying at 0 C was longer, at the end of the phase, the samples practically reached the fluid temperature at 0 C which meant that sublimation was completed. This is in accordance with the results obtained in sensory analyses. The sensory panel found samples freeze-dried after 20.5 h with 12 h of primary drying at 0 C and 8.5 h at 10 C more acceptable, than the ones with 8 h of primary drying at 0 C and 12.5 h at 10 C (Table 10). The best quality of TRCM from the assayed processes applied to chicken breast meat samples of 0.7 0.2 cm of thickness was obtained when the following parameters were used: slow freezing, 20.5 h of primary drying (12 h at 0 C and 8.5 h at 10 C) at 30 Pa. Using these conditions, freeze-dried chicken meat samples when rehydrated and cooked, looked and tasted similar to the fresh ones.
Table 10 Effect of different time of primary drying applied at 0 C and 10 C on sensory characteristics of cooked meat samples. Samples
Springiness
Deformation
Hardness
Juiciness
Chewiness
Acceptability
FCM Treatment 5 Treatment 6
Very high Very high Very high
Very low Very low Very low
Very low Very low Very low
Very high Very high High
Very high Very high High
A A A
FCM: fresh cooked meat; A: acceptable; NA: non-acceptable.
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4. Conclusions
References
Related to the effect of product and process parameters on the characteristics of TM samples, the following conclusions were obtained: sample thickness was critical for the determination of conditions of freeze-drying process in order to reach an adequate rehydration, quality and shelf-life of the freeze-dried chicken meat; when thickness increased, the process had to be more intensive and it was more difficult to obtain a quality product near to that of the fresh one, due mainly to the difficulty of reaching an adequate rehydration of the product. The speed of freezing affected some aspects of the quality of freeze-dried chicken meat. Those samples that were frozen more slowly had in general a better texture, sensory characteristics and percentage of rehydration than fast-frozen samples. The small differences between the pressures used in the primary drying of the process also affected the quality of the treated samples. Drying at the highest pressure (30 Pa) gave better results than the lowest one (25 Pa), being also more economical. On the other hand, the time of primary drying at the different temperatures would be fixed and determined in each particular case depending on sample thickness, and process parameters such as pressure and temperature. To sum up, the quality of TRCM samples depends on product characteristics and on the parameters of freeze-drying process, the sample thickness and time of drying being the most significant. Thus, besides a low humidity and water activity in the meat sample for the long-term preservation of the product, a high percentage of rehydration of the freeze-dried sample is needed to obtain a TRCM of similar sensory characteristics to FCM. From the results obtained in this work, it was demonstrated that it is possible to achieve good quality and long shelf-life in freezedried chicken, but it is necessary to adjust the different parameters for each thickness. As for further research, the optimization of the conditions of ozonization and packaging in modified atmospheres is being carried out, in order to apply the barrier technology to develop a lyophilized product stable at ambient temperature and of long shelf-life.
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Acknowledgements The authors would like to thank the Public University of Navarra for financial support and Pollos Iriarte for providing the raw matter.