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Journal of Thermal Analysis and Calorimetry

, Volume 133, Issue 1, pp 539–547 | Cite as

Investigation of fatty acid thermal transitions and stability in poultry pates enriched with vegetable components

  • Maria Marudova
  • Maria Momchilova
  • Ginka Antova
  • Zhana Petkova
  • Dinko Yordanov
  • Gabor Zsivanovits
Article

Abstract

The aim of the study was to describe the thermal characteristics of poultry pates enriched with vegetable components in relation to their chemical composition and technological process. Two poultry pates from chicken liver, chicken or turkey meat with vegetables were developed. The thermal characteristics of the raw materials and the ready pates were examined by differential scanning calorimetry; fatty acid profiles were detected by gas chromatography analysis. The study investigated the effect of such factors as heating/cooling rate and matrix effect of other components (e.g., proteins) in the raw materials and in the pates. It was observed that the cooling rate has a considerable effect on melting/crystallization temperature, enthalpy, and height of peaks in the process of pates fat crystallization, as well as peak height and enthalpy in the melting process. The first peaks formed during the crystallization were characterized by high instability, demonstrated by various peak shapes. The rapid cooling led to lowering of the melting point, assigned to the presence of unstable α crystals. The slow cooling led to mainly stable β′ crystals. The fraction of unsaturated fatty acids present in the fat was important for both crystallization rate and melting points in the raw materials and in the products as well. This effect was stronger in the pate products because of the presence of diverse components such as proteins. The results obtained could be used for the evaluation of thermal stability of pate fatty acids and further optimization of the pate thermal treatment.

Keywords

DSC Fatty acid profile Poultry pate Chemical composition 

Introduction

Fatty acids are among the basic compounds of the food, especially in case of diary and meat products. Their crystallization affects the rheological properties of the whole food product, depending on the aqueous content of the hydrophilic continuous phase. A knowledge about the influence of crystal phase of fat in cooked meat products is clearly lacking, but would be useful for the optimization of the organoleptic quality including mouthfeel of various cooked meat products [1].

The crystallization process may be divided into three individual stages: nucleation, crystal growth, and crystal ripening. It is not obligatory for these three events to occur in this sequence, once the primary nucleation has been activated [2]. The nucleation depends on the supercooling, and when nuclei have formed, they grow and develop crystals. Normally, a distinction is made between homogeneous, heterogeneous, and secondary crystal nucleation. Homogeneous nucleation and heterogeneous nucleation are as variants of primary nucleation, which occurs in the absence of the crystalline phase [3]. Homogeneous nucleation happens in a pure liquid, but requires considerable supercooling in order to occur at an appreciable rate. Heterogeneous nucleation happens at foreign surfaces, such as at the container wall or at some contaminating particles, and will depend on differences in interfacial free energies at liquid–crystal, liquid–foreign surface, and crystal–foreign surface, and accordingly on the shape of the foreign surface or the crystals. Certain very small foreign particles may induce heterogeneous nucleation, acting as catalytical impurities, especially at increasing supercooling [3, 4]. Usually, in food systems, supercooling is not occurring, as heterogeneous nucleation initiates crystallization. Secondary nucleation is due to the presence of crystals of the material [3].

The fat crystallization behavior in food emulsions differs from fat crystallization in bulk and strongly depends on the composition of fat protein layer [5, 6] and the protein-emulsifying capacity. The properties of the interface layer around the fat globules are due to different physicochemical interactions or chemical bonds, depending on the interdroplet medium agents. It was demonstrated that the fat crystallization within the emulsion droplets affects more directly the physical properties of the product through the stabilization of the emulsion [7, 8]. In this respect, the study and understanding of the fat crystallization in whipped fat emulsions is of a special interest. However, while the crystallization of fats in bulk phase is already far from being completely elucidated, that in emulsion is even more delicate to study due to a series of factors, generally unknown, that directly influence its crystallization, including the fat polymorphism, the fluctuations and the complexity of the fat composition and the nucleation kinetics in dispersed systems. For meat products like pate, the emulsions are even more complex as the lipid profile in the product is varying, depending on the triacylglycerol composition of the used fat.

The present research aims to investigate the effect of pretreatment of poultry pates enriched with vegetable components on the fatty acid thermal transitions by the method of differential scanning calorimetry (DSC).

Materials and methods

Two poultry pates chicken liver, chicken or turkey breast meat, and vegetables were used in the present research. The physical and chemical properties of the fat were investigated in two different products: raw fats in their tissue form and fats in the pate. The protein content was examined by Kjeldahl method, fatty acid compositions were determined by GC method, and phase transitions were detected by DSC method for the raw materials and the pate samples.

Poultry pate preparation

The full composition of the pates and the preparation technology for the poultry pates are given in Table 1 and Fig. 1. All of the raw materials have commercial origin. In our recipy as main raw material we used chicken meat, turkey meat and chicken liver. The main raw materials were subjected to preheat treatment (boiling). The additional raw materials—spices and additives—were weighed, according to their amount in the formulation. The meat raw materials were cooked to obtain a fine homogeneous mass, after which salt, spices, and vegetable supplements were added. The cream and butter were added to the product. A hot broth was also added during the curling. The curling continued until a homogeneous pate was obtained. The ready filling mass was filled tightly in glass containers (jars), which are cooked. The pasteurization like a heat treatment was done until temperature of 72 °C was reached in the center of the product. The jars were then cooled under a shower of cold running water to reach a temperature of 4 °C in the center of the product and stored in refrigerator for analysis.
Table 1

Composition of pate samples

Ingredient

Chicken pate/kg kg−1

Turkey pate/kg kg−1

Chicken liver

0.148

0.148

Chicken breast

0.398

 

Turkey breast

 

0.398

Water (hot broth)

0.106

0.106

Salt

0.001

0.001

Double cream

0.318

0.318

Butter

0.011

0.011

Black pepper

0.001

0.001

Nutmeg

0.001

0.001

Onion

0.005

0.005

Carrots

0.011

0.011

Total

1.000

1.000

Fig. 1

Poultry pate preparation

Fatty acid composition

The total fatty acid composition of the glyceride oil was determined by GC after transmethylation of the respective sample with 2% H2SO4 in absolute CH3OH [9]. Fatty acid methyl esters (FAME) were purified by thin-layer chromatography on 20 cm × 20 cm plates covered with 0.2 mm Silica gel 60 G layer (Merck) with mobile phase n-hexane/diethyl ether, 97:3 (v/v). Determination was performed on a gas chromatograph equipped with a 75 m × 0.25 mm × 18 μm (I.D.) capillary Supelco column and a flame ionization detector. The column temperature was programmed from 140 °C (hold 5 min), at 4 °C min−1, to 240 °C (hold 3 min); injector and detector temperatures were 250 °C. Hydrogen was the carrier gas at a flow rate 0.8 mL min−1; split was 50:1. Identification was performed by the comparison of retention times with those of a standard mixture of FAME subjected to GC under identical experimental conditions [10].

Differential scanning calorimetry

The phase transitions of the fats in the investigated samples were measured by a differential scanning calorimeter DSC 204F1 Phoenix (Netzsch Gerätebau GmbH, Germany) based on the heat-flux principle and cooled with intracooler. The heat flow and the temperature were calibrated with indium standard (T m = 156.6 °C, ∆H m = 28.5 J g−1) at all the heating/cooling rate, which are used in the experiments. The sample was hermetically sealed in an aluminum sample. An empty, hermetically sealed aluminum pan identical to the sample pan was used as reference. Experimental conditions were identical for all the products. The samples were heated to 80 °C and held for 30 min to ensure that the fat was totally melted and all the nuclei were destroyed [11]. The samples were subsequently cooled to – 60 °C at different cooling rates (1.0 °C min−1, 5.0 °C min−1, and 10 °C min−1). The melting curves were recorded by scanning the samples to 80 °C with heating rates at 1.0 and at 5.0 °C min−1.

Results and discussion

Fatty acid composition

The fatty acid composition of the raw materials and the pates is shown in Table 2.
Table 2

Fatty acid composition of fats and protein content of raw materials, chicken pate, and turkey pate

Fatty acids FA/%

Turkey breasts

Chicken liver

Chicken breast

Butter

Double cream

Chicken pate

Turkey pate

C 8:0

0.5

0.3

0.4

C 10:0

0.1

0.4

1.6

2.1

0.4

1.1

C 11:0

0.1

0.2

0.2

C 12:0

0.1

0.5

2.8

3.7

1.4

2.2

C 13:0

0.1

0.2

C 14:0

1.8

0.7

1.4

11.2

13.7

4.7

10.5

C 14:1

0.2

0.1

0.7

0.7

0.2

0.6

C 15:0

0.3

0.2

1.2

1.4

0.5

1.4

C 16:0

32.0

25.2

26.8

37.7

41.7

37.4

40.3

C 16:1

3.0

0.9

1.8

2.0

2.0

1.2

2.0

C 17:0

0.6

0.4

0.2

0.6

0.5

0.3

0.6

C 17:1

0.3

0.2

0.2

C 18:0

12.9

14.2

11.3

12.5

12.3

11.0

13.9

C 18:1

38.6

33.8

35.6

24.1

19.9

32.3

22.5

C 18:2 trans

0.3

0.1

0.2

C 18:2 (n-6)

9.5

21.0

18.4

3.1

0.7

9.9

2.2

C 18:3 (n-6)

0.1

0.4

0.1

0.3

C 18:3 (n-3)

0.5

2.0

0.7

0.1

0.1

0.1

0.9

C 20:0

0.1

0.4

0.5

0.5

0.2

0.3

0.4

C 20:1

0.2

0.3

C 20:2 (n-6)

0.1

0.3

0.2

0.3

0.1

0.1

C 20:3 (n-6)

0.1

0.2

C 20:4 (n-6)

0.6

0.2

0.2

0.1

0.1

C 20:5 (n-3)

0.3

C 22:2 (n-6)

0.8

Saturated FA/%

47.9

41.1

41.6

68.6

76.2

56.0

70.8

Unsaturated FA/%

52.1

58.9

58.4

31.4

23.8

44.0

29.2

Monounsaturated FA/%

42.0

34.8

37.4

27.1

22.8

33.7

25.6

Polyunsaturated FA/%

10.1

24.1

21.0

4.3

1.0

10.3

3.6

Fat content/%

2.7

2.8

1.7

82.1

27.5

7.0

4.7

Saturated FA in the product/g 100 g−1

1.3

1.2

0.7

56.3

21.0

3.9

3.3

Unsaturated FA in the product/g 100 g−1

1.4

1.6

1.0

25.8

6.5

3.1

1.4

Monounsaturated FA in the product/g 100 g−1

1.1

1.0

0.6

22.2

6.2

2.4

1.2

Polyunsaturated FA in the product/g 100 g−1

0.3

0.6

0.4

3.6

0.3

0.7

0.2

Proteins in the product/g 100 g−1

21.20

25.8

21.18

0.21

1.5

12.25

11.38

The predominant fatty acids in the studied fats from chicken liver, chicken breast, and turkey fillet are oleic (33.8–38.6%), palmitic (25.2–32.0%), and stearic acids (11.3–14.2%). The quantity of linoleic and linolenic acids in the raw materials ranges from 9.5 to 21.1% and from 0.5 to 2.0%, respectively, and the highest amount of these acids is observed in the chicken liver. The other fatty acids in the fat from the chicken meat are presented in insignificant quantities (0.1–3.0%). The fat from the liver contains minimal amounts of eicosatrienoic (0.1%) and arachidonic (0.6%) acids. Unsaturated fatty acids predominate in the fat from chicken meat (52.1–58.9%), and the higher amount of polyunsaturated fatty acids is observed in the fat of chicken liver and chicken breasts. Saturated fatty acids predominate in butter and cream (68.6 and 76.2%), which are used as emulsifiers in the preparation of pates, and there is a higher amount of palmitic acid (37.7 and 41.7%).

The fatty acid composition of chicken and turkey pates is different from that of raw materials due to the incorporation of cow’s butter and cream into their composition. The turkey pate has a lower fat content than the chicken (4.7 v/s 7.0%) and a lower saturated fatty acid content in the product (3.3 v/s 3.9%). Saturated fatty acids predominate in the fat from chicken and turkey pates (56.0 and 70.8%, respectively). The ratio of saturated to unsaturated fatty acids in the chicken pate is 1:0.8, while in the turkey pate, it is 1:0.4. The ratio of polyunsaturated to saturated fatty acids is 0.2 for chicken and 0.1 for turkey pate. These values are considerably lower than the optimum ratio of polyunsaturated and saturated fatty acids (1.0 ± 0.2) which is recommended for the prevention of cardiovascular disease [12]. The protein content of the chicken pate and the turkey pate is 12.25 and 11.38%, respectively (Table 2). Therefore, the fat/protein ratio for the chicken pate and the turkey pate is 0.57 and 0.41, respectively. These ratios may play a role in the formation of fat/protein layer in the pate emulsion.

Phase transitions in milk fats

The DSC curves of the dairy fat crystallization at different cooling rates and the subsequent melting are presented in Fig. 2. On both crystallization curves, two exothermic peaks (T c1, T c2) could be observed. The shape of the exotherms, as well as the peak temperatures and heights, changes depending on the cooling rate. The crystallization peaks are sharper and well separated and appear at higher temperatures when the cooling rate decreases. The application of higher cooling rate results in no separated peaks appearing at lower temperatures. Similar dependencies in milk fat were also observed by other authors [11, 13]. The increase in the cooling rate results in the formation of other polymorphic forms with higher crystallization temperatures. Based on Grotenhuis et al. [10], for cooling rates ≥ 2.5 °C min−1, the fat crystallizes in α and γ form, while for the rates ≤ 1 °C min−1, the most found form is β′, which is more stable.
Fig. 2

Effect of cooling rate—1 °C min−1 (blue) and 10 °C min−1 (black) on the crystallization (dotted line) and melting (thin line) of milk fat. All samples were heated at heating rate 5.0 °C min−1. (Color figure online)

As it can be seen from Fig. 2, the melting temperatures of the fat crystallized at lower cooling rate are higher in comparison with the fast cooled samples. Rapid cooling to a low temperature promotes a higher nucleation rate, which leads to the formation of numerous small crystals, which melt at lower temperature [14]. When the fat is slowly cooled, large crystals with higher melting temperature were formed.

The effect of the reheating rate on the fat melting is illustrated in Fig. 3. The two melting peaks differ in their shape. A wider peak is seen for the slower reheated sample compared to the faster reheated sample. The low-temperature peak at 6.9° C, which appears at faster heating, transforms to shoulder of the high-temperature peak at slower heating. The melting process at both heating rates finishes at the same temperature at about 36 °C. Enough energy at lower temperature is given to the sample in this case for realizing the melting.
Fig. 3

Effect of reheating rate—1 °C min−1 (blue) and 5 °C min−1 (black) on the melting (thin line) of milk fat. All samples were cooled at cooling rate 1 °C min−1. (Color figure online)

In all other measurements, standard reheating rate (1 °C min−1) was chosen for all the samples.

Phase transitions of meat and liver fats

The crystallization and melting curves of chicken liver, chicken breast, and turkey breast are presented in Figs. 4, 5 and Table 3.
Fig. 4

Crystallization of chicken liver (blue), chicken breast (black), and turkey fillet (red) at cooling rate 1 °C min−1. (Color figure online)

Fig. 5

Melting of chicken liver (blue), chicken breast (black), and turkey breast (red) at heating rate 1 °C min−1. (Color figure online)

Table 3

Crystallization and melting of chicken liver, chicken breast, and turkey breast at scanning rate 1 K min−1

 

Crystallization

Melting

Peak 1

Peak 2

Peak 3

Peak 1

Peak 2

Peak 3

Chicken liver

      

Onset/°C

29.0

− 44.5

48.0

Peak/°C

30.7

− 30.3

38.5

End/°C

31.6

− 26.3

42.0

H/J g−1

− 140.1

69.97

172.9

Chicken breast

      

Onset/°C

− 23.0

1.8

− 31.1

− 10.2

8.7

Peak/°C

− 5.5

3.3

− 25.8

− 7.3

18.9

End/°C

− 4.8

4.6

− 21.4

− 4.1

24.3

H/J g−1

− 61.77

− 32.34

82.96

11.1

18.42

Turkey breast

      

Onset/°C

− 45.9

− 13.5

14.1

− 23.8

− 6.4

19.4

Peak/°C

− 41.5

− 0.0

15.8

− 18.7

− 4.7

22.1

End/°C

− 38.3

0.9

17.3

− 17.1

− 0.5

37.1

H/J g−1

− 68.26

− 93.76

− 35.4

96.62

68.04

72.72

Although the liver and the meat fatty profiles are similar, big differences in the phase transitions are observed. Only one high-temperature crystallization peak at 30.7 °C is realized in the chicken liver fat, in comparison with the fat in the chicken breast and turkey breast, where three exothermic peaks are observed. The melting endotherms again are significantly different. The differences in the crystallization and melting behaviors of the liver fat and the rest meat fats are suggested to be due to the differences in the protein structure of the products and binding of the unsaturated fatty acid to the liver proteins. In this case, their crystallization is obstructed. The chicken liver fat interacts with the chicken liver binding protein to form liquid–crystalline state, which goes to thermal transition between 10 and 40 °C [15]. The chicken fat and the turkey fat melting behaviors are similar and in accordance with the research by other authors [16]. The poultry breast muscle proteins had quite different emulsion-forming properties [17]. They result in emulsified fats that crystallize and melt at a broad temperature range.

Fat crystallization and melting in poultry pates

The effect of cooling rate on the fat crystallization and melting in the chicken and turkey pates is shown on the DSC curves in Figs. 6 and 7, respectively, and Table 4.
Fig. 6

Effect of cooling rate—1 °C min−1 (black) and 10 °C min−1 (blue) on the crystallization (dotted line) and melting (thin line) of chicken pate. The heating rate for all samples is 1 °C min−1. (Color figure online)

Fig. 7

Effect of cooling rate—1 °C min−1 (black) and 10 °C min−1 (red) on the crystallization (dotted line) and melting (thin line) of turkey pate. The heating rate for all samples is 1 °C min−1. (Color figure online)

Table 4

Effect of cooling rate—1 and 10 °C min−1 on the crystallization and melting of chicken and turkey pates

 

Peak temperature/°C

Peak 1

Peak 2

Peak 3

Peak 4

Peak 5

Chicken pate

     

Melting after cooling at 10 °C min−1

− 17.0

5.3

23.3

Melting after cooling at 1 °C min−1

− 20.8

4.8

24.8

Cooling at 10 °C min−1

− 20.4

− 7.2

2.4

6.3

17.3

Cooling at 10 °C min−1

 

− 4.1

3.3

11.3

 

Turkey pate

     

Melting after cooling at 10 °C min−1

6.3

10.2

27.3

Melting after cooling at 1 °C min−1

5.1

10.0

24.6

Cooling at 10 °C min−1

3.1

7.7

14.5

17.7

Cooling at 10 °C min−1

− 1.0

4.5

10.5

 

The heating rate for all samples is 1 °C min−1

Several peaks indicating phase transitions could be identified. The slowly cooled samples from both chicken and turkey pates have five exotherms. In turn, rapidly cooled samples have just three, indicating that the cooling rate has more pronounced effect on the crystallization of pates compared to raw fats. For the last, the cooling rate affects just the shape and position of the peaks but not their number.

It is supposed that the fat crystallization in the rapidly cooled poultry pates is influenced by the presence of protein compounds in the emulsion, which inhibit the homonucleation and the crystal growth. Therefore, the crystallization occurs at lower temperatures, and the DSC curves are characterized by wider exothermal peaks. Some of the more stable crystal polymorphic states could not be realized in these crystallization conditions.

The formation of unstable crystals in the rapidly cooled samples results in lower melting points [18]. The difference in the melting endotherms for the rapidly cooled raw materials and the rapidly cooled pates is suggested to be due to the organization of the triacylglycerols in the pates. Based on microscopic experiment, larger droplets are more dominant for the slowly cooled pates compared to the rapidly cooled ones [1]. In contrast, the fat globules in the rapidly cooled pates were found to be less stable.

The differences in the melting behavior of the raw materials and the pates could be explained with fat crystallization mechanism in emulsion. The pates were expected to have lower melting points compared to the raw materials, due to the content of “impurities” that act as emulsion. The raw material fats were expected to be highly pure and crystallization depends on homogeneous nucleation, while the pate was expected to contain “impurities,” leading to heterogeneous nucleation. As a result, a temperature decrease in the range of 7–16 °C of every melting endotherms is observed—Figs. 6, 7, and Table 4. The melting of turkey pate fat occurs at lower temperatures in comparison with the chicken pate fat because of the lower fat/protein ratio and the formation of smaller emulsion droplets.

Vanapalli et al. [19] conducted a similar experiment with bulk oil and oil in an emulsion. They found that the crystallization of the emulsion occurred at a lower temperature than the crystallization of the bulk oil and assigned this difference to the presence of other compounds, while a mixture of the two materials seemed to retain both melting points. The higher amount of unsaturated acids is another reason for the different shift between the melting points of the raw materials and the pates. The unsaturated fatty acids interact more strongly with other compounds in the products, like proteins from the connective tissues in the raw fat and proteins from the liver in the pates, resulting in a larger difference in the melting points [20].

Conclusions

The thermal behavior of fats in the dairy and meat products was found to be affected both by the cooling rate and by the reheating rate. As far as the pates are food emulsions, the fat crystallization is obstructed and affected by fat/protein interaction, causing heterogeneous nucleation. Therefore, unstable crystals with low melting points are formed. The thermal treatment of the pate leads to desirable changes in the fat phase transitions and in this way influences the pate texture and functional properties.

Notes

Acknowledgements

The study was supported by the Project No. HTAI129 (Formulation and Design of Food-products and Beverages for Preventive Nutrition) of Agricultural Academy of Bulgaria.

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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2017

Authors and Affiliations

  1. 1.Department of Physics, Faculty of Physics and TechnologyUniversity of Plovdiv Paisii HilendarskiPlovdivBulgaria
  2. 2.Food Research and Development Institute (FoodRDI)PlovdivBulgaria
  3. 3.Department of Chemical Technology, Faculty of ChemistryUniversity of Plovdiv Paisii HilendarskiPlovdivBulgaria
  4. 4.Department of Meat and Fish TechnologyUniversity of Food TechnologyPlovdivBulgaria

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