PROCESS FOR PRODUCING POULTRY SAUSAGE

Abstract

The invention relates to a process for producing a firm poultry fat product and a process for producing poultry sausage solely based on poultry, and without additional bacon from pork or vegetable fat resp. The poultry fat product obtainable by the process may be produced solely on the basis of poultry skin which is comminuted and heated. The strength of the poultry fat product is sufficient at room temperature.

Claims

1. A process for producing a poultry fat product comprising the steps of: comminuting a first raw poultry skin mixed with water for generating a first comminuted raw poultry skin; a first heat treatment of the first comminuted raw poultry skin at from 55 C. to 75 C. for from 1 to 3 h for generating a first heat treated comminuted poultry skin; emulsifying the first heat treated comminuted poultry skin by fine grinding for producing an emulsion; comminuting a second raw poultry skin for generating a second comminuted raw poultry skin and mixing with water; a second heat treatment of the second comminuted raw poultry skin at from 70 C. to 90 C. for from 1 to 5 h for generating a second heat treated comminuted poultry skin; comminuting the second heat treated comminuted poultry skin for producing a gel precursor; bringing the emulsion and the gel precursor to a temperature involving a tolerance of at maximum 5 C. and mixing the emulsion and the gel precursor, the temperature being from 30 C. to 60 C., for generating a mixture of emulsion and gel precursor; and cooling the mixture of emulsion and gel precursor.

2. The process according to claim 1, characterized in that comminuting the first poultry skin is effected by grinding, followed by mixing with the water and cutting at from about 0 to 10 C.

3. The process according to claim 1, characterized in that from 0.7 to 2% of salt (w/w) is added to the water of the first and/or second raw poultry skin.

4. The process according to claim 1, characterized in that water at a weight portion of from 1:0.5 to 1:2 is added to the first and/or second raw poultry skin.

5. The process according to claim 1, characterized in that the first heat treatment is carried out at from 55 C. to 65 C. for from about 1 to 2 h.

6. The process according to claim 1, characterized in that comminuting the second raw poultry skin is effected by grinding, followed by mixing with water and cutting.

7. The process according to claim 1, characterized in that the second heat treatment is carried out at from 75 C. to 85 C. for from about 2.5 to 3.5 h.

8. The process according to claim 1, characterized in that particles of connective tissue are generated by cooking comminuted poultry skin in water or steam, followed by separating liquid, and these particles of connective tissue are added to the mixture of emulsion and gel precursor prior to cooling.

9. The process according to claim 1, characterized in that the cooled mixture of emulsion and gel precursor is contacted with salt after gelatinizing and leaked liquid is separated from the cooled mixture.

10. The process according to claim 1, characterized in that the cooled mixture of emulsion and gel precursor is comminuted, mixed with comminuted poultry lean meat and food additives, and cased.

11. A poultry fat product, obtainable by a process according to claim 1.

12. The poultry fat product according to claim 11, characterized by a pressure strength at 20 C. of at least 4,800 Pa, a brightness value L* of at least 80, and an extractable fat proportion of at maximum 65%.

13. The poultry fat product according to claim 11, characterized by a pressure strength of at least 22,000 Pa and a softening temperature of at least 34 C.

14. Use of raw poultry skin as a first and second raw poultry skin in a process according to claim 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0033] In the following, the invention will be described in more detail based on the examples referring to the figures in which:

[0034] FIG. 1 shows the particle size distribution of the first comminuted raw poultry skin, determined by sieving;

[0035] FIG. 2 shows the volumetric phase proportions of the first comminuted raw poultry skin;

[0036] FIG. 3 shows the interfacial tension of the aqueous phase of the first comminuted raw poultry skin;

[0037] FIG. 4 shows the relative molecular sizes of soluble proteins of the first comminuted raw poultry skin in terms of retention times in gel permeation chromatography;

[0038] FIG. 5 shows the brightness values of the aqueous supernatant of the first comminuted raw poultry skin after a first heat treatment;

[0039] FIG. 6 shows the color values of the aqueous supernatant of the first comminuted raw poultry skin after a first heat treatment;

[0040] FIG. 7 shows the interfacial activity of the aqueous supernatant of the first comminuted raw poultry skin after a first heat treatment;

[0041] FIG. 8 shows the emulsifier capacity of the aqueous supernatant of the first comminuted raw poultry skin after a first heat treatment;

[0042] FIG. 9 shows the relative molecular sizes of soluble proteins of the first heated comminuted poultry skin for first heat treatments of different lengths of time in terms of retention times in gel permeation chromatography;

[0043] FIG. 10 shows the interfacial activity for the first heat treated comminuted poultry skin after different times of first heat treatment;

[0044] FIG. 11 shows the emulsifier capacity of the first heat treated comminuted poultry skin after different times of first heat treatment;

[0045] FIG. 12 shows the analysis of fat extractable from the cooled gel from a second heat treated comminuted poultry skin after different second heat treatments;

[0046] FIG. 13 shows the pressure strength of the cooled gel from a second heat treated comminuted poultry skin after different second heat treatments;

[0047] FIG. 14 shows the extractable fat proportion of the cooled gel from a second heat treated comminuted poultry skin after different second heat treatments;

[0048] FIG. 15 shows the pressure strength of the heat-treated second comminuted poultry skin in dependence on the second heat treatment;

[0049] FIGS. 16A-F show microscopic images of the poultry fat product at different mixing ratios of emulsion (emulsion phase) and gel precursor (gel phase) without connective tissue particles;

[0050] FIGS. 17A-F show scanning electron microscopic images of the poultry fat product at different mixing ratios of emulsion (emulsion phase) and gel precursor (gel phase) without connective tissue particles;

[0051] FIG. 18 shows values of the fat proportion extractable from the poultry fat product at different mixing ratios of emulsion and gel precursor (gel) without connective tissue particles;

[0052] FIGS. 19A and B show the brightness or color of the poultry fat product at different mixing ratios of emulsion and gel precursor (gel) without connective tissue particles;

[0053] FIG. 20 shows the pressure strength of the poultry fat product at different mixing ratios of emulsion and gel without connective tissue particles;

[0054] FIGS. 21 to 23 show the temperature stability of the poultry fat product at different mixing ratios of emulsion and gel;

[0055] FIG. 24 shows the pressure strength of the poultry fat product having a content of connective tissue particles; and

[0056] FIG. 25 shows the moistness of the poultry fat product having a content of connective tissue particles.

[0057] In the figures, standard deviation is given for triplicate determinations, while the mean value of duplicate determinations is given without standard deviation.

EXAMPLE

Production of the Poultry Fat Product

[0058] For comminuted poultry skin a grinded raw mixture of 70% (w/w) of chicken breast skin and 30% (w/w) of turkey breast skin containing a water content of from 42.5 (batch 1) to 38.5% (w/w) (batch 2), from 46.2 (batch 1) to 49.5% (w/w) (batch 2) of fat, 9.78 (batch 1) or 10.8% (w/w) (batch 2) of total protein according to Kjeldahl (N*6.25), from 0.82 (batch 1) to 0.90% (w/w) of non-protein nitrogen according to ASU L07.00-14, and from 4.38 (batch 1) to 4.84% (w/w) of connective tissue was used.

[0059] Further comminuting of the poultry skin is effected by cutting a 1:1 mixture including water which has been added in the form of ice water during 10 rounds of cutting at 1,500 rpm, followed by 220 rounds of cutting at 5,000 rpm. Alternatively, comminuting is effected in the presence of 1:1 0.95% (w/w) of salt solution (NaCl). As a further alternative, the comminuting may be effected in the presence of ice water or 0.95% (w/w) of salt solution through cutting for 10 rounds at 1,500 rpm, followed by fine grinding in a mill, preferably while cooling, particularly to at maximum 5 C., preferably 3 C. of the mixture. The particle sizes were determined through wet sieving using standard sieves. The particle sizes are given in FIG. 1 as % of passage through the sieves. As a result it is shown that effective comminuting is achieved through cutting, while salt solution during cutting leads to less effective comminuting than water.

[0060] The particle sizes of fractions of <1 mm were determined using laser diffraction (Malvern Mastersizer 2000, suspended in tetra-sodium pyrophosphate solution) in terms of the Sauter diameter. Comminuting by cutting yielded a Sauer diameter of 66.8 m.

[0061] The suspensions generated by comminuting were centrifuged to determine the proportions of generated phases. It turned out that the majority of aqueous phase was generated by cutting in the presence of salt containing water. The result is plotted in FIG. 2, namely for the comminuting procedure either in the presence of water (cutter) or salt solution (cutter NaCl). In FIG. 2 the lower section of a column each shows the solid, the middle section shows the liquid supernatant, and the upper section shows the fat/cream layer. The measurement of the interfacial tension (dynamic interfacial tension, measured using a drop volume tensiometer DVT50 (KRSS) versus neutral oil) of the respective liquid phases of the suspensions showed an optimum of equilibrium values and minimum values in respect of comminuting through in salt solution; the results are shown in FIG. 3. Therein, a minimum value (right column, minimum) and a small equilibrium value (left column, equilibrium) indicate good emulsion formation or long-term stability of the emulsion. Also the measurement of the extractable fat proportion of the suspensions (by mixing and partitioning with a solvent, preferably petroleum benzene, followed by filtering off, with extracted fat being determined after evaporation of the solvent) shows that by cutting in salt solution (ca. 61% of total fat) an improvement of the interface condition (reduced fat extraction) is achieved compared to cutting in water (ca. 77% of total fat).

[0062] The analysis of the size distribution of solved proteins of the aqueous phases generated through cutting in water or salt solution using gel permeation chromatography (GPC, Waters 2695 Alliance Separations Module with Waters 2996 Photodiode Array Detector, Waters, USA; column: Superdex 200 10/300GL (GE Healthcare, Freiburg); isocratic with 0.5 ml/min 0.15 M disodium phosphate, 1% of NaCl (w/w), pH 6.8) showed that a relatively small proportion of high molecular sizes were generated, and that through cutting in salt solution the proportion of high molecular sizes is greater than through cutting in water. The results are shown in FIG. 4, where longer retention times indicate smaller molecules; the proportions are shown in terms of detected area percentages (GPC area proportion (%)), left columns cutting in water (cutting), right column cutting in salt solution (cutting NaCl). The greater proportion of solved protein of small molecular size through comminuting in salt solution supports the better properties of the emulsifier as outlined in the following.

[0063] Accordingly, for generating the first comminuted raw poultry skin comminuting through cutting in the presence of salt solution is preferred.

[0064] The first heat treatment of the first comminuted raw poultry skin was carried out after cutting in 1:1 salt solution, as generally preferred. In this respect, a temperature of from 55 to 65 C. for from 1 h to 2 h is preferred, in particular of 60 C. for 1.5 h, because this first heat treatment produced the most advantageous combination of brightness, color, interfacial tension and emulsifier capacity. The colors were determined in the L* a* b* color space, where L*=brightness, 0=black, 100=white; +a*=red, a*=green, +b*=yellow, b*=blue, from +60 to 60 in each case (measured using Spectralphotometer CM-600d, Konica-Minolta at standard light D65). This color space has a good correlation of geometric and sensed distance between colors.

[0065] FIG. 5 shows the brightness values L* after the first heat treatment at 60 C., 70 C., 80 C. for 0.5 h, 1 h and 5 h in each case, FIG. 6 the color values a* (left column) and b* (right column). The brightness and color values show that the first heat treatment each produces a first heat treated comminuted poultry skin with acceptable appearance.

[0066] FIG. 7 shows the interfacial tension (equilibrium left column, minimum right column) (drop volume tensiometer DVT 50) of the aqueous supernatant after the first heat treatment (first heat treated comminuted poultry skin), FIG. 8 the emulsifier capacity (determination of the maximal amount of oil emulsified in the laboratory experiment). These results show that with respect to the first heat treatment the optimal combination of interfacial tension and emulsifier capacity is achieved at a temperature in the range of from 55 to 65 C., preferably 60 C., for 0.5 h to 2 h, particularly for ca. 1 h.

[0067] The analysis of the protein content after a first heat treatment at 60 C. for from 1 h to 4 h showed that through the first heat treatment the content of soluble protein of the first heated comminuted poultry skin was more or less doubled after 1 h compared to the first comminuted raw poultry skin and hardly increased by extended treatment times. The analysis of the soluble proteins using GPC showed that a first heat treatment at 60 C. for 1 h already produced a significant reduction of the molecule sizes, whereas extended treatment times hardly resulted in a further rise in small molecular sizes. FIG. 9 shows the results of GPC, with the columns of each group being arranged in the order of the legend of FIG. 9; at >13 and >41 the value of before heating is zero.

[0068] The analysis of the interfacial tension of the aqueous supernatant after a first heat treatment at 60 C. for from 1 h to 4 h shows that the optimal (minimal) equilibrium value is reached after a treatment time of 1.5 h, and also a smaller value of the interfacial tension is reached for the first heat treated comminuted poultry skin. The results are shown in FIG. 10 (equilibrium left column, minimum right column). FIG. 11 shows the results of the measurement of the emulsifier capacity for this first heat treated comminuted poultry skin. The first heat treatment at 60 C. for ca. 1.5 h shows the highest emulsifier capacity.

[0069] The emulsification of the first heat treated comminuted poultry skin was effected by fine grinding using a rotor-stator disperser (1,000 rpm, engine, Kotthoff LDF) for about 2 min until the emulsion showed a bright color.

[0070] The gel was prepared by grinding the raw poultry skin, as it was used for generating the emulsion, which was comminuted and mixed 1:1 (v/v) with 0.95% (w/w) salt (NaCl) in water to generate the second comminuted poultry skin, which was subsequently subjected to a second heat treatment at 70 C., 80 C. or 90 C. for 2 h, 4 h or 6 h in each case, to generate the second heat treated comminuted poultry skin, and subsequent comminuting of the same. This final comminuting was effected using a laboratory grinder (Blend Tec).

[0071] The pressure strength is generally determined at 20 C., e.g. by measuring the force required for pushing a plastic cylinder into the sample for 4 mm. The pressure strength is the pressure corresponding to the exerted force per front surface of the cylinder, in the present case circular, having a diameter of 12.7 mm.

[0072] The analysis of the pressure strength (measurement of the force required for pushing in a plastic cylinder of 12.7 mm diameter by 4 mm, determined as the force per cylinder cross sectional area) of the spun down aqueous supernatant of the second heat treated poultry skin after gelatinizing by cooling revealed maxima for a second heat treatment at 90 C. for 4 h (ca. 1,800 Pa) and at 80 C. for 4 h (ca. 1,900 Pa).

[0073] FIG. 12 shows the results of the analysis of fat extractable from the cooled gel compared to a second comminuted raw poultry skin (cutter KCl). As evident, the second heat treatment deteriorated the emulsifying properties at elevated temperatures and for extended periods of time. Thus, a second heat treatment to 75 C. to 85 C., preferably 80 C., for from 3 h to 5 h, particularly 4 h, is preferred.

[0074] The second heat treatment results in markedly higher values of pressure strength of the cooled gel as shown in FIG. 13 compared to the second comminuted raw poultry skin. In order to achieve a high pressure strength the second heat treatment is thus preferably carried out at from 75 C. to 85 C., more preferably at from 80 C., for from 3 h to 5 h, particularly for 4 h.

[0075] The extractable fat proportion (extracted fat/total fat, in %) of the cooled gel from the second heat treated poultry skin compared to untreated second comminuted raw poultry skin is shown in FIG. 14. This result illustrates that also in case of the second heat treatment at 80 C. for 3 h or 90 C. for 2 h the fat is well incorporated within the matrix and, accordingly, is less extractable.

[0076] FIG. 15 shows the pressure strength of the heat treated second comminuted poultry skin as a function of the second heat treatment. The maximal strength of the cooled gel is measured for the second heat treatment at 80 C. for 3 h.

[0077] A comparison of the measured values in FIGS. 12 and 14, and FIGS. 13 and 15, respectively, for the same process parameters each shows variations between different batches of poultry skin.

[0078] Each of the emulsion and precursor were brought to a temperature of 60 C. and mixed to 90% gel precursor+10% emulsion, 75% gel precursor+25% emulsion, or 50% gel precursor+50% emulsion, and cooled in flat containers. The poultry fat product obtained in this way shows after dyeing of protein with FITC (absorption at 492 nm, emission 520 nm, green) and of fat with Nile red (absorption at 554 nm, emission at 606 nm, red) in confocal laser scanning microscopy at excitation with 488 nm and 514 nm or 488 nm, 568 nm and 647 nm a homogenous distribution of fat predominantly in drop shape, and a homogenous distribution of protein with only a very low amount of denatured protein. The microscopic images are shown in FIG. 16, in (A) and (B) for 90% gel+10% emulsion, in (C) and (D) for 75% gel+25% emulsion, and in (E) and (F) for 50% each of gel and emulsion, at different magnifications.

[0079] FIG. 17 shows scanning electron microscopic images (samples frozen in liquid nitrogen, broken through cryo-preparation, free water sublimated at 10 C. and vapor-deposited with gold, image taken at 185 C. in a vacuum) of the poultry fat product, in (A) and (B) for 90% gel+10% emulsion, in (C) and (D) for 75% gel+25% emulsion, and in (E) and (F) for 50% each of gel and emulsion, each at different magnifications. The images show that at 10% emulsion the protein network structure of the gel is essentially preserved, and this structure becomes more compact with an increasing amount of emulsion. At 75% gel+25% emulsion, the poultry fat product shows relative large gaps or blank volume, facilitating the leakage of water, e.g. when being contacted with salt, and leading to decreased strength.

[0080] The extractable fat proportion is shown in FIG. 18. These values in the range of 53% to 63% of total fat show sufficient stabilization of the fat in the poultry fat product.

[0081] The results of the optical analysis in FIG. 19 show sufficient brightness and acceptable color of the poultry fat product.

[0082] FIG. 20 shows the pressure strength of the poultry fat product of the indicated mixtures of gel and emulsion. The pressure strength for 25% and 50% emulsion are more or less the same. This is currently ascribed to the more compact structure of the poultry fat product with 50% each of gel and emulsion.

[0083] FIGS. 21, 22 and 23 resp. show the temperature stabilities of the poultry fat products, determined in terms of storage modulus G, reflecting the tension of the reversible stretch of the internal structure of the poultry fat product and thus being a measure of the strength of the indestructible structure. Therein, a greater storage modulus indicates a greater internal strength of the poultry fat product. The measurement was carried out at a frequency of 1 Hz and a temperature in the range of 5 C. to 45 C. The deduced boundary temperatures of the temperature stability are indicated each and show that the poultry fat product gelatinizes thermo reversibly and has sufficient strength, in particular with respect to a processing temperature of at maximum 5 C. and a storage temperature of at maximum 25 C.

[0084] FIG. 24 shows the pressure strength of the poultry fat product of the preferred embodiment with additional particles of connective tissue from which liquid was separated. With respect to the situation without additional particles of connective tissue (without), 5% (w/w) connective particles (2/0.5) or 10% (w/w) connective particles (2/1) the values for 90% gel+10% emulsion, 75% gel+25% emulsion, and 50% each of gel and emulsion, the values are shown. These results show that by admixing connective tissue particles the pressure strength of the poultry fat product may be increased to from 4-fold to 5-fold.

[0085] FIG. 25 shows the water content (moistness, %) of the poultry fat product of the preferred embodiment with admixed particles of connective tissue. The samples correspond to those of FIG. 24. As shown by the measured values (drying at 105 C. until mass constancy), the water content of the poultry fat product is ca. 15% to 18% higher compared to bacon from pork.