PROCESS FOR PRODUCING GELATIN FROM FISH SKIN BY OPTIMISATION OF THE EXTRACTION CONDITIONS

Abstract

A process for obtaining fish gelatin characterized because it comprises: (a) cleaning of fish skins; (b) washing of skins with water; (c) treating with diluted alkali solution with constant agitation; (d) washing of skins with water until the wash water is in a pH range between 6.8 and 7.2; (e) treating with diluted organic acid solution with constant agitation; (f) washing of skins with water until the wash water is in a pH range between 6.8 and 7.2 and subsequent runoff; (g) extracting gelatin by mixing the skins in an organic acid solution with a concentration of 0.2 to 0.3 weight percent by volume at a temperature of 55 to 65 C. and for 260 to 340 minutes; (h) filtering to remove skin debris and impurities; (i) drying; and (j) grinding.

Claims

1. A process for obtaining gelatin from fish skins of genus Coryphaena characterized in that the process comprises the following steps: (a) cleaning the fish skins; (b) washing the fish skins with water at a temperature of 10 to 12 C.; (c) treating the fish skins with a solution of a diluted alkali, at a temperature of 10 to 12 C., with constant agitation; (d) washing the fish skins with water at a temperature of 10 to 12 C., until the washing water is in a pH range between 6.8 and 7.2; (e) treating the fish skins with a citric acid solution in a percentage between 0.4% and 1.0% weight per volume, at a temperature of 10 to 12 C., and with constant agitation; (f) washing the fish skins with water at a temperature of 10 to 12 C., until wash water is in a pH range between 6.8 and 7.2, and then the wash water is drained; (g) extracting gelatin at an acid pH by mixing the fish skins in citric acid solution in a percentage from 0.2% to 0.3% weight per volume, at a temperature between 55 and 65 C., and for a time between 260 and 340 minutes; (h) filtering the gelatin of step (g) to remove skin debris and impurities; (i) drying the gelatin of step (h); and, (j) grinding the gelatin of step (i).

2. The process according to claim 1, characterized in that, in step (g), a ratio between the fish skins and the citric acid solution equal to 1:3 weight by volume is used, and with constant agitation.

3. (canceled)

4. The process according to claim 1, characterized in that, the step (c) is performed for a time between 6 and 8 hours.

5. The process according to claim 1, characterized in that, in step (e), the diluted alkali is sodium hydroxide in a percentage between 0.2 and 2.0% weight per volume.

6. (canceled)

7. The process according to claim 1, characterized in that, the step (e) is performed for a time between 1 and 2 hours.

8. (canceled)

9. The process according to claim 1, characterized in that, in step (i), the drying is carried out at temperatures below 60 C.

Description

DESCRIPTION OF THE FIGURES

[0027] FIG. 1: it shows the contours for the gel strength, as a function of the temperature and concentration variables of citric acid, it is observed the intercalation between the temperature and concentration variables of citric acid on the gel strength of the gelatins obtained. In the same, it can be seen that when the extraction of gelatin is carried out at low temperatures (approximately between 40.0 and 55.0 C.) and using low concentrations of citric acid (approximately between 0.1 and 0.5%) gelatins are obtained with the highest values of gel strength (>400 g); however, these values decrease considerably (from 370 to 280 g) when the temperature is increased from 62.5 C., independent of the concentration of citric acid.

[0028] FIG. 2: it shows the contours for protein extraction yield, as a function of temperature and citric acid concentration variables. It is observed the interaction between the temperature and concentration of citric acid variables on the extraction yield in obtaining the gelatins. Here, gelatins with higher yields are obtained with extraction at high temperatures (>55.0 C.) and using low concentrations of citric acid (approximately between 0.20 and 0.55%).

[0029] FIG. 3: it shows the flow diagram of the gelatin making process.

PREFERRED EMBODIMENT OF THE INVENTION

[0030] A Central Composite Design was used for the optimization. Table 1 shows the study variables and the values used for each variable in the design.

TABLE-US-00001 TABLE 1 Variables and their respective values used for the step corresponding to the central composite design. Variable Values used for the variables Temperature ( C.) 40 46.1 55 63.9 70 Time (minutes) 60 129 230 331 400 Concentration of 0.1 0.26 0.5 0.74 0.9 citric acid % (w/v)

[0031] Table 2 shows 20 treatments defined by the design and different combinations of the temperature, time and concentration of citric acid variables used, as well as the results obtained from gel strength and protein extraction yield in each of the treatments.

TABLE-US-00002 TABLE 2 Gel strength and protein extraction yield in the treatments made in the central composite design. Response Variables Study variables Yield of Temper- Concentration Gel protein ature Time of citric acid strength extraction Treatment ( C) (minutes) (%) (g) (%) 1 46.1 129 0.26 454.2 16.84 2 63.9 129 0.26 350 20.41 3 46.1 331 0.26 396.9 18.34 4 63.9 331 0.26 346.7 21.36 5 46.1 129 0.74 404.5 16.71 6 63.9 129 0.74 338.0 20.25 7 46.1 331 0.74 381.0 17.49 8 63.9 331 0.74 335.3 20.97 9 40.0 230 0.50 390.1 15.74 10 70.0 60 0.50 287.3 21.35 11 55.0 400 0.50 409.5 18.89 12 55.0 230 0.50 370.8 20.56 13 55.0 230 0.10 423.3 19.12 14 55.0 230 0.90 360.9 18.66 15 55.0 230 0.50 388.8 19.92 16 55.0 230 0.50 383.3 19.89 17 55.0 230 0.50 394.3 19.76 18 55.0 230 0.50 390.5 19.76 19 55.0 230 0.50 396.9 19.80 20 55.0 230 0.50 386.0 19.83

[0032] Table 3 shows optimization solutions for obtaining gelatins with gel strength values greater than 385 g and protein extraction yield greater than 20.0%.

TABLE-US-00003 TABLE 3 Solutions of optimization and responses for obtaining gelatin from fish skin. Yield of Optimi- Temper- Concentration Gel protein zation ature Time of citric acid strength extraction solutions ( C.) (minutes) (%) (g) (%) 1 56.8 331 0.26 389.1 20.58 2 56.2 331 0.27 390.6 20.48 3 57.1 331 0.29 386.4 20.66 4 56.2 296 0.26 394.6 20.26 5 56.7 265 0.26 395.6 20.17 minimum 56.2 265 0.26 maximum 57.1 331 0.29

[0033] In accordance with the above, a test was carried out on the skins of mahi-mahi or common dolphinsish (Coryphaena hippurus), according to the following process characteristics: [0034] (1) The mahi-mahi skins are cleaned by separating the remains of muscle, flakes and other impurities from the skins. [0035] (2) Washing the skins with cold water (10 C.). [0036] (3) The skins are treated with a cold solution (10 C.) of 0.2% (w/v) sodium hydroxide (NaOH) for 6 hours with constant agitation. [0037] (4) Next, the skins are then washed with cold water (10 C.) until the wash water is in a pH range between 6.8 and 7.2. [0038] (5) The skins are treated with a cold solution (10 C.) of citric acid (food grade) 0.48 (w/v) for 1 hour with constant agitation. [0039] (6) The skins are washed again with cold water (10 C.) until the wash water is in a pH range between 6.8 and 7.2 and then the skins are drained. [0040] (7) Gelatin extraction at acid pH is done by mixing the skins in a 0.26% (w/v) citric acid solution (food grade) at a temperature of 56.8 C. and a time of 331 minutes, using a mahi-mahi skin ratio: citric acid solution equal to 1:3 (w/v) and maintaining constant agitation. [0041] (8) Filtering to remove skin debris and impurities. [0042] (9) Drying in hot air by forced convection at a temperature of 50 C. [0043] (10) Finally, a grinding process is carried out to obtain the final powdered product.

[0044] The gelatin obtained from this example showed a gel strength of 386.6 g; a protein extraction yield of 20.4%; a viscosity of 11.0 cP; a protein percentage of 88.3%; and a pH of 4.9.

[0045] For reasonable generalization, the ranges to be protected in the attached claims are the concentration of citric acid (food grade) from 0.20 to 0.30% (w/v), the time from 260 to 340 minutes and the temperature from 55.0 to 65.0 C. for the extraction step.