DD274677A1 - METHOD FOR DETERMINING THE STABILITY OF EMULSIONS - Google Patents

Abstract

The invention relates to a method for determining the stability of emulsions, which finds particular application in the food, cosmetics, or pharmaceutical industry. The object of the invention is to specify the measurement conditions of an easy-to-use method for characterizing emulsion stability. The object is achieved by bringing the emulsions to be investigated into centrifuge cups or measuring cells and subjecting them to constant radial accelerations in speed-regulated centrifuges until constant layer heights of the continuous phase and the remaining emulsion have been reached.

Description

Inventor: Dr, Arndt Seifert

Dr. see Klaus Strenge

Prof. Dr. se. Gerald Muschiolik Manfred Schultz

Klaus Schubert

Dr. Lothar Richter

Method for determining the stability of emulsions Field of application of the invention

The invention relates to a method for determining the stability of emulsions by using the centrifugation. Such characterizations have significance in all areas, \ sc assessing the stability of emulsions with regard to the removal of the continuous phase is necessary for. In the life, cosmetics, pharmaceutical and photographic industries. Of particular importance are such provisions for the preparation of concentrated emulsions.

Characteristic of the known technical solutions

Emulsions are known to be distributions of liquid droplets in other liquids which are not miscible with the liquid droplets. Starting from these two liquid phases of an emulsion, the dispersed liquid droplets which form the so-called dispersed phase (also: disperse, inner, discontinuous phase) and the continuous phase surrounding the liquid droplets (also referred to as outer phase, dispersion medium, means) are processes for determining the stability by centrifugation, which relate to the coalescence of the emulsion droplets (coalescence), which may subsequently result in the separation of a liquid volume from the emulsion droplets. Such methods are z. From R.D. Void, K.L. Mittal and A.U. Hahn in E. Matijevic: Surface and Colloid Science, Vol. 10, Plenum Pres. 1978: 45 ff.

However, the determination of the coalescence stability is of minor importance for a number of emulsion applications, since already separation of the continuous phase leads to a limitation of their applicability, eg. For aesthetic reasons, mayonnaise.

There is a need to quantitatively characterize such Instabilitätseracheinungen by appropriate measures in order to determine the causes for the separation of the continuous phase of the emulsions by the influence of various variables and to be able to influence specifically.

Ea methods for characterizing the emulsion stability are known in which the Aufrahm- or Sedimentationageschwindigkeit under the influence of centrifugal forces or derived therefrom characteristics, eg. For example, the volumes of the continuous phase separated after various cycles of centrifugation + (eg, 10, 20, 30 min) are taken as a measure of emulsion stability. Such methods are z. By ER Garrett, J. Pharm. £ 1 - \)., 1962, p. ¹ 35 ff. 5 JE Robbers, VN Bhatiai, ibid., 50 (0), 1;) 61, p. 708 ff. Major disadvantages of these kinetically oriented methods are their conditional reliability and relatively low application latitude. Thus, contradictory correlations are often obtained especially in emulsions of very different composition.

A major disadvantage of some of the kinetically oriented processes is the need for costly analytical ultracentrifuges. In the DD-PS IO6 777 (Int Cl A 23 I, 1/00 Although a Verfanren for the preparation of food emulsions is described in which by concentration, preferably in a centrifuge, atabile and optimal in terms of fat and protein content Emulsions (mayonnaises, spreadable fats, ice creams) are obtained. However, no Kinweiae for characterizing the emulsion stability, the centrifugation conditions for concentration are given.

Indicate how to characterize the emulation property such as

- The permissible centrifugal pressure, which causes no sedimentation

the centrifugal pressure, which leads to the separation of the continuous phase

- The permissible centrifugal pressure for the separation of the continuous phase without separation of dispersed phase

- The binding capacity for the continuous phase and the possible accumulation of dispersed phase

are not obtained in the known methods.

Object of the invention

The aim of the invention is the development of a method for determining the stability of emulsions, which is characterized by a wide range of applications and high reliability, as well as low process costs.

Explanation of the essence of the invention

The object of the invention is to specify the measurement conditions of an easy-to-use method for the characterization of emulsion stabilities.

The object is achieved by the inventive method for determining the stability of separable by centrifugation emulsions based on the separation of the continuous phase of the emulsion in that the emulsions to be examined in Zentrifugenbecher- or measuring cells and these are subjected in speed-controlled centrifuges constant radial accelerations until constant layer heights (layer height end values) of the continuous phase and the remaining emulsion are reached, and the determination of the so-called stability pressures (in Pa) characterizing the stability of the emulsions by the relationships

^P Em. = To ² × 4 <J -cp × f (r) Pressure of the remaining emulsion

\ _t ?, = ύύ ² . $ kP · ^f ( ^r ) continuous phase pressure

the angular velocity of the rotor, known from the given speed, in S " ¹

the known or experimentally determined density difference of the dispersed phase (g ^ p) and the continuous

= the known or experimentally determined volume fraction of the dispersed phase

= ⁸ factors predetermined by the geometric shape of the centrifuge cells or cups used, which include the distances of the lower (r _u ) and upper (r) limits of the remaining emulsion and the continuous phase to the axis of rotation of the rotor in m

mean, done.

Surprisingly, it was found that in most emulsions under the influence of constant radial accelerations for the separated continuous phase and the remaining emulsion after a corresponding centrifugation time layer height end values (constant layer heights) d. H. laterally constant volumes can be achieved.

The determination of the layer height end values is carried out according to known methods.

Furthermore, the invention is based on the finding that the stability of the emulsions is precisely characterized by the so-called stability pressures (formula 1a) and (1b). The. Invention can be realized by various embodiments.

According to the method of the invention, the emulsion samples are centrifuged at a constant radial acceleration (rotor speed) up to the final values and then the measurement results according to 1a) and / or 1b) are compared.

Another. Variant is that the emulsion samples at different, constant rotor speeds up to the final values

the separated continuous phase and the remaining emulsion are centrifuged. The advantage of this variant is that the dimensions of the stability of the emulsions according to formulas 1a) and 1b) can be compared at several speeds.

A variant of the invention is further that the emulsion samples are first centrifuged at a constant rotor speed to the final values of the continuous phase and the remaining emulsion, then accelerated to a higher, constant rotor speed and centrifuged at this speed again to the final values usv /.

Because of these measurement conditions and the given relationships 1a) and 1b), the so-called stability pressures allow statements about the binding capacity for the continuous phase and the possible concentration of the emulsions. The higher the pressures of the remaining emulsion, the greater the binding capacity for the continuous phase, the more the emulsions are concentratable. The lower the pressures of the separated continuous phase, the greater the binding capacity of the emulsion for the continuous phase, the less can the emulsion be concentrated. The same applies under the abovementioned conditions for the layer height final values themselves.

In the case of emulsions which separate the continuous phase only on the action of centrifugal forces of a certain size, centrifuging is carried out at stepwise higher, constant rotor speeds until the occurrence of the first quantity of deposited continuous phase detectable by measurement. By applying these measurement conditions, another degree of stability is given for such emulsions, the critical pressure against the separation of the continuous phase. Here, the relationship 1a) is used.

With the aid of the measuring method according to the invention, the sniffing of the most varied parameters can be determined on the emulsion stability,

such as B. pH, emulsifier concentration.

'Ertsmals. Information relating to the determination of the process conditions for concentration of emulsions by Sentrifugation and the possible compressive stress of emulsions without

Separation of continuous phase obtained. The inventive method has a wide range of applications and high reliability, accuracy and sensitivity with respect to the determination of the stability of emulsions and is characterized by low equipment costs and low process costs. A significant advantage of the method is that it can be applied to ordinary laboratory centrifuges and ultracentrifuges.

Exemplary embodiments Example 1

Three O / W food emulsions of the composition shown in Table 1 were made

Tab. 1; Composition of the emulsion 1-3 (mass%):

36 rapeseed oil 6 sugar 1,5 salt

MOYIOIiP-310 - 97

Acetic acid, conc. Starch syrup powder

water

1 - 3

Bin. 1 Em. 2 Em «, 3

2.5 U5 U5_

0.7 0.7 0.35

53.3 49 ^ 3 55.65

pH I 4.1 I ₁ Q 4.1

'Former. modified field bean protein isolate

placed in Meßzelien and in a speed-controlled centrifuge (MOM, Budapest, type 31 ^ 0 / b) 5 different constant radial accelerations (rotor speeds) subjected until each Schichthöhen Endv / values for the continuous phase and the remaining emulsion were achieved and which results in a given

3 _k ρ of 998 kg / m ³ and f (r) of 1/2 (r ^ ² - * ₀ ) for the sector-shaped measuring cells used, the stability pressures according to 1b) gave (see Table 2).

it 7

Table 2 quantitatively shows the order of decreasing stability of the emulsions against the separation of aqueous phase, i. H. their capacity to bind a continuous phase: Em. 1 »Em. 3> Em. 2.

At each of the speeds, the final layer height values of the aqueous phase of Emulsion 1 are substantially lower than those of Emulsion 2 and 3. Under comparable centrifugation conditions, Emulsion 1 binds much more continuous (aqueous) phase. This statement is confirmed by the layer height end value of the remaining emulsion, the% by volume and the pressures of the separated aqueous phase.

With equal rssigsäureanteil in the recipe, the Frhöhung d ^ s protein content of 1.5 % (emulsion 2) to 2.5 % (emulsion 1), a significant improvement in water binding capacity, while at the same time can be dispensed with 5 % Stärkesiruppulver.

The increase of the acid content from 0.35 % (emulsion 3) to 0.7% (emulsion 2) leads to a somewhat poorer binding of continuous (aqueous) phase with the same content of protein of 1.5 % and starch syrup powder of 5%.

From emulsions 2 and 3, 43 or 38% by volume aqueous (continuous) phase can already be separated off at speeds of 2,000 rpm, from emulsion 1 only 16% by volume. Ie. nts under comparable Zentrifugationsbeding ^1, the dispersed (oil) phase can be kenzentrieren in the remaining emulsions strongest in the emulsion. 2 However, since emulsion 1 can be centrifuged without oil separation at least to 10,000 rpm to the final value of the remaining emulsion, an approximately equal enrichment of dispersed oil phase (42% by volume separated aqueous phase) can also be achieved in emulsion 1.

The results obtained are in agreement with other studies on stability determination of these emulsions, e.g. B ₀ rheological investigations and the life behavior under gravity.

men

Table 2:

Layer height final values of the continuous, aqueous phase and the remaining emulsion,% by volume of separated aqueous phase and pressures of the continuous, aqueous phase of the 0 / W emulsions 1-3 in the case of rotor

αϊ Π / min. 10 ³ enaanxen ve η d. uuu dis IU UUU UJT in the disperg. Oil phase - s no + = yes Emulsions 2 Layer height i end values in m. 10-3 watts. Ph. Em. abgetr. aq. phase Press d. aq. Phase Pa. 10 ⁵ - 1 1.6 8.4 16 0,052 - 2 4,3 5,7 43 0.14 - U; 4 3.8 6.2 38 0.12 - 1 2.9 7.1 29 0.38 + 2 5.2 4.2 55 0.66 ⁺ 3 6 4.6 4.6 50 0.59 - 1 3.6 6.4 36 1.05 + CVJ 5.5 3.8 59 1.6 + 3 8th 4.9 3.9 56 1.4 - 1 4.0 6.0 40 2.1 + 2 5.8 3.3 64 2.95 + 3 0 5.2 3.4 60 2.65 - 1 4.2 5.8 42 3.4 + 2 5.9 3.0 66 4.7 + 3 20 5.3 3.2 62 4.25 + 1

in / t

"Example 2

Two P / W dietetic emulsions having the composition indicated in Tab.

ΦηΉρΐΐ p. 3; Preparation and composition of O / W food emulsions to determine emulsion stability

Emulsion 1 :

Preparation from 70 g of 6% protein solution and 30 g of rapeseed oil. PH of the emulsion: 7.0

Emulsion 2:

Preparation from 60 g of emulsion 1 and dilute hydrochloric acid; pH of the emulsion 3> 9

were placed in measuring cells of the speed-regulated centrifuge used in Example 1 and 5 baw. 9 different constant radial accelerations were subjected until each layer height final values for the continuous phase and the remaining emulsion were achieved. With specification of 998 kg / m for Sk.t and the experimentally determined values for Sd, P. (913 kg / nT ⁵ ) and <PdiP. with the relationships 1a) and 1b), the stability pressures in Table 4 result.

Table 4:

Layer height final values of the continuous, aqueous phase and the remaining emulsion,% by volume of separated aqueous phase and pressures of the layers of the 0 / W emulsions 1 and 2 at a rotor speed of 2,000 to 50,000 rpm.

Emul sion Rpm. 10 ³ Layer final / m. 10 "aqueous phase menu in 3 f. Emuls. Vol.-JS deducted aq phase Press d Pa. aqueous phase 3r layer 10 ⁵ dist. emulsion 3n in 9d.P. 1 2 none 10.0 - - 0.011 0.34 2 0.68 9.3 6.8 0.02 0,013 1 4 none 10.0 - - 0,044 0.34 8th 10.0 - - 0.17 1 10 none 10.0 - - 0.27 0.34 2 3.4 6.55 34 2.7 0.32 0.51 1 20 5.2 4.8 52 16.1 1.1 0.74 2 4.45 .5,55 44.5 13.8 · 1.3 0.61 1 30 5.35 4.65 53.5 37.3 2.4 0.76 32 5.4 4.6 54 42.7 2.7 0.77 35 5.45 4.56 54.5 51.6 3.3 0.78 50 5.6 4.4 56 108.5 6.7 0.82

From Tubelle 4 shows that the emulsion 1 can be exposed to the pH of a pressure of at least 0.3 ♦ 1O ⁵ Pa (10,000 rev / min), without separation of aqueous (continuous) phase occurs. The increase in speed leads to 20 000 rpm during the transition, ie at least at a pressure of 1.1. 10 ^ Pa, for the separation of aqueous Phaee.

From the emulsion 2 adjusted by addition of acid to the pH value of 3.9, about 7% by volume v / aqueous phase, based on the total volume of the emulsion, can be separated off already at 2000 rpm. Comparing both emulsions at 20,000 rpm, ie under conditions of separation of aqueous phase from both emulsions, the emulsion 1 has a lower binding capacity for the aqueous phase (52% by volume separated aqueous phase) than for emulsion 2 (45% by volume of separated aqueous phase) This is in agreement with the layer height values of the aqueous phase and the remaining emulsion and the pressures calculated therefrom. Thus, the drcok of the aqueous phase of emulsion 1, which is more unstable to the separation of aqueous phase, is higher (16.10 Pa) than that of emulsion 2 (14 · 10 -4 Pa). Conversely, the pressure of the remaining emulsion of emulsion 2 is higher (1.3 · 10 ⁵ Pa), which indeed has a better binding capacity for the aqueous phase than that of emulsion (1.1 · 10 ⁵ Pa).

Furthermore, from the final layer height values and pressures at 20,000 rpm, ie. H. From the same rotational speed, more aqueous phase can be pressed out than from emulsion 2 at 50 000 rpm. separate from the aqueous phase, d. H. a very strong concentration of this emulsion is possible.

Claims (1)

( 12) claim A method for determining the stability of separable emulsions by centrifugation on the basis of the separation of the continuous phase from the emulsion, characterized in that the inspecting emulsions are placed in centrifuge beakers or cells and subjected to constant radial accelerations in speed-controlled centrifuges until constant layer heights of the continuous Phase and the remaining emulsion are reached, and the determination of stability stability of the emulsions characterizing stability (in Pa) by the relationships 1a) for printing ¹¹ Em " ^{63 2} '* $ · ΦΛ.Ρ. F (r) the remaining emulsion and or 1b) for printing ^P kp = W ² «S _k .p. - f Cr) the continuous phase tO ^{β is} the angular velocity of the rotor known from the given speed in s = the known or experimentally determined density difference dispersed phase (tt d.P.) and continuous phase (Q,). "-". TC.P · = the known or experimentally determined volume fraction of the dispersed phase. f (r) β given by the geometric shape of the centrifuge cells or cup predetermined factors, the distances of the lower (r _u ) and upper (r) limit of the remaining emulsion bzv /. the continuous phase to the axis of rotation of the rotor contained in m mean
he follows.