GB1585456A

GB1585456A - Soybean beverages

Info

Publication number: GB1585456A
Application number: GB23877/78A
Authority: GB
Original assignee: Alfa Laval AB
Current assignee: Alfa Laval AB
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-03-04

Description

(54) SOYBEAN BEVERAGES (71) We, ALFA-LAVAL AB, a Swedish body corporate, of Postfack, S--14700 Tumba, Sweden, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a process for the preparation of a soybean beverage, and more specifically, to a process for the preparation of a soybean beverage which is lipoxygenase inactive, free from trypsin inhibitors, with good digestability, sterile, homogenous with a good dispersibility and which has a bland odour and flavour.

Protein beverages in various forms based on soy beans have been tested and found acceptable in several countries. A continuing effort is being made to improve these products.

Ordinarily, soy milk does not have the characteristic flavour or smooth texture of cow's milk, nor has its nutritive value been as scientifically evaluated.

Nevertheless, its lon and successful use in East Asia and its use in feeding children allergic to cow's milk in the western hemisphere indicate that it has good nutritive properties.

Traditionally, soy milk is made by water extraction, the original method followed in China for several centuries. Protein and oil are extracted in the form of an emulsion in about the same ratio as they occur in the beans. Soybeans are soaked in water for several hours, until they are saturated and then ground with water. The slurry of beans and water is strained or filtered in order to remove insoluble residue. The milky-looking water extract contains about 65% of the total solids. After filtering, the soymilk is boiled for a couple of minutes and often sugar is added.

One main problem with the traditional soymilk is its strong disagreeable flavour. The flavour has been described as "beany", "bitter" and "painty".

Scientists, who have studied the problem have found that the enzyme lipoxygenase, which is naturally present in the soybean, is the cause of the trouble. As soon as the soybean is ground with water, the lipoxygenase acts on the unsaturated fatty acid chains, producing a large number of smaller molecular weight compounds. By means of modern sophisticated chemical techniques about 80 volatile components have been isolated from soymilk and about 40 of them identified.

At least 30 of these volatile compounds have some flavour impacts and, with few exceptions, the flavour of the compound is unpleasant. One compound in particular, ethyl vinyl ketone, has a typical beany flavour.

A large number of people have studied the problem of inactivating the lipoxygenase before it causes flavour damage, and several procedures have been proposed.

Another problem to consider is the number of growth depressant substances, mainly trypsin inhibitors and haemagglutein present in soybeans. In the original soymilk method the milk usually is boiled for some time, and because the trypsin inhibitors as well as haemagglutinin are heat-labile the nutritional value is improved.

Much scientific work is carried out to investigate and determine the effect of heat treating various soybean products, soymilk as well as soybean oil cakes and solvent-extracted soybean meal and flour. It has been found that about half of the growth-inhibiting effect of raw soybean meal fed to rats was due to its haemagglutinin content, but since the haemagglutinin activity is more readily destroyed by moist heat than the trypsin inhibitor, the level of trypsin inhibitor remaining in soybean products can serve as an index of the adequacy of heat treatment.

It has also been possible to determine that in order to obtain a meal of maximum nutritive value, sufficient heat must be applied not only to destroy the trypsin inhibitor but also to alter the protein in such a way that it may be more readily attacked by proteolytic enzymes. For example, it has been shown that after soybean flour, to which an equal volume of water has been added, was autoclaved at 100"C a small amount of native protein still remained after 3 hours heating, whereas the native protein completely disappeared after a few minutes heating at 1100C and 1 20 C.

It must be borne in mind, however, that heat treatment of soybeans normally drastically reduces the functional properties of the proteins therein. This means for example, that the aqueous dispersibility, i.e. the capacity to partially form a colloidal suspension and to partially dissolve in an aqueous fluid, is impaired to a large extent by ordinary heat treatment.

Under many circumstances the soy beverage must be sterile.

In the soy bean beverages manufactured until now, the digestibility has not been optimal because of the heat treatment technique used.

We have now developed a process of preparing a soybean beverage which is lipoxygenase active, free from trypsin inhibitors and sterile and which has good digestibility, homogeneity, dispersibility, and a bland odour and flavour.

The process according to the invention comprises: (a) heating to 70 to 1000C a suspension in water of flour made from dehulled soybeans, the suspension having a pH of 6.4 to 10 (the pH being optionally adjusted to 7 to 9 before the next step), (b) blowing superheated steam into the suspension while the latter is passed through a narrow conduit (which is preferably of circular cross-section) so as to raise the temperature of the suspension to 120 to 1600C (preferably 120 to 1470C), the suspension being held at such a temperature for sufficient time to inactivate the enzymes and trypsin inhibitors present in the flour and to partially degrade peptides in the flour without substantial denaturing of proteins therein.

(c) flashing off volatiles (including water vapour) from the suspension at reduced pressure, which causes cooling of the suspension, and then (d) cooling the suspension to no more than ambient temperature (for example, to about 15"C) and adjusting the pH of the suspension to nautrality (about 7).

The process according to the invention, which is preferably carried out in continuous fashion, results in a suspension of good nutritional value with no objectionable flavour, the suspension being ready to be packed in a sterile condition.

The time for which the suspension is held at a temperature in the range of 120 to 1600C in step (b) is preferably 10 seconds to 10 minutes (more preferably 10 to 400 seconds), longer times being required at lower temperatures in the above range and shorter times being required at higher temperatures.

Step (b) is preferably carried out in a VTIS apparatus, as described by us in a series of Technical Bulletins, such as Technical Bulletin VTIS/C No. TB60916E.

Such apparatus is generally used for injecting superheated steam into a liquid, such as milk, the liquid being rapidly heated thereby to, for example, about 143 C and held at such a temperature for a few seconds before being passed through an orifice to a vacuum vessel where volatiles are flashed off at reduced pressure. The apparatus used in the process according to the invention is preferably modified by including a holding tank, in the form of a pipe, between the steam injector and the orifice leading to the vacuum vessel, whereby the time for which the liquid can be held at the elevated temperature can be prolonged.

It is sometimes desirable to produce a low-carbohydrate beverage, in which case, carbohydrates are preferably leached out of the initial flour with water, in one or more steps. The solids produced by leaching in this way are preferably removed, for example, by centrifugal separation and then used to make the suspension from which the beverage is prepared in the process according to the invention.

In order that the present invention may be more fully understood, the following Examples are given by way of illustration only. Unless indicated to the contrary, all parts and percentages in the Examples are by weight.

Example I.

10 kgs of full fat, enzyme active soybean flour were suspensed in 100 kgs water.

The ratio flour/water may be varied according the the desired solids content and viscosity. The soybean flour may be "Diasoy" from Soya Foods Ltd., or may be produced from soybeans by crushing of the beans in 2-6 parts, removing the hulls by wind screening and grinding the remaining cores to the desired size, for example 100 y. The suspension was stirred by a mixer. 2M NaOH is added until the pH reached 9.3. The suspension could be kept for about an hour without deterioration but no holding time is required at this stage.

The suspension was then fed to a modified VTIS-apparatus, which comprised a heat exchanger for indirect heating of the liquid feed, a steam injector, where the liquid feed is passed successively through a relatively narrow channel in which steam is injected into the liquid, a holding tank in the form of a pipe and an orifice mounted before a vacuum vessel, from ;which the flash cooled liquid is fed to heat exchanger for cooling.

In this modified VTIS-apparatus, the temperature in the suspension was rapidly raised to 1470C and kept there for 90 seconds. Then the suspension was cooled in the heat exchanger to about 15"C, whereupon the pH was adjusted to 7.0 by the addition of 2M HCI. The soybean beverage was then sterile and ready for packing.

Example 2.

A suspension was prepared in the same way as in Example 1. The pH was adjusted to 4.3. After a leaching period of 30 minutes, the suspension was fed to a centrifugal separator, in which it separated into a solid phase with 24% dry solids and a clear liquid phase, containing most of the carbohydrates and other soluble material and some protein. The clear phase was evaporated to a feed product. The solid phase was mixed with 70 kgs water, and stirred for about I minute, whereupon the mixture was separated in a centrifugal separator to give a solid phase and a clear liquid phase. These solids were washed once more in this way, mixed with 70 kgs of water, whereafter the pH was adjusted to 9.3 by the addition of 2M NaOH.

Then the suspension was treated in a modified VTIS-apparatus of the type mentioned in Example I.

It may be noted, that it is more efficient to carry out the leaching in a countercurrent operation.

The soybean beverage prepared according to Example 1 was compared with ordinary, heated, defatted and dehulled soybeans obtained from Karlshamns Oljefabrik AB in a feeding trial with growing rats.

The aim of the study was to compare the nutritive properties of the two protein sources. Biological value (BV, as defined by H. H. Mitchell in J. Biol. Chem. 58, 873 (1923)), net protein utilization (NPU, as defined by H. V. McCollum and N.

Simmonds, The Newer Knowledge of Nutrition, (1929), Macmillan, New York) and true digestibility (TD, that is, the percentage of food nitrogen that is absorbed) were determined. The results are summarised in Table 1. There were no significant (P < 0.05) difference in nutritive properties of the soy milk and soy flour.

Digestibility was 90.2% for the flour indicating a satisfactory inactivation of the trypsin inhibitors present in soy. BV values of 59.3 and 60.0 and NPU values of 53.5 and 55.2 for the milk and flour, respectively, were close to values usually obtained for soy flour in our laboratory. These results suggest equal availability of the sulfur amino acids, the first limiting amino acids in soy, from the milk and the flour.

TABLE 1 Summary of BV Assays of Alfa-Laval Soybean Beverage Wt gain (g) Feed intake (g) Dietary Ret Treatment No. 0-4 5-9 0-4 5-9 BV TD NPU Soy Flour 1 8.4 10.9 32.7 47.7 61.5 91.8 56.4 2 5.4 8.8 37.1 49.8 58.6 89.8 52.6 3 10.8 11.4 39.5 53.7 61.3 91.6 56.2 4 10.7 9.3 36.1 49.6 60.0 91.7 55.0 5 8.9 11.9 35.8 54.7 61.7 90.2 55.6 a 60.6 91.0 55.2 T + 1.31 + 0.94 + 1.53 Alfa Laval Soy Milk 21 10.2 11.6 38.0 52.3 60.3 92.4 55.7 22 12.2 11.0 37.5 51.7 61.2 89.5 54.8 23 8.6 12.1 42.6 53.3 57.2 88.5 50.6 24 8.7 13.2 34.9 47.7 61.8 90.6 56.0 25 6.9 10.9 36.1 43.3 55.8 90.1 50.3 59.3 90.2 53.5 31 +2.62 + 1.48 + 2.80 a) Means + SD (N = 5) Conclusions: Processing conditions used for the preparation of neutral soy milk satisfactorily inactivated the trypsin inhibitor without adversely affecting protein quality.

As the odour and flavour were bland, the beverage was sterile with good dispersibility, all objectives were achieved.

WHAT WE CLAIM IS: l. A process of preparing a soybean beverage, which comprises: (a) heating to 70 to l000C a suspension in water of flour made from dehulled soybeans, the suspension having a pH of 6.4 to 10, (b) blowing superheated steam into the suspension while the latter is passed through a narrow conduit so as to raise the temperature of the suspension to 120 to 160"C, the suspension being held at said temperature for sufficient time to inactivate the enzymes and trypsin inhibitors present in the flour and to partially degrade peptides in the flour without substantial denaturing of proteins therein, (c) flashing off volatiles from the suspension at reduced pressure, and then (d) cooling the suspension to no more than ambient temperature and adjusting the pH of the suspension to neutrality.

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Claims

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TABLE 1 Summary of BV Assays of Alfa-Laval Soybean Beverage Wt gain (g) Feed intake (g) Dietary Ret Treatment No. 0-4 5-9 0-4 5-9 BV TD NPU Soy Flour 1 8.4 10.9 32.7 47.7 61.5 91.8 56.4

2 5.4 8.8 37.1 49.8 58.6 89.8 52.6

3 10.8 11.4 39.5 53.7 61.3 91.6 56.2

4 10.7 9.3 36.1 49.6 60.0 91.7 55.0

5 8.9 11.9 35.8 54.7 61.7 90.2 55.6 a 60.6 91.0 55.2 T + 1.31 + 0.94 + 1.53 Alfa Laval Soy Milk 21 10.2 11.6 38.0 52.3 60.3 92.4 55.7

22 12.2 11.0 37.5 51.7 61.2 89.5 54.8

23 8.6 12.1 42.6 53.3 57.2 88.5 50.6

24 8.7 13.2 34.9 47.7 61.8 90.6 56.0

25 6.9 10.9 36.1 43.3 55.8 90.1 50.3 59.3 90.2 53.5 31 +2.62 + 1.48 + 2.80 a) Means + SD (N = 5) Conclusions: Processing conditions used for the preparation of neutral soy milk satisfactorily inactivated the trypsin inhibitor without adversely affecting protein quality.

As the odour and flavour were bland, the beverage was sterile with good dispersibility, all objectives were achieved.

WHAT WE CLAIM IS: l. A process of preparing a soybean beverage, which comprises: (a) heating to 70 to l000C a suspension in water of flour made from dehulled soybeans, the suspension having a pH of 6.4 to 10, (b) blowing superheated steam into the suspension while the latter is passed through a narrow conduit so as to raise the temperature of the suspension to 120 to 160"C, the suspension being held at said temperature for sufficient time to inactivate the enzymes and trypsin inhibitors present in the flour and to partially degrade peptides in the flour without substantial denaturing of proteins therein, (c) flashing off volatiles from the suspension at reduced pressure, and then (d) cooling the suspension to no more than ambient temperature and adjusting the pH of the suspension to neutrality.
2. A process according to claim l, in which the pH of the suspension is

adjusted to 7 to 9 before step (b).
3. A process according to claim l or 2, in which the conduit is of circular crosssection.
4. A process according to any of claims l to 3, in which the temperature attained in step (b) is not more than 1470C.
5. A process according to any of claims l to 4, in which the suspension is held at said temperature for 10 to 400 seconds.
6. A process according to claim l, substantially as herein described in Example l or in Example 2.
7. A soybean beverage which has been prepared by a process according to any of claims l to 6.