Plant or animal proteins and hydrolysates of plant or animal proteins are often used as foaming agents in food products, notably in confectionery:
proteins as such, chosen as foaming agents that are stable over time,
protein hydrolysates, for their higher foaming capacity than for proteins.
Numerous documents describe the foaming properties of protein hydrolysates. The most recent documents discuss the enzymatic hydrolysis of proteins, whereas earlier works describe the alkaline hydrolysis of proteins.
For example, alkaline hydrolysates of milk proteins have been described for their use in extinguisher foams or as substitutes for egg proteins in aerated food products.
U.S. Pat. No. 2,522,050 describes a method for manufacturing foaming agents by alkaline hydrolysis of a soybean protein or milk protein in an aqueous solution containing calcium hydroxide or magnesium hydroxide at a pH of at least 10 and at a temperature said to be well below 100° C. (35-40° C.) for a long period (at least two days) in order to obtain a product having satisfactory foaming properties.
Thus, it should be noted that this document recommends:
selecting reaction temperatures less than or equal to 40° C.,
giving preference to hydroxides of calcium or of magnesium, and especially hydroxides of calcium in order to obtain hydrolysates of proteins displaying the best foaming properties,
giving preference to long reaction times.
Thus, patent GB 670,413 describes a method for preparing foaming agents by hydrolysis of proteins at room temperature for a period of at least 24 hours, hydrolysis being performed using a calcium hydroxide.
It is also mentioned in this patent that, although it is possible to hydrolyze proteins at a higher temperature, of the order of 100° C. and higher, this will be to the detriment of the desired foaming properties.
However, although hydrolysis with calcium hydroxide is often recommended, the hydrolysates produced have a very bad taste, which is a serious handicap. Generally they are in fact chalky and bitter, and moreover have a sulfury and rubbery taste.
Raising the temperature during hydrolysis with calcium hydroxide can reduce the reaction time, but increases the formation of these undesirable flavors.
To take account of all these requirements, patent EP 1,327,390 therefore proposes a method for aerating a food product containing carbohydrates using a hydrolysate of plant protein as foaming agent, said hydrolysate being obtained by subjecting the plant protein to hydrolysis in an aqueous solution with a pH of at least 10.
This alkaline hydrolysate then has an average length of peptide chain from 5 to 20 amino acids and an amount of free amino acids less than 15 wt % of the total matter derived from proteins.
However, to achieve this result, the original method of alkaline hydrolysis described in patent EP 1,327,390 requires combining alkali metal hydroxides and alkaline-earth hydroxides, i.e. combining at least one alkali metal hydroxide such as NaOH or KOH with at least one alkaline-earth hydroxide, for example Ca(OH)2 or Mg(OH)2.
Efficient alkaline hydrolysis, according to the terms of said patent EP 1,327,390, therefore can only be obtained by a quite particular manner of carrying out hydrolysis.
International patent application WO 95/25437 describes a method for producing hydrolysates of plant proteins with an improved coloration by extracting the proteins contained in vegetable flours at a pH above the isoelectric pH of the protein, optionally in the presence of adsorbents, and hydrolysis of the protein thus obtained in the presence of adsorbents with alkalis, acids and/or enzymes in a manner described as “known per se”.
The protein hydrolysates thus obtained can then be used notably as surfactants.
The method recommended for alkaline hydrolysis in fact consists in treating the aqueous alkaline suspension of the protein isolates once again with calcium oxides or hydroxides.
The solution obtained must then be filtered to remove the residues.
To obtain the peptides as such, the peptides must be treated further in the form of calcium salts with sodium hydroxide or potassium hydroxide, and the residual calcium must then be removed, for example in the form of calcium sulfate.
Separation of the salts with low solubility must finally be carried out in the presence of filter aids on filters and filter-presses.
The hydrolysates thus obtained, after concentration, have an average molecular weight varying from 100 to 30 000 dalton, preferably 100 to 10 000 dalton and especially from 2000 to 5000 dalton and a dry matter content from 5 to 50 wt %.
Patent EP 1,909,592 describes a method for producing protein hydrolysates enriched in manganese, intended in animal husbandry as controlled sources of supply of manganese, thus making it possible to avoid overdosage in the animal's diet, and to reduce all phenomena of interference with other dietary components.
To obtain these manganese-rich protein hydrolysates, treatment, for example with lime in certain conditions of pressure and temperature, of connective tissues derived from skin treated in a tannery had already been described in the prior art.
Patent EP 1,909,592 instead proposes obtaining protein hydrolysates enriched in manganese by using, as starting material, a conventional vegetable organic matter, and notably subjecting it to a treatment with lime.
Manganese enrichment of these proteins is then carried out by treating the calcium salts of the protein hydrolysates with manganese sulfates or other manganese salts at high temperatures, dissolved beforehand in sulfuric acid solutions.
It is further necessary to precipitate the residual calcium salts with ammonium bicarbonate, sodium bicarbonate or directly with carbon dioxide and/or other precipitants, for example oxalic acid and phosphoric acid.
International patent application WO 2008/001183 describes foodstuffs in the form of sticks, crackers or extruded products, rich in protein hydrolysates of animal or plant origin, with addition of or mixed with an excipient or a food-grade diluent.
These hydrolysates of plant or animal proteins have a protein content greater than or equal to 60 wt %.
The hydrolysates are produced starting from plant proteins, animal proteins or proteins from fermentation.
They are peptides or polypeptides, predominantly soluble in water in a pH range from 3 to 11.
The hydrolysates according to application WO 2008/001183 are preferably produced by the action of proteolytic enzymes.
The molecular weight of the hydrolysis products is between 200 and 100 000 dalton with a preference for molecular weights between 200 and 20 000 dalton.
Patent application WO 2007/079458 proposes substituting proteins for fats and carbohydrates. However, in their native form, proteins have physical and organoleptic properties that give them a very bad taste.
To make proteins more attractive as substitutes for fats, the native proteins are hydrolyzed to peptides and polypeptides, mainly by means of enzymes of the protease type.
These protein fragments are more soluble in water. They can then be incorporated in drinks (obtaining so-called “protein-concentrated” drinks), or added to solid foods to give them a less chalky taste.
However, enzymatic hydrolysis of native proteins has a major drawback: the protein hydrolysates are still very bitter and not all of them are thermally stable.
To reduce the bitterness, many solutions have been proposed, but are still rather unsatisfactory.
For example, prolonging the hydrolysis of the proteins has been tried, so as to obtain very short peptides, dipeptides, or even free amino acids.
Intensive hydrolysis of the proteins can reduce the bitterness significantly, but leads to “soapy” tastes. Moreover, the bitter and chalky aftertaste persists even after hydrolysis.
It is then recommended in application WO 2007/079458 to return to the more traditional method of alkaline hydrolysis, but to couple it with a reaction of enzymatic hydrolysis.
This double hydrolysis reaction then results in short peptide chains being obtained.
The method described in this application in fact consists in preparing a solution of proteins, adjusting the solution pH to a value of 10.4 or more to form a basic solution of proteins, and adding thereto a protease.
The protein hydrolysates thus obtained then have a very low molecular weight, on average from 2000 to 10 000 dalton.
These compositions can be thermally stable at a temperature of at least 87.8° C. (190° F.) for at least 5 minutes, and have reduced bitterness.
As for patent application WO 2008/110515, it describes a composition of partially hydrolyzed cereal proteins.
These protein hydrolysates then have between 20 and 80 wt % of partially hydrolyzed proteins of at most 25 000 dalton and of the order of 8 wt % of partially hydrolyzed proteins of at most 1400 dalton.
This particular weight distribution, i.e. a relatively high molecular weight fraction, endows these partial hydrolysates of cereal proteins with properties comparable to milk proteins, with fewer drawbacks than the milk proteins.
Moreover, such a partially hydrolyzed cereal protein has a pleasant texture in the mouth and is easily digestible.
However, the base material is preferably vital wheat gluten, and the process requires fine control of enzymatic hydrolysis so as to achieve a degree of hydrolysis of from 3 to 8.
This partial hydrolysis is usually carried out in the presence of one or more exo- and endopeptidase enzymes.
Finally, document GB 705 489 describes the hydrolysis of peanut proteins by sodium hydroxide, at 82° C. for 30 minutes; neutralization with HCl and the obtaining of “swelling” hydrolysates, whereas document U.S. Pat. No. 2,999,753 discloses alkaline hydrolysates of plant proteins obtained after treatment at 37-80° C. (100-175° F.) for 8 to 20 hours at a pH of 10.7-10.8.