The present invention relates to a process for producing a food product in powdered, granule or flake form, by drying a wet plant material in the form of a thin layer on a hot wall, in particular on the wall of a heating rollerxe2x80x94or a pair of rollers.
The expression xe2x80x9cplant materialxe2x80x9d will be understood to mean in the present description, and in the claims which follow, an edible plantxe2x80x94or plant portion, or a mixture of several plants, in particular of fruits, vegetables, mushrooms, cereals, herbs, and in general any plants which can serve for human consumption and/or as animal feed.
The purxc3xa9e and the juice which constitute the starting material may be obtained in particular by grinding, refining, blending and/or pressing of the plants in question, for example by grinding the pulp in the case of a fruit.
The dehydration of the material is carried out traditionally on the wall of a rotating cylindrical drum, with a horizontal axis rotating at low speed, in general made of chrome-plated metal.
The drum is internally heated, and possesses a heated metal wall on which the material to be dehydrated is continuously spread, such that it forms a thin and uniform layer thereon.
The temperature and the speed of rotation of the drum are chosen such that the desired drying is obtained before a complete revolution.
The dry product forms a film which is then recovered, still continuously, by scraping the wall, upstream of the point of deposition of the material to be treated.
This well-known technique is generally called xe2x80x9ccoatingxe2x80x9d technique.
In a variant, the material is applied against the drum, during the treatment, by means of one or more, also rotating, press rollersxe2x80x94called xe2x80x9csatellitesxe2x80x9d.
Another known technique, to which the present invention also applies, consists in passing the material between two press cylinders with heated walls, also made of chrome-plated metal, placed side by side, with their axes parallel and situated in the same horizontal plane.
The two cylinders rotate in opposite directions, their opposite generating lines being at a short distance from each other, and moving from the top downwards.
The material which is poured between the two rollers is therefore subjected to laminating, and forms a fine layer which is gradually dehydrated on the heated rollers.
These various techniques may be used both at atmospheric pressure and under vacuum; they make it possible to obtain rapid drying of the material.
Such processes are commonly used for drying juice and/or purxc3xa9e from fruit, vegetables or cereals, for the production of powder, granules, fine flakes, flakes and chips entering into the production of a wide range of food products, among which there may be mentioned, by way of examples, baby foods, mueslis, biscuit fillings, and dehydrated soups.
Except for a few rare exceptions, such as, for example banana and potato, which are very rich in starch, the starting materials cannot be treated as they are.
It is necessary to incorporate a drying aid therein.
This is particularly true for plants which are rich in sugar.
In the absence of an aid, the material sticks to the drum, or to the laminating cylinders, as well as to the scraping blade and a sticking phenomenon, or even caramelization of the product, is observed which is difficult to detach from the hot wall causing dehydration; the product obtained is of poor quality, both from the taste point of view and from the point of view of its appearance.
This sticking, which is accompanied by the appearance of black spots, is observed even when chrome-plated cylinders are used because of the high content of sugar in the mixtures to be dehydrated.
Traditionally, the aids which are used, to allow dehydration under good conditions, are composed of two components, namely a texturing agent and a lubricant.
The role of the texturing agent is to give the mixture substance, and to promote its deposition in the form of uniform layers on the heating wall, by increasing the level of dry matter in the mixture.
Its role is alsoxe2x80x94where appropriatexe2x80x94to confer a degree of unctuousness on the final product, when the latter is intended to be rehydrated before consumption.
The addition of this texturing agent is often essential, with the exception of certain specific plant applications, for example apple.
The percentage of texturing agent, depending on the applications, may be up to 70% by weight of dry matter content of the mixture.
As drying base, flour or starch from wheat, maize or rice is customarily used.
The lubricating agent traditionally used is soya bean lecithin.
Its role is to lubricate the roller, in order to avoid the mixture sticking to the hot wall thereof, and allows detachment of the dry product at the scraping blade, serving to extract the dehydrated product at the end of the treatment.
Soya bean lecithin also makes it possible to obtain a bright flake, with a pleasant appearance.
The lecithin dose traditionally used is between 0.5 and 1.5% by dry weight of the mixture.
With the exception of a few fruits and vegetables which are very rich in starch, such as banana and potato, soya bean lecithin is an ingredient which is judged to be essential in all formulas for the manufacture of flakes of plant materials having regular forms, with a bright appearance and with a uniform quality.
The object of the present invention is to provide a process for producing a dehydrated food product from a wet plant material, in particular in juice or purxc3xa9e form, by drying the said material in the form of a thin layer on a hot wall, which can dispense with soya bean lecithin as lubricating agent and as drying aid.
This interest to dispense with the use of soya bean lecithin results from considerations linked to the development of certain genetically modified raw materials, including soya bean, which does not offer the consumer complete assurance with regard to its natural character. In Europe, many manufacturers no longer wish to use ingredients containing, or likely to contain, genetically modified raw materials (maize and soya bean).
It may be thought that this will lead, in the short to medium term, to ingredients derived from the soya bean sector in food products being purely and simply banned.
The constraints which the Applicant imposed on itself in the search for a method of substitution were in particular the following:
use of a wholly plant and natural product;
use of a product exhibiting no risk of the presence of allergenic agents;
use of a product which is effective regardless of the plant material to be treated, and regardless of the formulationxe2x80x94with or without texturing agentxe2x80x94;
possibility of using in any applications, including for the preparation of baby foods;
use of a product not considered as a food additive requiring labelling with an xe2x80x9cExe2x80x9d code;
absence of lecithin, in particular soya bean lecithin.
Apart from these constraints, the invention of course set itself the objective of providing a process using a lubricating agent possessing the same properties, or practically the same properties, as soya bean lecithin as regards lubricating the roller and allowing effective detachment of the dry product film at the scraping blade and as regards the production of a dry product such as a flake, with a bright appearance and with a homogeneous quality.
Another imperative was also to search for a process using a product whose taste is neutral, so as not to influence the taste of the final product.
It was indeed suggested, to respond to these expectations, to incorporate fat, such as oil, directly into the product to be dried.
The introduction of fat before drying on a roller into mixtures rich in emulsifying proteins is possible. It is in particular the case for formulas with vegetable milk (EP-A-0 830 820), with goat milk (EP-A-0 409 138) or with animal products (Nielsen, 1984, Lebensmittel-Wissenschaft und Technol.), 17(3) 151-154).
On the other hand, in vegetable mixtures which are naturally not very rich in proteins, it is impossible to homogeneously incorporate vegetable oil. Whatever the quality of the mixture, the oil is not homogeneously distributed in the aqueous mixture (purxc3xa9e and/or juice with or without texturing agent) and there is partial phase separation during storage before drying. This phase separation is more or less rapid depending on the temperature of the mixture to be dried, and it may also occur if the mixture is pasteurized before the coating.
Surprisingly and unexpectedly, the Applicant has realized that the various objectives detailed above are achieved by distributing (by spreading) on the wall, during the whole drying operation, before depositing thereon the thin layer to be dried, a film exclusively composed of vegetable oil. According to an important characteristic of the invention, the process is used without addition of lecithin, in particular without addition of soya bean lecithin.
The quantity of oil distributed may be reduced. It is however sufficient to fulfil its role as lubricating agent and as drying aid.
This is particularly advantageous because the products treated naturally contain only very little fat, the quantity of oil which they are capable of absorbing through contact with the film will also be greatly reduced.
Moreover, according to other advantageous but nonlimiting characteristics of this process,
the said drying is carried out on the outer wall of at least one rotating cylinder;
the quantity of oil deposited is at most 1%, and preferably 0.5% by weight, relative to the weight of the dry matter;
the said spreading of oil is carried out by coating the wall with the aid of a roller;
the said spreading of oil is carried out by spraying, in particular micro-spraying;
there are distributed about 5 to 50, and preferably 10 to 20 g of oil/hour/m2 of wall;
the film of vegetable oil is distributed intermittently;
palm oil is used;
the wet plant material is a fruit and/or vegetable purxc3xa9e.
The term xe2x80x9cmicro-sprayingxe2x80x9d is understood to mean spraying an extremely small quantity of oil, in the form of a mist, so as to deposit on the wall a film which is as thin as possible.