NO840852L - PROCEDURE FOR CONDITIONING MICROBIAL CELL MASSES - Google Patents

Description

The invention relates to the preparation of microbial cell masses in order to transfer them to a form better suited for further processing.

Microbial cell masses are valuable sources of protein, which, however, are not readily usable for human nutrition. Thus, to avoid damage, the nucleic acids must be removed as best as possible from bacterial cell masses that have a high content of nucleic acids. Due to smell and taste as well as for reasons of shelf life, the best possible removal of the lipids is also necessary. For the removal of these interfering constituents, extraction procedures have already been proposed. During these extractions, however, a more or less large solid and thus associated protein loss occurs.

It has now been found that processing of microbial cell masses is considerably facilitated when the raw material is subjected to a thermal treatment before extraction of the lipids and nucleic acids.

The invention therefore relates to a method for conditioning microbial cell masses, the method being characterized by subjecting the dried cell masses to a heat treatment at temperatures of 105 - 160°C. Preferred embodiments of this invention are explained in more detail below.

The duration of the heat treatment depends on the starting material, especially its residual moisture, and of course on the treatment temperature. A duration of 3 - 40 minutes is appropriate, particularly advantageously 5 - 20 minutes, in a product temperature range of 105 - 140°C.

The raw microbial biomass that is used must have a water content of less than 10% by weight, preferably of approx. 3-5 percent by weight, which can be achieved by the usual product-friendly methods for contact drying, especially roller drying, or ready-made drying such as spray drying.

Dried raw materials with a volume weight above are preferred

400 g/l, a sieve weight over 500 g/l and a grain size distribution with 75% over 40 ym. A crude product, as it appears according to the method according to DE-PS 2633451, is preferred.

The method can be carried out in all common devices, in which the thermal energy is transferred by contact, radiation or convection using a gaseous medium.

The process products have a number of advantageous properties:

The improvement of the mechanical properties is not only apparent

in an increased durability and storage resistance, but also in an easier filling. and dosage, however, frémfo.r,.sit;.i, an improved ratio by a subsequent extraction of lipids and nucleic acids. These subsequent processes require multiple solid-liquid separations in the form of filtration, centrifugation, membrane separation processes and/or reverse osmosis. Surprisingly, the improvement of the mechanical properties does not have to be taken at the expense of a decrease in the extraction ratio, however, above all, the physiological properties of the end product are not affected, but are even clearly improved.

Particularly advantageous is a processing method according to DE-PS 2633666, where the lipid and nucleic acid content of the cell mass is reduced in a two-stage extraction method. In the first place, the cell masses are treated with an extraction mixture of ammonia and a polar solvent from the series of lower aliphatic alcohols in lower glycols or the lower alkyl ethers of low molecular weight glycol, which contain a maximum of 30 percent by weight (referred to the amount of solvent) of water. Methanol is preferred as solvent. The ammonia content is preferably 1-10 percent by weight, referred to the amount of solvent. In this first step, the lipids are extracted. This is followed by another extraction step where the nucleic acids are released as much as possible with water. You thus get approx. 60 - 80% of the raw material used as pure product.

If the conditioning according to the invention is carried out before this extraction procedure, a 10 - 30% higher solids yield occurs without the extraction result being affected with regard to the removal of lupids and nucleic acids. In addition, a clear improvement in the biological value of the end product appears.

From DE-PS 2745954, a method is known in which impure natural microbial protein in an aqueous medium is carried out at a temperature of approx. 4 0 - 150°C until considerable protein precipitation t whereupon the precipitated protein is separated and broken down enzymatically. This method thus serves the heating by precipitation of proteins from their aqueous solution and thus for the separation of other substances remaining in solution.

From DE-OS 2651464 it is known to break up an aqueous collection of microbial cells at relatively high temperatures and pressures. Temperatures of 60 - approx. 200°C. To destroy the cells, heat at 60°C for approx. 20 hours and at 200°C for approx. 2 hours. The released protein is then separated according to known methods from the cell fragments. In this method, the heating thus serves to transfer proteins into aqueous solution.

From these known methods, it could thus not be deduced that a thermal treatment of dry bacterial pulp leads to a product with improved processing technical properties, which is advantageous in a subsequent extraction procedure. Moreover, it was not expected that the process products showed improved nutritional and physiological properties.

The invention will be explained in more detail with the help of some examples.

Example 1

A according to example 2 in DE-PS 2633451 formed spray-dried cell mass with 2 - 4% residual moisture, a volume weight of 544 g/l, a shaking weight of 597 g/l and a grain size distribution with 90% > 40; ym is treated for 30 minutes in a fluidized bed at an air temperature of 160°C. Thereby, a product temperature of 120°C is maintained for 10 minutes. The product formed after cooling shows clearly reduced wear and an improved storage capacity when subjected to mechanical stress.

If 100 kg of the thus formed product according to example 1 according to DE-PS 2633666 is extracted, 75 kg of pure product is obtained with a nucleic acid content of 1.5% by weight, a fat content of 0.8% by weight and a protein content of > 90%.

The extracted product thus has the same fat and nucleic acid content as the product according to example 1 in DE-PS 2633666. However, the protein yield is, due to the practically quantitative solids yield in the extraction steps, around 15% higher.

Example 2

Determination of the PER value (PER = protein efficiency ratio) A thermally treated according to example 1 was compared

and subsequent extracted product ("invention") with a non-thermal pretreatment extracted product ("comparison-__--; ning") with respect to the PER value.

The test products were compared on the basis of a semi-purified diet (Gesellschaft fur Ernåhrungsphysiologie der Haustiere, Arbéitskreis fur Proteinbewertung, Vorschrift zur Proteinbewertung in Versuchen an wachsenden Råtten, Zeitschrift Tierphysiologische Tierernahrung Futtermittelkunde, 19, (1964), 305 - 308). , the amino acid equivalent being used at the expense of corn starch. As a control, a diet with casein was formed. The protein carrier, respectively the casein to be examined, was each time the only protein source in the diet.

The respective nitrogen concentration of the sum of the amino acids corresponded to 10% pure protein. All diets were supplemented with

DL-methionine. Male Dawley rats with an average weight of 70 g at the beginning of the experiment served as experimental animals. Per group, 12 animals were distributed by weight, so that even starting weights were achieved. The result shows the following table.

Claims (6)

1. Method for conditioning microbial cell masses, characterized in that the dried cell masses are subjected to a heat treatment at temperatures from 105 - _16'6°C. 2. Method according to claim 1, characterized in that the heat treatment lasts 3-40 minutes. 3. Method according to claims 1 and 2, characterized in that the heat treatment is carried out for 5 - 20 minutes at product temperatures from 105 to 140 °C. 4. Method according to claim 1, characterized in that during the heat treatment the thermal energy is transferred by means of contact, radiation or convection by means of a gaseous medium. 5. Conditioned microbial cell mass, obtained by heat treatment of a dried cell mass at temperatures from 105 - 160°C. 6. Use according to the conditioned microbial cell masses formed in claims 1 - 4, respectively the conditioned cell masses according to claim 5 as starting material for the extraction of lipids and nucleic acids in the production of foodstuffs.