This application is a national stage of International Application No. PCT/FR2015/053088, filed on Nov. 16, 2015, which claims the benefit of French Patent Application 1461022, filed Nov. 14, 2014, the contents of each of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the production of a dried yeast biomass, resulting from an ethanol fermentation process. More particularly, the present invention relates to a process which allows better exploitation of ethanol production coproducts.

PRIOR ART

The production of ethanol based on cereals has developed greatly throughout the world, in order to meet the desire to replace fuels of fossil origin with a renewable origin produced by agriculture.

The usual process starting from cereals consists of placing in an aqueous medium, enzymatic hydrolysis, fermentation usingSaccharomyces cerevisiaeand distillation. It generates ethanol, with respect to approximately one third of the dry matter, carbon dioxide with respect to another third of the dry matter, and the remainder is a coproduct that will generally be dried, so as to become spent distillation cereal grain intended to feed animals.

In the United States of America, the production of fuel ethanol is mainly based on corn and generates a spent corn grain, called “Corn DDGS” (Dried Distillers' Grains with Solubles).

In Europe, the production from cereals is mainly based on wheat, and generates a spent wheat grain. There is also a production of spent corn grain, or spent cereal grain, when the ethanol production is carried out from a mixture of various cereals (barley, rye, triticale, sorghum, oats, rice). It is possible to add a supplement in the form of starch of other origins (potato, cassava, sweet potato, pea), sugars from sweet plants (beetroot, sugarcane, chicory), or any other substrate that can be fermented by yeasts, either directly, or after hydrolysis.

The “Corn DDGs” and “Wheat DDGS” known from the prior art are however all very rich in fibers, and rich in vegetable proteins (in particular in gluten) and thus have a low content of essential amino acids, particular of lysine. In animal feed, the term “essential amino acids” is intended to mean those which are particularly required for the performance of livestock animals and are often deficient in animal rations: lysine, methionine, cystine, threonine, tryptophan, valine, arginine. Other amino acids may be useful for the animal, but considered to be non-essential since they are rarely deficient, such as glutamic acid.

The result is a poor economic exploitation of spent cereal grains, which are mainly used to feed ruminants (dairy cattle, beef cattle, sheep, goats), adult monogastric animals with low-protein needs, or fish and Crustacea of herbivorous type (carp, tilapia, shrimp). Spent cereal grains are used very little to feed animals with high protein needs: young livestock animals (piglets, calves, young poultry, young shrimp), dogs, cats, fish of carnivorous type (salmon, trout, bass, sea bream). These animals need a diet that is well balanced in terms of essential amino acids (lysine, methionine, threonine, tryptophan) in order to cover their requirement, to prevent intestinal losses of nitrogen which are sources of pollution, diarrhea, bad smells and disruption of the microbial flora of the colon.

However, there is a very advantageous fraction in the non-volatile part of the fermentation must: the yeast (in particularSaccharomyces cerevisiae) biomass.

The yeast biomass is well known from the prior art in human food and animal feed. It is a protein source of high quality, well balanced in terms of essential amino acids (for example brewer's yeast has a lysine content that is approximately two times higher compared with cereal proteins). The biomass of yeast, ofSaccharomyces cerevisiaetype, is recognized for its natural provision of group B vitamins, for its favorable effect on fiber digestion in herbivores (ruminants, horses, rabbits), for its beneficial effect on immunity, reduction of the harmful effects of mycotoxins, as a natural source of nucleotides or appetence factor for pets.

Yeast biomass is conventionally obtained during beer production, by filtration and then drying on a drum or spray-drying. It is thus a coproduct, which is not regularly available, and is dependent on beer production. Many breweries are not equipped to dry the liquid yeast, which will have to be transported over large distances in order to be dried.

Another way to produce yeast biomass is intentional production by fermentation on a substrate of carbohydrates (sucrose, starch hydrolyzate).

It is then a main product, and not a coproduct, the production cost of which is high, and which is not very accessible to the livestock animal feed and pet feed industry.

The authors of document FR 2 949 645, and also those of documents WO 2010/109203 and Use of cereal crops for food and fuel—Characterization of a novel bioethanol coproduct for use in meat poultry diets (Food and Energy Security, 2013, 2 (3), pp. 197-206) have proposed to improve the nutritional quality of DDGSs resulting from bioethanol production by attempting to isolate more particularly the yeast biomass. The two processes developed use whole cereals as vegetable raw materials. In other words, the processes comprise the conversion of a vegetable material rich in fibers and gluten. Consequently, the coproduct obtained according to these two processes always contains a high proportion of cereal proteins, the consequence of which is a low lysine content relative to total protein (less than 3 g of lysine per 100 g of protein).

Documents U.S. Pat. Nos. 2,698,826, 4,361,651, WO 03/063609 and DE 102007040068 describe processes for producing ethanol in which the fermentable musts are virtually free of residual fibers and of gluten.

Document EP 213023 describes a process for producing ethanol in which the fermentable must still comprises large amounts of fibers and of gluten. Because of the presence of large amounts of fibers in the fermentable must, the protein feed comprises a protein content of less than 25%. Furthermore, since all of the dry mass is recovered for the production of this protein feed and since no separation step is carried out before concentration then drying of this feed, it comprises large amounts of ash. This protein feed is similar to the DDGSs mentioned above.

Document WO 2008/0099733 describes, for its part, a process for producing ethanol in which a yeast milk having a dry mass of approximately 20% is recovered at the end of the fermentation and before distillation. This milk is evaporated under vacuum in order to recover the ethanol present. Part of this thick phase is further concentrated, recovered, and then dried as dry yeast. No separation step is carried out before concentration then drying of this yeast milk. All of the dry mass is thus recovered during the production of this dry yeast and it comprises, in particular, large amounts of ash.

The present invention relates to a process for producing ethanol, mainly based on cereals and more particularly on wheat, allowing optimum recovery of the yeast biomass, this yeast biomass having a low amount of ash and of vegetable proteins.

SUMMARY OF THE INVENTION

Thus, a first subject of the present invention is directed toward a process for recovering a composition rich in yeast proteins from a distillation residue resulting from ethanol production, comprising:

a) preparation of a fermentable must comprising at least 40% by dry weight of wheat starch dry matter;

b) enzymatic hydrolysis of the fermentable must;

c) fermentation of the hydrolyzate thus obtained;

d) distillation of the fermented product;

e) separation of the distillation residue so as to obtain

a first fraction (A) rich in yeast proteins and containing residual fibers anda second fraction (B) comprising soluble products of the distillation residue;
f) drying of the fraction (A) so as to obtain a composition rich in yeast proteins; characterized in that the fermentable must comprises less than 10% of vegetable proteins and a residual fiber content of between at least 3% and at most 6%.

A second subject of the present invention relates to a composition rich in yeast proteins, which composition can be obtained according to the process which is the subject of the present invention.

A third subject of the present invention is directed toward an animal feed comprising said composition rich in yeast proteins.

