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Food and feed yeast in Germany

Based on a paper presented at the sixth meeting of the FAO Technical Parcel on Wood Chemistry, Stockholm, 27-28 July, 1953

by ERWIN SCHMIDT, Vice-President, Zellstoffabrik Waldhof, Wiesbaden

The medicinal value of yeast has been known since ancient times. But that yeast also constitutes a valuable food for man and animal is a comparatively recent realization, and its introduction as such has only occurred during the last few decades. The wars in Europe encouraged research in this field because, owing to failure of imports from overseas, many countries were faced with a serious protein deficiency. Intensive research work and practical experience revealed that the value of yeast was by no means restricted to its high protein content of 50 percent but that the vitamins and other active factors it contained were at least equally important.

During the first world war, when Germany experienced an acute food and fodder shortage, plans were made for the large-scale production of feeding yeast from molasses with an addition of ammonium salts as a source of nitrogen. But after a while supplies of molasses failed and the newly-built yeast plants had to be shut down. In the 1930's, Professor Fink proposed that instead of molasses, an agricultural product, the sugars contained in sulphite pulp waste liquor or produced by the wood saccharification industry should be used. The latter alternative was expensive and, as regards the former, all the larger pulp mills in Scandinavia and Germany already had alcohol plants, so that major quantities of softwood waste liquor were not available.

Professor Fink found that Torula yeast could be grown on pentose as well as on hexose sugars, which meant that hardwood waste liquors were also suitable as a substrate. There were increasing amounts of beech waste liquor accruing in Germany for which no uses had yet been found.

While wood hydrolysis yields sugar with a pentose content of 20 percent and sulphite waste liquor of softwoods contains 25 percent pentoses, 85 percent of the sugars present in beech waste liquor are pentoses unsuitable for alcohol production but excellent for yeast-growing. On the waste liquor of each short ton of beech pulp produced, 200 to 240 lbs. of yeast can be grown. During the 1939-45 war the annual output of beech pulp amounted to about 340,000 short tons, so that the capacity for yeast could have been roughly 38,000 short tons, apart from any coming from the spentwort from sulphite alcohol plants. Actually, by the end of the var. facilities for the production of 22,500 short tons of fodder yeast a year had been established by the German chemical pulp industry alone, not counting the capacity of the wood saccharification industry which amounted to another 16,600 short tons Output of these two industries together reached its highest level in 1944, but even then amounted to only 16,500 short tons, due to the fact that some of the plants could not always be run at full capacity because of war damage and air attack.

Present Western German production is considerably smaller, altogether about 10,000 short tons of fodder yeast per year. The two yeast plants of Zellstoffabrik Waldhof account for the larger portion - 55 percent, brewers' yeast about 28 percent, and yeast grown on molasses roughly 17 percent. Roughly half the Waldhof yeast is exported, primarily to European countries - France, Belgium, Denmark and the Netherlands, and also to the United Kingdom.

Production method

The process used by the chemical pulp industry in Germany today is the continuous growing of Torula utilis according to the Waldhof process. The same process has been used in the United States for many years. Whereas the baking yeast industry operates discontinuously in a batch operation with addition of both wort and chemicals and uses surface-active oily materials for foam control, the Waldhof process employs no such antifoams. Consequently, a very pure palatable yeast is produced which alone makes it possible to use the product for human consumption. Advantage is taken of the foaming tendency of waste liquor, first, to obtain intimate contact of the liquor plus its yeast content with the air, and secondly, to use as little air as possible and thus render the process more economical. While in batch operations 400 to 1,000 cubic feet of air per pound of yeast are required, the Waldhof method calls for only 150 cubic feet per pound or between one-third and one-sixth.

In the Waldhof method the sulphite waste liquor comes in neutralized and cooled down to 90°F. It flows continuously to the fermenter while at the same time ammonium, potash, magnesium, and phosphate are continuously added. The propagator is designed to disperse air mechanically into the liquid. Simultaneously, it forces vertical circulation of the liquid through the central draft tube. This prevents the accumulation of non-breaking foam on the surface.

An aeration wheel acting as a centrifugal pump sucks in air and effects the conversion of the whole liquid into a uniform air-mixed foam which it keeps in constant circulation.

After a retention time of about three to five hours, depending on whether more hexose or more pentose sugars are added, the original yeast input has doubled itself and the sugars are practically consumed. Through a cock at the bottom of the fermenter the spent liquor with its high content of yeast is drawn off in quantities equal to the inflow of sugar-containing liquor at the top. A centrifugal device removes the air from the foamy liquor. The yeast is extracted by means of separators, washed several times and subsequently dried in towers or on drums.

Food values of yeast

Yeast has a high nutritive value not only because of its protein content but also because of the simultaneous presence of protein, vitamins and enzymes. The yeast cell, a self-sufficient living entity, produces everything that it needs for maintenance, growth and cell division, namely bios factors, enzymes, ferments and vitamins. By way of contrast, men and animals depend on a supply of many vitamins and active factors from outside because, in spite of their very complex organic structure, they are not themselves capable of synthesizing them. There are ten essential amino acids which must be present in a complete protein. However, foodstuffs contain these essential amino acids in a widely differing proportion and a good diet should therefore be composed of ingredients of both animal and vegetable origin, mixed so that each one of the essential amino acids is present in sufficient quantity.

TABLE 1. - AMINO ACID AND VITAMIN CONTENT OF FIVE FOODS IN COMPARISON WITH WHOLE EGG

Contents

Whole egg

Meat

Milk

Yeast

Peas

Wheat

Essential amino acids

Arginine

100

+13

-33

-27

+39

-30

Histidine

100

-10

+20

+13

-43

-5

Isoleucine

100

-21

-22

-7

-49

-55

Leucine

100

-13

+23

-17

-30

-26

Lysine

100

+6

+4

-14

-30

-65

Methionine

100

-22

-20

-71

-76

-76

Phenylalanine

100

-27

-16

-36

-24

-40

Threonine

100

+9

-6

+2

-20

-39

Tryptophane

100

-20

+7

-9

-53

-9

Valine

100

-21

-10

-9

-45

-44

Vitamins

B1, thiamine

100

+36

-73

+1540

+446

+58

B2, riboflavin

100

+3

-39

+1580

-21

-25

Niacin

100

462

-62

+1720

+75

+588

B6, pyrodoxine

100

-30

-90

+60

-93

-72

Pantothenic acid

100

+36

-75

-64



H, biotin

100

-96

-97

+100

-97

-100

In Table 1 the essential amino acids in whole egg, taken as 100, are compared with the contents of other foods. Some vitamins are included in the same manner. Whole egg protein is the best - but also the most expensive protein. The Table shows that all proteins, whether of plant or animal origin, differ from whole egg in having either a higher or a lower content of the various amino acids and vitamins. Milk and meat approach nearest to whole egg while peas differ most. As regards protein alone, the biological value of yeast equals that of the best vegetable protein.

Feeding experiments have shown that yeast, due especially to its high lysine and valine content, is an excellent supplement to cereal protein and that it improves considerably the nutritive value of cereal foodstuffs such as bread. For some time efforts have been made in Germany to enrich bread with dried yeast. Experiments carried out at the Mainz University and published in the Journal of Nutrition prove that adding 3 percent of a mixture composed of 1.25 dried milk, 1.26 soybean meal and 0.5 yeast leads to a maximum improvement of the biological value of bread. Unfortunately, the enrichment with yeast tends to increase the price of the bread. The added cost must be set against the proved fact that the diet deficiency in Germany after the last war was caused by inferior quality rather than by insufficient quantities of food. Man can stand underfeeding with energy-yielding foodstuffs for some time; but a deficiency of proteins and vitamins will cause serious damages to the inner organs and to the nervous system. It will also weaken the resistance of the human body to tuberculosis and other infectious diseases and lead to a marked decline of mental efficiency.

Feed yeast

As a feeding-stuff, yeast is of particular value for the growth of poultry and cattle. Naturally, the nutritive requirements of young animals differ from those of full-grown beasts. There have been rather fruitless disputes as to whether brewers' yeast or Torula yeast is better suited for growing animals, and comparative tests of different strains of yeast have given different results, as may easily be understood. The amount of vitamins and active factors which yeast may contain differs very greatly, depending on the growing process and the origin of the yeast, so that it is difficult to say what comes from the strain and what comes from the growing process.

The animal organism cannot build up all the protein complexes it requires from yeast protein alone: for the best results, yeast must be employed in a mixture with other animal and plant proteins.

In Germany, the yeast plants have for some time guaranteed the minimum vitamin content of yeast destined for admixture to protein concentrates for animal feeding, so that the manufacturers of ready-mixed feeds know the composition of the yeast and have no difficulty in determining the quantity to be incorporated into their products.

The fact that a mixture with yeast yields better results in animal feeding than can be obtained by feeding each ingredient separately is another proof of the great value of yeast as a supplement. In a paper delivered at Kiel University in February, Professor Nehring said that this effect was particularly noticeable with yeast and corn; while, taken separately, each had a biological value of 70, that of the mixture was 78. In his book on poultry feeding, Professor Römer reports that the feeding of a mixture of yeast, fish meal and dried buttermilk resulted in maximum egg production and was more successful than the separate feeding of each ingredient. Professor Römer ascribes the success of yeast in poultry farming above all to the fact that the vitamins and enzymes contained in the yeast stimulate the activity of the gonads and thus bring about an increased egg production, while at the same time the resistance to diseases in general is markedly improved.

In trout hatcheries, spleen has so far been to constitute the best feed. If the results obtained with spleen are taken as 100, pure yeast! by comparison has a value of only 62. A mixture of 1 part spleen with 2 parts yeast, however, scores 140. By the result is meant the over-all success - namely, the number of trout hatched on the one hand, and losses fine to disease on the other.

During the last war, feed yeast in Germany was highly successful in the form of so-called army fodder preserves. About 280,000 short tons of these presser! cakes containing 40 percent oats, 30 percent hay and chopped straw, 20 percent potato flakes and bran, and 10 percent yeast were produced annually, and delivered in units of 5 kilos. So great an importance was attached to these preserves that submarines took them to Narvik and airplanes carried them to Crete. Thorough experiments showed that the muscular strength of horses responded to yeast feeding particularly well.

As fowls are especially prone to deficiency diseases caused by a lack of B-vitamins, the case for tile use of yeast in poultry farming is strong. Observations made in Norway last year showed that leg deformities were likely to occur in chickens when yeast was eliminated from their diet. Feeding with yeast had its best effects during the first 4 to 5 weeks after hatching: it brought about higher gains ill weight, better growth and decreased mortality. For the fattening of ducks, too, yeast is today considered indispensable.

TABLE 2. - TWO TYPICAL QUALITY - MARKED ANIMAL FOODS

Type

Percentage

Protein concentrate 1


Cod meal

20


Fish meal

20


Dried yeast

1.5


Soybean, crushed

15


Alfalfa leaf meal

10


Fish solubles

5


Meat meal

5


Bone meal. gelatin not extracted

5


Mineral salt mixture with stable vitamin D2

5

Ready-mixed fodder 2


Milo, crushed

35


Whole wheat meal

15


Barley, crushed

12


Fish meal

12


Oats

6


Wheat germ meal

6


Dried yeast

5


Alfalfa leaf meal

5


Linseed meal

2


Mineral salt mixture with trace elements and added vitamins

2

1 For hogs calves and poultry
2 For sows and pigs

At Kiel, where the use of yeast for the fattening of hogs has been studied, gains in weight were found to result from better feed utilization rather than from the animal's greater appetite. This is of particular importance to countries such as Germany which, because of their limited fodder supplies, depend on importer! feeding-stuffs. The better feed utilization must no doubt be ascribed to the effect of the active factors contained in the yeast. The decline of pig mortality thanks to yeast also deserves special mention. In large-scale experiments made on a farm in the lower Rhine valley yeast reduced the mortality of pigs before the seventieth day from 21.4 to 10.3 percent. Yeast has moreover, proved useful in the rearing of fur bearers, Trial feeding of 136 silver foxes With yeast resulted in an increase in the number of living puppies from 1.1 to 3.2 per she-fox.

Table 2 gives the composition of' a ready-mixed fodder for sows and pigs and of a protein concentrate for hogs calves and poultry.

Table 3 shows examples of a protein concentrate and chick starter. The protein concentrate contains 25 percent yeast, so that the yeast proportion in the starter, a mixture of high-quality ingredients, is 5 percent. These examples will suffice to show how fodder-yeast is being used in Germany.

TABLE: 3. - EXAMPLES OF A PROTEIN CONCENTRATE AND A CHICK STARTER

Type

Percentage

Protein concentrate


Dried yeast

25


Cod meal

20


Soybean, crushed

20


Dried skim milk

20


Fish solubles

15

Chick starter


Protein concentrate, mixture as above

20


Ground milo

20


Wheat meal

15


Ground feeding-wheat

10


Rusk

10


Wheat bran

10


Barley germs, crushed

5


Carrot chips, dried and ground

3


Sugarbeet chips. Dried and ground

2


Alfalfa leaf meal

2


Feeding-lime

2


Crushed charcoal

1

Mention should he made of the feet that the high ergosterol content of yeast (about 0.4 percent) prompted the adoption of ultraviolet irradiation by which ergosterol is converted into vitamin D2. When cows are fed with this irradiated yeast their milk is rich in vitamin D. The vitamin D contained in irradiated yeast keeps stable for many years. A plant has been started in which ergosterol is extracted from yeast and converted directly into vitamin D, which may then he employed in precisely the desired quantities. In addition to ergosterol other valuable substances such as lecithin and nucleic acid and their derivatives, can he obtained from yeast.

Conclusion

Being able to produce this yeast of unique nutritive value in commercial installations, we are in the possession of a potential weapon with which to fight the evils of hunger anti famine. It is only potential, because yeast is an extremely complex material about which we still have much to learn in and out of the nutrition field. Nevertheless, there are hopes that research will reveal increasingly the great possibilities to improve by its means, the living-standards and life-expectancy of hunger stricken men and women all over the world


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