FEATURE
BREWERS’ YEAST PRODUCTS - excellent for use in aquafeeds
B
by Dr. Holger Kühlwein, Leiber GmbH, Germany
Inactivated, unextracted brewer’s yeast
rewers’ yeast and derived products have been successfully used in animal nutrition, including aquafeeds, for several decades now. Leiber GmbH, with two production sites in Germany and further facilities in Poland and Russia, have manufactured brewers’ yeast products for more than 60 years. The following article will shed more light on production background, well-known properties as well as new insights into by-products of beer production and their efficient use in aquaculture.
Inactivated brewers’ yeast is characterised by a moderate to high protein content of approximately 46 percent. Furthermore, high levels of minerals and trace elements, amino acids, vitamins and enzymes as well as many micro-nutrients are accumulated by the fermentation process. All components are organically bound and therefore highly bioavailable. Brewers’ yeast is especially well-known for its high levels of B vitamins (with the exception of vitamin B12), selenium and chromium. Table 1 compares B vitamin contents and important trace element levels of Leiber brewers’ yeast, soybean meal and fish meal.
Reinheitsgebot: German Purity Laws
Autolyzed brewers’ yeast
Beer brewing has a centuries-long tradition, and especially the famous Reinheitsgebot, sometimes called the “German Purity Law” of beer brewing. From the year 1516, this regulation has enormously contributed to the great acceptance of beer as a highquality, food-grade product. In fact, the Reinheitsgebot is a collective name for a series of regulations limiting the ingredients for beer brewing to water, barley (in specific cases wheat), hops and yeast. Consequently, processing this yeast to a refined quality by Leiber GmbH after the brewing process results in a premium, standardised, quality consistent, guaranteed non-GMO raw material free from other contaminants or additives (e.g. additional flavor components, enzymes or even antibiotics and heavy metals). The yeast used during beer brewing is Saccharomyces cerevisiae. The average cell size ranges between 5 – 13 µm with the yeast cell wall being approximately 200 nm thick (which constitutes 25 – 40 percent of the total dry mass of the cell). For animal nutrition and dietetic purposes, brewers’ yeast can be used as the whole, inactivated yeast cell (either drum-dried or spray-dried). Furthermore, several products derived from the yeast cell can be produced depending on the production process, e.g. autolysed yeast, yeast cell walls, yeast extracts and highly purified ß-glucans.
Vertebrate as well as invertebrate organisms do not possess the enzymes necessary for the breakdown of the yeast cell wall. When the whole, inactivated yeast is administered through the diet this can only be achieved through bacterial fermentation by the gut microbiota. Alternatively, the yeast collected from the breweries however may be subjected to a gentle autolysis process, instead of direct drying to produce inactivated, unextracted yeast. This action is achieved by the yeast’s own enzymes, which then leads to a break-up or perforation of the yeast cell wall. As a result, the highly valuable cell contents including amino acids, nucleotides and nucleosides, vitamins and trace elements, etc. are released, and are therefore considerably easier and earlier available to the organism during intestinal passage. This is especially beneficial for organisms with a short digestive tract like in shrimp. Another characteristic of autolysed brewers’ yeasts are high native levels of natural DNA and RNA components, named nucleotides, nucleosides and pyrimidine and purine bases. They are the building blocks for the synthesis of bases and nucleotides for doubling of the DNA (cell division). During periods of high requirements and physiological stress e.g. reproduction, high growth and immunological stress; there is a clearly higher demand for those components.
16 | March | April 2016 - International Aquafeed