February 2018

 

by Francesca Susca, PhD, Lallemand Animal Nutrition

 

From a palatability enhancer to a source of nutrients and functional ingredients, yeast and yeast derivative products are versatile and natural ingredients to keep in mind when formulating food for pets.

Yeast has been utilised as far back as ancient Egypt to leaven bread and ferment wine. Saccharomyces cerevisiae remains the most used organism in the food industry, and today it is used for the annual production of 60 million tons of beer and 30 million tons of wine!

Its exceptional fermentative and nutritional properties make yeast a valuable source of ingredients for pet nutrition too. But not all yeast nor yeast products are equivalent. After reviewing the multiple benefits and applications of yeast and yeast derivative products, this article aims to classify these products according to their composition, nutritional value, biological activities, and regulatory status, as well as their production process.

 

All about yeast

Animals have been fed various forms of yeast and yeast derivatives products for more than 100 years. The use of yeasts as a feed material or feed additive, in both poly and monogastric animals to help maintain health and well-being, has grown over the past 20 years, following the search for natural feed additive alternatives and growing scientific documentation of probiotics and yeast derivatives in both human and animal nutrition.

Yeasts are unicellular eukaryotic microorganisms of the fungi family. The yeast cell wall is made of glucans, glycoproteins, mannans and chitin. The intracellular chemical components of yeast cells include among others: amino acids, peptides, carbohydrates, salts, nucleic acidsand enzymes. The combination of these compounds make yeasts useful nutraceuticals for human nutrition but also attractive as nutritional supplements in animal feed.

There are about 60 different genera of yeasts, which are comprised of about 500 different species. Only a few of these species are used commercially, and Saccharomyces is one of them. Based on DNA homology, four distinct species of Saccharomyces have been identified.

All of them are of industrial importance, but thanks to its exceptional fermentative capacities and nutritional properties, Saccharomyces cerevisiae is the predominant microorganism used in food, beverage and baking. It is also the main yeast used in feed production processes.

Within the specie, there are thousands of different strains, each with a unique genetic makeup, leading to different outcomes in terms of metabolisms and activities. For example, there are hundreds of different strains of S. cerevisiae that can be used in winemaking, leading to different wine characteristics and aromatic profiles.

It is the same in animal nutrition: specific strains have demonstrated to be beneficial for ruminants, others for monogastrics animals, and it is also possible to combine specific strains to achieve a certain benefit.

Therefore, selecting the right yeast strain for a given application is critical and requires a high level of knowledge and expertise.

When it comes to formulating yeast products for petfood, there are several things to consider in order to make the most appropriate choice, including:

  • The specific properties of the yeast strain
  • The composition of the yeast derivative product
  • The desired benefits
  • The industrial process to be applied
  • The regulatory status

 

Live yeast

Live yeast is used for several different applications, such as in bread, beer and wine making, but also in animal nutrition as probiotics. One good example of live yeast used as a probiotic in both human and animal nutrition is Saccharomyces cerevisiae boulardii.

Isolated for the first time in 1920 from litchi infusion, it has been recognized for its benefits in human medicine for more than 50 years. In 1993, the first S. c. boulardii product was registered in the EU for animal nutrition. Today, it is marketed in more than 60 countries for either human or animals.

There are hundreds of research and publications on using S. c. boulardii in humans. Its benefits in farm animals have been already demonstrated, and some research on its beneficial effects in dogs has been already published, supporting its beneficial effects in promoting digestive health. Live yeast fed to animals are classified as zootechnical feed additives.

 

Whole inactive yeast cell

Whole yeast cells go through an inactivation process and are classified as feed materials. Whole yeast cells are mainly used as a palatability enhancer or as a natural source of nutrients such as B vitamins, high quality protein and minerals in petfood. Yeast contributes to the umami flavor characteristic but also can be used to reduce the addition of salt without affecting the flavor.

In addition, yeast can be enriched in vitamins or minerals. For instance, selenium-enriched yeast is produced by growing a specific yeast strain in the presence of measured amounts of inorganic selenium (Se). During yeast cell growth, this selenium is naturally incorporated by the growing yeasts within amino acids to form selenomethionine and selenocysteine.

Selenium-enriched yeast is documented as a source of highly bioavailable selenium for human and animal nutrition. For cats and dogs, selenium is an essential micronutrient required to sustain basic functions, such as antioxidant status, immune and thyroid functions.

 

Yeast fractions

After yeast inactivation, it is possible to go one step further by using a separator to obtain different yeast fractions: the yeast extracts and the yeast cell wall products (See Figure 1). Both fractions are considered as feed material falling into the yeasts products category of the European Register of Feed Material.

 

Yeast extracts

Yeast extracts are the soluble portions of the yeast. They are comprised of more than 60 percent proteins. They represent a valuable source of proteins, nutrients and minerals and can also be used as natural flavor enhancers thanks to their great content (around six percent) of glutamic acid.

 

Yeast cells walls

Yeast cell walls are rich in beta-glucans and mannan oligo saccharides (MOS), which are well known for their pathogen-binding and immune-modulation activities. They can contribute to microbiota balance and digestive well-being. Production processes have a great influence on the end-product qualities, the MOS contents and, hence, efficacy.

In particular, yeast cell walls issued from a primary production process with a selected yeast strain should be preferable (compared to byproducts from brewery or distillery production), thanks to the specific and carefully controlled production process, which ensures a consistent quality, purity and homogeneity of the final product. Thus, whenever choosing a yeast cell wall product, the following should be considered:

  • What is the origin of the product?
  • What is the strain and is it unique and specific for the benefit I want to achieve?
  • Has it gone through a specific production process?
  • Is the composition guarantee?

It is also important to look at the product sample appearance to understand the level of purity of the product, which gives a good insight into the quality of the product.

Cutting-edge techniques such as atomic-force microscopy (AFM) and single-molecule force spectroscopy (SMFS) allowed Lallemand to have a better understanding of the relationships between yeast structure and its function.

Yeast cell walls are usually defined by their quantitative biochemical composition, such as percent of mannans, ß-glucans, nucleotides, etc. We discovered that, while these parameters are important, they are not the only ones to consider. Physical characteristics (conformation, repartition of the molecules along the yeast cell wall, etc.) also have a significant influence on the properties of yeast fractions.

As said earlier, yeasts" biological properties are linked to the yeast strain genome. AFM has also shown that each strain reacts differently depending on the production process applied. Thus, for each strain, it is essential to determine the ideal production conditions that will yield the desired properties.

This knowledge has enabled us to selectstrains with different, complementary properties, each with its own optimal production process but with a synergistic effect on the immune system demonstrated in vitro.

Some preliminary results demonstrating the synergistic effect of such a specifically studied association of yeast fractions in supporting gut health and reinforcing the immune system in healthy dogs are available. In the in vitro phase, a significant increase of the beneficial bacteria has been seen, while in the in vivo the fecal IgA are already significantly increased, 21 days after supplementation, demonstrating the immunomodulatory properties of such a synergistic alliance of specifically selected yeast fractions.

 

Conclusions

From use as a flavor enhancer to a source of nutrients to functional ingredients, yeast is definitively a versatile natural ingredient to keep in mind whenever formulating food for beloved pets.

www.lallemandanimalnutrition.com

 

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