Yeast is more than the yeast we know: traveling on the jungle of yeast products

Yeast is the oldest microorganism associated to mankind. People have used yeast even before its discovery of existence. It was considered as miracle in bread making. In 1680 Dutchman, Antonie van Leeuwenhoek, observed yeast under a microscope for the first time. Then in 1857, French microbiologist Louis Pasteur confirms about the useful physiological properties of yeast to their use in the field of biotechnology. Fermentation of sugars by yeast is the largest application of this technology. Many types of yeasts are used for making many to satisfy the current huge need of mankind: baker's yeast in bread production, brewer's yeast in beer fermentation, ethanol yeast in production of biofuel is of some examples. Not all yeast is same, even strains make a huge difference.

In animal nutrition, different yeast species and their derivatives are used for more than 100 years. In the modern age of global stand against antibiotic usage in feed and proven benefits of yeast to animal health gives an opportunity to flood the market with various types of yeast products and picking the right one is just like a journey in the jungle.

?Yeast, There Is a Lot to Know

Till the day of whole genome sequencing of yeast, we know yeasts are single-cell, eukaryotic microorganisms under the kingdom of fungi. Like other typical single cell, they have a nuclear membrane, a cell wall, and a cytoplasmic content. But after the genome sequence and application of advance microscopic technology (AFM) now we can easily understand that yeast is more than the yeast we know.

Many aspects of yeast will confuse you. If you do not believe, let's try- is yeast an animal or a plant?

Despite of fungi, Yeast cells are quite resembled to animal cells. The cellular biology of yeast and animal more precisely humans are remarkably similar. Although yeasts are unicellular, they have many cellular organizations resemble to higher organisms. Yeast are heterotrophs like the organism of animal kingdom. In the presence of oxygen, yeast undergo aerobic respiration and convert carbohydrates into carbon dioxide and water. Yeast uses this mode of respiration to grow in bulk. In the absence of oxygen, yeasts undergo fermentation and convert carbohydrates into carbon dioxide and alcohol. No doubt these two efficient respirations in single organism makes yeast most important industrial microorganism. And naturally the research interest in yeast grew rapidly and thanks to this research interest we can learn even more about yeast. Among around 60 genera and about 1,500 species of yeasts only Saccharomyces cerevisiae is the main commercially used yeast thanks to its exceptional fermentative capacities and nutritional properties. Within this species, there are thousands of different strains with a unique genetic makeup makes them more specific in the purpose of use. Saccharomyces cerevisiae is used in making breed, wine, ethanol and as valuable component for animal health but how do you think all are same? Logically it should not be. Hence, better understanding of yeast and better know how on what differentiate them only can help you traveling on this jungle of yeast products.

Major Yeast Product Use in Animal

The main types of yeasts and yeast products used in animal nutrition are: Live yeasts, inactivated whole yeast, Autolyzed yeasts, Hydrolyzed yeasts, inactivated enriched yeasts, Yeast cell walls and Yeast extracts.

?ACTIVE YEAST

Active yeast is a living organism use for different purposes as per their specific abilities to induce desired effects. Active yeast is generally added to animal feeds for their probiotic effects. This can be found as pure active dry yeast that contain yeast cells only and yeast culture that is the combination of culture media and the untreated yeast cells. Metabolites such as peptides, alcohol, esters and organic acids are there and not guaranteed because all of it depends on substrate they used in the media. Pure active dry yeast is the only product meet the standard of probiotics. Even Not all probiotic yeasts are equal: specific yeast strains will have unique effects on targeted species. For example, a strain best for ruminant may not the best for monogastric or Vis versa. Thermostability is another challenge of having probiotic effects from active yeast. Yeast strain with specific effects, heat resistance by coating, proven effects on zootechnical performance are the major check list for selecting probiotic yeast.

?INACTIVATED YEAST

Inactivated yeast are the dead yeast or parts of yeast that have no activities as the living entities. Depending on the origin or source there are two types of inactivated yeast products- (1) Primary fermentation: the yeast is specifically produced and used as food/feed ingredients. (2)Secondary fermentation: the yeast is a by-product of another industry, such as bioethanol and brewing. Primary fermentation yeast can better ensure all the desired parameters and targeted effects over secondary fermentation yeast. However, every part of the yeast is valuable if it is obtained in standard physical, chemical & molecular specification.

?Inactivated whole yeast

Inactivated whole yeast is the yeast that are no longer living or active so they can’t produce any of the effects of live yeast, such as fermentation. Typically, these types of yeasts are obtained as a by-product of fermentation, often obtained from the brewing industry. Once harvested, the yeast is just treated to make it no longer active. In animal feed application this type of yeast is used a source of nutrients. It represents a highly valuable source of safe and bioavailable essential minerals, such as selenium and zinc, coupled with a natural reservoir of proteins, fibers and other essential nutrients.

?Yeast derivatives

This surely in the category of inactivated yeast, but further classified in the name of its valuable parts- yeast cell wall, Purified beta glucan, yeast extract. Yeast cell walls (YCW) are the insoluble fraction of autolyzed or hydrolyzed yeasts, obtained after the separation from the water-soluble cytoplasmic content. YCW is a double layered matrix with external MOS layer covering the internal layer rich in β-glucans. Pure beta glucan can be obtained by further washing of MOS layer in YCW.

Purity of Yeast Cell Wall and the cytoplasmic content depends on how you are master on the process of separation. Purity of yeast cell wall from the cytoplasmic content ensure the better prebiotic content in the products, while the purity of cytoplasmic content ensure the elevated nutritional content in the products. Because the most nutrient are present in cytoplasm, thus the cells must be lysed to release these nutrients so that they can be absorbed by the animal. On the other hand, to obtain the MOS & Beta glucan as bioactive molecule for specific effects, it needs to specially process to obtained it as potential for the induction of specific effects. For example, efficacy of MOS for undesirable pathogen binding & Beta glucan for immune modulation depends on their specific molecular structure pattern. Therefore, the bioavailability and efficacy of inactivated yeast and its derivatives mostly depends on the process to have the specific part of the whole cell inactivated yeast.

?Enriched yeast

Yeast can efficiently convert trace minerals to organic form in their metabolic process. For instance, yeast enriched with mineral represent an important source of organic mineral used in animal nutrition. During the fermentation process, inorganic mineral is added to medium, and yeast can incorporate it into the yeast proteins in the form of organic mineral.

?No doubt every part of yeast is valuable. It is wide used in animal nutrition as source of functional and nutritional ingredients. Each yeast product has its own characteristics and beneficial effects on animal growth performance and health. There are lot of yeast products in the market, including live yeasts and yeast derivatives. It is essential to understand the differences between products to select the more appropriate ones regarding their potential roles and desired effects when added to animal feed. Thus, each yeast product used for a specific application in animal nutrition must be carefully selected for its desired outcome.