Yeast nutritive needs

Mead is a traditional alcoholic beverage obtained by fermenting mead wort that contains 8-18% (v/v) ethanol. Its production has been known since ancient times. However, mead fermentation and maturation requires an extended period, often lasting several months to years. Mead still remains a relatively empirical and manual exercise, requiring large capacity vessels and the investment of considerable capital in terms of the raw material. In addition, the fermentation rate depends on several factors, such as honey variety, yeast strain, yeast nutrition, and pH. Due to the lack of scientific investigation, mead production has suffered in comparison with other alcoholic beverages and so more research is needed to optimize the production process. 

The nitrogenous components of grapes and must that are metabolically available to yeast are present as ammonium salts (NH4 ) and amino acids primary, collectively known as yeast assimilable nitrogen (YAN). Therefore, a complete evaluation of the nutritional status of juice or must requires measurement of both fractions. The total nitrogen content of juice not only contains YAN but peptides and proteins as well. However, the latter two fractions are not thought to play a significant role in the nutritional needs of Saccharomyces during fermentation. 

The observations of Wildiers (420) on the growth requirements of yeast, when small inocula were used for propagation in media of simplified composition, initiated the study of the growth requirements of yeasts in terms of the chemical composition of the medium needed for optimal growth. Thereafter, methods of study and an orientation of viewpoint were gradually evolved which resulted in a clear conception of the problems of yeast nutrition, which were seen to be no different in kind from those of other organisms (423). 

Leonian and Lilly (201) compared the relative requirements of 10 different strains of yeast for biotin, thiamin, inositol, pantothenic acid, and pyr idoxin, using 72 hour growth. No strain grew significantly without biotin, all were restricted without pantothenic acid, one was dependent upon thiamin, etc. Again inter-relations in growth effect were observed and, in general, it could not be said that the nutritional need for any one substance was absolute specific requirements depended on the presence of the other substances. 

Yeast protein is easily digested (87%) and provides amino acids essential to human nutrition. Most commercial yeasts show the following pattern of amino acids, among others, as percent of protein 8.2% lysine 5.5% valine 7.9% leucine 2.5% methionine 4.5% phenylalanine 1.2% tryptophan 1.6% cystine 4% histidine 5% tyrosine and 5% arginine. The usual therapeutic dose of dried yeast is 40 grams/day, which supplies significant daily needs of thiamine, riboflavin, niacin, pyridoxine, and general protein. 

Since selenized yeast is used in human nutrition, there is a need for full characterization of Se species. However, even more importantly, the quantitative analysis of biologically active selenomethionine is demanded. After a long-term intake of selenized yeast, the undesired accumulation in proteins occurs with increased... 

Ideally microbial cells should be consumable directly as food or food ingredients. However, because of their nucleic acid content the presence of undesirable physiologically active components the deleterious effects of cell wall material on protein bioavailability and the lack of requisite and discrete functional properties, rupture of cells and extraction of the protein is a necessary step. Importantly, for many food uses (particularly as a functional protein ingredient) an undenatured protein is required. For these reasons and for many potential applications of yeast protein(s) it is very desirable to separate cell wall material and RNA from the protein(s) for food applications. Much research is needed to develop a practical method for isolation of intact, undenatured yeast proteins from the yeast cell wall material to ensure the requisite nutritional and functional properties. 

Vitamins are not synthesized in the body, at least not in the amounts needed. On the other hand, hormones are produced within the body, to be secreted by specific glands. For example, vitamin D in the form called cholecalciferol (D3) is technically a hormone, being synthesized in the skin from the ultraviolet irradiation of 7-dehydrocholesterol, a metabolite or metabolic product of cholesterol. On the other hand, an almost identical form called ergocalciferol (D2) is synthetically prepared by the irradiation of ergesterol from yeast, and is the type used in nutritional supplements and fortified foods. It is therefore a vitamin (and large doses are considered toxic). 

Lactic acid bacteria have very limited synthetic capabilities and, reflecting this, the group is frequendy described as being fastidious. Simply stated, this means that LAB have complex nutritional requirements that they are metabolically incapable of meeting. This is seen in their habitat specificity which is restricted to decomposing plant tissue and in association with other microbes (i.e., yeasts) where they are able to glean decomposition products for their own needs. 

Carotenoids are natural pigments synthesized by plants and some microorganisms. Humans and animals are not able to synthesize and need to acquire them by alimentation [1]. These compounds are widely distributed in fruits, flowers, roots, seaweeds, invertebrates, fishes, birds, bacteria, fungi, and yeasts [2-4]. They are responsible for the red, yellow, and orange colors, but green, purple, or blue color could be obtained when carotenoids are botmd with some proteins [1]. Such molecules act as photosynthesis aid and for the photoprotection of their hosts [2-4]. Due to this, it is used in food and feed as colorant, flavoring, and nutritional supplement, being source of provitamin A. 

Consumption In Germany (1997/98), 0.926 x 10 mt of s. were produced, the shipment amounted to 1.012x10 mt. The largest amount of it, 0,627 X 10 mt, were consumed in animal nutrition for cattle feed or as a dried product (0.23 x 10 mt) with beet pulp to molassed pulp . For industrial consumption (fermentation products and yeast), 1.55 X 10 mt of s. were needed. Therefore, imports are necessary. 

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