Nutrients Organic acid

The elemental and vitamin compositions of some representative yeasts are Hsted in Table 1. The principal carbon and energy sources for yeasts are carbohydrates (usually sugars), alcohols, and organic acids, as weU as a few other specific hydrocarbons. Nitrogen is usually suppHed as ammonia, urea, amino acids or oligopeptides. The main essential mineral elements are phosphoms (suppHed as phosphoric acid), and potassium, with smaller amounts of magnesium and trace amounts of copper, zinc, and iron. These requirements are characteristic of all yeasts. The vitamin requirements, however, differ among species. Eor laboratory and many industrial cultures, a commercial yeast extract contains all the required nutrients (see also Mineral nutrients). 

In more detail the nutrient medium used may contain sources of carbon such as starch, hydrolyzed starch, sugars such as lactose, maltose, dextrose, sucrose, or sugar sources such as molasses alcohols, such as glycerol and mannitol organic acids, such as citric acid and acetic acid and various natural products which may contain other nutrient materials in addition to carbonaceous substances. 

Root products are all the substances produced by roots and released into the rhizo.sphere (Table 2) (17). Although most root products are C compounds, they include ions, sometimes O, and even water. Root products may also be classified on the basis of whether they have either a perceived functional role (excretions and secretions) or a nonfunctional role (diffusates and root debris). Excretions are deemed to facilitate internal metabolism, such as respiration, while secretions are deemed to facilitate external proces.ses, such as nutrient acquisition. Both excretion and secretion require energy, and some exudates may act as either. For example, protons derived from CO2 production in respiration are deemed excretions, while those derived from an organic acid involved in nutrient acquisition are deemed secretions. 

Nonaroinatic organic acids such as citric have been implicated in nutrient acquisition since last century (73) and, in spite of the certainty with which some... 

D. L. Jones and P. R. Darrah, Role of root derived organic acids in the mobilization of nutrients from the rhizosphere. Plant Soil 166 241 (1994). 

Nutrient availability also plays a major role in exudation, with deficiencies in N, P, or K often increasing the rate of exudation (218). It is believed that nutrient deficiency may trigger the release of substances such as organic acids or nonproteinogenic amino acids (phytosiderophores), which may enhance the acquisition of the limiting nutrient (219,220). An example here might be the release of phenolic acids such as caffeic acid in response to iron deficiency, which results in an increase in uptake of the cation (221). 

G. Cieslinski, K. C. J. Van Rees, and P. M. Huang. Low molecular weight organic-acids released from roots of durum wheat and flax into sterile nutrient solutions. Journal of Plant Nutrition 20 753 (1997). 

Another intriguing link between metals and organic acids has been claimed for the ubiquitous lichens, which are known to be able to dissolve minerals from rocks and to absorb the nutrients within their tissues. The basic unit of the lichen acids implicated is a chelating a-hydroxy carboxylic moiety (7). 

Gomis, D.B. and Alonso, J.J.M. 1996. Analysis for organic acids. In Handbook of Food Analysis, Vol. 1, Physical Characterization and Nutrient Analysis (L.M.L. Nollet, ed.) pp. 715-743. Marcel Dekker, New York. 

Because the anionic resin is weakly basic, the retention of stronger acids is favored. As a result, when processing orange juice, the retention of citric acid is favored with respect to the weaker organic acids, ascorbic and folic, which are well-recognized nutrients in orange juice. Also, mass action favors the removal of citric acid. 

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