Candida utilis production

Table 5 presents typical operating conditions and cell production values for commercial-scale yeast-based SCP processes including (63) Saccharomjces cerevisae ie, primary yeast from molasses Candida utilis ie, Torula yeast, from papermiU. wastes, glucose, or sucrose and Klujveromjces marxianus var fragilis ie, fragihs yeast, from cheese whey or cheese whey permeate. AH of these products have been cleared for food use in the United States by the Food and Dmg Administration (77). 

Most of the bacteria, yeasts, molds, and higher fungi of interest for SCP production are deficient in methionine and must be supplemented with this amino acid to be suitable for animal feeding or human food appHcations. Also, lysine—arginine ratios should be adjusted in poultry rations in which yeast SCP is used (62). Human feeding studies have shown that only limited quantities of yeast such as Candida utilis can be added to food products without adverse effects on flavor (63). 

An enzymatic process using partially purified pyruvate decarboxylase (PDC) with added pyruvate overcomes the problems of benzyl alcohol formation and limiting availability of pyruvate [3]. As a result increased concentrations, yields and productivities of PAC were achieved with concentrations of PAC in excess of 50 g f (330 mM) in 28 h and yields on benzaldehyde above 95% theoretical [4-6]. Screening of a wide range of bacteria, yeasts and other fungi as potential sources of stable, high activity PDC for production of PAC confirmed a strain of the yeast Candida utilis as the most suitable source of PDC [7]. 

Adams, J.P, Von Elbe, J.H., and Amundson, C.H., Production of a betacyanine concentrate by fermentation of red beet juice with Candida utilis, J. Food ScL, 41, 78, 1976. 

Well over 85,000 tons (76.500 metric tons) of yeast dry matter are produced in the United States alone each year. About 75% of this is in the form of bakers yeast, the remaining 25% represents about equal amounts of food yeast and feed yeast. This production issues from four types of manufacture (1) Bakers yeast is grown batchvvise in aerated molasses solutions. (2) Candida, utilis is obtained from wood pulp mill spent liquid. (3) K. fragiH.r is grown batchwise in cottage cheese whey, (4) Dried yeast is recovered as spent beer yeast. Worldwide production of all types of food and feed yeast is estimated at more than 450,000 dry tons (405.000 metric tons) per year. 

Due to the many applications and the industrial relevance of this class of molecules, several studies to identify strategies to increase their production have been conducted. In the recent work by Verwaal et al. [164], S. cerevisiae has been engineered with the genes from the [S-carotene production pathway from the yeast Phaffia rhodozyma, which is naturally able to produce these compounds. When these genes were cloned in Candida utilis, the carotenoids yields increased remarkably [165] and this led Verwaal et al. [164] to the idea that the production of p-carotene in S. cerevisiae could be improved by conferring properties from another yeast species. Like S. cerevisiae, P. rhodozyma also produces famesyl-diphosphate (FPP see Fig. 4) which is further converted into geranylgeranyl... 

Fig. 2. Pathway of ethanol utilization and ethyl acetate or acetaldehyde production by Candida utilis TCA cycle activity inhibited under ircn-limited conditions. Acetyl-CoA synthetase forward inhibited by acetaldehyde accumulated when elevated levels cf ethanol ( 3.5J w/v) present in the medium.

Armstrong, D.W Selective Production of Ethyl Acetate by Candida utilis. ACS Symp. Ser. 317. 254-265 (1986)... 

Selective Production of Ethyl Acetate by Candida utilis... 

Figure 5. Effect of selective inhibitors on product accumulation (24 h) by Candida utilis. Ethyl acetate ( ), acetaldehyde (H), acetic acid (O).

Figure 6. Change in product distribution at different levels of ethanol by Candida utilis. Ethanol (A), ethyl acetate (x), acetaldehyde ( ), acetic acid (T). (Reproduced with permission from Ref. 22. Copyright 1984, Science and Technology Letters.)...

The excellent paper by Armstrong shows that ethyl acetate, an important fruit aroma compound, can be produced by the yeast Candida utilis. He was able to increase production of ethyl acetate by manipulation of the carbohydrate source and regulation of iron levels in the media. 

Organic Acids. The ability of 33 strains of yeast to grow and produce pyruvic acid using dried citrus peel as a substrate was evaluated (22). Debaryomyces coudertii IFO 1381 and Candida utilis IF0 0396 produced yields of pyruvic acid near 82 mg/100 mL after 24 hours of fermentation at 30°C. Fermentation conditions were optimized with respect to nitrogen source (0.5% ammonium sulfate, dibasic phosphate concentration (0.1%), yeast extract concentration (0.01%), calcium carbonate concentration (1.0%), and magnesium sulfate concentration (0.01%). Pretreatment of citrus peel powder with the sodium form of Amberlite IR-120B was observed to enhance pyruvic acid production. Under optimized conditions, a maximum of... 

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