Citric acid

About: Citric acid is a research topic. Over the lifetime, 17745 publications have been published within this topic receiving 277125 citations. The topic is also known as: citrate & H3cit.

Citrate Metabolism by Enterococcus faecalis FAIR-E 229

Abstract: Citrate metabolism by Enterococcus faecalis FAIR-E 229 was studied in various growth media containing citrate either in the presence of glucose or lactose or as the sole carbon source. In skim milk (130 mM lactose, 8 mM citrate), cometabolism of citrate and lactose was observed from the first stages of the growth phase. Lactose was stoichiometrically converted into lactate, while citrate was converted into acetate, formate, and ethanol. When de Man-Rogosa-Sharpe (MRS) broth containing lactose (28 mM) instead of glucose was used, E. faecalis FAIR-E 229 catabolized only the carbohydrate. Lactate was the major end product, and small amounts of ethanol were also detected. Increasing concentrations of citrate (10, 40, 70, and 100 mM) added to MRS broth enhanced both the maximum growth rate of E. faecalis FAIR-E 229 and glucose catabolism, although citrate itself was not catabolized. Glucose was converted stoichiometrically into lactate, while small amounts of ethanol were produced as well. Finally, when increasing initial concentrations of citrate (10, 40, 70, and 100 mM) were used as the sole carbon sources in MRS broth without glucose, the main end products were acetate and formate. Small amounts of lactate, ethanol, and acetoin were also detected. This work strongly supports the suggestion that enterococcal strains have the metabolic potential to metabolize citrate and therefore to actively contribute to the flavor development of fermented dairy products.

Production of Organic Acids by Fungi

Abstract: Fungi, in particular aspergilli are well known for their potential to overproduce a variety of organic acids. These micro-organisms have an intrinsic ability to accumulate organic acids and it is generally assumed that this ability provides the fungi with an ecological advantage since they grow rather well at pH 3–5, while some species even tolerate pH values as low as 1.5. Organic acid production can be stimulated and in a number of cases conditions have been found that result in almost quantitative conversion of carbon substrate into acid. This is exploited in large-scale production of a number of organic acids, e.g. citric, gluconic and itaconic acid. Table 1 lists the most important organic acids for which a production process employing fungi has been described. In this chapter we will discuss different aspects of organic acid production, including biochemistry, production and applications. Since citric acid is by far the most important organic acid, in production volume as well as in knowledge available, emphasis will be on production of citric acid by Aspergillus niger. Production of itaconic acid, gluconic acid, and other acids for which fungal production processes have been described will be discussed in less detail. Finally, the reader is referred to a number of excellent reviews that have been written on organic acid production by fungi (Kubicek and Rohr 1986; Mattey 1992; Rohr et al. 1992, 1996a-c; Zidwick 1992; Kristiansen et al. 1999).