Calcium 5'-ribonucleotides is a chemical compound that is produced by enzymatic hydrolysis of RNA by 5′-phosphodiesterase from yeast. Industrially, it is obtained by the reaction of sodium 5'-ribonucleotides with calcium chloride.  Ribonucleotides are substances normally found in all human tissues.

What it is used for and where

Food

Ingredient included in the list of European food additives as E634 as a flavour enhancer to improve the taste of food and beverages (1). 

Safety

Ingestion of large quantities of these compounds by humans can increase uric acid levels and is not recommended for people with gouty diathesis and those taking diuretics that retain uric acid (2).

References_____________________________________________________________________

(1) Yamaguchi S, Ninomiya K. Umami and food palatability. J Nutr. 2000 Apr;130(4S Suppl):921S-6S. doi: 10.1093/jn/130.4.921S.

Abstract. Umami is the term that identifies the taste of substances such as L-glutamate salts, which were discovered by Ikeda in 1908. Umami is an important taste element in natural foods; it is the main taste in the Japanese stock "dashi," and in bouillon and other stocks in the West. The umami taste has characteristic qualities that differentiate it from other tastes, including a taste-enhancing synergism between two umami compounds, L-glutamate and 5'-ribonucleotides, and a prolonged aftertaste. The key qualitative and quantitative features of umami are reviewed in this paper. The continued study of the umami taste will help to further our general understanding of the taste process and improve our knowledge of how the taste properties of foods contribute to appropriate food selection and good nutrition.

(2) Calcium and sodium-5'-ribonucleotides (WHO Food Additives Series 6) (inchem.org) 

Benaiges MD, López-Santin J, Solà C. Production of 5'-ribonucleotides by enzymatic hydrolysis of RNA. Enzyme Microb Technol. 1990 Feb;12(2):86-9. doi: 10.1016/0141-0229(90)90078-5.

Abstract. Study of optimal operational conditions for RNA enzymatic hydrolysis to obtain 5'-ribonucleotides has been carried out. RNA from brewer's yeasts, obtained by ammonium extraction, was hydrolysed by a partially purified 5'-phosphodiesterase from barley rootlets. Temperature of 60 degrees C and pH 7 have been determined as the best operational conditions. Low RNA initial concentration (approximately 0.1%) and reaction time (approximately 1 h) have been identified as necessary to obtain a good yield of 5'-ribonucleotides.

Torii K, Kondoh T, Mori M, Ono T. Hypothalamic control of amino acid appetite. Ann N Y Acad Sci. 1998 Nov 30;855:417-25. doi: 10.1111/j.1749-6632.1998.tb10601.x. 

Abstract. Preference for umami taste materials, such as monosodium L-glutamate (MSG) and the 5'-ribonucleotides, inosine 5'-monophosphate (IMP) and guanosine 5'-monophosphate (GMP), varies as a consequence of protein nutrition. Rats fed diets deficient in dietary protein or an essential L-amino acid (AA), L-lysine (Lys), avidly consumed Lys, glycine and NaCl but not umami substances. However, when the rats' protein nutrition was normal or when they were recovering from deficiency, a preference for umami substances was evident. These data suggest that the central mechanism for recognition of protein malnutrition may be coupled with umami taste preference. To test this, Lys-deficient and normal rats were employed as a model for taste preference changes. AA levels in plasma and brain remain essentially unchanged throughout the day while the rat is on standard chow but are altered during Lys deficiency. The recognition site for the deficit in the rats' brains was localized to the ventromedial (VMH) and lateral (LHA) hypothalamus as determined by functional magnetic resonance imaging (fMRI, 4.7 Telsa). Studies of single neuron activity in the LHA of Lys-deficient rats suggested that neuronal plasticity occurred. Following Lys deficiency, cells responded specifically to Lys, both iontophoretically applied and during ingestion of AA. Other LHA neurons of nondeficient rats differentially responded to MSG. The present results suggest that the LHA and probably the VMH play important roles in recognition of deficient nutrients. Neural plasticity of hypothalamic cells helps maintain AA homeostasis. Furthermore, a preference for umami substances may be an indicator that the organism (rat or human) is free of protein malnutrition.