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.

Browning of Model Orange Juice Solution: Factors Affecting the Formation of Decomposition Products

Abstract: A model solution of orange juice was prepared and stored. Factors affecting browning and formation of such decomposition products as 3-hydroxy-2-pyrone (3OH2P), 5-hydroxymethylfurfural (HMF), furfural, 5-hydroxymaltol, and 2-furoic acid were examined. Ascorbic acid (AsA) was essential for browning, which was stimulated by amino acids and citric acid, and repressed by chelators and radical scavengers (RS). 3OH2P was derived from AsA. Its formation was stimulated by sugars and repressed by citric acid, chelating agents, and RS. HMF was derived from fructose. Furfural was derived from AsA, and its formation was stimulated by sugars and chelating agents and repressed by RS. 5-Hydroxymaltol and 2-furoic acid were derived from fructose and AsA respectively. We did not find any decomposition products showing the same formation pattern as the browning, but a furfural solution with added amino acids turned brown like the model orange juice solution. It might be an indicator for the browning of orange juice.

The Key Physiological Response to Alkali Stress by the Alkali-Resistant Halophyte Puccinellia tenuiflora is the Accumulation of Large Quantities of Organic Acids and into the Rhyzosphere

Abstract: Eight-week-old seedlings of Puccinellia tenuiflora were stressed by exposure to 1: 1 molar ratio mixtures either of the two neutral salts NaCl and Na 2 SO 4 or of the two alkali salts, NaHCO 3 and Na 2 CO 3 . To identify the physiological mechanisms involved in this plant's resistance to alkali stress, the relative growth rates, the quantities and compositions of organic acids accumulated and secreted through the roots into the rhyzosphere, the concentrations of inorganic ions, proline and other solutes accumulating in the shoots were measured. The results show that the organic acid constituents in the shoots and roots were much the same. These were predominantly malic acid, oxalic acid, citric acid and succinic acid. The total concentration of organic acids in the shoots increased strongly with increasing alkali stress. However, these either did not increase or they decreased slightly with increasing salt stress. Of the four organic acids, the concentration difference between salt- and alkali-stressed plants was most striking for citric acid. This became the dominant organic acid component under alkali stress. Results show that proline is the main organic osmolyte, whereas the contribution of betaine to osmotic adjustment is insignificant under either salt or alkali stress. The main organic acid accumulated was not only an important organic osmotic regulator, but also an important negative charge contributor, playing important roles in ionic balance and pH adjustment. The concentrations of Na + , K + , Cl - and of organic acid were 80.7% of all solutes under salt stress. The concentrations of Na + , K + , Cl - and of organic acid were 85.4% of all solutes under alkali stresses. The ionic balance was disrupted by the strong increase in Na + content under alkali stress. This perhaps explains why large amounts of the organic acids were accumulated. The organic acid concentration in the roots was lower than in the shoots. The roots secreted citric acid into the rhyzosphere only under alkali stress, secretion of the other organic acids was not detected. Therefore, citric acid secreted from the roots probably plays an important role in pH adjustment in the rhyzosphere of P. tenuiflora.

Influence of complex structure on the biodegradation of iron-citrate complexes

Abstract: The biodegradation of iron-citrate complexes depends on the structure of the complex formed between the metal and citric acid. Ferric iron formed a bidentate complex with citric acid, [Fe(III) (OH)2 cit]2- involving two carboxylic acid groups, and was degraded at the rate of 86 μM h-1. In contrast, ferrous iron formed a tridentate complex with citric acid, [Fe(II) cit]-, involving two carboxylic acid groups and the hydroxyl group, and was resistant to biodegradation. However, oxidation and hydrolysis of the ferrous iron resulted in the formation of a tridentate ferric-citrate complex, [Fe(III)OH cit]-, which was further hydrolyzed to a bidentate complex, [Fe(III)(OH)2 cit]2-, that was readily degraded. The rate of degradation of the ferrous-citrate complex depended on the rate of its conversion to the more hydrolyzed form of the ferric-citrate complex. Bacteria accelerated the conversion much more than did chemical oxidation and hydrolysis.