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.

Differential effects of drought and light levels on accumulation of citric and malic acids during CAM in Clusia

Abstract: Night-time citrate accumulation has been proposed as a response to stress in CAM plants. To address this hypothesis, gas exchange patterns and nocturnal acid accumulation in three species of Clusia were investigated under controlled conditions with regard to water stress and responses to low and high photosynthetic photon flux density (PPFD). Under high PPFD, leaves of Clusia nocturnally accumulated large amounts of both malic and citric acids. Under low PPFD and well-watered conditions, substantial night-time citrate accumulation persisted, whereas malate accumulation was close to zero. Malate accumulation and night-time CO2 uptake from the atmosphere declined in all three species during prolonged drought periods, whereas citrate accumulation remained similar or increased. Recycling of respiratory CO2 was substantial for both well-watered and water-stressed plants. The suggestion that citrate accumulation is energetically more favourable than malate accumulation is not supported if the source of CO2 for the formation of malate is respiratory CO2. However, the breakdown of citric acid to pyruvate in the light period releases three molecules of CO2, while the breakdown of malic acid releases only one CO2 per pyruvate formed. Thus, citric acid should be more effective than malic acid as a mechanism to increase CO2 concentration in the mesophyll and may help to prevent photoinhibition. Organic acid accumulation also affected the vacuolar pH, which reached values of 2·6–3·0 at dawn. At these pH values, the transport of 2H+/ATP is still feasible, suggesting that it is the divalent form of citrate which is being transported in the vacuoles. Since citrate is a well-known buffer, and Clusia spp. show the largest day-night changes in organic acid levels measured in any CAM plant, it is possible that citrate increases the buffer capacity of the vacuoles. Indeed, malate and titratable acidity levels are positively related to citrate levels. Moreover, Clusia species that show the highest nocturnal accumulation of organic acids are also the ones that show the greatest changes in citric acid levels.

Thermokinetic stability of phycocyanin and phycoerythrin in food-grade preservatives

Abstract: Phycocyanin (PC) and phycoerythrin (PE) are the main phycobiliproteins (PBPs) with application as colorants in food industries. In the present study, the thermokinetic stability of PBPs extracted and purified from a hot spring cyanobacterium, Nostoc sp. strain HKAR-2, was investigated. The individual components of PC and PE were isolated with a high purity ratio of 3.18 (A615/A280) and 7.2 (A563/A280), respectively. The thermokinetic stability of purified PC and PE was studied in the presence of edible preservatives such as benzoic acid, citric acid, sucrose, ascorbic acid, and calcium chloride over 30 days of incubation at 4, 25, and 40 °C. The rate of degradation (k value) of PC/PE was increased in the control (without preservative), while it declined in the presence of preservatives. The k value (day−1) was found to be the lowest for benzoic acid-treated PC/PE in comparison to the control at 4 °C. The rate of degradation also declined in benzoic acid-treated PC (0.008 day−1) and PE (0.012 day−1) at 40 °C in comparison with the control. Citric acid and sucrose were also found to maintain the stability of both PC and PE at the same temperature. Calcium chloride and ascorbic acid were shown to be the preservatives that support the least stability of PC and PE in comparison to the other preservatives studied. Overall, benzoic acid was found to be the best preservative for both PC and PE at 4 °C.