Showing papers on "Citric acid published in 1997"

Gelatin from cod skins as affected by chemical treatments

Abstract: Concentrations of sodium hydroxide, sulfuric and citric acids used in processing gelatin from cod skins affected both yield and quality. The highest yield of gelatin was obtained when low concentrations [0.1–0.2% (w/v)] of sulfuric acid and sodium hydroxide were applied to the skins followed by treatment with 0.7% (w/v) citric acid. The effects on bloom value, viscosity, odor, clarity, color and pH of the gelatin varied. However, the use of 0.7% (w/v) citric acid in different combinations with sodium hydroxide and sulfuric acid usually gave best results. Freezedried gelatin had considerably higher bloom value than air-dried gelatin.

Internal Detoxification Mechanism of Al in Hydrangea (Identification of Al Form in the Leaves)

Abstract: An internal detoxification mechanism for Al was investigated in an Al-accumulating plant, hydrangea (Hydrangea macrophylla), focusing on Al forms present in the cells. The leaves of hydrangea contained as much as 15.7 mmol Al kg-1 fresh weight, and more than two-thirds of the Al was found in the cell sap. Using 27Al- nuclear magnetic resonance, the dominant peak of Al was observed at a chemical shift of 11 to 12 parts per million in both intact leaves and the extracted cell sap, which is in good accordance with the chemical shift for the 1:1 Al-citrate complex. Purification of cell sap by molecular sieve chromatography (Sephadex G-10) combined with ion-exclusion chromatography indicated that Al in fractions with the same retention time as citric acid contributed to the observed 27Al peak in the intact leaves. The molar ratio of Al to citric acid in the crude and purified cell sap approximated 1. The structure of the ligand chelated with Al was identified to be citric acid. Bioassay experiments showed that the purified Al complex from the cell sap did not inhibit root elongation of corn (Zea mays L.) and the viability of cells on the root tip surface was also not affected. These observations indicate that Al is bound to citric acid in the cells of hydrangea leaves.

Specific Secretion of Citric Acid Induced by Al Stress in Cassia tora L.

Abstract: A rapid and sensitive assay method for Al-chelating activity was established to screen Al-chelating substances secreted from roots of Al-resistant species in response to Al stress. From one Al-resistant species, Cassia tora L., an Alchelating substance was detected in the root exudates when they were exposed to SO fM Al in 0.5 mM CaCl2 solution at pH 4.5; the dominant component was identified as citric acid. The secretion of citric acid was very low during the first 4 h after initiation of Al treatment, but increased markedly thereafter. A 3-h pulse with 50 //M Al also induced significant secretion of citric acid after 6 h. The lag between Al addition and secretion of citric acid suggests that inducible processes are involved. A dose-response experiment showed that the amount of secreted citric acid increased with increasing external concentrations of Al. Eight-d treatment of P deficiency did not induce the secretion of citric acid. Exposure to 50 //M of either lanthanum (La3*) or ytterbium (Yb3+) did not induce the secretion of citric acid either. These findings indicate that the secretion of citric acid is a response specific to Al stress in C. tora and constitutes a mechanism of Al resistance.

Effects of gas atmosphere, antimicrobial dip and temperature on the fate of Listeria innocua and Listeria monocytogenes on minimally processed lettuce

Abstract: The growth and survival of inoculated strains of Listeria innocua and L. monocytogenes on minimally processed lettuce were studied. The effects of package atmospheres (lettuce sealed within packages after flushing with 100% N 2 or without flushing with N 2 , lettuce sealed within perforated packages), antimicrobial dips (100 p.p.m. chlorine solution for 5 min, 1% citric acid solution for 5 min) and storage temperatures (3°C and 8°C) were investigated. Populations of L. innocua and L. monocytogenes on undipped lettuce stored at 3°C gradually decreased (by 1-1.5 log cycles) during a 14 day storage period. By contrast counts on lettuce stored at 8°C did not change significantly (P > 0.05). Flushing packages of lettuce with 100% N 2 followed by storage at 8°C resulted in a significant increase (P < 0.05, by 2-3 log cycles) in L. innocua and L. monocytogenes counts during storage. L. innocua, strain NCTC 11288, behaviour was similar to that of L. monocytogenes (strains ATCC, 19114 and NCTC 11994) under these storage temperatures and atmospheres. Using L. innocua as a model for L. monocytogenes, it was found that dipping lettuce in a chlorine or citric acid solution followed by storage at 8°C resulted in a significant increase (P < 0.05, by 2 log cycles) in L. innocua populations compared with undipped samples. It is concluded that N 2 flushing or use of antimicrobial dips combined with storage at 8°C, both enhanced the survival and growth of Listeria populations on shredded lettuce.

Catalytic Mechanism of Lipid Oxidation following High Pressure Treatment in Pork Fat and Meat

Abstract: Addition of citric acid (0.02%) inhibited the increased rate of lipid oxidation found in rendered pork fat following pressure treatment (650-800 MPa). This indicated that transition metal ions were probably released from complexes and became available to catalyze lipid oxidation in the pressure treated fat. In minced pork and washed fibers citric acid was less effective in inhibiting oxidation in pressure treated samples because of its pH lowering effects. However, the less acidic ethylenediaminetetraacetic-acid disodium salt (Na 2 EDTA) was an effective antioxidant in these pressure treated (400 MPa and 800 MPa) systems. This further indicated that metal catalysts (probably iron) were released from complexes during pressure treatment to catalyze lipid oxidation.

Influence of chelating agents and mechanical pretreatment on enzymatic retting of flax

Abstract: Adding chelating agents, i.e., oxalic acid and ethylenediamine-tetra-acetic acid (edta), substantially increases the retting effect on flax by the commercial enzyme products Ultrazym and Flaxzyme (Novo Nordisk), as shown by scanning electron microscopy, release of reducing sugars, and the Fried test. Degradation of pectin-rich citrus peel by these enzymes also increases with the addition of oxalic acid and edta, while citric acid has a low or insignificant effect. Oxalic acid at 50 mmol concentration reduces the amount of Flaxzyme required to effectively ret flax stems, according to the Fried test, by a factor of about 50. Retting with Flaxzyme and 50 mmol oxalic acid is completed in approximately half the time at 45°C, compared with that at 22°C. A mechanical pretreatment that crushes flax stems by pulling them over a surface at a 90° angle opens the flax structure and further increases the efficiency of enzymatic retting. These procedures appear to modify both the chemical and structural features of fla...

Overexpression of cytosolic malate dehydrogenase (MDH2) causes overproduction of specific organic acids in Saccharomyces cerevisiae.

Abstract: Saccharomyces cerevisiae accumulates l-malic acid through a cytosolic pathway starting from pyruvic acid and involving the enzymes pyruvate carboxylase and malate dehydrogenase. In the present study, the role of malate dehydrogenase in the cytosolic pathway was studied. Overexpression of cytosolic malate dehydrogenase (MDH2) under either the strong inducible GAL10 or the constitutive PGK promoter causes a 6- to 16-fold increase in cytosolic MDH activity in growth and production media and up to 3.7-fold increase in l-malic acid accumulation in the production medium. The high apparent Km of MDH2 for l-malic acid (11.8 mM) indicates a low affinity of the enzyme for this acid, which is consistent with the cytosolic function of the enzyme and differs from the previously published Km of the mitochondrial enzyme (MDH1, 0.28 mM). Under conditions of MDH2 overexpression, pyruvate carboxylase appears to be a limiting factor, thus providing a system for further metabolic engineering of l-malic acid production. The overexpression of MDH2 activity also causes an elevation in the accumulation of fumaric acid and citric acid. Accumulation of fumaric acid is presumably caused by high intracellular l-malic acid concentrations and the activity of the cytosolic fumarase. The accumulation of citric acid may suggest the intriguing possibility that cytosolic l-malic acid is a direct precursor of citric acid in yeast.

Stability of Betalain Pigments from a Cactacea Fruit

Abstract: The garambullo tree (Myrtillocactus geometrizans) which grows in the deserts of Mexico produces a purple fruit. The pigments were extracted, identified, and evaluated for their stability at different temperatures and pH values and in the presence of iron and chromium. One percent citric acid or ascorbic acid was added as a stabilizer, and a mixture of both was also used. On the basis of their visible light spectrum and chromatographic profile, the pigments were identified as betalains, which have a stability greater than that of red beet pigments and which are very stable at low temperatures. The pigment concentration was determined to be 214 mg/(100 g of dry weight). The energy of activation for bleaching of color was 87.09 ± 8.53 J K-1 mol-1 at pH 5.5. Ascorbic acid protects the red color even when it is exposed to drastic treatments such as sterilization. Metals decrease the stability of garambullo pigment; the effect of iron was greater than that of chromium. Garambullo pigment has the potential for u...

Parameters influencing the electrodeposition of Ni-Fe alloys

Abstract: The present work consists of an experimental analysis of the effects of electrolyte composition and various other operation variables on the electrodeposition of Ni-Fe alloys. Two kinds of electrolytic solutions were used: sulphates and chlorides. Boric acid, citric acid and l -ascorbic acid were added to the solutions, and the pH was fixed at either of two values: 2.0 or 3.0. The alloys were electrodeposited at different current densities (0.5, 1.0, 1.5 and 2.0 A dm−2) and for all the conditions investigated the deposits with larger iron content were carried out with lower cathodic efficiency. From these experiments and from the decomposition of polarisation plots it was observed that the anomalous codeposition occurs preferentially for the same conditions (SO4−2 media, pH 2.0 and lower current densities), in that the presence of a hydroxide film at the surface would be favoured, which could both enable the reduction of iron to occur at more noble potentials and allow the iron to discharge through its thickness whilst hindering the movement of nickel ions. Concerning the role of the additives, citric acid containing solutions produced deposits with the largest iron contents, while the presence of ascorbic acid had no pronounced effect. The iron content is lower in deposits from boric acid solutions.

Pervaporative dehydration of organic solvents

Abstract: Pervaporative separation of acetone/water and isopropanol (IPA)/water systems has been studied in the water-lean range of composition of the feed mixtures. Poly(vinyl alcohol) (PVA) membranes crosslinked with citric acid, adipic acid, maleic acid, glutaraldehyde, and glyoxal were used for this purpose. The sorption characteristics of all the membranes indicate that these membranes have a good sorption selectivity for water in view of the hydrophilic nature of PVA. The type of crosslinker used for crosslinking has been shown to have an important bearing on the permeation characteristics of the membranes. Thus, the trifunctional citric acid yields the highest selectivity but lowest flux. A comparison of the productive capacities of the various membranes indicates that the glutaraldehyde crosslinked membrane has the maximum productive capacity for IPA dehydration whereas maleic acid crosslinked membrane yields the highest productive capacity for acetone dehydration.

Influence of calcium on fungal growth, hyphal morphology and citric acid production in Aspergillus niger.

Abstract: Addition of 0.5 g/L CaCl2 to the fermentation medium lowered the final biomass dry mass by 35% and increased the uptake of phosphate and sucrose, and the production of citric acid by 15, 35 and 50%, respectively. In a medium deprived of Ca2+ the microorganism displayed both a pelleted and a filamentous form of growth, the hyphae being scarcely branched, without bulbous cells. An addition of Ca2+ induced a pelleted form of growth, highly branched hyphae and numerous bulbous cells. Bulbous cells growing in the presence of Ca2+ exhibited cell walls composed of laminated layers, and featured vesicles associated with the wall and/or the cell membrane, containing numerous inclusions. The cytotoxic effect of high concentrations of citric acid in the medium as well as an increase of the activity of N-acetyl-β-d-glucosaminidase, a lytic enzyme, might be involved in these morphological changes.

Polymerized Complex Synthesis of Perovskite Lead Titanate at Reduced Temperatures: Possible Formation of Heterometallic (Pb,Ti)-Citric Acid Complex

Abstract: Perovskite PbTiO3 powders were prepared by a polymerized complex technique at relatively low temperatures, viz. 400−600 °C. Heating of a mixed solution of citric acid (CA), ethylene glycol (EG), and Pb and Ti ions with a molar ratio of Pb/Ti/CA/EG = 1/1/10/40 at 130 °C produced a yellowish transparent polymeric gel without any precipitation, which after pyrolysis at 300 °C was converted to a powder precursor for PbTiO3. We suggest, based on the results of Raman and 13C NMR spectroscopies, that a heterometallic (Pb,Ti)−CA3 chelate complex formed in a starting Pb/Ti/CA/EG solution and it was thermally stable upon polymerization at 130 °C. Chemical analyses showed no PbO loss during calcination of powder precursors at 400−700 °C, which led to the conclusion that a solid-state reaction between isolated PbO and TiO2 particles was not responsible for PbTiO3 formation, but PbTiO3 formed directly by thermal decomposition of the powder precursor above 400 °C.

Biotransformation of Binary and Ternary Citric Acid Complexes of Iron and Uranium

Abstract: Citric acid forms ternary mixed-metal complexes with various metal ions involving the hydroxyl and carboxyl groups of citric acid. The coordination of the metal to citric acid has been shown to affect the biodegradation of the metal−citrate complexes and metal mobility in the environ ment. We investigated the formation and biodegradation of the ternary mixed metal Fe−U−citric acid complex. The presence of 1:1:2 Fe−U−citric acid in solution was confirmed by potentiometric titration, UV−vis spectrophotometry, gel-filtration chromatography, and extended X-ray absorption fine structure (EXAFS) analysis. Comparison of the EXAFS spectra shows that the 1:1:2 Fe−U−citric acid complex has structural characteristics similar to the 1:1 U−citric acid complex. Biotransformation studies of Fe(III)−citrate, U(VI)−citrate, and Fe−U−citrate complexes by Pseudomonas fluorescens showed that the binary 1:1 Fe−citric acid was readily biodegraded, whereas the 1:1 U−citric acid complex and the ternary 1:1:2 Fe−U−citric acid com...

Effects of metals on the microbial mineralization of organic acids

Abstract: The effects of chemical speciation on mineralization of organic compounds was studied using citric acid as a model substance. The degradation of14C-labeled Al-, Co-, Cu-, and Zn-citrate was followed in chemically well-defined media inoculated with mixed cultures of microorganisms (soil extracts from two soils). The degradation of citrate was completely inhibited when the acid was bound to Zn, Cu, or Co and partly inhibited when bound to Al. The mineralization of citrate as well as histidine was also followed by incubation of the complexes (Cu, Zn, Al) in the two soils. No effect of metals on the degradation of histidine was seen. The degradation of citrate in soils was also unaffected when complexed to Cu and Zn, whereas Al exerted an inhibited decomposition in both soils.

The modification of lactic acid based poly(ester-urethane) by copolymerization

Abstract: Copolymers of L-lactic acid (LLA) with DL-mandelic acid (DLMA), 4-hydroxybenzoic acid, 4-acetoxybenzoic acid, DL-malic acid, or anhydrous citric acid were synthesized via direct copolycondensation in the presence of 1,4-butanediol, using stannous octoate as catalyst. The effect of the comonomer and the comonomer ratio on polycondensation and the glass transition temperature were investigated. The glass transition temperature of amorphous poly(L-lactic acid-co-DL-mandelic acid) increased linearly from 33° to 56°C as the mandelic acid composition was increased from 0 to 45 mol %. For urethane synthesis, prepolymers of LLA and DLMA were condensation polymerized with compositions of 100/0, 90/10, and 80/20 (mol % in feed). The preparation of poly(ester-urethane) (PEU) was carried out in a stirred glass reactor, using 1,6-hexamethylene diisocyanate and isophorone diisocyanate in melt. The glass transition temperature of poly(L-lactic acid-co-DL-mandelic acid-urethanes) showed a marked increase with increased mandelic acid composition. The molecular weights of these urethanes were lower than for PEU based on poly(L-lactic acid). Such a depression in the degree of polymerization is attributed to the steric hindrance of the bulky phenyl group as a side chain of mandelic acid. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1865–1872, 1997

Quality maintenance of minimally processed Chinese cabbage with low temperature and citric acid dip

Abstract: Chinese cabbage (Brassica campestris L pekinensis group) was minimally processed using best preparation techniques and stored at 0 and at 5°C with and without dips in either citric acid, calcium chloride or ascorbic acid, all at 10 g litre−1. The visual quality, degree of chilling injury, pH and taste were evaluated. The most deleterious effects on quality were produced by black speck (gomasho) and browning. Citric acid inhibited the development of black speck and extended storage life from 10 days of the control to 14 days at 5°C. At 0°C the storage life was not extended by any dip, but citric acid improved quality by reducing black speck. Minimally processed Chinese cabbage treated with citric acid showed only a slight reduction of pH from 6·3 of the control to 6·1 (P⩽0·05) and taste was not significantly affected (P>0·05). Microbial spoilage was not apparent during storage at 0°C for 35 days and 5°C for 21 days under any treatment. © 1997 SCI.

Potassium hydroxycitrate for the suppression of appetite and induction of weight loss

Abstract: The present invention provides methods of suppressing appetite and causing weight loss by administering to a patient hydroxy citric acid in the form of a potassium salt extracted from Garcinia fruit. Methods of inhibiting cytoplasmic citric lyase and increasing fat metabolism in a patient are also described.