Insoluble Ca Research Articles

Rheological and calcium equilibrium changes during the ripening of Cheddar cheese

Abstract The small deformation rheological properties and the calcium (Ca) equilibrium of Cheddar cheese were investigated as a function of ripening time. The proportion of insoluble Ca as a percentage of the total Ca decreased from ∼72 to 57% between 3 days and 9 months; most changes occurred within the first 4 weeks. During ripening, the storage modulus ( G ′) of the cheese increased at low temperature, but decreased rapidly at high temperature. At temperatures >40 °C, the loss tangent increased to reach a maximum at a temperature of ∼70 °C in young cheese and there was a steady decline in this temperature during ripening. The maximum loss tangent values increased substantially during the first 4 weeks and then showed little change. Changes in the insoluble Ca content significantly correlated with pH 4.6 soluble nitrogen (pH 4.6 SN). Partial correlation analysis indicated that the insoluble Ca content was more significantly correlated with the rheological properties than was pH 4.6 SN.

An X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FT-IR) investigation of the long-term effect on the solidification/stabilization (S/S) of arsenic(V) in Portland cement type-V

The long-term effects on solidification/stabilization (S/S) of As 5+-bearing oxyanions (AsO 3− 4) in Portland cement type-V (OPC) have been investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FT-IR) techniques. The results of this study confirm our previous results that the early hydration of cement is inhibited by the presence of AsO 3− 4, and that the inhibition is mainly caused by the formation of highly insoluble Ca 3(AsO 4) 2 on the surface of hydrating cement particles. Arsenate analog of ettringite [Ca 6(Al 2O 6)(SO 4) 3·32H 2O] was identified in the early stages of hydration of pure Portland cement and As(V)-treated Portland cement [OPC-As(V)], but not in 10-year-old similar samples. The XRD and FT-IR results indicated interactions of oxyanions and cement particles to produce minor quantities of As 5+-bearing compounds in fresh as well as in 10-year-old samples. New As 5+-bearing phases, NaCaAsO 4·7.5H 2O and Ca 5(AsO 4) 3OH were identified in the 10-year-old OPC-As(V) samples by XRD analyses. Based on these results it is concluded that Portland cement may be considered as a potential matrix to immobilize As 5+-bearing wastes.

Changes in the proportions of soluble and insoluble calcium during the ripening of cheddar cheese.

In cheese, the concentration and form of residual Ca greatly influences texture. Two methods were used to determine the proportions of soluble (SOL) and insoluble (INSOL) Ca in Cheddar cheese during 4 mo of ripening. The first method was based on the acid-base buffering curves of cheese and the second was based on the extraction of the aqueous phase ("juice") of cheese under high pressure and determining the concentration of SOL Ca in the juice using atomic absorption spectroscopy. When cheese was acidified there was a strong buffering peak at pH approximately 4.8, which was due to the solubilization of residual colloidal calcium phosphate (CCP) of milk that remained in cheese as INSOL Ca phosphate. The area of this buffering peak in cheese was expressed as a percentage of the original area of this peak in milk and was used to estimate the concentration of residual INSOL Ca phosphate in cheese. There were no significant differences between the 2 methods. The proportions of INSOL Ca in cheese decreased from approximately 73 to approximately 58% between d 1 and 4 mo. These methods will be useful techniques to study the role of Ca in cheese texture and functionality.

Field-based nutritional response evaluation of the intolerant white lupin (Lupinus albus) cultivar Lucyanne to a lime-amended soil

Two field experiments examined the nutritional responses of the white lupin (Lupinus albus L.) agronomic cultivar Lucyanne to lime-amended soil. In the first, plots and boundaries of a pre-existing lime-rate experiment were sampled in 1993. The maximum shoot dry matter production occurred between soil pH 4·9 and 7·2. Whole-shoot Al concentrations increased below soil pH 4·9, and plants died at pH 4·4. Although dry matter production declined in soil above pH 7·2, no chlorosis or plant death was seen. Only the whole-shoot soluble Ca concentration changed from neutral to alkaline pH soil: it was greatest when grown in the alkaline-pH soil. In the second experiment, plants were grown in neutral pH or limed soil in 2000. Shoots were divided into specific tissue types and analysed for Fe III and Fe II, as well as soluble and insoluble Ca fractions. When sampled in April after over-wintering, the higher Ca concentration in the limed compared with neutral-pH soil-grown plants was due mainly to insoluble Ca. No plants were chlorotic and no differences between the treatments in the concentrations of either form of Fe were found. In June no plants were chlorotic, however the concentrations of both total and soluble Ca fractions were greater in the limed than the neutral-pH soil-grown plants, and there was more stem Fe III and less leaf Fe II in these plants. The present study shows that the cultivar Lucyanne is not a reliable crop plant above pH 7·2, and the loss of shoot dry matter can be attributed to nutritional responses at a sub-chlorotic level of stress.

Biosolids Decomposition after Surface Applications in West Texas

In a semiarid environment, climate is a critical factor in the decomposition of surface-applied biosolids. This study examined the effect of 2- to 7-yr exposure times on the composition of single applications of New York, NY biosolids in western Texas. Exposure time effects on organic matter, N, P, S, Cu, Cr, Pb, Hg, and Zn were studied near Sierra Blanca, TX. Due to organic matter decomposition, total organic C decreased from 340 g kg(-1) in fresh biosolids to 180 g kg(-1) in biosolids after 82 mo of exposure, whereas the inorganic ash content of the biosolids increased from 339 to 600 g kg(-1). Total N decreased from 50 to 10 g N kg(-1) and total S decreased from 12 to 6 g S kg(-1). Bicarbonate-available P in the biosolids decreased from 0.9 to 0.2 g kg(-1). Successive H2O extractions yielded soluble P concentrations consistent with dicalcium phosphate (dical) for fresh biosolids and tricalcium phosphate (trical) for biosolids exposed for 59 months or more. Sparingly soluble phosphates, such as dical and trical, potentially yield > 0.5 mg P L(-1) in runoff waters for extended periods after biosolids applications, especially after multiple applications. Selective dissolution of the biosolids indicated that as much as 66 to 78% of P exists as iron phosphates, 16 to 21% as Fe oxides, and 5 to 12% as insoluble Ca phosphates. Chemical analyses of ash samples suggest that Cu and Zn have been lost from biosolids through leaching or runoff and no losses of Pb, Cr, or Hg have occurred since application.

The development of potential screens based on shoot calcium and iron concentrations for the evaluation of tolerance in Egyptian genotypes of white lupin (Lupinus albus L.) to limed soils.

European cultivars of white lupin (Lupinus albus L.) grow poorly in limed or calcareous soils. However, Egyptian genotypes are grown successfully in highly calcareous soil and show no stress symptoms. To examine their physiological responses to alkaline soil and develop potential screens for tolerance, three experiments were conducted in limed and non-limed (neutral pH) soil. Measurements included net CO2 uptake, and the partitioning of Fe2+ and Fe3+ and soluble and insoluble Ca in stem and leaf tissue. Intolerant plants showed clear symptoms of stress, whereas stress in the Egyptian genotypes and in L pilosus Murr. (a tolerant species) was less marked. Only the intolerant plants became chlorotic and this contributed to their reduced net CO2 uptake in the limed soil. In contrast, Egyptian genotypes and L pilosus showed no change in net CO2 uptake between the soils. The partitioning of Ca and Fe either resulted from the stress responses, or was itself a stress response. L pilosus and some Egyptian genotypes differed in soluble Ca concentrations compared with the intolerant cultivars, although no significant difference was apparent in the Ca partitioning of the Egyptian genotype Giza 1. In a limed soil, Giza 1 maintained its stem Fe3+ concentration at a level comparable with that of plants grown in non-limed soil, whereas stem [Fe3+] of an intolerant genotype increased. Gizal increased the percentage of plant Fe that was Fe2+ in its leaf tissue under these conditions; that of the intolerant genotype was reduced. The potential tolerance of the Egyptian genotypes through these mechanisms and the possibility of nutritional-based screens are discussed.

Solidification/stabilisation of arsenic bearing fly ash from the metallurgical industry. Immobilisation mechanism of arsenic

When a fly ash waste material from a copper refining process containing large amounts of As 2O 3 is solidified using cement and lime, the arsenic concentration in the leachate can be lowered to ca. 5 mg/l in a saturated solution of Ca(OH) 2. It is shown that the decrease of the concentration in the leachate, mainly of As(III), is due to the formation of insoluble CaHAsO 3 in the leachate in the presence of Ca(OH) 2. This method is compared with a method whereby use is made of oxidation of the waste before solidification to oxidise As(III) to As(V) using H 2O 2. The arsenic concentration in the leachate of the extraction test of an oxidised S/S sample was lowered to ca. 0.5 mg/l, a factor of 10 below the one for a non-oxidised sample. It is shown that the decrease of the concentration in the leachate mainly of As(V) is due to the formation of insoluble Ca 3(AsO 4) 2 in the presence of Ca(OH) 2. Extensive use was made of the speciation program MINTEQA2, to clarify the immobilisation of arsenic.

Evidence for absorption of ionic calcium and soluble calcium complexes by the duodenum and cecum in the rat.

The absorption of dietary calcium (Ca) may in part be determined by the formation in the intestinal lumen of soluble Ca complexes and insoluble Ca salts. This study was undertaken to test the assumption that ionic Ca concentration (Ca2+) is the only species of Ca that is available for absorption. Bidirectional steady-state Ca fluxes were measured in vitro under short-circuit conditions across segments of the proximal duodenum and the cecum in the presence and absence of varying concentrations of soluble Ca citrate complexes. The presence of 5.0 mmol/L medium citrate reduced medium Ca2+ and cecal Ca mucosal-to-serosal fluxes (Jms) (29 +/- 18 versus 108 +/- 7 nmol Ca/cm2/h, P <.001), but did not reduce duodenal Ca Jms (31 +/- 5 versus 23 +/- 9, P not significant). Duodenal Ca Jms increased 106% as medium Ca citrate complex increased to 1.018 mmol/L and Ca2+ remained constant; cecal Jms increased by 48% under the same conditions. The formation of soluble Ca organic anion complexes with lactate, malate, and fumarate reduced medium Ca2+ and cecal Ca Jms decreased with the reduction of medium Ca2+. The results of this study indicate that Ca2+ is the form of Ca most readily absorbed by the small intestine and the colon. Soluble Ca citrate complexes are absorbed by the duodenum and, to a much lesser extent, by the cecum. The reduction of Ca Jms by citrate is caused by the reduction of medium Ca2+ through formation of Ca citrate complexes and not caused by a direct interaction of the anion with the intestinal epithelium.

Influência do cálcio nas características físicas e no teor de cálcio durante desenvolvimento e maturação da uva 'Itália'

O objetivo deste trabalho foi avaliar o efeito da aplicação pré-colheita de Ca nas características físicas e nos teores de Ca durante o desenvolvimento e maturação da uva (Vitis viniferaL.) 'Itália'. O experimento foi realizado na Empresa Timbaúba Agrícola S.A., em Petrolina, PE. Utilizaram-se doses de cálcio (0, 0,5, 1,0 e 1,5%) na forma de cloreto de cálcio diidratado, aplicadas via imersão dos cachos, durante 10 segundos, na fase de mudança de cor e início de amolecimento das bagas (57 dias após a formação dos frutos). Os cachos marcados foram avaliados aos 28, 43, 57, 72 e 92 dias após a formação dos frutos. O delineamento experimental foi inteiramente casualizado, em fatorial 4 x 5 (dose de Ca x fase do desenvolvimento), com quatro repetições. Níveis crescentes de Ca aumentaram os teores de Ca total e solúvel no engaço e na baga, além do Ca insolúvel no engaço. Na baga, os tratamentos não tiveram efeito quanto ao conteúdo de Ca insolúvel. As doses de 0,5 e 1,0% de Ca incrementaram ligeiramente o peso e o volume da baga, havendo resposta inversa nos frutos tratados com 1,5%.

Effect of Ca: P ratio on grower-finisher pig performance and mineral excretion

The level of calcium (Ca) in the diet affects the utilisation of phytic acid-phosphorus (P) through the formation of insoluble Ca phytate and/or reduction of phytase activity (Larsen 1993). High Ca: total P ratios (Ca: tP) (1.5:1 to 2.0:1) in corn-soya bean meal diets supplemented with microbial phytase decreased the utilisation of P for weanling (Lei et al., 1994) and growing-finishing (Liu et al., 1998) pigs. However, it is important to note that the majority of research using supplemental microbial phytase and Ca:P ratios was carried out using maize-soyabean meal based diets. The objective of this experiment is to examine the effect of Ca: tP ratio on the efficacy of microbial phytase and its effects on pig performance, nutrient digestion and mineral metabolism using wheat, barley and soya bean meal based diets.

Ingestion of the soluble dietary fibre, polydextrose, increases calcium absorption and bone mineralization in normal and total-gastrectomized rats

We previously demonstrated that feeding a highly fermentable and water-soluble dietary fibre, guar-gum hydrolysate (GGH) increased intestinal absorption of insoluble Ca salts in total-gastrectomized rats. In the present study, we examined the effects of feeding a less fermentable and water-soluble fibre, polydextrose (PD), on Ca absorption and bone mineralization in the normal and total-gastrectomized rats in comparison with the effects of GGH. Apparent Ca absorption was severely lowered by gastrectomy, and PD feeding (50 g/kg diet) partially restored the reduction of Ca absorption similarly to GGH feeding (50 g/kg diet). PD feeding also increased the Ca absorption in normal rats, but not GGH feeding. Femur Ca concentration was reduced with gastrectomy. Feeding PD for 21 d increased the bone Ca concentration in both normal and gastrectomized rats, but GGH feeding did not. In rats fed PD, pH of the caecal contents was lower than in rats fed fibre-free and GGH diets; however, soluble Ca concentration in the caecal contents was not different between the diet groups. Short-chain fatty acid concentrations were much lower in the PD groups than in the GGH groups. We also examined in vitro Ca absorption by using everted sacs of the small intestine. Addition of PD to the serosal medium of the ileal sacs increased Ca absorption, but addition of GGH did not. These results suggest that the small intestine rather than the large intestine is responsible for the increase in Ca absorption in rats fed PD, and suggests that the mechanism for the increase by PD may be different from that by GGH.

Calcium and phosphorus bioavailability in rats consuming oil from either raw sardines or sardines fried in olive oil Biodisponibilidad de calcio y fósforo en ratas alimentadas con grasa de sardina cruda o frita con aceite de oliva

Three diets were prepared containing 8% olive oil (OO), fresh sardine ( Clupea pilchardus) oil (SO), and oil from sardines fried in olive oil (FSO), respectively. After in vitro digestion, soluble (dialyzed and nondialyzed) and insoluble Ca and P fractions were determined. In vitro Ca availability tended to be higher with SO, and even more so with FSO, than with OO, while that of P increased only slightly with FSO. Growing rats consumed the diets for 28 days. Food intake and body weight increased with FSO more than with OO, but decreased markedly with SO, due to an imbalance in the n-3/n-6 fatty acid ratio. Absorption efficiencies of Ca and P were higher with SO than with the other diets during days 5-12. Because urinary Ca excretion was also greater with SO, apparent retention of both Ca and P was lower with this diet. With SO, carcass content of Ca and P was low but their concentrations were high. Apparent retention of these minerals and their carcass content were similar or higher with FSO than with OO. Therefore, although availability of Ca and P from raw and fried sardine oil diets was sufficient in vitro, consumption of raw sardine oil as the only dietary fat produced changes in calcium and phosphorus bioavailability, an effect of sardine oil which disappeared after frying in olive oil.

Influence of Various Types of Inorganic Salts on Dispersion Mechanisms of Comb-Type Polymer Containing Grafted Polyethylene Oxides Chains.

This paper discusses the influences of various types of inorganic salts on the fluidity of inorganic particle suspensions with comb-type polymer. By addition of anion which form insoluble salt with Ca2+, the fluidity of suspension with polymer and the amounts of polymer adsorbed on CaCO3 were remarkably reduced. It is thought that the adsorption of polymer is related to the concentration of Ca2+ in the liquid phase. When the concentration of Ca2+ in the liquid phase is reduced, the adsorbed amount of Ca2+ on the surface of CaCO3 decreases. By addition of soluble Ca salts or CaO, the fluidity of suspension with polymer and inorganic electrolytes containing anions which form insoluble salt with Ca2+ could be greatly improved, up to almost the same value of a suspension without inorganic electrolytes. This is because almost all the anions precipitated as insoluble Ca salts or the concentration of Ca2+ or cations such as Al3+ in the liquid phase increased and, as a result, the adsorption site of polymer increased.

Mitochondrial Clearance of Cytosolic Ca2+in Stimulated Lizard Motor Nerve Terminals Proceeds without Progressive Elevation of Mitochondrial Matrix [Ca2+

This study used fluorescent indicator dyes to measure changes in cytosolic and mitochondrial [Ca(2+)] produced by physiological stimulation of lizard motor nerve terminals. During repetitive action potential discharge at 10-50 Hz, the increase in average cytosolic [Ca(2+)] reached plateau at levels that increased with increasing stimulus frequency. This stabilization of cytosolic [Ca(2+)] was caused mainly by mitochondrial Ca(2+) uptake, because drugs that depolarize mitochondria greatly increased the stimulation-induced elevation of cytosolic [Ca(2+)], whereas blockers of other Ca(2+) clearance routes had little effect. Surprisingly, during this sustained Ca(2+) uptake the free [Ca(2+)] in the mitochondrial matrix never exceeded a plateau level of approximately 1 microM, regardless of stimulation frequency or pattern. When stimulation ceased, matrix [Ca(2+)] decreased over a slow ( approximately 10 min) time course consisting of an initial plateau followed by a return to baseline. These measurements demonstrate that sustained mitochondrial Ca(2+) uptake is not invariably accompanied by progressive elevation of matrix free [Ca(2+)]. Both the plateau of matrix free [Ca(2+)] during stimulation and its complex decay after stimulation could be accounted for by a model incorporating reversible formation of an insoluble Ca salt. This mechanism allows mitochondria to sequester large amounts of Ca(2+) while maintaining matrix free [Ca(2+)] at levels sufficient to activate Ca(2+)-dependent mitochondrial dehydrogenases, but below levels that activate the permeability transition pore.

Calcium forms in leaves of muskmelon plants grown with different calcium compounds

The time course trend of the various calcium (Ca) forms (soluble, bound, inorganic insoluble, and organic insoluble) was studied throughout the growing period in mature and young leaves of Cucumis melo L. cv. Revigal plants cultivated on rockwool under unfavorable conditions for Ca uptake. The following anions accompanying Ca were tested: NO3 ‐ as control, as well as EDTA2‐, Cl‐ and SO4 2‐ with two concentration levels equivalent to half and a quarter part of the Ca level of the control. The differences between mature and young leaves were very marked for all the forms. Generally, the inorganic insoluble Ca form was predominant in mature leaves, while the bound form showed the lowest levels. In young leaves, on the other hand, soluble Ca was usually the major form, whereas organic insoluble Ca was the least plentiful. The treatments with Ca‐EDTA (Ch‐#fr1/2> and Ch‐#fr1/4>) resulted in lower leaf Ca concentration than the other treatments. The ratios referring to the Ca contents of mature leaves/young leaves for the six Ca‐deficiency treatments varied from 5.0 to 18.5 (soluble Ca), 3.8 to 11.0 (bound Ca), 9.0 to 41.7 (inorganic insoluble Ca), and 9.0 to 47.7 (organic insoluble Ca). For the control, these ratios were 2.3 (soluble Ca), 1.6 (bound Ca), 22.3 (inorganic insoluble Ca), and 61.5 (organic insoluble Ca). The insoluble forms always showed higher ratios. For all treatments and sampling dates the total Ca level was approximately ten times higher in mature leaves than in young leaves and always in the following order: NO‐>Cl‐‐#fr1/2> ∼ SO42‐#fr1/2>> Cl‐‐#fr1/4> ∼ SO4 2‐‐#fr1/4>> Ch‐#fr1/2>>Ch‐#fr1/4>, which was the same order observed in the response as reflected by fruit and vegetative biomass production.

Fractions of calcium in the plant‐soil system affected by the application of olive oil wastewater

A pot experiment using calcareous soil was conducted in a growth chamber to examine the effects of olive oil wastewater applications on Ca fractions in the plant and on exchangeable Ca in soil after plant growth. The experimental treatments consisted of two rates of olive oil wastewater, two mineral fertilizer treatments including K, which supplied K in amounts equivalent to the K supplied by the olive oil wastewater treatments, a mineral fertilizer without K treatment (F), and a control. The pots were sown with ryegrass which was harvested 3 times at monthly intervals. The high rate of olive oil wastewater resulted in a prolonged increase in dry matter production. It also resulted in a reduction in the concentrations of soluble Ca, bound Ca, inorganic insoluble Ca and organic insoluble Ca in the plant shoots relative to the control and the F treatment. The low rate of olive oil wastewater produced similar but less marked effects, with decreases being observed in the soluble Ca and bound Ca fractions. After 3 months of plant growth, soil exchangeable Ca was higher in the control and F treatment soils than in the soils receiving olive oil wastewater or K fertilizer. At this time, there were no significant differences in exchangeable Ca between the soils receiving olive oil wastewater and those treated with K fertilizer.

The large intestine compensates for insufficient calcium absorption in the small intestine in rats.

We previously demonstrated that the large intestine compensated for decreased calcium (Ca) absorption caused by renal failure in rats fed a highly fermentable dietary fiber. In this study, we examined whether the large intestine compensated for insufficient Ca absorption in the rat small intestine without ingestion of a fermentable dietary fiber. Rats were fed one of four test diets containing either insoluble (carbonate) or soluble (gluconate, lactate, or citrate) Ca sources. The dietary Ca level was 2.0 g/kg, which is lower than the minimum requirement for rats (3.0 g/kg), to conduct the present study under a condition in which rats can maximally absorb Ca. To prevent Ca absorption in the small intestine, we replaced a primary phosphate (KH2PO4) with secondary phosphates (K2HPO4 and Na2HPO4) in diets. The apparent Ca absorption in the small intestine was estimated by adding chromic oxide (Cr2O3) as an insoluble and an unabsorbed marker to test diets and by measuring the ratio of Ca:Cr in the cecal content. The apparent Ca absorption in the whole intestine was estimated by the intake and fecal excretion of Ca. The apparent Ca absorption in the small intestine was significantly lower from the Ca carbonate diet than from the Ca gluconate, lactate, or citrate diets. The apparent Ca absorption in the whole intestine was not significantly different among the four groups, and the values were similar to the absorption rates in the small intestines of rats fed diets containing soluble Ca sources. These results show the following: (a) In rats fed 0.2% Ca diets containing soluble Ca salts, Ca is mostly absorbed in the small intestine, even in secondary phosphate intakes; (b) In contrast, in rats fed a 0.2% Ca diet containing an insoluble Ca salt (carbonate), Ca is not sufficiently absorbed in the small intestine. However, the large intestine compensates for the small intestinal Ca absorption decreased by dietary secondary phosphates.

The calcium demand of the calcicole sedge Schoenus nigricans

Summary Growth and reproduction of the perennial sedge Schoenus nigricans from calcareous wet dune-slacks was investigated in response to increasing proportion of calcium carbonate in dune sand to test the hypothesis that a high calcium supply is necessary to ensure a full life cycle of this calcicole species and counteract the population decrease in wet dune slacks. Plant growth and nutlet quality, but nor reproduction per se were significantly lower in plants grown for 30 months at 0.03% Ca compared to all other concentrations from 0.25 to 2% Ca. Plants at 0.03% Ca had the lowest nutlet mass. With increasing Ca supply, the Ca concentration in the roots increased more than that in leaves and shoots, where Ca was associated with the fractions being soluble in water and acetic acid. Ca-oxalate was not present. The insoluble Ca fraction was not affected by the external Ca supply, but was only related to the age of the tissue. A quotient of water-soluble calcium/water-soluble total cations of 0.15 seems to be sufficient for a good performance of S. nigricans in soils with 0.25% Ca or more, thus indicating a relatively low calcium demand of this calcicole species which has a high degree of Ca-tolerance.

Calcium Solubility, Intestinal Sojourn Time and Paracellular Permeability Codetermine Passive Calcium Absorption in Rats

To investigate the nonsaturable, paracellular pathway of intestinal Ca absorption, the luminal contents of 12-cm segments of the intestine of 8-wk-old male Sprague-Dawley rats were analyzed for pH, sojourn time and soluble and insoluble Ca over a 24-h period. The rats had been fed one of two high Ca diets for 2 wk: 1.5% Ca (diet group 3a) and 3.1% (diet group 5a). The pH of the small intestine increased from <6.6 to >8.0 from duodenum to ileum; transit time increased from 2.5 min in the duodenum to 58 min in the distal ileum, with the entire ileum accounting on the average for 74% of the transit time of 3 h. The amount of Ca solubilized throughout the intestine was 32 ± 3.3 µmol in diet group 3a and 53 ± 5.3 µmol in diet group 5a, i.e., 27% and 2.0% of the total luminal Ca. Because absorption by diet group 3a was 1.45 ± 0.23 mmol/d and that by diet group 5a was 2.50 ± 0.18 mmol/d, the amounts absorbed were 45.3 and 47.1 times greater than present in the lumen in soluble form at any one time. Thus, over a 24-h period, an average of 3.2% (46.2/1440) of the soluble Ca present in the lumen at any time was absorbed per min. Calculations involving the gradient between luminal and plasma Ca show that the rate of Ca diffusion from lumen to blood is <2% of what it would be if the paracellular path were unrestricted. Thus, intestinal sojourn time, Ca solubility and mucosal permeability to Ca are factors that determine the rate of passive Ca absorption.

Calcium solubilization and retention in the gastrointestinal tract in chicks (Gallus domesticus) as a function of gastric acid secretion inhibition and of calcium carbonate particle size.

In chicks, immature pullets and laying hens, the inhibition of gastric acid secretion by omeprazole, an H+,K(+)-transporting ATPase (EC 3.6.1.36) inhibitor, greatly increased proventricular and gizzard pH values. Consequently, gizzard soluble Ca concentration deceased and the insoluble Ca fraction increased. Inhibition of acid secretion increased duodenal pH values in immature pullets and laying hens but not in chicks. Duodenal soluble and ionic Ca concentrations were lowered by gastric acid inhibition in chicks and to a larger extent in immature pullets and laying hens. The use of Ca of coarse particle size increased the gizzard insoluble Ca fraction in chicks and pullets. However, it did not influence its soluble Ca fraction in chicks but tended to reinforce the negative effect of omeprazole on soluble Ca in the gizzard and duodenum of chicks and laying hens. Coarse particles of Ca led to an increase in gizzard and duodenal soluble Ca at the end of eggshell calcification in laying hens. An enhancement in the level of Ca in the diet from 10 to 36 g/kg increased gizzard soluble Ca and duodenal soluble and ionic Ca concentrations in immature and adult hens. Intestinal Ca retention and bone mineralization was unaffected by gastric acid inhibition in chicks but were largely diminished by the use of coarse particles of Ca. Gastric acid inhibition was associated in laying hens with decreased Ca retention to a small extent and with reduced eggshell quality. These observations confirm that gastric acid secretion is of importance for CaCO3 solubilization but question its role as a prerequisite for intestinal Ca retention in chicks and even in hens fed on a high Ca diet.