Total Oxalate Contents Research Articles

Oxalate content of selected pasta products

About 75% of kidney stones are composed primarily of calcium oxalate, and hyperoxaluria is a primary risk factor for this disorder. Since pasta products are widely consumed and absorbed dietary oxalate can make a significant contribution to urinary oxalate levels, the oxalate content of various types of pasta was analyzed using an enzymatic method. The majority of pasta products had total oxalate contents that ranged from 20 to 30 mg/100 g wet weight and soluble oxalate contents that ranged from 5 to 12 mg/100 g. Products lowest in total oxalate were spaghetti and brown rice pasta. Pasta products that contained vegetable powders among the listed ingredients were highest in oxalate, and the proportion of spinach powder in these samples was an important determinant of oxalate content. The overall data suggested that most types of pasta are at least moderately high in oxalate.

Low-oxalate Spinach Mutant Induced by Chemical Mutagenesis

Spinach (Spinacia oleracea L.) accumulates large amounts of oxalate, which reacts with calcium, inhibiting its absorption and forming urinary stones in humans. In this study, low-oxalate spinach mutant was induced through chemical mutation. Seeds of the gynomonoecious line of ‘Shin-Nippon’ were treated with 50 mM ethyl methane sulphonate (EMS) for 6 h. Self-fertilized M2 seeds were harvested from M1 plants individually. Total oxalate (water soluble and insoluble) concentrations of M2 plants were measured, and four low-oxalate plants were selected. Self-fertilized M3 seeds were harvested from these M2 plants individually. In the progenies of three M2 plants, oxalate concentration ranged from 9 to 19 mg·g−1FW; there were no low-oxalate plants; however, in the progeny of one M2 plant, five of eight plants had low oxalate; their concentration were lower than 2 mg·g−1FW. Self-fertilized M4 seeds were harvested from low-oxalate M3 plants individually. The progenies of low-oxalate M3 plants, named low-oxalate lines, were grown and compared with the original ‘Shin-Nippon’ and gynomonoecius line (wild types). Leaves of low-oxalate lines were slightly smaller and thinner than wild types, whereas the leaf number and color were similar. Oxalate concentrations of leaves in low-oxalate lines strongly decreased; one third to one sixth of those in wild types. Nitrate concentrations did not decrease in low-oxalate lines.

Effect of Salinity Stress on Dry Matter Yield and Oxalate Content in Napiergrass (Pennisetum purpureum Schumach)

Sodium is involved in elevation of oxalate content in some plant species and this element is abundant in saline soils. Oxalate causes precipitation of insoluble calcium oxalate in the rumen and kidneys. The intention of this study was to evaluate the effect of soil salinity stress on dry matter yield and oxalate content in pot-grown napiergrass (Pennisetum purpureum Schumach). Plants were cut three times at 56, 118 and 179 d after transplanting to the pots. Five salinity treatments were used containing various concentrations of NaCl solution as follows: 0, 100, 300, 600 and 900 mM. At 28, 42, 84, 98, 146 and 160 d after transplanting, plants were irrigated with one liter of the particular treatment for each application. Dry matter yield of napiergrass was not affected (p>0.05) by salinity treatments. Plants treated with 100 mM NaCl exhibited a higher soluble oxalate content compared to other treatments, but the differences were not statistically significant (p>0.05). Although salinity treatments had significant (p<0.05) effects on insoluble and total oxalate contents in plant tissue between the 100 and 900 mM NaCl treatments, the differences were too small to be considered biologically important. The present study indicates that where the soil is high in NaCl, napiergrass will tend to grow well and be low in oxalate. (Key Words : Napiergrass, Salinity, Sodium Chloride, Soluble Oxalate, Total Oxalate)

Oxalate-promoted forsterite dissolution at low pH

We ran a series of 124 semi-batch reactor experiments to measure the dissolution rate of forsterite in solutions of nitric and oxalic acid solutions over a pH range of 0–7 and total oxalate concentrations between 0 and 0.35 m at 25 °C. We found that the empirical rate law for the dissolution of forsterite in these solutions is r = 10 - 7.03 a H + 0.46 + 10 - 5.44 m ox 2 - 0.40 a H + 0.47 where a H + is the activity of hydrogen ions, m ox is the concentration of oxalate in molal, and the rate is given in (mol/m 2 s). The first term of the rate law expresses the dissolution rate for solutions with no oxalate and the second term expresses the additional rate produced by the presence of oxalate ions. Our experiments show that oxalate-promoted dissolution rates depend upon both oxalate concentration and pH. Based on this, we propose a reaction mechanism in which a hydrogen ion and an oxalate ion are simultaneously present in the activated complex for the reaction that releases H 4SiO 4 into solution. By analogy, we propose that water acts as a ligand in the absence of oxalate, so the first term of our rate law has a H 2 O m (=1) as a hidden term. Thus, our results suggest that both a proton and a ligand (either an anion or a water molecule) must be present in the activated complex for forsterite dissolution, suggesting that proton-promoted and ligand-promoted dissolution are simply two aspects of the same process, and that the distinction between the two is artificial. The increased dissolution rate of forsterite produced by oxalate ions at a concentration of 0.001 m, a concentration comparable to the amount of organic acids in typical soils, translates into an approximately a 6-fold increase in forsterite dissolution rates at pH > 4.2. This suggests that organic acids have a measurable, but not profound, effect on chemical weathering.

Oxalates in some Indian green leafy vegetables

The soluble and total oxalate contents of 11 leafy vegetables grown in India were determined. Spinach, purple and green amaranth and colocasia contained high levels of total oxalates, which ranged from 5,138.0±37.6 mg/100 g dry matter up to 12,576.1±107.9 mg/100 g dry matter. Seven other leafy vegetables (curry, drumstick, shepu, fenugreek, coriander, radish and onion stalks) contained only insoluble oxalate, which ranged from 209.0±5.0 mg/100 g dry matter to 2,774.9±18.4 mg/100 g dry matter. In vitro digestion of the samples showed that the gastric available oxalate was 10% lower than the values obtained from acid extraction and that intestinal available oxalate was 20% lower than the values obtained following hot water extraction. The percentage calcium bound in the insoluble oxalate fraction of the dried leafy vegetables ranged from 3.3% to 86.7% of the total calcium. Addition of four different sources of calcium (low fat milk, whole milk, calcium carbonate and calcium sulphate) resulted in a range of 32–100% reductions of intestinal available oxalate in the mixture.

Variability of Oxalobacter Formigenes and Oxalate in Stool Samples

The intestinal organism Oxalobacter formigenes is unique in using oxalate as its primary carbon and energy source. Intestinal colonization with O. formigenes may have clinical significance by decreasing intestinal oxalate and its absorption, thereby influencing the concentration of oxalate in plasma and urine, and the development of calcium oxalate stone disease. Because the oxalate content of the diet varies considerably, we hypothesized that the number of O. formigenes and amount of oxalate would vary in feces. To enumerate the number of O. formigenes in feces an accurate and reproducible real-time polymerase chain reaction assay was developed to quantify O. formigenes DNA. Stool samples were obtained from 10 colonized individuals to determine the levels of O. formigenes by this assay and the oxalate content by ion chromatography. Concentrations of O. formigenes ranged from lower than the limit of detection of 5 x 10(3) to 1.04 x 10(9) cells per gm stool. The total oxalate content of stool samples varied from 0.1 to 1.8 mg/gm and fecal water oxalate varied from 60 to 600 microM. All parameters measured varied within each stool collection, among stool collections on different days and among individuals. Notably in 7 of 10 individuals at least 1 stool sample contained no detectable O. formigenes. In addition, 7 of 10 subjects had a fecal colonization of less than 4 x 10(4) per gm stool. This study demonstrates that there is intrastool and interstool sample variability in the amount of O. formigenes measured by real-time polymerase chain reaction that did not correlate with the quantity of oxalate in stool. Most subjects had a fecal colonization of less than 4 x 10(4) per gm stool.

Oxalate in Grain Amaranth

Grain amaranth (Amaranthus spp.) is a widely adaptable C4 pseudo-cereal crop that has interesting nutritional characteristics including high protein and calcium concentrations and a lack of gluten. To date, no antinutrient has been found at problematic levels in grain amaranth; however, oxalate has not been thoroughly studied. Dietary oxalate is a potential risk factor for kidney stone development, and its presence in food lowers calcium and magnesium availability. Oxalate concentration and forms and calcium and magnesium concentrations were determined in 30 field-grown grain amaranth genotypes from the species A. cruentus, A. hybrid, and A. hypochondriacus. The effects of seeding date and fertilization with calcium ammonium nitrate were evaluated in field experiments conducted in multiple environments; the effects of cooking were also evaluated. Mean total oxalate concentration in the 30 genotypes analyzed was 229 mg/100 g, with values ranging between 178 and 278 mg/100 g, the greatest proportion being insoluble (average of 80%). Calcium concentration averaged 186 mg/100 g and ranged between 134 and 370 mg/100 g, whereas magnesium averaged 280 mg/100 g and ranged between 230 and 387 mg/100 g. Fertilization only marginally increased total oxalate concentration and had no effects on other variables. Seeding date had no effects on any of the variables studied. Boiling increased the proportion of soluble oxalate but did not affect total oxalate concentration. Grain amaranth can be considered a high oxalate source, however, as most is in insoluble form, and due to its high calcium and magnesium concentrations, oxalate absorbability could be low. This should be confirmed by bioavailability studies.

Atmospheric production of oxalic acid/oxalate and nitric acid/nitrate in the Tampa Bay airshed: Parallel pathways

Oxalic acid is the dominant dicarboxylic acid (DCA), and it constitutes up to 50% of total atmospheric DCAs, especially in non-urban and marine atmospheres. A significant amount of particulate H 2Ox/oxalate (Ox) occurred in the coarse particle fraction of a dichotomous sampler, the ratio of oxalate concentrations in the PM 10 to PM 2.5 fractions ranged from 1 to 2, with mean±sd being 1.4±0.2. These results suggest that oxalate does not solely originate in the gas phase and condense into particles. Gaseous H 2Ox concentrations are much lower than particulate Ox concentrations and are well correlated with HNO 3, HCHO, and O 3, supporting a photochemical origin. Of special relevance to the Bay Region Atmospheric Chemistry Experiment (BRACE) is the extent of nitrogen deposition in the Tampa Bay estuary. Hydroxyl radical is primarily responsible for the conversion of NO 2 to HNO 3, the latter being much more easily deposited. Hydroxyl radical is also responsible for the aqueous phase formation of oxalic acid from alkenes. Hence, we propose that an estimate of OH can be obtained from H 2Ox/Ox production rate and we accordingly show that the product of total oxalate concentration and NO 2 concentration approximately predicts the total nitrate concentration during the same period.

Determination of oxalates in Japanese taro corms using an in vitro digestion assay

An in vitro assay was used to extract gastric soluble and intestinal soluble oxalates from the corms of four different Japanese taro ( Colocasia esculenta (L.) var. Schott) cultivars (Akame, Ishikawa-wase, Yamato-wase and an unnamed cultivar). The oxalate contents were measured in the raw tissue and after boiling and baking the corms. Akame contained the highest levels of gastric soluble oxalates in the raw tissue (168.9 ± 12.0 mg/100 g fresh weight (FW)) and was significantly higher ( P < 0.001) than the other three cultivars (mean 86.5 ± 8.1 mg/100 g FW). There was no significant difference in gastric soluble oxalates between Ishikawa-wase, Yamato-wase and the unnamed cultivar. Raw Akame corms contained the highest levels of soluble oxalate after intestinal incubation 134.8 ± 9.8 mg/100 g FW. This was significantly different ( P < 0.001) from the other three cultivars, which contained a mean of 66.4 mg intestinal soluble oxalates/100 g FW. Boiling the Japanese taro corms for 40 min reduced the level of intestinal soluble oxalates in the cooked tissue to a low level (mean for all the cultivars, 17.7 mg/100 g FW) as the soluble oxalates were leached into the cooking water. In addition, the mean moisture content of the boiled corms increased to 83.2% compared to the mean moisture content of raw tissue (75.7%). Baking the four cultivars at 180 °C for 40 min led to a significant reduction in the moisture content of the tissue (from a mean of 75.7% moisture content in the fresh tissue to a mean of 50.7% when baked) and an effective concentration of gastric soluble oxalates in the cooked tissue (overall mean 276.1 mg/100 g FW) while the mean intestinal soluble oxalates rose to 187.2 mg/100 g FW. The results confirm that baked taro corms contain moderate amounts of soluble oxalates. The total gastric soluble oxalates of the four different taro corms were similar to the total oxalate contents determined using hot acid method, however the in vitro method used to extract intestinal soluble oxalate appeared to extract more oxalates when compared to the hot water extract method. Baked taro corms should be avoided by people who have an increased risk of renal calcium oxalate stone formation because they contain high levels of intestinal soluble oxalates.

Oxalate content of cormels of Japanese taro ( Colocasia esculenta (L.) Schott) and the effect of cooking

Taro ( Colocasia esculenta L. Schott) is a major starchy food crop in parts of Asia and the Pacific Islands and is grown as a minor crop in New Zealand. Soluble, insoluble and total oxalate content of the cormels of Japanese taro cultivars, Akame, Ishikawa-wase, Yamato-wase and an unnamed cultivar were determined by HPLC following hot water (80 °C) or hot acid (0.2 mol/L HCL) extractions. Oxalate analysis was carried out on the peeled raw, boiled (40 min) and baked corms (180 °C for 40 min). Akame contained the highest level of total oxalate (171.4±11.4 mg/100 g fresh weight (FW)) in the raw tissue and was significantly higher than the other three cultivars ( P<0.001). The raw tissue of the four cultivars contained a mean of 60.6% soluble oxalates; boiling reduced the level of soluble oxalate in the cooked tissue to below detectable levels as soluble oxalates leached into the cooking water. Baking led to a significant reduction in the moisture content of the taro concentrating oxalates in the cooked tissue (overall mean, 229.0±34.4 mg/100 g FW). The results from this study suggest that baked taro corms contain moderate amounts of oxalates.

Composition and availability of soluble and insoluble oxalates in raw and cooked taro ( Colocasia esculenta var. Schott) leaves

Taro ( Colocasia esculenta var. Schott) is a major staple food crop in parts of Asia and the Pacific Islands and is grown as a minor crop in New Zealand. Soluble, insoluble and total oxalate content of young and older leaves were determined by HPLC following hot water (80 °C) and hot (80 °C) acid (0.2 mol/L HCL) extractions. Young taro leaves contained 589 ± 35.8 mg total oxalates/100 g fresh weight (FW) while older taro leaves contained (443 ± 15.0 mg total oxalates/100 g FW). Soluble oxalates were 74% of the total oxalate content of the young and old leaves. Oxalate analysis was also carried out on leaves baked at 150°C for 1.5 h either alone or with 50 ml cows milk. The soluble oxalate content of the fresh baked tissue fell to a mean of 59% for both samples of leaves. Baking the young and old leaves with milk led to a further reduction of the soluble oxalate content in the cooked leaves (mean 21.4% of the total oxalates). The results from this study suggest that baked taro leaves should be regarded as a high oxalate food but baking with milk significantly reduces the amount of soluble oxalate that could be absorbed from the cooked leaves.

Oxalate Content of Cereals and Cereal Products

Detailed knowledge of food oxalate content is of essential importance for dietary treatment of recurrent calcium oxalate urolithiasis. Dietary oxalate can contribute considerably to the amount of urinary oxalate excretion. Because cereal foods play an important role in daily nutrition, the soluble and total oxalate contents of various types of cereal grains, milling products, bread, pastries, and pasta were analyzed using an HPLC-enzyme-reactor method. A high total oxalate content (>50 mg/100 g) was found in whole grain wheat species Triticum durum (76.6 mg/100 g), Triticum sativum (71.2 mg/100 g), and Triticum aestivum (53.3 mg/100 g). Total oxalate content was comparably high in whole grain products of T. aestivum, that is, wheat flakes and flour, as well as in whole grain products of T. durum, that is, couscous, bulgur, and pasta. The highest oxalate content was demonstrated for wheat bran (457.4 mg/100 g). The higher oxalate content in whole grain than in refined grain cereals suggests that oxalic acid is primarily located in the outer layers of cereal grains. Cereals and cereal products contribute to the daily oxalate intake to a considerable extent. Vegetarian diets may contain high amounts of oxalate when whole grain wheat and wheat products are ingested. Recommendations for prevention of recurrence of calcium oxalate stone disease have to take into account the oxalate content of these foodstuffs.

Total and soluble oxalate contents in Thai vegetables, cereal grains and legume seeds and their changes after cooking

This study was conducted to determine soluble and total oxalate contents in common vegetables, cereal grains and legume seeds and the effect of household cooking on these substances. Each food sample was randomly purchased from three main representative markets in metropolitan area of Bangkok, Thailand. Soluble and total oxalates were determined by high-performance liquid chromatography (HPLC). The limit of quantitation for the oxalates was 3 mg/100 g. All studied vegetables contained relatively small amounts of total oxalate (<100 mg/100 g), except chinese convolvulus ( Lpomoea reptans), acacia pennata ( Acacia pennata), and cultivated bamboo shoot ( Bambusa spp.), contained total oxalate more than 150 mg/100 g which can be significantly reduced after cooking by boiling. Among the legume seeds, soybeans ( Glycine max (L.) Merrill) and peanuts ( Arachis hypogaea L.) contained highest and moderate amounts of total oxalate, 204±14 mg and 142±35 mg/100 g, respectively. Rice contained negligible amount of total oxalate (<3 mg/100 g). There was significant reduction ( P < 0.05 ) in total oxalate due to cooking by boiling, percentage loss ranged form 18% in coconut heart top stems ( Cocos nucifera Linn.) to 76% in A. pennata. Similar findings appeared in soluble oxalate, significant loss ( P < 0.05 ) ranged from 30% in cooked white stems swamp morning glory ( Lpomoea aquatica, Forsk) to 83% in cooked cultivated bamboo shoot ( Bambusa spp.). Loss of oxalates in various foods is likely due to their leaching loss in cooking water.

Oxalate contents of species of the Polygonaceae, Amaranthaceae and Chenopodiaceae families

A high dietary oxalate intake influences mineral and trace element absorption in humans and may lead to calcium oxalate stone formation due to the ability of oxalate to form insoluble complexes with divalent cations in the gastrointestinal tract. The soluble and total oxalate contents of species in the Polygonaceae, Amaranthaceae and Chenopodiaceae families were measured using an HPLC-enzyme-reactor method. Polygonaceae, Amaranthaceae and Chenopodiaceae include most of the foods with excessively high oxalate concentrations. Amaranth is a specie of the Amaranthaceae family, Polygonaceae include buckwheat, rhubarb, and sorrel, whereas beetroot, mangold, spinach, and quinoa are species of the Chenopodiaceae family. Obviously, oxalate is accumulated in these plant families in each plant tissue, i.e., in leaves, stems, hypocotyl-root and nuts. The highest oxalate content was found in leaves and stems of plants in these families. Soluble oxalate ranged from 59 to 131 mg/100 g in roots and nuts, and from 258 to 1029 mg/100 g in leaves and stems. Total oxalate ranged from 143 to 232 mg/100 g in roots and nuts, and from 874 to 1959 mg/100 g in leaves and stems. Patients with calcium oxalate stone disease should be advised to avoid these oxalate-rich foods.

High-performance liquid chromatographic analysis of soluble and total oxalate in Ca- and Mg-amended liquid cultures of three wood decay fungi

Two brown-rot wood decay fungi, Fomitopsis pinicola and Meruliporia incrassata, and the white-rot species Phanerochaete chrysosporium were grown for 4 weeks in liquid culture at 0.35, 0.70, 1.05, and 5.00 mM calcium (Ca) and 1.35 and 2.70 mM magnesium (Mg) concentrations. Soluble and total oxalate levels were quantified using a revised ion-exchange HPLC protocol developed specifically for resolving oxalate and other organic acid anions from medium components. Total oxalate concentrations in brown-rot filtrate were not significantly different among treatments; however, soluble oxalate decreased significantly with increasing Ca concentration. Higher Mg concentrations increased soluble oxalate levels only slightly. There was a significant decrease in medium pH at 5.00 mM Ca for all species, as well as an apparent increase in decarboxylation activity in brownrot fungi. Total and soluble oxalate levels in the white-rot cultures were generally below detection for all treatments. The results show a significant influence of Ca on soluble oxalate concentrations not seen previously in the brown-rot species Postia placenta.

High-performance liquid chromatographic analysis of soluble and total oxalate in Ca- and Mg-amended liquid cultures of three wood decay fungi

AbstractTwo brown-rot wood decay fungi,Fomitopsis pinicolaandMeruliporia incrassata, and the white-rot speciesPhanerochaete chrysosporiumwere grown for 4 weeks in liquid culture at 0.35, 0.70, 1.05, and 5.00 mM calcium (Ca) and 1.35 and 2.70 mM magnesium (Mg) concentrations. Soluble and total oxalate levels were quantified using a revised ion-exchange HPLC protocol developed specifically for resolving oxalate and other organic acid anions from medium components. Total oxalate concentrations in brown-rot filtrate were not significantly different among treatments; however, soluble oxalate decreased significantly with increasing Ca concentration. Higher Mg concentrations increased soluble oxalate levels only slightly. There was a significant decrease in medium pH at 5.00 mM Ca for all species, as well as an apparent increase in decarboxylation activity in brown-rot fungi. Total and soluble oxalate levels in the white-rot cultures were generally below detection for all treatments. The results show a significant influence of Ca on soluble oxalate concentrations not seen previously in the brown-rot speciesPostia placenta.

Chemical and nutritional quality changes in germinating seeds of Cajanus cajan L.

Changes in the chemical constituents and nutritive quality of germinating seeds of pigeon pea, Cajanus cajan L. were studied in seeds that were germinated for 0, 1, 2, 3, 4 and 5 days. The differently germinated seeds were analysed for proximate composition, mineral elements, structural carbohydrates, calorific value, nutritive and non-nutritive matter and certain antinutritional factors. Germination significantly altered the nutrient composition of the seed, causing marked increase in calorific value. Crude protein, soluble carbohydrate, cellular and organic cellular contents, cellulose, lignin, non-nutritive matter, total oxalate and phytic acid contents of the seed were negatively correlated with germination, whereas the reverse was the case with the seed's contents of fat, crude fibre, total ash, soluble ash, acid-insoluble ash, cell wall carbohydrate, hemicellulose, iron, manganese, calcium, magnesium, copper, phosphorus, food energy, digestible energy, tannins, total phenolics and trypsin inhibitory activity. It was concluded that the increased contents of tannins, total phenolics and trypsin inhibitory activity of the seed during the progressive germination might limit its nutritive quality.

Comparison of extraction methods for the determination of soluble and total oxalate in foods by HPLC-enzyme-reactor

Food oxalate analysis in foods is problematic due to the wide range of interfering substances. To prevent oxalate generation during sample preparation mild and rapid extraction methods were evaluated. Soluble oxalate was extracted with distilled water and total oxalate was extracted with 2 N hydrochloric acid. Filtrates were analysed using the HPLC enzyme reactor method. Evaluation yielded a high level of precision and recovery. Glyoxylic acid, d/l malic acid, isocitric acid, oxaloacetic acid, pyruvate, mesoxalic acid, ascorbic acid, d(+) glucose, d(−) fructose, chlorogenic acid, caffeic acid could be excluded as a source of oxalate generation during extraction with hot acids. The soluble and total oxalate content of about 150 food samples were investigated.

Dissolution of Nickel Oxide in Oxalic Acid Aqueous Solutions

The dissolution of nickel oxide (bunsenite) in acid solutions containing oxalic acid has been studied at 70.0°C. The dependencies of the rate of dissolution on total oxalate concentration and on pH have been explained by assuming a mechanism involving the transfer of two different surface complexes, I and II, that predominate in different pH ranges. The rate law is R=k1{I}+k2{II}, where {} denotes surface concentration. The values k1Ns=3.04×10−3 mol Ni m−2 s−1, k2Ns=1.84×10−3 mol Ni m−2 s−1, together with the stability constants K1=675 mol−1 dm3 and K2=60 mol−1 dm3 fit all the results very well. The species formed in more acidic media is both more stable and more reactive. The possible structures of I and II are discussed on the basis of Fourier transform IR spectroscopy evidence in the literature.

Oxalate Content of Raw and Cooked Oca (Oxalis tuberosa)

Oca (Oxalis tuberosa Mol.) or New Zealand yam, in common with other members of this genus, contains oxalate, an antinutritive factor. Twelve South American and two New Zealand cultivars of oca were analysed for the total oxalate contents of tubers. Total oxalate levels ranged from 80 to 194 mg/100 g wet matter (WM). As these tubers are normally cooked before consumption, the oxalate levels were measured after they had been cooked by three conventional cooking methods. Oxalate levels ranged from 77 to 220 mg/100 g WM for boiled and steamed tubers, while the levels of oxalate found in baked tubers were significantly increased when compared to the raw tubers. The oxalate content of the baked tubers ranged from 164 to 335 mg/100 g WM. Total calcium content of the raw tubers ranged from 7.5 to 15.5 mg/100 g WM; cooking had little effect on the calcium content. Among cultivars mean oxalate/calcium ratio of the raw, boiled and steamed tubers ranged from 2.5 to 9.9. Baked tubers had a significantly increased oxalate/calcium ratio (mean for all cultivars 9.5).