Insoluble Oxalate Contents Research Articles

Antioxidants Capacity, Phenolic and Oxalate Content from Two Varieties of Solanum melongena at Different Maturity Stages

Aims: To investigate the antioxidant activities, total phenolic and oxalate contents in two varieties of eggplant (Solanum melongena) (terung telunjuk (TT) and terung rapuh (TR)) at different maturity stages.
 Study design: Each sample was extracted three times (n=3) for the antioxidant activities, total phenolic and oxalates content. All the data were analysed by using ANOVA and Tukey Pairwise tests.
 Place and duration of study: Malaysian Agricultural Research and Development Institute (MARDI), between December 2019 and October 2020.
 Methodology: Two varieties of eggplant (TT and TR) were cultivated and the samples were tagged and the fruits were harvested according to their maturity stages (stage 1 – stage 4). Samples were freeze dried and extracted to evaluate the antioxidant activities as well as the total phenolic and oxalate contents.
 Results: Total phenolic contents (TPC) in TR were lower from stage 1 to stage 3 but high at over mature stage (stage 4) meanwhile TPC in TT increased upon maturity. The DPPH assay from the fruit extracts of TT in all maturity stages showed a stronger antioxidant activity as compared to TR, in which fruit of TT from stage 3 was double in antioxidant activity as compared to TR. The FRAP assay of both eggplants showed extracts of TT having a higher ferric reduction power in all stages as compared to TR. Meanwhile, both eggplant varieties showed different total, soluble and insoluble oxalate contents in all maturity indices. TT had the highest total oxalate content at stage 1 as compared to TR while the soluble oxalate content increased in TR in all maturity stages. The highest percentage of soluble oxalate content was observed in TR at stage 4 with 95.5%. Conclusion: Phytochemical findings from these eggplant varieties showed their potentials to improve livelihood and public health. More comprehensive studies on the bioactive compounds, structural elucidation and pharmacological evaluation are to be conducted to understand the possible effects of these phytochemical results.

Oxalate contents of Thai rice paddy herbs (L. aromatica and L. geoffrayi) are affected by drying method and changes after cooking

Food processing, including drying and cooking, generally influences the physical and chemical qualities of food products. The present study assessed the changes in oxalate contents of two rice paddy herbs (phak-kha-yaeng in Thai), Limnophila aromatica (phak-kha-yaeng khao) and Limnophila geoffrayi (phak-kha-yaeng daeng), as affected by different drying methods, namely hot-air, freeze and vacuum drying. The entire, soluble and insoluble oxalate contents of the cooked samples were also evaluated. Dried samples showed a significant increase in soluble oxalate content compared to fresh samples except for hot-air dried phak-kha-yaeng daeng, while entire and insoluble oxalate contents in dried samples were significantly decreased. Levels of soluble oxalates which were 30% in fresh phak-kha-yaeng khao and 46% in fresh phak-kha-yaeng daeng can be significantly reduced after cooking by boiling. In addition, the cooking of both the hot-air dried phak-kha-yaeng samples also showed greater losses in oxalates than those of other samples studied. Hot-air drying should be considered as a suitable drying method for phak-kha-yaeng with respect to reducing its oxalates. The present study has provided useful information for the drying of vegetables or plant foods to reduce the risk of consuming plant foods which contain high levels of oxalates.

Determination of Oxalates in Corms of Selected Taro (Colocasia esculenta) Varieties in Malaysia Using Ultra High-Performance Liquid Chromatography

Aims: To determine the oxalate contents in different varieties of taro (Colocasia esculenta) collected in Peninsular Malaysia.
 Study Design: Ultra High-Performance Liquid Chromatography (UHPLC) with UV detector (Diode Array Detection, (DAD)) was used to determine the total and soluble oxalate contents in different varieties of taro corms. Meanwhile, the insoluble oxalate content (calcium oxalate) was estimated from the subtraction of soluble oxalate content from total oxalate content.
 Place and Duration of Study: Malaysian Agriculture Research and Development Institute (MARDI Headquarters), Persiaran MARDI-UPM, 43400 Serdang, Selangor, Malaysia between December 2018 to December 2019.
 Methodology: 9 different varieties of taro were collected from different locations in Peninsular Malaysia. All the samples were analysed for their oxalate contents. Extractions were carried out to determine the total oxalate and soluble oxalate contents. All the samples were analysed using UHPLC. The generated data of oxalate contents were analysed using Analysis of Variance (ANOVA).
 Results: There is a significant difference (P <.05) between the oxalate content in the examined varieties with respect to the amount of total, soluble and insoluble oxalate contents. The putih variety has significantly the highest amount of total oxalate content with 218.8 ± 28.2 mg/100 g DW (dry weight) followed by the udang variety with 184.2 ± 24.7 mg/100 g DW and the wangi variety with 178.3 ± 5.1 mg/100 g DW. Tapak badak variety has the lowest total oxalate content with 70.5 ± 20.1 mg/100 g DW. Result showed that wangi variety has significantly the highest soluble oxalate content with 135.1 ± 4.8 mg/100 g DW followed by udang with 100.9 ± 49.8 mg/100 g DW. The lowest soluble oxalate content was found in tapak badak with 17.7 ± 2.9 mg/100 g DW.
 Conclusion: Despite many factors contributing to the difference in oxalate content between varieties, this study would help researchers or policy makers to suggest potential taros for commercial cultivation.

Oxalic acid content and pharmacobotany study of the leaf blades of two species of Annona (Annonaceae)

Annona muricata L. and A. squamosa L. are species of the Annonaceae family widely used in traditional medicine in Brazil for the treatment of noncommunicable diseases. However, this species may contain, for example, calcium oxalate crystals, that can precipitate in the kidneys and contribute to the formation of kidney stones. There are still few studies on the content of oxalic acid present in medicinal species. Thus, the objective of this work was to conduct a comparative anatomical and histochemical study between the species and determining its content of oxalic acid. Semipermanent histological slides were prepared, following common plant anatomy procedures, for analysis of the leaf blades in optical microscopy, polarization and scanning electron microscopy coupled with energy-dispersive X-ray spectrometry. To determine the total, soluble and insoluble oxalate content was used titration with potassium permanganate. The anatomical characterization allowed identifying the characters useful in the differentiation of the species and the druses. The histochemistry revealed the location of the metabolites and, along with the chemical microanalyses, demonstrated that the druses are of calcium oxalate. Annona squamosa presented the highest level of total oxalate. The study assists in the quality control of A. muricata and A. squamosa and brings new information on its oxalic acid content.

Oxalate Contents of Raw, Boiled, Wok-Fried and Pesto and Juice Made from Fat Hen (Chenopodium album) Leaves.

The total, soluble, and insoluble oxalate contents of fresh and wok-fried fat hen (Chenopodium album) leaves were extracted and measured using High pressure liquid chromatography. The total oxalate content of the raw leaves was 1112.4 mg/100 g dry matter (DM), and the levels were significantly reduced by boiling (682.8 mg/100 g DM) or cooking the leaves in a wok (883.6 mg/100 g DM). The percentages of soluble oxalate contents in the total oxalates of the raw and boiled leaves were similar (mean 75%), while the proportion of soluble oxalate content in the wok-fried leaves was reduced to 53.4% of the total, giving a significant increase in the insoluble oxalate content of the wok-fried leaves. The percentage of insoluble calcium in the total calcium was significantly reduced (p < 0.05) when the leaves were boiled, but the insoluble oxalate content significantly increased (67.2%) in the wok-fried leaves when compared to the content of the original raw leaves. Processing the cooked leaves into pesto or extracting the juice gave final products that contained significantly reduced total and soluble oxalate contents. The addition of calcium chloride to the juice caused a very small reduction in the soluble oxalate content in the juice.

Oxalate content of raw, wok-fried, and juice made from bitter gourd fruits.

The total, soluble, and insoluble oxalate contents of fresh and wok‐fried bitter gourd (Momordica charantia) fruits were extracted and measured using HPLC chromatography. Frozen bitter gourds were imported from Vietnam, and two cultivars characteristic of bitter gourd fruits grown in India and Malaysia were grown locally in the North Island of New Zealand. The mean total oxalate contents of ripe fruits from Vietnam, India, and Malaysia were 85.90 ± 8.60 mg/100 g wet matter (WM), while the mean total oxalates fell to 88.06 ± 0.95 mg/100 g FM when the fruits were wok‐fried. The mean soluble oxalate content of the total oxalate was 54.42% of the ripe fruits and 58.14% of the wok‐fried fruits. The three cultivars of bitter gourds were processed into juice by the addition of standard ingredients and then processed through a screw press to remove excess fiber. The final juices had an overall mean value of 27.11 mg of total oxalates/100 g WM; the mean soluble oxalate content was 85.5% of the total, which was much higher than that measured in the cooked gourds (mean 70.7%).

Anatomy, histochemistry and oxalic acid content of the leaflets of Averrhoa bilimbi and Averrhoa carambola

Averrhoa bilimbi L. and A. carambola L., Oxalidaceae, are the only two species of the genus Averrhoa L. Their leaves are widely used in folk medicine as an adjuvant in the treatment of diabetes. Some species may contain, for example, calcium oxalate crystals, which may lead to risk in its use when there is predisposition of individuals with reduced renal activity. Therefore, there are still few studies on the content of oxalic acid present in them, highlighting the importance of this investigation. The objective of this work was to conduct a comparative anatomical and histochemical study between the species and determining its content of oxalic acid. Semipermanent histological slides were prepared, following common plant anatomy procedures, for analysis of the leaflets in optical microscopy, polarization and scanning electron microscopy coupled with energy-dispersive X-ray spectrometry. To determine the total, soluble and insoluble oxalate content was used titration with potassium permanganate. The anatomical characterization allowed identifying the characters useful in the differentiation of the species. The histochemistry revealed the location of the metabolites. Chemical microanalyses demonstrated that the crystals are of calcium oxalate. A. carambola presented the highest levels of total oxalate and soluble oxalate. The study assists in the identification and quality control of A. bilimbi and A. carambola and brings new data on its oxalic acid content, which are important, in view of the medicinal use of the species.

Effects of maturity at harvesting and primary processing of cocoa beans on oxalate contents of cocoa powder

The total, soluble and insoluble oxalate contents of cocoa beans (Theobroma cacao L.) harvested at four different maturity stages: immature, mature, half ripe and fully ripe were extracted and measured using HPLC chromatography. The mean total oxalate content of the four maturity stages was 632 ± 20 mg/100 g dry matter (DM); soluble oxalates were 89% of the total oxalates. Natural fermentation of the whole beans had a small effect on the soluble oxalate content of the raw cocoa powder produced following three to seven days of fermentation. Fermentation of the beans with pectinase had no significant effect on the total oxalate contents of the raw cocoa powder. Soluble oxalates in the cocoa powder were reduced by fermentation with added pectinase (581 vs 613 mg soluble oxalate/100 g DM). For both fermentation treatments, increasing fermentation duration increased the insoluble oxalate content and reduced the proportion of soluble oxalate. There were no differences in the total oxalate contents between samples dried by freeze, oven or sun drying. However oven dried cocoa powder contained the highest level of soluble oxalate (648 ± 11.0 mg/100 g DM) compared to the other two drying methods.

Oxalate Content of Taro Leaves Grown in Central Vietnam.

Leaves were harvested from four different cultivars of Colocasia esculenta and three cultivars of Alocasia odora that were growing on nine different farms in central Vietnam. The total, soluble and insoluble oxalate contents of the leaves were extracted and measured using HPLC chromatography. Total calcium determinations were also carried out on the same samples. The total oxalate content of the leaves ranged from 433.8 to 856.1 mg/100 g wet matter (WM) while the soluble oxalate ranged from 147.8 to 339.7 mg/100 g WM. The proportion of soluble oxalate ranged from 28% to 41% (overall mean 35%) of the total oxalate content of the leaves. The equivalent insoluble oxalate proportion ranged from 59% to 72% of the total (overall mean 65%). There was little difference between the Colocasia esculenta and Alocasia odora taro cultivars, although the total oxalate content was significantly higher in Alocasia odora cultivars. The overall mean total calcium content was 279.5 mg/100 WM and the percentage of insoluble calcium bound as calcium oxalate ranged from 31.7% to 57.3% of the total calcium content (overall mean 47.1%). The oxalate content in taro leaves is a major factor to consider when different cultivars of taro are recommended for human or animal consumption.

Effect of Processing on the Oxalate and Calcium Concentrations of Two Local Dishes, C&amp;amp;#417;m H&amp;amp;#7871;n and Canh Chua B&amp;amp;#7841;c H&amp;#224;, Prepared from Taro Stems

Stems of sweet taro (Colocasia esculenta) grown in Thua Thien Huế Province in Vietnam and were used as an ingredient to prepare two local dishes, Cơm Hến and Canh Chua Bạc Ha. This study investigated the effect of simple processing treatments used to prepare these popular dishes on the total, soluble and insoluble oxalate and calcium contents of the taro stems. Raw stems were used to prepare Cơm Hến. Three treatments, removing the skin then washing and slicing, slicing and washing, or slicing and then allowing the stems to wilt overnight were compared to the whole raw stems with the skin retained. Overall, processing the stems reduced the soluble oxalate contents by a mean of 8% when compared with the original raw stems. The mean total calcium bound in the insoluble oxalate fraction of the three processing treatments was 43.3% ± 2.0%. Canh Chua Bạc Ha was prepared by boiling peeled taro stems. In this experiment the peeled stems were boiled for 10, 15 and 20 min and this resulted in 63.4%, 74.5% and 76.6% reductions in soluble oxalate content, respectively, when compared to the original peeled stems. Boiling for 20 min was the most effective way to reduce both the total and soluble oxalate contents of the stems. 39% of the total calcium in the raw taro stems was bound to the insoluble oxalate fraction and this was reduced to a mean of 17.2% ± 2.6% by the three cooking treatments.

Oxalate Content of Miner’s Lettuce Irrigated with Water or Fertilizer Solutions

The total, soluble and insoluble oxalate contents of the small, large and cauline leaves and small and large stems of miner’s lettuce (Claytonia perfoliata ) plants which had been irrigated with tap water or a soluble fertilizer were extracted and measured using HPLC chromatography. Overall, all plant parts of miner’s lettuce analyzed contained high levels of total and soluble oxalates; however plants irrigated with fertilizer contained lower levels of oxalates compared with plants irrigated with water. On a dry matter basis, the small leaves contained higher levels of total oxalate when compared to the total oxalate in the large leaves. Soluble oxalate in the leaves of plants irrigated with water ranged from 2.6 to 7.5 mg/100g dry matter (DM) and was significantly higher (P < 0.05) than the leaves of the fertilizer-watered plants, which ranged from 1.8 to 2.8 mg/100g DM. The soluble oxalate in the small and large stems of the fertilizer-watered plants ranged from 1.20 to 1.5 mg/100g DM and was significantly lower (P < 0.05) than the water-treated small and large stems, which ranged from 3.75 to 4.4 mg/100g DM. It is recommended that the leaves of miner’s lettuce should be consumed in moderation.

Oxalate Content of the Herb Good-King-Henry, Blitum Bonus-Henricus.

The total, soluble and insoluble oxalate contents of the leaves, stems and buds of Good-King-Henry (Blitum Bonus-Henricus) were extracted and measured using HPLC chromatography. The large, mature leaves contained 42% more total oxalate than in the small leaves and the soluble oxalate content of the large leaves was 33% higher than the smaller leaves. Cooking the mixed leaves, stems and buds in boiling water for two minutes significantly (p < 0.05) reduced the total oxalate when compared to the raw plant parts. Pesto sauce made from mixed leaves contained 257 mg total oxalate/100 g fresh weight; this was largely made up of insoluble oxalates (85% of the total oxalate content). Soup made from mixed leaves contained lower levels of total oxalates (44.26 ± 0.49 mg total oxalate/100 g fresh weight) and insoluble oxalate made up 49% of the oxalate contents. The levels of oxalates in the Good-King-Henry leaves were high, suggesting that the leaves should be consumed occasionally as a delicacy because of their unique taste rather than as a significant part of the diet. However, the products made from Good-King-Henry leaves indicated that larger amounts could be consumed as the oxalate levels were reduced by dilution and processing.

Effect of Calcium Concentration in Growth Medium on Oxalate Content and Evaluation of the Role of Guttation in the Regulation of Oxalate in Eddo

The effects of calcium concentrations in the growth medium on oxalate content of leaf blades, petioles and corms and the involvement of guttation in the regulation of oxalate homeostasis were investigated in eddo (Colocasia esculenta (L.) Schott var. antiquorum Hubbard & Rehder). The plants were grown hydroponically in solutions containing 0 mM calcium, 1 mM calcium nitrate (control), 15 mM calcium nitrate or 15 mM calcium chloride. Total oxalate content (soluble plus insoluble) of leaf blades, petioles and corms did not differ with the calcium concentration in solutions containing 1 mM or 15 mM calcium nitrate or 0 mM calcium. The soluble oxalate content of these parts decreased as the calcium concentration of the solution was increased. Solutions containing 15 mM calcium nitrate or 15 mM calcium chloride gave a significantly lower proportion of soluble oxalate content to total oxalate content in each part, especially in leaf blades than 0 mM calcium or 1 mM calcium nitrate. In contrast, a positive correlation was found between insoluble oxalate content and calcium concentration in the solution. These results demonstrate that high calcium concentrations in the growth medium reduce soluble oxalate content of the plant. Soluble oxalate was detected in eddo guttation fluid. Soluble oxalate content in this fluid (mg mL−1) and the amount of soluble oxalate exuded by guttation (mg leaf−1 night−1) were significantly lower in the solutions containing 15 mM calcium than in those containing 0 mM and 1 mM calcium. These results indicate that guttation may affect the concentration of soluble oxalate in the plant bodies although not strongly contributing to a decrease in soluble oxalate content in eddo grown under high calcium conditions.

Calcium and Oxalate Contents of Curly Leaf (&amp;lt;i&amp;gt; Petroselinum crispum&amp;lt;/i&amp;gt;) and Flat Leaf (&amp;lt;i&amp;gt; P. crispum var. neapolitanum &amp;lt;/i&amp;gt;) Parsley Cultivars

The total, soluble and insoluble oxalate contents of the leaves and stems of curly leaf (Petroselinum crispum) and flat leaf (P. crispum var. neapolitanum) parsley cultivars were extracted from fresh tissue and measured using HPLC chromatography. There were no significant differences between the total and insoluble oxalate contents of the leaves between the flat leaf and curly leaf cultivars. There was a small difference (P < 0.05) between the soluble oxalate contents of the leaves of the two cultivars. The mean total, soluble and insoluble oxalates of the leaves of the two cultivars were 1137.0, 177.9 and 959.3 mg/100 g dry matter (DM), respectively. The mean total, soluble and insoluble oxalate contents of the stems were 1680.7, 386.2 and 1294.5 mg/100 g DM, respectively, and these were significantly higher than the mean values for the leaves of the two cultivars. Insoluble oxalate made up a mean of 77.0% of the curly leaf stems and leaves compared to a mean of 84.4% found in the flat-leaved cultivar. Unavailable calcium, that is, calcium bound to oxalate as insoluble oxalate, made up a mean of 26.9% of the total calcium in the leaves of both cultivars while the unavailable calcium made up 45.0% of the total calcium in the stems of the two cultivars. Overall, the oxalate contents of both parsley cultivars are relatively high, on a dry matter basis, but their overall contribution to dietary intake is likely to be quite small as parsley is an herb that is only used in small amounts to garnish foods.

Effect of Kimchi Fermentation on Oxalate Levels in Silver Beet (Beta vulgaris var. cicla).

Total, soluble and insoluble oxalates were extracted and analyzed by high performance liquid chromatography (HPLC) following the preparation of kimchi using silver beet (Beta vulgaris var. cicla) stems and leaves. As silver beet contains high oxalate concentrations and consumption of high levels can cause the development of kidney stones in some people, the reduction of oxalate during preparation and fermentation of kimchi was investigated. The silver beet stems and leaves were soaked in a 10% brine solution for 11 h and then washed in cold tap water. The total, soluble and insoluble oxalate contents of the silver beet leaves were reduced by soaking in brine, from 4275.81 ± 165.48 mg/100 g to 3709.49 ± 216.51 mg/100 g fresh weight (FW). Fermenting the kimchi for 5 days at 19.3 ± 0.8 °C in 5 L ceramic jars with a water airtight seal resulted in a mean 38.50% reduction in total oxalate content and a mean 22.86% reduction in soluble oxalates. The total calcium content was essentially the same before and after the fermentation of the kimchi (mean 296.1 mg/100 g FW). The study showed that fermentation of kimchi significantly (p < 0.05) reduced the total oxalate concentration in the initial mix from 609.32 ± 15.69 to 374.71 ± 7.94 mg/100 g FW in the final mix which led to a 72.3% reduction in the amount of calcium bound to insoluble oxalate.

Oxalate content of Indian spinach dishes cooked in a wok

Total, soluble and insoluble oxalate contents of four different traditional wok-cooked dishes, based on spinach (palak) with added spices, were determined by HPLC chromatography. Four different palak dishes were cooked with three different combinations of spices. During the final stage of cooking an Indian cottage cheese, paneer, was added to one dish. Each combination was cooked for 15min in a wok to give the saak dishes while other dishes containing the same combination of Indian spices and paneer were cooked for a further 10min, until they were dry to give the saak bhaji dishes. Cooking spinach in a wok to make saak and saak bhaji resulted in mean reductions of 17.6% of soluble oxalate compared to the raw spinach, soluble oxalate reductions were not observed in the plain palak saak dishes while the addition of ginger gave a mean increase in the total and soluble oxalates (23% and 43%, respectively) compared to palak saak. Addition of paneer, an Indian cheese product resulted in an overall reduction in total and soluble oxalates by dilution. Palak, palak saak and palak saah with ginger contained a mean of 1.7 and 6.9g soluble oxalate/standard serving respectively while the two palak paneer dishes contained a mean of 0.6g soluble oxalate/standard serving.

Total, Soluble and Insoluble Oxalate Contents of Ripe Green and Golden Kiwifruit.

Three bulk samples of two different cultivars of kiwifruit, green (Actinidia deliciosa L.) and golden (Actinidia chinensis L.) were bought ripe, ready to eat from a local market. The aim of the study was to determine the oxalate composition of each of the three fractions of kiwifruit, namely skin, pulp and seeds. The pulp consisted of 90.4% of the edible portion of the two cultivars while the skin and seeds made up a mean of 8.0% and 1.6% respectively. Total oxalate was extracted with 2.0 M HCL at 21 °C for 15 min and soluble oxalates extracted at 21 °C in water for 15 min from each fraction. The total and soluble oxalate compositions of each fraction were determined using ion exchange HPLC chromatography. The pulp of golden kiwifruit contained lower amounts of total oxalates (15.7 vs. 19.3 mg/100 g FW) and higher amounts of soluble oxalates (8.5 vs. 7.6 mg/100 g FW) when compared to the green cultivar. The skin of the green cultivar contained lower levels of insoluble oxalates (36.9 vs. 43.6 mg/100 g FW), while the seeds of the green cultivar contained higher levels of insoluble oxalates 106.7 vs. 84.7 mg/100 g FW.

Bioavailability Analysis of Oxalate and Mineral Content in Selected Edible Mushrooms

Total, soluble, insoluble oxalate and mineral content of 20 edible mushrooms were measured using spectroscopic and enzymatic methods. Total oxalate content ranged from 45 (Hericium erinaceus) to 104 (Morchella conica), mg/100 g dry matter (DM), while the soluble oxalate levels ranged from 34 (Lactaius delicious) to 65 (Phellinus florida) mg/100g DM but not detected in Hericium erinaceus, Sparassis crispa, Geastrum arinarius, Boletus edulis, Helvella crispa, and Ganoderma lucidum respectively and very low in Lactaius delicious (34), Russula brevepis (35), and Cantharellus clavatus (37) mg/100g DM. The Ca, P, K and Mg content showed range of 1.35-12.56 mg/g for Ca, 1.22-3.82 mg/g for P, 15.4-25.4 mg/g for K and 1.19-4.71 mg/g for Mg. Overall, the percentage of soluble oxalate content of the selected mushrooms ranged from 34 to 65% of the total oxalate content which suggests that, the selected edible mushrooms presents no risk to people liable to kidney stone formation while other foods like some spices and vegetables can supply significant amounts of soluble oxalates and therefore should be used in moderation as good vegetable, which might be important for human nutrition.

Effects of UV-B Radiation on Oxalate Content of Silver Beet Leaves

Silver beet (&lt;em&gt;Beta vulgaricus &lt;/em&gt;var. &lt;em&gt;cicla&lt;/em&gt;) a common vegetable in New Zealand is known to contain high levels of oxalates in the leaves. Silver beet plants were grown in afield trial under glass and perspex sheets which filtered sunlight reaching the plants. After eight weeks of growth, the plants were harvested and the total, soluble and insoluble oxalate content of the leaves of the plants grown under the two filter treatments and a no-frame control were measured. Perspex allowed the transmission of UV-A, UV-B and photosynthetically active radiation (PAR), whereas glass excluded UV-B radiation. No significant differences between the perspex treatment and the no-frame control were observed when the data was compared on a wet matter (WM) or dry matter (DM) basis Shielding the growing plants with glass significantly reduced the total oxalate and soluble oxalates to 83 and 84% respectively when compared to the perspexand no-frame treatments.

Effect of simple processing methods on oxalate content of taro petioles and leaves grown in central Viet Nam

This study investigated the total, soluble and insoluble oxalate contents of the petioles and the leaves from two different cultivars, Mon Cham (purple stem) and Chia Voi (light green stem), of taro (Alocasia odora) grown in central Viet Nam. These cultivars were processed by wilting for 18 h, resulting in an overall 5.9% reduction of soluble oxalates and washing in cold water for 5 min, resulting in a 26.2% reduction in soluble oxalate content. Soaking the petioles and the petioles and leaves for 10 h in water kept at 36–38 °C resulted in a mean 69.5% reduction in the soluble oxalate content of the raw tissues. Boiling for 60 min was the most effective way to reduce the soluble oxalate levels in the cooked tissue. A mean 84.2% reduction in soluble oxalate in the petioles and the petioles and leaves was achieved after boiling for 60 min while mean reductions of 62.1% were achieved when both materials were boiled for only 10 min.