Total and soluble oxalate content of some Indian spices.

Spices, such as cinnamon, cloves, cardamom, garlic, ginger, cumin, coriander and turmeric are used all over the world as flavouring and colouring ingredients in Indian foods. Previous studies have shown that spices contain variable amounts of total oxalates but there are few reports of soluble oxalate contents. In this study, the total, soluble and insoluble oxalate contents of ten different spices commonly used in Indian cuisine were measured. Total oxalate content ranged from 194 (nutmeg) to 4,014 (green cardamom) mg/100 g DM, while the soluble oxalate contents ranged from 41 (nutmeg) to 3,977 (green cardamom) mg/100 g DM. Overall, the percentage of soluble oxalate content of the spices ranged from 4.7 to 99.1% of the total oxalate content which suggests that some spices present no risk to people liable to kidney stone formation, while other spices can supply significant amounts of soluble oxalates and therefore should be used in moderation.

Bioavailability of soluble oxalate from tea and the effect of consuming milk with the tea.

OBJECTIVES: To measure the availability of oxalate normally extracted when making tea from two commercially available black teas bought from a supermarket in Christchurch, New Zealand in July 2001. DESIGN, SUBJECTS AND INTERVENTION: A randomized double crossover study. Six students and four staff consumed six cups of each brand of tea both with and without added milk over a 24 h period. A total urine collection was taken for the initial 6 h followed by a further 18 h. The oxalate content of the urine voided was measured using an enzyme kit method and the availability of the soluble oxalate consumed was measured for the 6 h and the total 24 h sample. SETTING: University campus. RESULTS: The mean soluble oxalate content of black tea in the two different commercial tea bags was respectively 6.1 and 6.3 mg soluble oxalate/g tea. The mean availability of the oxalate extracted from tea measured over a 6 h period ranged from 1.9 to 4.7% when tea was consumed without milk. The availability of the soluble oxalate from tea ranged from -3.0 to 2.3% for each of the two brands of tea investigated over a 24 h period. CONCLUSION: These studies show that consuming black tea on a daily basis will lead to a moderate intake of soluble oxalate each day, however the consumption of tea with milk on a regular basis will result in the absorption of very little oxalate from tea.

Comparison of isothiocyanate yield from wasabi rhizome tissues grown in soil or water.

The isothiocyanate (ITC) yield of wasabi, the Japanese horseradish (Wasabi japonica), was measured on its release from glucosinolates in the rhizomes of plants grown in two traditional ways. Mature plants of 18 months old were harvested from two different commercial farms located in the South Island of New Zealand. At one farm, the plants were grown in raised soil beds, while the plants at the other farm were grown in gravel irrigated by river water. Following harvest, the rhizomes from each growth medium were divided into five size groups based on the weight and length of the rhizomes. The different sized rhizomes were also subdivided into proximal, medial, and distal portions of the rhizomes and each portion was further subdivided into epidermis plus cortex, and vascular plus pith. The individual and total ITC contents of each portion (proximal, medial, and distal) of the rhizomes were measured using dichloromethane extraction followed by the GC-FPD. The total ITC content of the rhizomes grown in soil increased (13 times) linearly from 6 to 114 g of rhizome weight, while the mean ITC content of the water-grown wasabi increased (10 times) nonlinearly for similar sized rhizomes. Water-grown rhizomes in the weight range from 18 to 45 g gave significantly (P = 0.030) higher total ITC (1-2 times) than similarly sized soil-grown rhizomes. Analysis of the tissues showed that the total and the individual ITCs were found in significantly higher levels (73 and 64%, respectively) in the skin and cortex tissue compared to the vascular and pith tissues. Analysis of the ITC content of the different locations of the wasabi rhizome showed that the distal portion of the rhizome contained significantly higher levels of both total and individual ITCs compared to the medial and proximal portions of the rhizome.

Oxalates in oca (New Zealand yam) (Oxalis tuberosa Mol.).

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 analyzed for total and soluble oxalate contents of the tubers. The range of total oxalate levels was 92-221 mg/100 g of fresh weight. Levels of soluble and total oxalate extracted from the tubers were not significantly different, suggesting that no calcium oxalate is formed in the tubers. The oxalate concentrations obtained in this study for oca suggest that previously reported values are too low and that oca is a moderately high oxalate-containing food. This is the first report of a tuber crop containing moderate to high levels of soluble oxalates in the tubers and no insoluble oxalates.

The response of some organic microsensor coatings to a variety of vapors.

Six organic compounds were spray-coated onto surface acoustic wave devices which were then exposed to vapors of acetone, diethyl ether, dichloromethane, chlorobenzene, benzene, and acetonitrile. Changes in the resonant frequency of the device or in the resistance of the coating were collected by computer-controlled data acquisition. Different patterns of response to the six vapors were observed for each of the coatings.

Synthesis of new microsensor coatings and their response to vapors-III Arylphosphonic acids, salts and esters.

Phosphonic acids, phosphonate esters and cyclohexylammonium phosphonates, spray-coated onto surface acoustic wave (SAW) devices, were exposed to vapors of chloroethyl ethyl sulfide (CEES), dimethyl methylphosphonate (DMMP), and water. Changes in the resonance frequency of the device or the resistance of the coating were collected by computer-controlled data acquisition. Two of the esters showed major reversible and selective response to CEES, and one of the acids showed similar behavior with DMMP.

Synthesis and response of new microsensor coatings-II Acridinium betaines and anionic surfactants.

Four acridinium betaines and two ionic surfactants were synthesized, and evaluated as chemical microsensor coatings by exposure to vapors of chloroethyl ethyl sulfide (CEES) and dimethyl methylphosphonate (DMMP). Two of the acridinium betaines showed selective and reversible responses (of 9.8 and 6.8 kHz) as SAW (surface acoustic wave) coatings in the detection of CEES vapor: there appears to be a connection between the long alkyl chain (C-12 and C-14) in the acridinium molecules and the response. Response times were generally less than 30 sec but desorption was significantly slower. The ionic surfactant coatings show small SAW changes (> 0.5 kHz) in response to DMMP vapor, and somewhat greater responses (20- and 68-fold), as chemiresistors, to CEES vapor. In each case the response occurred within 3 min, with return nearly to baseline levels within 6 min of cessation of exposure to the vapor. The responses were reproducible within +/- 5%.

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.

The effect of soaking and cooking on the oxalate content of taro leaves.

Pacific Island people commonly eat taro (Colocasia esculenta var. Schott) as a staple food in their home islands and also like to consume this familiar food when living in New Zealand. Some of these foods are imported from the islands and some attempts are, currently, being made to grow these crops in New Zealand. The taro leaves in this experiment were grown in a greenhouse in the North Island of New Zealand. The soluble oxalate content of the raw leaves was 236.10 mg oxalate/100 g wet matter (WM). Soaking the raw leaves in water for 30 min marginally reduces the soluble oxalate content by leaching into the tap water. Soaking for 18 h results in a 26% reduction in the soluble oxalate content of the raw leaves. During the soaking treatments the insoluble oxalate (calcium oxalate) content of the leaves remained constant (mean 171.64 mg oxalate/100 g WM). Boiling the taro leaves resulted in a 36% loss of soluble oxalates, while the soluble oxalate content of baked tissue was very similar to the raw tissue. The mean insoluble oxalate content of the raw, boiled and baked tissue was 226.28 mg oxalate/100 g WM. Overall, boiling the taro leaves was an effective way of reducing the soluble oxalate content of the cooked tissue.

Antioxidant activities of New Zealand-grown tomatoes.

The objective of this study was to compare the antioxidant activities, total phenolics, lycopene and ascorbic acid content of four commercial tomato cultivars (Excell, Tradiro, Flavourine and Campari) of New Zealand, grown under similar hydroponic conditions. The mean antioxidant activity of the four cultivars, as measured with the ABTS radical decolourization assay, ranged from 2329 to 3268 micromole TEAC/100 g dry matter (DM) in the hydrophilic extracts and from 178 to 303 micromole TEAC/100 g DM in the lipophilic extracts. The major antioxidant components per 100 g DM were phenolics (343-451 mg gallic acid equivalents in hydrophilic extract and 53-74 mg gallic acid equivalents in lipophilic extract), flavonoids (175-204 mg rutin equivalents), ascorbic acid (153-195 mg) and lycopene (33-54 mg). Ascorbic acid and flavonoids were found to contribute 28-38% and 29-34%, respectively, to the antioxidant activity of the hydrophilic extract of tomatoes. The results showed that the smallest cultivar (Campari) had significantly (P < 0.05) higher antioxidant activities, total phenolics and flavonoids than the larger sized cultivars (Excell, Tradiro and Flavourine). This could be attributed to the significantly (P < 0.05) higher surface area/volume ratio of the small cultivar (0.15) when compared with the large-sized cultivars (0.10-0.12). The tomato cultivar (Flavourine) with a brighter red colour (higher a*/b* value), had a higher lycopene content as well, which suggests that the a*/b* value of tomatoes can be used as an indicator of their lycopene content. The phenolics (r = 0.84**) and flavonoids (r = 0.88**) were significantly related to the antioxidant activity of the hydrophilic extract, which suggests that measurement of total phenolics or flavonoids can be used as indicators of the antioxidant activity of tomatoes.

Change in colour and antioxidant content of tomato cultivars following forced-air drying.

Three New Zealand grown tomato (Lycopersicon esculentum L.) cultivars, Aranka, Encore, and Flavourine, were analysed for colour (CIELAB L(*) a(*) b(*) values), ascorbic acid, total phenolics, lycopene, and total antioxidant activity (ABTS assay). Colour analyses of the air-dried tomatoes showed that the colour degradation as measured by the L(*) a(*) b(*) values was minimal, and the colour was not significantly different (p < 0.05) between each of the dried cultivars. In general, there was no significant difference (p < 0.01) between the fresh cultivars in terms of antioxidant components or total antioxidant activity. The average values obtained for antioxidant components in the three fresh cultivars were: ascorbic acid, 276 mg/100 g DM, total phenolics, 613 mg gallic acid equivalents (GAE)/100 g dry matter (DM) and lycopene 38 mg/100 g DM. Total antioxidant activity of the fresh cultivars was 2917 micromole Trolox equivalent antioxidant capacity (TEAC)/100 g DM. Following forced air-drying treatment at 42 degrees C for 48 hr, all cultivars showed significant decreases in ascorbic acid, total phenolics and total antioxidant activity, and increases in extractable lycopene contents. This study was undertaken to identify cultivars that would provide the best colour and nutrient contents after commercial air drying.

Chemical composition of walnuts (Juglans regia L.) grown in New Zealand.

Walnuts (Juglans regia L.) were collected during the 1997 harvest from 12 different cultivars of trees grown in a replicated trial in an experimental orchard at Lincoln University. Two US commercial cultivars (Tehama and Vina), three European commercial cultivars (Esterhazy, G139, G120) and eight New Zealand selections (Rex, Dublin's Glory, Meyric, Stanley, 150, 151, 153) were evaluated. The total oil content ranged from 62.6 to 70.3% while the crude protein ranged from 13.6 to 18.1%. Dietary fiber ranged from 4.2 to 5.2% while the starch content made up no more than 2.8% of the remaining portion of the kernel. The amino acid content of the walnuts was similar between cultivars and the patterns of essential amino acids were characteristic of a high quality protein.

The bioavailability of oxalate from Oca (Oxalis tuberosa).

PURPOSE: It is believed that soluble oxalate has higher bioavailability than insoluble oxalate. Oca (Oxalis tuberosa) is moderately high in oxalate and contains oxalate in soluble form only. We estimated the bioavailability of oxalate in oca based on the urinary excretion of oxalate after oxalate loading with oca to estimate the bioavailability of oxalate in oca. We also clarified whether bioavailability differs in various oxalate loads from the same food source and studied the effect of an additional calcium source on the bioavailability of oxalate from oca. MATERIALS AND METHODS: Four men and 4 women ingested 50, 100 and 150 gm. oca as well as 100 gm. oca with 100 gm. sour cream. Oxalate was measured in a 6-hour urine sample from each volunteer. RESULTS: The mean bioavailability of oxalate from oca plus or minus standard deviation was 1.44% +/- 1.31% during the 6-hour period after intake. There was no significant difference in oxalate bioavailability among oxalate intake levels in this study, although oca consumption with sour cream significantly decreased the uptake of oxalate (p <0.01). The variation in bioavailability among individuals was high in our study. CONCLUSIONS: The bioavailability of oxalate in oca appears to be similar to that in spinach. However, bioavailability varies among individuals and depends on other constituents of a combined meal.

Chemical composition of hazelnuts (Corylus avellana L.) grown in New Zealand.

Hazelnut (Corylus avellana L.) samples were collected from all replications of six different cultivars of trees grown in an experimental orchard at Lincoln University. Five cultivars were originally imported from overseas, three from the USA and two from Europe, and one cultivar was selected locally. Representative samples of nuts were harvested from 12-year-old trees in autumn 1995. The total oil content of the hazelnuts ranged from 54.6 to 63.2% while the crude protein ranged from 14.3 to 18.2%. Dietary fibre ranged from 9.8 to 13.2% while the starch and free glucose content together made up no more than 5% of the remaining portion of the kernel. The amino acid content of the hazelnuts was similar between each cultivar and the pattern of essential amino acids was characteristic of a high quality protein.

Oxalate content of foods and its effect on humans.

Oxalic acid and its salts occur as end products of metabolism in a number of plant tissues. When these plants are eaten they may have an adverse effect because oxalates bind calcium and other minerals. While oxalic acid is a normal end product of mammalian metabolism, the consumption of additional oxalic acid may cause stone formation in the urinary tract when the acid is excreted in the urine. Soaking and cooking of foodstuffs high in oxalate will reduce the oxalate content by leaching. The mean daily intake of oxalate in English diets has been calculated to be 70-150 mg, with tea appearing to contribute the greatest proportion of oxalate in these diets; rhubarb, spinach and beet are other common high oxalate-content foods. Vegetarians who consume greater amounts of vegetables will have a higher intake of oxalates, which may reduce calcium availability. This may be an increased risk factor for women, who require greater amounts of calcium in the diet. In humans, diets low in calcium and high in oxalates are not recommended but the occasional consumption of high oxalate foods as part of a nuritious diet does not pose any particular problem.

Soluble and insoluble oxalate content of mushrooms.

Six different cultivars of edible fungi were bought from a local supermarket in Uppsala, Sweden and three different cultivars of wild growing fungi were harvested from the forest adjoining the city. The edible portions of the raw fungi were then analysed for total and soluble oxalate content. A portion of each fungi was then cooked by first boiling in a small amount of water followed by frying in a small amount of butter. The total oxalate content of the raw, commercially grown mushrooms ranged from 58.9 to 104.1 mg/100 g DM while the values for the total oxalate content of the cooked mushrooms ranged from 48.9 to 124.6 mg/100 g DM. Apart from cultivars ostronskivling and piopino the cultivated mushrooms contained mostly insoluble oxalates. Mushrooms harvested from the forest contained only soluble oxalate with the levels ranging from 29.3 to 40.2 mg/100 g DM in the raw tissue. Cooking marginally lowered the soluble oxalate content of these mushrooms. The levels of soluble and insoluble oxalates of all the mushrooms analysed were low compared to other common oxalate-containing vegetables.

Fatty acid content of New Zealand-grown walnuts (Juglans regia L.).

Walnut (Juglans regia L.) samples were collected during the 1994 and 1995 harvest from ten different cultivars of trees grown in a replicated trial in an experimental orchard at Lincoln University, New Zealand. Two US commercial cultivars (Tehama and Vina), three European commercial cultivars (Esterhazy, 139, G120) and five New Zealand selections (Rex, Dublin's Glory, Meyric, McKinster, Stanley) were evaluated. Total oil was extracted using a cold press and individual fatty acids were analysed by GLC. The total oil content of the nuts ranged from 62.4 to 68.7%. The oleic acid content of the oils ranged from 14.3 to 26.1% of the total fatty acids, while the linoleic acid content ranged from 49.3 to 62.3% and the linolenic contents from 8.0 to 13.8%.

Fitch diets in New Zealand: an analytical survey.

Fitch diets from 30 farms were surveyed and analysed for moisture, protein, carbohydrate, fibre, ash, fat and individual fatty acids, fat peroxide value, and infinity-tocopherol. The dietary raw materials most often used were mutton, fish, poultry, beef and cereals. Eight of the 30 breeders added no vitamin or other supplements. Analytical mean (range) values on a wet matter basis were: moisture, 66.3 (49.6-76.8)%; protein, 16.5 (12.4-21.2)%; carbohydrate, 2.5 (<0.1-8.7)%; fibre, 0.4 (0.1-1.0)%; ash, 3.7 (1.2-8.3)%; fat, 10.6 (1.4-26.1)%; peroxide value, 5.7 (0.3-110) m.equiv x /kg fat; infinity-tocopherol, 13 (0.6-103) mg/kg; calculated gross energy value, 7.2 (3.7-13.7) MJ/kg. Protein contributed 42 (20-79)% of the gross energy value; fat, 49 (15-74) %, and carbohydrate, 6 (0-20) %. Polyunsaturated fatty acids (PUFA's) comprised 10 (3.6-39) % of the total fatty acids. The ratio of infinity-tocopherol to PUFA was 2.1(0.1-10.5) mg/g. Results of the survey are discussed in the light of nutrient requirements for the fitch.