A Comparison of Two Extraction Methods for Food Oxalate Assessment

Abstract

Hyperoxaluria is a primary risk factor for the formation of calcium oxalate-containing kidney stones. Increased dietary oxalate intake and/or intestinal absorption may provide the critical quantity of additional oxalate that triggers the formation of kidney stones. The accurate determination of food oxalate is highly dependent on oxalate extraction, the first step in oxalate analysis. Potential problems include the possibility of elevated oxalate due to in vitro conversion from various oxalate precursors such as ascorbate and failure to dissolve all pre-existing calcium oxalate crystals. The primary objective was to compare the efficiency of the hot and cold extraction methods in extracting oxalate from 50 dry herb and 10 fresh fruit samples. Regardless of the method of extraction, leaves of Atriplex halimus and kiwifruit exhibited the highest concentrations of both total and soluble oxalate among the herbs and the fruits, respectively. The hot extraction method appeared to extract more total oxalate compared to the cold extraction method while there was no significant difference between the methods in efficiency of extracting soluble oxalate. The overall data suggested that the use of the hot acid method will yield a more accurate assessment of the total oxalate content of foods.

Fractional pretreatment of raw and calcium oxalate-extracted agave bagasse using ionic liquid and alkaline hydrogen peroxide

“…The flasks were placed in a shaking water bath at 80 °C for 30 min. The extracts where further diluted with 50 cm 3 of deionized water and then transferred into 15 cm 3 centrifuge tubes and centrifuged at 10600x g for 10 min [27]. The supernatants were filtered through Whatman #1 filter paper, washed with deionized water and the recovered biomass was vacuum oven dried at 45 °C for 48 h before compositional analysis.…”

Determination of Minerals in Herbal Infusions Promoting Weight Loss

“…Herbal tea B contained fennel seeds, which may have increased the content of water-soluble oxalates in the infusion. As reported by Al-Wahsh [26], seeds of fennel ( Foeniculum vulgare Mill.) contain 1086 mg of total oxalate in 100 g −1 dry weight and 194 mg of soluble oxalates in 100 g −1 dry weight.…”

“…Their content in apples is 2.2 mg·100 g −1 fresh weight and in oranges 2.9 mg·100 g −1 fresh weight [26]. The literature does not provide data on the content of soluble oxalates in the other plant ingredients of the analysed herbal tea, i.e.…”

Oxalate in Foods: Extraction Conditions, Analytical Methods, Occurrence, and Health Implications

“…For soluble oxalates, results increased significantly after extraction at 80 • C compared to extraction at 21 • C and there were no significant differences between extractions of 15 or 30 min, proposing that soluble oxalate should be extracted with distilled water for 15 min at room temperature. In contrast, other authors suggested that room temperature might not be enough for the complete extraction of oxalates, leading to an underestimation [5]. This theory is also supported by Kusuma et al [65] who considered that extraction temperatures above 65 • C are required for efficient extraction of total oxalates and pH should be at least 1.…”

“…According to the literature, various methods have been employed for the determination of oxalate in foods, including enzymatic assays [4][5][6][7][8][9][10][11], spectrofluorimetry [12], spectrophotometry, amperometry [9,13,14], electrochemical [15,16], capillary electrophoresis [17,18], titration [19][20][21][22][23][24][25][26][27], gas chromatography (GC) [28], and high-performance liquid chromatography (HPLC). HPLC is the most recently referenced method used for the determination of oxalates because of its high sensitivity, accuracy, versatility, and reliability, despite being expensive to purchase, repair, and maintain [29].…”