Comparison of an alkaline picrate and a pyridine-pyrazolone method for the determination of hydrogen cyanide in cassava and in its products

A determination of hydrogen cyanide in fresh cassava tissues and in processed cassava products using an alkaline picrate procedure and a pyridine-pyrazolone method which uses Conway vessels has been made. Results obtained for the fresh cassava tissues by the two methods were similar. Statistically significant higher values for processed cassava products were obtained by the alkaline picrate method which measured both glycosidic and non-glycosidic cyanide. The suggestion is reaffirmed that hydrogen cyanide in processed cassava products may exist in two forms: glycosidic and non-glycosidic (entrapped) cyanide.     

Proximate composition,mineral contents,hydrogen cyanide and phytic acid of 5 cassava genotypes

Five cassava genotypes Rayong 5, Kaesetsart 50 (KU50), Rayong 2, Hanatee and KMUL 36-YOO2 (YOO2), were used in this study. Investigations showed that cassava contained 9.2–12.3% moisture, 1.2–1.8% crude protein, 0.1–0.8% crude lipid, 1.5–3.5% crude fibre, 1.3–2.8% ash, 80.1–86.3% carbohydrate, 1406–1465 kJ 100 g⁻¹ DM and 95–135 mg g⁻¹ of phytic acid. Mineral contents were 10.9–39.9, 15.2–32.3 and 9.3–54.1 mg g⁻¹ for Ca, Mg and P, respectively, and 221–328, 4.7–25.8, 1.41–4.25, 0.29–1.73 and 1.2–4.44 mg g⁻¹ for K, Na, Zn, Mn, Cu, and Fe, respectively. HCN content ranged from 8.33 to 28.8 mg HCN/kg dry weight basis. A linear relationship between Ca and P and carbohydrate and energy existed with correlation coefficients of 0.99 and 0.82, respectively. Phytate: total p ranged from 77% to 88% and a linear relationship existed between phytate and total p with a correlation coefficient of 0.975.     

Determination of total nitrogen and cyanide nitrogen in cassava

Heating of intact cassava leaves causes liberation of hydrogen cyanide. This phenomenon appears to be caused by β-glucosidase-catalysed decomposition of the cyanogenic glycosides linamarin and lotaustralin. Because of these losses, many previously determined values for total nitrogen in cassava (and other cyanogenic plants) are probably in error as plant materials used for Kjeldahl determinations are often dried at 70–90°C. Liberation of cyanide from intact cassava leaves by heating at 80°C is more complete than liberation by the homogenisation methods commonly used. Homogenisation of cassava leaf tissues with liquid nitrogen or dry ice gives somewhat lower values, and these materials are often not readily available in areas where cassava is studied. The basis of a relatively simple procedure for the isolation of hydrogen cyanide from cassava leaves is suggested.     

Preparation of linamarin from cassava leaves for use in a cassava cyanide kit

A simple method is described for the preparation, from very young cassava leaves, of a dilute hydrochloric acid solution of linamarin. Linamarin extraction from the leaves is virtually quantitative. The linamarin solution is used in the preparation of standard linamarin filter paper discs that are needed to monitor the performance of picrate kits for determination of the total cyanide content of cassava roots and cassava products. These standard discs are stable indefinitely if stored in the refrigerator, but very slowly lose linamarin activity if stored for more than one month at room temperature.     

Preparation of linamarase solution from cassava latex for use in the cassava cyanide kit

A simple method is described for the preparation of linamarase from cassava latex (sap). Latex, obtained from the end of the petiole (stalk) of cassava leaves, is mixed with water and the solution filtered to give a crude solution of enzyme. This solution may be stored indefinitely in the deep freeze. It may be used without any purification in kits for determination of cyanogens in cassava tubers and cassava products (flour, gari, etc). Immobilisation of linamarase in filter paper discs in the presence of a stabiliser (gelatin/PVP-10) reduces its activity to 25% and in the absence of stabiliser to only 4%.     

Moisture-pressure combination treatments for cyanide reduction in grated cassava

Several cyanide-associated health disorders have been linked with frequent consumption of mildly toxic cassava (Manihot esculenta crantz) products in individuals on a low-protein diet. Production of bread from cassava often involves application of prolonged physical pressure (pressing) to the freshly grated root for several hours. This study aimed to determine effects of pressure and wetting on grated cassava. Six treatments were applied: confining pressure for 12 h, wetting for 4 h at 25 °C, 2 h at 25 °C, 2 h at 40 °C, and 2 h at 50 °C, or each of the above followed by pressure for 12 h. Treatments released cyanide from samples in the order: 2-h wet at 50 °C + pressing >4-h wet at 25 °C + pressing = 2-h wet at 40 °C + pressing >2-h wet at 25 °C + pressing = 4-h wet at 25 °C >12-h pressing. Wetting for 2 h at 50 °C followed by pressure for 12 h reduced cyanide levels by at least 20% more than that of any other treatment. The combination of moisture and pressure enhanced the contact time between linamarin and linamarase to increase the release of hydrogen cyanide.     

Food security in Latin America

Although the nutrition situation in most Latin American countries is improving and malnutrition is easing, worrisome factors are emerging. Huge rural-to-urban migrations have been accompanied by a worsening nutrition situation in rural populations, especially in Mexico, Colombia, and Brazil, a phenomenon not readily apparent from average food availability and malnutrition data. Average figures can also mask the severe nutrition problems that persist in four densely populated areas: the Caribbean Islands, Central America, the Andean region, and parts of Brazil. Although globalization is improving the nutritional status of many population groups in Latin America, it is also creating new pressures. Latin American countries dependent on agriculture are especially vulnerable.     

Cyanogenicity of cassava varieties and risk of exposure to cyanide from cassava food in Nigerian communities

BACKGROUND: High‐cyanogenic cassava varieties are cultivated in many tropical communities that are free of neurological syndromes attributed to consumption of cassava foods. This study was done in four geographical areas of Nigeria (northern, southwestern, southeastern and an area endemic for ataxic polyneuropathy) to determine if cyanogenicity of cassava is associated with geographical area, altitude or level of cyanogenic compounds in gari, a popular cassava food in West Africa. RESULTS: Mean levels of cassava cyanogens were 153, 127, 68 and 65 mg HCN equivalents (eq.) kg^?1 dry weight (DW) in the endemic, southeastern, southwestern and northern areas respectively (P < 0.0001), while mean levels of gari cyanogens were 9, 4, 7 and 13 mg HCN eq. kg^?1 DW in the respective areas (P < 0.0001). The mean altitude was 35 m in the endemic area, 55 m in the southeastern area, 220 m in the southwestern area and 273 m in the northern area (P < 0.0001). Altitude was associated with cyanogenicity of cassava in univariate and multivariate models (P < 0.0001). One hundred and twenty‐six (93%) farmers and 255 (77%) processors did not perceive cassava or its food products as toxic. CONCLUSION: The findings indicate that cyanogenicity of cassava is determined by environmental factors rather than by conscious selection of varieties by farmers. Farming high‐cyanogenic cassava is not associated with high levels of residual cyanogens in gari. Cassava is not perceived as toxic by farmers and processors. Copyright © 2008 Society of Chemical Industry     

Reduction of cyanide content of cassava flour in Mozambique by the wetting method

Fifty cassava flour samples from Mogincual District of Nampula Province in Mozambique were found to contain, on average, 43 mg HCN equivalents/kg flour (ppm), of total cyanide, which is typical for a year of average rainfall. Five gram samples of the 30 flour samples of highest cyanide content were mixed with water and left for 5 h at 30 °C and it was found that the mean% retention of cyanide was 16.7%. Using 500 g instead of 5 g samples caused an increase in the % retention due to accumulation of the very weak acid, HCN, in the damp flour mass, which also decreased its pH and somewhat reduced the rate of breakdown of linamarin catalysed by linamarase. This problem was overcome by spreading out the damp flour in an approximately 0.5 cm thick layer on a tray, which allowed the release of HCN.     

A simple and rapid method for isolating cassava leaf linamarase suitable for cassava cyanide determination

A simple method was developed for isolating cassava leaf linamarase. It involved homogenising the leaves in a buffer containing polyvinylpolypyrrolidone, followed by ammonium sulphate precipitation, filtration and partial purification of the enzyme by hydrophobic interaction chromatography. All stages of the enzyme preparation were carried out at room temperature and it was completed within 90 min. A linamarin-indicator strip for checking the activity of the enzyme preparation was also developed. This isolation technique which has been developed into a simple kit should be suitable for laboratories in developing countries where the enzyme is needed to determine the cyanogenic potential of cassava and its products. © 1997 SCI.     

Influence of sugar and cyanide concentrations and paste viscosities of cassava flour on fried cassava chip quality

The quality of fried chips made from cassava flour depended on total soluble sugar (TSS) concentration and on some paste viscosity parameters of the flour. Chip colour darkened as TSS content increased. Taste was not affected by total HCN content but became bitter as TSS levels increased. Chip HCN concentration was minimal if flour with low HCN was used. Greater surface expansion of the dried chips during frying produced crisper chips. Expansion during frying correlated positively with maximum and setback viscosities of the flour paste.     

Amylase activities and cyanide tolerance of five cassava tuber spoilage molds

Studies on the amylase activities and tolerance to cyanide by five spoilage molds of cassava tuber were carried out. None of the test fungi grew in 0.1 g/ml concentration of potassium cyanide while only Aspergillus aculeatus and A. niger grew in 0.05 g/ml. Except for B. theobromae, all the other four molds synthesised amylases on the 2nd day of incubation. Highest amylase activities by the molds were recorded between pH 6–7 and at 25°C. The molds degraded satisfactorily the raw starch and protein contents of the blended cassava tuber pulp. Total reducing sugars were detected in large quantities from the mold deteriorated cassava tuber.     

拉美地区锂资源分布及开发现状分析

锂属于世界稀缺性战略资源,拉美地区锂储量异常丰富,产量也居世界前列。拉美地区已发现锂矿资源多为现代盐湖中含锂卤水,发现拥有锂矿资源的国家主要有智利、阿根廷、玻利维亚、秘鲁和巴西等。文章通过对拉美地区锂资源分布及开发利用现状进行分析,总结了我国企业开展境外锂矿开发合作中的困境,并对拉美重要含锂资源国家开展锂矿矿产资源勘查开发的可进入性及优先进入目的国进行了评价与讨论,这为国内地勘单位和企业到拉美进行锂矿勘查、开发投资提供科学指导。     

Total cyanide levels in bread made from wheat/cassava composite flours

Cyanide levels were determined in cassava flours and bread. It was found that incubation media had no effect on cyanide determination. For all the cyanide to be released, incubation was carried out with linamarase extract for 14 h, followed by prolonged aeration of the media. Cassava flour with low initial levels of HCN gave cyanide-free bread, whereas there was a retention of 8% of the original HCN in loaves obtained from cassava flours with initial high levels of HCN.     

Effect of non-enzymic browning, starch and sugars on total cyanide determination in cassava by an enzymic assay

Maillard (non-enzymic) browning pigments and gelatinized starch interfered in the assay of total cyanide in cassava products by an alkaline picrate-enzymic method. Interference from browning pigments in cyanide determinations was overcome by adding charcoal followed by filtration, while gelatinized starch was precipitated by the addition of ethanol. Glucose, fructose and maltose but not sucrose also interfered in the assay and produced high total cyanide results. A more specific reaction than alkaline picrate is still required for free cyanide estimations in cassava products.