Residual cyanide concentrations during the extraction of cassava starch

Cassava starch is traditionally extracted on a small scale in many tropical countries. The process consists of wet-milling the washed roots, washing the starch from this milled pulp on vibrating trays or in mixing tanks, sedimenting the starch in wooden canals or concrete tanks and sun-drying the product. This process was analysed during six production runs in two factories. The distribution of cyanide followed a similar pattern in both factories. Most of the cyanogenic glucosides (bound cyanide) in the roots are converted to free cyanide during the milling operation. Between 40 and 70% of the total cyanide appears in the water used to wash the starch from the disintegrated tissue, and between 5 and 10% appears in the fibrous residue used in animal feed. This residue also contains between 12 and 23% of the starch present in the cassava. The eluted starch is allowed to sediment for 1–3 days, after which it contains less than 4% of the cyanide present in the raw material. The dried product contains less than 1% of the quantity of cyanide present in the raw material; the residual concentration is 1–5 p.p.m. The factors involved in the removal of the cyanide during starch extraction are discussed, and their importance to more efficient large-scale processes is indicated.     

Cassava Starch Processing at Small Scale in North Vietnam

In Northern Vietnam, small‐scale cassava starch processing is conducted in densely populated craft villages, where processors face difficulties to expand their activities. Three different processing systems were studied among a cluster of three communes in the Red River Delta, producing up to 430 t of starch (at 55% dry matter) per day. The first system, type A, is a cylindrical rasper and a manual sieve, the second, type B, is a cylindrical rasper and stirring‐filtering machine and the third, type C, used equipment for both the rasping and filtering stages. Moisture, starch, crude fibers and ash content analysis were carried out on samples collected from the A‐B‐C manufacturing processes to establish the mass balance of starch. Production capacity, water consumption, electrical requirements and capital‐labor costs per tonne of starch (12% moisture) were also reported. A‐B‐C manufacturing processes enabled 75% recovery of the starch present in fresh roots. No significant change was observed in the composition of starch. Upgrading from system A to B and subsequently to C resulted in an increase in the extraction capacities (up to 0.9 t of peeled roots per hour), the extraction efficiencies during the extraction stage (up to 93%), and an increase in the water consumption and electrical power (up to 21 m³ and 55 kWh per tonne of starch, respectively). The highest amount of total solids carried in the waste‐water was obtained with type C (up to 17% of the dry weight of fresh roots, compared to 10% and 13% for type A and B, respectively). This may lead to a higher chemical oxygen demand (COD) and biological oxygen demand (BOD) in waste‐water, which can result in more polluted waste‐water than compared with the type A and B technologies. Upgrading the rasping‐extraction technologies also resulted in higher profits and reduction of labor per tonne of starch (up to 18 US$ and 26 man‐hours respectively). The diagnosis proposed in this study can be applied in different contexts to recommend technological options by considering space, energy and capital‐labor availabilities.     

Effects of processing of grated cassava roots by the 'screw press' and by traditional fermentation methods on the cyanide content of gari

The extent of the loss of hydrocyanic acid (HCN) from grated cassava roots, selected from both the sweet and bitter varieties, was compared in the roasted grit (gari) derived from their fresh pulp which had been dewatered and fermented by two different processes; the quick (1-day) 'screw press' method (QSP) and the slow (3-day) traditional one (STD), respectively. The relative amounts of HCN which had disappeared after 1 day, in the case of QSP, and 3 days, in respect of STD, were comparable (92–100%) for either free (non-glycosidic) or bound (glycosidic) cyanide content of the two cultivars, indicating that the former method was more efficient than the latter in the detoxification of the grated pulp. The QSP method appeared to retain some of the bound cyanide while with the STD method, virtually no bound cyanide was detectable. About 83–91% of the total HCN content of the grated roots was present as free cyanide. It would seem that varietal differences in HCN contents of cassava may not be a critical factor in the preferential selection of the roots for 'garification'.     

Total cyanide determination of plants and foods using the picrate and acid hydrolysis methods

A general method has been developed for determination of the total cyanide content of all cyanogenic plants and foods. Ten cyanogenic substrates (cassava, flax seed, sorghum and giant taro leaves, stones of peach, plum, nectarine and apricot, apple seeds and bamboo shoot) were chosen, as well as various model compounds, and the total cyanide contents determined by the acid hydrolysis and picrate kit methods. The hydrolysis of cyanoglucosides in 2 M sulfuric acid at 100^oC in a glass stoppered test tube causes some loss of HCN which is corrected for by extrapolation to zero time. However, using model compounds including replicate analyses on amygdalin, the picrate method is found to be more accurate and reproducible than the acid hydrolysis method. The picrate kit method is available free of charge to workers in developing countries for determination of cyanide in cassava roots and cassava products, flax seed, bamboo shoots and cyanide containing leaves. For eleven different samples of flax seed and flax seed meal the total cyanide content was 140–370 ppm. Bamboo shoots contained up to 1600 ppm total cyanide in the tip reducing to 110 ppm in the base. The total cyanide content of sorghum leaves was 740 ppm 1 week after germination but reduced to 60 ppm 3 weeks later. The acid hydrolysis method is generally applicable to all plants, but is much more difficult to use and is less accurate and reproducible than the picrate method, which is the method of choice for plants of importance for human food.     

The retail market for fresh cassava root tubers in the European Union (EU): the case of Copenhagen,Denmark — a chemical food safety issue?

BACKGROUND: A number of retail shops in Copenhagen sell fresh cassava roots. Cassava roots contain the toxic cyanogenic glucoside linamarin. A survey was made of the shop characteristics, origin of the roots, buyers, shop owner's knowledge of toxicity levels, and actual toxicity levels. RESULTS: Shops selling fresh cassava were shown mostly to be owned by persons originating in the Middle East or Afghanistan, buyers were found to predominantly be of African origin, and sellers' knowledge concerning the potential toxicity was found to be very restricted. Seventy‐six per cent of the roots purchased had a total cyanogenic potentials (CNp) above the 50 mg HCN equivalents kg^?1 dry weight (d.w.) proposed as acceptable by an EU working group. Two of 25 roots purchased had CNp higher than 340 mg HCN eq. kg^?1 d.w. CONCLUSION: The EU has previously made risk assessments concerning cassava and cyanogenic compounds. In the light of the conclusions drawn, the EU needs to make decisions about how to deal with the regulation and control of fresh cassava roots imported to the European food market. Also cassava root products and cassava leaves should be considered. Copyright © 2009 Society of Chemical Industry     

Cyanogenic potential of fresh and frozen cassava on retail sale in three Irish cities: a snapshot survey

Imported cassava roots can be found on retail sale in several Irish cities and towns. Fresh roots (n = 36 roots) and peeled frozen root pieces (n = 28 packs) were randomly purchased from five retailers in Belfast, Dublin and Limerick and assayed for cyanogenic potential (CNp). Total CNp of fresh root parenchyma varied from 37.5 to 242.9 mg kg^?1 as HCN, dry weight basis – dwb), averaging 104.4 mg kg^?1 HCN (dwb). Total CNp of frozen root parenchyma (n = 28 packs) ranged from 28.5 to 258.6 mg kg^?1 HCN (dwb), averaging 81.7 mg kg^?1 HCN (dwb). Around 78% of fresh roots, and 93% of packs of frozen parenchyma, complied with the Codex Alimentarius definition of ‘sweet’ cassava, but most (86.1% and 64.3%, respectively) exceeded European Union NETTOX recommendations for total CNp. In around one‐third of frozen parenchyma packs, nonglycosidic cyanogens accounted for 83–100% of total CNp. The toxicological implications are briefly discussed.     

Rapid wetting method to reduce cyanogen content of cassava flour

In 2005 a simple wetting method was developed that reduced total cyanide content of cassava flour 3–6-fold. The method involved spreading wet flour in a thin layer and standing in the shade for five hours to allow evolution of HCN gas. We found that breakdown of linamarin catalysed by linamarase to acetone cyanohydrin, followed by its spontaneous decomposition to HCN and acetone was greatly increased by standing the wet flour in the sun. Treatment for two hours in the sun gave the same amount of total cyanide remaining as five hours in the shade. This rapid treatment in the sun may be more acceptable to rural women in Democratic Republic of Congo, than five hours in the shade. The two methods are offered as alternatives for use in rural Africa. With adequate linamarase present the residual cyanogen remaining after the wetting treatment was acetone cyanohydrin.     

Development of a sensitive picrate method to determine total cyanide and acetone cyanohydrin contents of gari from cassava

The sensitivity of the normal picrate method for determination of total cyanide in cassava was increased tenfold using a small 1 cm² picrate paper, eluted using 0.5 mL instead of 5 mL of water as in the normal method. The absorbance was measured in a 2 mm cuvette in the spectrophotometer. The sensitive method was calibrated against the normal picrate method. The total cyanide content in mg HCN equivalents/kg sample = ppm, is calculated from the absorbance (A) by the equation ppm = A × 45.7 which is applicable from 0.1 to 50 ppm. A new method to determine acetone cyanohydrin was developed based on irreversible denaturation of linamarase in 0.1 M HCl at 30 °C for 1 h. Five gari samples from Mozambique gave a mean total cyanide content of 12 ppm (range 6–15 ppm) and mean acetone cyanohydrin content of 11 ppm (range 5–14 ppm). Acetone cyanohydrin liberates cyanide quantitatively in the human intestine.     

Effect of pulsed electric field pre-treatment on the debittering process of cherry kernels

Cherry kernels occur in significant amounts as waste material during the processing of fruits. However, their subsequent use is limited due to the presence of cyanogenic glycosides, which are potentially dangerous to human health. In this study, the application of pulsed electric fields (PEF) was investigated as pre-treatment to improve the debittering process and to facilitate the degradation of cyanide precursors, naturally present in cherry kernels. Diverse PEF treatments were carried out at constant electric field strength of E = 2.2 kV/cm and specific energy input was varied between 10 and 50 kJ/kg, varying the number of pulses. Two different debittering procedures were performed with a common incubation time 0–20 h at 40 °C: a) incubation of whole kernels in deionized water; b) incubation of whole kernels without water stored in air at 80% relative humidity. HPLC analysis was used to examine the kinetics of the amygdalin and HCN contents. In both debittering methods, the PEF-treated samples with the highest intensity (2.2 kV/cm, 50 kJ/kg) showed higher and faster detoxification efficiency for the investigated compounds as compared to the untreated sample. In particular, the PEF treated samples incubated with water showed a reduction in the amygdalin and HCN contents of up to 86% (up to 72% of the raw material content.). Moreover, the PEF pre-treatment led to comparable efficiency in amygdalin reduction in both debittering processes: 86% reduction for the incubation with water and 81% for the incubation without water. Consequently, the combined application of PEF and the debittering process including incubation without water has remarkable potential as an industrial application due to its inherent reduced water consumption, and therefore, diminished wastewater management issues. A further advantage of this process is the minimizing of sugar loss typically occurring during the debittering through soaking.     

Improved enzymic assay for cyanogens in fresh and processed cassava

The assay for cassava cyanogens developed at the Natural Resources Institute has been modified to overcome some of the problems encountered when the assay is applied to cassava products. Inclusion of 25% ethanol in the extraction medium increased the volume of recovered extract from heat-processed cassava products, eliminated the need for centrifugation and did not interfere with any aspect of the assay. Greater cyanohydrin recovery was noted and the calculation for cyanogen contents was changed to take into account the total extract volume. The separate assay of the three cyanogens (glucosides, cyanohydrins and free cyanide) was achieved by buffering aliquots of the extract followed by appropriate treatment. The importance of assaying for free cyanide (HCN) at pH 4 was demonstrated. Above this pH, cyanohydrin degradation also produces free cyanide, giving rise to misleading values. The efficiency of the extraction medium in recovering added linamarin and cyanohydrin from cassava foods was determined. Recoveries of cyanohydrin were improved using the ethanol/acid medium. The stability of the cyanogens in the ethanol/acid extraction medium was tested at ambient and refrigeration temperatures. Over a two-month period, refrigerated extracts showed acceptable variation as compared with normal variation within the assay (5%) for total and non-glycosidic cyanogens but the levels of free cyanide showed heavy losses (15–56% lost). Since the relative toxicities of the three cyanogens have yet to be ascertained, the relative amount of each cyanogen may be important when assessing the safety of cassava products.     

Some characteristics of the roots of the winged bean [Psophocarpus tetragonolobus (L.) DC]

Three accessions of winged bean [Psophocarpus tetragonolobus (L.) DC] tuberous roots from Thailand were examined for their crude protein (N × 6.25), non-protein nitrogen and starch contents. The roots were further analysed for their trypsin inhibitor and urease activities and for the presence of tannins and cyanogenic compounds. Crude protein was found to be high in comparison with other root crops (5.7–6.7% fresh weight) and this contained a high proportion of non-protein nitrogen (7.4–15.0%). Amino acid content of the crude protein, when compared with mature winged bean seeds, revealed a deficiency in the sulphur-containing amino acids but an exceptionally high aspartic acid content. Starch was the major carbohydrate present in the flesh of the roots (21.7–32.1% fresh weight). Root samples were found to contain high levels of trypsin inhibitory activity (13.5–30.1 TIU mg^?1 fresh weight). No urease activity or cyanide could be detected in any of the root accessions studied.     

Processing factors affecting the level of residual cyanohydrins in gari

Intake of cyanogens in gari, a food processed from cassava roots, is implicated in the causation of tropical ataxic neuropathy (TAN). This neurological syndrome is endemic in some communities in south‐western Nigeria. Studies have shown that methods of processing cassava roots determine the quantity of cyanogens in gari. This study was conducted to investigate the effects of the method of dewatering and the duration of fermentation on cyanogens in gari. Cassava roots (400 kg) were peeled, washed, grated and divided into 14 woven polyethylene sacks. The mash in seven of the sacks was dewatered continuously during fermentation, while the mash in the remaining seven sacks was fermented without dewatering, but dewatered at the end of fermentation. Cassava mash from each treatment was roasted into gari at 24 h intervals up to 168 h. Mean cyanohydrin content in gari roasted from cassava mash dewatered continuously during fermentation was 10.8 mg HCN eq kg^?1 dw (CI 9.7–11.9), while mean cyanohydrin content in gari roasted from cassava mash dewatered after fermentation was 6.3 mg HCN eq kg^?1 dw (CI 5.3–7.4). Mean linamarin content was 4.0 mg HCN eq kg^?1 dw (CI 3.1–4.9) and mean HCN content was 1.6 mg kg^?1 dw (CI 1.3–1.9) in gari roasted from cassava mash dewatered continuously, while mean linamarin content was 3.2 mg HCN eq kg^?1 dw (CI 2.3–4.0) and mean HCN content was 1.2 mg kg^?1 dw (CI 0.9–1.5) in gari roasted from cassava mash dewatered after fermentation. The method of dewatering cassava mash and the duration of fermentation were significantly associated with the level of cyanohydrin in gari (p < 0.001). This study shows that dewatering of cassava mash continuously during fermentation contributes to the dietary cyanide load in TAN‐affected communities. © 2002 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 survey of total hydrocyanic acid content in ready-to-eat cassava-based chips obtained in the Australian market in 2008

Cassava (Manihot esculenta Crantz) is a widely consumed food in the tropics that naturally contains cyanogenic glycosides (cyanogens, mainly composed of linamarin, acetone cyanohydrin, and hydrocyanic acid). If cassava is not adequately processed to reduce the level of cyanogens prior to consumption, these compounds can lead to the formation of hydrocyanic acid in the gut. Exposure to hydrocyanic acid can cause symptoms ranging from vomiting and abdominal pain to coma and death. In 2008, a survey of ready-to-eat (RTE) cassava-based snack foods was undertaken to determine levels of cyanogens measured as total hydrocyanic acid. This survey was undertaken in response to the New South Wales Food Authority being alerted to the detection of elevated levels of cyanogens in an RTE cassava-based snack food. This survey took 374 samples of RTE cassava chips available in the Australian marketplace. Significant variation in the levels of total hydrocyanic acid were observed in the 317 samples testing positive for cyanogens, with levels ranging from 13 to 165 mg of HCN equivalents per kg (mean value, 64.2 mg of HCN eq/kg for positive samples). The results from this survey serve as a timely warning for manufacturers of RTE cassava chips and other cassava-based snack foods to ensure there is tight control over the levels of cyanogens in the cassava ingredient. Evidence from this survey contributed to an amendment to the Australia New Zealand Food Standards Code, which now prescribes a maximum level for hydrocyanic acid in RTE cassava chips of 10 mg of HCN eq/kg, which aligns with the Codex Alimentarius Commission international standard for edible cassava flour.     

Picrate paper kits for determination of total cyanogens in cassava roots and all forms of cyanogens in cassava products

The simple semiquantitative picrate method for the determination of total cyanogens in cassava flour has been modified by increasing the concentration of the picrate solution used to make up the picrate papers, such that a linear Beer's Law relation between absorbance and cyanogen content is obtained over the range 0–800 mg HCN equivalents kg⁻¹ cassava. The method has been adapted to determine the total cyanogen content of cassava roots and the results compared using the picrate method and the acid hydrolysis method for six different roots from five cultivars. The agreement between the results is satisfactory. The simple method for determination of total cyanogens in cassava roots in the field is available in kit form. The methodology has been modified to allow determination of the three different forms of cyanogens present in cassava flour, viz HCN/CN⁻, acetone cyanohydrin and linamarin. HCN/CN⁻ is determined by the picrate method in which cassava flour is reacted with 0.1 M sulphuric acid for 3 h at room temperature. HCN/CN⁻ plus acetone cyanohydrin is also determined by the picrate method after treating cassava flour with 4.2 M guanidine hydrochloride at pH 8 for 3 h at room temperature. A comparison has been made of the amounts of the three cyanogens present in six cassava flour samples using the semiquantitative picrate and the acid hydrolysis methods. The agreement between the two methods is satisfactory, which shows that the new methodology works well. The picrate method for determination of the three cyanogens in cassava flour is also available as a kit. © 1999 Society of Chemical Industry     

Effectiveness of different processing methods in reducing hydrogen cyanide content of flaxseed

A study was conducted to determine the effectiveness of reducing the hydrogen cyanide (HCN) content of flaxseed (FS) by processing. FS was processed by oven heating, single or repeated pelleting alone or in a mix with corn or other ingredients, autoclaving, and microwave roasting. The comparative effectiveness in reducing HCN in FS by these processes was monitored through HCN measurements by alkaline titration. The HCN content was 377 mg kg^?1 in raw feed‐grade FS and 139 mg kg^?1 in a human food‐grade FS. All processing methods tested significantly (p < 0.05) reduced the HCN content of FS. Autoclaving FS reduced its HCN content by 29.7%. Microwave roasting of FS reduced the HCN content by 83.3%. Because of the 5.7% water loss recorded after 4 min of FS roasting, this reduction could be related to more evaporation of the newly formed HCN. Pelleting FS once reduced HCN content by 13.3%, and three and six repeated pelleting processes reduced HCN content by 29.0% and 54.9% respectively. When FS was pelleted in a mix with 50% corn, the HCN reduction was even greater. After pelleting six times, HCN reduction reached 63.8%. However, the greatest reduction in HCN content was 73.8%, and was obtained when FS was mixed with several ingredients and pelleted twice. The HCN reduction could be the result of deactivation of the glycosidase, or the evaporation of HCN formed from cyanogenic glycosides. The HCN reduction increased as the number of pelletings and the temperature of the pelleted product increased. The greater and prolonged exposure to a higher temperature by several pelletings seems to promote a greater HCN reduction. The appropriate processing of FS is essential for the use of this oilseed in animal feeding. Copyright © 2003 Society of Chemical Industry     

Processing Techniques to Reduce Toxicity and Antinutrients of Cassava for Use as a Staple Food

ABSTRACT: Cassava is a valuable source of food for developing countries, but it contains highly toxic cyanogen compounds and antinutrients. Cyanogens are found in 3 forms in cassava: cyanogenic glucoside (95% linamarin and 5% lotaustratin), cyanohydrins, and free cyanide. Different processing techniques exist to remove cyanogens and their effectiveness depends on the processing steps and the sequence utilized, and it often is time‐dependent. Pounding or crushing is the most effective for cyanogenic glucoside removal because it ruptures cell compartments, thus allowing direct contact between linamarin and the enzyme linamarase that catalyzes the hydrolytic breakdown. Crushing and sun‐drying cassava roots made into flour removes 96% to 99% of total cyanogens, whereas soaking and sun‐drying into lafun or fufu, or soaking and fermenting and roasting into gari or farina, removes about 98% of cyanogens. For cassava leaves, which have 10 times more cyanogens than roots, pounding and boiling in water is an efficient process to remove about 99% of cyanogens. Other strategies to reduce toxicity include development of low‐cyanogen cassava varieties and cassava transgenic lines with accelerated cyanogenesis during processing. Although phytate and polyphenols have antioxidant properties, they interfere with digestion and uptake of nutrients. Fermentation and oven‐drying are efficient processing methods to remove phytate (85.6%) and polyphenols (52%), respectively, from cassava roots. Sun‐drying the leaves, with or without prior steaming or shredding, removes about 60% phytate. Cassava is a nutritionally strategic famine crop for developing countries and, therefore, reducing its toxicity and improving its nutritional value is crucial.     

Application of a picrate semi‐quantitative screening assay for the cyanogenic potential of cassava roots at a remote field site

The purpose of this research was to test the accuracy of the picrate screening assay (PSA) in the evaluation of the cyanogenic potential of cassava roots at a remote field site under conditions of unusual difficulty. To do this, a PSA was conducted in the field and compared to data collected previously on five of the same cassava varieties using the Cooke colorimetric enzymic assay. PSA data were collected for 10 different cassava varieties in the Tukanoan Indian village of Yapú in the Colombian Amazon region. The PSA results agree with Tukanoan classifications of cassava; that is, those classified as ‘sweet’ by the Tukanoans generally had low‐to‐moderate parenchymal cyanogenic potential (0–50 mg kg⁻¹ fwb of HCN), while those that they classify as ‘bitter’ had high parenchymal cyanogenic potential (≥100 mg kg⁻¹ fwb of HCN). The PSA results also agree with the data collected using the Cooke colorimetric enzymic assay. The data suggest that the PSA is an appropriate test of the cyanogenic potential of cassava roots in remote field sites. © 2000 Society of Chemical Industry     

An enzymatic assay for the total cyanide content of cassava (Manihot esculenta Crantz).

An enzymatic assay for the cyanide contents of cassava parenchymal tissue (peeled root), cassava peel or cassava leaves is described. The material is homogenised in orthophosphoric acid; filtered through glass-fibre paper and aliquots of the filtrate are neutralised and incubated with exogenous linamarase for 15 min. The cyanogenic glucosides present are hydrolysed to free cyanide which is estimated spectrophotometrically. The acid extraction solution inactivates endogenous linamarase, and assay of aliquots without enzyme treatment gives the free (non-glycosidic) cyanide contents of the extracts. The acid extracts are stable for at least 4 days at 4°C, and the steam-distillation/aspiration of earlier methods is unnecessary. The detection limit is < 0.01 mg (0.1 parts 10^?6) cyanide per 100 g fresh weight and peeled root, and 40-50 samples per day can be handled easily. Analyses of eight cultivars indicated longitudinal and radial cyanide gradients in the roots, and the problem of sampling bulky roots is discussed.     

Bitter taste in cassava roots correlates with cyanogenic glucoside levels

Cassava roots contain cyanogenic glucosides. Malawian farmers classify cultivars into two groups based on the perceived danger of eating raw roots that they associate with bitterness. In the vernacular, cultivars that produce roots with bitter taste are called vyakubaba (bitter), whereas those yielding non‐bitter roots are called vyakuzizra (cool). In the scientific literature they are distinguished as ‘bitter’ or ‘sweet’. Roots from ‘bitter’ cultivars are processed prior to consumption. We studied the ability of farmers to predict the cyanogenic glucoside levels of 492 roots from the 10 most commonly grown cultivars. Twenty‐eight farmers predicted the taste of each of the cultivars that they grew, and scored bitterness on a five‐point scale by tasting the root tip. Thereafter cyanogenic glucosides were determined on half of the root, while a taste panel scored the taste of the other half. The mean cyanogenic glucoside level in 132 roots from ‘cool’ cultivars was 29 mg HCN eq kg^?1 fresh weight (CI 25–33, range 1–123) and in 360 roots from ‘bitter’ cultivars was 153 mg HCN eq kg^?1 fresh weight (CI 143–163, range 22–661). Farmers' distinction of ‘cool’ and ‘bitter’ cultivars predicts glucoside levels. The tasting of the tip of the root improved the farmers' prediction of toxicity. Scoring of bitterness by a trained taste panel showed a stronger correlation with glucoside levels (r² = 0.67). This suggests that cyanogenic glucosides confer the bitter taste, notwithstanding the probability of additional modifying intrinsic factors. Copyright © 2004 Society of Chemical Industry