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     

Cyanide content in whole-root chips of ten cassava cultivars and its reduction by oven drying or sun drying on trays

The effect of sun drying on trays for 48 hr and of oven drying in an air-forced oven at 60°C for 24 hr on the cyanide content of chips of ten cassava varieties was studied. Fresh cassava chips from whole roots of these varieties showed significantly different total cyanide contents among them with values in the range of 100–900 mg/kg on a dry matter basis; most of the varieties studied exhibited cyanide contents in the range of 200–600 mg/kg. The free cyanide proportion in the fresh chips was in the range of 30–40% of their total cyanide. Sun and oven drying reduced the cyanide content in the dried chips to approximately 15–30% of the initial cyanide content of fresh chips. In addition, the free cyanide content in dried chips accounted for approximately 60–80% of their total cyanide value.     

Reduction of cyanide levels during anaerobic digestion of cassava

During the methanogenic fermentation of cassava peel in a plug flow digester, cyanide bound as linamarin in cassava was released as HCN in the fermentation liquor, and then eliminated by the activity of free enzymes and by non-enzymatic reactions. The raw cassava peel contained (1) the enzyme permitting the hydrolysis of linamarin and the liberation of HCN (linamarase), and (2) a cyanide detoxification enzyme (β-cyanoalanine synthase). Cyanide removal was sufficiently fast to maintain a cyanide concentration in the fermentation liquor which was non-inhibitory for the methanogenic microflora.     

An automated enzymic assay for determining the cyanide content of cassava (Manihot esculenta crantz) and cassava products

An automated enzymic method for the analysis of cyanide in cassava and cassava products is described. A total of 300 analyses a day can be handled easily. A wide range of free (nonglycosidic) or bound (cyano-substituted glycosides) cyanides (0.4–40 μg HCN ml^?1) can be assayed in the extracted solutions. The upper limit of detection for the bound cyanide can easily be increased by another three-fold by assaying it under partial hydrolysis conditions. The two enzymic methods, manual and automated on Technicon's AutoAnalyzer, agreed well for the free and the bound cyanide in the leaf and the peeled storage root samples.     

Transformation and Balance of Cyanogenic Compounds in the Cassava Starch Manufacturing Process

The balance of total cyanogenic compounds and distribution of each compound including bound cyanide, cyanohydrin and free cyanide were evaluated in a cassava starch factory, having a production capacity around 100 t starch per day. The production of starch began with transferring washed roots to the rasper, followed by a series of extractors, separators, dewatering centrifuge and flash dryer, with an average water consumption of 11.4 t per ton dry starch. The total amount of cyanogenic compounds entering the process varied from 28 to 43 kg HCN equivalent per day, depending on the root quality. In roots, 64% of bound cyanide was primarily found and it significantly decreased to 22% after rasping whereas the cyanohydrin content increased from 34% to 62%. Most of cyanogenic compounds, predominantly present as cyanohydrin (55 to 70%), was discharged in liquid and solid wastes, accounting for 92% and 5% of total cyanide in roots, respectively. Only a negligible amount of cyanogenic compounds remained in the starch products, having less than 2 mg HCN equivalent per kilogram dry starch. Typically, water from the separators with 91% total cyanide content was recycled to the root washer before being discharged as wastewater, whereas the liquid from the coarse extractor (43% of total cyanide) was recycled to the rasper. This could cause the accumulation of cyanogen in the process and, therefore, in the finished products. With knowledge of the balance and transformation of cyanogens in starch processing, it is possible to assure the quality of low‐cyanide starch by modifying starch process features such as water circulation and pH adjustment.     

Hydrocyanic acid levels in fermented cassava

The extent of loss of hydrocyanic acid during the fermentation of cassava tubers selected from both sweet and bitter varieties in the traditional method (whole unpeeled tubers) compared with the fermentation of peeled tubers and crushed pulps with or without the addition of water. Although the traditional fermentation is terminated after 3–4 days, in this study the fermentation was allowed to proceed for 8 days. Loss of cyanide from the whole tubers was 8047% after 8 days and was only 51–53% after 4 days. Loss of cyanide from the whole sweet tuber was not significant after 5 days. The loss of cyanide from the peeled tubers was comparable to the whole tubers after 8 days of fermentation. However, there was a marked decrease in free cyanide in the 1st day of fermentation of the peeled tubers compared to whole tubers. The loss in cyanide in the crushed pulp, which occurred primarily in the 1st day, appears to be due to the action of endogenous linamarase rather than hydrolysis by fermentation. When water is added to the crushed pulp the reduction in cyanide was 83–91% with marked decrease in bound cyanide in the 1st day of fermentation. It seems that autohydrolysis is enhanced by addition of water to the crushed pulp.     

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.     

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.     

Changes in cassava toxicity during processing into gari and ijapu--two fermented food products.

Grated cassava to which tap water was added at levels of 25%, 50% and 75% (v/w) was held at 30 degrees C, 40 degrees C or 50 degrees C and examined over a 6 h period for cyanide content, pH and titratable acidity (TTA). During the come-up time, i.e. the time between addition of water and attainment of desired holding temperature (between 14 and 47 min), reductions in bound cyanide of ca 54-85% occurred, depending on the level of added water and holding temperature. The corresponding losses for the control samples, to which no water was added, were ca 25-33%. The biggest reduction in the bound cyanide of > 99% (from 89.0 to 0.6 ppm) occurred in grated cassava with 75% added water held at 50 degrees C. There was little or no change in pH during the period of study. The reduction of processing time for certain cassava products based on separation into detoxication and flavour development/fermentation stages is discussed.     

Effect of processing methods on quality and acceptability of fufu from low cyanide cassava

The effects of steeping whole and grated tubers and of periodic change of water during steeping on the quality and acceptability of fufu from low-cyanide cassava were evaluated. Steeping increased the acidity and reduced the pH and cyanide content of cassava. Grating the tuber before steeping improved aroma, and periodical change of water during steeping improved taste, colour and texture of fufu over that produced by the traditional method. Fufu from low-cyanide cassava had an acceptability similar to that of fufu from high-cyanide cassava. However, oven drying of the flour significantly reduced acceptability of fufu.     

The Effect of Root Maturity, Preprocess Holding and Flour Storage on the Quality of Cassava Biscuit

Effect of root maturity (12 and 23 months) and flour storage on physical, chemical, and sensory attributes of cassava biscuits was evaluated. Pulp and flour of 12 months were higher than the 23 months mature roots. Moisture, crude protein, crude fat, and cyanide contents of the cassava flour varied between 10.1% and 10.3%, 2.2% and 2.4%, 0.2% and 0.3%, and 12.1 and 13.4 mg HCN/100 g, respectively. Diastatic activity of the flour ranged from 115 to 243 mg maltose for fresh and roots stored for 3 days. Water-holding capacity of the roots and peak viscosity of flours decreased during storage. Sensory results showed that cassava biscuits were acceptable and compared favorably with the wheat biscuits.     

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.     

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.     

Quality of ‘Abacha’ from Fresh Cassava Roots and Dried Chips

This study was undertaken to determine the possibility of producing acceptable ‘abacha’ from dried chips. The ‘abacha’ slices were processed from dried cassava chips and fresh roots of four cassava varieties, TMS 98/2101, NR/87184, TMS 97/4779 and NR87184. The proximate composition, chemical and sensory properties as affected by the processing method and variety were evaluated. The proximate composition of the ‘abacha’ (on dry basis) showed moisture content range of 9.53 – 10.48%, protein 1.07 – 1.66%, ash 2.06 – 2.56%, fibre 1.72 – 1.95, fat 0.39 – 0.58% and carbohydrate content of 83.59 – 85.05%. The chemical composition of the wet ‘abacha’ slices showed pH of 5.60 – 5.80, total titratable acidity (TTA) of 0.047 – 0.063, and hydrogen cyanide (HCN) value of 7.80 – 10.41 mg/100 g. Generally, the TTA of the ‘abacha’ samples was not significantly (p > 0.05) affected by the method of processing ‘abacha’ and the variety used. Drying the wet ‘abacha’ reduced the pH to 5.20 – 5.30, increased the TTA to 0.213 – 0.230% and further reduced the HCN content to 7.32 – 8.63 mg/100 g. The HCN of all the ‘abacha’ samples processed from dried chips were significantly (p < 0.05) lower than the HCN of ‘abacha’ processed from fresh cassava root in some of the varieties. The lower sensory scores for ‘abacha’ made from dried chips shows that they were inferior to the ones from fresh cassava, although they were also accepted by the consumers. It also compared favourably with the ‘abacha’ processed from fresh cassava root in chemical qualities. This shows that when the need arises ‘abacha’ slices can be processed from dried cassava chips.     

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     

EFFECT of UNIT OPERATIONS of PRODUCTION ON the CYANIDE CONTENT and ACCEPTABILITY of GARI

The effect of holding, pressing, initial moisture content, sunheating, and garifying, on pH, total titratable acidity (TTA) and residual cyanide content of cassava mash, cake and gari, were evaluated. A new method to make gari with very low residual cyanide was developed.
Increasing holding time decreased pH, cyanide content, but increased TTA of mash and gari when initial moisture content of mash was greater or equal to 63–65%. Reducing the initial moisture content of mash below 60% increased pH, reduced the residual cyanide, but increased the TTA in the mash. the optimum holding period was 72 h beyond which there was no reduction in residual cyanide content. Pressing and garifying further reduced the residual cyanide of cassava mash and gari, respectively. Sensory properties of gari prepared by the new laboratory method were similar to those of gari produced by the traditional method.     

PROCESSING TECHNIQUES AND HYDROCYANIC ACID CONTENT OF CASSAVA-BASED HUMAN FOODSTUFFS IN NIGERIA

The hydrocyanic acid content of peeled cassava tubers from various localities in Eastern Nigeria (major cassava growing and consuming area) varied from 26 ± 1.6 to 38 ± 2.6 mg/100g fresh weight. There was no correlation between the cyanide contents of cassava tubers and locality. Processing the tubers with the highest cyanide content into different forms of cassava-based foodstuffs (i.e. Garri, Fufu, cassava cake and cassava chips for cassava salad) consumed in Nigeria resulted in an undetectable amount of cyanide. It is concluded that these cassava-based foodstuffs consumed in Nigeria are free from cyanide toxication, and the incidence of ataxic neuropathy associated with prolonged consumption of cassava as a result of its cyanide content should not be due to prolonged consumption of processed cassava products.     

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.     

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.     

Cassava detoxication during tapé fermentation with traditional inoculum

Tapé ketela is a traditional Indonesian fermented cassava product using ragi as inoculum. Cassava fermented with 0.2–0.4% ragi produced a characteristic flavour and sweet-sour alcoholic taste. After 3 days' fermentation the pH decreased from 6.54 to 5.06–5.17, titratable acidity increased from 0.07 to 0.22–0.26%, reducing and total sugars increased from 1.1 to 21.4–22.0% and 3.9 to 22.9–23.5%, respectively, while alcohol content increased from less than 0.01 to 2.02–2.12%. Total cyanide loss during fermentation was 58–87%. Most cyanide was lost during steaming (40–70%) while 9–35% was lost during 3 days fermentation. Sensory evaluation revealed no significant differences in flavour, texture and colour (P > 0.01) of tapé prepared by two different methods. Tapé prepared from dried cassava (gaplek) did not develop characteristic organoleptic properties.