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.     

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.     

The effect of pre‐harvest pruning of cassava upon root deterioration and quality characteristics

One of the major constraints of cassava as a crop is its perishability. Physiological deterioration, parenchymal blue–black vascular streaking, often starts within 24 h after harvest. This paper presents the results of a detailed study of the effects of pre‐harvest pruning upon post‐harvest physiological deterioration (PPD) and some other quality characteristics. Six cultivars, grown at CIAT (Centro International de Agricultura Tropical), with varying intrinsic susceptibility to PPD, were assessed at pruning–harvest intervals of 0, 2, 4, 6, 8, 10, 15, 20, 25, 28 and 39 days. After harvesting, the roots were analysed. For the unpruned plants a low susceptibility was found to coincide with a low dry matter content and a high sugar content. After pruning, the susceptibility for all cultivars was drastically reduced, reaching a minimum of around 25% of the original value for a pruning–harvest interval of up to 25 days. Beyond this interval the plants slowly develop new leaf canopy, normal assimilation sets in again and the starch content increases. Analysis of the cassava roots revealed a relationship between the combined sugar and starch contents and the interval duration, and that sugar and starch contents were inversely related to each other. The sugar content increased with the interval period, probably as a result of starch hydrolysis. Other properties such as the contents of dry matter, cyanogen, scopoletin, amylose and reducing sugars and the starch pasting properties were not affected by pruning to a comparable, interval‐dependent, extent. It is concluded that the sugar content, ie the sugar/starch ratio, of cassava roots is positively related to their resistance to post‐harvest physiological deterioration. © 2000 Society of Chemical Industry     

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.     

Protein Contents,Amino Acid Compositions and Nitrogen-to-Protein Conversion Factors for Cassava Roots

Root protein contents of 15 cassava varieties ( Manihot esculenta Crantz) ranged from 5 to 19 g kg⁻¹ dry matter. Intervarietal differences in amino acid profiles of cassava roots were evident. Differences in the levels of aspartic acid, glutamic acid and arginine were most notable. The nitrogen-to-protein conversion factors ( k _AA ) based on nitrogen recovered from total amino acid analyses including ammonia ranged from 4·75 to 5·87, showing that the traditional conversion factor of 6·25 was not valid for cassava root proteins. Conversion factors ( k _P ) for 15 cassava varieties based on Kjeldahl nitrogen ranged from 2·49 to 3·67. Therefore an average k _P value of 3·24±0·31 may provide a better estimate of the protein content in cassava roots.     

不同食用木薯品种（系）薯片加工适宜性研究

为了解不同食用木薯品种(系)炸薯片在品质上的差异,探讨其影响因子,筛选适宜加工薯片的木薯品种(系),以12个优良食用木薯品种(系)为材料进行炸片加工,对薯片进行感官评价及薯片含水率、质构等测定,并进行主成分分析和与鲜薯营养品质的相关分析。结果表明:NK-10感官评价值、内聚性和弹性值最高,SC9和M33硬度较大,咀嚼性差异不显著。相关性分析发现,木薯薯片感官组织状态、色泽与鲜薯支链淀粉含量分别呈显著相关(P<0.05)和极显著相关(P<0.01),相关系数分别为0.674、0.795。主成分分析获得了4个主成分,解析贡献率分别为34.325%、23.627%、16.900%、13.205%,品系NK-10综合评分最高,为0.875,其次是M9的0.565、ST的0.401。该研究表明木薯品种(系)NK-10、M9、ST适宜用于炸片加工。薯片口感、风味、含水率、咀嚼性、色泽和组织状态可作为其品质鉴定的重要指标,且木薯炸薯片的组织状态和色泽受到鲜薯支链淀粉含量的影响。     

发酵条件对木薯嫩梢腌制蔬菜营养品质和风味的影响

目的 探究发酵条件对木薯(ManihotesculentaCrantz)嫩梢腌制蔬菜(pickledvegetableswithcassava tendershoots,PVCT)营养品质和风味影响。方法 分别采用模糊数学感官综合评价法、电感耦合等离子体发射光谱法、高效液相色谱法和顶空固相微萃取-气相色谱-质谱法对不同原料配比和发酵时间条件下的PVCT感官评分、元素、有机酸和挥发性成分进行分析。结果 木薯嫩梢、橄榄酱、食盐水浓度配比为100:15:2 (m:m:c)时,感官评分最高,且有较高的K、Mg和P元素含量(分别为1126.74、206.00、276.88 mg/100 g, DW)和适中的Ca、Zn和Mn等元素(分别为503.41、11.06、12.84 mg/100 g, DW)。发酵腌制10 d后脂肪含量达到最低值,为1.78 g/100 g,蛋白质含量在腌制的第15 d到达最高值,为28.34 g/100 g。亚硝酸盐含量在发酵10 d后趋于稳定,约为0.97 mg/kg; PVCT经炒制后氰化物含量符合国家安全标准,约为0.0595 mg/kg;单宁含量对PVCT风味影...     

Detoxification of cassava during fermentation with a mixed culture inoculum

The efficacy of a mixed culture inoculum in detoxifying intact cassava tuber and peel pieces was investigated. Fermented cassava tuber and peel pieces had more linamarase activity than the non-fermented control samples and this might have resulted partly from the release of endogenous linamarase from the retted tuber/peel pieces and partly due to the microbial linamarase. Approximately 24–26% of the total cyanide remained in the bound form in the fermented tuber while 67–79% existed as bound cyanide in the non-fermented controls. In cassava peels, only 15–33% of total cyanide remained in bound form after 72 h fermentation while 58–59% cyanide existed in bound form in the parallel non-fermented control peels. Free cyanide which could be easily eliminated through sun-drying was present at higher concentrations in the fermented tuber and peel compared with the non-fermented samples. The study showed that cassava tuber and peel could be extensively detoxified through fermentation with a mixed culture inoculum.     

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.     

Production of a Lactobacillus plantarum starter with linamarase and amylase activities for cassava fermentation

Lactobacillus plantarum strain A6 isolated from cassava, cultured on cellobiose MRS medium showed a growth rate of 0.41 h^?1, a biomass yield of 0.22 g g^?1, and produced simultaneously an intracellular linamarase (76.4 U g^?1 of biomass) and an extracellular amylase (36 U ml^?1). The synthesis of both enzymes was repressed by glucose. The use of such a strain as a cassava fermentation starter for gari production had the following influences: a change from a hetero-fermentative pattern observed in natural fermentation to a homofermentation, a lower final pH, a faster pH decline rate and a greater production of lactic acid (50 g kg^?1 DM). However, this starter did not appear to play a significant role in cassava detoxification, since it was observed that the level of endogenous linamarase released during the grating of the roots was sufficient to permit the complete and rapid breakdown of linamarin.     

木薯渣中乳酸菌的分离鉴定及其产酸能力分析

该研究利用传统培养法从自然发酵木薯渣中分离得到9株菌,通过菌株形态、生理生化特征及16S rDNA基因序列分析方法对菌株进行鉴定。结果显示,这9株菌均为乳杆菌属（Lactobacillus sp.）,其中菌株Y5、Y13、M14为干酪乳杆菌（Lactobacillus casei）,菌株Y6、Y12、M12为植物乳杆菌（Lactobacillus plantarum）,菌株Y7为丘状乳杆菌（Lactobacillus collinoides）,菌株M9为副干酪乳杆菌（Lactobacillus paracasei）,菌株M11为类布氏乳杆菌（Lactobacillus parabuchneri）;产酸及耐酸试验结果表明这5种菌均具有较强的产酸能力及耐酸性,发酵6 h后发酵液中pH值可达4.5以下,其中菌株Y12和M14的产酸能力最强,在15 h后其pH值均在3.6以下,可用于木薯渣或其他青贮饲料发酵剂的研制。     

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     

Cyanogenesis in somatic embryos and plantlets of cassava (Manihot esculenta Crantz)

A protocol was established for high frequency cyclic somatic embryogenesis and plant regeneration for the cassava variety PRC 60a. Linamarin content and linamarase activity were determined in various tissues of secondary somatic embryos and regenerated plants. Neither linamarin nor linamarase activity were detected in embryogenic callus and somatic embryos. The stems and leaves of regenerated plants, however, contained variable amounts of linamarin and linamarase activity whereas, in the root tissues, only linamarin was detected. This study suggests that the pathway for linamarin biosynthesis may be absent or not switched on in the embryogenic callus and somatic embryos. This system would be useful for investigating cyanogenesis in cassava. © 1999 Society of Chemical Industry     

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.     

Effect of variety on the heat transfer coefficient during drying of fermented ground cassava

The effect of variety on the heat transfer coefficient of four cassava cultivars (TMS 30555, TMS 30572, NR 8082 and one Native type) was investigated. The cultivars were dried at an air temperature of 142 °C, air velocity of 1.397 m/s⁻¹ and relative humidity of 55%. The heat transfer coefficient obtained varied from 0.0622 to 0.0725 kJ kg s °C. The heat transfer coefficient varied for some cultivars, while some cultivars had close heat transfer coefficient. NR 8082 had the lowest heat transfer coefficient while TMS 30555 had the highest heat transfer coefficient. The cultivars with high heat transfer coefficient were found to have low bulk density, smaller particle diameter, high drying rate, low specific heat capacity and high carbohydrate fat and protein contents than other cultivars.