Influence of cultivars and processing methods on the cyanide contents of cassava (Manihot esculenta Crantz) and its traditional food products

Scientific African 5 (2019) e00119

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Influence of cultivars and processing methods on the cyanide contents of cassava (Manihot esculenta Crantz) and its traditional food products Youchahou Njankouo Ndam a, Pauline Mounjouenpou b,∗, Germain Kansci c, Marie Josiane Kenfack c, Merlène Priscile Fotso Meguia b, Nina Sophie Natacha Ngono Eyenga b, Maximilienne Mikhaïl Akhobakoh b, Ascenssion Nyegue a a

Laboratory of Microbiology, Department of Microbiology, Faculty of Science, University of Yaoundé I, P.O. Box: 812, Yaoundé, Cameroon Laboratory of Food Technology, Institute of Agricultural Research for Development (IRAD); P.O. Box: 2067, Cameroon Laboratory of Metabolism and Food Science, Department of Biochemistry, Faculty of Science, University of Yaoundé I, P.O. Box: 812, Yaoundé, Cameroon

b c

a r t i c l e

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Article history: Received 8 November 2018 Revised 25 May 2019 Accepted 2 August 2019

Keywords: Cyanide Cassava cultivars Traditional processing Detoxification

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a b s t r a c t Cyanide is a toxic substance found in several plants roots amongst which cassava. The objectives of this study were to quantify cyanide contents in the roots of the main cassava varieties cultivated in Cameroon and evaluate the effect of some traditional cassava processing methods on their initial contents. Ten local and ten improved varieties of cassava samples were collected in the locality of Mbankomo, Ongot village, Centre region. These roots were processed into traditional foods: “Chips”, “Gari” and “Fufu”. The cyanide content was determined in the parenchyma, cortex, and cassava derived foods. Local varieties had cyanide contents varying from 79.34±3.58 to 181.33±0.48 ppm, while contents in improved varieties varied from 61.03±9.44 to 118.04±7.16 ppm. Cyanide content quantitative classification revealed that studied cassava varieties fell within the range “moderately” to “highly” toxic. Results showed no clear link between morphological characteristic and cyanide contents of the studied cassava varieties. Although cyanide contents were higher in the cortex varying from 117.80±11.32 to 210.07±9.15 ppm for local, and from 98.43±15.49 to 155.44±12.11 ppm for improved varieties. Processing of cassava into different traditional foods contributed to reduce cyanide content. Elimination rates were as a function of the process involved: 47%, 80% and 91%, respectively, for “Chips”, “Gari” and “Fufu”. Cassava processing reduce cyanide content, however extent of reduction varies from one product to another. © 2019 Published by Elsevier B.V. on behalf of African Institute of Mathematical Sciences / Next Einstein Initiative. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Corresponding author. E-mail address: [email protected] (P. Mounjouenpou).

https://doi.org/10.1016/j.sciaf.2019.e00119 2468-2276/© 2019 Published by Elsevier B.V. on behalf of African Institute of Mathematical Sciences / Next Einstein Initiative. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/)

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Introduction Cassava (Manihot esculenta Crantz, Euphorbiaceae) is a staple food consumed worldwide with an estimated 800 million consumers [1]. It is cultivated mainly for its roots and leaves [2,3] and have acceptable production yield in poor soils with low nutrient availability [3]. In Cameroon, cassava root is a very significant food product with annual production estimated at 4.5 million tons, for revenue estimated at 700 million US dollars. Cultivated in all the five agro-ecological zones (approximately 205 0 0 0 ha) of the country, it constitute 80% of edible roots in the forest zone [2–4]. Cassava is the first source of starchy foods in all the Southern half of Cameroon, with 43% of market shares of roots and tubers including 26% for derived products and 17% for fresh root. Each Cameroonian household consumes approximately 75 kg of cassava per year and “Chips”, “Gari” and “Fufu” constituting the most consumed cassava - derived traditional food [5]. Despite the nutritional and commercial benefits, cassava contains toxic substances that limit its utility: the most important being cyanogen which is responsible for the bitter taste of some cassava cultivars name ‘bitter’ [1]. This substance is the result of the enzymatic hydrolysis of molecules such as linamarin, lostaustralin, and acetone cyanohydrin [6,7]. Linamarin being the most important cyanogenic compoundis synthesized in the leaves through N-hydroxylation of valine and isoleucine, and distributed to the roots [8]. This compound is stored in vacuoles of cassava cells and is known to be more concentrated in leaves and root cortex when compared to root parenchyma [9]. Linamarin and linamarase react when cassava cells are mechanically damaged when harvesting, and release acetone cyanohydrin which decomposes to release cyanide [7,8,10], either by hydroxyl nitrile lyase or spontaneously when the pH is greater than 5 [8]. Cyanidric acid is the cause of many health problems which explains the prevalence of several neurological diseases including ataxic neuropathy, cretinism, and xerophthalmia in forest areas where cassava is the staple food [11]. In addition, it causes thyroid disorders, goiter and stunting in children [12]. An irreversible spastic paralysis and tropical ataxic neuropathy termed “konzo” is one of the diseases contracted as a result of acute or chronic exposure to cassava cyanogen [8]. It is due to this high toxicity that the Nigerian Industrial Standards (NIS) and Codex Alimentarius Commission (CAC) recommended the maximal residual cyanogen to be 10 ppm in cassava products [13,14]. Variable toxicity levels of cassava have been reported in literature with total content depending on altitude, geographic location, period of harvesting, crop variety and seasonal conditions. In regards to seasonal conditions, cyanide content of cassava tends to increase during drought periods due to water stress on the plant [15,16] than during raining periods. In Mozambique, more than 55% of fresh sweet roots became extremely toxic during drought periods. Similar observations were recorded in the Democratic Republic of Congo [17] and other countries in Africa [9]. Splittstoesser and Tunya [18] reported that cassava grown in wet areas contain relatively lower amount of cyanide than those grown in arid ones. In general, cassava cultivars contain cyanogenic glucosides although wide variation in the concentration of cyanogen exists among cultivars ranging from 1 to 20 0 0 mg/kg [9,19]. So, in order to be suitable for human consumption, cassava must be processed. Numerous processing techniques are found worldwide which not only increase palatability and extend shelf life, but also decrease cyanogenic potential of cassava [20,21]. These methods consist of different combinations of peeling, chopping, grating, soaking, drying, frying, boiling and fermenting. The most efficient methods being grating and crushing as they remove cyanide due to the intimate contact in the finely-divided wet parenchyma between linamarin and the hydrolyzing enzyme linamarase, which promotes rapid breakdown of linamarin to hydrogen cyanide gas that escapes into the air [9]. This, in combination with wetting, fermentation and drying can reduce cyanide contents up to 99%. The most common agent of cyanide extraction is 0.1 M of phosphoric acid. The main method used to measure cyanide extracted from plant material is spectrophotometry through colored reactions [22,23]. Other methods based on biosensor [24,25], HPLC [26], hydrolyze followed by distillation in a strong basic solution [27] have also been developed. Nevertheless, the picrate paper method coupled with spectrophotometry was reported to be reliable, effective and easy to use [12]. This method was therefore adopted for this study. Taking into consideration cyanide toxicity, and in order to inform on the risks related to the cyanogenic consumption of cassava, this study was aimed at determining the cyanide content of the most consumed varieties of cassava in Cameroon and to evaluate the effects of some traditional processing method on the residual content of processed products. Materials and methods Study site Plant material was collected in the locality of Mbankomo. This site was chosen for its availability in most of the cassava varieties cultivated in Cameroon and also to avoid the influence of agroecology on variability of cyanide content. Plant material, morphological characterization and sampling Twenty (20) cassava cultivars (Manihot esculenta, Crantz) of 12 months old consisting of 10 improved and 10 local varieties were studied. These cultivars were selected because they are the most consumed species. Local names were identified and morphological characterization of each cultivar was described (Table 1). These characteristics were mainly the color of leaves, stems, petioles, skin roots [3,28]. Preparation of parenchyma and cortex was performed by collecting, washing

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Table 1 Morphological description of studied cassava cultivars. Cassava cultivars

Morphologicalcharacterization Codes

Stems

Petioles

Skin roots

Champion 0110 92/0326 961,414 040 95,109 8034 Fonctionnaire 8017 8061 Pola Rouge Beul Madaga Mbida and Mbani Minbourou LeBlanc (Ntanghe) Macoumba Man Mbong NgonEzele OwonaEkani MnomEwondo

A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 L1 L2 L3 L4 L5 L6 L7 L8 L9 L10

White White/green Chestnut + vertical features Shestnut + small features White/green Purple Chestnut Shestnut + small features Chestnut Chestnut White Chestnut Chestnut + vertical features Chestnut White Chestnut White White Chestnut Chestnut + vertical features

Green Green Red Red Red Red Green–yellow Green Yellow–red Red–green Green–yellowish Red Green Green Red blade Red Red–green (face-back) Red Green Red–green

White White White White Red White White Red White White Red White Red Red White Red White White Red White

and peeling each cassava root cultivar. Parenchyma obtained after roots peeling was immediately ground fresh for cyanide quantification while cortex was sundried for 5 days. Preparation of traditional cassava derived products Roots of each cassava variety (improved and local) were processed into “Chips”, “Gari” and “Fufu”, according to the protocol described by USAID/CORAF/SONGHAI [29]. - Preparation of “Chips”: 1 kg of fresh cassava roots of each cultivar was washed, peeled and cut manually into small pieces (approximately 5 cm of length and sun dried for 5 days. - Preparation of “Gari”: 1 kg of fresh cassava roots of each cultivar was washed, peeled and grated manually with a scraper to obtain a fine paste. It was then put into bags and firmly tightened. The bags were pressed to eliminate excess of water. The cassava paste was allowed to dry fermentation for four days. The fermented paste was manually crushed, coarsely sieved, and sun dried for approximately 4 h. The product obtained was roasted on low heat without oil addition. - Preparation of “Fufu”: 1 kg of fresh cassava roots of each cultivar was washed peeled and immersed in water during a period of five days for wet fermentation to occur. After softening, pieces of tuber were manually crushed and the obtained paste was pressed and sun dried for 5 days. Various samples were ground, stored into polyethylene bags and kept at room temperature in the laboratory for further use. Analysis of total cyanide content by the picrate paper method Cyanide contents of samples were determined by the picrate paper method developed by Mburu et al. [12]. This method consisted of placing picrate paper at the entry of a small transparent plastic bottle (5 × 2 cm) containing 1 g of sample and 1 mL of phosphate buffer at pH 8. The bottle was hermetically closed and left to ambient temperature for 24 h. The change in color of picrate paper from yellow to chestnut – red indicated the release of cyanide contained in the sample and its absorption by picrate paper. Thus, the picrate paper was removed, placed in a test tube and 5.0 mL water was added. The absorbance of the solution was measured at 510 nm using a spectrophotometer (brand JENWAY). A calibration curve of absorbance and cyanide content was obtained from potassium cyanide solution (KCN) used as standard at concentrations of 1, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 μg. The regression model was a linear function f(ABS) = ax + b). Statistical analysis Data was analyzed using software SPSS for Windows versus 12.0 (SPSS Inc, Chicago, IT). Samples were described using descriptive analysis. Analysis of variance (ANOVA) was used to show the difference of cyanide content in various cultivars and compare the average contents in their processed products. Values of p < 0.05 were considered statistically significant.

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Fig. 1. Total cyanide contents in the cortex of 20 cassava cultivars.

Results and discussion Cyanide content in the cortex and parenchyma of cassava cultivars Cortex and parenchyma cyanide content of 20 cassava cultivars are illustrated in Fig. 1. The obtained results revealed that cassava cortex contained high cyanide content, compared to cassava parenchyma: cyanide content of cortex varied from 98.43±15.49 ppm to 155.44 ±12.11 ppm and 117.80±11.32 ppm to 210.07 ±9.15 ppm for the improved and local varieties, respectively. Cyanide content of cassava parenchyma ranged from 61.03±9.44 ppm to 118.04±7.16 ppm for improved cultivars and 79.34±3.58 ppm to 181.33±0.48 ppm for local cultivars. Improved varieties suchas 92/0326, 040, 95,109, 8034, 8017, 8061 with production yield of 35 ± 10 tons/ha produced less cyanide content (61.03 to 96.77 ppm) when compared to other improved varieties (Champion, 0110, 961,414, Fonctionnaire with cyanide content that varied from 102.69 to 118.04 ppm). The lower content were obtained with 8017 (61.03±9.45 ppm) and 8034 (61.37±12.06 ppm) cultivars, and the higher content with 0110 (116.43±3.75 ppm) and 961,414 (118.04±7.16 ppm). Similarly, the local varieties such as Pola Rouge Beul, Macoumba, Man Mbong, Ngon Ezele, Owona Ekani, Mnom Ewondo with production yield of 20 ± 10 tons/ha, produced less cyanide content (79. 34 to 97.84 ppm) when compared to other local varieties (Madaga, Mbida and Mbani, Minbourou and Le Blanc (ntanghe) with cyanide content that varied from 104.53 to 181.33 ppm). The local cultivar Ngonezele (79.34±3.58 ppm) presented the lower cyanide content, and Madaga (181.33±0.49 ppm) presented the higher content. Obtained results showed that cyanide content was relatively higher in local cultivars than improved ones; similar results were obtained by Akinfala when studying the nutritive value of whole cassava plant as replacement for maize in the starter diets for broiler chicken [30]. Although, depending of the cassava genotype, some cultivars can have better cyanide potential than others belonging to the same group (local or improved varieties) [22]. The significant differences in the cyanide contents observed with the studied cultivars corroborate those of Adeniji [31], Faezah et al. [32], and Siritunga et al. [33] who linked wide variability of cyanide content in cassava roots to cultivar differences, growing conditions of plant (i.e. soil type, humidity, temperature), maturity of plant, nutritional status of the plants, prevailing seasonal and climatic conditions during the time of harvest as well impact of environmental pollution and application of inorganic fertilizers. Also, significant variations in cyanide content amongst cassava roots of the same cultivar in different agro-ecological zones have been reported [12,32]. In the same way, Ubwa et al. [14] reported that the cyanide content of cultivars varied from one local government to another and also from one farm to another. In the parenchyma of studied samples, cyanide contents were above the WHO recommendations [34]. Given that, high content of cyanide generally lead to high content of starch [35], high cyanide content observed in some improved cultivars as Champion, 0110, 961,414, Fonctionnaire, added to their high yield production (35 ± 10 tons/ha) are factors indicating better economic profitability for farmers. Cardoso et al. [9] and CIAT [19] has reported that the cyanide content of cassava varieties

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Fig. 2. Means cyanide contents of local and improved cassava cultivars parenchyma and some traditional foods.

generally vary between 1 and 20 0 0 ppm [9,19]. The cyanide contents (ranging from 61.03 to 181.33 ppm) of studied cultivars are in accordance with those found in other African producer countries such as Ivory Coast, Benin, Congo, Burundi, Ghana, Nigeria where people have quickly recognized the need to transform cassava into derived products (Chips, Chikwangue, Fufu, Gari, Attieke and Tapioca [36,37] whose profit is usually higher than the fresh roots. Nevertheless, cassava varieties cultivated in Cameroon are less cyanogenic than those of Tanzania (contents varied from 1090 to 1550 ppm [38]), India (average value of 1100 ppm [39]), but are high cyanogenic compare to varieties cultivated in Amazonia (average content of 454 ppm [40]), and in Pacific countries (level range from 13 to 151 mg/kg). Concerning root parts, cassava root cortex contains higher cyanide content when compare to parenchyma. Therefore, peeling of cassava cortex considerably reduces cyanide levels in raw cassava root [14,41]. Siritunga et al. [33] explained that variation in cyanide content in different parts of cassava roots can be due to differential translocation of cyanogenic glycosides and their metabolizing enzymes in the different cellular compartments [42]. Given that cortex is used in animal feed, it is very important to run a periodic check on the level of cortex toxicity in order to make recommendations concerning their incorporation in feed rations [30]. The obtained results made it possible to classify semi-quantitatively roots of different cultivars following the guide of Nambisan [39] who grouped cassava in three classes according to the total cyanide content: cassava is known as "inoffensive" when the cyanide content lies between 0 and 50 ppm, “moderately toxic” for contents between 50 and 100 ppm and “highly toxic” for contents >100 ppm. The studied cultivars could be classified into 2 classes: - Moderately toxic cassava: Pola Rouge Beul, Macoumba, Man Mbong, NgonEzele, OwonaEkani,MnomEwondo, 92/0326, 040, 95,109, 8034, 8017 and 8061. - Highly toxic cassava: Madaga, Mbida and Mbani, Minbourou, Le Blanc (ntanghe), Champion, 0110, 961,414 and Fonctionnaire. Morphological characterization and cyanide content of cassava cultivars Results showed a wide variation existing among cassava leaf, stem and root of the studied cultivars. There is not clear link between morphological characteristic and cyanide content: varieties such as Minbourou, Le Blanc (Ntanghe), Ngon Ezele and Owona Ekani had the same morphological characteristics concerning the root, stems and petioles color and were, respectively, grouped into different classes: high and low cyanide content. However, literature has established a significant correlation between cyanide potential of cassava roots and leaves. The cyanide content was higher in younger leaves compared to older ones, suggesting that cyanide potential of roots drops as plant ages [22,43,44]. These characteristics, which include leaf morphology, stem color, branching habit and storage root shape and color, could not be clearly link to cyanide content, but may influence cassava yield and resistance to insect pests and diseases [45]. A proper understanding of these variations in plant characteristics would assist the selection of cassava types with the desired traits and will contribute to improved crop establishment and increased yields. Effect of processing on the cyanide content of cassava cultivars Fig. 2 illustrates means of cyanide contents of cassava parenchyma and that of traditional processed products, from all 20 cassava cultivars (improved and local). The evaluation of cyanide content of cassava cultivars showed that the toxicity of cassava dropped significantly with processing and was dependent on the operating process used. After cutting of the parenchyma and sun drying for five days (Chips), the residual cyanide content of Chips reduced by 46.71% for improved and 48.37% for local cultivars. This decrease was more significant when the parenchyma underwent a dry fermentation (white

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gari) with toxicity reduction of 81.13% and 79.14%, respectively, for improved and local cultivars. "Fufu" which resulted from a wet fermentation showed highest reduction of cyanide content by 89.42% and 94.08% for local and improved cultivars respectively. The processing of “Chips” which primarily involved peeling, cutting and drying fairly contributed to reduce cassava toxicity (47%). However, these results differed from those of Dufour [40] who reported cyanide content reduction of up to 80% by sun drying. According to this author, the maximum degree of cyanide reduction of 75.2% was observed with bitter white cassava roots where cyanide content was between 500 and 667 ppm. At the same time, Montagnac et al. [41] obtained detoxification rate of 71.3% of initial value by peeling and grating. The operations of peeling and parenchyma skin grating were the first substantial step in the process of lowering cassava toxicity because cyanogenic glycosides are distributed in large amounts in the skin [41]. However, it was noted that the cultivars exhibited various profiles of cyanogen elimination after sundrying. This could be due to the fact of the cassava sections which did not have the same size, more especially as it has been reported that when the cassava sections are small and spread out finely for drying, the cyanide escapes more easily into the air [41,46]. Sun drying of cut out chunks of parenchyma seemed to be a less effective means in the release of cyanide because it does not allow intimate contact between the hydrolysis enzyme (linamarase) and its substrate (linamarin) which promotes rapid breakdown of linamarin to hydrogen cyanide gas that escapes into the air. Parenchyma is generally cut longitudinally and much of plant cells remain intact, with the linamarin imprisoned in the cell, while the linamarase is localized on the cellular wall [7,8,10]. When sun drying is insufficient, the enzyme can be denatured or trapped in the matrix of the dried cassava, preventing the conversion of cyanogenic glycosides into cyanide which is volatile [46]. This process facilitated detoxification indicating that cutting cassava parenchyma in slight sections for one night would allow a good detoxification of the foodstuffs [47]. “Gari” is a traditional cassava processed product. The mean residual cyanide content of Gari samples was about 20 ppm and was superior to the safety level of 10 ppm [34] and Codex STAN176-1989 recommended total cyanide content of 2 mg/kg in “Gari”. Cyanide contents of the studied cassava samples remained lower when compared to the results of Djoulde et al. [48] on “Gari” coming from 25 localities of Cameroon (114±16 ppm), and the total cyanide contents of “Gari” samples sold in Port-Harcourt markets in Nigeria which reach the value of 30 ppm [49]. It is worth noting that these studies indicated no specification on the cassava cultivar used. Due to the increasing demand of “gari” in local markets, producers often shorten certain steps in the production process [47,49,50,51]. Processing of “Gari” involves the following operating units: peeling, grating, dry fermentation, drying and roasting are very effective in the release of cyanide because of the intimate contact between the linamarin and the hydrolysis enzyme (linamarase) in the wet and finely ground parenchyma. This intimate contact promotes rapid break down of linamarin to hydrogen cyanide gas that escapes into the air. This process contributed to reduce the toxicity to approximately 80% irrespective of the cultivar. It is important to note that dry fermentation is less efficient than wet fermentation [52,53]. Yeoh and Sun [47] and Agbor-Egbe and Mbome [54] reported better detoxification rate (reaching approximately 95%) by peeling and grating of the root’s internal structure, followed by fermentation, drying and roasting. Generally, white Gari has higher cyanide content when compared to yellow Gari. Chiedozie and Paul [55] reported that the addition of palm oil in “Gari” processing caused reduction in cyanide content. However, the relative low elimination rate obtained from “Gari” processing could be explained by the environmental and fermentation conditions. Cassava transformation into «Fufu» resulted in residual cyanide content of 9.8 ± 6.95 ppm and 6.54±7.22 ppm for improved and local cultivars respectively. These values are in conformity with WHO legislation [34] who recommends the level of safety at 10 ppm. Cyanide elimination rates of the present study was similar to those reported by Iwuoha et al. [56] who showed that soaking for five to six days at a pH of 4 to 4.5 reduced the cyanide up to 94.7%. Agbor-Egbe and Mbome [54] obtained a reduction of cyanide content of 90% after soaking for 72 h. Soaked Cassava increases the process of cyanide elimination because the roots which are completely submerged in water can support bacterial growth allowing the production of linamarase [57]. Moreover, since cyanide is water soluble and volatile, the operations of soaking, followed by manual crushing and then sun drying could have resulted in the lowest cyanide content observed in “Fufu” [39], although “Fufu” of higher cyanide contents have been sampled in certain villages of Cameroon and markets of Nigeria [48,49]. This was usually due to high demand in local markets, causing the producers to neglect the various step of fermentation, which according to them, was regarded as a waste of time with little effect on cassava detoxification [51]. However, a method of standardized transformation of bitter cassava roots with contents of cyanide > 400 ppm, consisting of peeling, scraping of the external layer of the parenchyma, fermentation and oven drying at 60 °C was tested successfully in Burundi [58]. Furthermore, Toummou et al. [59] reported in comparing the effect of traditional and improved cassava processing in cassava derived products that the concentration of cyanogenic compounds in chips of Cassava from improved processing (shucking + fermentation + drying) obtained after grating of cassava root without skin is significantly lower than the levels in traditional processing. Conclusion The objectives of this work were to determine cyanide content of 20 main cassava varieties collected in the locality of Ongot in Cameroon and evaluate the impact of traditional processing of cassava-derived foodstuffs on this content. Accordingly, cassava varieties of this locality can thus be classified as “moderately” to “Highly” toxic. Cassava varieties Pola Rouge Beul, Macoumba, Man Mbong, Ngon Ezele, Owona Ekani, Mnom Ewondo, 92/0326, 040, 95,109, 8034, 8017, 8061 are mod-

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erately toxic and can be used directly for the humans consumption after peeling, scraping the skin and boiling. Madaga, Mbida and Mbani, Minbourou, Le Blanc (ntanghe), Champion, 0110, 961,414 and Fonctionnaire are highly toxic and can be used for flour, starch and ethanol processed. This study highlighted that traditional processing reduce cyanide content of products and that elimination rate depended on the process involved: Fufu (91%), Gari (80%) and Chips (47%). Wet fermentation is thus an effective way of detoxifying cassava. The level of detoxification with Chips processing was not that discounted. Thus, efforts remain to be made with Chips which presented the lowest levels of cyanide detoxification and furthermore with Gari to reach level recommended by the Codex Alimentarius (2 ppm). Reduction in the cyanogenic potential of cassava could be realize during each processing step, resulting in an almost detoxification of the product. While all methods abate the cyanide levels, the effectiveness of these methods depend on the processing steps and the sequence used and is often time-dependent. Moreover, based on the results presented here, in order to increase detoxification, future investigations are needed to scrape the skin of the parenchyma after peeling before continuing the transformation operations, since it was showed that cyanogenic glycosides are distributed in large amounts in its skin. Finally, improved varieties 92/0326, 040, 95,109, 8034, 8017, 8061 can be recommended to farmers due to their high production yield and less cyanide content. Declaration of Competing Interest Authors declare that they have no conflicts of interest. CRediT authorship contribution statement Youchahou Njankouo Ndam: Formal analysis, Investigation, Writing - original draft. Pauline Mounjouenpou: Conceptualization, Methodology, Writing - review & editing, Supervision. Germain Kansci: Writing - review & editing. Marie Josiane Kenfack: Formal analysis, Investigation, Writing - original draft. Merlène Priscile Fotso Meguia: Investigation, Writing - original draft. Nina Sophie Natacha Ngono Eyenga: Investigation, Writing - original draft. Maximilienne Mikhaïl Akhobakoh: Investigation, Writing - original draft. Ascenssion Nyegue: Writing - review & editing. Acknowledgments The authors are thankful to the Institute of the Agricultural Research for Development (IRAD, NkolbissonYaoundé) for plant material providing and identification of varieties. References [1] FAO (20 0 0) (Food and Agriculture Organization). Défendre la cause du manioc. http://www.fao.org/nouvelle/20 0 0/0 0 0405-f.htm. [2] A.F. Ngome, M.F.C. Amougou, P.I. Tata, S.A. Ndindeng, M.Y.C. Mfopou, L.D. Mapiemfu, T.S. Njeudeng, Effects of cassava cultivation on soil quality indicators in the humid forest of Cameroon, Greener J. Agric. Sci. 3 (2013) 451–457. [3] N.C. Temegne, B.I. Mouafor, A.F. 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