From cassava to gari: mapping of quality characteristics and end-user preferences in Cameroon and Nigeria

User’s preferences of cassava and cassava products along the value chain are supported by specific root quality characteristics that can be linked to root traits. Therefore, providing an evidence base of user preferred characteristics along the value chain can help in the functional choice of cassava varieties. In this respect, the present paper presents the results from focus group discussions and individual interviews on user preferred quality characteristics of raw cassava roots and the derived product, gari, – one of the major cassava products in Sub-Saharan Africa – in major production and consumption areas of Cameroon and Nigeria. Choice of cassava varieties for farming is mainly determined by the multiple end uses of the roots, their agricultural yield and the processing determinants of roots that support their major high-quality characteristics: size, density, low water content, maturity, colour and safety. Processing of cassava roots into gari goes through different technological variants leading to a gari whose high-quality characteristics are dryness, colour, shiny/attractive appearance, uniform granules and taste. Eba, the major consumption form of gari in Cameroon and Nigeria, is mainly characterised by its textural properties: smoothness, firmness, stickiness, elasticity and mouldability. Recommendations are made, suggesting that breeding will have to start evaluating cassava clones for brightness/shininess, as well as textural properties such as mouldability and elasticity of cassava food products, for the purpose of supporting decision-making by breeders and the development of high-throughput selection methods of cassava varieties. Women are identified as important beneficiaries of such initiatives giving their disadvantaged position and their prominent role in cassava processing and marketing of gari.     

Role of dewatering and roasting parameters in the quality of handmade gari

Gari is a common cassava precooked dried semolina in sub-Saharan Africa. Our study investigated the role of process parameters and mash water content on gari quality during traditional roasting stage. The statistical analysis for eight quality criteria revealed that gari quality is highly influenced by the process parameters adopted by the operators. To emphasise the twin impact of roasting parameters and mash water content, different mashes with varying water content were roasted leading to different adjustments of the roasting conditions according to the operators. When the variability of the water content becomes greater, a greater variability in the final quality of the obtained garis was observed between operators (lightness, swelling capacity, starch content, texture and colour). These results suggest that technological improvements to the gari process could be achieved by appropriate management of the roasting and dewatering parameters.     

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

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

Mechanism of cyanogen reduction in cassava roots during cooking

The cyanogen elimination profile during cooking of cassava roots was investigated and correlated with the changes in cyanogenic β-glucosidase (GLase) activity monitored at close intervals in the cook water and root. Cyanogenic β-glucosidase (GLase) activity was detected in the cook water within 5 min of starting cooking. Whilst significant decrease in the GLase activity was noticed in cook water and root within 15 and 10 min, respectively, for varieties M4 and H165, H1687 GLase activity decreased tremendously only at 20 and 15 min in the cook water and root, respectively. There was no GLase activity in cook water after the 30 min pre-boiling phase while GLase activity was present in the roots even after 60 min of cooking. The decrease in GLase activity at 15–20 min pre-boiling phase led to accumulation of cyanogens in cook water. The cyanogen fractions (glucosidic and non-glucosidic) increased significantly with cooking in the cook water in the case of varieties M4 and H165 while their levels were almost static throughout the post-boiling phase for H1687. The amount of HCN escaping through steam did not bear a direct relationship with the initial cyanogen content in cassava roots. Although free cyanogen is highly volatile, all of it does not escape through steam and a certain quantity appears to be stabilised in the cook water. ©1997 SCI     

Quality of cassava foods in Sierra Leone

Gari and foofoo (fermented cassava foods) were purchased in the Freetown markets of Sierra Leone and analysed for factors associated with quality. Sellers were generally knowledgable about the source of the products which all originated from the country areas outside Freetown. The mean cyanide contents were higher (8.6 mg kg^?1 DM for gari and 28.2 mg kg^?1 DM for foofoo) than the amounts suggested by the Codex specification and, because of the distribution of the values around the mean, some samples necessarily contained unacceptable amounts of cyanide. Cyanogens were present as the cyanohydrin or as free cyanide; no glucoside was detected. Microbiological analysis of the samples showed high counts for total organisms, fungi and Enterobacteriaceae (10⁶–10⁷ g^?1). The mean water content of gari was 119 g kg^?1 which falls within the recommended limit of 120 g kg^?1 but again, due to the distribution of values around the mean, some samples had considerably higher water contents than that limit. Titratable acidity and pH were measured and the mean pH values were 4.18 for foofoo and 4.55 for gari. The particle size and swelling power of gari samples were also measured as these relate to consumer acceptance. The data show the quality of current cassava foods marketed in a major urban centre in Sierra Leone. As centralised processing develops, improvements can be made to those quality parameters which have been identified as important.     

Identification of critical versus robust processing unit operations determining the physical and biochemical properties of cassava-based semolina (gari)

The gari-making process involves several unit operations (U.O.), some of which strongly influence the quality of the end product. Two contrasting process scales (laboratory-scale vs conventional) were compared in order to identify which U.O. were affected by the change of scale. U.O. that changed end-product characteristics depending on process scale were deemed critical; whereas U.O. that resulted in similar characteristics were deemed robust. The classification depended on quality attributes considered: rasping and roasting were critical for physical properties, in particular particle size which ranged from 0.44 to 0.89 mm between the two process scales; and robust for biochemical properties. In contrast, fermentation and pressing were critical for biochemical properties such as lactic acid content (0.93–1.88 g/100 g dry matter after pressing), which influences the perception of flavour, and robust for physical properties. This classification between critical and robust operations help quality control of gari, by pinpointing which U.O. control specific quality characteristics.     

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.     

An improved microdiffusion method with solid-phase detection for the determination of total cyanogens in fresh cassava. Comparison to the method of Cooke (1978)

A microdiffusion method with solid-phase detection for the determination of total cyanogens (=cyanogenic potential, CNp) in fresh cassava roots was developed and evaluated against the classical spectrophotometric method of Cooke (J Sci Food Agric 29 (1978) 345–352). Using seven different cassava cultivars, a significant difference (approx 15%) in the determined CNp was observed only for one of these. The new method offers several advantages over the earlier described spectrophotometric methods. Filtration of homogenates is not necessary, neither is cooling nor heating. The developed colour is stable on the reaction sheet, so that levels may be measured immediately or when appropriate, and be filed for documentation purposes. Further the solid-phase reaction may be measured in different ways according to the instrumentation available, ie reflectometry as used in this study, or absorption of transmitted light using a TLC-densitometer or a microplate reader. The amount of enzyme (linamarase) used per analysis is lower than for the spectrophotometric assays, giving economic advantages to the present assay. In addition to the extract, only three solutions are used when performing the assay, ie the buffer, the substrate solution for standards, and the enzyme solution. The assay may be run either according to a ‘slow’ overnight protocol or to a ‘fast’ protocol at 40°C. © 1998 SCI.     

Processing factors affecting the osmotic dehydration of diced green peppers

A 2^5–2 fractional factorial design was used to investigate the effect of salt (2–10%), sorbitol (0–10%) concentration, agitation (0–80 r.p.m.), tissue to solution ratio (1:3 to 1:6) and temperature (20–50 °C) on weight loss, solids gain, salt and sorbitol uptake, water activity, tissue brix and solution brix, during osmotic dehydration (OD) of diced green peppers. Results showed that salt and sorbitol concentration were the most significant factors. In the first half hour of the osmotic process, salt and sorbitol significantly increased weight loss, solids gain and tissue brix, and decreased water activity. Temperature was also a significant factor. It increased weight loss during the first 2 h of the process, and decreased water activity after 20 h of osmosis. Agitation and tissue to solution ratio were less important.     

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     

全麦粉营养及加工过程中影响血糖的主要因素分析

全麦粉中由于含有更为丰富的维生素、矿物质、脂肪酸、膳食纤维和植物化学物质等,通常被认为比普通精制小麦粉更富有营养,以全麦制品代替精制主食有助于降低非传染性疾病的发生风险。随着世界范围内糖尿病患病率不断上升,大部分人群都可以从低血糖生成指数（Glycemic index,GI）食物中受益。然而,小麦的品种、颗粒大小等因素均会影响全麦制品的GI值以及食用全麦制品后的血糖反应,主要与原料及加工过程中淀粉结构的变化有关。因此,在保证全麦制品感官、食用品质的基础上,如何进一步降低全麦制品的GI值成为有效提升全麦制品营养功效品质的重要问题。本文综述了国内外关于全麦营养及加工方式对消化特性的影响研究进展,以期为全麦粉及其制品的研究和应用提供参考。     

木薯生料发酵制备燃料乙醇的工艺条件研究

试验对木薯生料发酵制备乙醇的工艺条件进行了优化研究,对影响发酵过程的生料淀粉水解酶用量、料液比、发酵初始pH和发酵温度四个因素在单因素试验的基础上进行了正交试验优化,得到最佳发酵条件为生料水解酶用量4 mL/kg,料液比1∶3.5,初始pH4.5,发酵温度37℃,根据优化条件进行验证试验,总糖消耗率与淀粉利用率分别为83.29%和79.80%,但与低温水解发酵工艺相比尚有一段距离。     

营养学在肉制品加工领域的应用

将营养学与肉制品的加工设计相结合,从不同人群的营养需求出发,研发出适合各类人群的肉制品,可丰富肉制品的品种,提升肉制品产品的针对性与适用性。我国开始在预包装食品中实施营养食品标签管理规范,标志着我国食品产业的监管从食品安全向食品安全与食品营养并重的方向转移,它符合全球食品业和消费者追求营养,追求健康的潮流,这同时也给肉制品加工带来了机遇与挑战。     

Evaluation,modification and comparison of two rapid assays for cyanogens in cassava

Two rapid semi-quantitative assays for total cyanogens in cassava were evaluated. These were the well-known rapid picrate paper test, and a recently proposed rapid paper test involving the reagent tetra base (TB, 4,4′- methylenebis-(N, N-dimethylaniline)). A precise colorimetric assay was used as a control in the evaluative work. After primary evaluation, both assay methods underwent some modification regarding the interpretation of sample scores. As a result, the reliability of the picrate assay was greatly improved. The TB assay was modified in the interests of safety. Evaluation of this assay over a range of temperatures between 20 and 35°C showed no significant temperature effects upon performance when the new scoring interpretation system was used. The level of endogenous linamarase activity in the sample was found to be an influential factor in rapid assay performance. In a series of comparative trials in three distinct ecosystems, the newly modified picrate assay produced correct results in 68% of cases. This compared with 66% of results correct in the TB assay. It was observed that the TB assay performed more reliably with low cyanogen samples, whilst the picrate assay was more reliable with intermediate cyanogen samples.     

织物防紫外线的影响因素

通过正交试验设计的方法来确定试验方案,对具有不同结构参数的织物的紫外线透过率、透湿量、透气量进行测试,并对试验结果分别进行方差分析和回归分析,得出了既能保证织物防紫外线性能好,又能满足织物透湿性、透气性能也较好的影响因素的主次顺序,可为产品设计者开发出更好的防紫外线产品提供参考.     

乳蛋白质加工过程中影响因素的探讨

介绍了蛋白质是乳中最重要的营养成分,牛乳中蛋白质含量为3．3％左右。阐述了牛乳的加热、原料乳的酸度、异常乳、均质处理及微生物对乳蛋白质的影响。在加工过程中,通过采取相应的措施使牛乳蛋白不受破坏并保持优良的品质,从而在人体内得到高效率吸收。     

营养型桑葚酒加工工艺的研究

以新鲜桑葚果实为原料,果肉破碎加入0.04%果胶酶取汁后,加入适量蜂蜜并接入法国KD活性干酵母0.3g/L,18℃~20℃下发酵12d后,陈酿3~4个月,经澄清等工艺处理,可得到含糖量高,酒精度较低,口味酸甜适宜的营养型桑葚酒。     

The effects of variety,drying procedure,fineness of grinding and dietary inclusion level on the bioavailability of Cassava (Manihot esculenta crantz) starch

The bioavailability of raw cassava starch from dried, whole roots, as affected by a number of variables, both inherent and processing-induced, was determined in a series of feeding trials using the rat as a test animal. Apparent starch digestibility was in excess of 99% and was unaffected by cassava variety, cyanide content, drying process, fineness of grinding, dietary inclusion level (up to 50% of the diet) and age of the animal. A high level of residual cyanide (406.6 mg kg^?1 dried cassava chips) reduced feed intake and weight gain. Since the floor-drying procedure, whilst effectively reducing the cyanide to an acceptable level, was without effect on the digestibility of cassava starch, it is recommended that this process be adopted for drying high cyanide cultivars of cassava destined for the animal feed market. This will allow cassava to be incorporated in the diet at a higher inclusion level with no undesirable effects on animal performance.     

织物悬垂性影响因素分析

织物面料制成服装或窗帘等家居用品后，其力学性能构成悬垂性。文章利用实验测试的方法对织物的结构参数和机械性能进行研究，分析织物结构参数和机械性能与悬垂性之间的关系。结果表明，织物的断裂伸长、纬向弯曲刚度和活络率与悬垂性能之间存在密切的关系，而织物厚度和质量对悬垂性的影响不显著。