State of Knowledge Report

State of Knowledge on Quality Traits of Cassava: Fresh & Boiled & Pounded

Cassava Namulonge, December 2018

Ephraim NUWAMANYA, NaCRRI, Kampala, Uganda Enock WEMBABAZI, NaCRRI, Kampala, Uganda

Anna Ritah NANYONJO, NaCRRI, Kampala, Uganda William ESUMA, NaCRRI, Kampala, Uganda

Robert KAWUKI SSEZI, NaCRRI, Kampala, Uganda

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This report has been written in the framework of RTBfoods project.

To be cited as:

Ephraim NUWAMANYA, Enock WEMBABAZI, Anna Ritah NANYONJO, William ESUMA, Robert KAWUKI SSEZI. 2018. State of Knowledge on Quality Traits of Cassava: Fresh & Boiled & Pounded Cassava. Kampala (Uganda). RTBfoods Project Report, 12 p.

Image cover page © Dufour D. for RTBfoods.

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CONTENTS

1 Introduction .................................................................................................................................. 3

2 Composition and structure of raw material ................................................................................... 4

2.1 Composition .......................................................................................................................... 4

2.2 Structure ............................................................................................................................... 6

3 Processing condition .................................................................................................................... 6

4 Sensory analysis and consumer preference ................................................................................. 7

4.1 Method .................................................................................................................................. 7

4.2 Results .................................................................................................................................. 7

5 Product characterization and relationship with sensory evaluation ............................................... 8

5.1 Evolution of composition and structure with processing ........................................................ 8

5.2 Instrumental Texture assessment and relationship with sensory evaluation .......................... 9

5.3 Relationship between composition and sensory evaluation ................................................... 9

6 References ................................................................................................................................. 10

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1 INTRODUCTION For this literature review, more than 20 articles and other documents related to fresh cassava roots and the product profile cooked cassava in Uganda and Africa in general, were analyzed. These articles cover topics ranging from the chemical composition of fresh cassava roots, cyanogenesis in cassava, utilization of fresh cassava in industry and others. A number of studies reviewed have also focused on understanding the effects of bio fortification on cassava and comparing the composition and nutritional relevance of the bio fortified and non-bio-fortified counterparts (Ayetigbo et al., 2018). Other articles have focused on the effect of PPD on the characteristics of the root with emphasis on the disastrous effects of PPD on root sensory and nutritional quality (Muyinza et al., 2016). In some cases, the published material describe the physicochemical characteristics of clones from different breeding populations and breeding targets that would allow the breeder to select the best performing clones (Nuwamanya et al., 2010). Location specific studies relating to boiled cassava have also been carried out (Oloya et al., 2013). The studies describe the comparative advantages of improved varieties in respect to the local varieties in relation to nutrition and farmer acceptability properties. In addition, some of these studies are mainly focusing on specific targeting of varieties to industrial exploitation given the different compositional attributes. Therefore at the moment, most of the research findings are focused on understanding the composition different cassava varieties.

Boiled cassava is mainly consumed in the East, Central and southern parts of Africa. It is the main form of consumption in East African countries of Uganda, Kenya, Tanzania, Rwanda, Burundi, and South Sudan. In addition, specific communities in countries like Democratic Republic of Congo, and central African Republic (CAR) also boil and eat fresh cassava. In most of these countries, sweet cassava varieties with considerably low cyanide contents are the most preferred. However, in the very countries, varieties with high cyanide contents are processed through fermentation to produce low cyanide processed flour products. New products from fresh cassava are also common such as fried cassava chips which also depend on cassava roots with similar properties as those of boiled cassava.

While little work has been undertaken in understanding the boiled cassava profiles and the composition of fresh/raw and boiled roots, there is need to further understand the effect of effect of boiling as a simple processing technique on cassava. The effect of nutrient increase including biofortification on boiled products of cassava need also to be understood. This is important for the release of cassava varieties that meet the acceptance criteria for cassava. In addition, sensory and acceptability studies of the boiled cassava products have not been carried out extensively. There is a very big gap in efforts geared towards providing an ideal cassava for the boiled root consumers. This is clearly observed in the poor adoption rates of some of the varieties being developed by breeding programs today. It can also be related to why, despite high yielding and disease resistant varieties availed; farmers still prefer their local varieties.

Another important area for consideration is the understanding and identification of processing traits of cassava. Such traits need to be harmonised with local processing procedures especially where farmers use primary processing techniques such as boiling and pounding cassava. Root composition has a significant on such products and hence affects their utilisation. Cassava with higher fiber contents for example are not good for processing the boiled and pounded cassava product common in central and western Uganda known as Mugunu.

In addition, the anti-nutritional composition of cassava roots has not been duly elucidated as to inform the utilisation of boiled cassava products that are safe for consumption. While studies on cyanide have been extensive, other anti-nutritional factors have not been duly studied with little known about the effects of such on the acceptability of boiled cassava. In addition, no specific studies have been undertaken to identify the many anti-nutrients in cassava and how they are related to the primary components of the cassava root such as starch.

Finally studies are required that compare the root composition and the nutritional relevance of the root for a certain target population. In Uganda for example, cassava has been blamed for leading to malnutritional disorders related to protein and vitamin deficiencies. In other cases, negative effects on health especially of children have been registered in popular cassava consuming communities. Thus

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supplementation strategies in such cases could be important much as the extent of such supplementations are not clear at the moment.

2 COMPOSITION AND STRUCTURE OF RAW MATERIAL

2.1 Composition Please provide, and briefly comment, a comprehensive table ofraw material composition indicating methods used and references

Product Raw material composition Methods used

+references Cassava (fresh, boiled)

• Cassava fresh roots harvested from different varieties produce differing boiled root products with different acceptability levels.

• Cassava fresh root composition: Fresh roots of cassava contain about 150 Kcal of energy with Dry matter contents ranging from 15-40% depending on the variety. On the other hand, the roots have specific moisture contents exceeding 60% depending on the variety, agroecology, and harvest time and rainfall distribution. In addition, cassava roots have low protein (0.3-5.0%) and lipids (0-0.5%) contents compared to the high percentage of carbohydrates (25-35%) in the fresh roots. The dietary fiber ranges from 0.5-4.0% while the ash content ranges from 0.5-1.8%. The roots also contain a number of vitamins including thiamine, riboflavin, niacin, ascorbic acid, and vitamin A. The bio fortified varieties have vitamin A contents ranging 5-15ppm on fresh basis. The mineral content of the root is low and the main minerals in the root include Iron, Potassium, Magnesium, Copper, Zinc, Sodium and Manganese. In addition, cassava also carries anti nutrients especially cyanide which ranges from about 10-1000ppm (wet basis) depending on the variety

• Dry matter content (DMC) is determined using the oven-dry method as described by (Nuwamanya et al., 2010, 2011), with a slight modification in temperature. Four quarters from the previously sectioned roots are cut into thin slices using a knife. Triplicates of 200g are weighed off using an electronic weighing scale (GraviTekTM, China) and dried in an air-forced oven (Leader engineering, Cheshire, England) at 60oC1 until constant weight or for an extended period of 24-28 hours. The DMC is expressed as a percentage of fresh root weight as:

• "DMC " (" %" )" = " "Dry sample weight" /"Fresh sample weight" " ×100"

• Determination of cyanide content: Cyanide content is determined using the method of Howard et al., 1994. Fifty grams (50g) of fresh cassava root is extracted by 160 ml of 1M orthophosphoric acid by homogenization

Dry matter and moisture determination by Oven method. Nuwamanya et al., 2010, 2011.

Energy determination by bomb calorimeter.(Henken et al., 1986)

Protein determination by Kjehdahl method (Sweeney et al., 1989) (,

Ash determination by combustion in a furnace at 5500C method, and mineral composition determination by (Charles et al., 2005, Montagnac et al., 2009)

1 These drying conditions are required due to the conditions around NaCRRI, e.g. power outages at night.

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using a waring blender (Waring, New Hartford, USA). The homogenate is centrifuged for 30 minutes at 12000 rpm, 4oC using a refrigerated centrifuge (Hermle Z300K, Wehingen, Germany). The supernatant containing the extracted linamarin (0.1 ml) is buffered with 0.4 ml of phosphate buffer (pH 7.0) and hydrolysed to cyanide using linamarase enzyme. The released cyanide is chlorinated using 0.1 ml of 0.4 % (w/v) Chloramine T solution, followed by reaction with 0.6 ml of 0.2M Isonicotinic/ barbituric acid solution (pH 6.5). Cyanide is quantified spectrophotometrically (Biowave ii+, Cambridge, England) by measuring absorbance of the colored complex at a wave length of 605 nm, against standard potassium cyanide. The cyanide content is expressed in parts per million (ppm).

• Cassava total carotenoid determination: To determine carotenoid retention, total carotenoid content is analysed both on fresh and processed samples, using an icheckTM carotene kit (BioAnalyt Laboratory, Germany) (www.bioanalyt.com). Fresh samples are analysed within 4 hours of harvest, in a dark room, to minimize losses resulting from photo oxidation. Opposite quarters from the previously sectioned roots are selected chopped into small pieces and pooled. About 5 g of the finely chopped root samples are pounded and ground into a smooth and fine paste using a mortar and pestle. To aid grinding of the sample, 20 ml of distilled water are added gradually and the resulting solution is transferred into a 50 ml calibrated tube. The tube content is shaken thoroughly and 0.4 ml of the solution is injected into the iExTM CAROTENE vial using the syringe and needle provided with the kit. Vials are placed on a solid surface for approximately 5 min, shaken again and allowed to stand until two solution phases appear inside the vial: a clear upper phase and a turbid lower phase. At this point, the absorbance of the vial content (the upper solution phase) is measured at a wavelength of 450 nm using the iCheckTM CAROTENE device. Total carotenoids content is calculated as:

TCC (Ppm)= WsVs

× A

Where Ws = weight of sample, Vs = volume of solution transferred to the tube and A = absorbance of the iExTM CAROTENE vial contents. The processed samples are treated in a similar manner for carotenoids content, and percentage retention calculated using the formula described by Chavez et al., (2007). % retention = c1× wb

c2× wb' ×100 where;

𝑐𝑐1= carotenoids content in processed roots,𝑐𝑐2 = carotenoids content in fresh roots,𝑤𝑤𝑏𝑏 = weight of processed roots, 𝑤𝑤𝑏𝑏′ = weight of unprocessed roots.

Modified methods for DM Benesi et al., 2005

Modified Bradbury, 1994 methods commonly used

I Check method used (www. bioanalyt.com)

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2.2 Structure Please provide, and briefly describe and comment, pictures of the structure of raw material indicating methods used and references

Picture Description and references

Harvested roots. Sliced roots Waste peels

3 PROCESSING CONDITION Cassava roots are picked fresh from the garden and treated with different processing methods. The methods have been developed at NaCRRI for routine handling of samples and are modified depending on the intended use of the sample.

At least four mature roots are obtained from each clone depending on the size and the type of analysis to be carried out. These are peeled, washed under running water and wiped with a paper towel to dry off the water. Roots from each clone are bulked together and each root is sectioned longitudinally into four quarters. Opposite quarters from roots of like clones were again bulked together and randomly selected for each of the analyses, including analyses on the fresh samples.

Samples for making flour, samples are dried in a forced air oven (Leader engineering, Cheshire, England) at 60oC until uniform weight. Thereafter, they are milled into flour using a laboratory mill (Christy turner, Ipswich, England).

The samples for steaming are wrapped in perforated aluminium foil (to avoid direct contact with water) and cooked in water at a temperature of 90°C depending on the agreed processing time.

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4 SENSORY ANALYSIS AND CONSUMER PREFERENCE

4.1 Method Sensory evaluation of the samples is carried out by a panel of atleast 15 panelists, using a 9-point hedonic scale (Yeh et al., 1998).

• 1 = Dislike extremely, 2 = Dislike very much, 3 = Dislike moderately, 4 = Dislike slightly, 5 = Neither like nor dislike, 6 = Like slightly, 7 = Like moderately, 8 = Like very much and 9 = Like extremely.

The sensory panel is composed of males and females, selected from different research programs from the National Crops Resources Research Institute (NaCRRI)-Uganda. The panel is trained in order to increase/enhance their ability to discriminate and describe product differences and their ability to discriminate and scale attribute intensity for at least three times prior to the evaluation. The samples are randomly coded, including the control sample (i.e. a known variety already released1) and are presented individually to the panelists, on coded serving plates. Each panelist is provided with two liters of distilled water for rinsing the mouth after tasting each sample. The study is blinded in a way that every panelist is only aware of the processing method but not the identity of the cassava clone to evaluate.

• Attributes score include appearance, aroma, taste, mouth feel, mealiness and overall acceptability.

4.2 Results Discussion of results on consumer of boiled cassava

A number of studies carried out have identified cassava cyanogenic potential and boiled root mealiness as two of the most important traits that influence the consumption of fresh cassava. Bakayoko et al. (2009) showed that improved cassava varieties have low cyanogenic potential ranging between 10-30 mg HCN/kg fresh root and had a mealiness index between 1.7-2.0 using a mealiness scale of 1-3 where 3 is very mealy and 1 is fairly mealy. The other sensory parameter determined in this study was melting point which is an equivalent of softness/cooking, where a tooth pick was used to determine the softness of root and hence cooking . In this study, the time for determining such parameter was 30 minutes in boiling water. While other studies addressing a similar subject have been conducted, most of them are related to the use of products of cassava roots and in most instances flour.

Quality criteria for decision making on boiled cassava

In the different studies reviewed, the basic criteria for determining the quality of boiled cassava is the cyanide content. However, starch quality and composition has also been identified as it affects other quality characteristics such as texture while degradation of cell components such as pectin degradation has been shown to improve mealiness. In addition, other nutritional components such as the color and softness of the cassava roots have been identified in such a case (Bechoff et al., 2017). This implies that important genetic factors are responsible for determining the quality of boiled roots. However, measuring such traits is still a challenge that needs to be addressed.

Diversity of boiled cassava in relation to sensory analysis (range of variation of attributes)

Indeed some studies have provided clues on how such traits can be measured. One classical study in Benin (Padonou et al., 2005) showed that resistance to penetration could be used to

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describe boiled root mealiness or friability. The study also shows the possibility of determining mealiness from understanding the starch properties, but also other components (pectins, cell wall materials).

5 PRODUCT CHARACTERIZATION AND RELATIONSHIP WITH SENSORY EVALUATION

5.1 Evolution of composition and structure with processing

It has been reported that cassava raw tissue shows decreasing or constant peak yield force values as depending on the age of the root. It has been shown that during boiling a gradual first‐order softening during cooking is observed (Beleia et al., 2004).

In regard to physico-chemical properties, the textural, rheological and gelatinization properties vary considerably among the varieties. The interaction between physicochemical properties and structural make-up of the tuber parenchyma was shown to have a great influence on cooking quality and rheological properties of cassava (Sajeev et al., 2010).

Information on the effect of boiling as a processing method on the biophysical properties of cassava roots is scanty. Apart from studies detailing the effect of boiling on consumer properties, little is known about the effect on such properties such as dry matter content, starch and cell wall material. Earlier studies (Cooke et al., 1978, Essers et al., 1981, Nambisan, 1994, Coursey, 1973) focused on the effect of boiling as a simple processing method on the cyanogenic potential of the root. In these studies, it was observed that simple processing resulted into smaller reductions in cyanide content. The studies also showed that such parameters are instead affected by age and the environment where increase in plant age results into increase in Dry matter content, pectin contents and starch contents (Franck et al., 2011). However, such effects have not been discussed in light of subjecting roots to different boiling conditions. In addition, specific studies have been undertaken that detail the relationship between different root components during root boiling.

However, no such studies have been performed on Ugandan cassava varieties.

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5.2 Instrumental Texture assessment and relationship with sensory evaluation

Instrumental assessment Relationship with

sensory evaluation Penetrometer assessment of softness on root samples

The roots from the field locations are stored in a -80°C freezer to avoid deterioration prior to evaluation2. The samples for a given block are removed from the freezer and thawed in cold water for phenotyping. After thawing, two roots per plot (genotype) are peeled and sliced into 3 cm sections. For each genotype, four sections are randomly selected from the two roots and loosely wrapped in perforated aluminum foil. The selected sections are heated (cooked) in a water bath set at a constant near boiling temperature of 90°C, with a single section randomly selected without replacement for each genotype at the end of four cooking time points: 15, 30, 45 and 60 min. At each time point, the 7.9 mm diameter tip of a digital penetrometer (Model number: FHT-1122, Vetus Industrial Company Limited, Hefei, China) is pushed to a depth of 1 cm into three different sides of a cooked root section (i.e., three technical measurements per root section). Softness is recorded as the maximum force used to penetrate the root section, and the three technical measurements are averaged for each root section.

High correlations (r>0.9) observed with sensory analysis

Consumer and penetrometer assessment of root softness in field

During consumer testing, a sample of cassava varieties is evaluated by consumers using the local varieties identified as hard or soft (from socioeconomic studies) as references. Two or more recently released varieties are also included and used for reference to the variety in question. Freshly harvested roots are treated as described above.

The cooking method followed is usually a traditional approach to boiling cassava, and the process of preparation is performed in close collaboration with farmers to most closely emulate the community use of cassava. After the cassava roots had cooked for 50 min, they are withdrawn from the wood fire. Of the total root sections cooked for each variety, 30 root sections are used for measuring softness with the penetrometer, while the remaining 110 root sections are used for sensory evaluation by consumers.

High correlation (r>0.78) observed (Paula et al., unpublished)

5.3 Relationship between composition and sensory evaluation

Data on such subject has not been generated and needs to be done. No specific information related to boiled product from cassava have been provided.

2 Freezing before boiling evaluation may change the texture compared to boiling fresh roots. The method is under review to boil fresh samples directly (possible when harvested close to the institute), or use a different storage method for roots harvested further afield (waxing).

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Evaluation of cyanogenic potential and organoleptic properties in cassava (Manihot esculenta Crantz.) roots of improved varieties in Cote dIvoire. African Journal of Food Science, 3(11), 328-333.

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21. Ayetigbo, O., Latif, S., Abass, A., & Müller, J. (2018). Comparing Characteristics of Root, Flour and Starch of Biofortified Yellow-Flesh and White-Flesh Cassava Variants, and Sustainability Considerations: A Review. Sustainability, 10(9), 3089.

22. Muyinza, H., Nuwamanya, E., Wanda, K., Waigumba, S. P., Kwagala, I., Nyamutoka, P., ... & Abass, A. (2017). Technical report: efficacy of pruning, waxing and relative humidity storage in extending shelf-life of fresh cassava roots. Extending the shelf-life of fresh cassava roots for increased incomes and postharvest losses reduction.

23. Oloya, B., Adaku, C., Ntambi, E., & Andama, M. (2017). Detoxification of Nyar-Udota Cassava Variety in Zombo District by Fermentation. International Journal of Nutrition and Food Sciences, 6(3), 118-121.

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