Andrew Westby

Cassava Utilization, Storage and Small-scale Processing

The importance of cassava in the world is mainly a reflection of the agronomic advantages of the crop. However, if the contribution that cassava can make to the livelihoods of poor people is to be increased, there is a need to consider also its postharvest handling, processing and marketing. There are three major limitations to the increased utilization of cassava roots: poor shelf-life, low protein content and their naturally occurring cyanogens. Rapid postharvest deterioration means that processing is more important than for any of the other root crops. In addition to producing storable products, processing can also add value to the crop and provide employment opportunities. Both cassava roots and leaves can be used as food, but economically the roots are usually more important, although in parts of some African countries, the leaves may be as important or more important than the roots. The tuberous roots can be 15–100 cm in length and reach a weight of 0.5–2.0 kg (Knoth, 1993). They have no function in vegetative propagation, which is done using stem cuttings. The roots contain large carbohydrate reserves, mainly as starch. Although the function of the starch-bearing tissue is not completely clear, it is assumed that it helps the plant to survive unfavourable conditions such as drought. This chapter considers world cassava utilization and the nutritional value of the root and leaves for human consumption. The current state of knowledge on cassava storage and smallscale processing is presented with the emphasis on sub-Saharan Africa.

Review of the effect of fermentation on naturally occurring toxins

Lesser developed countries require food processing technologies that are technologically appropriate, suitable for tropical regions and that are affordable in rural and urban economies. Household-level fermentation is one such technology that has been developed indigenously for a wide range of food commodities. These include cereals and legumes, root crops, fruit and vegetables, dairy products, fish and meat (Steinkraus, 1983, 1989; Campbell-Platt, 1987, 1994). As a unit operation in food processing, fermentation offers a large number of advantages, including: food preservation, improved food safety, enhanced flavour and acceptability, increased variety in the diet, improved nutritional value, reduction in anti-nutritional compounds and in some cases, improved functional properties. Fermentation is a very important low-cost food processing technique and a common means of preservation in lesser developed tropical countries (Cooke et al., 1987) where preservation techniques such as refrigeration, freezing, canning or modified atmosphere packaging are prohibitively expensive. Problems are compounded in communities with low levels of disposable incomes and where limited infrastructure available in the food processing industry greatly restricts the use of more advanced technologies.

Priority research questions for the UK food system

The rise of food security up international political, societal and academic agendas has led to increasing interest in novel means of improving primary food production and reducing waste. There are however, also many ‘post-farm gate’ activities that are critical to food security, including processing, packaging, distributing, retailing, cooking and consuming. These activities all affect a range of important food security elements, notably availability, affordability and other aspects of access, nutrition and safety. Addressing the challenge of universal food security, in the context of a number of other policy goals (e.g. social, economic and environmental sustainability), is of keen interest to a range of UK stakeholders but requires an up-to-date evidence base and continuous innovation. An exercise was therefore conducted, under the auspices of the UK Global Food Security Programme, to identify priority research questions with a focus on the UK food system (though the outcomes may be broadly applicable to other developed nations). Emphasis was placed on incorporating a wide range of perspectives (‘world views’) from different stakeholder groups: policy, private sector, non-governmental organisations, advocacy groups and academia. A total of 456 individuals submitted 820 questions from which 100 were selected by a process of online voting and a three-stage workshop voting exercise. These 100 final questions were sorted into 10 themes and the ‘top’ question for each theme identified by a further voting exercise. This step also allowed four different stakeholder groups to select the top 7–8 questions from their perspectives. Results of these voting exercises are presented. It is clear from the wide range of questions prioritised in this exercise that the different stakeholder groups identified specific research needs on a range of post-farm gate activities and food security outcomes. Evidence needs related to food affordability, nutrition and food safety (all key elements of food security) featured highly in the exercise. While there were some questions relating to climate impacts on production, other important topics for food security (e.g. trade, transport, preference and cultural needs) were not viewed as strongly by the participants.

Retention and bioaccessibility of β-carotene in blended foods containing orange-fleshed sweet potato flour

The retention and bioaccessibility of β-carotene (BC) in blended foods made with part orange-fleshed sweet potato (OFSP) flour (30%) were examined. Chapatis and porridges were prepared by local processors under field conditions (FC) in Uganda (n=10). While the retention of all-trans-BC in porridges (69 to 93%) and chapatis (70 to 97%) varied between the processors, there was no overall difference between the two products and this was probably because of the variability in FC. BC retention in mandazis was similar to that of chapatis and porridges. Processing in FC significantly increased the amount of cis-isomers, in particular 13-cis-BC. The bioaccessibility of the BC as measured by their transfer into micelles was evaluated using an in vitro digestion procedure in various OFSP-derived products. After in vitro digestion, the percentage of micellarized all-trans-BC was greater in products cooked with oil, chapati (73%) and mandazi (49%), as compared with the boiled ones, porridge (16%) and puréed from boiled root (10%). In all the products, the incorporation into micelles for 13-cis-BC was significantly higher to that of all-trans-BC. When taking into account the bioaccessibility of all-trans-BC and 13-cis-BC isomer, an edible portion of porridge (one mug), boiled root (half a root), mandazis (two), or chapati (one) could provide a significant part of the daily vitamin A requirements of a child under 6 years (respectively 20, 46, 75, or 100%). These data support the promotion/consumption of locally cooked OFSP food products to tackle vitamin A deficiency in sub-Saharan Africa.

A study of the role of tissue disruption in the removal of cyanogens during cassava root processing.

Sun-drying as a means to reduce the cyanogen content of cassava roots is commonly known to be inefficient. This paper reports on modifications to the processing procedure used for sun-drying and their effectiveness at removing potentially toxic cyanogenic glucosides. Commonly used processing methods were compared. Crushing cassava root pieces prior to drying was found to significantly improve the efficiency of cyanogen removal by, on average, 22% during laboratory experiments and 12% during field trials. The crushing procedure was optimized and a low cost prototype crusher developed. A reduction in the processing time resulted from crushing the root disks prior to drying. The processing method involving crushing was ranked second in terms of efficiency of cyanogen removal in a comparative study of sun-dry processing methods that are commonly used in East Africa. Pounding cassava to small pieces in a traditional pestle and mortar prior to drying was the most efficient, providing 90% removal of cyanogens. Pounding and crushing cassava prior to sun-drying were significantly better than all other root preparation pre-treatments evaluated.

Postharvest handling, transport and quality of sweet potato in Tanzania

Summary Commercial consignments of sacks of sweet potato, Ipomoea batatas (L) Lam, cvs. Polista and SPN/0, were surveyed, over two seasons, from harvest to markets at Mwanza and Dar es Salaam in Tanzania. The handling and transport system resulted in up to 20% and 86% of roots with severe breaks and skinning injury respectively. Reductions in market value were up to 13%. Impact loggers located at the centre of sacks indicated that the most severe impacts (greater than 20 g) occurred during unloading and loading from road vehicles and ships. However, skinning injury and broken roots were correlated with a large number of minor impacts (2 g or lower). Cultivar or season did not generally affect the responses. The use of cardboard boxes filled with fewer roots instead of overfilled polypropylene sacks and adoption of improved management procedures in the handling and transport are recommended.

Influence of pre-harvest curing and mechanical injury on the quality and shelf-life of sweet potato (Ipomoea batatas (L.) Lam) in East Africa

Summary This research investigates various methods of reducing root damage and the effect of damage on subsequent storage under tropical conditions. The methods investigated for reducing root damage were pre-harvest curing and the use of alternative types of post-harvest packaging. Pre-harvest curing by pruning the plant canopy 14 d before harvest significantly reduced the level of skinning injury in roots during harvesting and post-harvest handling in sacks. When the roots were stored for 14 d, pre-harvest pruning reduced the occurrence of rotten roots. Transporting 20 kg of roots in fibre-board boxes reduced skinning injury whereas it was greatest when transported in polypropylene sacks weighing either 20 or 100 kg. Skinning injury and broken roots reduced shelf life, as measured by weight loss, when roots were stored under tropical conditions. Skinning injury was also associated with the increased occurrence of rots. The implications for sweet potato handling systems in East Africa are discussed.

Ergonomics evaluation of a manually operated cassava chipping machine.

A manually operated machine for chipping cassava was evaluated. Six farmers took part in the study, with physiological, postural, and subjective measurements being taken. Using the machine resulted in drudgery and postural discomfort. Following an iterative design process and using appropriate anthropometric measurements, an improved, adjustable prototype was developed. This was tested with the six farmers and six novice users. It was found to reduce discomfort and physiological strain, allowed a faster work-rate (with novice users) and was preferred by all users. The study demonstrated how ergonomics can play an important role in reducing drudgery and improving user satisfaction in technology development and transfer in developing countries.

Physical losses could partially explain modest carotenoid retention in dried food products from biofortified cassava

Gari, a fermented and dried semolina made from cassava, is one of the most common foods in West Africa. Recently introduced biofortified yellow cassava containing provitamin A carotenoids could help tackle vitamin A deficiency prevalent in those areas. However there are concerns because of the low retention of carotenoids during gari processing compared to other processes (e.g. boiling). The aim of the study was to assess the levels of true retention in trans–β-carotene during gari processing and investigate the causes of low retention. Influence of processing step, processor (3 commercial processors) and variety (TMS 01/1371; 01/1368 and 01/1412) were assessed. It was shown that low true retention (46% on average) during gari processing may be explained by not only chemical losses (i.e. due to roasting temperature) but also by physical losses (i.e. due to leaching of carotenoids in discarded liquids): true retention in the liquid lost from grating negatively correlated with true retention retained in the mash (R = -0.914). Moreover, true retention followed the same pattern as lost water at the different processing steps (i.e. for the commercial processors). Variety had a significant influence on true retention, carotenoid content, and trans-cis isomerisation but the processor type had little effect. It is the first time that the importance of physical carotenoid losses was demonstrated during processing of biofortified crops.

Cassava traits and end-user preference: Relating traits to consumer liking, sensory perception, and genetics

ABSTRACT Breeding efforts have focused on improving agronomic traits of the cassava plant however little research has been done to enhance the crop palatability. This review investigates the links between cassava traits and end-user preference in relation with sensory characteristics. The main trait is starch and its composition related to the textural properties of the food. Pectin degradation during cooking resulted in increased mealiness. Nutritional components such as carotenoids made the cassava yellow but also altered sweetness and softness; however, yellow cassava was more appreciated by consumers than traditional (white) varieties. Components formed during processing such as organic acids gave fermented cassava products an acidic taste that was appreciated but the fermented smell was not always liked. Anti-nutritional compounds such as cyanogenic glucosides were mostly related to bitter taste. Post-harvest Physiological Deterioration (PPD) affected the overall sensory characteristics and acceptability. Genes responsible for some of these traits were also investigated. Diversity in cassava food products can provide a challenge to identifying acceptance criteria. Socio-economic factors such as gender may also be critical. This review leads to questions in relation to the adaptation of cassava breeding to meet consumer needs and preference in order to maximize income, health and food security.