Keith Tomlins

Using a discrete choice experiment to elicit the demand for a nutritious food: Willingness-to-pay for orange maize in rural Zambia

Using a discrete choice experiment, this paper estimates the willingness to pay for biofortified orange maize in rural Zambia. The study design has five treatment arms, which enable an analysis of the impact of nutrition information, comparing the use of simulated radio versus community leaders in transmitting the nutrition message, on willingness to pay, and to account for possible novelty effects in the magnitude of premiums or discounts. The estimation strategy also takes into account lexicographic preferences of a subset of our respondents. The results suggest that (a) orange maize is not confused with yellow maize, and has the potential to compete with white maize in the absence of a nutrition campaign, (b) there is a premium for orange maize with nutrition information, and (c) different modes of nutritional message dissemination have the same impact on consumer acceptance.

Survey of Ghanaian cocoa farmer fermentation practices and their influence on cocoa flavour

Abstract A survey of 56 cocoa farms in Ghana was carried out during the 1986 main crop to assess the influence of fermentation practices (post-harvest pod storage, cultivar, weight of ferments, number of turns and timing, drying) on quality. Variations in the frequency of turning of the ferments was noted with cocoa-producing region and cultivar. Sensory evaluation of chocolate samples made from the cocoa beans indicated that a short pod-storage and fermentation with a single turn after three days produced the most acceptable cocoa. The acceptability varied by region with the Eastern region producing the most acceptable cocoa. As with acceptability, chocolate flavour significantly improved with a short pod-storage time. A composite sample was average in terms of its sensory characteristics, supporting the concept that blending facilitates the balanced flavour characteristic of Ghana cocoa.

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.

Effect of fermentation and drying practices on the chemical and physical profiles of Ghana cocoa

Abstract A series of 12 cocoa fermentations were carried out at the Cocoa Research Institute of Ghana in 1987. The cocoa fermentations were varied by cultivar (Amelonado, Amazon and Hybrid), post-harvest pod storage time (1 and 7 days) and fermentation method (heap and box). During each fermentation, chemical (sugars, ethanol, organic acids and pH) and physical (moisture, temperature and pulp cotyledon ratio) changes were monitored. A large number (104) of statistically significant differences were found, indicating that the choice of cultivar, method of fermentation and duration of post-harvest pod storage, affect the chemical and physical profiles of cocoa fermentations. However, after the fermented beans were either sun or mechanically dried, the quality of the beans as measured by the cut-test and organic acid concentration, revealed only one significant difference, that of a higher proportion of mouldy beans when the beans had been subjected to the longer 7-day pod-storage period prior to splitting and fermenting.

Digital imaging based classification and authentication of granular food products

In the food industry there are many types of product that are in the form of particles, granules or grains. Consistent material size and quality within any given sample is an important requirement that is well known in industry. In addition it is possible that samples of material may be of unknown type or have been subject to adulteration, thus making material authentication a real requirement. The present work implements an advanced, but cost-effective, digital imaging and image processing technique to characterize granular foodstuffs either in real time process control or in an off-line, sample-based, manner. The imaging approach not only provides cost-effective and rugged hardware when compared with other approaches but also allows precise characterization of individual grains of material. In this paper the imaging system is briefly described and the parameters it measures are discussed. Both cluster and discriminant analyses are performed to establish the suitability of the measured parameters for authenticity study and a simple fuzzy logic is implemented based on the findings. Tests are performed, using rice as an example, to evaluate the performance of the system for authenticity testing, and encouraging results are achieved.

Prediction of quality and origin of black tea and pine resin samples from chromatographic and sensory information: evaluation of neural networks

Abstract The accuracies of neural network and statistical methods were similar for classifying the origin of black teas from their phenolic composition. When the data are non-normal, as was the case for the pine resin samples, the neural network offered a significant improvement. Neural networks were less accurate than stepwise multiple regression as a model for predicting black tea score and price from their chemical composition and sensory attributes. The accuracy improved and the training time was reduced when training variables chosen by stepwise multiple regression were selected. An advantage of the neural network model is that a single model could predict several parameters simultaneously. The selection criterion of neural networks could be estimated by inspection of the most positive weights derived from two-layer trained networks.

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.

Cassava (Manihot esculenta Crantz) and Yam (Dioscorea spp.) Crops and Their Derived Foodstuffs: Safety, Security and Nutritional Value

Cassava (Manihot esculenta Crantz) and yam (Dioscorea spp.) are tropical crops consumed by ca. 2 billion people and represent the main source of carbohydrate and energy for the approximately 700 million people living in the tropical and sub-tropical areas. They are a guarantee of food security for developing countries. The production of these crops and the transformation into food-derived commodities is increasing, it represents a profitable business and farmers generate substantial income from their market. However, there are some important concerns related to the food safety and food security. The high post-harvest losses, mainly for yam, the contamination by endogenous toxic compounds, mainly for cassava, and the contamination by external agents (such as micotoxins, pesticides, and heavy metal) represent a depletion of economic value and income. The loss in the raw crops or the impossibility to market the derived foodstuffs, due to incompliance with food regulations, can seriously limit all yam tubers and the cassava roots processors, from farmers to household, from small-medium to large enterprises. One of the greatest challenges to overcome those concerns is the transformation of traditional or indigenous processing methods into modern industrial operations, from the crop storage to the adequate package of each derived foodstuff.

Consumer acceptance of quality protein maize (QPM) in East Africa

BACKGROUND Undernutrition in sub-Saharan Africa remains problematic, and quality protein maize (QPM) can benefit populations whose diets are heavily based on maize and who are consequently at risk for inadequate intakes of quality protein. However, changes in the chemical composition of QPM may affect its sensory characteristics and, hence, acceptance. Acceptance tests were therefore conducted to evaluate QPM varieties in three East African countries using central location tests with one or two varieties in each country, using the most popular preparations: ugali (Tanzania), githeri (Kenya) and injera (Ethiopia). In total, 281 urban and rural consumers of both sexes and varying levels of education evaluated the products on standard sensory criteria: appearance, aroma, texture, taste and overall, using a Likert scale. RESULTS The results show that African consumers can differentiate QPM products from their conventional counterparts, indicating that the QPM trait results in distinguishable sensory changes. Analysis by ordinal mixed regression models showed that consumers found QPM acceptable and even preferable to conventional maize. CONCLUSION The sensory characteristics of QPM are therefore no impediment to its adoption; on the contrary, when coupled with good agronomic performance, they may help its utilization, leading to a positive impact in nutritionally vulnerable populations.