Spatial distribution of total phenolic content, enzymatic activities and browning in white yam (Dioscorea rotundata) tubers.

Browning in raw and processed yams resulting from enzymes, polyphenol oxidase (PPO) and peroxidase (POD), activities is a major limitation to the industrial utilization of Dioscorea varieties of yams. Two elite cultivars of D. rotundata species were selected to study the spatial distribution of total phenols and enzymes (PPO and POD) activities. The intensities of tissue darkening in fresh yam chips prepared from the tuber sections of cultivars during frozen storage were also studied. Total phenolic content was observed to be highest in the head and mid sections of the cultivars than at the tail end. PPO activity did not have any specific distribution pattern whereas POD activity was found to be more concentrated in the head than in the middle and tail regions. Browning was found to be most intense in the head regions of the two cultivars studied; and was observed to correlate with total phenol and dry matter contents of tubers. Between the two enzymes, POD activity appeared to be more related to browning than PPO.

Variations in agronomic and grain quality traits of rice grown under irrigated lowland conditions in West Africa.

Rice breeding in West Africa has been largely skewed toward yield enhancement and stress tolerance. This has led to the variable grain quality of locally produced rice in the region. This study sought to assess variations in the agronomic and grain quality traits of some rice varieties grown in this region, with a view to identifying sources of high grain yield and quality that could serve as potential donors in their breeding programs. Forty-five varieties were grown under irrigated conditions in Benin and Senegal with two trials in each country. There were wide variations in agronomic and grain quality traits among the varieties across the trials. Cluster analysis using paddy yield, head rice yield, and chalkiness revealed that 68% of the total variation could be explained by five varietal groupings. One group comprising seven varieties (Afrihikari, BG90-2, IR64, Sahel 108, WAT311-WAS-B-B-23-7-1, WAT339-TGR-5-2, and WITA 10) had high head rice yield and low chalkiness. Of the varieties in this group, Sahel 108 had the highest paddy yield in three of the four trials. IR64 and Afrihikari had intermediate and low amylose content, respectively, with the rest being high-amylose varieties. Another group of varieties consisting of B6144F-MR-6-0-0, C74, IR31851-96-2-3-2-1, ITA222, Jaya, Sahel 305, WITA 1, and WITA 2 had high paddy yield but poor head rice yield and chalkiness. The use of materials from these two groups of varieties could accelerate breeding for high yielding rice varieties with better grain quality for local production in West Africa.

Macromolecular Traits in the African Rice Oryza glaberrima and in Glaberrima/Sativa Crosses, and Their Relevance to Processing.

Molecular properties of proteins and starch were investigated in 2 accessions of Oryza glaberrima and Oryza sativa, and in one NERICA cross between the 2 species, to assess traits that could be relevant to transformation into specific foods. Protein nature and organization in O. glaberrima were different from those in O. sativa and in NERICA. Despite the similar cysteine content in all samples, thiol accessibility in O. glaberrima proteins was higher than in NERICA or in O. sativa. Inter-protein disulphide bonds were important for the formation of protein aggregates in O. glaberrima, whereas non-covalent protein-protein interactions were relevant in NERICA and O. sativa. DSC and NMR studies indicated only minor differences in the structure of starch in these species, as also made evident by their microstructural features. Nevertheless, starch gelatinization in O. glaberrima was very different from what was observed in O. sativa and NERICA. The content of soluble species in gelatinized starch from the various species in the presence/absence of treatments with specific enzymes indicated that release of small starch breakdown products was lowest in O. glaberrima, in particular from the amylopectin component. These findings may explain the low glycemic index of O. glaberrima, and provide a rationale for extending the use of O. glaberrima in the production of specific rice-based products, thus improving the economic value and the market appeal of African crops. PRACTICAL APPLICATION: The structural features of proteins and starch in O. glaberrima are very different from those in O. sativa and in the NERICA cross. These results appear useful as for extending the use of O. glaberrima cultivars in the design and production of specific rice-based products (for example, pasta), that might, in turn, improve the economic value and the market appeal of locally sourced raw materials, by introducing added-value products on the African market.

Upgrading the quality of Africa's rice: a novel artisanal parboiling technology for rice processors in sub-Saharan Africa.

In order to increase the quality of locally produced rice, the artisanal parboiling process in West and Central Africa was reconceptualized. A novel parboiling unit was constructed using stainless steel (Inox 304) and fitted directly on an improved stove made from fired bricks. The heat profile at different locations in the unit, the physicochemical properties, cooking properties of the parboiled rice, and the fuel efficiency of the stove were evaluated and compared with that of the traditional system. The heat flow in the new unit was from the top to the bottom while the reverse occurred in the traditional unit. The percent impurities and heat-damaged grains, swelling and water uptake ratios, amylose content, stickiness, and cohesiveness were lower for rice produced using the improved technology (IT) compared to the traditional technology (TT). Whole grains (%), lightness (L*), yellowness (b*), cooking time, viscosity were higher for rice produced using the IT compared to the TT. Most of physicochemical and cooking properties of rice produced using the IT were not different from that of premium quality imported rice and this was achieved when steaming time was between 20-25 min. The improved stove recorded a lower time to boil water and specific fuel consumption and a higher burning rate and firepower at the hot-start high-power phase compared to the traditional stove. Most end users rated the IT as easy and safe to use compared to the TT. The new technology was code-named "Grain quality enhancer, Energy-efficient and durable Material (GEM) parboiling technology."