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Correlation of cooking time with water absorption and changes in relative density during boiling of cassava roots

The review has been published in a special issue called “Consumers have their say: Assessing preferred quality traits of roots, tubers and cooking bananas, and implications for breeding” in the International Journal of Food Science and Technology, led by the RTBfoods project.

Consumers by far prefer cassava varieties that cook quickly and fracture or disintegrate in the mouth, making the mealiness and soft texture of boiled roots a very high priority trait for breeders. Cooking quality of boiled cassava is multi-dimensional (texture, boiling time), and the result of complex processes that depend on several parameters. Current methods to evaluate cooking time (CT) are slow and labor-intensive however, making it difficult to routinely screen improved cassava genotypes for short cooking time.

This article describes improved protocols for assessing cooking time faster and demonstrates that cooking quality is closely linked with water absorption during boiling. We evaluated 36 genotypes harvested monthly from 8 to 11 months after planting. Both the genotypes and the age of the plant influenced cooking time. During boiling, roots absorbed water (WAB) and thus reduced their relative density (DEN). We classified three groups of genotypes with increasing CT (≤25min, 25 to 40min, >40min), associated with decreasing WAB, respectively 15.3±3.1, 10.7±1.7 and 4.9±3.8% of initial root weight. A similar trend was observed for changes in DEN. In roots with short CT, final density was only 46.3% (±9.8) of the initial value. In contrast, in roots with intermediate and long CT, final densities were 54.5% (±11.1) and 75.9% (±6.9) of the initial DEN, respectively.

Both WAB and DEN are therefore good predictors of CT, with the highest correlations (r2 > 0.6) found at 30-min boiling. These alternative protocols facilitate screening large numbers of cassava genotypes for CT, which is critical to fully integrate cooking quality criteria in the selection process, and thus increase the adoption rate of improved varieties. After initial development at CIAT, the RTBfoods project is now working to transfer these new methods to more partners in Uganda, Nigeria and Benin, who can put them to use for their own crops and products such as boiled cassava, boiled yam and boiled sweet potato.

Published: 28/10/2020