Résumé
During Period 4, RTBfoods partners involved in WP2 implemented the standard operating protocols (SOPs) developed in previous periods to characterize the target product profiles: boiled roots and tubers (cassava, Yam, sweet potato, plantain), paste (Fufu, pounded Yam, matooke) and granulated products (gari-eba, attiéké). For sensory characterizations by trained panels, 10 SOPs are now available: boiled cassava (2), gari-eba, attiéké, Fufu, boiled Yam, pounded Yam, boiled plantain, matooke, and boiled sweet potato. Key sensory attributes common to several products include firmness/hardness, stickiness, colour, smoothness, moldability and sweetness / sourness, fibrousness, moisture/mealiness, stretchability and bitterness. Several of these sensory attributes were correlated with instrumental texture parameters, in particular sensory firmness (or hardness or softness) assessed either in the mouth or by hand can be reliably predicted by the hardness parameters measured by penetrometry, TPA, and texture-extrusion. For the first time, mealiness of boiled cassava was correlated with a parameter of the texture-extrusion test, as well as with water absorption. Mouldability and stretchability were correlated with TPA measurements especially on destructured products (Gari/Eba and pounded Yam). For textural characterizations, 7 SOPs were developed and validated: boiled cassava (2), matooke, boiled Yam, pounded Yam, gari-eba, Fufu. These were implemented for several product profiles and several genotypes of various RTBs (typically 20 to 50 genotypes per product profile). Multivariate statistical analyses (e.g. PCA) of the resulting datasets allowed the classification of RTB genotypes into good, intermediate and poor quality, thus demonstrating the ability of postharvest quality measurements to contribute to varietal selection for breeding. Several correlations between textural parameters and sensory attributes were also identified (as discussed above), which also confirmed that instrumental texture is a valid approach to predict how consumers perceive RTB products. SOPs for several kitchen tests were also finalized, which bring additional information on the functional quality traits of RTB products in complement to texture measurements, including water absorption, cooking time, swelling of gari upon addition of hot water, and pounding time of paste products (pounded Yam, Fufu). Processing ability criteria were also investigated such as ease of peeling, ease of sieving the dewatered cassava mash, retting ability (softening, foaming, turbidity, pH). In the case of boiled cassava, the water absorption protocol in particular offers relatively short analysis time (30 minutes/sample) and is well correlated with sensory mealiness, cooking time and textural parameters, thus qualifying as medium-throughput phenotyping method for screening cassava breeding populations. In 2021, more than 4000 genotypes were characterized by water absorption, including from Nextgen and HarvestPlus populations. This development constitutes an important contribution of RTBfoods to improving cassava breeding and selection operations of other projects, and demonstrates the potential of the RTBfoods approach to develop breeding selection tools for a variety of post-harvest quality traits. Finally, biochemical proof of concept studies provided further evidence of the role of pectins in determining textural characteristics of RTB products, in particular non-destructured such as boiled or steamed. Starch and amylose contents also contributed to texture of boiled sweet potato and boiled Yam.