Impacts de la fermentation du cacao sur la croissance de la flore microbienne et la qualite des feves marchandes

La fermentation du cacao est une opération essentielle dans la production de fèves marchandes pour la fabrication du chocolat. Elle demeure un processus entièrement microbien difficile à contrôler de sorte que la qualité marchande du cacao produit, reste variable et aléatoire. La présente étude a pour objectif d’étudier l’influence du type de   fermentation sur la croissance de la flore microbienne et la qualité des fèves marchandes. De façon spécifique, il s’agit d’étudier l’impact des fermentations en caisse, sur feuilles de bananier et sur bâche plastique conduites selon les techniques paysannes sur la qualité des fèvesmarchandes issues de ces trois types de fermentations. Ainsi, la croissance de la flore microbienne (levures et moisissures, bactéries acétiques et lactiques, bacillus) impliquée dans le processus de  fermentation des fèves de cacao a été évaluée par dénombrement selon la méthode de dilution décimale. Les souches ont été identifiées par des méthodes biochimiques et morphologiques, sur géloses sélectives. Lesparamètres physico-chimiques (pH et température) de la masse  fermentaire ont été suivis. La technique de Cut Test a permis d’évaluer la qualité des fèves fermentées et séchées. Les résultats ont montré la même succession microbienne mais avec des temps d’apparition variables dans toutes les fermentations. Cependant, les fermentations en caisse et en bâche offraient une meilleure croissance des bactéries acétiques avec des pics de 8 106 et 44 104 UFC/g de fèves, respectivement. De même, la croissance des levures est 17 fois plus importante dans la fermentation conduite sur des feuilles de bananier que dans les fermentations sur bâche et en caisse. Le développement des bactéries lactiques est plus accru au niveau de la fermentation conduite sur bâche (891 109 UFC/g) que celles conduites en caisse (18 108 UFC/g) et sur des feuilles de bananier (153 107UFC/g). Bien que l’on obtient un cacao globalement de même qualité (Grade I) avec les trois types de fermentation, le pourcentage de fèves brunes, caractéristiques d’un cacao bien fermenté est plus élevé (80 %) dans les fermentations conduites en caisse et sur des feuilles de bananier contre 74 % en fermentation conduite sur bâche. Le pH et la température augmentent et évoluent globalement, de la même façon dans les trois types de fermentations. Les résultats de cette étude montrent que le type de fermentation appliqué aux fèves peut contribuer à l’identification d’espèces microbiennes à haut potentiel technologique pouvant permettre d’obtenir des fèves de qualité marchande satisfaisante et participer à la sélection de starters pouvant intervenir dans les programmes d’amélioration de la fermentation du cacao.Mots clés : Cacao, fermentation, levures, bactéries, bacillus, moisissures

Bubble nucleation on nano- to micro-size cavities and posts: An experimental validation of classical theory

Recently reported data suggest that bubble nucleation on surfaces with nano-sized features (cavities and posts) may occur close to the thermodynamic saturation temperature. However, according to the traditional theory of heterogeneous bubble nucleation, such low nucleation temperatures are possible only for surfaces with micro-scale cavities. Motivated by this apparent contradiction, we have used infrared thermometry to measure the nucleation temperature of water on custom-fabricated nano- to micro-scale cavities (from 90 nm to 4.5 μm in diameter) and posts (from 60 nm to 5 μm in diameter), machined on ultra-smooth and clean silicon wafers using electron beam lithography. Our cavity data are in agreement with the predictions of the Young-Laplace equation, thus re-affirming the correctness of the classic view of heterogeneous bubble nucleation, at least for the water-silicon system investigated here. The data also suggest that individual posts of any size have an insignificant effect on bubble nucleation, as expected from theory.MIT Energy Initiative (Seed Fund Program

Smallholder farmers' adaptation to climate change and determinants of their adaptation decisions in the Central Rift Valley of Ethiopia

Background: The agricultural sector remains the main source of livelihoods for rural communities in Ethiopia, but faces the challenge of changing climate. This study investigated how smallholder farmers perceive climate change, what adaptation strategies they practice, and factors that influence their adaptation decisions. Both primary and secondary data were used for the study, and a multinomial logit model was employed to identify the factors that shape smallholder farmers’ adaptation strategies. Results: The results show that 90% of farmers have already perceived climate variability, and 85% made attempts to adapt using practices like crop diversification, planting date adjustment, soil and water conservation and management, increasing the intensity of input use, integrating crop with livestock, and tree planting. The econometric model indicated that education, family size, gender, age, livestock ownership, farming experience, frequency of contact with extension agents, farm size, access to market, access to climate information and income were the key factors determining farmers’ choice of adaptation practice. Conclusion: In the Central Rift Valley of Ethiopia, climate change is a pressing problem, which is beyond the capacity of smallholders to respond to autonomously. Farmers’ capacity to choose effective adaptation options is influenced by household demography, as well as positively by farm size, income, access to markets, access to climate information and extension, and livestock production. This implies the need to support the indigenous adaptation strategies of the smallholder farmers with a wide range of institutional, policy, and technology support; some of it targeted on smaller, poorer or female-headed households. Moreover, creating opportunities for non-farm income sources is important as this helps farmers to engage in those activities that are less sensitive to climate change. Furthermore, providing climate change information, extension services, and creating access to markets are crucial

Linear and nonlinear instability in vertical counter-current laminar gas-liquid flows

We consider the genesis and dynamics of interfacial instability in gas-liquid flows, using as a model the two-dimensional channel flow of a thin falling film sheared by counter-current gas. The methodology is linear stability theory (Orr-Sommerfeld analysis) together with direct numerical simulation of the two-phase flow in the case of nonlinear disturbances. We investigate the influence of three main flow parameters (density contrast between liquid and gas, film thickness, pressure drop applied to drive the gas stream) on the interfacial dynamics. Energy budget analyses based on the Orr-Sommerfeld theory reveal various coexisting unstable modes (interfacial, shear, internal) in the case of high density contrasts, which results in mode coalescence and mode competition, but only one dynamically relevant unstable internal mode for low density contrast. The same linear stability approach provides a quantitative prediction for the onset of (partial) liquid flow reversal in terms of the gas and liquid flow rates. A study of absolute and convective instability for low density contrast shows that the system is absolutely unstable for all but two narrow regions of the investigated parameter space. Direct numerical simulations of the same system (low density contrast) show that linear theory holds up remarkably well upon the onset of large-amplitude waves as well as the existence of weakly nonlinear waves. In comparison, for high density contrasts corresponding more closely to an air-water-type system, although the linear stability theory is successful at determining the most-dominant features in the interfacial wave dynamics at early-to-intermediate times, the short waves selected by the linear theory undergo secondary instability and the wave train is no longer regular but rather exhibits chaotic dynamics and eventually, wave overturning.Comment: 30 pages, 14 figure

Global Assessment Report on Disaster Risk Reduction 2019

The Global Assessment Report on Disaster Risk Reduction (GAR) is the flagship report of the United Nations on worldwide efforts to reduce disaster risk

Transformation, adaptation and development: relating concepts to practice

In recent years there has been a growing number of academic reviews discussing the theme of transformation and its association with adaptation to climate change. On the one hand this has stimulated exchange of ideas and perspectives on the parameters of transformation, but it has also given rise to confusion in terms of identifying what constitutes a non-incremental form of adaptation on the ground. What this article aims to do instead is help researchers and practitioners relate different interpretations of transformation to practice by proposing a typological framework for categorising forms of change that focuses on mechanisms and objectives. It then discusses how these categorisations link to the broader conceptions and critiques noted above, with the idea that this will enable those who seek to analyse or plan adaptation to better analyse what types of action are potentially constitutive of transformation. In doing so, it should equally assist in the identification and specification of critical questions that need to be asked of such activity in relation to issues of sustainability and equity. As the term transformation gains ground in discussions of climate change adaptation, it is necessary to take a step back, review quite what commentators mean when they use the word, and consider the implications on people, especially the most vulnerable and marginalised, of “doing” or promoting transformation in its different forms

Everyday vulnerabilities and ''social dispositions'' in the Malian Sahel, an indication for evaluating future adaptability to water crises?

International audienceSince the 1970s, precipitation in the Sahel has decreased and become very irregular, leading to widespread drought, whilst the human need for water has rapidly increased. A new ''dispositions''-based approach was adapted in order to analyse human interactions with environmental hazards and applied to the case of Hombori village in northeastern Mali. This article explores how the population and political stakeholders perceive, live with and respond to the increasing scarcity of water. It also explores how their current vulnerability and ability to cope with variations in available water resources indicate future adaptability to climate shocks. On the one hand, this research shows how the population copes with variations in water resource availability: the population's socio-spatial organisation explains the inhabitants' exposure to this problem and some of the factors affecting vulnerability, the elderly and women being the hardest hit. The water issue is generally managed on a ''day-to-day'' basis and considered a big problem only in the dry season, thus lowering any incentive for self-protection. The main two variables that could explain this kind of risk management are the conflicting local governance and current social rules. On the other hand, the discussion of results, based on a conceptual model of social responses, explains why these current ''social dispositions'' to cope with and even address the water scarcity issue do not guarantee future adaptability to climate change

Ambivalence towards discourse of disaster resilience

This paper investigates empirically how the international aid community (IAC)—donors and practitioners—considers and implements disaster resilience in a specific country setting, Nepal, and throughout the rest of the world. A key finding is that there is ambivalence about a concept that has become a discourse. On a global level, the IAC utilises the discourse of resilience in a cautiously positive manner as a bridging concept. On a national level, it is being used to influence the Government of Nepal, as well as serving as an operational tool of donors. The mythical resilient urban community is fashioned in the IAC's imaginary; understanding how people create communities and what type of linkages with government urban residents desire to develop their resilience strategies is missing, though, from the discussion. Disaster resilience can be viewed as another grand plan to enhance the lives of people. Yet, regrettably, an explicit focus on individuals and their communities is lost in the process

Livelihood and vulnerability in the wake of Typhoon Yolanda: lessons of community and resilience

Livelihood strategies that are crafted in ‘extra-ordinary’ post-disaster conditions should also be able to function once some semblance of normalcy has resumed. This article aims to show that the vulnerability experienced in relation to Typhoon Yolanda was, and continues to be, directly linked to inadequate livelihood assets and opportunities. We examine the extent to which various livelihood strategies lessened vulnerability post-Typhoon Yolanda and argue that creating conditions under which disaster survivors have the freedom to pursue sustainable livelihood is essential in order to foster resilience and reduce vulnerability against future disasters. We offer suggestions to improve future relief efforts, including suggestions made by the survivors themselves. We caution against rehabilitation strategies that knowingly or unknowingly, resurrect pre-disaster vulnerability. Strategies that foster dependency, fail to appreciate local political or ecological conditions or undermine cooperation and cohesion in already vulnerable communities will be bound to fail. Some of the livelihood strategies that we observed post-Typhoon Yolanda failed on some or all of these points. It is important for future policy that these failings are addressed