Black spot disease is the major postharvest disease affecting Victoria ('Queen') pineapple in Reunion Island. Fusarium ananatum , the main causal agent of black spot was inoculated in 'MD2' and Victoria ('Queen'), a resistant and a susceptible cultivar respectively. A metabolomics approach, of healthy and inoculated fruitlets allows us to determine which putative metabolites are involved in the black spot disease. The phenolic compounds seemed to be determining markers of black spot. Based on those results, we conducted follow ‐ up work on evolution of black spot disease with a focus on phenolic compounds. Coumaroylquinic and chlorogenic acids increased drastically in the infected fruitlets in both cultivars post ‐ inoculation. Hydroxycinnamic acid increased more rapidly in 'MD2' than in Victoria ('Queen') cultivar. 'MD2' infected fruitlets reached higher levels in hydroxycinnamic acids in a shorter period than Victoria ('Queen') cultivar. In healthy fruits of 'MD2', coumaroylquinic acid and hydroxybenzoic acids are produce naturally as the fruit matures. These compounds are known to play a major role in the plant disease resistance. (Resume d'auteur)
Ochratoxin A (OTA) is a carcinogenic toxin produced by certain moulds. It contaminates numerous foodstuffs, notably coffee, in which it can be found at all stages of the technological process, from field to cup. The purpose of this study was to take stock of the critical stages in coffee processing, be it during post-harvest treatments, or during processing into a consumable product, with regard to OTA contamination. The quality and type of post-harvest processes showed a not insubstantial effect on the degree of OTA contamination in green beans. Agronomic defects (insect and fungus attacks) also contributed to the high level of OTA in green coffee. Various studies undertaken on the impact of roasting on OTA degradation revealed thermal degradation of OTA. However, initial contamination of the beans, the process used and the degree of roasting strongly influenced that degradation, hence the residual OTA concentration in roasted beans. Lastly, it appeared that it is the control of contamination upstream, through good agricultural practices and post-harvest treatments, that is the best way for ensuring a contamination-free beverage.
The purpose of our work was to examine the impact of four wet processing methods on the quality of roasted coffee, with three degrees of roasting. The volatile fraction of the coffees was analysed by combining Headspace-SPME (HS-SPME), GC-olfactometry (GC-O) and mass spectrometry (GC-MS). Post-harvest processing has a major impact on the aroma quality of the roasted coffees produced by those processes. This was more or less acknowledged for differentiating between the dry and wet methods. Our work has shown that modifications to the wet method also lead to aromatic differences in roasted coffees. Coffee produced by the traditional wet method was of better aromatic quality than coffee produced by the mechanical method recently introduced because it uses less water and is more ecological. Indeed, this last aspect resulted in coffees with more aroma defects. The fact of carrying out microbial mucilage removal in water or under dry conditions also led to differences between the coffees. Mucilage removal in water gave coffees with more particular fruity, floral and caramel attributes, whereas dry mucilage removal gave more neutral coffees. When the latter process was also combined with dry pulping, sourness defects occurred with light roasting and those coffees developed bitterness and harshness with darker roasting. Light roasting made it possible to more effectively distinguish between treatments based on aroma criteria associated with the volatile compounds produced during post-harvest processing. Dark roasting also enabled a distinction to be made, but based on aromatic criteria linked to the thermal reactions of roasting. Medium roasting enabled the least distinction to be made between treatments, undoubtedly because a higher degree of roasting cancelled out the olfactory differences detected with light roasting, which were associated with highly volatile compounds, such as esters, and because that degree of roasting was not yet high enough to give aroma and sensory differences associated with roasting. The next stage in this work will be to analyse volatile compounds of green coffee produced during post-harvest processing, along with chemical compounds that are precursors of the thermal aroma that develops during roasting, and which also play a role in the taste of roasted coffee, in order to gain a clearer understanding of the differences seen in our work on roasted coffee. (Resume d'auteur)
Les souches productrices d'Ochratoxine A (A. ochraceus et A. niger) representent 3 a 25% de la contamination fongique du cafe Arabica mexicain. Aucune souche d'Aspergillus carbonarius et de Penicillium verrucosum n'a ete isolee sur les differents cafes. L'etude de l'impact du type de traitement post-recolte sur la contamination et la toxinogenese pour l'OTA a montre qu'A. ochraceus est sensible a la competition avec la flore autochtone du cafe, alors que ce n'est pas le cas pour A. niger qui colonise le milieu facilement. Cependant A. niger ne produit pas la toxine aussi rapidement et en aussi grande quantite qu'A. ochraceus. Les procedes sec et avec depulpage et demucilagination mecaniques donnent des resultats sensiblement differents de ceux obtenus avec le procede humide traditionnel utilisant une demucilagination microbienne: ce dernier procede est moins favorable a la croissance fongique meme s'il y a peu de difference sur l'aptitude a la production d'Ochratoxine A. La presence du stade de fermentation microbienne est cependant un facteur de limitation de risque au meme titre que l'obtention d'une baisse rapide de l'Aw pendant le sechage. (Resume d'auteur)
In cocoa fermentation exists a wide microbial diversity; the most important microorganisms are yeasts, lactic acid bacteria (LAB), and acetic acid bacteria (AAB). Such diversity can result that fermented cocoa quality is not always the same. The use of microbial consortia can steer the process, allowing the production of fermented cocoa beans with homogeneous quality and safety. For that reason, it was proposed to use indigenous microorganisms to formulate defined inoculums to conduct the small- fermentation of Mexican cocoa. A total of 54 strains were isolated from the spontaneous fermentation of cocoa. These included yeasts (Candida, Rhodotorula, Saccharomyces and Yarrowia), LAB (Lactobacillus and Lactococcus), and AAB (Acetobacter and Gluconobacter). The cocoa fermentations were inoculated with an inoculum composed of lipolytic Yarrowia, Lactococcus lactis, and Acetobacter aceti, only varying the form of inoculation (mixed or microbial succession) and were compared with spontaneous fermentation. It was observed that fermentation conducted by succession inoculation form showed similar behavior to the spontaneous process, obtaining well-fermented cocoa beans with homogeneous quality and safety.
