Search

Spores of psychrotolerant strains of the foodborne pathogen Bacillus cereus can multiply during storage of cooked or pasteurized, refrigerated foods and can represent a risk if these cells are not eliminated during reheating of food product before consumption. We determined the heat-resistance of psychrotolerant B. cereus vegetative cells at different heating temperatures in laboratory medium and compared it with that of thermotolerant B. cereus vegetative cells. The z values, based on times for a 3 logio reduction, of the vegetative cells of the three psychrotolerant phylogenetic groups of B. cereus varied between 3.02 degrees C and 4.84 degrees C. The temperature at which a 3 logio reduction was achieved in 10 min varied between 47.6 degrees C and 49.2 degrees C for psychrotolerant vegetative cells and it was around 54.8 degrees C for thermotolerant vegetative cells. Moreover, 0.4 min at 60 degrees C would be sufficient for a 6 logio CFU/ml reduction of the most heat resistant psychrotolerant B. cereus vegetative cells. These data clearly showed that psychrotolerant B. cereus vegetative cells can be rapidly eliminated by a mild heat treatment such as food reheating.

La betterave sucrière est la deuxième plante en termes de production de sucre avec 19,6% du sucre produit dans le monde entre 2015 et 2016, derrière la canne à sucre. Cultivée dans les zones tempérées comme le nord de la France et la Belgique, elle est sensible au stress thermique modéré. En effet, une augmentation de 1°C de la température moyenne entraîne une perte de rendement de 29%. Dans le cadre du réchauffement climatique et afin de fournir aux agriculteurs des variétés ayant une meilleure résistance à la chaleur, la compréhension des réponses de la betterave sucrière au stress hyperthermique est nécessaire. Pour cela, une étude des réponses physiologiques et métaboliques a été effectuée avec trois hybrides : un hybride de type sucré avec 18% de sucre dans sa racine, un hybride de type lourd avec un meilleur rendement que la moyenne mais avec seulement 17% de sucre dans sa racine, et un hybride dit « résistant » au stress hyperthermique, ayant le meilleur rendement aux champs avec des températures plus élevées. Alors que la photosynthèse nette n’était pas modifiée en condition de stress, une croissance plus rapide de la rosette a été observée aux stades jeunes pour les trois hybrides. Une approche de modélisation suggère qu’une croissance de la rosette plus rapide contrecarre les effets du stress hyperthermique sur la production racinaire. Cette hypothèse est confirmée par le fait que l’hybride le plus performant a la croissance foliaire la plus rapide. Le stress hyperthermique provoque une forte diminution du stockage transitoire du carbone dans les feuilles matures. Dans les feuilles en cours de développement, le stockage transitoire du carbone, dont la moitié sous forme d’amidon, était seulement maintenu chez l’hybride le plus performant. Un calcul intégrant les besoins en carbone de la croissance foliaire suggère que ce maintien contribue significativement au maintien du rendement chez cet hybride. Par ailleurs, un marqueur putatif de la sensibilité au stress hyperthermique a été identifié lors de cette étude. Au final ce travail a permis de mieux comprendre comment la betterave sucrière répond à l’élévation de la température et ainsi proposer de nouvelles stratégies pour l’amélioration de cette espèce

The aim of FP7-OPTIFEL project is to create new products based on fruits and vegetables, supplemented with nutrients to fight elderlies’ nutritional deficiencies. The microbial safety of these products is of great importance due to elderlies’ vulnerability. The foodborne pathogen Bacillus cereus can resist to pasteurization and psychrotrophic strains can multiply during food storage at low temperatures. Therefore we verified if psychrotrophic Bacillus cereus could be destroyed when reheating the food before consumption, by measure of the heat resistance of psychrotrophic Bacillus cereus vegetative cells. We studied six psychrotrophic strains belonging to three different phylogenetic groups (group II, V and VI) and two thermophilic strains (group VII) at temperatures representative of food reheating. These Bacillus cereus strains were cultivated in optimal condition and heat resistance was determined with vegetative cells in stationary phase. Bacillus cereus vegetative cells suspensions were heated at five or more different temperatures for five different heating times. Survival curves and thermal death curves were established and the kinetic parameters δ (decimal reduction time at temperature T) and Z (temperature dependence of δ) were derived by linear regression. At 48°C, δ value o vegetative cells of psychrotrophic strains varied from 3 to 8 min. For all strains, the heat-sensitivity (Z values) varied between 1.6 °C and 5.6 °C. Z value was not different among the Bacillus cereus phylogenetic groups, and similar between the psychrotrophic and thermophlic groups. These Z values were low compare to other bacteria, for example to Salmonella enterica Z value can varied between 7.71 and 11.19 and for Staphylococcus aureus between 7.46 and 13.98 (Amado et al., 2013). Six log 10 reduction of the most resistant psychrotrophic Bacillus cereus could be obtained by reheating 3 min at 53°C.

On estime aujourd'hui à 25% les pertes d'aliments post-récolte et en aval, en raison de leur altération par des microorganismes. L'étude menée ici illustre le risque d'altération engendré par une rupture dans la chaîne du froid, en prenant comme modèle un aliment liquide pasteurisé et réfrigéré, riche en nutriments et dont la température ne doit pas dépasser 4°C.

The aim of this study was to evaluate the efficiency of selection of potato families in early generations for heat tolerance. Thirty families were evaluated in the seedling generation (SG), first clonal generation (FCG) in the field and greenhouse under high temperature conditions, and second clonal generation (SCG) under mild temperatures. The mean of the families was obtained in each generation. The 16 most productive families in FCG were selected, and the clones of these families were evaluated in experiments in the winter and rainy crop seasons. The results showed that family selection for tuber shape may be applied as of the SG. It was also observed that family selection in the FCG and SCG for yield and tuber specific gravity contributed to identification of clones tolerant to heat and responsive to environmental improvement. Resumo O objetivo deste trabalho foi avaliar a eficiência da seleção de famílias de batata nas gerações precoces para tolerância ao calor. Foram avaliadas 30 famílias na geração seedling (SG), primeira geração clonal (FCG) em campo e casa de vegetação sob condições de temperaturas elevadas e segunda geração clonal (SCG) sob temperaturas amenas e obtidas as médias das famílias em cada geração. Foram selecionadas 16 famílias mais produtivas na FCG e os clones dessas famílias foram avaliados em experimentos nas safras de inverno e "das águas". Os resultados mostraram que a seleção de famílias para formato de tubérculos pode ser aplicada desde a SG. Também observou-se que a seleção de famílias na FCG e SCG para produtividade e peso específico de tubérculos contribuiu para a identificação de clones tolerantes ao calor e responsivos a melhoria ambiental.