Mise au point de technologies combinées pour la préservation de la viande et du brocoli

Dans les pays industrialises, les aliments prets a manger sont en plein essor. Ceci est du principalement au changement des habitudes des consommateurs demandant encore plus d’aliments faciles a utiliser. Cependant, ces aliments posent un probleme sanitaire vu leur instabilite microbienne et physico-chimique durant l’entreposage. Le procede industriel faisant intervenir le lavage et la coupe favorise l’acceleration de la senescence des vegetaux et la contamination croisee. Les bacteries souvent rencontrees sont Listeria monocytogenes, Escherichia coli, Salmonella Typhimurium et Clostridium sporogenes. Le controle de cette contamination passe generalement par l’ajout d’additifs, le chauffage et l’emballage sous atmosphere controlee. Cependant, avec la demande croissante d’aliments sans additifs, il devient difficile de controler la qualite microbiologique des aliments prets a manger. L’utilisation d’antimicrobiens naturels est tres etudiee, mais tres peu sont presentement sur le marche car ils sont instables et leur concentration minimale inhibitrice contre les pathogenes affecte souvent les proprietes sensorielles. Ce projet vise a developper des combinaisons de traitements (d’antimicrobiens naturels, enrobage, pretraitement au calcium, emballage conditionne et irradiation) afin d’assurer la qualite, l’innocuite et la protection des valeurs nutritives, sensorielles et physico-chimiques des legumes et de la viande prets a manger. Dans ce projet de maitrise, nous avons developpe une formulation antimicrobienne a base d’huile essentielle, d’acide organique et d’un antifongique par la determination de la concentration minimale inhibitrice et l’etude des interactions possibles. Cette formulation a ete par la suite immobilisee dans une matrice polymerique permettant d’avoir une meilleure stabilite et disponibilite des antimicrobiens naturels. L’efficacite antimicrobienne de l’enrobage antimicrobien lorsqu’il est applique seul ou combine a l’irradiation a ete evaluee sur le brocoli. Nous avons egalement evalue l'effet de la combinaison du pretraitement au calcium et l’enrobage a base d'alginate sur la qualite physico-chimique et microbienne du brocoli pret a manger. D’autre part, une marinade a base d’epices et d’extraits de vegetaux a ete utilisee pour evaluer son efficacite antimicrobienne in situ sur la viande seule ou combinee a l’irradiation gamma. Nous avons pu selectionner, in vitro, 6 agents antimicrobiens parmi 27. Ces antimicrobiens ont demontre une efficacite a eliminer les pathogenes alimentaires. L’etude de l’interaction entre ces 6 antimicrobiens a permis de mettre au point une formulation antimicrobienne (huile essentielle lemongrass + diacetate de sodium + natamycine) ayant demontree un effet additif contre Escherichia coli, Salmonella Typhimurium et Aspergillus niger et un effet synergetique contre Listeria monocytogenes. D’autre part, l’analyse in situ a permis de mettre en evidence un effet synergique entre l’irradiation gamma a faible dose et l’enrobage antimicrobien pour reduire Escherichia coli, Listeria monocytogenes, Salmonella Typhimurium et Aspergillus niger dans le brocoli. Un effet synergique a ete observe aussi entre l’irradiation gamma et l’ajout de la marinade pour reduire Escherichia coli, Salmonella Typhimurium et Clostridium sporogenes dans la viande emballee sous vide. Combiner l’ajout de la marinade, l’irradiation gamma et l’emballage sous atmosphere controlee semblent etre une alternative interessante pour proteger contre l’oxydation des lipides, la perte des vitamines et la decoloration de la viande durant une conservation a 4 °C. Nous avons pu demontrer aussi que l'application de l’enrobage d'alginate seul ou en combinaison avec un pretraitement de calcium a permis de maintenir la fermete et la couleur verte du brocoli au cours du stockage. Les traitements utilises en combinaison ont permis egalement la reduction du taux de respiration et la perte de masse et l'augmentation de la duree de conservation du brocoli pret a manger. Les resultats obtenus lors de cette etude sont d’un grand interet pour l’industrie alimentaire permettant ainsi, le developpement de nouveaux produits repondant a une demande croissante des consommateurs. Ce travail presente une nouvelle alternative surtout pour les patients immunodeprimes, qui sont condamnes a manger des aliments avec de faibles valeurs nutritionnelles causees par les procedes de decontamination durs en les protegeant des maladies d'origine alimentaire et en augmentant la qualite nutritionnelle des aliments. Abstract In developed countries, the ready-to-cook product category is in continuous growth due the consumer’s increasing demand for convenient foods. However, these commodities pose a health problem due to their microbiological and physico-chemical instability during storage. The industrial process involving washing and cutting promotes vegetable senescence and cross-contamination. The often encountered bacteria are Listeria monocytogenes, Escherichia coli, Salmonella Typhimurium and Clostridium sporogenes. The control of this contamination typically requires the addition of additives, heating and packaging under controlled atmosphere. However, with the growing demand for preservative-free food, it becomes difficult to control the microbiological quality. The use of natural antimicrobial agents for the preservation of food is widely studied in the literature; however, very few are currently used in food industry because of their instability and their ability to affects the sensory properties of food at their determined minimum inhibitory concentration against pathogens. This project aims to develop treatment combinations (natural antimicrobials, edible coating, controlled atmosphere, calcium pretreatment and irradiation) to ensure the quality, safety and the protection of the nutritional value, sensory and physicochemical of ready-to-cook meat and vegetables. In this project, we have developed an antimicrobial formulation based on essential oil, organic acid and an antifungal by determining their minimum inhibitory concentration and the evaluation of prior synergistic effect between selected antimicrobials by the checker board method. This formulation was subsequently immobilized in a polymer matrix to have better stability and availability of natural antimicrobial. Its antimicrobial efficacy alone or combined with irradiation was evaluated on broccoli floret. Also, we evaluated the effect of combining calcium pretreatment and alginate coating on the physicochemical and microbial quality of broccoli florets. On the other hand, a commercial marinade was used to evaluate its antimicrobial efficacy in situ when it was applied alone or in combination with gamma irradiation on the meat. The effect of combining the addition of marinade to irradiation on sensory, nutritional and physicochemical quality of meat was also evaluated. In this study, we selected in vitro 6 antimicrobials among 27. These antimicrobials have demonstrated a high effectiveness in eliminating food pathogens. The study of the interaction between these six antimicrobial agents allowed the development of an antimicrobial formulation (Lemongrass essential oil + sodium diacetate + natamycin) which have demonstrated an additive effect against E. coli, Salmonella Typhimurium and Aspergillus niger and a synergistic effect against Listeria monocytogenes. On the other hand, the analysis in situ has demonstrated a synergistic effect between a low dose gamma irradiation and antimicrobial coating to reduce E. coli, L. monocytogenes, S. Typhimurium and A. niger on broccoli. A synergistic effect was also observed between gamma irradiation and the addition of the marinade to reduce E. coli, Salmonella Typhimurium and Clostridium sporogenes on meat packed under vacuum. Based on the experimental findings, the combination of the marinade, gamma irradiation and packaging under modified atmosphere treatments was found to be a promising approach to extend the shelf-life of ready-to-cook pork loin as well as to protect against lipid oxidation, the loss of vitamins and meat discoloration. Applying alginate coating alone or in combination with calcium pretreatment allowed maintaining the firmness and the green color of broccoli floret during storage. Treatments allowed also the reduction of the respiration rate and the loss of weight and the increase of the shelf-life of treated broccoli which is very beneficial for food industry. The obtained results in this study are of great interest for the food industry allowing the development of new products to meet growing consumer demand. This work presents a new alternative especially for immunocompromised patients who are condemned to eat foods with low nutritional values caused by the harsh decontamination processes, and this by protecting them from foodborne illness and increasing the nutritional quality of food.