-Compared to many cheeses, lipolysis of Emmental is generally low. It concerns about 1-2% of cheese fat and the amount of free fatty acids (FFAs) varies from 2 to 7 g . kg -1 of ripened cheese. In this work, we studied the extent of lipolysis due to propionic acid bacteria (PAB). The release of FFAs during the ripening of Emmental cheeses made from microfiltered milk, with or without propionic acid bacteria (PAB) was followed. The usual cooking step in the cheese process (up to 50 o C and 30 min) inactivated the lipoprotein lipase (EC 3.1.1.34) and the main factor in the lipolysis of Emmental cheese was shown to be the lipolytic activity of PAB. This activity was strain-dependent and not related to the production of propionic acid in cheese. The most abundant FFAs were palmitic acid, oleic acid, myristic acid and stearic acid as in milk fat and it was concluded that lipolytic activity of PAB is non-specific. Lastly, an interaction still not elucidated was evidenced between certain PAB strains and thermophilic lactobacilli strains regarding lipolysis extent in Emmental cheese.propionic acid bacteria / lipolysis / free fatty acid / Emmental cheese Résumé -Contribution des bactéries propioniques à la lipolyse de l'emmental. La lipolyse est comme la protéolyse et la glycolyse un phénomène majeur de l'affinage des fromages. Comparativement à de nombreux autres fromages, la lipolyse de l'emmental est généralement limitée. Elle porte sur environ 1 à 2% de la matière grasse du fromage et la teneur en acides gras libres (AGL) varie de 2 à 7 g . kg -1 dans le fromage affiné. Dans plusieurs expérimentations en fromagerie pilote, nous avons étudié l'intensité de la lipolyse générée par les bactéries propioniques. La libération des AGL au cours de l'affinage d'emmentals fabriqués à partir de lait microfiltré ensemencé ou non en bactéries propioniques, démontre que la cuisson habituelle du caillé en cuve (au moins 50 o C pendant 30 min) inactive la lipoprotéine lipase (EC 3.1.1.34) et que l'activité lipolytique des bactéries propioniques est majoritairement responsable de la lipolyse de l'emmental. Cette activité est souche dépendante et n'est pas corrélée avec l'intensité de la fermentation propionique. Des lactobacilles thermophiles homofermentaires interagissent avec les bactéries propioniques sur la lipolyse de l'emmental, par un
Domagała J., Pluta-Kubica A., Pustkowiak H. (2013): Changes in conjugated linoleic acid content in Emmental-type cheese during manufacturing. Czech J. Food Sci., 31: 432-437. The fatty acids composition including the conjugated linoleic acid content in the milk and in the samples of Emmental-type cheese during the manufacturing and ripening period was determined. The highest amount of volatile and the lowest amount of saturated fatty acids were observed at the end of ripening. In turn, the highest content of monoun-saturated fatty acids was found in the curd, however, it declined during processing. The richest in polyunsaturated fatty acids were the cheese samples after the warm room stage, however, the amount of these fatty acids became highly significantly lower at the end of ripening. The level of conjugated linoleic acid increased during manufacturing. Its content in the milk and the curd was highly significantly lower than at the other stages of production.
Success in making a cheese acceptable in both flavour and texture depends partly on curd properties which determine the retention of fat and moisture and, thus, cheese yield and composition (Green & Grandison, 1993). When considering farmhouse and/or Appelation d'Origine Contrôlée cheese where milk treatments are not allowed, curd properties depend only on milk composition and clotting characteristics, which are subject to wide fluctuations over the year owing to the cow's stage of lactation and nutritional factors (O'Keeffe, 1984; Macheboeuf et al. 1993). These variations often result in seasonal differences in the chemical or sensory properties of the cheese (Kefford et al. 1995) which are sometimes difficult to understand (Grandison et al. 1985). Only a few studies have assessed the cheesemaking quality of milk by actually making ripened cheese; most studies report milk coagulation properties and curd firmness.The object of this work was to study the influence of the chemical composition and clotting characteristics of the milk on the chemical and sensory properties of ripened cheeses when milk characteristics vary widely.
-Qualitative aspect of proteolytic activity of thermophilic lactobacilli using in Swiss cheeses. The average peptidic pattern was established from 253 French Emmental cheeses sampled in 50 factories. It contained 53 peptidic peaks, 4 of which were the most important in quantity. Two Lactobacillus helveticus strains and five Lactobacillus delbrueckii ssp. lactis strains were tested in Emmental experimental cheesemaking in association with three different propionic strains (21 cheeses). The Propionibacterium freudenreichii strains did not affect the peptidic pattern of ripened Emmental cheese. On the other hand, 13 peptidic peaks were significantly influenced by the thermophilic lactobacilli strain. The two species of thermophilic lactobacilli were discriminated by three peptidic peaks. Seven peptidic peaks were correlated with the ammonia amount in ripened Emmental cheese. No significant correlation was found between peptidic peaks and SN/TN and NPN/TN. At the same time, the peptidic pattern produced by the seven lactobacilli strains were studied in laboratory. The most specific peptidic peak of the French Emmental cheese were not found by using the Hammarsten casein as substrate. Another substrate, similar to hard cooked cheeses, lyophilized and sterilized by ionisation was tested. This substrate was obtained with microfiltered milk and Streptococcus thermophilus strains only. This substrate digested by thermophilic lactobacilli allowed to find the specific peptidic peaks of the French Emmental cheese. For example, the 14th peak obtained in laboratory was significantly different according to lactobacilli species, as it was observed in the Emmental cheese experiments. This peak distinguished the strains inside the Lb. delbrueckii ssp. lactis too.
-Conjugated linoleic acid (CLA), and especially rumenic acid, are isomers of linoleic acid which have a great potential in human nutrition for their beneficial properties. The most important sources of natural CLA are milk and dairy products such as cheese. This study was delineated to assess the effects of sampling according to the cheese wheel, the seasonal and regional influence on CLA content in French Emmental cheese and, finally, the effects of culinary preparation of three different dishes (gratin, béchamel sauce and cheese fondue) and processed cheese. The rumenic acid content of Emmental cheese varied between 0.6% and 1.5% of total fatty acids according to the season and region of production, and appeared homogeneous through the cheese wheel. The culinary utilization and processing did not change the rumenic acid content of Emmental cheese.
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