A. Dasen

Ripening and quality of Swiss-type cheese made from raw, pasteurized or microfiltered milk

Abstract Experimental mini-cheeses were made from raw (Ra), microfiltered (MF), pasteurized (Pa) (72 °C, 30s) or pasteurized mixed with microfiltration retentate (PR) milk to study the influence of the indigenous microflora and pasteurization on the quality of Swiss-type cheese. To estimate biochemical transformations during cheese ripening, several methods were used: nitrogen fractionation (water-soluble fraction and phosphotungstic acid (PTA)-soluble fraction), urea-polyacrylamide gel electrophoresis of caseins, reverse phase liquid chromatography of the water-soluble fraction, lactate and volatile fatty acids. Microbial populations were also enumerated. At the end of ripening, in comparison with MF and Pa milk cheeses, Ra and PR milk cheeses exhibited higher overall aroma intensity and pungency, characteristics which correlated with higher populations of facultatively heterofermentative lactobacilli (108 cfug−1), propionibacteria (108 cfug−1), and enterococci (106cfug−1). These cheeses had high levels of PTA-soluble N and acetic, propionic and isovaleric acids. MF and Pa milk cheeses, although somewhat different from one another, were very different from the two other types of cheese. Pa milk cheese had a lower pH than MF milk cheese, and contained a higher proportion of γ-caseins due to the activation of plasmin. Moreover, Pa milk cheese was more acidic, but demonstrated a higher overall aroma intensity. The addition of raw milk flora (retentate) to Pa milk restored almost all the biochemical and sensory characteristics of Ra milk cheese measured in this study.

Origin and diversity of mesophilic lactobacilli in Comté cheese, as revealed by PCR with repetitive and species-specific primers

The objectives of this work were to describe the diversity of mesophilic lactobacilli in Comte cheese at the strain and species levels, to determine the origin(s) of this non-starter microflora, and to get a collection of well characterised strains from Comte cheeses. Strains were isolated from milks, starter cultures and eight cheeses from two factories, with four cheeses made from the same vat in each factory. Strain and species assignations were performed with a combination of two PCR-based methods, amplification with the pairs of repetitive primers ERIC1/ERIC2 and REP–1R-Dt/REP2-D, and amplification with specific primers for Lactobacillus zeae, Lactobacillus paracasei and Lactobacillus rhamnosus. The reliability and reproducibility of these methods were assessed using 49 collection strains of mesophilic lactobacilli commonly detected in cheeses. A total of 488 isolates of mesophilic lactobacilli was collected and was assigned to 44 different strains and three different species. Lactobacillus paracasei and Lactobacillus rhamnosus were the predominant species in milks, starter cultures and cheeses, and constituted 98.7% of the isolates. Strain diversity was found at both individual cheese and factory levels. Thirteen and fifteen different strains were detected throughout cheesemaking and ripening in two individual cheeses made in different factories; only 11 different strains were detected in the two corresponding mature cheeses. The data strongly suggest that most mesophilic lactobacilli strains originate from raw milk.

Activité protéolytique de souches de lactobacilles thermophiles isolées de levains et de Comté. I. Validation sur minifromages des techniques de laboratoire

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Activité protéolytique de souches de lactobacilles thermophiles isolées de levains et de Comté. I. Validation sur minifromages des techniques de laboratoire Y Bouton, P Guyot, A Dasen, R Grappin

Characterizing ripening of Gruyère de Comté: Influence of time × temperature and salting conditions on eye and slit formation

Abstract Gruyere de Comte is a Swiss-type, hard cheese, made of raw milk and produced exclusively in a limited area, in the East of France. Comte cheese is regularly salted on the surface throughout the ripening period, with simultaneous rubbing. This process leads to an important bacterial surface growth (10 11 CFU/g), a production of NH 3 (50 ppm), and a regular increase of the salt level. The kinetics of salt intake and its final level strongly influence the propionic fermentation and eye formation, as well as the primary proteolysis. Hydrolysis of α s 1 - CN decreases regularly with the salt level, whereas plasmin activity is maximum at 2·3% salt/moisture. Variations in the ripening time × temperature cycle influence the rate of hydrolysis of α s 1 - CN and to a lesser extent of β-CN. The improntance of the propionic fermentation increases with the temperature of ripening. The modifications of the rheological properties of Comte during ripening appear to be time × temperature dependent. Slit formation is closely related to cheese composition and also to the nature and extent of proteolysis. It was shown that when several of the following physicochemical characteristics: low moisture, high fat, high NaCl, low calcium and high level of protein breakdown are associated, the rheological properties are modified in such a way (increase of the shortness), that the cheeses are more likely to have slits. The relative importance of the anisotropy of the rheological properties explains the direction of the slits which are always parallel to the surfaces. A high correlation (r = 0·96) was found between the log of the fracture strain difference and the slit intensity. From all the results obtained in various studies, it appears that monitoring both the nature and extent of proteolysis through milk quality, cheese making, and ripening conditions, is a major challenge to produce regularly high quality Comte cheese.