Uncooked Cheese Research Articles

Characterization of cooked cheese flavor: Volatile components.

The aim of this work was to identify volatiles that contribute to the aroma of cooked cheese, including the role of fat content in their development during cooking. Volatiles and odorants in cooked mature Cheddar were identified using a combination of SPME (solid-phase microextraction)/GC-O (gas chromatography-olfactometry) and SPME/GC-MS (gas chromatography-mass spectrometry). A selection of the odorants was quantitated in six cheeses, uncooked and cooked, (mature Cheddar, high-, medium-, and low-fat mild Cheddar, mozzarella, and Parmesan). Many compounds showed significant differences between cooked and uncooked cheese; Strecker aldehydes, pyrazines, and furanones were all significantly higher in cooked cheeses than in uncooked cheese, while ethyl esters (key odorants in uncooked cheese) were not detected in any of the cooked cheese. Principal component analysis demonstrated that fat concentration in mild Cheddar was positively correlated with the formation of potential odorants (the Strecker aldehydes, methanethiol, 2-methylketones, and fatty acids) upon cooking. Potential lipid precursors for these compounds are discussed. PRACTICAL APPLICATION: This research can be used by the dairy industry to develop better cheeses, especially low- and reduced-fat cheeses, for use in cooked applications such as toppings for pizzas and ready meals. Alternatively, this research describes key volatile compounds in cooked cheese that can be used by the flavoring industry to develop authentic cooked cheese flavorings.

Population dynamics and bidirectional transfer of Listeria monocytogenes and Shiga toxin-producing Escherichia coli during cheese production in wooden vats

Wooden vats are used in the production of some traditional cheeses as the biofilms on wooden vat surfaces are known to transfer large quantities of microbes to cheese. However, the safety of using wooden vats for cheese production remains controversial as the porous structure of wood provides an irregular surface that may protect any attached pathogen cells from cleaning and sanitation processes. On the other hand, the absence of pathogens in wooden vats has been reported in multiple studies and wooden materials have not been associated with foodborne illness outbreaks. The present study determined the survival of Listeria monocytogenes and Shiga toxin-producing Escherichia coli (STEC) during the production of an uncooked pressed cheese in wooden vats as well as their ability to transfer to the wood and then to milk used in subsequent batches of cheese production in the absence of formal cleaning. Results from the study indicate that pathogens inoculated in milk grew during production of the uncooked cheese, but showed limited ability to colonize the wooden vats and contaminate subsequent batches. These results suggest that the risks of using wooden vats to produce cheese is low if the milk is of high microbiological quality.

Lacticaseibacillus Strains Isolated from Raw Milk: Screening Strategy for Their Qualification as Adjunct Culture in Cheesemaking.

The microbial ecology fundamentals of raw milk and long-ripened cheeses consist of a complex interaction between starter lactic acid bacteria (SLAB) and non-starter LAB (NSLAB). Although NSLAB aromatic properties are paramount, other phenotypic traits need to be considered for their use as adjunct cultures, such as the capability to endure technological parameters encountered during cheesemaking. The present study focused on the isolation and characterization of NSLAB from spontaneously fermented raw cow's milk coming from 20 dairies that produce Grana Padano PDO cheese. From 122 isolates, the screening process selected the 10 most diverse strains belonging to Lacticaseibacillus spp. to be phenotypically characterized. The strains were tested for their growth performance in milk in combination with the application of technological stresses, for their ability to produce volatile compounds after their growth in milk, and for their ability to use different nutrient sources and resist chemicals. The complex characterization qualified the strains 5959_Lbparacasei and 5296_Lbparacasei as the best candidates to be used as adjunct strains in the production of raw milk and long-ripened cheeses, provided that antibiotic resistance is measured before their employment. Other strains with interesting aromatic capabilities but lower heat resistance were 5293_Lbparacasei, 5649_Lbparacasei and 5780_Lbparacasei, which could be candidates as adjunct strains for uncooked cheese production.

Characterisation of Cooked Cheese Flavour: Non-Volatile Components.

This work examined the role of selected non-volatile compounds in cooked cheese flavour, both as tastants and as precursors of aroma generation in the Maillard reaction. The effect of cooking on the concentration of selected non-volatile compounds (organic acids, sugars, amino acids, γ-glutamyl dipeptides, and diketopiperazines) in six cheeses (mature Cheddar, mozzarella, Parmesan, and mild Cheddar (low, medium, and high fat)) was determined. Sugars, amino acids, and γ-glutamyl dipeptides were extracted and analysed by LC, whereas diketopiperazines were extracted by solid-phase extraction and analysed by GC-MS. Sugars, amino acids, and γ-glutamyl dipeptides decreased in concentration during cooking, whereas diketopiperazines and some organic acids increased in concentration. Diketopiperazines were above the taste threshold in some cooked cheeses and below the threshold in uncooked cheeses. The role of fat content in cooked cheese flavour is discussed. Furthermore, γ-glutamyl dipeptide concentration increased during 24 months of ageing in low, medium, and high-fat Cheddars, with similar levels of γ-glutamyl dipeptide detected in aged low and high-fat Cheddars. This work will give valuable insight for the dairy industry to inform the development of cheeses, especially low-fat variants, for use in cooked foods.

Fungal diversity of “Tomme d'Orchies” cheese during the ripening process as revealed by a metagenomic study

Tomme d'Orchies is an artisanal pressed and uncooked cheese produced and marketed in the north of France. This study aimed at showing the fungal microbiota evolution of this cheese using a metagenetic based Illumina technology targeting the ITS2 domain of 5.8S fungal rDNAs. To this end, samples were taken from the rind and the core of different cheeses, after 0, 1, 3, 7, 14 and 21days of ripening. The data underpinned the prevalence of Yarrowia lipolytica and Galactomyces geotrichum for both microbiotas. Unusual species including Clavispora lusitaniae, Kazachstania unispora and Cladosporium cladosporioides were also detected, but their origins remain to be ascertained. The metagenomic revealed also the presence of Kluyveromyces and Debaryomyces species.

The effect of cooking time on curd composition and textural properties of sheep Halloumi cheese

The effect of cooking time on the chemical characteristics, the textural properties and the volatile compounds of Halloumi cheese curd were studied. Sensory evaluation of the 1-day Halloumi cheese was also carried out. Cooking the cheese curd for 30min significantly decreased its moisture content compared to the uncooked cheese curd. The cheese curds cooked for 30 and 60min were found to have higher Ca and P contents in comparison with the uncooked cheese curd. After being cooked, the cheese curds exhibited higher values for hardness compared to the uncooked cheese curd due to their lower moisture contents. The cooking process affected the content of most volatile compounds. Alcohols which were found to be the main group of volatile compounds of the tested samples, consisted 85.50% of the total volatile compounds in the uncooked cheese curd and were significantly reduced reaching a percentage of 65.31% and 30.78% after cooking the cheese curd for 30 and 60min, respectively. Instead, the volatile substances that were formed during thermal processing, such as γ-decalactone, 3-hydroxy-butanal, 2-furan-methanol and 2-hydroxy furanone increased significantly. The cheese curd that was cooked for 60min was more yellowish in appearance compared to the cheese curd that was cooked for 30min due to its higher value b (yellowness). The Halloumi cheese (end product) that was produced by cooking the cheese curd for 30min achieved significantly higher sensory scores than the one that was produced by cooking the cheese curd for 60min.

Optimized enrichment for the detection of Escherichia coli O26 in French raw milk cheeses

Our main objective was to optimize the enrichment of Escherichia coli O26 in raw milk cheeses for their subsequent detection with a new automated immunological method. Ten enrichment broths were tested for the detection of E. coli O26. Two categories of experimentally inoculated raw milk cheeses, semi-hard uncooked cheese and 'Camembert' type cheese, were initially used to investigate the relative efficacy of the different enrichments. The enrichments that were considered optimal for the growth of E. coli O26 in these cheeses were then challenged with other types of raw milk cheeses. Buffered peptone water supplemented with cefixim-tellurite and acriflavin was shown to optimize the growth of E. coli O26 artificially inoculated in the cheeses tested. Despite the low inoculum level (1-10 CFU per 25 g) in the cheeses, E. coli O26 counts reached at least 5.10(4) CFU ml(-1) after 24-h incubation at 41.5 °C in this medium. All the experimentally inoculated cheeses were found positive by the immunological method in the enrichment broth selected. Optimized E. coli O26 enrichment and rapid detection constitute the first steps of a complete procedure that could be used in routine to detect E. coli O26 in raw milk cheeses.

Is microbial diversity an asset for inhibitingListeria monocytogenesin raw milk cheeses?

This study aimed at determining if microbial diversity can be an asset to guarantee the microbial safety of raw milk cheeses. Our results show that microbial consortia from the surface of raw milk cheeses can self-protect against Listeria monocytogenes. Indeed, 10 complex microbial consortia among 34 tested from the surfaces of raw milk Saint-Nectaire cheeses were particularly effective for reducing the growth of L. monocytogenes on cheese surfaces in comparison of a commercial ripening culture, despite the high pH values on the surfaces. One of these consortia (TR15) was selected and propagated on cheese surfaces to create a collection of strains belonging to lactic acid bacteria, Gram-positive and catalase-positive bacteria, Gram-negative bacteria and yeasts. On the surfaces of uncooked cheeses, defined consortia consisting of combinations of several isolates from this collection displayed weaker antagonist activity against L. monocytogenes than the complex consortium TR15. The results from plate counting and analysis by single strand conformation polymorphism (SSCP) converged to show that microbial dynamics in cheeses TR15 differed from that of the defined consortia. TR15 cheeses had the highest levels of cultivable lactobacilli and leuconostocs. Their SSCP profiles were the richest in peaks and were characterised by the presence of Marinilactibacillus psychrotolerans, Carnobacterium mobile, Arthrobacter nicotianae or A. arilaitensis, Arthrobacter ardleyensis or A. bergerei and Brachybactrerium sp. Further investigation will be necessary to gain a better understanding of the microbial interactions involved in inhibiting L. monocytogenes.

Relationship between milk fat and protein contents and cheese yield

The relation between the useful material content (protein+fat content) of milk and cheese yield was analyzed on 189 manufactures of pressed uncooked cheeses. These manufactures were realized under controlled conditions in the same experimental cheese dairy, within the frame- work of eight different experiments, from milks of high hygienic quality (cows free of clinical mas- titis) partially skimmed so as to have a fat/protein ratio of 1.15. The fat+protein content of manufactured milks varied from 55 to 85 g.kg -1 . The relation between fat+protein content and cheese yield was lin- ear for this wide range of variation. Fat+protein content accounted for 77% of fresh yield and 87% of dry matter yield variability. Once the effect of fat and protein contents have been taken into account, other milk parameters (pH, κ-casein variants) may have a significant effect on cheese yield, but in a marginal way. milk / fat and protein contents / cheese yield

Cheesemaking, compositional and functional characteristics of low-moisture part-skim Mozzarella cheese from bovine milks containing κ-casein AA, AB or BB genetic variants

Low-moisture part-skim Mozzarella cheeses were made, at pilot scale (450 kg), on five occasions at weekly intervals from milks containing κ-casein AA, AB or BB genetic variants. Compared with κ-casein A variant milks, the κ-casein B variant milks were associated with higher concentrations of casein (P<0·001), whey protein (P<0·02) and total protein (P<0·001), superior curd-forming properties (P<0·05) and increased cheese yields (P<0·05). The moisture-adjusted (to 465 g/kg) cheese yields for the κ-casein AA, AB and BB cheeses were 91·5, 100·6, and 102·5 kg/1000 kg milk respectively. κ-Casein variant had no significant effect on the proteolysis and ripening of uncooked cheese or on the functionality (melt time, flowability and stretchability) of the cooked cheese during the course of a 90 d ripening period.

Effect of altering the daily herbage allowance to cows in mid lactation on the composition, ripening and functionality of low-moisture, part-skim Mozzarella cheese.

Milk was collected from three spring-calving herds, on different daily herbage allowances (DHA) of perennial rye-grass (16, 20 or 24 kg dry matter (DM)/cow for a 17 week period. On five occasions, at weekly intervals in the middle of the period, the three different milks were converted into low-moisture part-skim Mozzarella cheese. Increasing the DHA resulted in significant increases in the concentrations of protein in the cheesemilk (P < 0.05) and cheese whey (P < 0.02). The moisture-adjusted cheese yield increased significantly (P < 0.01) on raising the DHA from 16 to 24 kg grass DM/cow. DHA had no significant effects on any of the gross compositional values of the cheese (although moisture and fat-in-DM levels tended to decrease and increase respectively with increasing DHA). The hardness of the uncooked cheese and functionality of cooked cheese (i.e. melt time, flowability, stretch and viscosity) were not significantly influenced by DHA over the 115 d ripening period at 4 degrees C.