Volatile composition and proteolysis in traditionally produced mature Kashar cheese

Twelve samples of raw milk mature Kashar cheese at different stages of ripening were collected from retail outlets. The average pH, moisture, fat-in-dry matter, protein, salt-in-dry matter and titratable acidity contents of the samples were 5.33, 39.39%, 45.20%, 27.33%, 6.62% and 0.65% (as lactic acid), respectively. Indices of proteolysis varied from 10.72% to 23.75% and 7.09% to 12.26% for pH 4.6-soluble and 12% trichloroacetic acid-soluble nitrogen fractions, respectively, and total free amino acid concentrations ranged from 6.36 to 36.03 mg Leu g⁻¹ of cheese. The cheeses were analysed for volatile compounds by Solid Phase Microextraction and Gas Chromatography-Mass Spectrometry (GC-MS). A total of 113 compounds were detected and identified belonging to the following chemical groups: acids (eleven), esters (sixteen), ketones (sixteen), aldehydes (six), alcohols (twenty-seven), sulphur compounds (seven), terpenes (seven) and miscellaneous compounds (twenty-three). The potential effect of each compound on the flavour profile of Kashar cheese is discussed. Acids, esters, ketones and alcohols were found at considerable levels in the samples. Kashar cheeses obtained from different retail outlets displayed some differences in terms of chemical composition, proteolysis and patterns of aroma compounds; and may be attributed to their production technologies and age-related variations.     

SPME/GC-MS Characterization and Comparison of Volatiles of Eleven Varieties of Turkish Cheeses

In this study, the volatile aroma profiles of a variety of economically important cheeses for the Turkish dairy sector were characterized. A total of 75 samples belonging to 11 Turkish cheese varieties, including Civil, Canak, Dil, Divle Tulum, Ezine, Hellim, Malatya, Mihalic, Orgu, Urfa, and Van Otlu, were comparatively studied for their volatile profiles. One hundred and twelve volatile compounds were identified in the cheeses by solid-phase microextraction combined with gas chromatography-mass spectrometry and the results are discussed based on their chemical classes (31 esters, 7 acids, 18 ketones, 3 aldehydes, 24 alcohols, 10 terpenes, and 19 miscellaneous compounds). Esters, ketones, and alcohols were the most abundant classes identified and were highly dependent on the variety of cheese. Principal component analysis was applied to aid the interpretation of the gas chromatography-mass spectrometry data and to distinguish the cheeses. Divle Tulum cheese had high levels of aldehydes, ketones, and alcohols and separated from all the other cheeses, and the cheeses including Dil, Hellim, Malatya, Orgu, and Urfa grouped together. The last group of cheeses had low levels of volatiles stemming probably from the restricting effect of scalding or cooking that are employed in the manufacture of these cheeses and on the biochemical and/or microbial activity. Civil, Ezine, and Mihalic cheeses had somewhat different aroma profiles, but they were closely located near the cheeses including Dil, Urfa, Orgu, etc. The results suggest that each variety of cheese had different volatiles profile and that the manufacturing technique as well as ripening conditions of the cheeses played a major role on the individual volatile profiles.     

Effects of including silage in the diet on volatile compound profiles in Montasio cheese and their modification during ripening

Effects of including silage in the diet on volatile compound profiles and their modification during ripening of Montasio cheeses were examined. Twelve farms were selected and grouped according the type of forage in the ration: hay-based diets (four farms); hay and corn silage-based diets (four farms); and diets based on hay, corn silage and grass silages (four farms). For cheesemaking, 1000 kg of milk collected from two consecutive milkings was sampled from each farm and processed in the same cheese factory. Cheeses were ripened in the same cellar, in controlled humidity (78-85% relative humidity) and temperature (9-12 degrees C), until analysis. After 68 (62-74), 200 (194-206) and 360 (354-366) d of ripening, a cheese from each batch was analysed for moisture, protein and fat, volatile fatty acids (VFA) and volatile compounds. These latter were analysed by dynamic reverse carrier gas headspace gas chromatographic mass spectrometry (GC-MS) technique, scanning from m/z 29 to m/z 300 at 0.5 s cycle time. Total and individual VFA contents of cheeses did not differ between the different dietary treatments and increased linearly (P<0.01) during ripening, indicating that there were no appreciable defects of fermentation. Sixty-two volatile compounds were identified in the cheese samples: 12 aldehydes, 9 ketones, 16 alcohols, 17 esters, 2 hydrocarbons, 4 sulphur-containing compounds and 2 terpenes. Diet significantly affected the amount of total alcohols, ethanol, isobutanol, 1-penten-3-ol, 2-methyl-1-butanol and the sum of all the volatile compounds. Significant variations of 33 volatile compounds (9 aldehydes, 4 ketones, 6 alcohols, 10 esters, 1 hydrocarbons, 2 sulphur containing compounds, and 1 terpene) were observed during ripening. These results suggest that the influence of diet composition on volatile compounds of matured cheeses are related more to effects on microbial and chemical fermentations in cheese during ripening rather than to a direct transfer of molecules from milk.     

Influence of exopolysaccharide‐producing cultures on the volatile profile and sensory quality of low‐fat Tulum cheese during ripening

The objective of this investigation was to compare the composition and changes in the concentration of volatiles in low‐fat and full‐fat Tulum cheeses during ripening. Tulum cheese was manufactured from low‐ or full‐fat milk using exopolysaccharide (EPS)‐producing or non‐EPS‐producing starter cultures. A total of 82 volatile compounds were identified belonging to the following chemical groups: acids (seven), esters (21), ketones (14), aldehydes (six), alcohols (14) and miscellaneous compounds (20). The relative amounts of acids, alcohols and aldehydes increased in the cheeses made with EPS‐producing cultures during 90 days of ripening. Differences were found in the volatile profile of full‐fat Tulum cheese compared with the low‐fat variant, especially after 90 days of ripening. Exopolysaccharide‐producing cultures changed the volatile profile, and the EPS‐producing cultures including Streptococcus thermophilus + Lactobacillus delbrueckii subsp. bulgaricus + Lactobacillus helveticus (LF‐EPS2) produced cheese with higher levels of methyl ketones and aldehydes than the non‐EPS cultures. In the sensory analysis, full‐fat Tulum cheeses and the cheese produced with the EPS‐producing culture containing Lb. helveticus (LF‐EPS2) were preferred by the expert panel. It was concluded that the use of EPS‐producing starter cultures in the manufacture of low‐fat Tulum cheese had the potential to improve the flavour.     

Volatile compounds and proteolysis in traditional Beaten (Bieno sirenje) ewe's milk cheese

Beaten ewe's milk cheese is a traditional autochthonous type of cheese manufactured in Macedonia with a relatively high nutritional value and sensory characteristics. The objective of this study was to characterise the gross composition, proteolysis and volatile profiles of the cheese that is supplied from different retails. The ranges for gross composition were from 31.53% to 42.83% (w/w) for moisture, 41.99% to 50.98% (w/w) for fat‐in‐dry matter, 2.03% to 8.25% (w/w) for salt content and 20.74% to 33.35% (w/w) for protein. Proteolysis results showed various levels of soluble nitrogen ranged from 3.15 to 33.50 for water‐soluble nitrogen (WSN) and from 1.11% to 6.79% for nitrogen soluble in 12% trichloroacetic acid (TCA‐SN). The ranges for total free amino acids were from 1.65 to 8.06 mg Leu/g. Lower proteolysis was observed in the cheese samples due to high salt contents. In total, 65 volatile compounds were identified in Beaten cheese. As a conclusion, the variation of the peptide profile, electrophoresis and volatile contents of Beaten cheeses are due to the lack of standardised manufacture protocols.     

Effect of Penicillium roqueforti and incorporation of whey cheese on volatile profiles and sensory characteristics of mould‐ripened Civil cheese

In this study, four different types of mould‐ripened Civil cheese were manufactured. A defined (nontoxigenic) strain of a Penicillium roqueforti (SC 509) was used as secondary starter for the manufacture of mould‐ripened Civil cheese with and without addition of the whey cheese Lor; in parallel, secondary starter‐free counterparts were manufactured. A total of 83 compounds were identified. Ketones, alcohols and esters were the principal classes of volatile components. Principal component analysis of the headspace volatiles grouped cheeses by age and type. P. roqueforti inoculated cheese was clearly separated from the other cheeses at 180 days of ripening, and these cheeses were characterised with high levels of ketones (e.g., 2‐butanone, 2‐heptanone). Differences in the panel scores between the cheese samples were not significant during the first stage of ripening (up to 60 days); as ripening proceeded, these differences were become evident and P. roqueforti inoculated cheeses received higher scores than others. Addition of Lor in the manufacture of mould‐ripened Civil cheese caused lower points by the sensory panel, and the cheese inoculated with P. roqueforti and Lor‐free was the best type of mould‐ripened Civil cheese. The results showed that the use of P. roqueforti in the manufacture of mould‐ripened Civil cheese has significant impact on the volatile profiles and sensory attributes.     

Study of the chemical composition,proteolysis, volatile compounds,and textural properties of industrial and traditional Beaten (Bieno sirenje) ewe milk cheese

The objective of this study was to determine the gross composition, proteolysis, and volatile and texture profiles during ripening of industrial (IND) and traditional (TRD) Beaten (Bieno sirenje) cheeses made by using ewe milk. In the course of the analyses, statistical differences were determined in some physicochemical parameters, nitrogen fractions, and total free amino acid levels between TRD and IND types of cheese. Higher levels of proteolysis were observed in IND cheeses than in TRD cheeses during ripening. Levels of residual β- and α_s-caseins were 72.2 and 48.7%, respectively, in 180-d-old TRD cheeses. However, the residual levels were 52.8% for β-casein and 18% for α_s-casein in IND cheeses. Similar differences were noted for the reversed-phase HPLC peptide profiles of 2 types of cheeses. Also, higher concentrations of peptides were eluted in IND cheeses than in TRD cheeses during ripening. A total of 73 volatile compounds, including alcohols (16), esters (17), acids (14), terpenes (7), ketones (5), aldehydes (4), and miscellaneous (10) were identified. The IND cheeses contained higher levels of carboxylic acids, esters, alcohols, and terpenes than the TRD cheeses; however, the same levels of methyl ketones were determined in the 2 types of cheeses at the end of ripening. These may be due to some differences (e.g., pasteurization and scalding temperature, among other factors) in the manufacture of the 2 types of Beaten cheeses. The textural profile of Beaten cheeses showed that TRD production method resulted in firmer, less fracturable, and stiffer cheeses than the IND production method. In conclusion, the results suggest that the use of industrial production method (pasteurization of cheese milk and curd scalding at 70°C) in the manufacture of Beaten ewe milk cheese enriched the volatile profile of the cheese.     

Volatile fraction and sensory characteristics of Manchego cheese. 1. Comparison of raw and pasteurized milk cheese

Manchego cheese can be manufactured from raw or pasteurized ewes' milk. An automatic purge and trap apparatus, coupled to a GC-MS was used to isolate. identify and compare the relative amounts of the volatile components of raw and pasteurized Manchego cheese during ripening. The majority of volatile compounds were more abundant in raw milk (RM) cheeses than in pasteurized milk (PM) cheeses. Alcohols and esters predominated in the profile of RM Manchego cheese, while methyl-ketones and 2,3-butanedione were quantitatively important in PM cheeses. Branched chain alcohols were much more abundant in RM cheeses. The discriminant analysis separated 100% samples into RM or PM cheeses by using only 16 volatile compounds. Aroma intensity was correlated with esters, branched chain aldehydes and branched chain alcohols in RM cheeses, and with esters, branched chain aldehydes, 2-methyl ketones and 2-alkanols in PM cheeses. Diacetyl was positively correlated with the aroma attribute 'toasted' and negatively correlated with aroma quality in PM cheeses.     

Variations in volatile compounds and flavour in Idiazabal cheese manufactured from ewe's milk in farmhouse and factory

Stage of lactation, use of bulk milk or milk from individual flocks, and cheese‐making in farmhouse or industrial factory are important factors affecting the production and quality of Idiazabal cheese. The volatile composition of cheese samples made from raw ewe's milk in farmhouses or industrial plants at two different times of the year and aged for 90 and 180 days was analysed by dynamic headspace coupled to GC‐MS. Short‐chain fatty acids, primary and secondary alcohols, methyl ketones and ethyl esters were the most abundant compounds in the aroma of Idiazabal cheese samples. Differences in the volatile composition were found between farmhouse and industrial cheeses made at different times of the year and ripened for 90 or 180 days. Likewise, the sensory profiles of the farmhouse and industrial cheeses were significantly different, regardless of the time of the year and ripening time. The results for the principal component analysis (PCA) performed on the sensory attributes of the cheese samples showed two PCs defined as ‘farmhouse flavour factor’ and ‘industrial flavour factor’. Farmhouse cheeses showed high scores for buttery, milky and toasty odours, and buttery and nutty flavours, whereas industrial cheeses showed high scores for sharp, rennet and brine odours, and rennet and rancid flavours. The percentages of methyl ketones such as 3‐hydroxy‐2‐butanone, 2‐butanone, 2‐pentanone and 2‐heptanone, and acids such as n‐propanoic, 2‐methylpropanoic and 3‐methylbutanoic acids were higher in farmhouse cheeses than in industrial cheeses. On the other hand, the percentages of esters such as ethyl butanoate and ethyl hexanoate, and alcohols such as 3‐methyl‐1‐butanol, and acids like n‐hexanoic acid were higher in industrial cheeses than in farmhouse cheeses. Relationships between sensory attributes and volatile compounds were studied on the basis of the differences found in sensory profile and volatile composition between farmhouse and industrial cheeses. Copyright © 2005 Society of Chemical Industry     

Effect of some technological parameters on microbiological, chemical and sensory qualities of Civil cheese during ripening

The objective of this research was to determine the effects of different ripening methods [brine salting, dry salting, incorporating with Lor cheese (LR) and vacuum packaging] of Civil cheeses on its microbiological, chemical and sensory properties. Civil cheeses were analysed on the 2nd, 30th, 60th and 90th day of ripening. Chemical compositions of the cheeses were significantly different. While the highest dry matter and titratable acidity values were determined on dry salted cheeses, the highest fat and fat in dry matter contents were found in Civil cheese ripened together with LR. The water-soluble nitrogen and ripening index values were lower in cheese ripened incorporating with LR. Excessive proteolysis was not seen in any of cheese samples. The ripening in different methods affected microbiological and sensory properties of Civil cheese. Panellists preferred vacuum packaging and dry-salting cheeses compared to the other samples on the 90th day of ripening.     

Physicochemical and textural characteristics and volatile compounds of semihard goat cheese as affected by starter cultures

Today, cheese is valued because of its high nutritional value and unique characteristics. Improving the texture and flavor of cheese by selecting suitable starter cultures is an important way to promote the development of cheese industry. The effect of starter cultures on the physicochemical and textural properties and volatile compounds during the ripening of semihard goat cheese were investigated in this work. Different starter cultures—mesophilic (M) and thermophilic starters (T), Lactobacillus plantarum ssp. plantarum ATCC 14917 (Lp), a mix of the M and T starters (M1), and mix of the M, T, and Lp starters (M2)—were used in the production of the goat cheeses. Volatile compounds were determined by a solid-phase microextraction/gas chromatography-mass spectrometric (SPME/GC-MS) method. The results showed that the moisture content of cheeses produced with the 5 kinds of starter cultures decreased after maturation, whereas ash content increased. The pH values of goat cheeses decreased first and then increased during maturity, and the pH value of M2 cheese was the lowest among the cheeses. The hardness and chewiness of the cheeses increased with increasing maturity, whereas cohesiveness, springiness, and resilience showed the opposite tendency. The 60-d-old cheese made with Lp had the highest chewiness, cohesiveness, springiness, and resilience, whereas the 60-d-old cheese made with M2 had the highest hardness. A total of 53 volatile components were identified by SPME/GC-MS, and carboxylic acids, alcohols, ketones, and esters were the 4 major contributors to the characteristic flavors of the cheeses. Volatile components and their contents differed greatly among the produced cheeses. The M2 cheese contained the highest relative content of the main volatile compounds (90.10%), especially butanoic acid and acetoin. Through a comprehensive comparison of the results, we concluded that M2 cheese had a dense texture and milky flavor, and M2 is a potential starter culture candidate for the production of goat cheese.     

Characterization of the chemistry, biochemistry and volatile profile of Kuflu cheese, a mould-ripened variety

The chemistry, biochemistry and volatile compounds of Kuflu cheese, a Turkish mould-ripened variety were studied. A total of 29 samples were analysed and the titratable acidity, moisture, salt-in-moisture, fat-in-dry matter and total protein contents (as mean values) were 0.96%, 49.97%, 7.49%, 12.18% and 37.84%, respectively, and the pH of the cheeses was 6.29. Indices of proteolysis (i.e., the levels of pH 4.6- and trichloroacetic acid-soluble nitrogen) were high; however, these values were lower than those of other Blue cheeses probably due to proportionally higher levels of total nitrogen and salt-in-moisture in Kuflu cheese samples. Urea-polyacrylamide gel electrophoresis of the pH 4.6-insoluble fractions of the cheeses showed that both α_s1- and β-caseins were extensively degraded, but β-casein was less degraded than α_s1-casein. RP-HPLC peptide profiles of the pH 4.6-soluble fractions from Kuflu cheeses showed that some minor quantitative differences were found between the samples, while peptide profiles of the samples were qualitatively similar. One hundred and thirty-eight compounds were identified in the volatile fractions of Kuflu cheese by gas chromatography-mass spectrometry (GC-MS) using a solid-phase microextraction technique. Ketones and alcohols were the principal class of volatile components in Kuflu cheeses, and terpenes and sulphur compounds were found at substantial levels in the majority of the samples, but aldehydes and lactones were present at low levels. The RP-HPLC and GC-MS data were analysed by principal component analysis based on their peptide and volatile profiles, respectively. Kuflu cheeses obtained from different markets had some differences in terms of chemical composition, proteolysis and patterns of aroma compounds.     

Characterisation of Urda whey cheese: Evolution of main biochemical and microbiological parameters during ripening and vacuum packaged cold storage

In this study, the main biochemical and microbiological characteristics of Urda, a traditional Greek whey cheese, were determined during ripening at 19 ± 2 °C for 25 days followed by vacuum packaging and storage at 5 °C until day 360. Few differences in pH, water activity, acid degree value, moisture, salt, protein and fat contents were observed between Urda cheeses produced from sheep or goat milk whey at all sampling days (1, 25, 90, 180 and 360). Cheese microbiota was dominated by mesophilic lactic acid bacteria, but high numbers of enterococci, aerobic gram-negative bacteria and Enterobacteriaceae were also present. Increases in all the soluble nitrogen fractions of cheeses occurred, primarily during cold storage. Ketones and terpenes were the most abundant volatile compounds in fresh (1-day) sheep and goat cheeses, respectively, whereas free fatty acids were the most abundant compounds in mature (180-day) cheeses, followed by ketones.     

Cheese supplementation with five species of edible seaweeds: Effect on proteolysis,lipolysis and volatile compounds

The effect on the biochemical characteristics of Ibérico semi-hard cheese supplemented with Himanthalia elongata (HE), Laminaria ochroleuca (LO), Porphyra umbilicalis (PU), Ulva lactuca (UL) or Undaria pinnatifida (UP) seaweeds was investigated. Addition of 1% dehydrated seaweed to curd increased total free amino acids in LO cheese and decreased them in HE and UP cheeses at 60 days with respect to control cheese. Lipolysis was markedly enhanced in UL cheese, which showed on day 60 a 6.0-fold higher concentration of total free fatty acids than control cheese. Seventy-six volatile compounds were detected in cheeses with seaweeds and 54 in control cheese. Aldehydes and alcohols reached higher levels in the control cheese, esters and ketones in PU cheese, acids and sulphur compounds in UL cheese, hydrocarbons in HE and PU cheeses, and furans in HE and UP cheeses.     

High-pressure processing decelerates lipolysis and formation of volatile compounds in ovine milk blue-veined cheese

Enzyme-rich cheeses are prone to over-ripening during refrigerated storage. Blue-veined cheeses fall within this category because of the profuse growth of Penicillium roqueforti in their interior, which results in the production of highly active proteinases, lipases, and other enzymes responsible for the formation of a great number of flavor compounds. To control the excessive formation of free fatty acids (FFA) and volatile compounds, blue-veined cheeses were submitted to high-pressure processing (HPP) at 400 or 600 MPa on d 21, 42, or 63 after manufacture. Cheeses were ripened for 30 d at 10°C and 93% relative humidity, followed by 60 d at 5°C, and then held at 3°C until d 360. High-pressure processing influenced the concentrations of acetic acid and short-chain, medium-chain, and long-chain FFA. The effect was dependent on treatment conditions (pressure level and cheese age at the time of treatment). The lowest concentrations of acetic acid and FFA were recorded for cheeses treated at 600 MPa on d 21; these cheeses showed the lowest esterase activity values. Acetic acid and all FFA groups increased during ripening and refrigerated storage. The 102 volatile compounds detected in cheese belonged to 10 chemical groups (5 aldehydes, 12 ketones, 17 alcohols, 12 acids, 35 esters, 9 hydrocarbons, 5 aromatic compounds, 3 nitrogen compounds, 3 terpenes, and 1 sulfur compound). High-pressure processing influenced the levels of 97 individual compounds, whereas 68 individual compounds varied during refrigerated storage. Total concentrations of all groups of volatile compounds were influenced by HPP, but only ketones, acids, esters, and sulfur compounds varied during refrigerated storage. The lowest total concentrations for most groups of volatile compounds were recorded for the cheese pressurized at 600 MPa on d 21. A principal component analysis combining total concentrations of groups of FFA and volatile compounds discriminated cheeses by age and by the pressure level applied to HPP cheeses.     

Dynamic Headspace Analyses of Volatile Compounds of Cheddar and Swiss Cheese during Ripening

The volatile compounds of Cheddar and Swiss cheeses during ripening for 9 wks at 11°and 21°C, respectively, were analyzed by a dynamic headspace analyzer/gas chromatograph every week. The compounds were identified by a combination of retention times and mass spectra. The volatile compounds of Cheddar increased 5.6 and Swiss cheese 15 times as ripening increased from 0 to 9 wks. The amount of volatile compounds of Swiss cheese was 2.6 times greater than that of Cheddar cheese during ripening. The volatile compounds were ketones, alcohols, aldehydes, esters, acids, sulfur compounds, benzenes, and hydrocarbons. Ketones and alcohols accounted for 92% of volatiles from Cheddar cheese and 88% of those from Swiss cheese.     

The compositional properties,proteolytic–lipolytic maturation parameters and volatile compositions of commercial enzyme‐modified cheeses with different cheese flavours

Eight different commercial enzyme‐modified cheeses (EMCs) were analysed, and the distinctive/common features of the products and production methods were investigated. Results showed that the total free fatty acid contents of EMC samples were 10 to 100 times higher than the values reported for the related cheese varieties. A total of 37 volatile compounds were identified, and acids were found as the most dominant group in all EMC samples. While furan compounds and 2‐acetylpyrrole were most intensively detected in the goat cheese EMC, methyl ketones were found in the highest amounts in Blue cheese EMC.     

Volatile compounds produced in cheese by Enterobacteriaceae strains of dairy origin

The formation of volatile compounds in fresh cheese by 10 Enterobacteriaceae strains of dairy origin (4 Hafnia alvei, 2 Serratia liquefaciens, 1 Enterobacter cloacae, 1 Enterobacter sakazakii, and 2 Escherichia coli strains) was investigated. Small cheeses were made from pasteurized cow's milk separately inoculated with 1-3 x 10(3) CFU/ml of each of the Enterobacteriaceae strains, with glucono-8-lactone added to achieve a pH value of 5.2 in the curds. All strains reached counts close to 10(8) CFU/g in 1-day-old cheeses and survived well from day 1 to day 8. Cheeses were analyzed for volatile compounds by gas chromatography-mass spectroscopy, after extraction by dynamic headspace using a purge and trap apparatus. Sixty-one volatile compounds were determined in cheeses, 31 of which were further investigated. Significant increases of aldehydes, sulfur compounds, and aromatic compounds were recorded from 2-h curd to 1-day-old cheese, and of ketones, alcohols, and acids from 2-h curd to 8-day-old cheese. Acetaldehyde, 2-methyl propanal, and 3-methyl butanal predominated among aldehydes; 2,3-butanedione, 2,3-pentanedione, and 3-hydroxy 2-butanone among ketones; ethanol, 2-methyl propanol, and 3-methyl butanol among alcohols; and ethyl acetate among esters. Hierarchical cluster analysis of strains using the data of 31 volatile compounds separated clearly the strain of E. sakazakii, which produced high amounts of volatile compounds, from the other Enterobacteriaceae strains.     

Role of the microbial population on the flavor of the soft-bodied cheese Torta del Casar

The purpose of this work was to investigate the influence of the spontaneous microbial population on the flavor of Torta del Casar cheese. A total of 16 batches of cheeses with different microbial qualities were used. Their physicochemical and microbial characteristics were evaluated during ripening and then related with the volatile compounds, taste, and flavor properties of the finished cheeses. Acids were the most abundant volatile compounds, followed by alcohols and carbonyls. The amount of acetic acid and several alcohols were linked to cheeses with higher counts of lactic acid bacteria (LAB), whereas Enterobacteriaceae counts were associated with semivolatile fatty acids. The gram-positive catalase-positive cocci counts were correlated with esters and methyl ketones. Although the role of the LAB in the flavor development of Torta del Casar is the most relevant, other microbial groups are necessary to impart the flavor of the cheese and to minimize the possible off-flavor derived from excessive concentrations of LAB metabolites, such as acetic acid.     

Comparison of purge and trap and solid phase microextraction techniques for studying the volatile aroma compounds of three European PDO hard cheeses

Solid phase microextraction (SPME) and purge and trap (P&T) methods were compared to establish their effectiveness for the extraction of cheese aroma compounds from selected raw milk protected designation of origin (PDO) cheeses. The profiles of the volatile fraction from each cheese variety obtained by using the two extraction methods were significantly different. SPME fibres were more effective for extracting medium and high boiling compounds, P&T was better for extracting the highly volatile compounds. Gruyère Switzerland cheeses showed high concentrations of alkenes, aldehydes, methyl ketones, butane-2,3-dione, unsaturated alcohols, branched chain acids and 2,6-dimethyl pyrazine. Manchego cheeses contained high concentrations of alkanes, alkanols, prop-2-en-1-ol, propan-2-one and butan-2-one and their corresponding reduction products propan-2-ol and butan-2-ol, propyl esters and aromatic compounds. Ragusano cheeses contained high concentrations of fatty acids and ethyl and butyl esters. Discriminant analyses, performed separately for each extraction method, correctly classified all the samples by their PDO origin.