Screening of indoles in cheese

 Indole and skatole (3-methylindole) are formed from tryptophan by microbial activity. Depending on their concentration, they may either contribute to an unpleasant odour, as described for pig meat, or alternatively to a positive aroma profile, as during ripening of cheese. In a screening study, the two indoles in various types of cheese were determined, by both HPLC and GC. It was found that the two compounds mainly occur in mould cheese, such as Camembert and are even more pronounced in blue-veined cheese. The concentrations in unripened cheese were up to 700 ng/g fat for indole and 50 ng/g fat for skatole. The formation of the two indoles increases when proteolysis during ripening provides more tryptophan. Skatole formation appears to be specifically favoured by a low pH and anaerobic conditions. Received: 14 May 1997     

Growth and metabolic activity of a cheese starter in CO2-acidified and non-acidified refrigerated milk

 The growth and activity of two Lactococcus strains and one Leuconostoc strain in CO₂-acidified and non-acidified refrigerated milk were evaluated separately and as a mixed culture to determine their suitability for use as a starter in the manufacture of Afuega’l Pitu, an acid-coagulated Spanish cheese, from refrigerated CO₂-acidified milk. The growth of the strains studied and their production of organic acids were similar in CO₂-acidified and non-acidified refrigerated or fresh milk, indicating that CO₂ treatment does not affect the metabolic activity of the strains. However, refrigeration enhanced the production of acetaldehyde, ethanol and diacetyl in CO₂-acidified and non-acidified milk. The level of diacetyl was also greater in refrigerated CO₂-acidified milk than in refrigerated non-acidified milk. It was concluded that refrigerated milk acidified with CO₂ can be satisfactorily used in the manufacture of Afuega’l Pitu cheese, and that this technique can be also used in the production of other acid-coagulated cheeses. Received: 1 July 1997 / Revised version: 1 September 1997     

Volatile compounds in pressed ewes' milk cheese with saffron spice (Crocus sativus L.)

Saffron spice has been successfully used as an ingredient in dairy products as a means of diversification. The objective of this work was to determine the influence of saffron on the volatiles' profile of a pressed ewes' milk cheese. This was performed by means of a modern extraction technique based on headspace sorptive extraction. Results showed that safranal was the only volatile that could be identified and quantified from saffron spice. Most volatile compounds were present in all cheeses but at different concentrations. Differences between control and saffron cheeses were observed, but as ripening time increased, these differences were less evident.     

Growth and metabolic activity of a cheese starter in CO2-acidified and non-acidified refrigerated milk

 The growth and activity of two Lactococcus strains and one Leuconostoc strain in CO₂-acidified and non-acidified refrigerated milk were evaluated separately and as a mixed culture to determine their suitability for use as a starter in the manufacture of Afuega’l Pitu, an acid-coagulated Spanish cheese, from refrigerated CO₂-acidified milk. The growth of the strains studied and their production of organic acids were similar in CO₂-acidified and non-acidified refrigerated or fresh milk, indicating that CO₂ treatment does not affect the metabolic activity of the strains. However, refrigeration enhanced the production of acetaldehyde, ethanol and diacetyl in CO₂-acidified and non-acidified milk. The level of diacetyl was also greater in refrigerated CO₂-acidified milk than in refrigerated non-acidified milk. It was concluded that refrigerated milk acidified with CO₂ can be satisfactorily used in the manufacture of Afuega’l Pitu cheese, and that this technique can be also used in the production of other acid-coagulated cheeses. Received: 1 July 1997 / Revised version: 1 September 1997     

Characterization of a traditional semi-hard Italian cheese produced by soaking in wine

A traditional type of semi-hard cheese which, after a ripening period in the warehouse, is soaked in wine or fermented must, was studied. In particular, the effect of the soaking phase on the characteristics of the cheese and on the profiles of the volatile compounds was investigated. The study proved that it is the alcohols and the short-chain ethyl esters which chiefly contribute to the distinctive aromatic fraction of the product. These compounds migrate from the wine into the cheese as a result of the different concentrations existing between the two systems.     

Characterization of cheese proteolysis by capillary electrophoresis and reverse-phase HPLC analyses of peptides

 The possibilities of reverse-phase high performance liquid chromatography (RP-HPLC) and capillary electrophoresis (CE) when used for separation of cheese peptides are discussed. A CE method using a coated capillary column and a low pH buffer was developed to analyze the water-soluble fraction of a 6-month-old cow’s milk cheese. The CE patterns were compared with the chromatograms obtained by RP-HPLC using a C18 column and a gradient of acetonitrile in water. The CE method gave shorter analysis times but RP-HPLC provided lower coefficients of variation of the retention times and better detection limits. In addition, the elution behavior of peptides in CE strongly depended on the sample matrix. The results show that both techniques provide complementary information for the analysis of cheese peptides. Received: 10 June 1997 / Revised version: 20 October 1997     

Effect of cooking conditions on the flavour compounds and composition of shrimp (Parapenaeus longirostris) broth

 To achieve a shrimp broth with the best flavour, the whole shrimp must be cooked at 85°C for 30 min in a 0.5% NaCl solution in proportions 1 : 2 (w : v). Quantitatively, the main components of the broth were nitrogen substances, the most abundant of these being peptides of molecular weight less than 600 Da. Levels of ATP metabolites were also determined [the more abundant compounds were inosine, guanosine 5′-monophosphate (GMP) and inosine 5′-monophosphate (IMP)], as were free sugars (glucose, fructose and ribose) and fat content. The free amino acid composition was also determined. A significant correlation (P <0.0001) between cooking temperature and different nitrogen fractions was observed. Received: 22 September 1997 / Revised version: 13 November 1997     

Impact of physiological state of starter culture on ripening and flavour development of Swiss–Dutch‐type cheese

The changes in the physiological state and metabolism of starter culture in 15kg Swiss–Dutch‐type cheese blocks during two‐stage ripening were studied. The analyses were performed on samples from three layers of cheese between the rind and the core. Cell membrane integrity, intracellular esterase activity and bacteria culturability were chosen as physiological state indicators. Cheese flavour development was determined by static headspace gas chromatography. During warm room ripening, the number of cells with intact cell membranes and displaying intracellular esterase activity increased. Lactic acid bacteria underwent resuscitation and regained their culturability. A lack of homogeneity within the cheese was noticed in relation to bacterial activity and the volatiles concentration.     

Identification of the character impact flavour compounds of Swiss cheese by sensory studies of models

Flavour models were developed for two samples (A and B) of Swiss cheese which differed in their ripening stage and flavour profile. The models were based on an unripened, freeze-dried cheese of the Mozzarella type. Compounds which, in previous studies had been screened as contributors to the odour and taste of Swiss cheese, were added to the base in various combinations and at concentrations equal to those found in Swiss cheeses A and B. Models composed of methional, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone, acetic acid, propionic acid, lactic acid, succinic acid, glutamic acid, sodium, potassium, calcium, magnesium, ammonium, phosphate and chloride were judged to meet the flavour of Swiss cheese very well.     

Changes in the profile of volatile compounds in wines stored under oxygen and their relationship with the browning process

 Eight young white wines produced in Aragon from Macabeo and Chardonnay grapes were stored under an oxygen atmosphere in the dark at room temperature. Changes in the colour and volatile compound composition were recorded over a period of 13 weeks. Significant changes in the volatile compound composition were detected through analysis of variance (ANOVA) of repeated measures, considering both grape variety and browning tendency as discriminant categories. The amounts of fatty acids and fermentation esters in the wine were significantly changed by the oxidative storage. Some of these changes can be attributed to acid-ester hydrolysis equilibria, but not others, such as the decrease in concentrations of octanoic and decanoic acids. The oxidative storage also affected most of the unsaturated fatty-acid-derived compounds: trans-2-octenal, trans-2-nonenal, trans-2-decenal and 1-octen-3-ol were all found to increase in the first stages of storage, while hexanol decreased slightly. Volatile phenols behaved very differently: while phenol and 4-ethylphenol initially increased and later decreased, eugenol increased through the process and 4-vinyl-guaiacol disappeared. Benzaldehyde and furfural increased while methionol and terpenols disappeared. Only furfural was found to be linked with the tendency of the wine to brown, while only linalool and benzaldehyde were found to be linked whith the grape variety. The levels of some odorants previously isolated by sniffing detection were temptatively monitored, and significant changes in their concentrations were found to occur during the process. Received: 16 December 1996 / Revised version: 27 March 1997     

Changes in the profile of volatile compounds in wines stored under oxygen and their relationship with the browning process

 Eight young white wines produced in Aragon from Macabeo and Chardonnay grapes were stored under an oxygen atmosphere in the dark at room temperature. Changes in the colour and volatile compound composition were recorded over a period of 13 weeks. Significant changes in the volatile compound composition were detected through analysis of variance (ANOVA) of repeated measures, considering both grape variety and browning tendency as discriminant categories. The amounts of fatty acids and fermentation esters in the wine were significantly changed by the oxidative storage. Some of these changes can be attributed to acid-ester hydrolysis equilibria, but not others, such as the decrease in concentrations of octanoic and decanoic acids. The oxidative storage also affected most of the unsaturated fatty-acid-derived compounds: trans-2-octenal, trans-2-nonenal, trans-2-decenal and 1-octen-3-ol were all found to increase in the first stages of storage, while hexanol decreased slightly. Volatile phenols behaved very differently: while phenol and 4-ethylphenol initially increased and later decreased, eugenol increased through the process and 4-vinyl-guaiacol disappeared. Benzaldehyde and furfural increased while methionol and terpenols disappeared. Only furfural was found to be linked with the tendency of the wine to brown, while only linalool and benzaldehyde were found to be linked whith the grape variety. The levels of some odorants previously isolated by sniffing detection were temptatively monitored, and significant changes in their concentrations were found to occur during the process. Received: 16 December 1996 / Revised version: 27 March 1997     

Influence of ultrasound on mass transport during cheese brining

 The effect of ultrasound on mass transfer during cheese brining has been investigated. The rate of water removal and NaCl gain increased when ultrasound was applied in comparison with brining performed under static or dynamic conditions, suggesting that ultrasound improves both external and internal mass transfer. A simple diffusional model was developed to simulate mass transport during acoustic brining. Model parameters were estimated using experimental data from acoustic brining experiments carried out on cheese cylinders of 1.7×10^–2m radius and 3×10^–2 m height at different temperatures (5, 15 and 20  °C). Effective water (D _W) and NaCl (D _S) diffusivities estimated using the proposed model ranged from 5.0×10^–10m²/s and 8.0×10^–10 m²/s at 5  °C to 1.3×10^–9m²/s and 1.2×10^–9 m²/s at 20  °C. Both D _W and D _S varied with temperature according to the Arrhenius equation. Through the proposed model, water losses and NaCl gains of the experiments used in the parameter identification were accurately simulated (average %var=98.2%) and also of two additional acoustic experiments carried out under different conditions of temperature (10  °C) and sample size and geometry [parallelepiped of (6×2.5×1.25)×10^–2 m] to those used in the parameter identification (average %var=98.4%). Received: 22 September 1998 / Revised version: 20 November 1998     

A comparative biochemical study of two industrially produced short‐ripened cow's milk cheeses with PDO status: Rennet‐curd Tetilla cheese and acid‐curd Cebreiro cheese

The aim of this study was to characterise industrial Tetilla and Cebreiro Protected Designation of Origin (PDO) Spanish cheeses from a biochemical point of view and to relate some of the biochemical parameters to the cheesemaking process. Some differences in the amounts of organic acids and free amino acids between the two types of cheese were attributed to milk characteristics and the processing technology. The most abundant volatile compounds in both types of cheese were ethanol, isopropanol and diacetyl. The simple and nonspecific volatile profiles of the cheeses appear to be related to the commercial mesophilic DL‐starters used in the manufacturing process.     

Intervarietal comparison of proteolysis in commercial cheese

 Proteolysis in different varieties of cheese, i.e. Cheddar, British, Dutch and Swiss types and Italian varieties, was compared by polyacrylamide gel electrophoresis (PAGE) and reverse-phase high-performance liquid chromatography (RP-HPLC). Urea-PAGE of the water-insoluble fraction (WISF) of cheese appeared to be unable to distinguish between Cheddar and Dutch-type cheeses, whereas it could be used to distinguish Emmental from Parmesan and both of these from Cheddar and Dutch types. Urea-PAGE of the 70%-ethanol-insoluble fraction of the water-soluble extract (WSE) showed large inter-varietal differences but there were also some intra-varietal differences. RP-HPLC of the 70%-ethanol-soluble and -insoluble fractions of the WSEs of cheeses was more effective than urea-PAGE of the WISFs or of the 70%-ethanol-insoluble fraction of the WSEs of cheeses when classifying cheese according to variety. However, analysis of a larger number of cheese samples is required to verify this result. One of the problems with using either urea-PAGE or RP-HPLC to identify cheese is that the characteristics analysed by these techniques change as ripening progresses. Received: 22 September 1997 / Revised version: 8 June 1998     

Application of principal component analysis to chemical characteristics of Mahon cheese

 This paper describes a method suitable for the analysis of diglycerides (DG) in cheese. The method, also suitable for other foods, is essentially based upon the solid-phase extraction (SPE) of DG followed by capillary gas chromatographic analysis with a polar stationary phase (TAP). SPE is applied to avoid the column overloading caused by triglycerides; however, SPE is able to catalyse isomerization from the 1,2-form to the 1,3-form. This introduces an error into the results, as the two forms have different origins and are produced at different stages of ripening. A comparison between the use of silica and diol phases was made and it was seen that no isomerization occurred when the diol phase was used. Repeatability and recovery trials were carried out and the coefficient of variation (relative standard error) of the former trial was approximately 10%. Finally, it is demonstrated that it is possible to re-use the SPE cartridge at least four times. Received: 15 July 1996/Revised version: 19 September 1996     

Application of principal component analysis to chemical characteristics of Mahon cheese

 The chemical composition of the seven existing types of Mahon cheese, manufactured under the “Mahon” cheese Appellation of Origin, were studied. Of the cheeses, four were industrial (fresh, half-ripened, ripened and old-ripened) and three were traditionally manufactured (half-ripened, ripened and old-ripened). The chemical parameters were evaluated using ANOVA, Tukey’s multiple range test and principal component (PCA) analyses. Significant differences were found between Mahon cheeses ripened for different times in terms of moisture and non-protein nitrogen (NPN) contents (p <0.001); these differences were found to be independent of the manufacturing methodology, i.e. industrial or traditional. The ash and fat contents of industrially manufactured cheeses were significantly different from those in traditionally manufactured cheeses (p <0.001). PCA reduced chemical variables to two independent components: the first principal component was high in moisture, NPN content and water activity; the second, in NaCl, ash and fat contents. These results indicate that the seven types of Mahon cheese described by the “Mahon” cheese Appellation of Origin can be differentiated by their chemical characteristics. Received: 4 April 1997 / Revised version: 4 July 1997     

Volatile fraction of DOP “Castelo Branco” cheese: Influence of breed

“Castelo Branco” cheese is a Portuguese DOP cheese made from raw ewe’s milk coagulated with Cynara cardunculus, ripened for at least 40 days. “Merino da Beira Baixa” pure race is frequently used to produce milk for this cheese, however, exotic races such as Assaf and crusade of these two races are also used. The aim of this work has been to compare the volatile profile and sensory characteristics of DOP “Castelo Branco” cheeses manufactured during winter season with milk of breeds from Merino, Assaf and crusade of these two races and identify volatile compounds that can distinguish these cheeses.     

Changes of lactose, lactic acid, and acetic acid contents in Serra cheese during ripening

 Changes in the quantities of lactose, lactic acid and acetic acid in Serra cheese were monitored using a triplicate two-way factorial design over a ripening period of 35 days (sampling at 0, 7, 21 and 35 days) throughout the cheesemaking season (sampling in November, February and June). The amount of lactose in total solids of cheese (TS) decreased slowly from 6.17% to 0.21% (w/w_TS) as ripening time elapsed. As a result of sugar metabolism, the lactic acid content increased from 0.07% at day 0 to 2.10% (w/w_TS) by 35 days, whereas the acetic acid content increased from 0.00% to 0.24% (w/w_TS) during the first week. The lactose content was statistically correlated with the lactic acid content but not with the acetic acid content. Received: 18 November 1996     

Prediction of the ripening times of Manchego cheese using multivariate statistical analyse: a preliminary study

 Multiple linear regression, principal component regression, and partial least squares (PLS) regression were used to calculate ripening time in standard Manchego cheeses based on water activity (Aw), pH, and other proteolysis parameters. The root mean square error of prediction by cross-validation was used to study the prediction accuracy of the models. PLS regression yielded the best predictions of ripening time and was used to predict the ripening times of eight commercial Manchego cheeses. Received: 8 October 1997 / Revised version: 20 January 1998     

Prediction of the ripening times of Manchego cheese using multivariate statistical analyse: a preliminary study

 Multiple linear regression, principal component regression, and partial least squares (PLS) regression were used to calculate ripening time in standard Manchego cheeses based on water activity (Aw), pH, and other proteolysis parameters. The root mean square error of prediction by cross-validation was used to study the prediction accuracy of the models. PLS regression yielded the best predictions of ripening time and was used to predict the ripening times of eight commercial Manchego cheeses. Received: 8 October 1997 / Revised version: 20 January 1998