Composition of the water-soluble fraction of different cheeses

Volatile and nonvolatile compounds present in the water-soluble fraction (WSF) and water-soluble fraction with molecular weight lower than 1000 Da (WSF < 1000 Da) of six Spanish cheeses, Cabrales, Idiazábal, Mahón, Manchego, Roncal, and a goat's milk cheese, were analyzed. Different nitrogen fractions (determined by Kjeldahl method), caseins (by capillary electrophoresis), peptides and amino acids (by HPLC), and volatile components (by dynamic headspace coupled to GC-MS) as well as mineral content in the cheese fractions were analyzed and compared. The different nitrogen and volatile compounds identified in the WSF were characteristic of each cheese variety. Cabrales cheese displayed the highest content of free amino acids and the highest quantity and variety of volatile compounds. The WSF < 1000 Da fraction was less representative, especially for volatile compounds, as some of the components were lost in the ultrafiltration. Alcohols were better recovered than ketones and esters.     

The addition of Propionibacterium freudenreichii to Raclette cheese induces biochemical changes and enhances flavor development

Two mixtures of Propionibacterium freudenreichii commercial strains were tested as adjunct cultures in pasteurized milk Raclette cheese to investigate the ability of propionibacteria (PAB) to enhance flavor development. Cheese flavor was assessed by a trained sensory panel, and levels of free amino acids, free fatty acids, and volatile compounds were determined. The PAB level showed a 1.4 log increase within the ripening period (12 weeks at 11 degrees C). Eye formation, which was not desired, was not observed in PAB cheeses. PAB fermented lactate to acetate and propionate and produced fatty acids by lipolysis, branched chain volatile compounds derived from isoleucine and leucine catabolism and some esters. One of the experimental cheeses received the highest scores for odor and flavor intensity and was characterized by higher frequencies of detection for some minor notes ("propionic"and "whey" odor, "sweet" taste). PAB can therefore be considered as potential adjunct cultures to enhance or modify cheese flavor development.     

Starter bacteria are the prime agents of lipolysis in cheddar cheese

To assess the contribution of starter lactic acid bacteria (LAB) to lipolysis in Cheddar cheese, the evolution of free fatty acids (FFAs) was monitored in Cheddar cheeses manufactured from pasteurized milks with or without starter. Starter-free cheeses were acidified by a combination of lactic acid and glucono-delta-lactone. Starter cultures were found to actively produce FFAs in the cheese vat, and mean levels of FFAs were significantly higher in starter cheeses over ripening. The contribution of nonstarter LAB toward lipolysis appears minimal, especially in starter-acidified cheeses. It is postulated that the moderate increases in FFAs in Cheddar cheese are primarily due to lack of access of esterase of LAB to suitable lipid substrate. The results of this study indicate that starter esterases are the primary contributors to lipolysis in Cheddar cheese made from good quality pasteurized milk.     

Identification of a powerful aroma compound in munster and camembert cheeses: ethyl 3-mercaptopropionate

With the view to investigate the presence of thiols in cheese, the use of different methods of preparation and extraction with an organomercuric compound ( p-hydroxymercuribenzoate) enabled the isolation of a new compound. The analysis of cheese extracts by gas chromatography coupled with pulse flame photometry, mass spectrometry, and olfactometry detections led to the identification of ethyl 3-mercaptopropionate in Munster and Camembert cheeses. This compound, described at low concentrations as having pleasant, fruity, grapy, rhubarb, and empyreumatic characters, has previously been reported in wine and Concord grape but was never mentioned before in cheese. A possible route for the formation of this compound in relation with the catabolism of sulfur amino acids is proposed.     

Evaluation of APHA and AOAC methods for phosphatase in cheese

Varieties of market cheese were analyzed for alkaline phosphatase by the modified rapid colorimetric method of the American Public Health Association (APHA) and the official AOAC method, 16.304-16.306. In the APHA method, 5 g cheese (pH less than 7.0) is macerated with 2 mL 1:1 carbonate buffer, or 2 mL water (for cheese with pH greater than 7.0). Addition of 0.1 mL magnesium acetate (1 mg magnesium) to test portions of cheese extracts yielded reproducible and quantitative recovery of added phosphatase. In the AOAC method, macerating 0.5 g cheese with 1 mL borate buffer before adding milk phosphatase improved recovery among cheeses. Addition of magnesium ion increased phosphatase activity in some cheeses. Phosphatases in blue mold-ripened and Swiss cheeses were inactivated by heat faster than was milk phosphatase, yet milk phosphatase added to various soft cheeses was completely inactivated at 60 degrees C for 10 min. The lability of phosphatase was due to the heat-denaturing effect of NaCl present in finished cheeses. Some Mexican style soft cheeses contained both heat-labile and heat-stable phosphatases. These data suggest that the phosphatase test to differentiate milk and microbial phosphatases on the basis of repasteurization and analysis of cheese is no longer valid.     

Removal of cholesterol from Cheddar cheese by beta-cyclodextrin

This study was carried out to determine the cholesterol removal rate and resulting changes in flavor, fatty acid and bitter amino acid production in reduced-cholesterol Cheddar cheese, made by cream separation followed by 10% beta-cyclodextrin (beta-CD) treatment. The cholesterol removal from the cheese was 92.1%. The production of short-chain free fatty acids (FFAs) increased the ripening time in control and cream-treated cheeses. The quantity of short-chain FFAs released between treatments during ripening was different, while not much difference was found in the production of neutral volatile compounds in the samples. Reduced-cholesterol cheese produced much higher levels of bitter amino acids than the control. In sensory analysis, the texture score of control Cheddar cheese increased significantly with ripening time; however, that of the cream treatment group decreased dramatically with ripening time. On the basis of our results, we conclude that the cheese made from beta-CD-treated cream had a higher rate of cholesterol removal and ripened rapidly.     

Comparison of ELISA and HPLC for the determination of histamine in cheese.

A competitive direct enzyme-linked immunosorbent assay (CD-ELISA) for histamine in cheese was compared with a reversed-phase liquid chromatography (RP-HPLC) method. Cheese was homogenized with phosphate-buffered saline (PBS), centrifuged, and filtered, and the supernatant was diluted with PBS for CD-ELISA. For RP-HPLC, biogenic amines (histamine, tyramine, putrescine, and cadaverine) were derivatized with 9-fluorenylmethylchloroformate, followed by reversed-phase chromatography and fluorescence detection. Detection limits and mean recoveries (10-1000 mg/kg) were 2 mg/kg and 93% for CD-ELISA and 1 mg/kg and 99% for RP-HPLC, respectively. Analysis of 50 commercial cheeses according to both methods showed good agreement for histamine (r = 0.979; concentration range = 2-1800 mg/kg). At a threshold level of 10 mg/kg, the ELISA gave no false-negative and three false-positive results. The results show that the ELISA is suitable for the determination of histamine in cheese.     

Identification of the production chain of Asiago d'Allevo cheese by nuclear magnetic resonance spectroscopy and principal component analysis

In the present work, a rapid and simple NMR method to discriminate Asiago d'Allevo cheese samples from different production chains is described. A fast and reproducible extraction of the organic fraction was employed. By applying chemometric analysis to NMR data, it is possible to differentiate PDO Asiago cheese produced in alpine farms from that produced in lowland and mountain industrialized factories. PCA of both (1)H and (13)C NMR spectra showed a good separation of alpine farm products from the other ones, whereas the lowland and mountain industrialized cheeses are undistinguishable. The samples were differentiated on the basis of a higher content of unsaturated fatty acids, principally oleic, linoleic, linolenic, and conjugated linoleic acids for the alpine farm cheeses and a higher content of saturated fatty acids for the industrialized products. Conjugated linoleic acid and 1-pentene are also discriminating components.     

Characterization of aroma compounds responsible for the rosy/floral flavor in Cheddar cheese

The aroma-active compounds that contribute to the rosy/floral flavor in Cheddar cheese were characterized using both instrumental and sensory techniques. Two cheeses (>12 months old) with rosy/floral flavor and two Cheddar cheeses of similar ages without rosy/floral flavors were selected. After direct solvent extraction/solvent-assisted flavor evaporation and separation into neutral/basic and acidic fractions, samples were analyzed by gas chromatography-olfactometry with aroma extract dilution analysis. Selected compounds were quantified using internal standard methodology. Some of the intense aroma-active compounds in the neutral basic fraction of the rosy/floral cheeses included 2-phenethanol (rosy), phenylethyl acetate (rosy), and phenylacetaldehyde (rosy/floral). Quantification, threshold analysis, and sensory analysis of model cheeses confirmed that increased concentrations of phenylacetaldehyde and phenylacetic acid caused rosy/floral flavor when spiked into Cheddar cheese.     

产脂肪酶乳酸菌对新疆传统奶酪脂肪酸及风味的影响

为了改善奶酪品质,奶酪生产过程中通常会添加脂肪酶或者产脂肪酶乳酸菌来提升产品品质。该研究以前期筛选的4株高产脂肪酶乳酸菌为发酵剂,分别随机选取3株乳酸菌复配制作酸凝奶酪。试验组：A组T1-5和T1-3属融合魏斯氏菌（Weissella confusa）、H1-6属瑞士乳杆菌（Lactobacillus helveticus）,B组H1-6、T1-5、B2-5属植物乳杆菌（Lactobacillus plantarum）,C组H1-6、T1-3、B2-5,D组T1-3、T1-5、B2-5,对照组（E组）（添加商业发酵剂）,分析发酵剂对传统奶酪pH值、滴定酸度和脂肪氧化情况的影响,并利用气相色谱法（Gas Chromatography,GC）检测奶酪中脂肪酸变化、利用气相色谱-离子迁移谱（Gas Chromatography-Ion Mobility Chromatography,GC-IMS）分析奶酪中风味物质的变化。结果表明：A,B,C,D组4组奶酪的pH值、过氧化值（Peroxide value,POV值）明显低于E组（对照组）（P < 0.05）,A,B组奶酪滴定酸度比对照E组高（P < 0.05）;A,B,C,D组奶酪中饱和脂肪酸（Saturated Fatty Acids,SFA）含量、单不饱和脂肪酸（Monounsaturated Fatty Acids,MUFA）含量和多不饱和脂肪酸（Polyunsaturated Fatty Acids,PUFA）含量均显著高于E组（P < 0.05）;4个试验组样品中亚油酸（C18∶2n6c）含量明显高于对照组（E组）（P < 0.05）。GC-IMS及主成分分析结果显示,A、B组奶酪挥发性风味物质种类多,且相似度较高,其中2-庚酮、丁醛、乙酸丁酯是主要呈味物质;C、E两组奶酪中风味物质比较相似,风味物质主要以乙酸乙酯、乙酸丙酯、己酸乙酯等酯类为主;D组与其他4组有所差异,主要挥发性风味物质为乙酸丁酯、3-辛酮、庚醛等。结合感官评定,A、B两组奶酪整体风味和口感较好,评分较高。筛选得到的产脂肪酶乳酸菌可以作为发酵剂用于提升新疆传统奶酪品质。     

Volatile compounds produced in cheese by pseudomonas strains of dairy origin belonging to six different species

Production of volatile compounds by seven Pseudomonas strains belonging to six different species, Ps. brenneri, Ps. graminis, Ps. libanensis, Ps. lundensis, Ps. putida, and Ps. rhodesiae, was investigated, with the aim of elucidating their possible contribution to the volatile profile of cheese. Laboratory-scale cheeses were made from pasteurized milk of low bacterial counts separately inoculated with approximately 10(5) colony-forming units/mL of each Pseudomonas strain and ripened for 12 days at 10 degrees C. A total of 122 volatile compounds were identified in cheeses by GC-MS of the dynamic headspace. The abundance of 62 compounds, belonging to eight chemical groups (aldehydes, ketones, acids, esters, alcohols, hydrocarbons, benzene compounds, and sulfur compounds) increased during ripening for at least one of the strains. Most groups of volatile compounds were more abundant in the outer part of cheeses than in the inner part, in agreement with the aerobic metabolism of the genus Pseudomonas and coinciding with the higher counts in the outer part. Production of volatile compounds in cheese by Pseudomonas was shown to be species-dependent.     

Time course and specificity of lipolysis in Swiss cheese

Controlling lipolysis in cheese is necessary to ensure the formation of desirable flavor. To get a better understanding of the mechanism of lipolysis in Swiss cheese, cheeses were manufactured with and without (control) the addition of Propionibacterium freudenreichii. Products of lipolysis were quantified throughout ripening. Half of the free fatty acids (FFA) released in milk (3.66 mg/g fat), in particular the short-chain FFA, were lost in the whey during curd drainage, whereas diglycerides and monoglycerides were retained within the curd. P. freudenreichii was responsible for the release of most FFA during ripening (10.84 and 0.39 mg/g fat in propionibacteria-containing and control cheeses, respectively). Indices of lipolysis displayed low specificity. All types of FFA were released, but butyric and palmitic acids more significantly, which could be due to a low sn-1,3 regioselectivity. All glycerides were hydrolyzed in the following order: monoglycerides>diglycerides>triglycerides. The results of this study show the quantitative and qualitative contributions of the different lipolytic agents to Swiss cheese lipolysis.     

Differential characteristics of fatty acids in cheese from milk of various animal species by capillary gas chromatography

The kind of milk used in the manufacture of cheese has been identified by analysis of the fatty acids. The milk fat is extracted from the cheese and saponified. The methyl esters of the fatty acids are prepared and determined by capillary column gas chromatography. Seven major fatty acids are separated and quantitated, namely, C8:0, C10:0, C12:0, C14:0, C16:0, C18:0, and C18:1. Many of the 21 simple ratios that can be formed from these 7 quantities are characteristic of the type of milk from which the fatty acids were obtained. The method allows the identification of cheese prepared with the milk of cows, buffalo, sheep, or goats. Substitution or adulteration of milk can also be detected.     

Current knowledge of soft cheeses flavor and related compounds

Cheese aroma is the result of the perception of a large number of molecules belonging to different chemical classes. The volatile compounds involved in the soft cheese flavor have received a great deal of attention. However, there has been less work concerning the volatile compounds in the soft smear-ripened cheeses than in the mold-ripened cheeses. This paper reviews the components that contribute to the characteristic flavor in the soft cheeses such as surface-ripened, Camembert-type, and Blue cheeses. The sensory properties and quantities of the molecules in the different cheeses are discussed.     

Modified atmosphere packaged cheddar cheese shreds: influence of fluorescent light exposure and gas type on color and production of volatile compounds

The influences of fluorescent light exposure and packaging atmosphere on the headspace volatiles and color of Cheddar cheese shreds were evaluated using gas chromatography-mass spectrometry and spectrocolorimetry, respectively. Cheddar cheeses were packaged under atmospheres of 100% carbon dioxide or 100% nitrogen and stored at 4 degrees C under fluorescent light for 6 weeks. Cheeses stored under carbon dioxide contained higher concentrations of aldehydes and fatty acids and lower concentrations of alcohols and esters than cheeses stored under nitrogen. Carbon dioxide atmospheres potentiated light-induced oxidation in shredded Cheddar cheeses, as evidenced by aldehyde and fatty acid headspace volatiles measured following storage. Color bleaching occurred only in cheeses packaged under carbon dioxide and exposed to light. The shift in color is proposed to be due to an interaction between carbon dioxide and high-intensity light, leading to the oxidation of the pigment molecule, bixin. The results have significant implications for procedures used to handle and store pigmented cheeses to ensure desirable flavor and consumer acceptability.     

Changes in the volatile composition of a semihard ewe milk cheese induced by high-pressure treatment of 300 MPa

The effect of high-pressure (HP) treatment (300 MPa, 10 min) on the volatile profile of semihard ewe milk cheeses was investigated. The HP treatment was applied at two different stages of ripening (1 and 15 days; 3P1 and 3P15) and microbiota, proteolysis indexes (soluble nitrogen and total free amino acid content), and volatile compounds were assayed at 15, 60, 90, and 150 days of ripening. The intensity of odor and aroma of cheeses was also assayed. 3P1 cheeses presented the highest content of free amino acids and were characterized by the lowest amounts of aldehydes, ketones, short-chain free fatty acids, and terpenes and higher levels of ethanol and ethyl esters. 3P15 cheeses were characterized by the highest content of short-chain free fatty acids and pyruvaldehyde and the lowest abundance of secondary alcohols and were more similar to control cheeses than those HP-treated on the first day. Intensities of odor and aroma were not significantly influenced by the HP treatment. However, the panellists found some differences in 3P1 as compared with control and 3P15 cheeses in what they perceived as lower odor and aroma quality.     

Simple and accurate method for determination of ethylene chlorohydrin in dried spices and condiments

A simple and accurate method is described for the determination of ethylene chlorohydrin (ECH) by using capillary gas chromatography (GC) and flame ionization detection. Acetonitrile-methanol was chosen as the extraction solvent in preference to other solvents because its use reduced the number of compounds detected by the GC system, thus enabling easier identification and quantitation of ECH. The coefficient of variation for the method is 2.7% at 5 ppm, and recovery is good, even for the standard addition of 1 ppm. Fifteen different spices and condiments were analyzed using this method; 20% were identified as positive for ECH. The method also identifies the related compound ethylene bromohydrin (EBH).     

Wavelength dependence of light-induced lipid oxidation and naturally occurring photosensitizers in cheese

Degradation of the potential photosensitizers, riboflavin, chlorophyll, and porphyrin, in Danbo cheese by monochromatic light of wavelength 366, 436, or 546 nm was studied. Three cheeses were investigated, two conventional (16% fat and 25% fat) and one "organic" (25% fat). The effect of illumination was measured by fluorescence spectroscopy and analyzed using multiway and multivariate data analysis. Riboflavin was found to degrade only by 436 nm light, whereas chlorophylls and porphyrins also were influenced by 436 and 546 nm light. The organic cheese had the largest chlorophyll content both before and after similar light exposure, and no change in chlorophyll of this cheese was observed for any of the illumination wavelengths. Upon light exposure of the cheeses, volatile compounds were formed, as analyzed by gas chromatography-mass spectrometry (GC-MS). The relative concentrations of methyl butanoate, 1-pentanol, benzaldehyde, 2-butanone, 2-heptanone, and butyl acetate were found to weakly correlate with the surface fluorescence intensity. 1-Pentanol and the ketones are secondary lipid oxidation products, consistent with a chemical coupling between photosensitizer degradation and formation of volatile lipid oxidation products.     

Production of hard-type cheese using free or immobilized freeze-dried kefir cells as a starter culture

This study provides a contribution to hard-type cheese starter culture production through the use of a freeze-dried culture in the ripening of hard-type cheeses. The effect of initial cell concentration, ripening temperature, and cell immobilization of kefir on the degree of openness, mold spoilage, microbial associations, physicochemical characteristics, and aroma-related compounds was studied. Use of kefir starter cultures resulted in cheese with an increased shelf life and resistance to spoilage as compared to control cheeses without kefir inoculants. Furthermore, the freeze-dried kefir culture improved aroma, taste, and texture characteristics while increasing the degree of openness in comparison to traditional hard-type cheese products. The kefir culture resulted in an increase in counts of total aerobic bacteria, yeasts and molds, lactococci, and lactobacilli until the 15th day of ripening. From then on, only lactobacilli counts increased, reaching levels up to 9.17 log CFU/g in cheeses ripened at 5 degrees C using freeze-dried kefir cells immobilized on casein. SPME-GC/MS analysis revealed major differences in volatile composition, especially with regard to alcohols (up to 75%), carbonyl compounds (up to 75%), and esters (up to 64%) between cheeses made with kefir cells and cheeses made without kefir inoculants.     

Combined extraction-cleanup column chromatographic procedure for determination of dicofol in avian eggs

Dicofol in avian eggs was completely oxidized to dichlorobenzophenone (DCBP) when a hexane Soxhlet extraction procedure was used. This degradation did not occur with other avian tissues (muscle and liver). For this reason, a combined extraction-cleanup column chromatographic procedure, without added heat, was developed for the determination of dicofol in avian eggs. Homogenized subsamples of eggs were mixed with sodium sulfate, and the mixture was added as the top layer on a column prepacked with Florisil. The dicofol and other compounds of interest were then eluted with ethyl ether-hexane. The extracts, relatively free from lipids, were quantitated on a gas chromatograph equipped with a 63Ni electron-capture detector and a methyl silicone capillary column. Recoveries from chicken eggs, fortified with dicofol and other DDT-related compounds, averaged 96%. Analysis of eggs of eastern screech-owls, fed a meat diet containing 10 ppm technical Kelthane, showed that both dicofol and DCBP were present. Results were confirmed by gas chromatography/mass spectrometry. This method is rapid and reliable, involves a minimum of sample handling, and is well suited for high volume determination of dicofol in eggs and other avian tissues.