Javier Fontecha

Gas chromatographic method for determining free fatty acids in cheese

SummaryA rapid gas chromatographic method for the analysis of individual free fatty acids (FFA) in cheese has been developed. Lipds were extract from a cheese paste acidified with diethyl ether and tetramethylammonium hydroxide (TMAM) was used for converting the FFA to TMA-soaps, which are transformed to methyl esters in the chromatographic injector. The effect of lactic acid was determined. The reproducibility of the method was studied and the coefficient of variation for the total FFA was found to be 2.2%. Recovery of individual FFA was in the range 87 to 106%.

A high-performance direct transmethylation method for total fatty acids assessment in biological and foodstuff samples

Isolation is the main bottleneck in the analysis of fatty acids in biological samples and foods. In the last few decades some methods described direct derivatization procedures bypassing these steps. They involve the utilization of methanolic HCL or BF3 as catalysts, but several evidences from previous works suggest these reagents are unstable, lead to the formation of artifacts and alter the distribution of specific compounds as hydroxy fatty acids or CLA. However, the main issue is that they are excellent esterification reagents but poor in transterification, being not suitable for the analysis of all lipid classes and leading to erroneous composition quantitations. The present research work is a comprehensive comparison of six general methylation protocols using base, acid or base/acid catalysts plus a proposed method in the analysis of total fatty acids in lipid standards mixtures, foodstuff and biological samples. The addition of aprotic solvents to the reaction mixture to avoid alterations was also tested. Results confirmed that procedures solely involving acid catalyst resulted in incomplete derivatizations and alteration of the fatty acid profile, partially corrected by addition of the aprotic solvent. The proposed method combining sodium methoxyde and sulfuric acid showed absence of alteration of the FAME profile and the best values for response factors (short chain fatty acids to PUFA), accuracy in the determination of total cholesterol and derivatization performance, thus showing a high reliability in the determination of the total fatty acid composition in biological samples and foods.

Improved Gas Chromatographic Method for the Determination of the Individual Free Fatty Acids in Cheese Using a Capillary Column and a PTV Injector

SummaryA gas chromatographic method with a capillary column and a programmed temperature vaporizer injector has been used to analyze the individual free fatty acids in cheese. The lipids were extracted from an acidified cheese slurry with diethyl ether and treated with tetramethylamonium hydroxide (TMAH) to convert the free fatty acids to tetramethylammonium soaps (TMA-soaps), which were subsequently pyrolyzed to methyl esters in the injector. Carrying out injection at the initial column temperature resulted in lower dispersion of the results, but the solvent front prevented quantitative determination of butyric and caproic acids, and an injector temperature of 300°C was therefore employed. Under the conditions tested, trimethylamine (tma) flash-off did not affect the determinations. The accuracy of the method improved at higher free fatty acid contents (coefficient of variation of 0.53% for a total free fatty acid content of 9000 mg/kg as opposed to 7.0% for a total free fatty acid content of 1400 mg/kg). The recovery rate for individual free fatty acids ranged between 91 and 103%.

Characterization of the Aroma-Active, Phenolic, and Lipid Profiles of the Pistachio (Pistacia vera L.) Nut as Affected by the Single and Double Roasting Process

The pistachio (Pistacia vera L.) nut is one of the most widely consumed edible nuts in the world. However, it is the roasting process that makes the pistachio commercially viable and valuable as it serves as the key step to improving the nuts hallmark sensory characteristics including flavor, color, and texture. Consequently, the present study explores the effects of the single-roasting and double-roasting process on the pistachios chemical composition, specifically aroma-active compounds, polyphenols, and lipids. Results showed the total polyphenol content of increased with the roasting treatment; however, not all phenolic compounds demonstrated this behavior. With regard to the aroma and aroma-active compounds, the results indicated that roasting process results in the development of characteristics and pleasant aroma of pistachio samples due to the Maillard reaction. With regard to lipids, the pistachio roasting treatment reduced the concentration of CN38 diacylglycerides while increasing the amount of elaidic acid.

Comprehensive Study of the Lipid Classes of Krill Oil by Fractionation and Identification of Triacylglycerols, Diacylglycerols, and Phospholipid Molecular Species by Using UPLC/QToF-MS

Krill oil represents an interesting source of bioactive lipid components, being suitable as a functional ingredient. This oil is characterized by its high concentration of long-chain omega-3 fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The contents of EPA and DHA were similar to those in fish oils, but with the difference that almost the half are located in phospholipids (mainly phosphatidylcholine). This might explain its higher absorption and bioavailability. This highly unsaturated oil maintains stable due to the presence of astaxanthin, a potent antioxidant, which assures the stability of the omega-3 fatty acids. However, there is lack of investigations reporting a deep comprehensive description of the krill oil (KO) lipid composition. The characterization includes new data of its neutral and polar components and the identification of triacylglycerols, diacylglycerols, and molecular species that has been done by different chromatographic techniques as gas chromatography–mass spectrometry/flame ionization detector (GC-MS/FID), flash chromatography–evaporative light scattering detector (FC-ELSD), and HPLC-ELSD. Also phospholipid molecular species by using ultraperformance liquid chromatography/quadruple-time-of-flight mass spectrometry (UPLC/QToF-MS) have been determined.

Effects of freezing and frozen storage on the microstructure and texture of ewe's milk cheese

Semi-hard ewes milk cheeses, frozen immediately after manufacture either slowly at −35 °C or rapidly at −80 °C and stored at −20 °C for 4 months were studied for microstructural and textural characteristics during subsequent ripening. Two control groups were used to establish the effect of freezing: the fresh unfrozen cheese and cheese thawed immediately after freezing. Freezing proper did not result in any marked changes in the textural parameters of the cheeses, but considerable changes were found in slowly frozen cheeses after 4 months of frozen storage. Shear strength values were lower in all frozen and stored cheeses, particularly in cheese samples frozen slowly compared to those in the unfrozen control batch. This parameter and firmness values were significantly lower in both slowly and rapidly frozen cheeses at the completion of ripening. Ripening tended to offset differences in elasticity, noticeable in the cheeses during the first 30 days of ripening. Light microscopy and electron microscopy revealed small cracks and ruptures in the cheeses which could not be observed by the naked eye. More extensive damage to the cheese microstructure was found in slowly frozen cheese samples stored frozen for 4 months.

Determination of cholesterol in milk fat by gas chromatography with direct injection and sample saponification

SummaryA rapid and direct gas chromatographic (GC) method for determining free cholesterol in milk fat using a capillary column and programmed-temperature vaporizer-injector was assayed. It was compared with other procedures involving saponification of fat, solvent extraction of unsaponifiable matter — with and without fractionation by thin-layer chromatography — and transformation of sterols into silyl derivatives prior to GC analysis. This paper proposes an alternative to other published procedures. Repeatability of the method was assessed and the coefficient of variation determined as 2.1 %. The alternative saponification method exhibited comparable accuracy (coefficient of variation=1.8 %). Recovery ranged from 99.1 % to 105.6 %.

Biochemical characteristics of a semi-hard ewe's-milk cheese

ZusammenfassungDie physiko-chemische, sensorische und mikrobiologische Charakteristik von drei industriellhalb-reifen Schafskäsen wurde während der 90-Tage-Reifungszeit untersucht. Die Käse wurden mit einem ausgewählten Starter mitLactococcus lactis subsp.lactis und subsp.cremoris hergestellt. Die gesamte Keimzahl war während der Herstellung und Reifungszeit normal. Der Nicht-Cascin-Stickstoff (NCN) war mittelmäßig (23,8% des Gesamt-Stickstoffes, TN), aber der Aminosäure-Stickstoff war hoch (73,6% NCN und 1,92% TN). Der Abbau vonαs-(66%) undβ-Cascinen (17%) nach 90 Tagen ist verantwortlich für die gute Texture und Sensorik des Käses.AbstractPhysicochemical, organoleptic and microbiological characteristics of three batches of industrial semihard ewes milk cheeses were studied over a 90-day ripening period. Cheeses were made with a selected starter containingLactococcus lactis subsp.lactis and subsp.cremoris. The total microbial count was normal throughout manufacture and the ripening period. The level of noncasein nitrogen (NCN) was moderate (23.8% of the total nitrogen, TN) but non-protein nitrogen and amino-acid nitrogen were high: 73.6 (% NCN) and 1.92 (% TN) respectively. Breakdown ofαs-(66%) andβ-caseins (17%) at 90 days provided the cheeses with excellent textural and sensory characteristics.

Production of Conjugated Linoleic and Conjugated α-Linolenic Acid in a Reconstituted Skim Milk-Based Medium by Bifidobacterial Strains Isolated from Human Breast Milk

Eight bifidobacterial strains isolated from human breast milk have been tested for their abilities to convert linoleic acid (LA) and α-linolenic acid (LNA) to conjugated linoleic acid (CLA) and conjugated α-linolenic acid (CLNA), respectively. These bioactive lipids display important properties that may contribute to the maintenance and improvement human health. Three selected Bifidobacterium breve strains produced CLA from LA and CLNA from LNA in MRS (160–170 and 210–230 μg mL−1, resp.) and, also, in reconstituted skim milk (75–95 and 210–244 μg mL−1, resp.). These bifidobacterial strains were also able to simultaneously produce both CLA (90–105 μg mL−1) and CLNA (290–320 μg mL−1) in reconstituted skim milk. Globally, our findings suggest that these bifidobacterial strains are potential candidates for the design of new fermented dairy products naturally containing very high concentrations of these bioactive lipids. To our knowledge, this is the first study describing CLNA production and coproduction of CLA and CLNA by Bifidobacterium breve strains isolated from human milk in reconstituted skim milk.

Bioactive Milk Lipids

Current information about the nutritional composition of milk fat is required for the consumer and therefore essential for the successful development of dairy industries as well as marketing their products. The progress in the knowledge concerning some milk fat components that possess biological properties and health benefits beyond their nutritional significance, has a growing interest in the dairy industry to design and formulate products that incorporate specific bioactive components derived from milk. In the last two decades, special attention has been paid to the fatty acid (FA) composition on all short, medium chain and branched fatty acid as well as linoleic conjugated acid (CLA) in milk and dairy products. Trans monounsaturated fatty acids profiles from dairy fat have gained increasing relevance because they may have metabolic properties distinct from those of other origins, hydrogenation reaction for instance. Other minor lipid compounds with biological activity, phospholipids and cholesterol are part of the fat globule membrane. This review summarizes the current knowledge in milk fat research with a brief overview of the importance of dairy lipids as biological molecules with emphasis on the different bioactive compounds present in this fraction.