Agustín Olano

Determination of furosine in milk samples by ion-pair reversed phase liquid chromatography

SummaryAn ion-pair, reversed-phase, liquid chromatographic procedure using UV detection for quantitation of furosine is described. The standard plot was linear (r>0.999) over a 5 ng range. An authentic synthesised sample of furosine was used for calibration. Commerical milk samples were analyzed by the described procedure.

Changes in the carbohydrate fraction of milk during heating processes

Abstract Carbohydrate composition of commercial pasteurized, UHT, sterilized and dried milk samples, and laboratory heat-treated milks was determined by gas-liquid chromatography. Glucose, galactose and lactulose were present in all types of commercial milk samples. The concentrations of galactose and lactulose increase with the severity of the heating process. The amount of glucose present in commercial milks was similar to that found in unheated milk. Epilactose was only detected in sterilized milk samples. UHT and sterilized milks can be differentiated by their lactulose, galactose or epilactose content.

Structural Characterization of Bovine β-Lactoglobulin−Galactose/Tagatose Maillard Complexes by Electrophoretic, Chromatographic, and Spectroscopic Methods

To investigate the influence of the type of carbonyl group of the sugar on the structural changes of proteins during glycation, an exhaustive structural characterization of glycated beta-lactoglobulin with galactose (aldose) and tagatose (ketose) has been carried out. Conjugates were prepared via Maillard reaction at 40 and 50 degrees C, pH 7, and a w = 0.44. The progress of the Maillard reaction was followed by indirect formation of Amadori and Heyns compounds, advanced glycation end products, and brown polymers. The structural characterization of glycoconjugates was conducted by using a number of analytical techniques such as RP-HPLC, isoelectric focusing, MALDI-ToF, SDS-PAGE, size exclusion chromatography, and spectrofluorimetry (tryptophan fluorescence). In addition, the surface hydrophobicity of the beta-lactoglobulin glycoconjugates was also assessed. The results showed a higher reactivity of galactose than tagatose to form the glycoconjugates, probably due to the higher electrophilicity of the aldehyde group. At 40 degrees C, more aggregation was produced when beta-lactoglobulin was conjugated with tagatose as compared to galactose. However, at 50 degrees C hardly any difference was observed in the aggregation produced by galactose and tagatose. These results afford more insight into the importance of the functional group of the carbohydrate moiety during the formation of protein-carbohydrate conjugates via Maillard reaction.

Determination of hydroxymethylfurfural in commercial jams and in fruit-based infant foods

Abstract Fifty six commercial samples, 38 jams with several fruit and sugar contents and 18 fruit-based infant foods, were analysed for pH, dry matter and hydroxymethylfurfural (HMF) content. Samples of jams had pH and dry matter values similar to those reported in the literature. Fruit-based infant foods presented higher values of pH and lower dry matter than jam samples. HMF was found in all samples of jams, regardless of the pH, sugar or dry matter, from traces to 7.17 mg/100 g product (mean value close to 1.35 mg/100 g product). Three samples of fruit-based infant foods did not show appreciable amounts of HMF and the average value for the rest of samples was 0.29 mg/100 g product. The difference between the values of HMF in jams and in fruit-based infant foods may be in part due to the lower fruit concentration in the latter. In general terms, the considerable variations of HMF content found in the analysed samples may be an indication of differences in the processing conditions.

Mass spectrometric characterization of glycated β-lactoglobulin peptides derived from galacto-oligosaccharides surviving the in vitro gastrointestinal digestion

A mass spectrometric study has been carried out to elucidate the structures of glycated peptides obtained after in vitro gastrointestinal digestion of bovine β-lactoglobulin (β-LG) glycated with prebiotic galacto-oligosaccharides (GOS). The digests of both native and glycated β-LG were analyzed by MALDI-MS, LC-ESI-MS, and LC-ESI-MS/MS. MALDI-MS profiles showed marked differences mainly related to the lower intensity of ions corresponding to the digest of glycated β-LG. Overall, 58 and 23 unglycated peptides covering 97% and 63% of the mature β-LG sequence could be identified in the digests of native and glycated samples, respectively. The LC-ESI-MS analyses corroborated the MALDI-MS results regarding the unglycated peptides but they also enabled an extensive investigation into the digest of glycated β-LG. Thus, a total of 19 peptides glycated with GOS from two to seven hexose units could be identified. The tandem mass spectra of glycated peptides were mostly characterized by two neutral losses of 1026/1056, 864/894, 702/732, 540/570, 378/408, and 216/246 u, corresponding to the formation of the furylium ion and its subsequent “CHOH” loss, indicative of the peptide glycation with hepta-, hexa-, penta-, tetra-, tri-, and disaccharides, respectively. Also, other minor ionic species containing the furylium ring linked to different galactose units could be also detected, showing the diversity of the fragmentation pattern of peptides glycated with larger size carbohydrates. Finally, the putative GOS glycation sites could be determined at the NH2-terminal Leu residue and at Lys residues located in positions 14, 47, 75, 77, 83, 91, 100, 135, and 138.

Study on nonenzymatic browning in cookies, crackers and breakfast cereals by maltulose and furosine determination

Nonenzymatic browning development has been investigated in commercial cookies, crackers and breakfast cereals by determination of maltulose and furosine. In addition, maltose, lactose, lactulose, fructose, glucose and 2-furoylmethyl-GABA were also determined in the samples studied. Maltulose and furosine were present in all samples of cookies, crackers and breakfast cereals. Differences found among samples may be attributed to variations in composition and processing conditions. The maltose/maltulose ratio showed a wide range in the samples studied and could probably be attributed to differences in heating intensity during processing. Thus, maltose/maltulose ratio might serve as indicator of the heat load during manufacture. Furosine and 2-furoylmethyl-GABA may arise from Maillard reactions in some of the ingredients before manufacture of the cereal products: this appears to be a major drawback for the use of these compounds as suitable indicators to differentiate between commercial cereal products. However, in the cereal industry, where exact ingredient composition is known, measurement of the maltulose and furosine formed might be used as indicators to monitor processing conditions during the manufacture of cereal products.

Ratio of lactulose to furosine as indicator of quality of commercial milks

Storage of ultra high temperature (UHT) milk at high ambient temperatures gave rise to a decrease of the ratio of lactulose to furosine contents. The lactulose/furosine (Lu/Fu) ratio in UHT milks resulted to be around 16 times higher than in commercial powder milk samples so, the determination of the Lu/Fu ratio in freshly processed UHT milk seems to be useful to detect the presence of reconstituted milk.

Chemical changes during microwave treatment of milk

Abstract Raw milk was heated in a microwave oven at 2450 MHz in order to study the effect on the main chemical changes taking place during heating processes: lactose isomerization, Maillard reaction and protein denaturation. Lactulose, epilactose, furosine and undenaturated whey proteins were measured as indicators of the heat damage in milk. Comparison with control samples treated by conventional heating showed a rate enhancement of the studied reactions during microwave treatment. These differences are supposed to be due, at least to some extent, to uneven heating of the milk in the microwave oven.

Proteolysis during storage of UHT milk: differences between whole and skim milk

Proteolysis during storage of UHT skim and whole milks processed by either direct or indirect systems has been studied. All the proteolysis indices determined (measurement of free amino groups, PAGE of caseins and PAGE and reversed-phase HPLC of the fraction soluble at pH 4.6) revealed greater proteolytic degradation during storage of skim milks compared with that of whole milks subjected to the same UHT treatments. Increased activities of both native milk proteinase and proteinases of bacterial origin were observed in skim UHT milks. The different behaviour of UHT skim and whole milks on storage would have to be taken into account in establishing the process conditions.

Analysis of free carbohydrates in milk using micropacked columns

SummaryA gas chromatographic method using a micropacked column is described for the analysis of lactose, galactose, lactulose and epilactose in processed milks. The method is evaluated for precision and accuracy using phenyl-β-glucoside as an internal standard. Recoveries near 100% were found for lactulose concentrations higher than 0.1 mgml−1, showing coefficients of variation from 5.9 to 9.4%.