Aims: To study the ability of Lactobacillus casei and Lact. plantarum strains to convert methonine to cheese ¯avour compounds. Methods and Results: Strains were assayed for methionine aminotransferase and lyase activities, and amino acid... more
Aims: To study the ability of Lactobacillus casei and Lact. plantarum strains to convert methonine to cheese ¯avour compounds. Methods and Results: Strains were assayed for methionine aminotransferase and lyase activities, and amino acid decarboxylase activity. About 25% of the strains assayed showed methionine aminotransferase activity. The presence of glucose in the reaction mixture increased conversion of methionine to 4-methylthio-2-ketobutanoate (KMBA) and 4-methyl-thio-2-hydroxybutanoate (HMBA) in all strains. The methionine aminotransferase activity in Lact. plantarum and Lact. casei showed variable speci®city for the amino group acceptors glyoxylate, ketoglutarate, oxaloacetate and pyruvate. None of the strains showed methionine lyase or glutamate and methionine decarboxylase activities. Conclusions: The presence of amino acid converting enzymes in lactobacilli is strain speci®c. Signi®cance and Impact of the Study: The ®ndings of this work suggest that lactobacilli can be used as adjuncts for ¯avour formation in cheese manufacture.
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Yeast plasma membrane ATPase is inactivated up to 80% in the absence of catabolism of exogenous nutrients (exogenous catabolism). This inactivation, that is not accompanied by a decrease in the cellular content of ATPase, is due to an... more
Yeast plasma membrane ATPase is inactivated up to 80% in the absence of catabolism of exogenous nutrients (exogenous catabolism). This inactivation, that is not accompanied by a decrease in the cellular content of ATPase, is due to an irreversible decrease of the Vmax and does not require protein synthesis. The inactivated enzyme maintains the ability to be regulated by fermentable sugars but shows important alterations in the characteristics of this regulation. Upon addition of glucose, the Vmax of the inactivated enzyme increases as well as its Ki for vanadate but, in contrast to the normal enzyme, its affinity for ATP or its pH optimum do not increase. It is concluded that in the absence of exogenous catabolism an irreversible modification of the yeast plasma membrane ATPase takes place that affects several of its kinetic properties.
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To determine whether the energy balance of goats or characteristics of the diet consumed were the principal factors that determined milk production, feeding and digestion trials were carried out using two groups of 5 Granadina goats. The... more
To determine whether the energy balance of goats or characteristics of the diet consumed were the principal factors that determined milk production, feeding and digestion trials were carried out using two groups of 5 Granadina goats. The concentrate fraction of both diets was the same, but the forage fraction of the diets differed. In diet 1, the forage was in the form of long alfalfa hay, and, in diet 2, forage was in the form of pelleted alfalfa. Intake and the forage to concentrate ratio of the two diets were not significantly different, although diet 2 was more digestible. The amount of fat and protein in the milk depended on energy intake and not on dietary treatment. The milk protein of goats fed diet 2 was higher in casein. No sensible differences were noted in the fatty acid composition of the milk. Nitrogen and metabolizable energy utilization for milk production was greater for goats fed diet 2. According to the results obtained, it would seem advantageous to use pelleted alfalfa rather than alfalfa hay in the diets of goats.
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Abstract The aim of this work was to investigate the presence of antioxidant and ACE-inhibitory activity in ovine αs2-casein and bovine κ-casein hydrolysates with antibacterial activity. Several pep-tides which had been previously... more
Abstract The aim of this work was to investigate the presence of antioxidant and ACE-inhibitory activity in ovine αs2-casein and bovine κ-casein hydrolysates with antibacterial activity. Several pep-tides which had been previously identified in these hydrolysates were selected in ...
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This paper presents an overview of existing capillary electrophoretic methods for the study of milk proteins. The main methods of analysis of caseins, whey proteins and peptides are examined with particular attention to their application... more
This paper presents an overview of existing capillary electrophoretic methods for the study of milk proteins. The main methods of analysis of caseins, whey proteins and peptides are examined with particular attention to their application to the evaluation of the quality of dairy products. Aspects such as the study of protein polymorphism, evaluation of heat treatments, detection of adulteration and assessment of proteolysis are considered in detail.
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Whey protein concentrate (WPC) enriched in β-lactoglobulin (β-Lg) was hydrolyzed using Corolase PP® and thermolysin to produce hydrolyzates with antioxidant activity. The optimization of the main experimental variables involved in the... more
Whey protein concentrate (WPC) enriched in β-lactoglobulin (β-Lg) was hydrolyzed using Corolase PP® and thermolysin to produce hydrolyzates with antioxidant activity. The optimization of the main experimental variables involved in the process, such as type of enzyme, and hydrolysis conditions, concretely enzyme to substrate ratio, time and temperature, were evaluated using response surface methodology. A central composite circumscribed (CCC) design
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A capillary electrophoresis method for the simultaneous determination of whey proteins, caseins and their degradation products, such as para-κ-casein, was proposed. The effect of several parameters (pH, ionic strength and concentration of... more
A capillary electrophoresis method for the simultaneous determination of whey proteins, caseins and their degradation products, such as para-κ-casein, was proposed. The effect of several parameters (pH, ionic strength and concentration of urea in the electrophoresis buffer and applied voltage) on the analysis time and on the separation efficiency of the major milk proteins was studied. Using a hydrophilically coated capillary, in combination with electrophoresis buffer 0.48 M citric acid–13.6 mM citrate–4.8 M urea at pH 2.3, and a separation voltage of 25 kV, a complete separation of β-lactoglobulin and para-κ-casein was achieved, permitting the quantification of both components.
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In this work, the angiotensin-converting enzyme (ACE)-inhibitory and radical-scavenging activities of the beta-lactoglobulin (beta-Lg)-derived peptides WY f(19-20), WYS f(19-21), WYSL f(19-22), WYSLA f(19-23), WYSLAM f(19-24), and WYSLAMA... more
In this work, the angiotensin-converting enzyme (ACE)-inhibitory and radical-scavenging activities of the beta-lactoglobulin (beta-Lg)-derived peptides WY f(19-20), WYS f(19-21), WYSL f(19-22), WYSLA f(19-23), WYSLAM f(19-24), and WYSLAMA f(19-25) have been determined. The ACE-inhibitory activity (IC50) varied from 38.3 to 90.4 microM, with the exception of WYS (>500 microM). All beta-Lg-derived peptides also exhibited radical-scavenging activity (oxygen radical absorbance capacity (ORAC) values ranged from 4.45 to 7.67 micromol Trolox equivalents/micromol of peptide). The presence and position of amino acids Trp, Tyr, and Met were proposed to be responsible for the antioxidant activity. The equimolar amino acid mixtures of all the peptides showed ORAC values lower than those of the corresponding peptides, indicating that the peptidic bond or the structural conformation had a positive influence on this activity. Finally, positive antioxidant effects of WYS, WYSL, and WYLA with ascorbic acid were observed, whereas WY and WYSLAM showed negative effects, both cases for different molar ratio mixtures. These results should be taken into account in the development of new food ingredients on the basis of peptides from beta-Lg.
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In this study, bovine β-lactoglobulin A (β-Lg A) was hydrolysed with thermolysin under non-denaturing and heat-denaturing conditions. The peptides released during hydrolysis were identified by HPLC–MS/MS. A total of 25 peptides were... more
In this study, bovine β-lactoglobulin A (β-Lg A) was hydrolysed with thermolysin under non-denaturing and heat-denaturing conditions. The peptides released during hydrolysis were identified by HPLC–MS/MS. A total of 25 peptides were identified in the hydrolysate obtained at 37°C for 5min. Some of these peptides survived to further proteolysis even at higher incubation temperatures. Furthermore, novel cleavage sites localised in the most buried zones of β-Lg and available for thermolysin were recognised when the incubation temperature increased in the range between 60 and 80°C. Three new peptides, LDA, LKPTPEGD, and LQKW, appeared after 30min hydrolysis at these incubation temperatures, but they were not identified in the 30-min hydrolysates obtained at 37 and 50°C. Of special interest was the peptide LQKW, corresponding to the fragment f(58–61) that had been previously described as a potent angiotensin-converting enzyme-inhibitor (IC50 value of 34.7μM).
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Matrix-assisted laser desorption ionisation time-of-flight mass spectrometric analysis of the tryptic digest of β-casein A2 and β-casein B was performed before and after the separation of the peptides by LC. The overlapping of the... more
Matrix-assisted laser desorption ionisation time-of-flight mass spectrometric analysis of the tryptic digest of β-casein A2 and β-casein B was performed before and after the separation of the peptides by LC. The overlapping of the chromatograms showed that all peaks were present in both samples, except for one only found in the tryptic digest of the A2 variant and two in the B variant. Experimental masses could be assigned to those peptides produced by tryptic digest of β-casein variant. This peptide mapping strategy and current methodological improvements represent a promising tool for the identification of milk genetic variants with the difference of an amino acid substitution.
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The effect of CO2 on the growth of psychrotrophic milk spoilage organisms was studied, both in raw fresh milk and in pure cultures of three species of Pseudomonas growing in sterilised milk. Changes of sensory properties of CO2-treated... more
The effect of CO2 on the growth of psychrotrophic milk spoilage organisms was studied, both in raw fresh milk and in pure cultures of three species of Pseudomonas growing in sterilised milk. Changes of sensory properties of CO2-treated samples after heat treatment were also analysed. Inhibition of psychrotrophic growth at 7 degrees C in milk treated with CO2 to a pH 6.2 or 6.0 was impaired by a gradual reduction of the CO2 content during storage. Growth inhibition was considerably improved by pH adjustment at 24-h intervals. Sensory analysis showed significant differences between non-acidified and acidified samples after heat treatment at 75 degrees C for 20 s or 110 degrees C for 5 min. No sensory differences were found between non-acidified and acidified milks degassed before heat treatment.
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Polymorphism of ovine alpha s-caseins was studied by capillary electrophoresis at pH 3.0 +/- 0.1. Individual caseins (CN) were selected according to their genetic variants, as determined by PAGE and isoelectric focusing. The ovine... more
Polymorphism of ovine alpha s-caseins was studied by capillary electrophoresis at pH 3.0 +/- 0.1. Individual caseins (CN) were selected according to their genetic variants, as determined by PAGE and isoelectric focusing. The ovine caseins, containing different genetic variants of alpha s1-CN and alpha s2-CN, were fractionated by cation-exchange FPLC. The alpha s1-CN variants A, B and C, and the fast moving alpha s2-CN variant were identified by a capillary electrophoresis method. The fast moving alpha s2-CN variant, so-called for its behaviour in PAGE, also had a faster electrophoretic mobility than the common alpha s2-CN when analysed by the present technique. The capillary electrophoresis method gave excellent, rapid, automated separation of alpha s1-CN and alpha s2-CN variants and was suitable for screening studies.
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A Western blotting method for the detection of whey milk proteins in commercial soymilks was applied to assess the food safety. Soy proteins and milk proteins were separated by SDS-PAGE in PhastSystem equipment. After the electrophoretic... more
A Western blotting method for the detection of whey milk proteins in commercial soymilks was applied to assess the food safety. Soy proteins and milk proteins were separated by SDS-PAGE in PhastSystem equipment. After the electrophoretic separation, immunodetection with anti-bovine alpha-lactalbumin and anti-bovine beta-lactoglobulin antisera was performed. Adulteration with bovine protein in percentages of 0.1% in soy protein can be detected. Western blotting of bovine alpha-lactalbumin and bovine beta-lactoglobulin was applied to detect adulteration by bovine milk proteins in different soymilks: powdered soymilk and soy infant formulas.
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A new capillary electrophoresis (CE) method was used to analyse raw, pasteurised and UHT milk samples. Some para-κ-casein-related peaks were observed in raw and pasteurised milks stored at 6°C for 5 or more days, and in UHT milks stored... more
A new capillary electrophoresis (CE) method was used to analyse raw, pasteurised and UHT milk samples. Some para-κ-casein-related peaks were observed in raw and pasteurised milks stored at 6°C for 5 or more days, and in UHT milks stored at 20°C for 30, 60 or 90 d. The presence of these peaks was attributed to the action of proteases from psychrotrophic bacteria on κ-casein. In the CE analysis, the area of pure κ-casein digested with a proteinase-containing cell-free extract from Pseudomonas fluorescens B52 was gradually reduced and several peaks with migration times close to para-κ-casein like those found in the stored milks, appeared. On the other hand, in the sample of κ-casein treated with chymosin, only one peak corresponding to para-κ-casein was formed. The analysis of the tryptic digests of these samples by high performance liquid chromatography (HPLC) coupled to electrospray mass spectrometry (ES-MS) revealed the presence of fragments 1-105, 1-103, 1-104, 1-106 and 1-107 of κ...
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A capillary electrophoresis method has been applied to the detection of illegal addition of milk from goat and/ or cow in Halloumi cheese, traditionally made with sheep milk. The electrophoretic profiles of the casein from Halloumi... more
A capillary electrophoresis method has been applied to the detection of illegal addition of milk from goat and/ or cow in Halloumi cheese, traditionally made with sheep milk. The electrophoretic profiles of the casein from Halloumi cheeses have revealed that caprine para-kappa-casein and bovine alphas1-casein peaks point to the presence of low percentages of goat's and/or cow's milk added to Halloumi cheese. Stepwise multiple linear regression has been used to predict these percentages with a standard error of the estimation of 2.14%. The analytical method combined with the statistical application is valid for the prediction of percentages higher than 2% of goat's and percentages of 5% of cow's milk added to the cheese either in fresh or ripened cheese. The standard error of estimation was higher for the prediction of cow's milk than for goat's milk.
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Identification of biologically active peptides in food matrices is a challenging task in food technology. In the present study, we propose a strategy for the rapid identification of peptides in complex food fractions and targeting of... more
Identification of biologically active peptides in food matrices is a challenging task in food technology. In the present study, we propose a strategy for the rapid identification of peptides in complex food fractions and targeting of potentially bioactive peptides according to previous studies of activity-structure relationship. A large number of peptides included in the Mr 3000 permeate of a fermented
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Whey protein concentrate (WPC) enriched in β-lactoglobulin (β-Lg) was hydrolyzed using Corolase PP® and thermolysin to produce hydrolyzates with antioxidant activity. The optimization of the main experimental variables involved in the... more
Whey protein concentrate (WPC) enriched in β-lactoglobulin (β-Lg) was hydrolyzed using Corolase PP® and thermolysin to produce hydrolyzates with antioxidant activity. The optimization of the main experimental variables involved in the process, such as type of enzyme, and hydrolysis conditions, concretely enzyme to substrate ratio, time and temperature, were evaluated using response surface methodology. A central composite circumscribed (CCC) design
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ABSTRACT
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Yoghurt fortification with caseinates, co-precipitate and blended dairy powders in a low-fat yoghurt model system was studied. These dairy products were characterised for pH, moisture, lactose, mineral and protein fractions. Milk proteins... more
Yoghurt fortification with caseinates, co-precipitate and blended dairy powders in a low-fat yoghurt model system was studied. These dairy products were characterised for pH, moisture, lactose, mineral and protein fractions. Milk proteins were characterised by polyacrylamide ...
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Commercial soybean products for human consumption (soybean protein isolate, soybean flour, textured soybean, and soybean powdered milks) are characterized for the first time by Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis... more
Commercial soybean products for human consumption (soybean protein isolate, soybean flour, textured soybean, and soybean powdered milks) are characterized for the first time by Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE) using the PhastSystem®, a semi-automatic electrophoretic system. It makes SDS-PAGE very fast and gives very sharp bands that simplify the identification. The time from loading the gel to characterization