In emulsions lipid oxidation is mainly influenced by the properties of the interface. The aim of this work was to investigate the effects of droplet size and interfacial area on lipid oxidation in protein-stabilized emulsions. Emulsions, made of stripped sunflower oil (30% vol/vol) and stabilized by BSA were characterized by surface area values equal to 0.7, 5.1, and 16.3 m 2 ·cm −3 oil. The kinetics of O 2 consumption and conjugated diene (CD) formation, performed on emulsions and nonemulsified controls, showed that emulsification prompted oxidation at an early stage. On condition that oxygen concentration was not limiting, the rates of O 2 consumption and CD formation were higher when the interfacial area was larger. Protein adsorbed at the interface probably restrained this pro-oxidant effect. Once most of the O 2 in the system was consumed (6-8 h), CD remained steady at a level depending directly on the ratio between oxidizable substrate and total amount of oxygen. At this stage of aging, the amounts of primary oxidation products were similar whatever the droplet size of the emulsion. Hexanal and pentane could be detected in the headspace of emulsions only at this stage. They were subsequently produced at rates not depending on oil droplet size and interfacial area.Paper no. J10026 in JAOCS 79, 425-430 (May 2002).KEY WORDS: Conjugated dienes, droplet size, interfacial area, lipid oxidation in emulsions, oxygen, protein, volatile compounds.Many foods are oil-in-water emulsions stabilized by protein and lipid surfactants in a protein or polysaccharide matrix. In these systems, oxidation of unsaturated FA leads to the formation of volatile compounds, which are major contributors to the aroma or to undesirable off-odors and off-flavors (1). Oxidation in bulk and emulsified oils is influenced by several common factors, but additional factors are important in emulsions (2). These include the structure of the emulsions and the physicochemical properties of the aqueous phase and of the droplet membrane. The size of the oil droplets is often claimed as an important factor. On one hand, small droplet size signifies a large surface area, implying a high potential of contact between diffusing oxygen, water-soluble free radicals and antioxidants, and the interface. It also implies a high ratio of oxidizable FA located near the interface to FA embedded in the hydrophobic core of the droplets (3). Decreasing the size of the oil droplets is therefore expected to favor development of oxidation. On the other hand, when the droplet size decreases, the number of lipid molecules per droplet diminishes and the amount of surface-active compounds adsorbed at the interface is increased. This could limit initiation and propagation, as surface-active compounds may act as a barrier to the penetration and diffusion of pro-oxidants or even interfere with oxidation. For instance, homogenization is reported to protect milk fat from oxidation catalyzed by metal complexes (4) because casein, which adsorbs to the droplet surface, is an efficie...

Aims: The aim of this study was to isolate and identify bacteriocin-producing lactic acid bacteria (LAB) issued from Mongolian airag (traditional fermented mare's milk), and to purify and characterize bacteriocins produced by these LAB. Methods and Results: Identification of the bacteria (Enterococcus durans) was carried out on the basis of its morphological, biochemical characteristics and carbohydrate fermentation profile and by API50CH kit and 16S rDNA analyses. The pH-neutral cell-free supernatant of this bacterium inhibited the growth of several Lactobacillus spp. and food-borne pathogens including Escherichia coli, Staphylococcus aureus and Listeria innocua. The antimicrobial agent (enterocin A5-11) was heat stable and was not sensitive to acid and alkaline conditions (pH 2-10), but was sensitive to several proteolytic enzymes. Its inhibitory activity was completely eliminated after treatment with proteinase K and a-chymotrypsin. The activity was however not completely inactivated by other proteases including trypsin and pepsin. Three-step purification procedure with high recovery yields was developed to separate two bacteriocins. The applied procedure allowed the recovery of 16% and 64% of enterocins A5-11A and A5-11B, respectively, present in the culture supernatant with purity higher than 99%. SDS-PAGE analyses revealed that enterocin A5-11 has a molecular mass of 5000 Da and mass spectrometry analyses demonstrates molecular masses of 5206 and 5218 Da for fractions A and B, respectively. Amino acid analyses of both enterocins indicated significant quantitative difference in their contents in threonine, alanine, isoleucine and leucine. Their N-termini were blocked hampering straightforward Edman degradation. Conclusions: Bacteriocins A5-11A and B from Ent. durans belong to the class II of bacteriocins. Significance and Impact of the Study: Judging from molecular masses, amino acid composition and spectrum of activities, bacteriocins A5-11A and B from Ent. durans show high degree of similarity with enterocins L50A and L50B isolated from Enterococcus faecium (Cintas et al. 1998(Cintas et al. , 2000 and with enterocin I produced by Ent. faecium 6T1a, a strain originally isolated from a Spanish-style green olive fermentation (Floriano et al. 1998).

Transmissible spongiform encephalopathies are caused by accumulation of highly resistant misfolded amyloid prion protein PrPres and can be initiated by penetration of such pathogen molecules from infected tissue to intact organism. Decontamination of animal meal containing amyloid prion protein is proposed thanks to the use of proteolytic enzymes secreted by thermophilic bacteria Thermoanaerobacter, Thermosipho, and Thermococcus subsp. and mesophilic soil bacteria Streptomyces subsp. Keratins alpha and beta, which resemble amyloid structures, were used as the substrates for the screening for microorganisms able to grow on keratins and producing efficient proteases specific for hydrolysis of beta-sheeted proteic structures, hence amyloids. Secretion of keratin-degrading proteases was evidenced by a zymogram method. Enzymes from thermophilic strains VC13, VC15, and S290 and Streptomyces subsp. S6 were strongly active against amyloid recombinant ovine prion protein and animal meal proteins. The studied proteases displayed broad primary specificities hydrolyzing low molecular mass peptide model substrates. Strong amyloidolytic activity of detected proteases was confirmed by experiments of hydrolysis of PrPres in SAFs produced from brain homogenates of mice infected with the 6PB1 BSE strain. The proteases from Thermoanaerobacter subsp. S290 and Streptomyces subsp. S6 are the best candidates for neutralization/elimination of amyloids in meat and bone meal and other protein-containing substances and materials.

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-The aim of this study was to investigate the angiotensin I-converting-enzyme (ACE)-inhibitory activity of tryptic hydrolysates of ovine β-lactoglobulin, and of yoghurts made by using different starters. Ovine β-lactoglobulin (a mixture of variants A and B at a ratio of 50/50) was subjected to trypsin activity. The degree of hydrolysis of native whole β-lactoglobulin reached 56, 72, 93 and 95% after 1, 2, 8 and 24 h, respectively. ACE-inhibitory activity of tryptic hydrolysates increased with the time of hydrolysis, yielding 85, 88 and 92% after 2, 12 and 24 h, respectively. The determination of ACE-inhibitory activity of some tryptic peptides separated by RP-HPLC and identified by mass spectroscopy showed that the more hydrophilic peptides showed the higher activity. Yoghurts obtained by fermentation of ovine milk with four different sets of starters, and their fractions soluble or not at pH 4.6 also showed an ACE-inhibitory activity. The maximum activity was obtained in the case of insoluble fractions at pH 4.6 of yoghurts made with the set of starters YC-183. ovine milk / tryptic peptide / yoghurt / ACE-inhibitory activity Résumé -Activité inhibitrice de l'enzyme de conversion de l'angiotensine I (ECA) de peptides trypsiques de la β-lactoglobuline du lait de brebis et de yoghourts obtenus à partir de diffé-rents levains. Une activité inhibitrice de l'enzyme de conversion de l'angiotensine I (ECA) a été recherchée dans les peptides trypsiques de la β-lactoglobuline du lait de brebis et dans des fractions issues de yoghourts fabriqués à partir de différents ferments lactiques. La β-lactoglobuline ovine (un mélange des variants A et B) a été soumise à une hydrolyse trypsique. Les degrés d'hydrolyse de la β-lactoglobuline ont atteint 56, 72, 93 et 95 % respectivement après 1, 2, 8 et 24 h d'hydrolyse. L'activité inhibitrice de l'ECA des hydrolysats trypsiques augmentait avec la durée de l'hydrolyse, atteignant 85, 88 et 92 % respectivement après 2, 12 et 24 h. La détermination de l'activité inhibitrice de l'ECA de quelques peptides trypsiques séparés par CLHP en phase inversée et identifiés par spectrométrie de masse a montré que les peptides les plus hydrophiles présentaient l'activité la plus