Jean-Marc Chobert

Improvement of functional properties of β-lactoglobulin glycated through the Maillard reaction is related to the nature of the sugar

The improvement of functional properties of proteins available in large quantity using non-toxic chemical modifications is of a great interest for the food industry. In this study, the Maillard reaction was used to improve the functional properties (solubility, heat stability, emulsifying and foaming properties) of β-lactoglobulin (BLG) glycated with several sugars (arabinose, galactose, glucose, lactose, rhamnose or ribose). Protein samples were heated in the presence or absence (heated control) of different sugars for three days at 60°C. Subsequent glycation induced a modification of the solubility profile shifting minimum solubility towards more acidic pH. Glycated proteins exhibited a better thermal stability when heated at pH 5 as compared to native or heated control. Glycation of BLG with arabinose or ribose (the most reactive sugars) improved its emulsifying properties. Foaming properties were better when BLG was glycated with glucose or galactose (moderately reactive sugars). These results suggest that the nature of the sugar is an essential factor for improving the functional properties of glycated proteins by processes of Maillard reaction.

Detection and characterization of a novel antibacterial substance produced by Lactobacillus plantarum ST 31 isolated from sourdough.

Lactobacillus plantarum ST31 isolated from sourdough produced an antimicrobial substance inhibiting other strains of the genera Lactobacillus, Leuconostoc, Pediococcus, Streptococcus, Bacillus and some foodborne pathogens including Staphylococcus aureus. This antimicrobial substance was inactivated by proteolytic enzymes. Consequently, it was characterized as a bacteriocin and was designated plantaricin ST31. This bacteriocin was stable in the pH range 3-8 and it was not affected by amylolytic enzymes. Production of plantaricin was pH and temperature dependent, and maximum yields were obtained in MRS broth cultures maintained at pH 6 and incubated at 30 degrees C in the exponential phase to the early stationary growth phase of the producer organism. This bacteriocin was purified by using consecutive ammonium sulfate and reversed-phase chromatography. It is a peptide of 20 amino acid residues with a mass of 2755+/-0.3 Da, as determined by electrospray mass spectrometry. The sequence of Plantaricin ST31 showed no similarity to those of other bacteriocins. Plantaricin ST31 production appeared to be chromosomally encoded.

Purification and characterization of two bacteriocins produced by lactic acid bacteria isolated from Mongolian airag.

Aims:  The aim of this study was to isolate and identify bacteriocin‐producing lactic acid bacteria (LAB) issued from Mongolian airag (traditional fermented mares milk), and to purify and characterize bacteriocins produced by these LAB.

Isolation and partial biochemical characterization of a proteinaceous anti-bacteria and anti-yeast compound produced by Lactobacillus paracasei subsp. paracasei strain M3.

New proteinaceous active substance produced by Lactobacillus paracasei subsp. paracasei strain M3 used as a starter for Bulgarian yellow cheese was identified and studied. It displayed bactericidal and fungistatic activities. Its activity was checked against over 60 bacterial and yeast strains. It was efficient against Bacillus subtilis ATCC 6633, several L. delbrueckii species, Helicobacter pylori NCIPD 230 and some yeast species, for example Candida albicans, C. pseudointermedia NBIMCC 1532, C. blankii NBIMCC 85 and Saccharomyces cerevisiae NBIMCC 1812. The synthesis of the substance by producing strain was detected in the late logarithmic growth phase during batch fermentation. Anion exchange chromatography, reversed phase chromatography (RPC) on C4 column and HPLC on C18 column were used for partial purification of this antimicrobial compound. The gene responsible for the synthesis of the active substance is located on the bacterial chromosome.

Comparative study of the amino acid sequences of the caseinomacropeptides from seven species

occur in milk as large and stable calcium phosphate complexes called micelles. When milk is treated with a low amount of a protease such as chymosin (rennin EC 3.4.23.4), the micelles become clotted. This is the result of the hydrolysis of a labile peptide bond in K-casein, which then loses its ability to stabilize casein micelles. The soluble carbo- hydrate-rich C-terminal fragment, caseinomacropeptide (CMP), which is released accounts for about one third of K-casein polypeptide chain. The N-terminal frag- ment, para+-casein, which polymerizes is insoluble. might have been conserved during the course of evo- lution. Such regions may presumably be involved in the stabilization of casein micelles or responsible for the sensitivity of K-casein to chymosin and other proteolytic enzymes. The primary structures of caprine K-casein [9-lo], water buffalo [ 1 l] and porcine [ 121 CMPs have been completely established. That of human CMP [ 121 has been nearly elucidated. Some data concerning the amino acid sequence of bovine K-casein were published in 1970 by Joll& et al.

Induction of New Physicochemical and Functional Properties by the Glycosylation of Whey Proteins

Nucleophilic primary amino groups of whey proteins (β-lactoglobulin and α-lactalbumin) were modified with reducing sugars in mild heat conditions. After 49 hr of heating (60°C) at pH 6.5, 20–30% of β-lactoglobulin amino groups were substituted with aldohexoses (galactose, mannose, glucose) and lactose, whereas up to 70% and 90% of β-lactoglobulin amino groups were modified with ribose and glyceraldehyde, respectively. Gel electrophoresis and reversed-phase HPLC coupled with electrospray ionization mass spectrometry of glycosylated proteins indicated that the substitution was random. Consequently, highly heterogeneous families of glycosylated proteins were generated. Proteins substituted with hexoses and lactose exhibited higher solubility and improved emulsifying properties as compared with nonglycosylated proteins, in the whole pH range studied. In contrast, proteins glycosylated with ribose and glyceraldehyde showed lower solubility close to their isoelectric points. β-Lactoglobulin modified with ribose and glyceraldehyde displayed substantial differences in denaturation behavior as compared with native protein. When compared with β-lactoglobulin, glycosylation of α-lactalbumin was quicker. There was no difference in glycosylation yields nor rates of α-lactalbumin in presence and absence of calcium.

Lactobacillus salivarius: Bacteriocin and probiotic activity

Lactic acid bacteria (LAB) antimicrobial peptides typically exhibit antibacterial activity against food-borne pathogens, as well as spoilage bacteria. Therefore, they have attracted the greatest attention as tools for food biopreservation. In some countries LAB are already extensively used as probiotics in food processing and preservation. LAB derived bacteriocins have been utilized as oral, topical antibiotics or disinfectants. Lactobacillus salivarius is a promising probiotic candidate commonly isolated from human, porcine, and avian gastrointestinal tracts (GIT), many of which are producers of unmodified bacteriocins of sub-classes IIa, IIb and IId. It is a well-characterized bacteriocin producer and probiotic organism. Bacteriocins may facilitate the introduction of a producer into an established niche, directly inhibit the invasion of competing strains or pathogens, or modulate the composition of the microbiota and influence the host immune system. This review gives an up-to-date overview of all L. salivarius strains, isolated from different origins, known as bacteriocin producing and/or potential probiotic.

Improvement of the antimicrobial and antioxidant activities of camel and bovine whey proteins by limited proteolysis.

The compositions and structures of bovine and camel milk proteins are different, which define their functional and biological properties. The aim of this study was to investigate the effects of enzymatic hydrolysis of camel and bovine whey proteins (WPs) on their antioxidant and antimicrobial properties. After enzymatic treatment, both the antioxidant and the antimicrobial activities of bovine and camel WPs were improved. The significantly higher antioxidant activity of camel WPs and their hydrolysates as compared with that of bovine WPs and their hydrolysates may result from the differences in amounts and/or in accessibilities of antioxidant amino acid residues present in their primary structures and from the prevalence of alpha-lactalbumin and beta-lactoglobulin as proteolytic substrates in camel and bovine whey, respectively. The results of this study reveal differences in antimicrobial and antioxidant activities between WP hydrolysates of bovine and camel milk and the effects of limited proteolysis on these activities.

Proteolysis of β-lactoglobulin and β-casein by pepsin in ethanolic media

Abstract Limited proteolysis of β-lactoglobulin and β-casein by pepsin was performed in the presence of varying concentrations of ethanol. β-Lactoglobulin started to be cleaved by pepsin only in ethanol concentrations greater than 20%, when its secondary structure began to change. In 25% ethanol, the rate of hydrolysis of β-lactoglobulin was slow (40% remained intact after 40 h of hydrolysis) and many short and hydrophilic peptides were observed. The rate of hydrolysis of β-lactoglobulin reached its maximum in 30 and 35% ethanol (80% of β-lactoglobulin was hydrolysed after 10 h), and a mixed population of hydrophilic and hydrophobic peptides of different lengths was observed. Large hydrophobic peptides appeared first, then some shorter products. The rate of hydrolysis of β-lactoglobulin decreased at ethanol concentrations equal to or higher than 40%, when only a few long, hydrophobic peptides were produced. As seen by circular dichroism, the addition of ethanol to β-casein induced α-helix formation and reduced the rate of casein hydrolysis without changing the peptide profile. The only exception was the yield of a single peptide (Pro81 − Met93).

Purification and characterization of a new bacteriocin active against Campylobacter produced by Lactobacillus salivarius SMXD51

Strain SMXD51, isolated from chicken ceca and identified as Lactobacillus salivarius, produced a component that inhibits the growth of Gram-positive and Gram-negative bacteria and especially Campylobacter jejuni. The active peptide from the cell-free supernatant of Lb. salivarius SMXD51 was purified in three steps: (i) precipitation with 80% saturated ammonium sulfate, (ii) elution on a reversed phase SPE UPTI-CLEAN cartridge using different concentrations of acetonitrile, (iii) final purification by reversed phase HPLC on a C(18) column. The mode of action of this peptide of 5383.2 Da was identified as bactericidal, and its amino acid composition was established. This new bacteriocin SMXD51 appears potentially very useful to reduce Campylobacter in poultry prior to processing.