Changes in peptic digestibility of bovine beta-lactoglobulin as a result of food processing studied by capillary electrophoresis and immunochemical methods

The protein dynamics of bovine and caprine β-lactoglobulin differ as a function of pH

The properties of milk proteins differ between mammalian species. β-Lactoglobulin (βlg) proteins from caprine and bovine milk are sequentially and structurally highly similar, yet their physicochemical properties differ, particularly in response to pH. To resolve this conundrum, we compared the dynamics of both the monomeric and dimeric states for each homologue at pH 6.9 and 7.5 using hydrogen/deuterium exchange experiments. At pH 7.5, the rate of exchange is similar across both homologues, but at pH 6.9 the dimeric states of the bovine βlg B variant homologue have significantly more conformational flexibility compared with caprine βlg. Molecular dynamics simulations provide a mechanistic rationale for the experimental observations, revealing that variant-specific substitutions encode different conformational ensembles with different dynamic properties consistent with the hydrogen/deuterium exchange experiments. Understanding the dynamic differences across βlg homologues is essential to understand the different responses of these milks to processing, human digestion, and differences in immunogenicity.

A Response Surface Methodology (RSM) Approach for Optimizing the Attenuation of Human IgE-Reactivity to β-Lactoglobulin (β-Lg) by Hydrostatic High Pressure Processing

The response surface methodology (RSM) and central composite design (CCD) technique were used to optimize the three key process parameters (i.e., pressure, temperature and holding time) of the high-hydrostatic-pressure (HHP) processing either standalone or combined with moderate thermal processing to modulate molecular structures of β-lactoglobulin (β-Lg) and α-lactalbumin (α-La) with reduced human IgE-reactivity. The RSM model derived for HHP-induced molecular changes of β-Lg determined immunochemically showed that temperature (temp), pressure (p²) and the interaction between temperature and time (t) had statistically significant effects (p < 0.05). The optimal condition defined as minimum (β-Lg specific) IgG-binding derived from the model was 505 MPa at 56 °C with a holding time of 102 min (R² of 0.81 and p-value of 0.01). The validation carried at the optimal condition and its surrounding region showed that the model to be underestimating the β-Lg structure modification. The molecular change of β-Lg was directly correlated with HHP-induced dimerization in this study, which followed a quadratic equation. The β-Lg dimers also resulted in the undetectable human IgE-binding.

Immunoreactivity of lactic acid-treated mare's milk after simulated digestion

The similarity of mare's milk to breast milk makes it an interesting substrate for the creation of dairy beverages. The aim of this study was to determine the immunoreactivity of the digested mare's milk products carried out by lactic acid fermentation with Lactobacillus casei LCY, Streptococcus thermophilus MK10 and Bifidobacterium animalis Bi30. Simulation of digestion with saliva, pepsin and pancreatin/bile salts was carried out. The immunoreactivity of the milk proteins was assessed by competitive ELISA. The separation of proteins was studied using a tricine SDS-PAGE method. It has been demonstrated that lactic acid fermentation significantly decreases the immunoreactivity of β-lactoglobulin, β-casein, κ-casein and bovine serum albumin. The level of reduction was connected to the type of bacterial strain. The simulated digestion processes caused the decline of immunoreactivity, and the decreases obtained in the experiment were as follows: lactoferrin: 95%, β-lactoglobulin: 94%, β-casein: 93%, α-lactalbumin: 82%, α-casein: 82%, bovine serum albumin: 76% and κ-casein: 37%. The results of the study indicated that microbial fermentation with tested strains is a valuable method for reducing the immunoreactivity of mare's milk proteins. However, further studies with other bacterial strains are needed to gain a higher level of elimination or total reduction of mare's milk immunoreactivity to possibly introduce fermented mare's milk into the diet of patients with immune-mediated digestive problems.

Lactobacillus delbrueckii subsp. bulgaricus CRL 454 cleaves allergenic peptides of β-lactoglobulin

Whey, a cheese by-product used as a food additive, is produced worldwide at 40.7 million tons per year. β-Lactoglobulin (BLG), the main whey protein, is poorly digested and is highly allergenic. We aimed to study the contribution of Lactobacillus delbrueckii subsp. bulgaricus CRL 454 to BLG digestion and to analyse its ability to degrade the main allergenic sequences of this protein. Pre-hydrolysis of BLG by L. delbrueckii subsp. bulgaricus CRL 454 increases digestion of BLG assayed by an in vitro simulated gastrointestinal system. Moreover, peptides from hydrolysis of the allergenic sequences V41-K60, Y102-R124, C121-L140 and L149-I162 were found when BLG was hydrolysed by this strain. Interestingly, peptides possessing antioxidant, ACE inhibitory, antimicrobial and immuno-modulating properties were found in BLG degraded by both the Lactobacillus strain and digestive enzymes. To conclude, pre-hydrolysis of BLG by L. delbrueckii subsp. bulgaricus CRL 454 has a positive effect on BLG digestion and could diminish allergenic reactions.

Capillary electrophoresis for monitoring bioprocesses

Chemical characterization and monitoring of fermentation broths and cell culture media provide significant information on the changes occurring within these complex and dynamic systems. Analytical methods based on CE in capillaries and microchips are attractive for integration in instrumental tools to obtain this critical data, improving the understanding and control of bioprocesses. In this review, the use of CE for chemical characterization and monitoring fermentations is discussed, organized by analyte class, including organic acids, pharmaceuticals, proteins, sugars, amino acids, and metabolites published between 1992 and October 2012. A section is dedicated to the roles CE plays throughout the wine making process, where applications range from characterization and increase in fundamental understanding of the fermentation to forensic applications, verifying the authenticity of the wine.

In search of a tolerance-induction strategy for cow's milk allergies: significant reduction of beta-lactoglobulin allergenicity via transglutaminase/cysteine polymerization

OBJECTIVE

To explore the use of β-lactoglobulin polymerized using microbial transglutaminase and heating to identify whether protein polymerization could reduce in vivo allergenicity and maintain in vitro and ex vivo immunoreactivity for use in tolerance-induction protocols.

METHODS

Based on previous protocols applied in mice and children, we performed in vivo challenges (using a skin prick test) with native and polymerized β-lactoglobulin in adult patients with an IgE-mediated allergy to plactoglobulin. In vitro humoral immunoreactivity was analyzed using immunoblotting. Cell-mediated immunoreactivity was analyzed using ex vivo challenges with native and polymerized β-lactoglobulin and monitored by leukocyte adherence inhibition tests.

RESULTS

The skin tests demonstrated that there was a significant reduction in immediate cutaneous reactivity after polymerization. Polymerization did not decrease the immunoblotting detection of s-IgE specific to β-lactoglobulin. Cell-mediated immunoreactivity, as assessed by ex vivo challenges and leukocyte adherence inhibition tests, did not exhibit significant differences between leukocytes challenged with native versus polymerized β-lactoglobulin.

CONCLUSIONS

The polymerization of β-lactoglobulin decreased in vivo allergenicity and did not decrease in vitro humoral or ex vivo cell-mediated immunoreactivity. Therefore, we conclude that inducing polymerization using transglutaminase represents a promising technique to produce suitable molecules for the purpose of designing oral/ sublingual tolerance induction protocols for the treatment of allergies.

Tolerability of a fully maturated cheese in cow's milk allergic children: biochemical, immunochemical, and clinical aspects

BACKGROUND

From patients' reports and our preliminary observations, a fully maturated cheese (Parmigiano-Reggiano; PR) seems to be well tolerated by a subset of cow's milk (CM) allergic patients.

OBJECTIVE AND METHODS

To biochemically and immunologically characterize PR samples at different maturation stage and to verify PR tolerability in CM allergic children. Seventy patients, with suspected CM allergy, were enrolled. IgE to CM, α-lactalbumin (ALA), β-lactoglobulin (BLG) and caseins (CAS) were tested using ImmunoCAP, ISAC103 and skin prick test. Patients underwent a double-blind, placebo-controlled food challenge with CM, and an open food challenge with 36 months-maturated PR. Extracts obtained from PR samples were biochemically analyzed in order to determine protein and peptide contents. Pepsin and trypsin-chymotrypsin-pepsin simulated digestions were applied to PR extracts. Each PR extract was investigated by IgE Single Point Highest Inhibition Achievable assay (SPHIAa). The efficiency analysis was carried out using CM and PR oral challenges as gold standards.

RESULTS

The IgE binding to milk allergens was 100% inhibited by almost all PR preparations; the only difference was for CAS, mainly α(S1)-CAS. Sixteen patients sensitized to CM tolerated both CM and PR; 29 patients tolerated PR only; 21 patients, reacted to both CM and PR, whereas 4 patients reactive to CM refused to ingest PR. ROC analysis showed that the absence of IgE to BLG measured by ISAC could be a good marker of PR tolerance. The SPHIAa using digested PR preparations showed a marked effect on IgE binding to CAS and almost none on ALA and BLG.

CONCLUSIONS

58% of patients clinically reactive to CM tolerated fully maturated PR. The preliminary digestion of CAS induced by PR maturation process, facilitating a further loss of allergenic reactivity during gut digestion, might explain the tolerance. This hypothesis seems to work when no IgE sensitization to ISAC BLG is detected.

Capillary electrophoresis for the analysis of contaminants in emerging food safety issues and food traceability

This review presents an overview of the applicability of CE in the analysis of chemical and biological contaminants involved in emerging food safety issues. Additionally, CE-based genetic analyzers' usefulness as a unique tool in food traceability verification systems was presented. First, analytical approaches for the determination of melamine and specific food allergens in different foods were discussed. Second, natural toxin analysis by CE was updated from the last review reported in 2008. Finally, the analysis of prion proteins associated with the "mad cow" crises and the application of CE-based genetic analyzers for meat traceability were summarized.

Effect of exopolysaccharides on the hydrolysis of beta-lactoglobulin by Lactobacillus acidophilus CRL 636 in an in vitro gastric/pancreatic system

An analysis of the peptides generated by hydrolysis of BLG by nonproliferating cells of the strain Lactobacillus acidophilus CRL 636 was carried out. The effect of polysaccharides (pectin, and two EPS synthesized by two Streptococcus thermophilus strains, EPS1190 and EPS804) on BLG digestibility using an in vitro gastric/pancreatic system was analyzed. Polysaccharides are commonly used in the dairy industry to improve food texture; these hydrocolloids may interact with proteins, affecting their digestibility. Nonproliferating cells of Lb. acidophilus CRL 636 were able to hydrolyze 52% of BLG. Twenty-six resulting peptides with molecular masses in the range 544-4119 Da were identified by LC-MS/MS. These peptides resulted mostly from the hydrolysis of the more accessible N-terminal part of BLG. Degradation of BLG by pepsin was poor (8%). When BLG was previously hydrolyzed by Lb. acidophilus CRL 636, peptic hydrolysis was of 54.8%, while when pectin and EPS1190 were added, hydrolysis was higher (58.2 and 57.2%, respectively). Peptides crossing 8 kDa dialysis membranes after trypsin/chymotrypsin hydrolysis were analyzed by HPSEC. The produced peptides were smaller when BLG was hydrolyzed previously by the Lb. acidophilus strain. Moreover, in the presence of pectin, the amount of the larger peptide (3.5 kDa) observed in the size exclusion chromatograms was considerably decreased. Our studies showed that prehydrolysis of BLG by Lb. acidophilus CRL 636 had a positive influence on BLG digestibility and that polysaccharides may change the peptide profile yielded by trypsin/chymotrypsin hydrolysis, releasing smaller size peptides, which are known to be less immune-reactive. Moreover, Lb. acidophilus CRL 636 was able to hydrolyze the main epitopes (41-60, 102-124, and 149-162) of BLG, reducing its allergenic content.

The role of protein digestibility and antacids on food allergy outcomes

Digestion assays with simulated gastric fluid have been introduced for characterization of food proteins to imitate the effect of stomach proteolysis on dietary compounds in vitro. By using these tests, dietary proteins can be categorized as digestion-resistant class 1 (true allergens triggering direct oral sensitization) or as labile class 2 allergens (nonsensitizing elicitors). Thus the results of these digestion assays mirror situations of intact gastric proteolysis. Alterations in the gastric milieu are frequently experienced during a lifetime either physiologically in the very young and the elderly or as a result of gastrointestinal pathologies. Additionally, acid-suppression medications are frequently used for treatment of dyspeptic disorders. By increasing the gastric pH, they interfere substantially with the digestive function of the stomach, leading to persistence of labile food protein during gastric transit. Indeed, both murine and human studies reveal that antiulcer medication increases the risk of food allergy induction. Gastric digestion substantially decreases the potential of food proteins to bind IgE, which increases the threshold dose of allergens required to elicit symptoms in patients with food allergy. Thus antiulcer agents impeding gastric protein digestion have a major effect on the sensitization and effector phase of food allergy.

Whey fermentation by thermophilic lactic acid bacteria: evolution of carbohydrates and protein content

Whey, a by-product of the cheese industry usually disposed as waste, is a source of biological and functional valuable proteins. The aim of this work was to evaluate the potentiality of three lactic acid bacteria strains to design a starter culture for developing functional whey-based drinks. Fermentations were performed at 37 and 42 degrees C for 24h in reconstituted whey powder (RW). Carbohydrates, organic acids and amino acids concentrations during fermentation were evaluated by RP-HPLC. Proteolytic activity was measured by the o-phthaldialdehyde test and hydrolysis of whey proteins was analyzed by Tricine SDS-PAGE. The studied strains grew well (2-3log cfu/ml) independently of the temperature used. Streptococcus thermophilus CRL 804 consumed 12% of the initial lactose concentration and produced the highest amount of lactic acid (45 mmol/l) at 24h. Lactobacillus delbrueckii subsp. bulgaricus CRL 454 was the most proteolytic (91 microg Leu/ml) strain and released the branched chain amino acids Leu and Val. In contrast, Lactobacillus acidophilus CRL 636 and S. thermophilus CRL 804 consumed most of the amino acids present in whey. The studied strains were able to degrade the major whey proteins, alpha-lactalbumin being degraded in a greater extent (2.2-3.4-fold) than beta-lactoglobulin. Two starter cultures were evaluated for their metabolic and proteolytic activities in RW. Both cultures acidified and reduced the lactose content in whey in a greater extent than the strains alone. The amino acid release was higher (86 microg/ml) for the starter SLb (strains CRL 804+CRL 454) than for SLa (strains CRL 804+CRL 636, 37 microg/ml). Regarding alpha-lactalbumin and beta-lactoglobulin degradation, no differences were observed as compared to the values obtained with the single cultures. The starter culture SLb showed high potential to be used for developing fermented whey-based beverages.