Impact of two thermal processing routes on protein interactions and acid gelation properties of casein micelle-pea protein mixture compared to casein micelle-whey protein one.

The influence of two heating protocols (protocol 1 and 2) on protein interactions and acid-induced gelation properties of casein micelle-pea protein mixture (CM-PP) was investigated and then compared to casein micelle-whey protein mixture (CM-WP). The CM:PP and CM:WP protein weight ratio for mixtures was 7.5:2.5, for a total protein content of 4% (pH 6.7). Protocol 1 consisted of a heat treatment (85 °C for 1 h) of CM-PP and CM-WP mixtures, respectively. Regarding protocol 2, casein micelle, pea protein and whey protein stock dispersions were individually pretreated by heating (85 °C for 1 h) before the mixtures were made and heated in the same conditions of protocol 1 (85 °C for 1 h). Heat pretreatment carried out in the protocol 2 significantly increased PP hydrophobicity and reinforced weak interactions of the initial pea protein particles. This pretreatment on protein stock dispersions led to twofold smaller pea protein particles compared to whey protein aggregates. The hydrophobic interactions between pea proteins and casein micelles promoted by the two heating protocols have greatly contributed to improve acid gelation functionalities of CM. Regardless of the heating protocol, acid-induced gelation of the CM-PP mixtures led to the formation of gel networks with a significant increase in stiffness and firmness compared to casein micelle or CM-WP mixtures gels.

Comparison of the Effect of Hydrostatic and Dynamic High Pressure Processing on the Enzymatic Activity and Physicochemical Quality Attributes of 'Ataulfo' Mango Nectar.

The effects of hydrostatic (HHP) and dynamic (HPH) high-pressure treatments on the activity of pectin methylesterase (PME) and polyphenol oxidase (PPO) as well as the physicochemical quality attributes of 'Ataulfo' mango nectar were assessed. HHP reduced PME relative activity by 28% at 100 MPa for 5 min but increased PPO activity almost five-fold. Contrarily, HPH did not affect PME activity, but PPO was effectively reduced to 10% of residual activity at 300 MPa and at three passes. Color parameters (CIEL*a*b*), °hue, and chroma were differently affected by each type of high-pressure processing technology. The viscosity and fluid behavior were not affected by HHP, however, HPH changed the apparent viscosity at low dynamic pressure levels (100 MPa with one and three passes). The viscosity decreased at high shear rates in nectar samples, showing a shear-thinning effect. The results highlight how different effects can be achieved with each high-pressure technology; thus, selecting the most appropriate system for processing and preserving liquid foods like fruit beverages is recommended.

Effect of pH change on size and nanomechanical behavior of whey protein microgels.

Microgels specific structural and functional features are attracting high research interest in several applications such as bioactives and drug delivery or functional food ingredients. Whey protein microgels (WPM) are obtained by heat treatment of whey protein isolate (WPI) in order to promote intramolecular cross-linking. In the present work, atomic force microscopy (AFM) was used in contact mode and in liquid to investigate WPM particles topography and mechanical properties at the nanoscale at native pH (6.5) and acid pH (5.5 and 3.0). Prior to AFM, WPM particles were captured on a gold substrate via low energy interactions by means of specific monoclonal antibodies. AFM images clearly showed an increase in the size of WPM particles induced by pH decrease. AFM in force spectroscopy mode was employed to monitor the elasticity of WPMs. The obtained effective Young's modulus data showed a significant increase in stiffness at pH 5.5 and pH 3.0, over 15-fold compared to native pH. These findings indicate that the mechanical profile of the WPM network varied with the pH decrease. The WPM topographic and nanomechanical changes induced by acidification were most likely due to substantial changes in the shape and inner structure of WPM particles. Our results suggest that internally cross-linked structures, modified by acidification could display interesting functional properties when used as a food ingredient.

Binding analysis between monomeric ß-casein and hydrophobic bioactive compounds investigated by surface plasmon resonance and fluorescence spectroscopy.

ß-Casein, a phosphoprotein representing 37% of the bovine milk caseins, has specific features promoting its application as a nanocarrier for hydrophobic bioactives. In this study, the interactions of ß-casein with curcumin and vitamin D3 under the same physico-chemical conditions were investigated. The interaction kinetics have been studied by surface plasmon resonance (SPR) and fluorescence spectroscopy. The KD value for curcumin-ß-casein interaction has been successfully evaluated (4.1 ±â€¯0.7 × 10-4 M) using SPR by fitting data to a 1:1 Langmuir interaction model. Conversely, the SPR responses obtained for vitamin D3 show that the interactions between this hydrophobic compound and the ß-casein immobilized on the sensor chip were below the sensitivity of the SPR apparatus. Moreover, the fluorescence quenching data show that curcumin has higher affinity to ß-casein (KA = 23.5 ±â€¯1.9 × 104 M-1) than vitamin D3 (KA = 5.8 ±â€¯1.1 × 104 M-1).

Potentialities and Limits of Some Non-thermal Technologies to Improve Sustainability of Food Processing.

In the whole food production chain, from the farm to the fork, food manufacturing steps have a large environmental impact. Despite significant efforts made to optimize heat recovery or water consumption, conventional food processing remains poorly efficient in terms of energy requirements and waste management. Therefore, in the few last decades, much research has focused on the development of alternative non-thermal technologies. Some of them, such as membrane separation processes, hydrostatic or dynamic high pressure, dense phase or high-pressure carbon dioxide, and pulsed electric fields (PEFs) have been extensively studied for cold pasteurization, concentration, extraction, or food functionalization. However, it is still difficult to evaluate the actual advantages or limits of these innovative processing technologies to replace conventional processes. Thus, the overall aim of this paper is to present an overview of the most relevant studies dealing with the potentialities and limits of these non-thermal technologies to improve sustainability of food processing. After a brief presentation of the physical principles of these technologies, the paper illustrates how these technologies could play a decisive role for sustainable food preservation or valorization of raw materials and by-products.

Atomic Force Microscopy Study of the Topography and Nanomechanics of Casein Micelles Captured by an Antibody.

Casein micelles (CMs) are colloidal phospho-protein-mineral complexes naturally present in milk. This study used atomic force microscopy (AFM) in a liquid environment to evaluate the topography and nanomechanics of single native CMs immobilized by a novel capture method. The proposed immobilization method involves weak interactions with the antiphospho-Ser/Thr/Tyr monoclonal antibody covalently bound to a carboxylic acid self-assembled monolayer (SAM) on a gold surface. This capture strategy was compared to the commonly used covalent immobilization method of CMs via carbodiimide chemistry. With this conventional method, CMs remained mainly mobile during AFM measurements in liquid, disturbing the evaluation of their average size and elastic properties. Conversely, when captured by the specific antibody, they were successfully immobilized and their integrity was preserved during the AFM measurement. The characterization of both CM topography and elastic properties was carried out in a liquid ionic environment at native pH 6.6. The CMs' capture efficiency via antibody was concurrently proved by surface plasmon resonance. The calculation of casein micelles' width, height, and contact angle was carried out from the recorded 2D AFM images. CMs were characterized by a mean width of 148 ± 8 nm and a mean height of 42 ± 1 nm. Weak forces were applied to single captured CMs. The obtained force versus indentation curves were fitted using the Hertz model in order to evaluate their elastic properties. The elasticity distribution of native CMs exhibited a unimodal trend with a peak centered at 269 ± 14 kPa.

Inhibitor and substrate binding induced stability of HIV-1 protease against sequential dissociation and unfolding revealed by high pressure spectroscopy and kinetics.

High-pressure methods have become an interesting tool of investigation of structural stability of proteins. They are used to study protein unfolding, but dissociation of oligomeric proteins can be addressed this way, too. HIV-1 protease, although an interesting object of biophysical experiments, has not been studied at high pressure yet. In this study HIV-1 protease is investigated by high pressure (up to 600 MPa) fluorescence spectroscopy of either the inherent tryptophan residues or external 8-anilino-1-naphtalenesulfonic acid at 25°C. A fast concentration-dependent structural transition is detected that corresponds to the dimer-monomer equilibrium. This transition is followed by a slow concentration independent transition that can be assigned to the monomer unfolding. In the presence of a tight-binding inhibitor none of these transitions are observed, which confirms the stabilizing effect of inhibitor. High-pressure enzyme kinetics (up to 350 MPa) also reveals the stabilizing effect of substrate. Unfolding of the protease can thus proceed only from the monomeric state after dimer dissociation and is unfavourable at atmospheric pressure. Dimer-destabilizing effect of high pressure is caused by negative volume change of dimer dissociation of -32.5 mL/mol. It helps us to determine the atmospheric pressure dimerization constant of 0.92 µM. High-pressure methods thus enable the investigation of structural phenomena that are difficult or impossible to measure at atmospheric pressure.

UHPH-processed O/W submicron emulsions stabilised with a lipid-based surfactant: physicochemical characteristics and behaviour on in vitro TC7-cell monolayers and ex vivo pig's ear skin.

Submicron O/W emulsions formulated with sesame oil plus a lipid-base surfactant, and with or without retinyl acetate (RAC) as a model hydrophobic biomolecule, were prepared by single-pass homogenisation at ≥ 200 MPa (UHPH) and an initial fluid temperature (Tin) of 24°C. These emulsions were characterised by a monomodal distribution (peak maximum at 260 nm) and a 2-year potential physical stability at ambient temperature. Submicron droplets were investigated in term of (i) physicochemical characteristics (size distribution curves; ζ-potential value), and (ii) impact on TC7-cell monolayers (MTT-assay and cell LDH-leakage). Submicron droplets ± RAC did not affect or increased significantly (p=0.05) TC7-cell metabolic activity after 4-24h of exposure indicating absence of cellular impairment, except when high amounts of droplets were deposed on TC7-cells. Indeed, the lipid-based surfactant deposed alone on TC7-cells at high concentration, induced some significant (p=0.05) cell LDH-leakage, and therefore cell-membrane damage. Cellular uptake experiments revealed a significant (p=0.05) time-dependent internalisation of RAC from submicron droplets, and cellular transformation of RAC into retinol. The turnover of RAC into retinol and therefore RAC bioaccessibility appeared faster for RAC-micelles of similar size-range and prepared at atmospheric pressure with polysorbate 80, than for submicron O/W emulsions. Permeation experiments using pig's ear skin mounted on Franz-type diffusion cells, revealed RAC in dermis-epidermis, in significantly (p=0.05) higher amounts for submicron than coarse pre-emulsions. However, RAC amounts remained low for both emulsion-types and RAC was not detected in the receptor medium of Franz-type diffusion cells.

Identification of Saccharomyces cerevisiae strains for alcoholic fermentation by discriminant factorial analysis on electronic nose signals

An electronic nose (E-nose) coupled to gas chromatography was tested to monitor alcoholic fermentation by Saccharomyces cerevisiae ICV-K1 and Saccharomyces cerevisiae T306, two strains well-known for their use in oenology. The biomass and ethanol concentrations and conductance changes were measured during cultivations and allowed to observe the standard growth phases for both yeast strains. The two strains were characterized by a very similar tendency in biomass or ethanol production during the fermentation. E-nose was able to establish a kinetic of the production of aroma compounds production and which was then easy to associate with the fermentation phases. Principal Component Analysis (PCA) showed that the data collected by E-nose during the fermentation mainly contained cultivation course information. Discriminant factorial analysis (DFA) was able to clearly identify differences between the two strains using the four main principal components of PCA as input data. Nevertheless, the electronic nose responses being mainly influenced by cultivation course, a specific data treatment limiting the time influence on data was carried out and permitted to achieve an overall performance of 83.5 percent.