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.

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.

The foaming properties of camel and bovine whey: The impact of pH and heat treatment.

The effect of heat treatment (70°C or 90°C for 30min) on the foaming and interfacial properties of acid and sweet whey obtained from bovine and camel fresh milk was examined. The maximum foamability and foam stability were observed for acid whey when compared to sweet whey for both milks, with higher values for the camel whey. This behavior for acid whey was explained by the proximity of the pI of whey protein (4.9-5.2), where proteins were found to carry the lowest negative charge as confirmed by the zeta potential measurements. Interfacial properties of acid camel whey and acid bovine whey were preserved at air water interface even after a heat treatment at 90°C. These results confirmed the pronounced foaming and interfacial properties of acid camel whey, even if acid and sweet bovine whey exhibited the highest viscoelastic modulus after heating.

Performances of different protocols for exocellular polysaccharides extraction from milk acid gels: Application to yogurt.

Dextran or xanthan were used as model exocellular polysaccharides (EPS) to compare the extraction efficiency of EPS from skim milk acid gels using three different protocols. Extraction yields, residual protein concentrations and the macromolecular properties of extracted EPS were determined. For both model EPS, the highest extraction yield (∼80%) was obtained when samples were heated in acidic conditions at the first step of extraction (Protocol 1). Protocols that contained steps of acid/ethanol precipitation without heating (Protocols 2 and 3) show lower extraction yields (∼55%) but allow a better preservation of the EPS macromolecular properties. Changing the pH of acid gels up to 7 before extraction (Protocol 3) improved the extraction yield of anionic EPS without effect on the macromolecular properties of EPS. Protocol 1 was then applied for the quantification of EPS produced during the yogurt fermentation, while Protocol 3 was dedicated to their macromolecular characterization.

The effect of pH and heat treatments on the foaming properties of purified α-lactalbumin from camel milk.

The effect of pH (4.3 or 6.5) and heat treatment (70°C or 90°C for 30min) on the foaming and interfacial properties of α-lactalbumin extracted from camel milk were studied. The increased temperature treatment changed the foaming properties of camel α-lactalbumin solution and its ability to unfold at the air-water interface. At neutral pH, heat treatment was found to improve foamability, whereas at acid pH (4.3) this property decreased. Foams were more stable after a heat treatment at pH 4.3 than at 6.5, due to higher levels of protein aggregation at low pH. Heat treatment at 90°C for 30min affected the physicochemical properties of the camel α-lactalbumin by increasing free thiol group concentration at pH 6.5. Heat treatment also caused changes in α-lactalbumin's surface charge. These results also confirm the pronounced aggregation of heated camel α-lactalbumin solution at acid pH.

Foaming and adsorption behavior of bovine and camel proteins mixed layers at the air/water interface.

The aim of this work was to examine foaming and interfacial behavior of three milk protein mixtures, bovine α-lactalbumin-ß-casein (M1), camel α-lactalbumin-ß-casein (M2) and ß-lactoglobulin-ß-casein (M3), alone and in binary mixtures, at the air/water interface in order to better understand the foaming properties of bovine and camel milks. Different mixture ratios (100:0; 75:25; 50:50; 25:75; 0:100) were used during foaming tests and interfacial protein interactions were studied with a pendant drop tensiometer. Experimental results evidenced that the greatest foam was obtained with a higher ß-casein amount in all camel and bovine mixtures. Good correlation was observed with the adsorption and the interfacial rheological properties of camel and bovine protein mixtures. The proteins adsorbed layers are mainly affected by the presence of ß-casein molecules, which are probably the most abundant protein at interface and the most efficient in reducing the interfacial properties. In contrast of, the globular proteins, α-lactalbumin and ß-lactoglobulin that are involved in the protein layer composition, but could not compact well at the interface to ensure foams creation and stabilization because of their rigid molecular structure.

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.