Impact of pulsed electric field intensity on the cream separation efficiency from bovine milk and physico-chemical properties of the cream.

Low-temperature (9-12 °C) pulsed electric field (PEF) was investigated in milk before cream separation at different intensities (9-27 kV/cm, 66 µs, 16-28 kJ/L) regarding its potential to render processing more sustainable, retain a high physico-chemical quality, enhance functional properties, and gently modify the structure of the milk fat globule membrane (MFGM). Cream volume per L milk were most efficiently increased by 31 % at the lowest PEF intensity in comparison to untreated milk and cream (P < 0.05). Untreated and PEF-treated milk and obtained cream were assessed with compositional (fat, protein, casein, lactose, and total solids content) and particle size distribution analyses, showing no significant differences (P ≥ 0.05) and, thus, indicating retention of 'native-like' product quality. Overrun and stability of cream, whipped for 20 and 60 s at 15000 rpm using a high-shear mixer, were improved most notably by the lowest and the highest PEF intensities, achieving up to 69 % enlarged overrun and up to 22 % higher stability, respectively (P < 0.05), than in untreated whipped cream. Protein component analyses for milk and cream were carried out by sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Noticeable differences between untreated and PEF-treated milk were not observed, but the SDS-PAGE results for cream showed noticeably different bands for some of the protein components, indicating structural changes in MFGM-, whey-, and phospho-proteins due to PEF and/or separator processing effects. More intense bands of xanthine oxidase, xanthine dehydrogenase, butyrophilin, bovine serum albumine, adipophilin (ADPH), and glycoproteins PAS6/7 were observed specifically at 21 kV/cm. Gentle electroporation of both MFGM layers by PEF was determined based on the changes in MFGM monolayer components, such as ADPH and PAS 6/7, exhibiting intensified bands. PEF intensity-dependent impact on the structure of MFGM and casein, leading to a reconfiguration of the cream matrix due to different structuring interactions among proteins, among milk fat globules, and between fat and protein components, was suggested. Overall, low-temperature PEF applied at different intensities showed great potential for gentle, efficient, and functional properties-tailored dairy processing and may also enable effective extraction of highly bioactive ingredients from dairy sources.

Impact of Physicochemical Modifications in Casein Promoted by UV-C on the Peptide Profile of Gastric Digestion and the Transepithelial Transport of Peptides.

Caseins are the main proteins in milk, and their structure and spatial conformation are responsible for their slow digestion rate. The release of bioactive and ß-casomorphin peptides from casein digestion may induce allergic responses during consumption. Spectroscopic techniques were used to observe the structural changes in casein conformation induced by Ultraviolet light irradiation (UV-C). Raman spectroscopy results showed more pronounced peaks at 618 and 640 cm-1 for phenylalanine and tyrosine moieties of the photolyzed micellar casein, respectively, suggesting changes in the micelle structure. The decrease in the intensity of Raman signals for tryptophan and tyrosine corroborates to the UV-C-induced modifications of the micelle structure. Particle size distribution showed a decrease in the average micelle size after 15 min of UV-C exposure, while low-temperature, long-time (LTLT) pasteurization led to the formation of large aggregates, as observed by atomic force microscopy. UV-C did not impact the formation or transport of peptides, as observed by using the Caco-2 cell as a model for peptide absorption. However, the absence of the opioid peptide SRYPSY from κ-casein and only 20% of the concentration of opioid peptide RYLGY were noted. This work demonstrated that UV-C can be utilized to induce the physicochemical modification of dairy products, promoting a higher digestion rate and reducing allergenicity.

Structural changes induced by high-pressure processing in micellar casein and milk protein concentrates.

Reconstituted micellar casein concentrates and milk protein concentrates of 2.5 and 10% (wt/vol) protein concentration were subjected to high-pressure processing at pressures from 150 to 450 MPa, for 15 min, at ambient temperature. The structural changes induced in milk proteins by high-pressure processing were investigated using a range of physical, physicochemical, and chemical methods, including dynamic light scattering, rheology, mid-infrared spectroscopy, scanning electron microscopy, proteomics, and soluble mineral analyses. The experimental data clearly indicate pressure-induced changes of casein micelles, as well as denaturation of serum proteins. Calcium-binding αS1- and αS2-casein levels increased in the soluble phase after all pressure treatments. Pressurization up to 350 MPa also increased levels of soluble calcium and phosphorus, in all samples and concentrations, whereas treatment at 450 MPa reduced the levels of soluble Ca and P. Experimental data suggest dissociation of calcium phosphate and subsequent casein micelle destabilization as a result of pressure treatment. Treatment of 10% micellar casein concentrate and 10% milk protein concentrate samples at 450 MPa resulted in weak, physical gels, which featured aggregates of uniformly distributed, casein substructures of 15 to 20 nm in diameter. Serum proteins were significantly denatured by pressures above 250 MPa. These results provide information on pressure-induced changes in high-concentration protein systems, and may inform the development on new milk protein-based foods with novel textures and potentially high nutritional quality, of particular interest being the soft gel structures formed at high pressure levels.

Effect of heat-assisted pulsed electric fields and bacteriophage on enterohemorrhagic Escherichia coli O157:H7.

Pulsed electric fields (PEF), heat-assisted PEF (H-PEF), and virulent bacteriophage (VP) are non-thermal techniques for pathogen inactivation in liquids that were investigated individually, and in combination (PEF/VP, H-PEF/VP) to control enterohemorrhagic Escherichia coli (EHEC) O157:H7 in Luria-Bertani broth (LBB) and Ringer's solution (RS). Treated cells were subsequently incubated at refrigeration (4°C) and temperature-abuse conditions (12°C) for 5 days. When EHEC cells grown in LBB were subjected to non-thermal processing and subsequently stored at 12°C for 5 days, reductions in count of between 0.1 and 0.6 log cycles were observed and following storage at 4°C the decrease in counts varied between 0.2 and 1.1 log10 . For bacteria cells suspended in RS values ranged from 0.1 to ≥3.9 log cycles at both storage temperatures. The most effective treatments were H-PEF and H-PEF/VP, both producing a >3.4 log cycle reduction of cells suspended in non-nutrient RS. Analysis of EHEC recovery on selective and non-selective media indicated no occurrence of sub-lethal damage for VP, PEF/VP, and H-PEF/VP-treated cells. The findings indicate that combining PEF and lytic phage may represent a suitable alternative to conventional fluid decontamination following further process optimization.

Change in Color and Volatile Composition of Skim Milk Processed with Pulsed Electric Field and Microfiltration Treatments or Heat Pasteurization.

Non-thermal processing methods, such as pulsed electric field (PEF) and tangential-flow microfiltration (TFMF), are emerging processing technologies that can minimize the deleterious effects of high temperature short time (HTST) pasteurization on quality attributes of skim milk. The present study investigates the impact of PEF and TFMF, alone or in combination, on color and volatile compounds in skim milk. PEF was applied at 28 or 40 kV/cm for 1122 to 2805 µs, while microfiltration (MF) was conducted using membranes with three pore sizes (lab-scale 0.65 and 1.2 µm TFMF, and pilot-scale 1.4 µm MF). HTST control treatments were applied at 75 or 95 °C for 20 and 45 s, respectively. Noticeable color changes were observed with the 0.65 µm TFMF treatment. No significant color changes were observed in PEF-treated, 1.2 µm TFMF-treated, HTST-treated, and 1.4 µm MF-treated skim milk (p ≥ 0.05) but the total color difference indicated better color retention with non-thermal preservation. The latter did not affect raw skim milk volatiles significantly after single or combined processing (p ≥ 0.05), but HTST caused considerable changes in their composition, including ketones, free fatty acids, hydrocarbons, and sulfur compounds (p < 0.05). The findings indicate that for the particular thermal and non-thermal treatments selected for this study, better retention of skim milk color and flavor components were obtained for the non-thermal treatments.

Factors affecting the inactivation of the natural microbiota of milk processed by pulsed electric fields and cross-flow microfiltration.

Prior to processing milk and cream were standardised and homogenised. Skim milk was cross-flow microfiltered (CFMF) prior to treatment with pulsed electric fields (PEF) or high temperature short time (HTST) pasteurization. The effect of temperature of the skim milk and product composition on the efficacy of PEF treatment was determined. The electrical conductivity of the product was related to fat and solids content and increased 5% for every g/kg increase of solids and decreased by nearly 0·7% for every g/kg increase of fat. From the three microbial groups analyzed (mesophilic, coliform, and psychrotroph) in milks differences (P<0·05) in the inactivation of mesophilic microorganisms were observed between the counts following PEF treatment, while HTST pasteurization resulted in higher reductions in all different counts than those obtained after PEF. Increasing the skim milk temperature prior to PEF treatment to about 34°C showed equivalent reductions in microbial counts to skim milk treated at 6°C in half the time. The reductions achieved by a combination of CFMF and PEF treatments were comparable to those achieved when CFMF was combined with HTST pasteurization. A higher reduction in coliform counts was observed in homogenised products subjected to PEF than in products that were only standardised for fat content.