Transmembrane Pressure during Micro- and Diafiltration of Milk Affects the Release of Non-Sedimentable Caseins Norbert Raak, Özgenur Coşkun, Milena Corredig Foods, 2023 Membrane filtration, especially in combination with diafiltration, can affect the colloidal structure of casein micelles in milk and concentrated milks. The partial dissociation of casein proteins from the casein micelles into the serum phase has been shown to depend on diafiltration conditions. This dissociation can affect the technological functionality of the milk concentrates. The present study aimed at determining the contribution of the gel layer deposited onto the membrane during filtration in the colloidal equilibrium between soluble and micellar caseins. Skimmed milk was concentrated by microfiltration combined with diafiltration using a cross-flow spiral-wound membrane at two transmembrane pressure (TMP) levels, causing differences in the extent of the gel layer formed. Non-sedimentable casein aggregates were formed to a greater extent at a low TMP compared to a high operating TMP. This difference was attributed to the greater compression of the deposit layer during filtration at a high TMP. This study contributes new knowledge to the understanding of how to modulate the functionality of milk concentrates through the control of processing conditions.
Cold ultrafiltered or microfiltered milk retentates: A systematic comparison of the effects of compositional differences on their gelation functionality Özgenur Coşkun, Lars Wiking, Milena Corredig Journal of Dairy Science, 2023 The colloidal stability of casein micelles suspensions prepared using ultrafiltration (UF) and microfiltration (MF) was studied by testing acid- and rennet-induced destabilization. Skim milk and 4× (based on volume reduction) concentrates were obtained by processing under similar conditions, at temperatures below 10°C. Concentrates were subjected to different levels of diafiltration (DF), resulting in samples with comparable casein volume fractions but different amounts of proteins and ions in the serum phase. The novelty of the work is the systematic comparison of MF and UF concentrates of similar history. More specifically, concentrates similar in ionic composition but with or without serum proteins were compared, to evaluate whether whey proteins and β-casein depletion from the micelles will play a role in the processing properties, or whether these are affected solely by the ionic balance. Microfiltered micelles' apparent diameter decreased by about 50 nm during the specific hydrolysis of κ-casein by chymosin, whereas those in skim milk control showed a decrease of about half that size. All concentrates subjected to extensive DF showed smaller hydrodynamic diameters, with reductions of ~18 and 13 nm for MF and UF, respectively. Highly diafiltered UF retentates showed a delayed onset of rennet-induced gelation, due to low colloidal calcium, compared with other samples. Low-diafiltered samples showed weak storage modulus (~1 Pa) after 60 min of onset of gelation. In addition, onset pH increased with diafiltration to ~5.8 for UF and ~6 for MF in high-diafiltered samples. These results clearly demonstrated that the functional properties of casein micelles change during membrane concentration, and this cannot be solely attributed to changes in ionic equilibrium.
Heat induced interactions in whey protein depleted milk concentrates: Comparison of ultrafiltration and microfiltration Özgenur Coşkun, Norbert Raak, Milena Corredig Food Hydrocolloids, 2023 The physical and chemical changes of 4x milk concentrates prepared by ultrafiltration (UF) and microfiltration (MF) combined with diafiltration were studied after heating in situ to 85 °C and subsequent cooling. Skim milk (1x) was analyzed as control. The concentrates had comparable pH, colloidal casein and colloidal calcium and phosphate, but differed in whey proteins and serum calcium and phosphate, allowing investigating the effect of soluble phase composition on viscosity changes and protein aggregation during heating. In heated samples, there was a decrease in the apparent diameter of the protein particles, as well as a decrease in bulk viscosity compared to unheated concentrates. On the other hand, the turbidity increased. Particles’ diffusivity measured by diffusive wave spectroscopy was slower in UF concentrate compared to the MF counterpart, both before and after heating, demonstrating the effect of protein aggregates in the soluble phase in changing the bulk properties of the concentrates. In this work, by comparing 4x MF and UF fresh concentrates with reduced calcium, and with similar processing history, it was demonstrated that the presence of whey proteins drives casein dissociation. MF concentrates showed increased heat stability compared to UF concentrates, with lower viscosity after heating. It was also observed that cooling kinetics affect the dissociation of caseins in heated skim milk. A fine control of diafiltration for ions and whey protein depletion is critical for control of the technological quality of the concentrates.
Pilot scale assessment for seed protein enrichment of gluten-free breads at varying water content levels and after protein modification treatments Özgenur Coşkun, Halime Pehlivanoğlu, İbrahim Gülseren Journal of Food Processing and Preservation, 2020 Three different seed protein concentrates were utilized in protein enrichment of gluten-free breads and their influence on texture, volume, color, and visual parameters were evaluated. First, protein concentrates (PC) were obtained from black cumin, grape seed, and pumpkin seed meals. For the original recipe, inclusion of proteins lowered loaf volumes, while volumes were improved when water content was increased (8% or 15%). Considering color, pumpkin seed protein concentrate (PSPC) samples demonstrated the highest level of similarity to controls, while black cumin protein concentrate samples were distinctly darker. Protein concentrates significantly increased firmness and decreased springiness of the crumb with the exception of PSPC samples, while further water inclusion enhanced the firmness attribute. When Maillard conjugation or TGase treatments were administered, firmness increased after both treatments, however, treated proteins enhanced cell distribution and homogeneity. The results showed current PCs can be utilized in enrichment of gluten-free breads. Practical applications Gluten-free bread formulations generally lack the texture and satiety of normal breads, especially due to the technical functionality of gluten proteins. Based on plant protein enrichment, a range of gluten-free breads were manufactured with increased protein content. The current findings on the textural attributes and water-holding capacities are applicable to various baked goods. Protein supplementation can also lower glycemic index in bread formulations.
