Transmembrane Pressure during Micro- and Diafiltration of Milk Affects the Release of Non-Sedimentable Caseins.

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.

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 ß-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.

Influence of Maillard reaction conditions and solvent extraction on the surface activity and foaming characteristics of black cumin protein concentrates.

Cold press manufacture of black cumin (BC) oil leads to the formation of BC press cakes that contain significant amounts of protein. Here, an attempt was made to enhance the functionality of BC protein concentrates obtained from cakes based on Maillard conjugation using 3 different of carbohydrates. Molecular weight distribution of the conjugates was determined via electrophoretic techniques. The extent of carbohydrate binding was measured by RP-HPLC-RID. Surface activity and elasticity was studied using drop shape tensiometry. The extent of glucose binding accounted for up to 85% for a protein:glucose ratio of 1:2. Foaming capabilities were moderately enhanced due to Maillard conjugation in the absence of solvent extraction, while due to solvent induced partial denaturation, further enhancement of foaming performance took place. Furthermore, sugar binding capabilities were enhanced upon solvent treatment, while surface pressure and foaming capacity were not necessarily improved. Adsorption rate at the air-water surface and dilational elasticity was highly dependent on molecular size of reacting sugars. In addition, oil remaining in the samples also had a bearing on the extent of Maillard conjugation. Consequently, tailoring of processing conditions could enhance foaming characteristics of BC proteins and ensure their utilization in food foams and other food dispersions.