Rehydration behaviour of spray-dried micellar casein concentrates produced using microfiltration of skim milk at cold or warm temperatures

peer-reviewedMicrofiltration (MF) of skim milk, when combined with diafiltration (DF), facilitates the manufacture of liquid micellar casein concentrate (MCC), which can be spray-dried into high-protein (≥80% protein, dry-basis) powders. MCC powders rehydrate slowly, which is typically considered a defect by end-users. This study compared the impact of cold (<10 °C) or warm (50 °C) MF/DF on the rehydration characteristics of MCC powders (MCCcold and MCCwarm, respectively). The wetting properties of the MCC powders, measured using optical tensiometry, were found to be equivalent. However, pronounced differences in dispersion characteristics were measured, and, after 90 min rehydration at 50 °C, liberated casein micelles accounted for only 7.5% of total particle volume in MCCwarm compared with 48% in MCCcold. Due to its superior dispersion characteristics, MCCcold yielded 50–60% less sediment during analytical centrifugation experiments. Cold MF/DF may improve the solubility of MCC powders by accelerating the release of casein micelles from powder particles during rehydration

Characterization of the microstructure of dairy systems using automated image analysis

International audienceA sound understanding of the microstructure of dairy products is of great importance in order to predict and control their properties and final quality. The aim of this study was to develop an automated image analysis procedure to characterize the microstructure of different dairy systems. A high pressure freezing coupled with freeze-substitution (HPF-FS) protocol was applied prior to transmission electron microscopy(TEM) in order to minimize any modification of the microstructure of the dairy systems investigated. The developed image analysis procedure was first validated on synthetic images of suspensions, and then on two types of concentrated milk suspensions. Microstructural data relating to casein micelles in milk suspensions were taken from the literature. The established procedure was then applied to the two corresponding rennet-induced milk gels, prepared from the same milk concentrates used for suspensions preparation. The automated image analysis procedure allowed the reliable estimation of several characteristic microstructural parameters including area fraction, porosity, boundary length per unit area, particle aggregate size, inter-particle aggregate distance and tortuosity. The relative ease of estimating these microstructural parameters from the automated image analysis method could make it useful for routine measurements of milk gels. Moreover, the method enabled a useful discrimination between two different types of milk gels. This novel approach can contribute to a better understanding of the effects of processing on the structure-property relationships in dairy products, and may be applied to other food systems

Interplay between soluble and insoluble protein/calcium/phytic acid complexes in dispersions of faba bean and pea protein concentrates around neutral pH

International audiencePulses are rich in proteins and a good source of calcium. However, antinutritional compounds such as phytic acid can bind to proteins and minerals to form complexes, reducing their digestibility and bioavailability, respectively. This study investigated interactions and potential complex formation between phytic acid, calcium, and proteins in pea and faba bean concentrate dispersions. The solubility of the 3 compounds was measured at pH 6.5, 7.0 and 7.5. Formation of complexes was investigated by chelating calcium upon EDTA addition or by removing proteins via ultrafiltration. Protein profiles were compared using Size Exclusion Chromatography (SEC). For both pea and faba bean, protein solubility increased with increasing pH. Phytic acid solubility was minimum at pH 7.0, while simultaneously calcium solubility was maximum. Protein solubility increased with EDTA addition compared to the control at pH 6.5 (pea and faba bean) and 7.0 (pea), supporting the presence of insoluble binary complexes between calcium and proteins. The concomitant rise in phytic acid solubility for pea (pH 6.5 and 7.0) highlighted the formation of either insoluble binary (phytic acid to calcium) or ternary complexes. Also, the formation of soluble protein complexes with phytic acid and, possibly, with calcium was highlighted. Small amounts of soluble ternary complexes were observed at pH 7.5. SEC results showed an increase in globulin's (especially legumin) solubility after calcium chelation; this demonstrated the formation of insoluble complexes mediated by calcium. This study highlighted that the different protein fractions from pulses must be considered separately in their ability to establish complexes with calcium and phytic acid

Heat-induced gelation of micellar casein/plant protein oil-in-water emulsions

International audienceThe heat-induced gelation of oil-in-water emulsions stabilised by mixtures of micellar caseins (MC) and plant proteins (PLP) was investigated in order to assess the potential of PLP to replace milk proteins for the development of novel food products. The aim of this work was to investigate how the heat-induced gelation of MC/PLP oil-in-water emulsions is affected by sunflower oil content (0, 5, 10 and 15% w/w) and total protein content in the aqueous phase (C; from 1 to 4% w/w) at different protein compositions (MC/PLP = 100/0 to 0/100) and pH 5.8. Two types of PLP were used: soy proteins (SP) and pea proteins (PP). Storage moduli (G') were measured during heating ramps from 20 to 90 °C and heat-induced gelation was characterised by an increase in G' at a gelation temperature (Tg). The gel stiffness (Gel) was determined after 1 h at 90 °C and the microstructure of the emulsion gels was observed by confocal laser scanning microscopy (CLSM). Tg increased when an increasing fraction of MC was replaced by SP or PP, due to binding of calcium to PLP. Tg decreased with increasing oil content in the MC/PLP emulsions mainly up to 10% w/w oil, explained by protein interactions at the oil-water interface. Generally, MC could be successfully replaced by PLP while maintaining the same Gel. Gel increased with increasing oil content, suggesting that oil droplets acted as active fillers in the emulsion gels, which was confirmed by CLSM images. Gel slightly increased with increasing C from 1 to 4% w/w. It was also shown that PLP can be used instead of whey proteins in MC/whey protein oil-in-water emulsions while maintaining the same Gel

Rehydration behaviour of spray-dried micellar casein concentrates produced using microfiltration of skim milk at cold or warm temperatures

Microfiltration (MF) of skim milk, when combined with diafiltration (DF), facilitates the manufacture of liquid micellar casein concentrate (MCC), which can be spray-dried into high-protein (≥80% protein, dry-basis) powders. MCC powders rehydrate slowly, which is typically considered a defect by end-users. This study compared the impact of cold (<10 °C) or warm (50 °C) MF/DF on the rehydration characteristics of MCC powders (MCCcold and MCCwarm, respectively). The wetting properties of the MCC powders, measured using optical tensiometry, were found to be equivalent. However, pronounced differences in dispersion characteristics were measured, and, after 90 min rehydration at 50 °C, liberated casein micelles accounted for only 7.5% of total particle volume in MCCwarm compared with 48% in MCCcold. Due to its superior dispersion characteristics, MCCcold yielded 50–60% less sediment during analytical centrifugation experiments. Cold MF/DF may improve the solubility of MCC powders by accelerating the release of casein micelles from powder particles during rehydration