Abstract
The objective of this study was to determine the effect of adding low concentrations of calcium-binding salts on the prevention of low-temperature gelation in milk protein concentrates (MPC). The MPC were created by a combination of ultrafiltration and diafiltration, standardized from 14 to 17% (wt/vol) protein content and mixed with one of 5 calcium-binding salts (sodium citrate, sodium hexametaphosphate, sodium polyphosphate, sodium pyrophosphate, and sodium monophosphate) adjusted to a pH of 6.75. The flow properties, apparent viscosity, and gel strength were determined for MPC containing a wide range of calcium-binding salt concentrations. Low-temperature gelation occurred in MPC with 16.0% and higher protein content. Low-temperature gelation at 16.0% protein content was prevented by the addition of any of the 5 salts tested at low concentrations (0.30 mM or less; sodium citrate, sodium hexametaphosphate, sodium polyphosphate, sodium pyrophosphate or sodium monophosphate), with sodium polyphosphate and sodium monophosphate being the most consistent in preventing low-temperature gels. All MPC samples exhibited shear-thinning behavior (n = 0.52-0.72), which increased (lower n values) as the protein content increased and decreased by addition of salt. At concentrations of salt above 1.00 mM, thermally irreversible gels were observed with relative strength dependent on the salt and protein content.
Highlights
Reductions in transportation cost by removing water from milk through the production of milk powders and milk protein concentrates (MPC) can have a large ef-Kieferle et al (2019) showed that for both liquid and reconstituted MPC, increasing the protein content resulted in higher viscosity at low temperature (10°C) and increased shear-thinning behavior
Salt-free MPC at 14.2 and 15.1% protein content did not form low-temperature gel (LT-gel) but formed salt-induced gels when salts were added at 3.0 mM or above for sodium citrate, sodium hexametaphosphate, sodium pyrophosphate, and sodium monophosphate, and 5.0 mM or above for sodium polyphosphate
At 16.0% protein content, LT-gels consistently formed in salt-free MPC and were prevented by the addition of calcium-binding salts
Summary
Reductions in transportation cost by removing water from milk through the production of milk powders and milk protein concentrates (MPC) can have a large ef-Kieferle et al (2019) showed that for both liquid and reconstituted MPC, increasing the protein content resulted in higher viscosity at low temperature (10°C) and increased shear-thinning behavior. Protein-protein interactions in reconstituted MPC at ~12% protein content resulted in gel-like behavior and flow prevention, whereas fresh MPC remained liquid with up to 13% protein content. They reported that predicting a precise viscosity based on protein content was not reliable, due to differences in composition and processing history. Experiments by Lu et al (2015, 2017) further explored the relationship between protein content and temperature in reconstituted micellar casein concentrates In these studies, they found that a protein content of 17 to 18% at around 7°C resulted in a low-temperature gel (LT-gel)
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