Prevention of Low Temperature Gelation in Milk Protein Concentrates

open_access
Open Access
Author:
Goulder, David
Graduate Program:
Food Science
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 10, 2021
Committee Members:
Federico Miguel Harte, Thesis Advisor/Co-Advisor
Greg Ziegler, Committee Member
Robert Roberts, Program Head/Chair
John Neil Coupland, Committee Member
Keywords:
gel
gelation
low temperature gel
jammed system
voluminosity
intrinsic viscosity
apparent viscosity
flow behavior
shear thinning
rheology
chelating salt
calcium binding salt
milk protein concentrate
MPC
filtration
shear sweep
caesin
whey
isolate
volume fraction
maximum volume fraction
ulatrafiltration
diafiltration
sodium citrate
sodium hexametaphosphate
sodium polyphosphate
sodium pyrophosphate
sodium monophosphate
Abstract:
When concentrated milk protein (≥ 16% ) is stored at low temperatures (≤ 8 °C) a gel forms. This gel, while thermally reversible, is the primary barrier preventing the widespread use of liquid milk protein concentrates (MPC). Liquid MPCs have a lower cost (per kg protein) than MPC powder and retain a more native protein functionality, thus preventing low temperature gelation is of interest to the food and beverage industry. Low Temperature gelation (LT-gelation) in milk protein concentrates was prevented by the addition of calcium binding salts and by the substitution of whey proteins for casein. MPCs were produced by a combination of ultrafiltration and diafiltration (50 °C; 10kDa filter). LT-gels occurred in MPCs with ≤ 16.0% protein content (80:20 casein:whey). The addition of sodium citrate, sodium hexametaphosphate, sodium polyphosphate or sodium monophosphate (≤ 0.3 mM) prevented LT-gelation in MPCs with 16% (w/v) protein content. At concentrations ≥ 1 mM non-reversible salt induced gels were formed in MPCs with 14-16% protein content. The firmness of the gels increased with increasing protein content. All MPC samples mixed with salt that remained liquid at 16% protein content exhibited shear thinning behavior (n = 0.52-0.72), which increased (lower n values) as the protein content increased and decreased when salt was added. In a separate experiment, a series of MPC-WPI mixtures were tested at 20% total protein content, and LT-gels were prevented when the casein content was ≤ 7.2% w/w. Whereas pure WPI exhibited Newtonian behavior at concentrations ranging from 1-25% w/w, all MPC-WPI mixtures exhibited shear thinning behavior which increased as the proportion of casein increased (n = 0.94-0.56; 20% total protein). The contribution of whey proteins to apparent viscosity, flow behavior and the consistency coefficient was smaller than that of casein. The liquid to gel transition in MPC-WPI mixtures held at 4 °C was consistent with previous reports indicating voluminosity (ν) and volume fraction (Φ) as main mechanism explaining jamming in dairy systems. A calculated νc= 5.0 mL/g for casein and νw= 2.34 mL/g for whey protein resulted in Φmax= 0.68 where LT-gelation occurred for MPC-WPI mixtures. LT-gelation was prevented in all MPC-WPI where the Φ was below 0.68. Low temperature gelation in milk protein concentrates has been prevented by the addition of calcium binding salts or by changing the ratio of casein and whey proteins to increase the proportion of whey. These solutions will enable the food and beverage industry to utilize liquid MPCs rather than relying on expensive powders. This may be of special interest to manufacturers of processed cheese who already add calcium binding salts to their products and often rely on MPC powder to increase the protein content / yield of their cheeses. Manufacturers of high protein dairy beverages can also benefit, as the majority of products on the market add one or more calcium binding salts (the same salts chosen for this study). They may also be able to drastically increase the total protein content (a key marketing claim) while retaining similar viscosity / mouthfeel and stability by adjusting the ratio of casein and whey.