Date of Award:

2016

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Advisor/Chair:

Donald J. McMahon

Abstract

Highly concentrated micellar casein concentrate (HC-MCC), a potential ingredient for cheese making, containing ~20% casein with ~70% of serum proteins removed by microfiltration, and diafiltration of skim milk, and then further concentrated by vacuum evaporation. The objectives of this research were to investigate solubilization, cold gelation, rennet coagulation properties of recombined HC-MCC and cream for its use in cheese making.

In Chapter 3, either mixing thawed HC-MCC in water at high temperature (~50C) or addition of trisodium citrate can achieve complete dispersion and more than 80% solubility of HC-MCC in water (3% protein). Overnight storage helps to fully disperse HC-MCC, but only reaches ~30% of solubility at 20C. Cold-gelation of HCMCC is thermally reversible and reducing protein levels in HC-MCC can decrease its CGT. The HC-MCC with less than 16% of protein does not gel at 5C. We propose that cold-gelation of HC-MCC occurs when the kinetic energy of the casein micelles is sufficiently reduced to inhibit their mobility in relation to adjacent casein micelles.

In Chapter 4, the recombined concentrated milk (RCM) by mixing thawed frozen HC-MCC and cream with 12% casein at pH 6.6 does not gel until cooled below 12°C. Addition of either sodium citrate or high levels of calcium increased CGT, although low levels of calcium did not impact CGT. Cold gelation of RCM was thermally reversible, even when citrate was added to partially chelate calcium. We propose that cold gelation of RCM occurs when protein strands that have been partially released from the casein micelles entangle, restrict their mobility and form a fine stranded gel network. The RCM at a casein level of 12% (wt/wt) has potential for use in cheese making.

In Chapter 5, reducing rennet level can increase coagulation time of RCM (11% casein) without impact on curd firmness or firming rate. Decreased coagulation temperature helps to increase coagulation time and decrease curd firmness rate, but also increases the initial viscosity of RCM. Pre-acidified RCM has no advantage in increasing coagulation time, decreasing curd firmness or firming rate. Microstructure of RCM and its coagulum indicates that the increased curd firmness probably results from the highly inter-linked and longer protein strands in RCM curd. Reducing rennet level can be applied to slow down rennet coagulation of RCM (11% casein) in cheese making.

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