The Effect of Emulsifying Salts on Casein Micelle Structure in Response to Varied Environmental Conditions

Open Access
- Author:
- Culler, Mitchell Dewitt
- Graduate Program:
- Food Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 22, 2018
- Committee Members:
- Federico Miguel Harte, Thesis Advisor/Co-Advisor
Robert F Roberts, Committee Member
Gregory Ray Ziegler, Committee Member
John Neil Coupland, Committee Member - Keywords:
- Casein
Casein Micelles
Temperature
pH
Dairy
Food Science
Milk
Cheese
Emulsifying Salts - Abstract:
- The Code of Federal Regulations (CFR) lists 13 emulsifying salts (ES) to be used in the production of pasteurized process cheese. Although these ES are widely used commercially, their method of action in a cheese system is not completely understood, as evidence has been found that the ES can interact with proteins, and their usage is therefore based on an empirical, trial-and-error approach. Further complicating the matter, current research in this area uses inconsistent methods to study the topic, making it difficult to draw conclusions from previous work. Additionally, the interactions between casein proteins in micelles have been shown to change in response to temperature or pH, thus affecting their interactions with ES. In this investigation, 10 of the ES listed in the CFR were investigated for their effects on casein micelle integrity by means of measuring the turbidity (absorbance at 400 nm) of milk-ES systems in order to determine the effect of an ES on a milk protein-based system and how this effect may change for a given ES under varied temperature and pH. In a first study, ES solutions consisted of a mixture of ES in a 1-in-20 dilution of protein free serum (PFS; permeate from 3 kDa molecular weight cut-off (MWCO) skim milk ultrafiltrate) in water to obtain ES concentrations from 0 to 248 mM. Pasteurized skim milk was added to solutions containing specific ES ranging in concentration from 0 to 248 mM and pH 5, 5.8, 6.8, 7.8, and 8.8. The turbidity of the samples was measured at 400 nm immediately after mixing (time, t = 0), after 30 s (t = 30s), and after 30 min (t = 30 min). The resulting decrease in turbidity was modeled using an exponential decay equation, with parameter C* representing a critical salt concentration used as a benchmark level of dissociation that can be used to compare between the effects of ES at varying conditions of pH and temperature. At pH values 5.8 and 6.8, the ES caused the greatest decrease in turbidity of the diluted milk system. At pH 5, the ES had the least effect on the turbidity of the system. SHMP was found to have the strongest dissociative effect, with C* equal to 0.33 mM for t=0 at pH 6.8. In contrast, the largest C* concentration calculated at pH 6.8 was monosodium phosphate at 278.22 mM. Increased time resulted in lower C* values. Next, an automated device was built consisting of three pumps, a continuous flow UV-VIS cell, light source, spectrometer, and a heat exchanger. The prototype automatically modified salt concentration (0 to 246 mM) and temperature (5 to 50°C) while recording the turbidity of a diluted skim-milk system. An aqueous solution with continuously variable salt concentration was achieved by making two solutions; both buffered using 5% PFS and one containing 250 mM of an ES. Their ratio was varied to comprise 96% of the total flow through an in-line UV-VIS flow cell. The remaining 4% of the flow was pasteurized skim milk. Temperature and pH were found to have highly specific effects on a given salt’s ability to cause dissociation. The C* concentrations for ST and SPT increased with pH, but did not change significantly in response to varied temperature in the 5 to 50°C range. By contrast, the C* concentration of SAD was approximately 15 times lower at pH 7.8 and 50°C than at pH 5.8 and 5°C. The results also suggest the formation of intermediate protein aggregates for several salts at temperature and pH of 50°C and 7.8, respectively.