The effect of emulsifying salts on the turbidity of a diluted milk system with varying pH and protein concentration

Abstract

Solutions of 10 commonly used emulsifying salts (ES) listed in the Code of Federal Regulations (21CFR133.179) for pasteurized process cheese were tested for their effect on the turbidity of a diluted milk system at different pH and protein concentrations to characterize the conditions that affect micellar structure. Emulsifying salt solutions were made by mixing the ES in a 1-in-20 dilution of water in skim milk ultrafiltrate (3 kDa molecular weight cut-off) to obtain ES concentrations from 0 to 248 mM. Skim milk was added to solutions containing nanopure water, skim milk ultrafiltrate, and a 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 as the optical density at 400 nm immediately after mixing (time, t = 0), after 30 s (t = 30s), and after 30 min (t = 30min). Emulsifying salts were found to cause a decrease in the turbidity of the system, which was modeled using an exponential decay model, where C* represents a threshold salt concentration at which rapid dissociation occurs. 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. Sodium hexametaphosphate was found to have the strongest dissociative effect, with a C* value of 0.33 mM for t = 0 at pH 6.8. In contrast, the largest C* value calculated at pH 6.8 was monosodium phosphate at 278.22 mM. Increased time resulted in lower C* values. The model established for this study can be used to predict the dissociation of casein micelles in the presence of various types of ES.

Critical phosphate salt concentrations leading to altered micellar casein structures and functional intermediates

“…For a given phosphate salt, turbidity (absorbance) values recorded at different salt concentrations were modeled with an exponential decay function (Culler et al, 2017):…”

“…Three types of emulsifying salts are used in processed cheese, namely, phosphate, citrate, and tartrate salts. Recently, we reported 4 trends that can be observed in the turbidity of diluted milk with increasing concentrations of these salts, which are (1) no appreciable decrease in turbidity, (2) continuous decrease in turbidity, (3) turbidity decreases and reaches a constant phase, and (4) turbidity decreases, but then increases at higher salt concentrations (Culler et al, 2017). Among these salts, phosphates are commonly used and can be categorized into 2 sub-groups: monomeric phosphates, also called orthophosphates (single phosphate group) and polymeric phosphates, or polyphosphates (multiple phosphate groups; Lucey et al, 2011).…”

Effects of direct current magnetic field treatment time on the properties of pork myofibrillar protein

“…The turbidity was measured as reported by Culler et al . (2017) with slight modification. The DC‐MF‐treated MP (5 mg mL −1 ) was diluted to 1 mg mL −1 with buffer#4, followed by measuring the absorbance at 600 nm with a spectrophotometer (TU‐1900, Beijing General Analysis Instrument Co., Ltd., Beijing, China).…”

Physicochemical properties of skim milk powder dispersions prepared with calcium-chelating sodium tripolyphosphate, trisodium citrate, and sodium hexametaphosphate

“…Casein micelles are dissociated into small clusters, and specific caseins are released by mechanisms of chelators that govern protein-mineral equilibria, resulting in the reduced amount of diffusible calcium and depletion of CCP (de Kort et al, 2011). Therefore, the reduced turbidity of dispersions with casein micelles after addition of calcium-chelating agents has been reported frequently (Mizuno and Lucey, 2005;Pitkowski et al, 2008;Culler et al, 2017). The extent of turbidity reduction of casein micelle dispersions depends on the type and concentration of chelators with the decreasing chelating ability of polyphosphate > citrate > orthophosphate (Van Wazer and Callis, 1958).…”

“…The extent of turbidity reduction of casein micelle dispersions depends on the type and concentration of chelators with the decreasing chelating ability of polyphosphate > citrate > orthophosphate (Van Wazer and Callis, 1958). For example, milk after adding 1 mM sodium hexametaphosphate (SHMP) and 100 mM sodium tartrate at pH 7.8 had comparable turbidity after 30 min of equilibrium (Culler et al, 2017). The type of calcium chelators added also affects heat stability of casein micelle dispersions; better stability was reported for dispersions with added disodium uridine monophosphate than for those with added trisodium citrate (TSC) or SHMP after sterilization at 126°C, although the former is a weaker calcium chelator (de Kort et al, 2012).…”