RESUMO
Our objectives were to determine the level of milk-derived whey protein (MDWP) removal necessary to achieve no detectable sulfur/eggy flavor in ultrapasteurized fat-free micellar casein concentrate (MCC) beverages (6.5% protein) and in the same beverages containing 1 and 2% milk fat. Micellar casein concentrate with 95% MDWP removal was produced from skim milk (50°C) with a 3×, 3-stage ceramic microfiltration (MF) process using 0.1-µm pore size graded permeability membranes (n = 3). In experiment 1, MCC-based beverages at about 6.5% (wt/wt) true protein were formulated at a fat content of 0.15% fat (wt/wt) at 4 different levels of MDWP removal percentages (95.2%, 91.0%, 83.2%, and 69.3%). In experiment 2, a similar series of beverages at 3 MDWP removal percentages (95.2%, 83.2%, and 69.3%) with 0.1, 1, and 2% fat content were produced. The purity (or completeness of removal of whey protein by MF) of MCC was determined by the Kjeldahl method and sodium dodecyl sulfate (SDS)-PAGE. Sensory properties of beverages were documented by descriptive sensory analysis, and volatile sulfur compounds were evaluated using solid-phase microextraction followed by gas chromatography-triple quadrupole mass spectrometry. The purity of MCC measured by the Kjeldahl method (casein as a percentage of true protein) was higher after thermal treatment than before, whereas MCC purity evaluated by SDS-PAGE was unchanged by heat treatment. The purity of MCC had an effect on the flavor profile of thermally processed beverages at 6.5% protein made with fresh liquid MCC. No sulfur/eggy flavor was detected in MCC beverages when 95% of the MDWP was removed (MCC purity about 93 to 94%) from skim milk by microfiltration at 0.1, 1, and 2% fat. As the fat content of 6.5% protein beverages produced with MCC increased, sulfur/eggy flavor intensity and hydrogen sulfide concentration decreased. However, the effect of increasing milk fat on reducing sulfur/eggy flavor in MCC-based beverages at 6.5% protein was less than that of increasing MDWP removal from MCC. Sulfur off-flavors in neutral-pH dairy protein beverages can be mitigated by use of high-purity MCC or by incorporation of fat in the beverage, or both.