Depletion of Whey Proteins and Calcium by Microfiltration of Acidified Skim Milk Prior to Cheese Making

Abstract

Pasteurized skim milk was microfiltered (0.2-μm membrane) on a system equipped to provide uniform transmembrane pressure of 262 kPa (inlet:outlet pressure differential of 138 kPa, and crossflow velocity of 7.5 m/s). Retentates were gradually acidified to pH 6.6, 6.3, and 6.0 with glucono-delta-lactone during processing to promote solubilization of micelle-bound colloidal minerals into the serum phase of milk for subsequent transfer into permeate. Compositional characteristics of highly concentrated skim milk retentates (concentration factor 8 to 9) and composited permeates were determined to quantify retention and permeation of whey protein and Ca at specified pH conditions and to evaluate the suitability of retentate for cheese making. Final retentates contained an average 27.7% total solids, 20.2% total protein, 17.9% casein, 2.2% whey protein, 4.9% lactose, 2.3% ash, 0.62% Ca, and 0.4% fat. Dry basis retentate Ca and whey protein content significantly differed with pH level and contained 2.8, 2.4, and 1.9 weight percentage of Ca; and 7.2, 7.7, and 8.1 weight percentage of whey protein at pH levels of 6.6, 6.3, and 6.0, respectively. Microfiltration at pH 6.0, as compared with pH 6.6, reduced retentate Ca content by 20.1% but whey protein content was 12.6% higher. Retentate and butter oil were used to produce Mozzarella cheese with a normal Ca content and partial whey protein incorporation. Skim milk microfiltration, combined with in-process pH adjustment, is a useful method to produce highly concentrated retentate reduced in Ca and whey protein content with good potential for cheese manufacture.