Transmission of Major and Minor Serum Proteins during Microfiltration of Skim Milk: Effects of Pore Diameters, Concentration Factors and Processing Stages

Abstract

Effects of pore diameters (100, 50, and 20 nm), concentration factors (1–8) and processing stages (1–5) on the transmission of major serum proteins (β-lactoglobulin and α-lactalbumin) and minor serum proteins (immunoglobulin (Ig) G, IgA, IgM, lactoferrin (LF), lactoperoxidase (LPO), xanthine oxidase (XO)) during ceramic microfiltration (MF) of skim milk were studied. Holstein skim milk was microfiltered at a temperature of 50 °C, a transmembrane pressure of 110 kPa and a crossflow velocity of 6.7 m/s, using a tubular single stainless steel module that consisted of three ceramic tubes, each with 19 channels (3.5 mm inner diameter) and a length of 0.5 m. For MF with 100 nm and 50 nm pore diameters, the recovery yield of major serum proteins in permeate was 44.3% and 44.1%, while the recovery yield of minor serum proteins was slightly less by 0%–8% than 50 nm MF. MF with 20 nm pore diameters showed a markedly lower (by 12%–45%) recovery yield for both major and minor serum proteins, corresponding with its lower membrane flux. Flux sharply decreased with an increasing concentration factor (CF) up to four, and thereafter remained almost unchanged. Compared to the decrease (88%) of flux, the transmission of major and minor serum proteins was decreased by 4%–15% from CF = one to CF = eight. With increasing processing stages, the flux gradually increased, and the recovery yield of both major and minor proteins in the permeate gradually decreased and reached a considerably low value at stage five. After four stages of MF with 100 nm pore diameter and a CF of four for each stage, the cumulative recovery yield of major serum proteins, IgG, IgA, IgM, LF, LPO, and XO reached 95.7%, 90.8%, 68.5%, 34.1%, 15.3%, 39.1% and 81.2% respectively.

Transmembrane Pressure during Micro- and Diafiltration of Milk Affects the Release of Non-Sedimentable Caseins

“…This is typically due to the gradual formation of a deposit layer on the membrane, causing a higher resistance to permeation [8]. Additionally, the continuous increase in feed viscosity with increasing concentration lowered the permeate flow, as previously demonstrated [6,7]. In the concentration step, the development of the flux with processing time was identical in both independent trials, demonstrating the reproducibility of the process.…”

“…The permeate flux increases with TMP until it reaches a plateau, referred to as the limiting flux, where the formation of a deposit layer on the membrane with increasing TMP counteracts the permeation [4]. When the concentration factor of the feed increases, the limiting flux decreases and is reached at a lower TMP [5][6][7]. In addition, the composition of the permeate may change with TMP due to the formation of the deposit layer.…”

“…The deposit layer was moreover shown to be composed of both casein micelles and the whey protein β-lactoglobulin [12], meaning a further decrease in whey protein permeation due to attachment to the deposit layer. Diafiltration with water was shown to increase flux due to a reduction in feed viscosity via the removal of lactose, minerals, and proteins [6,7]. However, the diafiltration medium has an effect.…”

Effects of Drying Methods on Serum Protein Powder Properties

“…Fresh raw milk was purchased from Tianzi Dairy Co., Ltd. (Wuxi, Jiangsu, China). The fat, bacteria and somatic cells in the milk were removed using the same equipment and methods as described previously [ 4 ]. As shown in Figure 1 , the obtained milk was subjected to microfiltration to separate serum proteins and casein using a 100 nm ceramic membrane at 50 °C, and 110 kPa with four concentration factors and four filtration stages (three diafiltrations).…”

“…During this process, heating is the main factor that can affect these functional proteins due to the thermal denaturation of the structure of proteins. Presently, microfiltration of skim milk to remove bacteria and to separate whey and casein has been widely used to obtain native serum proteins [ 4 ], and they are an excellent source of serum protein powder.…”