Short communication: Effects of nanofiltration and evaporation on the physiochemical properties of milk protein during processing of milk protein concentrate

Abstract

The aim of this work was to evaluate the effects of nanofiltration and evaporation concentration technologies on the physiochemical properties of milk protein concentrate (MPC) during processing. Skim milk, ultrafiltered milk, evaporated milk, nanofiltered milk, evaporated MPC, and nanofiltered MPC samples were collected at different processing stages. Chemical composition, microstructure of casein micelles, free sulfhydryl content, and surface hydrophobicity of the samples were determined. The insolubility index of MPC was also determined. Casein micelles aggregated compactly after evaporation while surface hydrophobicity increased and free sulfhydryl content decreased in evaporated milk compared with skim milk. However, the microstructure of the casein micelles was relatively undisturbed after nanofiltration, with reduced surface hydrophobicity and free sulfhydryl content. No significant difference was found in chemical composition between the 2 MPC preparations: approximately 61.40% protein and 28.49% lactose. In addition, the particulate microstructures of both MPC were similar. However, the insolubility index of evaporated MPC was significantly (0.58mL) higher than that of nanofiltered MPC. Nanofiltration may be an effective way to improve the solubility of MPC products.

Comparison of nanofiltration and evaporation technologies on the storage stability of milk protein concentrates

“…The effects of evaporation and nanofiltration on the components of milk, especially milk proteins, were significantly different. The cumulative alteration of physiochemical properties of milk protein may be the main cause of this differential solubility (Cao et al 2015). The results of insolubility index in the present study showed that solubility of MPC reduced with the increase in storage time and temperature, which are in accordance with previous studies.…”

“…Casein micelles compactly aggregated after evaporation with higher surface hydrophobicity. But, after nanofiltration, casein micelle aggregation was not as severe as that after evaporation (Cao et al 2015). This indicated milk protein processed by evaporation was less stable compared with that processed by nanofiltration, which may contribute to less protein-protein interaction or cross-linking caused by Maillard reaction resulting in better dissolution ratios of micelle constituents and solubility of NF-MPC even after storage at 45°C.…”

“…Since nanofiltration allows lower temperatures, the milk proteins would be exposed to lower heat treatment, leading to less denaturation and enhanced solubility. Our previous study (Cao et al 2015) adopted nanofiltration technology instead of traditional evaporation to produce MPC, and the results indicate nanofiltration to be an effective technology to improve the solubility of MPC.…”

Effect of gelling temperature and calcium chloride concentration on rheological and microstructural properties of acid‐induced gels of milk protein concentrates

“…Evaporation is the traditional process of concentrating MPC, however, the downside of this process is that it could cause an undesired denaturation of milk proteins due to the high temperatures that are required. In order to minimize this adverse effect, MPC has more recently been produced using an alternative process called nanofiltration, which ensures less denaturation and enhanced solubility of proteins (Cao, Wang, et al, ; Cao, Zhang, et al, ). Nanofiltration is an innovative membrane separation technique that is now commonly applied to milk concentrations in the dairy industry.…”

“…A pressure‐driven membrane technology, the process is intermediate between ultrafiltration and reverse osmosis, and is known to be highly efficient in retarding organic compounds with a high molecular weight, such as lactose or protein (Pan, Song, Wang, & Cao, ). Recent reports have noted that nanofiltration improves the solubility and even the storage stability of MPC products (Cao et al, ; Cao, Zhang, et al, ), because compared with skim milk, casein micelles aggregated compactly after evaporation, while surface hydrophobicity increased and free sulfhydryl content decreased in evaporated milk. However, the microstructure of the casein micelles was relatively undisturbed after nanofiltration, with surface hydrophobicity and free sulfhydryl content reduced.…”