The effects of microfluidization on the physical, microbial, chemical, and coagulation properties of milk

Authors: Bucci, Anthony; Van Hekken, Diane; Tunick, Michael; Renye, John; Tomasula, Peggy

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2018
Publication Date: 8/1/2018
Citation: Bucci, A.J., Van Hekken, D.L., Tunick, M.H., Renye Jr, J.A., Tomasula, P.M. 2018. The effects of microfluidization on the physical, microbial, chemical, and coagulation properties of milk. Journal of Dairy Science. 101:1-12.

Interpretive Summary: Fresh style, high moisture cheeses such as Cottage Cheese and Queso Fresco have particulate textures and are prone to spoilage by the natural bacteria in milk. ARS researchers are investigating the use of microfluidization, which pressurizes milk at higher pressures than the homogenizers now used by the dairy industry, to distribute milk components in ways that further highlight the texture of these cheeses, and at the same time reduce spoilage. In this first study, the major components of milk remain unchanged with microfluidization, spoilage bacteria were significantly reduced, and cheese making properties were altered. These results demonstrate the potential of this technology to generate new cheese products, meeting the evolving needs of dairy consumers.

Technical Abstract: This work examines the use of mild heat treatments in conjunction with multiple pass microfluidization to generate unique cheesemilk for potential use in soft cheeses such as Queso Fresco and Cottage Cheese. Raw, thermized, and high temperature, short time pasteurized milk samples, standardized to the 3% (w/w) fat content used in cheesemaking, were processed at four inlet temperature and pressure conditions: 42C/75 MPa, 42C/125 MPa, 54C/125 MPa, and 54C/170 MPa. Processing-induced changes in the chemical, microbial, and physical properties resulting from the intense pressure, shear, and cavitation milk experiences as it is microfluidized were compared to the non-microfluidized controls. A pressure-dependent increase in exit temperature was observed for all microfluidized samples, with inactivation of alkaline phosphatase in raw and thermized samples at 125 and 170 MPa. Microfluidization of all samples under the four inlet temperature and processing pressure conditions resulted in a stable emulsion of sub-micron sized fat droplets ranging from 0.108 to 0.134 microns, compared to 3.9 (control) and 2.5 (homogenized control) microns. Additionally, it ruptured the milk fat globular membrane and fractionated casein micelles, forcibly dispersing hydrophobic and hydrophilic components throughout the liquid phase, producing an unfavorable thermodynamic state. Therefore, confocal imaging showed scattered agglomerates one to three microns in size as stable micelles reformed during storage. There were no changes in fat, lactose, ash content, or pH indicating the major components of milk remained unaffected by microfluidization. However, the protein content was reduced from 3.1 to 2.2%, likely a result of near infrared spectroscopy improperly identifying the micellar fragments embedded into the fat droplets. Microbiology results indicated a decrease in mesophilic aerobic and psychrophilic milk microflora with increasing temperature and pressure, suggesting microfluidization may be used to eliminate bacteria. The viscosities of milk samples were similar but tended to be higher after treatment at 54C and 125 or 170 MPa. These samples exhibited the longest renneting times and the weakest gel firmness, indicating that formation of the casein matrix, a critical step in the production of cheese, was affected. Low temperature and pressure (42C/75MPa) exhibited similar renneting properties to controls. Based on these results, 42C/125MPa and 54C/125MPa were selected for future cheese making studies.