Eastern Regional Research Center, Dairy & Functional Foods Research Unit, USDA, Agricultural Research Service (ARS), Wyndmoor, PA 19038.
Eastern Regional Research Center, Dairy & Functional Foods Research Unit, USDA, Agricultural Research Service (ARS), Wyndmoor, PA 19038.
J Dairy Sci. 2018 Aug;101(8):6990-7001. doi: 10.3168/jds.2017-13907. Epub 2018 May 16.
This work examines the use of mild heat treatments in conjunction with 2-pass microfluidization to generate cheese milk for potential use in soft cheeses, such as Queso Fresco. Raw, thermized, and high temperature, short time pasteurized milk samples, standardized to the 3% (wt/wt) fat content used in cheesemaking, were processed at 4 inlet temperature and pressure conditions: 42°C/75 MPa, 42°C/125 MPa, 54°C/125 MPa, and 54°C/170 MPa. Processing-induced changes in the physical, chemical, and microbial properties resulting from the intense pressure, shear, and cavitation that milk experiences as it is microfluidized were compared with nonmicrofluidized 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 4 inlet temperature and processing pressure conditions resulted in a stable emulsion of fat droplets ranging from 0.390 to 0.501 μm, compared with 7.921 (control) and 4.127 (homogenized control) μm. Confocal imaging showed coalescence of scattered fat agglomerates 1 to 3 μm in size during the first 24 h. We found no changes in fat, lactose, ash content or pH, indicating the major components of milk remained unaffected by microfluidization. However, the apparent 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 that microfluidization may eliminate bacteria. The viscosities of milk samples were similar but tended to be higher after treatment at 54°C and 125 or 170 MPa. These samples exhibited the longest coagulation 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 (42°C/75 MPa) exhibited similar coagulation properties to controls. The results suggest that microfluidization at lower pressures may be used to manufacture high-moisture cheese with altered texture whereas higher pressures may result in novel dairy ingredients.
这项工作研究了在 2 次微射流处理过程中使用温和的热处理来生成奶酪乳，以潜在地用于制作软奶酪，如菲达奶酪。将标准化至用于奶酪制作的 3%（wt/wt）脂肪含量的生乳、热杀菌乳和高温短时间巴氏杀菌乳样品在 4 个入口温度和压力条件下进行处理：42°C/75 MPa、42°C/125 MPa、54°C/125 MPa 和 54°C/170 MPa。与非微射流对照相比，比较了由于强烈的压力、剪切和空化作用而导致的在微射流处理过程中乳经历的物理、化学和微生物性质的变化。观察到所有微射流样品的出口温度随压力呈依赖性增加，在 125 和 170 MPa 时生乳和热杀菌乳中的碱性磷酸酶失活。在 4 个入口温度和处理压力条件下，所有样品的微射流处理导致脂肪液滴的稳定乳液，范围从 0.390 至 0.501 μm，而对照为 7.921 μm（对照）和 4.127 μm（均质化对照）。共焦成像显示，在最初的 24 小时内，大小为 1 至 3 μm 的分散脂肪聚集体发生聚结。我们发现脂肪、乳糖、灰分含量或 pH 值没有变化，表明乳的主要成分不受微射流处理的影响。然而，表观蛋白质含量从 3.1%降低至 2.2%，可能是由于近红外光谱错误地识别嵌入脂肪液滴中的胶束片段。微生物学结果表明，随着温度和压力的升高，嗜温需氧菌和嗜冷乳微生物群减少，这表明微射流可能会消除细菌。随着处理温度在 54°C 和 125 或 170 MPa 下升高，牛奶样品的粘度相似但趋于升高。这些样品表现出最长的凝固时间和最弱的凝胶硬度，表明在奶酪生产中的关键步骤，即酪蛋白基质的形成受到了影响。低温和低压力（42°C/75 MPa）表现出与对照相似的凝固特性。结果表明，在较低压力下的微射流处理可能用于制造具有改变的质地的高水分奶酪，而较高的压力可能导致新型乳制品成分。
