Van Hekken D L, Tunick M H, Farkye N Y, Tomasula P M
Dairy and Functional Foods Research Unit, Eastern Regional Research Center, Agricultural Research Service, United States Department of Agriculture, Wyndmoor, PA 19038.
J Dairy Sci. 2013 Oct;96(10):6147-60. doi: 10.3168/jds.2012-6212. Epub 2013 Aug 21.
Queso Fresco (QF), a popular high-moisture, high-pH Hispanic-style cheese sold in the United States, underwent high-pressure processing (HPP), which has the potential to improve the safety of cheese, to determine the effects of this process on quality traits of the cheese. Starter-free, rennet-set QF (manufactured from pasteurized, homogenized milk, milled before hooping, and not pressed) was cut into 4.5- × 4.5- × 15-cm blocks and double vacuum packaged. Phase 1 of the research examined the effects of hydrostatic HPP on the quality traits of fresh QF that had been warmed to a core temperature of 20 or 40 °C; processed at 200, 400, or 600 MPa for 5, 10, or 20 min; and stored at 4 °C for 6 to 8d. Phase 2 examined the long-term effects of HPP on quality traits when QF was treated at 600 MPa for 3 or 10 min, and stored at 4 or 10 °C for up to 12 wk. Warming the QF to 40 °C before packaging and exposure to high pressure resulted in loss of free whey from the cheese into the package, lower moisture content, and harder cheese. In phase 2, the control QF, regardless of aging temperature, was significantly softer than HPP cheeses over the 12 wk of storage. Hardness, fracture stress, and fracture rigidity increased with length of exposure time and storage temperature, with minor changes in the other properties. Queso Fresco remained a bright white, weak-bodied cheese that crumbled and did not melt upon heating. Although high pressures or long processing times may be required for the elimination of pathogens, cheese producers must be aware that HPP altered the rheological properties of QF and caused wheying-off in cheeses not pressed before packaging.
新鲜奶酪（QF）是一种在美国销售的广受欢迎的高水分、高pH值的西班牙风味奶酪，经过高压处理（HPP），这种处理有可能提高奶酪的安全性，以确定该过程对奶酪品质特性的影响。无发酵剂、凝乳酶凝固的QF（由巴氏杀菌、均质化牛奶制成，装模前研磨，不压制）被切成4.5×4.5×15厘米的块状并进行双真空包装。研究的第一阶段考察了静水高压处理对预热至核心温度20或40℃的新鲜QF品质特性的影响；在200、400或600兆帕下处理5、10或20分钟；并在4℃下储存6至8天。第二阶段考察了QF在600兆帕下处理3或10分钟，并在4或10℃下储存长达12周时高压处理对品质特性的长期影响。在包装和高压处理前将QF预热至40℃导致奶酪中的游离乳清流失到包装中，水分含量降低，奶酪变硬。在第二阶段，无论老化温度如何，对照QF在储存的12周内明显比高压处理的奶酪软。硬度、断裂应力和断裂刚度随暴露时间和储存温度的延长而增加，其他特性变化较小。新鲜奶酪仍然是一种亮白色、质地柔软的奶酪，加热时会碎而不会融化。虽然消除病原体可能需要高压或较长的处理时间，但奶酪生产商必须意识到，高压处理改变了QF的流变特性，并导致未在包装前压制的奶酪出现乳清分离现象。
