2017新托福听力解析:超高压灭菌

　　Pasteurization makes food safe by heating microbes to death. But the high temperatures can destroy some nutrients too. A possible alternative? Ultrahigh pressure. Which may also actually increase concentrations of some nutrients, at least in tropical and subtropical fruit. That’s according to research presented at the national meeting of the American Chemical Society in Denver. [Carmen Hernandez-Brenes et al, High hydrostatic pressure processing as a strategy to increase carotenoid contents of tropical fruits]

　　In what’s called Pascalization, food is placed in a vessel, which is force-filled with water. The contents experience extreme pressures of 40,000 to 80,000 pounds per square inch. As a comparison, pressures three miles below the ocean surface are less than 7,000 pounds per square inch. The vessel’s pressure conditions kill bacteria, viruses and molds.

　　Researchers tried Pascalization on the pulp of avocados, papayas and mangos. They measured the levels of carotenoids, an important group of antioxidants. Carotenoids in the avocado and papaya increased overall by about 50 percent, with some individual carotenoids rising more than 500 percent. The mango mysteriously remained unchanged.

　　The researchers next hope to find out exactly how the high pressures are inducing the synthesis of more carotenoids. Pascalization may give food scientists plenty to chew over.

　　—Cynthia Graber

　　食物的巴氏灭菌法通过高温杀死微生物，但是高温同样能够使营养流失。那是否有替代方法呢?当然有，那就是超高压灭菌。实际上，用超高压灭菌还可以增加某些营养物质，至少对于一些热带和亚热带水果，超高压灭菌具有这样的效果。这一理论公布于在丹佛召开的美国化学学会年会上[Carmen Hernandez-Brenes et al, High hydrostatic pressure processing as a strategy to increase carotenoid contents of tropical fruits]。

　　利用超高压灭菌的方法称为Pascalization。这种方法把食物装入一个容器，然后把水压入，注满容器。这样，容器内的压力能够达到40000-80000磅/平方英尺。这一数字背后的压力有多大呢?来一个对比吧。在海面下3英里的深度，水压也不到7000磅/平方英尺。在这样的超高压环境下，细菌、病毒和霉菌都会被杀死。

　　研究人员利用Pascalization对鳄梨、番木瓜和芒果的果肉进行了灭菌。随后，研究人员测定了果肉内一类抗氧化物——类胡萝卜素的含量。结果鳄梨和番木瓜的类胡萝卜素总量增加了大约50%，个别种类的类胡萝卜素增加量能达到500%。而芒果的类胡萝卜素则保持稳定。

　　研究人员下一步将尝试解释为什么超高压能够增加类胡萝卜素的合成。也许，Pascalization方法不仅能够提高食物的风味，也能吊起科学家的胃口。

　　—C