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　　As many San Franciscans have noticed, sourdough bread stays fresher longer than the regular stuff. Sourdough’s extended freshness is due to extra fermentation that traps more moisture in the dough¹. But now we know that sourdough’s longevity² is also because it can ward³ off mold. Because bacteria in some sourdough starters(起动装置；开胃菜；发酵剂；酵母) actually produce mold-killing compounds - essentially⁴ natural preservatives⁵(防腐剂).

　　Most sourdough starters contain strains(气质；性情；种类) of Lactobacillus(乳酸菌) bacteria, like the poster child Lactobacillus sanfranciscensis. Eight years ago, researchers isolated⁶ another strain called Lactobacillus hammesii from a French sourdough starter.

　　They've now discovered that the strain pumps out a potent⁷ antifungal as it digests bread flour. So they baked bread with the L. hammesii starter, sliced it, and waited. The loaf resisted mold for 12 days, a few days more than L. sanfranciscensis sourdough, and twice as long as typical bread. Those results are in the journal Applied⁸ and Environmental Microbiology.

　　L. hammesii isn't the most common sourdough strain. But the researchers say it could eliminate the need for added preservatives, which would mean store-bought sourdough that's additive-free and lasts for weeks. Assuming you can wait that long to eat it.

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1 dough
n.生面团；钱，现款
参考例句：
She formed the dough into squares.她把生面团捏成四方块。 The baker is kneading dough.那位面包师在揉面。

2 longevity
n.长命；长寿
参考例句：
Good habits promote longevity.良好的习惯能增长寿命。 Human longevity runs in families.人类的长寿具有家族遗传性。

3 ward
n.守卫，监护，病房，行政区，由监护人或法院保护的人（尤指儿童）；vt.守护，躲开
参考例句：
The hospital has a medical ward and a surgical ward.这家医院有内科病房和外科病房。 During the evening picnic,I'll carry a torch to ward off the bugs.傍晚野餐时，我要点根火把，抵挡蚊虫。

4 essentially
adv.本质上，实质上，基本上
参考例句：
Really great men are essentially modest.真正的伟人大都很谦虚。 She is an essentially selfish person.她本质上是个自私自利的人。

5 preservatives
n.防腐剂( preservative的名词复数 )
参考例句：
The juice contains no artificial preservatives. 这种果汁不含人工防腐剂。 Meat spoils more quickly without preservatives. 不加防腐剂，肉会坏得快。来自《现代英汉综合大词典》

6 isolated
adj.与世隔绝的
参考例句：
His bad behaviour was just an isolated incident. 他的不良行为只是个别事件。 Patients with the disease should be isolated. 这种病的患者应予以隔离。

7 potent
adj.强有力的，有权势的；有效力的
参考例句：
The medicine had a potent effect on your disease.这药物对你的病疗效很大。 We must account of his potent influence.我们必须考虑他的强有力的影响。

8 applied
adj.应用的；v.应用，适用
参考例句：
She plans to take a course in applied linguistics.她打算学习应用语言学课程。 This cream is best applied to the face at night.这种乳霜最好晚上擦脸用。