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科学家们研发出新低热量米饭 可以降低肥胖率

张微

2015年03月25日08:15    来源:中国科技网    手机看新闻
原标题:科学家们研发出新低热量米饭 可以降低肥胖率

  中国科技网3月23日报道(张微 编译)用一种全新的、简单的方法做米饭可以减少高达60%的卡路里。

  科学家们研发出一种全新的、简单的煮米饭的方法,可以将人体吸收的热量减少一半以上,从而降低肥胖率,这对于以大米为主食的国家特别重要。

  超重或肥胖的人群数量正在稳步上升。随着生活方式的改变以及伏案工作的增加,他们的饮食也发生了变化。食物种类增多,有更多的食物可供选择。除了消耗更多的脂肪和糖,人们还可以选择食用淀粉类碳水化合物,如大米,每杯含有的热量是240卡路里。

  “由于肥胖是一个日益严重的健康问题,特别是在许多发展中国家,所以我们想要找到以食物为基础的解决方案,”斯里兰卡化学科学学院的项目研究团队主任Sudhair A. James说。“我们发现增加水稻中抗性淀粉(RS)的浓度是一个解决问题的新途径。”通过特殊的加热和烹饪方法,科学家们得出的结论是“如果将最好的水稻品种进行处理,那么能够减少大约50%-60%的卡路里。”

  他解释说淀粉既有可消化的也有不可消化的。淀粉是大米的一个组成部分,两种类型的淀粉在大米中都存在。不同于可消化类型的淀粉,RS不能在小肠中分解,在小肠内碳水化合物代谢成葡萄糖和其它单糖并被血液吸收。因此,研究人员认为如果他们能够将可消化的淀粉转化为RS,那么就可以降低大米中热量。

  大米中富含淀粉(每杯中1.6盎司),Sudhair A. James说。“碳水化合物在你的体内转化成葡萄糖之后,剩余的热量转变成一种多糖的碳水化合物被称为糖原,”他解释道。“你的肝脏和肌肉中储存糖原用作热量,然后快速地将它们转化回人体所需的葡萄糖。问题是,过多的葡萄糖没能全部转化成糖原,最终就转变为脂肪,从而导致体重超标或肥胖。”

  研究团队利用来自斯里兰卡的38种大米做了实验,研发了一种新的烹饪米饭的方法,增加RS的成分。在该方法中,他们在沸水中加了一茶匙椰子油。然后加入半杯大米,他们煮了40分钟,但研究人员发现其中一种大米可以煮20-25分钟。最后,他们将米饭冷冻了12个小时。这个方法比传统煮饭方法,将RS含量提高了10倍,非强化大米。

  为什么用这个简单的烹饪方法就能降低食物中的热量?Sudhair A. James解释说,在烹饪过程中油进入到淀粉颗粒中,改变了它的结构,使其具有抗消化酶的作用。这意味着人体吸收的热量会降低。“冷却这个步骤很重要,因为直链淀粉——淀粉中水溶性的部分,在糊化过程中会留下淀粉颗粒,” Sudhair A. James解释说。“冷却12小时就导致米粒外层直链淀粉分子间氢键的形成,这也能转化成抗性淀粉。” Sudhair A. James指出,重新加热大米再食用,不会影响RS的含量。

  Sudhair A. James指出下一步将继续研究哪一种水稻品种最适合降低卡路里的烹饪过程。研究团队还将研究除了椰子油之外,还有哪些油也具有这种效果。

  New low-calorie rice could help cut rising obesity rates

  Scientists have developed a new, simple way to cook rice that could cut the number of calories absorbed by the body by more than half, potentially reducing obesity rates, which is especially important in countries where the food is a staple.

  The number of people who are overweight or obese is steadily increasing. As lifestyles change and people become more sedentary, their diets also change. Serving sizes grow, and more food options become available. In addition to consuming more fats and sugars, people may choose to fill up on starchy carbohydrates like rice, which has about 240 calories per cup.

  "Because obesity is a growing health problem, especially in many developing countries, we wanted to find food-based solutions," says team leader Sudhair A. James, who is at the College of Chemical Sciences, Colombo, Western, Sri Lanka. "We discovered that increasing rice resistant starch (RS) concentrations was a novel way to approach the problem." By using a specific heating and cooking regimen, he says, the scientists concluded that "if the best rice variety is processed, it might reduce the calories by about 50-60 percent."

  He explains that starch can be digestible or indigestible. Starch is a component of rice, and it has both types. Unlike digestible types of starch, RS is not broken down in the small intestine, where carbohydrates normally are metabolized into glucose and other simple sugars and absorbed into the bloodstream. Thus, the researchers reasoned that if they could transform digestible starch into RS, then that could lower the number of usable calories of the rice.

  And rice is loaded with starch (1.6 ounces in a cup), says James. "After your body converts carbohydrates into glucose, any leftover fuel gets converted into a polysaccharide carbohydrate called glycogen," he explains. "Your liver and muscles store glycogen for energy and quickly turn it back into glucose as needed. The issue is that the excess glucose that doesn't get converted to glycogen ends up turning into fat, which can lead to excessive weight or obesity."

  The team experimented with 38 kinds of rice from Sri Lanka, developing a new way of cooking rice that increased the RS content. In this method, they added a teaspoon of coconut oil to boiling water. Then, they added a half a cup of rice. They simmered this for 40 minutes, but one could boil it for 20-25 minutes instead, the researchers note. Then, they refrigerated it for 12 hours. This procedure increased the RS by 10 times for traditional, non-fortified rice.

  How can such a simple change in cooking result in a lower-calorie food? James explains that the oil enters the starch granules during cooking, changing its architecture so that it becomes resistant to the action of digestive enzymes. This means that fewer calories ultimately get absorbed into the body. "The cooling is essential because amylose, the soluble part of the starch, leaves the granules during gelatinization," explains James. "Cooling for 12 hours will lead to formation of hydrogen bonds between the amylose molecules outside the rice grains which also turns it into a resistant starch." Reheating the rice for consumption, he notes, does not affect the RS levels.

  He says that the next step will be to complete studies with human subjects to learn which varieties of rice might be best suited to the calorie-reduction process. The team also will check out whether other oils besides coconut have this effect.

(责编:赵竹青、马丽)


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