一般认为,在排除营养不良的前提下,吃素(植物性食物)比吃荤(动物性食物)使人更健康。以往对吃素有益的解释是:植物的根茎叶富含纤维,植物纤维可被肠道微生物降解成丁酸等短链脂肪酸,从而产生抗炎效应。 然而,对于非纤维类淀粉食物,其健康效应(如抗癌作用)并未得到合理解释。8月4日出版的《癌症预防研究》(CPR)杂志发表了一篇最新论文,对此作出了全新的解释。 研究证明,抗性淀粉(不是精米做的大米饭或精面做的面包)可以抑制一种促结直肠癌小干扰RNA(miRNA)——miR-17-92的合成。相反,红肉(不包括鸡鱼肉)则具有完全相反的作用,即促进 miR-17-92 合成。 抗性淀粉存在于半生不熟的香蕉、煮熟后凉拌的土豆(土豆沙拉)、粗粮、豆类中,因此多吃这类食物可以预防结直肠癌。同时,应尽量少吃或不吃牛羊肉。不过,吃完红肉再补充抗性淀粉,可抵消前者产生的有害效应。 参试者为23位年龄从50岁到75岁的健康志愿者(17男6女),实验以4周为一个周期。每天吃300克瘦肉者,其结直肠组织中的 miR-17-92含量提高30%,而每天 吃 300克 瘦肉 后再 吃40克抗性淀粉 者, miR-17-92的含量则保持基础水平。 附:抗性淀粉(360百科) 很早以前,耦合淀粉就被当作 食品添加剂 使用,尤其使用在需要高度稳定粘度的食品中,因为这种淀粉有着使用量少并且安全性高的特点。而且,这种淀粉也可被当作医学成分使用,比如填充物,包扎物,分解质和增稠物质。目前研究发现,这种特殊的消化特点被大量使用于控制 药物载体 的稀释上面。在许多领域中这种淀粉消化特点是很重要的,但是淀粉在生物体外的因退化而改变的数据却很少出现在文献中。众所周知, 碳水化合物 又称多糖,人们食用碳水化合物后要在体内被 胃酸 及酶消化分解为单糖—— 葡萄糖 以后才能吸收并进入血液,抗性淀粉由于消化吸收慢,食用后不致使血糖升高过快,也就是可以调节 血糖 水平,因此成为一种功能性淀粉,特别适宜糖尿病患者食用,食用抗性淀粉后不容易饥饿,有助于糖尿病人维持正常的血糖,减少饥饿感(特别是午夜)。抗性淀粉存在于某些 天然食品 中,如 马铃薯 、 香蕉 、 大米 等都含有抗性淀粉,特别是高 直链淀粉 的 玉米淀粉 (high amylose corn starch)含抗性淀粉高达60%。抗性淀粉也可通过某些 加工方法 提高其含量,如将原淀粉加热使其糊化并迅速冷却,则此糊液产生老化,或将淀粉制品在冰箱内贮存,都可增加抗性淀粉含量;还可添加脂肪使淀粉变性以增加抗性淀粉含量,因脂肪可使淀粉分子内部的 螺旋结构 凝固而趋于稳定,可抵抗 酶 的侵蚀。 抗性淀粉可抵 抗酶 的分解,在体内释放 葡萄糖 缓慢,具有较低的 胰岛素 反应,可控制 血糖 平衡,减少饥饿感,特别适宜糖尿病患者食用;抗性淀粉具有可溶性 食用纤维 的功能,食后可增加排便量,减少便秘,减少结肠癌的危险;抗性淀粉可减少血 胆固醇 和三甘油脂的量,因食用抗性淀粉后排泄物中胆固醇和三甘油脂的量增加,因而具有一定的减肥作用;抗性淀粉可以增值,据资料介绍,玉米原淀粉20美分/磅,制成功能性抗性淀粉作为食物配分,价格可提高至2.5美元/磅,价值增加10倍。 Eating resistant starch may help reduce red meat-related colorectal cancer risk Date: August 4, 2014 Source: American Association for Cancer Research Summary: Consumption of a type of starch that acts like fiber may help reduce colorectal cancer risk associated with a high red meat diet, according to a study. Red meat and resistant starch have opposite effects on the colorectal cancer-promoting miRNAs, the miR-17-92 cluster, said one researcher. This finding supports consumption of resistant starch as a means of reducing the risk associated with a high red meat diet. Consumption of a type of starch that acts like fiber may help reduce colorectal cancer risk associated with a high red meat diet, according to a study published in Cancer Prevention Research , a journal of the American Association for Cancer Research. Red meat and resistant starch have opposite effects on the colorectal cancer-promoting miRNAs, the miR-17-92 cluster, said Karen J. Humphreys, PhD, a research associate at the Flinders Center for Innovation in Cancer at Flinders University in Adelaide, Australia. This finding supports consumption of resistant starch as a means of reducing the risk associated with a high red meat diet. Total meat consumption in the USA, European Union, and the developed world has continued to increase from the 1960s, and in some cases has nearly doubled, added Humphreys. Unlike most starches, resistant starch escapes digestion in the stomach and small intestine, and passes through to the colon (large bowel) where it has similar properties to fiber, Humphreys explained. Resistant starch is readily fermented by gut microbes to produce beneficial molecules called short-chain fatty acids, such as butyrate, she added. Good examples of natural sources of resistant starch include bananas that are still slightly green, cooked and cooled potatoes , whole grains, beans, chickpeas, and lentils. Scientists have also been working to modify grains such as maize so they contain higher levels of resistant starch, said Humphreys. After eating 300 g of lean red meat per day for four weeks, study participants had a 30 percent increase in the levels of certain genetic molecules called miR-17-92 in their rectal tissue, and an associated increase in cell proliferation. Consuming 40 g of butyrated resistant starch per day along with red meat for four weeks brought miR-17-92 levels down to baseline levels. The study involved 23 healthy volunteers, 17 male and six female, ages 50 to 75. Participants either ate the red meat diet or the red meat plus butyrated resistant starch diet for four weeks, and after a four-week washout period switched to the other diet for another four weeks. Story Source: The above story is based on materials provided by American Association for Cancer Research . Note: Materials may be edited for content and length. Journal Reference : K. J. Humphreys, M. A. Conlon, G. P. Young, D. L. Topping, Y. Hu, J. M. Winter, A. R. Bird, L. Cobiac, N. A. Kennedy, M. Z. Michael, R. K. Le Leu. Dietary Manipulation of Oncogenic MicroRNA Expression in Human Rectal Mucosa: A Randomized Trial . Cancer Prevention Research , 2014; 7 (8): 786 DOI: 10.1158/1940-6207.CAPR-14-0053
学过生物化学的人都知道,草木(如秸秆)的化学组成是纤维素,粮食(如大米)的化学组成是淀粉。纤维素与淀粉在结构上类似,都是D-葡萄糖的聚合体,只不过纤维素含β-糖苷键,而淀粉含α-糖苷键,但两者的用途却有天壤之别:富含纤维素的青草只能作饲料喂养牲畜,而人可以把以淀粉为主要成分的大米、麦子、红薯当饭吃! 据估计,到2050年,世界人口将达到90亿!如何解决全球人口的吃饭问题是一项巨大挑战。假如有谁能将草木“变成”粮食,那么人类从此就不会挨饿了!这在过去也许是一个遥不可及的梦想,可是现在真的有人能够做到了。美国佛吉尼亚理工学院的华裔学者Zhang Y-H团队在《美国科学院院刊》上在线发表论文,报道了他们成功地将纤维素转化成淀粉的最新研究结果。 从纤维素到淀粉的转化是由来自细菌、真菌和植物的4种酶共同催化完成的,它们是内切葡聚糖酶(endoglucanase)、纤维二糖水解酶(cellobiohydrolyase)、纤维二糖磷酸化酶(cellobiose phosphorylase)、α-葡聚糖磷酸化酶(alpha-glucan phosphorylase)。由玉米秸秆中的纤维素转化为淀粉的产率达到30%,其余的纤维素则被水解为游离的葡萄糖。 有趣的是,由此获得的直链淀粉对淀粉酶的水解作用有抗性,也就是在消化过程中并不会完全水解成葡萄糖。因此,它既能像淀粉那样让人充饥,又类似纤维素有清肠功效,有助于大幅度降低肥胖及糖尿病的发病率。 上述生产过程易于实现规模化和产业化,而且节能环保,造价低廉,既不需要购置昂贵的设备,也不需要加热和添加化学试剂,用纳米磁珠结合的固定化酶可以反复使用。由此获得的直链淀粉不仅可以用来生产食品(可提供20%-40%热量),还可以制造生物降解性食品包装材料,并能作为氢能的贮存库。 原文链接: C. You, H. Chen, S. Myung, N. Sathitsuksanoh, H. Ma, X.-Z. Zhang, J. Li, Y.- H. P. Zhang. Enzymatic transformation of nonfood biomass to starch . Proceedings of the National Academy of Sciences , 2013; DOI: 10.1073/pnas.1302420110
Development of an Efficient Agrobacterium-mediated Gene Targeting System for Ric.pdf 该文章报道了利用悬浮培养的愈伤进行高效的水稻淀粉合成酶基因的敲除方法,很有借鉴意义。 fficient gene targeting system for rice