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楼主 / 無極
- 时间: 2011-12-05 19:50养生界一直有种说法,夏季隔夜菜,特别是隔夜蔬菜不能吃,说隔夜菜中有大量细菌,而且亚硝酸盐含量很高。
真是这样的吗?如果超标,到底有多严重?红烧肉、红烧鱼呢,是不是也超标?
近日,记者就此问题,专门赴浙江大学生物系统工程与食品科学学院食品科学与营养系实验室,测了测隔夜菜亚硝酸盐的含量。之所以只测亚硝酸盐含量,是因为隔夜菜中的细菌可以用加热的方式杀死,而亚硝酸盐却是加热去不掉的。
炒四个菜看问题有多大
为了测测隔夜菜亚硝酸盐的含量,实验人员请杭州一家知名中高档连锁餐厅的厨师烧了4个菜:炒青菜、韭菜炒蛋、红烧肉和红烧鲫鱼。
餐厅厨师长石瑞得知我们是用来做亚硝酸盐实验的,特地选用了最新鲜的食材。4个菜烧好后,石厨师长亲自打包,分别装进4个保鲜盒。
石厨师长说,剩菜时间放久了,营养成分会流失,还容易滋生细菌。肠胃不好的人吃了很容易拉肚子,这种情况平时碰到很多,所以他们一般会建议顾客,打包的菜要在2个小时内吃完。不过对于剩菜放久了亚硝酸盐是否会超标,石厨师长说,倒还真不清楚。
肉类亚硝酸盐比蔬菜高
为了让大家对剩菜中亚硝酸盐含量变化有个更客观的了解,实验人员特地将4个菜分成了4份,分别装入一次性降解餐盒,包上保鲜膜后,分别贴上半小时、6小时、18小时、24小时的标签。然后,将这些样本都放进实验室冰箱,在4℃下冷藏,这个温度也是普通家用冰箱设置的温度。
实验人员先把菜肴研磨成浆状,称取1g(注:g克)样品置于锥形瓶中,加蒸馏水稀释。暗处静置15分钟,由快速检测仪直接读取亚硝酸盐含量。为保证测试结果的准确性,每个样品都测试3次,最后取平均值。
出锅后半小时,炒青菜、韭菜炒蛋、红烧肉这三个菜的检测结果是,亚硝酸盐含量都没有超过我国《食品中污染物限量标准》的最高限值,即蔬菜类4mg/kg、肉类3mg/kg(注:mg毫克,kg公斤)。但红烧肉中亚硝酸盐含量比韭菜炒蛋和炒青菜要高。对此实验人员说,肉类菜肴一般比蔬菜类加入更多的调味料,调味料中本身就含有硝酸盐,这些硝酸盐被微生物转化为亚硝酸盐,就导致了红烧肉中亚硝酸盐含量较高。
红烧肉亚硝酸盐率先超标
6小时后,差不多为中饭到晚饭的时间间隔。许多老年人或者双职工家庭在休息天、中午烧的菜,晚上再吃很普遍。
实验人员打开冰箱,把贴有“6小时”标签的炒青菜、韭菜炒蛋、红烧肉和红烧鲫鱼取出来,然后放进微波炉,用中低火加热1分钟,拿出微波炉后,这些菜肴看起来仍然很新鲜。
实验人员对这些菜肴的亚硝酸盐含量进行了测定,结果发现,6小时后剩菜中亚硝酸盐含量都有所增加,炒青菜增加了16%,韭菜炒蛋增加了6%,红烧肉增加了 70%。其中,红烧肉中亚硝酸盐含量达4.2558mg/kg,已超过了国家《食品中污染物限量标准》中“肉类3mg/kg”的限量标准。
冰箱放18个小时全超标
18小时后,实验人员又从冰箱中拿出贴有“18小时”标签的4个菜,用微波炉加热后作检测。检测结果发现,炒青菜中亚硝酸盐含量增幅非常大,比6小时增加了443%,红烧鲫鱼增加54%,韭菜炒蛋增加47%,红烧肉中亚硝酸盐含量变化不大。
从这实验看出,隔夜菜放到第二天中午,炒青菜、红烧肉、红烧鲫鱼亚硝酸盐含量都超过了国家标准。
菜肴放冰箱24小时吃不得
距离4个菜烧好的时间差不多过去24小时后,实验人员从冰箱中拿出最后一批贴有“24小时”标签的4个菜肴,同样用微波炉加热后作检测。
检测结果发现,跟18小时相比,4个菜肴亚硝酸盐含量继续大幅增加,且全部超过了《食品中污染物限量标准》的限量标准,其中炒青菜超标34%,韭菜炒蛋超标41%,红烧肉超标84%,红烧鲫鱼超标141%。
实验人员说,出锅后24小时,荤菜亚硝酸盐含量超标厉害,是因为红烧的菜肴,所用的调料中本身就含有硝酸盐,而且荤菜蛋白质含量高,24小时后,微生物分解了大量蛋白质化合物,促使硝酸盐转化为亚硝酸盐。
常温下亚硝酸盐含量上升更快
为了解冰箱冷藏与常温下菜肴亚硝酸盐含量的变化,实验人员还将一份红烧鲫鱼样本在常温下放置了4小时然后测定其亚硝酸盐含量。结果显示亚硝酸盐含量的三次测试平均值为8.9483mg/kg,超过国家限量标准一倍以上,比在冰箱中放了24小时超标得还要多。
据都市快报:
蔬菜越不新鲜 亚硝酸盐含量越
浙江大学生物系统工程与食品科学学院食品科学与营养系实验室沈建福副教授介绍,以前他们实验室做过生的蔬菜的亚硝酸盐含量测定,结果发现蔬菜中都含有亚硝酸盐,但没有超过国家标准。总的趋势是,越不新鲜的蔬菜,亚硝酸盐含量越高,而那些烂了的蔬菜,亚硝酸盐超标比较明显。
蔬菜中之所以含有亚硝酸盐,是因为蔬菜生长过程中要施氮肥,硝酸盐就是从氮肥中来的。硝酸盐没有毒性,但空气中的微生物会进入到剩菜中,而常温下微生物更加活跃,会产生一种还原酶,这种酶可以让菜肴中的硝酸盐转化成亚硝酸盐。
沈老师说,从生的蔬菜含亚硝酸盐的情况看,熟菜的亚硝酸盐含量只多不少。“理论上,剩菜放的时间越长,微生物的活动越厉害,亚硝酸盐含量也就越高。而且不同的菜,亚硝酸盐含量也是不同的。”
摄入3克亚硝酸盐
即可中毒致人死亡
亚硝酸盐可使血中低铁血红蛋白氧化成高铁血红蛋白,失去运氧的功能,致使组织缺氧,重则死亡。成人摄入0.2至0.5克即可引起中毒,3克即可致死。若长期食用还可引起食管癌、胃癌、肝癌和大肠癌等疾病。
卫生部发出预警
严防亚硝酸盐引发中毒
近期,一些地方食物中毒事故高发,特别是亚硝酸盐中毒和集体食堂食物中毒多发。前日,卫生部在其官方网站发布关于预防和控制食物中毒发生的预警公告。公告要求,要严防亚硝酸盐以及微生物污染等引发的食物中毒,进一步加强对食品生产、流通和餐饮环节的监管。
今年上半年报告的化学性食物中毒多为误食亚硝酸盐引起,常见于工地食堂和小餐饮业。为此,集体食堂和餐饮业要加强管理,严禁购买、使用工业用盐,防止误食亚硝酸盐。建筑工地要加强对工业用亚硝酸盐的管理,严禁与其他食物及原料混放。集体食堂和餐饮业要严格按照《食品添加剂使用标准》正确使用亚硝酸盐,严禁超量、超范围使用。食品安全监管部门要对用作食品添加剂的亚硝酸盐的生产、流通环节加强监管。
此外,夏秋季是食物中毒高发季节,特别是今年我国大部分地区气温较常年偏高,湿度偏大,导致食品及其原料易受到微生物污染。特别是食用鱼、虾、贝等海产品要谨防副溶血性弧菌食物中毒,食用罐头、腌渍、发酵食品要谨防肉毒杆菌食物中毒。
同时,食品安全监管部门要切实加强对食品生产、流通和餐饮环节的监管,提高公众的食品安全意识。卫生部门应当加强食源性疾病的监测与报告,及早发现食品安全隐患。 -
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- 时间: 2012-4-30 18:19
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- 时间: 2012-4-30 18:23
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- 时间: 2012-4-30 18:31
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- 时间: 2012-4-30 18:54
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- 时间: 2012-4-30 20:41Will eat leftover food cause cancer? Expert: is actually nutrient loss
Posted in Life News
”Noon meal becomes cause of gastric carcinoma in young women, eating leftover food 3.6 times times higher risk of gastric cancer! “Overnight how can you eat a meal? This is a subject of controversy in recent years constantly, and also heat up on Twitter recently, because of the “noon meal becomes cause of gastric carcinoma in young women”, causing forward on Twitter for another round of binge. “Experts say, placing time overnight after food is cooked for a long time, under the action of bacteria, nitrate into nitrite, has a carcinogenic effect, heat cannot be removed. So be sure not to eat leftover lunches! “It sounds really is” sensational “, was used by many dishes of white-collar workers are worried. This is really any reason? How can you eat vegetables for overnight?
Leftover food toxic on the origins of “nitrite cause cancer” said
Yangzi evening news reporter after inquiry found that leftover food toxic on the most important argument is the following passage:
”As some of the leaves contain higher concentrations of nitrates in vegetables, cooked place for too long, under the action of bacterial decomposition, nitrate into nitrite, has a carcinogenic effect, heat cannot be removed. ”
What is the actual situation? Diet expert with combination of traditional Chinese and Western medicine hospital in Nanjing zijin Museum Xu Dacheng Deputy Chief physician said, itself in many vegetables contain nitrates and nitrites. Containing nitrite in vegetables, because during the growth of vegetables to nitrogen, nitrate nitrogen is coming from.
In General, less than the content of nitrite in vegetables cooked in vegetables. Leftovers on the longer, nitrite increased the possibility of more. But needs pointed out that of is, nitrate itself is nontoxic of, but vegetable in Cook cooked Hou if placed time had long, in bacteria of decomposition role Xia, will transformation into Asia nitrate, Asia nitrate is human over intake will makes people appears dizziness hypoxia symptoms, while reached must limited of Asia nitrate also has may and human within of other food, and drug of some material occurs reaction, formed strong carcinogenic real-the-the Asia nitrate amine.
Xu Dacheng, Deputy Director of Chinese medicine practitioners say, in his clinic had reception a couple of colorectal cancer patients, has a habit of eating leftover food for many years. “Cancer causes for the formation of more complex, however, there has yet to be ascertained, but may be associated with this lifestyle, that would also eat leftover food is the reason they are pathogenic. “Director Xu said.
General overnight dishes of nitrite content sufficient to cause cancer
Xu Dacheng, Deputy Director of Chinese medicine practitioners said, in fact, although compared with fresh vegetables, content of nitrite in vegetables will increase overnight, but the case of a normal diet will not reach the amount of cancer. Such as green leaf vegetables, for example, according to a scientific experiment shows that, without turning into the refrigerator after cooking, green vegetables such as spinach nitrite contents after about 24 hours rising from 3mg/kg to 7mg/kg. Human intake of 0.2G nitrite poisoning may occur, this shows that to achieve intoxication, on a need to eat at least dozens of kilograms of leftover vegetables, normal, which is obviously impossible.
Leftover food on health is actually nutrient losses
Despite the leftover food cause cancer that only at the theoretical level, but experts still suggested that they’d better eat less because the overnight loss of food is nutrition for maximum adverse health effect.
Experts suggest that it is best not to eat leftovers, if special circumstances require with overnight dishes, in addition to the above said note overnight vegetable fresh-keeping, also have a choice. Such as leaf vegetables, especially dark green vegetables, is not suitable for rice. To select some like eggplant, melon, potato, carrot, cauliflower, mushrooms etc as preferred dishes with rice. Reporter Yu Dandan
www.chinastudygroup.or...-loss.html
冰箱里放24小时,亚硝酸盐含量全部严重超标ZT
