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酸菜的科学:细菌发酵 | The Science of Sauerkraut: Bacterial Fermentation

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酸菜发酵的第一阶段涉及厌氧细菌,这就是为什么切碎的包菜和盐需要装在密封的容器中的原因。在此阶段,周围的环境不是酸性的,只是包菜。这种细菌(主要是亮粘菌)会产生二氧化碳(取代罐子里最后的氧气痕迹)和乳酸,而乳酸是厌氧呼吸的自然副产物。最终,罐子内的环境变得太酸性,以至于这些细菌无法生存,它们消失了,取而代之的是能更好地应对酸性条件的细菌,例如乳酸杆菌。

乳酸菌利用厌氧呼吸进一步发酵包菜中残留的所有糖分。这样会产生更多的乳酸,直到酸菜的pH值达到约3。这些细菌会受到高盐浓度(因此大多数酸菜含有约2-3%的盐)和低温的抑制,这就是为什么将发酵罐放在室温而不是冰箱。在pH3时,乳酸菌停止发酵,酸菜可以储存直到需要。

所有这些细菌有助于产生浓烈的酸性味道。但是,微生物生长有多种方式可能会出错。乳酸菌的过度生长,例如,如果罐子在发酵过程中储存在太高的温度下,可能会导致德式酸菜形成错误的稠度。同样地,如果酸菜太早变酸,则乳酸菌会过早起作用,导致酸菜变软。尽管制成的酸菜酸度过高,病原体无法生存,但真菌的孢子可能会沉积在表面并扩散,使食物变质。

尽管酸菜是德语单词,但该菜被认为起源于中国,其中包菜在米酒或盐水中发酵。这是通过加尼吉斯汗(Ghengis Khan)入侵者传到欧洲的,在那里包菜用盐干腌。由于酸菜可以长期保存,并且是维生素C的来源,因此受到荷兰水手的青睐,当他们航行去美国时,荷兰人随身带了它。库克船长还随身带去了澳大利亚,因为酸菜中含有多种维生素和矿物质,长时间在海上航行很难获得。

因为在包菜叶上发现了酸菜发酵所需的细菌,所以这是一道非常容易和健康的菜。您只需要包菜!通过利用细菌的作用,可以使用包菜和盐水之类的简单成分来制作健康的菜肴,这种菜肴可以保存很长时间,直到原始的水果和蔬菜开始变质。

文章摘录:https://blogs.scientificamerican.com/lab-rat/the-science-of-sauerkraut-bacterial-fermentation-yum/

The first stage of sauerkraut fermentation involves anaerobic bacteria, which is why the shredded cabbage and salt need to be packed in an airtight container. At this stage, the surrounding environment is not acidic, just cabbagey. The bacteria, mostly Leuconostoc species, produce carbon dioxide (replacing the last vestiges of oxygen in the jar) and lactic acid, which is a natural by-product of anaerobic respiration. Eventually, the conditions within the jar become too acidic for these bacteria to survive and they die out, replaced with bacteria that can better handle the acidic conditions such as Lactobacillus species.

The lactobacillus further ferments any sugars remaining in the cabbage, using anaerobic respiration. This produces more lactic acid until the sauerkraut reaches a pH of about 3. These bacteria are inhibited by high salt concentrations (so most sauerkraut contains around 2-3% salt) and low temperatures, which is why the fermenting jars should be left at room temperature rather than in the fridge. At pH3 the lactobacillus stop fermenting and the sauerkraut can be stored until needed.

All these bacteria help to create the tangy acidic taste; however, there are ways that microbial growth can go wrong. Overgrowth of the lactobacillus, for example, if the jar is stored at too high a temperature during fermentation, can cause the sauerkraut to form the wrong consistency. Likewise, if the sauerkraut gets too acidic too early the lactobacillus gets in on the action early leading to soft sauerkraut. Although the finished sauerkraut is far too acidic for pathogens to live in, fungal spores may settle on the surface and spread, spoiling the food.

Although sauerkraut is a German word, the dish is thought to have originated in China with cabbage fermented in rice wine or brine. This spread to Europe by way of Ghengis Khan’s invaders where the cabbage was dry-cured with salt. As sauerkraut keeps for long periods and is a source of vitamin C, it was favoured by the Dutch sailors, who took it with them when they travelled to America. Captain Cook also travelled with it to Australia, as sauerkraut contains a range of vitamins and minerals that are difficult to obtain when travelling for long periods at sea.

As the bacteria required for sauerkraut fermentation are found on the cabbage leaves, it’s a very easy and healthy dish to produce. All you need is cabbage! By exploiting the actions of bacteria simple ingredients such as cabbage and salty water can be used to produce a healthy dish that can be stored long past the time when raw fruit and vegetables will have begun to spoil.

Article extract: https://blogs.scientificamerican.com/lab-rat/the-science-of-sauerkraut-bacterial-fermentation-yum/

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