Testing for biological molecules · 检测生物分子
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| carbohydrate/ˌkɑːbəʊˈhaɪdreɪt/ | 碳水化合物 | tàn shuǐ huà hé wù |
| lipid/ˈlɪpɪd/ | 脂质 | zhī zhì |
| reducing sugar/rɪˈdjuːsɪŋ ˈʃʊɡə/ | 还原糖 | huán yuán táng |
| emulsion/ɪˈmʌlʃn/ | 乳浊液 | rǔ zhuó yè |
| semi-quantitative/ˈsemi ˈkwɒntɪteɪtɪv/ | 半定量 | bàn dìng liàng |
| acid hydrolysis/ˈæsɪd haɪˈdrɒləsɪs/ | 酸水解 | suān shuǐ jiě |
Which molecules are in your food?
- Living things are built from carbohydrates 碳水化合物, lipids 脂质, proteins and nucleic acids.
- Simple chemical tests reveal which are present in a sample.
- Each test has a clear colour change.
你的食物里有哪些分子?
- 生物由 碳水化合物(carbohydrates)、脂质(lipids)、蛋白质(proteins) 和 核酸(nucleic acids) 构成。
- 简单的化学测试揭示样品中存在哪些。
- 每个测试都有一个清晰的颜色变化。
The four food tests
| Test | Finds | Positive result |
|---|---|---|
| Benedict's (heat) | reducing sugar 还原糖 | blue → green → orange → brick-red |
| iodine | starch | orange-brown → blue-black |
| emulsion 乳浊液 (ethanol then water) | lipid | white, cloudy emulsion |
| biuret (room temperature) | protein | blue → purple |
Benedict's test: blue turns green, then orange, then brick-red as more reducing sugar is present.
四种食物测试
| 测试 | 检测 | 阳性结果 |
|---|---|---|
| 本尼迪克特(Benedict's)(加热) | 还原糖 | 蓝 → 绿 → 橙 → 砖红 |
| 碘液(iodine) | 淀粉 | 橙棕 → 蓝黑 |
| 乳浊液(emulsion)(先乙醇后水) | 脂质 | 白色、浑浊的 乳浊液 |
| 双缩脲(biuret)(室温) | 蛋白质 | 蓝 → 紫 |
本尼迪克特测试:随着还原糖增多,蓝色变绿,然后橙,然后砖红。
A sample is heated with Benedict's solution and turns brick-red. This shows the presence of: · 一个样品用本尼迪克特溶液加热后变砖红。这表明存在:
Benedict's test (with heat) detects reducing sugars; a positive result goes blue → green → orange → brick-red. · 本尼迪克特测试(加热)检测还原糖;阳性结果从蓝 → 绿 → 橙 → 砖红。
Orange-brown iodine solution turns blue-black. This detects: · 橙棕色的碘液变蓝黑。这检测:
The iodine test detects starch — the orange-brown solution turns blue-black. · 碘液测试检测淀粉——橙棕色的溶液变蓝黑。
In the biuret test, a positive result for protein turns the solution from blue to ______. · 在双缩脲测试中,蛋白质的阳性结果使溶液从蓝色变为 ______。
Biuret solution turns blue → purple when protein is present (no heating needed). · 当存在蛋白质时,双缩脲溶液从蓝 → 紫(不需要加热)。
A positive emulsion test for a lipid gives a clear blue solution. · 脂质的阳性乳浊液测试给出一个清澈的蓝色溶液。
A positive emulsion test gives a white, cloudy emulsion — not a colour change. · 阳性乳浊液测试给出一个白色、浑浊的乳浊液——不是颜色变化。
Match each test to the molecule it detects. · 把每个测试与它检测的分子配对。
Benedict's → reducing sugar; iodine → starch; emulsion → lipid; biuret → protein. · 本尼迪克特 → 还原糖;碘液 → 淀粉;乳浊液 → 脂质;双缩脲 → 蛋白质。
Semi-quantitative 半定量 Benedict's
- The normal Benedict's test only says yes/no. A semi-quantitative version gives a rough amount.
- First standardise it on known concentrations, then estimate an unknown by the time to the first colour change (more sugar → faster), or by comparing the final colour to standards.
半定量的本尼迪克特测试
- 普通的本尼迪克特测试只说有/无。一个 半定量(semi-quantitative) 的版本给出大致的量。
- 先在已知浓度上 标准化 它,然后用 到第一次颜色变化的时间(糖越多 → 越快)估计一个未知样,或把最终颜色与标准品比较。
Testing for non-reducing sugars
- Sugars like sucrose are non-reducing — they give a negative Benedict's test.
- To detect them: do a normal test (stays blue) → add dilute hydrochloric acid and heat (acid hydrolysis 酸水解 splits the sugar) → cool and neutralise → repeat Benedict's. A brick-red result now shows a non-reducing sugar was present.
A non-reducing sugar gives a negative test until acid hydrolysis splits it — then Benedict's turns red
- Step through it below.
测试非还原糖
- 像 蔗糖(sucrose) 这样的糖是非还原的——它们给出 阴性 的本尼迪克特测试。
- 检测它们:做一个普通测试(保持蓝色)→ 加稀 盐酸(hydrochloric acid) 并加热(酸水解(acid hydrolysis) 把糖分开)→ 冷却并 中和 → 重复本尼迪克特测试。现在一个砖红结果表明存在过非还原糖。
非还原糖给出阴性测试,直到酸水解把它分开——然后本尼迪克特测试变红
- 在下面一步步走过去。
Testing for a non-reducing sugar · 检测非还原糖
Step through the trick: a non-reducing sugar stays blue, so you hydrolyse it with acid, neutralise, then re-test. · 一步步走过这个技巧:一种非还原糖保持蓝色,所以你用酸 水解 它,中和,然后重新测试。
To test for a non-reducing sugar such as sucrose, you first: · 要检测像蔗糖这样的非还原糖,你首先:
Acid hydrolysis breaks the non-reducing sugar into reducing sugars; after neutralising, Benedict's now gives brick-red. · 酸水解把非还原糖分解成还原糖;中和之后,本尼迪克特现在给出砖红。
Put the non-reducing sugar test in order. · 把非还原糖测试按顺序排列。
You must hydrolyse the non-reducing sugar into reducing units first, neutralise the acid, then the second Benedict's test works. · 你必须先把非还原糖水解成还原性单元,中和酸,然后第二个本尼迪克特测试才有效。
You've got it
- Benedict's (heat) → reducing sugar (brick-red); iodine → starch (blue-black)
- emulsion → lipid (white cloudy); biuret → protein (purple)
- semi-quantitative Benedict's estimates amount (time to change / colour standards)
- non-reducing sugar: hydrolyse with acid + heat, neutralise, then retest
你掌握了
- 本尼迪克特(加热)→ 还原糖(砖红);碘液 → 淀粉(蓝黑)
- 乳浊液 → 脂质(白色浑浊);双缩脲 → 蛋白质(紫色)
- 半定量 本尼迪克特估计量(到变化的时间 / 颜色标准品)
- 非还原糖:用酸 + 加热水解,中和,然后重新测试