C for Chili, Chili for Vitamin C

朱芷瑩 Chu Tsz Ying , 何鎧均 Ho Hoi Kwan, 何穎賢 Ho Wing Yin, 梁潔欣 Leung Kit Yan, 王逸姿 Wong Yat Gee

Synopsis 

Recently, healthy eating has become a really hot topic in the territory. People are more concerned about their nutrition content of food. In the past few month, the atypical pneumonia has already spread widely in dozens of countries and cities. People are searching for the anti-SARS products. To keep up with the pace of trend, scientists are busy doing investigation on upgrading the nutrition value. New medicines appear almost every single day, and in the professionally decorated advertisements, they are said to be the best ways to keep your body fit and have no side effects. 

 Nevertheless, why don’t we simply develop our balanced diet through the natural nutrients?

 Vitamins are an important element in our daily diet and vitamin C is among the most popular ones. It is a well-known element to prevent scurvy and cold. And new discoveries appear saying that vitamin C can also help to cure cancer and even AIDS.

Vitamin C is named ascorbic acid, a weak diprotic acid. It is a water-soluble molecule, which is able to form hydrogen bond via its hydroxyl (-OH) and carbonyl (C=O) groups to H₂O molecules. It is also easily oxidized in air and sensitive to heat and light. Since it is contained in the watery part of fruits and vegetables, it is easily lost during cooking in water.

Everyone knows that fresh citrus fruits, like oranges and kiwifruit, are the main sources of vitamin C. However, from our investigation, peppers and chilies contain even more!

In our project, we investigated the vitamin C content of different peppers and chilies and find out the effect on vitamin C concentration of various conditions:

1.      Freshly prepared;

2.      Exposed to air;

3.      Soaked in water;

4.      Boiled in water for different time intervals and

5.      Cooked in oil for different time intervals

These are to imitate different cooking methods used in our daily life, so that we can find out the best conditions to treat food with vitamin C. For further comparison, we also had experiments on oranges, kiwifruits, tomatoes, chili sauces and pepper products.

Methodology

To detect vitamin C, we carried out the DCPIP test for each food sample under the above conditions.

In the DCPIP test, we made use of the strong reducing power of Vitamin C (ascorbic acid), as many plant tissues contain ascorbic acid oxidase, ascorbic acid is oxidized to form dehydroascorbic acid. Adding in 3% metaphosphoric acid to the extract during the experiment will inactivate the oxidase, and thus prevent the loss of ascorbic acid to oxidation. The dye, 2,6-dichlorophenol indophenol (DCPIP), is blue in its basic solution. In acidic medium, it turns pink (DCPIPH). When ascorbic acid is detected, the pink DCPIPH is reduced to colourless DCPIPH₂.

To find to the actual amount of Vitamin C in the food samples, we titrated DCPIP solution with standardized ascorbic acid solution. Using the molarity and volume of solution measured, the relative amount of vitamin C in the food samples can be calculated.

 Investigation

 We hypothesized that the amount of vitamin C will eventually drop in all conditions due to its special characteristic.

 From our experimental results, we can compare the content of Vitamin C in different conditions easily.

 1.      When the foods are freshly cut without any treatments, red hot chilies have the highest amount of Vitamin C. This is even higher than kiwifruit, the highest in fruit and vegetables. While the red hot chilies, green peppers and yellow peppers are the top three, kiwifruit has only got a quarter of that.

2.      Amount of Vitamin C decreases in food samples after a specific treatment. In short, Vitamin C is greatly reduced if the food sample is soaked in water while the amount only decreases slightly if cooked in oil.

We also discovered that high temperature has little effect on Vitamin C which is against the common belief of people. To further prove our experimental results obtained, controls of boiling ascorbic acid were carried out. It can be concluded that high temperature starts to reduce the amount of Vitamin C after it is boiled for 25 minutes.

3.      For chili and pepper sauces and the canned food contain very little vitamin C. But surprisingly, the amount of Vitamin C in the Cantonese food, stuffed-peppers(煎釀三寶) is similar to that of the freshly cut peppers.

4. Red hot chilies have the highest amount of Vitamin C as mentioned above, the price however is not expensive at all. And for peppers, the imported green peppers are fresh and in good quality, a single pepper is already large enough for making a dish.

In overall, red hot chilies had the most amount of Vitamin C, while Thailand green chilies got the least.

The amount of Vitamin C remains approximately the same when boiled in oil. The non-fat-soluble property of Vitamin C retains it in the food samples.

Conclusion

From our investigation, some new ideas of cooking are discovered. Never wash the peppers or other vegetables in water for a long time. Exposure of food samples reduces amount of Vitamin C. If prolonged cooking is necessary, soup cooking is recommended. In producing canned food long-timed processing reduces the vitamin C content. To retain the highest amount of vitamin C in the peppers and chilies, other than eating them raw, fry with little oil for healthy eating!

We strongly advise you to have peppers and chilies in your diet. They do have much higher amount of vitamin C than any common vegetables and fruits!

內容摘要

        現今科技日新月異的社會上，健康飲食成為城中的熱門話題。人們對食物的營養亦越來越關注。最近非典型肺炎肆虐本港，市民四處搜羅「抗炎佳品」。為了緊貼潮流，科學家都致力硏究提升食物質素的方法。差不多每天都有「健康食品」登場，在美侖美煥的廣告包裝下，它們不單沒有副作用，更是解決健康問題的不二法門。

         事實上，我們為何不透過最天然的養份攝取所需的營養呢？

         維生素是我們日常飲食的主要元素之一，而維生素C更是無人不曉。維生素C能夠協助我們防止患上壞血病和傷風；除此之外，近年還有硏究報告指出維生素C可以治療癌症和「世紀絕症」之一的愛滋病。

         維生素C又名抗壞血酸，是一種弱雙質子酸。它是水溶性的分子，能透過氫氧基(-OH)和羰基(C=O)，轉換成水分子，然後產生氫鍵。維生素C很容易被空氣氧化，而且對熱能和光線敏感。維生素C儲存在水份高的水果和蔬菜中，因此極容易在煮食其間流失。

         相信大家都知道新鮮的柑橘屬水果，例如：橙和奇異果，都是維生素C的主要來源。可是，從我們的探討所得，椒類蔬菜所含的維生素C比其他蔬果還要多！

         在這個專題硏習中，我們嘗試探究各種椒類蔬菜經過不同的處理後的維生素C含量：1. 未經任何處理；2. 用水浸一天；3. 暴露在空氣下兩天；4. 在水中煮；5. 用油煮。這些處理是模仿我們日常的煮食方式，再分析究竟哪種辦法能令維生素C的流失減至最低。為了能夠作出相應的比較，我們也為橙、奇異果、蕃茄、辣椒醬及椒類製品進行測試。

實驗方法

我們利用二氯酚靛酚測試對各項食物樣本進行檢測。

         由於植物組織含有抗壞血酸氧化酶，在二氯酚靛酚測試中我們利用抗壞血酸的還原能力，使其被氧化成去氫抗壞血酸。而混入3%偏磷酸能有效地阻止氧化酶的活動，從而防止抗壞血酸被氧化。染料２,６二氯酚靛酚( DCPIP )，它的基本色為藍色。 在酸性介質，它會轉為粉紅色( DCPIPH )。 當抗壞血酸被偵測到的時候，粉紅色的 DCPIPH 被還原成無色狀態的 DCPIPH₂。

        要計算出食物樣本中的維生素C含量，我們利用滴定法把有標準濃度的抗壞血酸劑混入二氯酚靛酚劑。利用摩爾濃度和實驗中所需的溶液劑量，便能計算出食物樣本中相對維生素C的含量。

         我們最初假設由於維生素C的特質，食物中的含量在不同的情況下都會下跌。

         從我們的實驗結果，我們能很容易地比較在不同的情況下維生素C含量。

 1.      測試未經任何處理的食物樣本，我們發現指天椒含有最高的維生素C含量。這結果更比被稱為有豐富維生素C的奇異果還要高。奇異果的維生素C含量只及穩佔三甲的指天椒、 燈籠綠椒及燈籠黃椒的四分一左右。

2.      食物樣本的維生素C含量在經過處理後都下降了。簡單來說，泡在水中的食物樣本維生素C含量被大大減少，而用油煮的食物樣本只有較輕微的下跌。

        我們也發現高溫對於維生素C的影響並不是人們所說的大。為了進一步驗證實驗結果，我們進行了抗壞血酸的對照實驗。總結實驗結果，高溫對維生素C的影響，只在烹調25分鐘後出現。

3.      所有的辣椒醬和罐裝食物都只含極少，甚至不含維生素C。可是，中式小吃 ─ 煎釀三寶 ─ 的維生素C含量跟新鮮的食物樣本卻十分相近。

4.      以上所說指天椒含有最多的維生素C，而它的價錢也不太昂貴。至於其他的椒類蔬菜，進口燈籠綠椒都是新鮮和高品質的，而且一個燈籠綠椒已足夠完成一個菜。

總的來說，指天椒含有最多的維生素C，泰國青尖椒則含最少維生素C。

我們從探究中領略到一些煮食的新竅門。絕不能把蔬果長時間泡在水裡。食物暴露在空氣中也減少維生素C含量。倘若必須要長時期烹調，我們建議以蔬果煮湯喝。在製作罐頭食品當中，食物都經過長時間的加工或調味，維生素C亦因此而流失。除了吃未經烹煮的蔬菜外，要在椒類蔬菜保留最多的維生素C， 以小量的油稍煎便可享受此健康美食。

我們強烈建議大家在日常用膳時多吃椒類蔬菜，它們的維生素C含量實在比其他蔬果高得多呢！