Page 12 - Science Focus (Issue 19)

Have you ever had a dish containing garlic and A combination of volatile sulfur compounds
had your mouth stinking for a very long time? You
brushed your teeth several times and used the most
minty mouthwash, but they all seemed to be useless.
This article suggests a scientific approach to you to
deal with garlic breath so that you will not embarrass
yourself in future interviews or important events.
To tackle this problem, we have to first delve
into the chemistry of garlic breath. The secret lies
in the sixteenth element in the periodic table: sulfur
(S). Garlic has many compounds that contain sulfur,
such as allicin, allyl methyl sulfide, allyl mercaptan
and diallyl disulfide. These are volatile compounds
that give chopped garlic its distinctive pungent odor.
After ingesting garlic, these volatile compounds
would also evaporate in the person’s breath, giving
an unpleasant smell. Smelly sulfur compounds are
not only found in garlics, in fact the nasty smell
of farts and rotten eggs is due to the presence of
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hydrogen sulfide (H2S) .
contributes to the distinct smell of garlic breath.
While most of the sulfur-containing compounds
found in garlic are metabolized relatively quickly,
allyl methyl sulfide (AMS) is metabolized more slowly
than the rest because an effective way to digest
AMS is lacking in our body [1] and it can be detected
in the breath for as long as 30 hours after ingestion
of raw garlic [2]. The persistence of AMS is the reason
why your breath still stinks the next morning after
having garlic for dinner. AMS and other volatile
organosulfur compounds are absorbed from the gut
into the bloodstream and then expelled into expired
air inside the lungs [1]. This is why brushing teeth and
mouthwashes are ineffective in treating garlic breath.
Thankfully, there are a few effective ways for
deodorizing a garlic breath situation. The first is
to make use of specific raw foods to disable the
production of smelly compounds in the body.
In a study conducted by scientists in Ohio State
University [3], it was found that
raw foods high in polyphenols
can reduce the amount of
AMS in the breath after garlic
Garlic
Breath…
and How to Deal
With It?
ඹ಄ຯޱᔅ
ੋʜʜ
By Kit Kan 簡迎曦
ingestion. Polyphenols are a group of antioxidant The next time you enjoy a slice of garlic bread,
compounds present in plants and they can capture do not forget to have a glass of milk and an apple to
some organosulfur compounds and neutralize go with it to prevent garlic breath and to make it a
their odors to some extent. However, an enzyme nutritious meal!
called polyphenol oxidase can oxidize polyphenols
into a more potent free radical form. The free
radicals generated can effectively remove a stinky 1 Remark: The myths and facts about farts were introduced in
compound of garlic breath called allyl mercaptan, Issue 015.
preventing it from being further metabolized by
the body into its longer-living cousin AMS [3]. 您曾否試過因為吃了以蒜頭入饌的菜式，而令口腔在之
Common fruits high in polyphenols like apple, 後一段很長的時間都充斥著蒜頭的味道？儘管你已經刷了
plum, cherry, peach and grape were all shown
to have a deodorizing effect [4, 5], with apple’s 幾次牙，並用上最濃薄荷味的漱口水，但似乎並沒有甚麼作
effect experimentally confirmed by data showing 用。本文會從科學角度，提出一些方法處理蒜頭帶來的口氣，
a reduction in AMS level [3]. Like most enzymes, 這樣你就不會在以後的面試或重要日子中因蒜頭味口氣而
polyphenol oxidase would become denatured at 感到尷尬了。
high temperatures, so it is most effective to eat your 解決問題之先，我們必須要了解蒜頭味口氣的化學原
fruits raw and not cooked.
If you are not a fan of fruits, do not worry. Other 理。其秘密在於週期表中的第 16 個元素：硫（S）。蒜頭
含有許多含硫的化合物，例如大蒜素（allicin），烯丙基甲
studies have shown that drinking milk is also effective
in treating garlic breath [6]. Volatile sulfur compounds 基硫醚（allyl methyl sulfide/AMS），烯丙基硫醇（allyl
mercaptan）和二烯丙基二硫（diallyl disulfide）等。這些
can be classified into hydrophilic (water-loving) and
hydrophobic (oil-loving) by their chemical structures. 都是揮發性化合物，使切碎的蒜頭具有獨特的刺激性氣味。
The concentrations of these compounds (including 進食蒜頭後，這些揮發性化合物會揮發至呼吸氣息中，散發出
AMS) were shown to be reduced in the oral and 令人討厭的氣味。帶臭味的硫化物不單存在於蒜頭，事實上，屁
nasal cavity after drinking milk. As milk consists of 和腐爛雞蛋的難聞氣味就是源於當中的硫化氫 (H2S)。
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mainly water and a few percent of fat, it can dissolve
both hydrophilic and hydrophobic organosulfur 蒜頭味口氣的獨特味道由不同揮發性硫化物混合而成。
compounds and reduce their volatility. In addition, 雖然蒜頭中大多數硫化物的代謝都相對較快，但烯丙基甲基
casein, a protein found in milk, was shown to be able 硫醚（AMS）的代謝速度卻比其餘的慢，這是因為我們體內
to chemically react with disulfide compounds, such
缺乏有效分解 AMS 的途徑 [1]，因此進食生蒜頭後長達 30
as diallyl disulfide. It has been postulated that diallyl
小時，在呼吸中仍然可以檢測到 AMS [2]。長時間殘留的
disulfide can be metabolized into AMS through a AMS 就是為甚麼我們在晚餐吃了蒜頭後，口氣在第二天早
reductive pathway with glutathione, a mild reducing
上仍然久久不散的原因。AMS 和其他揮發性有機硫化物是
agent used by our cells to reduce disulfide bonds
[7]. Milk with its fat and casein contents can help to 從腸道被吸收到血液，然後排至肺部的呼出空氣中 [1]，這就
是為甚麼刷牙和漱口水都無法有效去除蒜頭味口氣的原因。
lower the amount of diallyl disulfide, a hydrophobic
molecule, available to our system, and in turns less
AMS will be formed. These can explain why drinking 幸好，有幾種有效的方法可以去除蒜頭帶來的口氣。第
milk is a possible way to reduce garlic breath. 一是生吃某些特定食物來阻止體內產生帶有臭味的化合