Homemade Guacamole Dip and The Science of Enzymatic Browning

To those who are not familiar with Guacamole, it's a traditional Mexican dip or salad made with ripe avocados and usually served with chips. At least here in Malaysia, Guacamole is not something that you can get easily. We don't grow avocado trees, and the fruit itself is foreign hence can be expensive.

Buying & Storing

I like avocado slices on toast and I usually get them from Tesco only when they are on sale (usually RM2+ per avocado instead of RM6+). To check for ripeness, you need to press the avocado fruit lightly with thumb. If it's hard, then it's unripe. Soft texture means the fruit is ripe and ready to eat. Visually ripen avocados are dark green in colour and the overripe ones are dark brown. If you want to know more about avocado and its benefits, you can refer to the journal down below;

Supermarkets like AEON, Tesco and Giant usually sell unripe avocados, but you can do the ripening process by placing the avocados at room temperature for 2-3 days (kawan i bagi tip letak buah tu dalam beras, sehari je dah masak). However, if you don't want to use your unripe avocados right away, put them in the fridge since it can prolong and prevent them from ripening for at least 3-4 weeks. I will explain more on this later. 

A little interesting science fact is that avocados are like apple, they turned brown faster after being cut open due to oxidation and dehydrogenation of a colourless compound called polyphenols. Like in many other fruits, avocados contained polyphenols (specifically catechol). When there's a contact with oxygen in the air, polyphenols will turn into o-quinones, a compound that is reddish-brown in colour (in avocado, it's 1,2-benzoquinone), and this process is being speed up by an enzyme (also present in the avocado, polyphenol oxidase). Since quinones are highly reactive, they will undergo few more chemical reactions to the point where they yield melanin, a black-brown pigment. Yes, it's the same pigment that what gives human, colours; more melanin, deeper skin tone. This whole chemical process is called as "enzymatic browning".

How to Keep Guacamole from Turning Brown

Now we know why slices avocado quickly turn brown, but why am I talking science here? well with the same knowledge, we can prevent avocado or more specifically, our guacamole from browning, although to be honest that would not be entirely possible due to air exposure.

(II) Temperature

Like I said above, by storing avocado in the fridge can prevent it from ripening faster. At certain low temperature, the enzyme activity of polyphenol oxidase is inhibited, therefore the chemical process will not be activated, hence no or slow enzymatic browning. So kalau ada leftover, simpanlah kat dalam freezer ye. 

(III) pH

Okay, this time around we are not talking about face cleanser and its pH but how pH level can affect enzymatic browning. Generally, acidity can inhibit enzyme activity. So by adding citrus juice or vinegar into guacamole, it can slow down the browning effect and that is also why people have been adding lime juice into the recipe! I mean, apart from the citrusy taste, it's good to know there's another reason behind it. 

Guacamole Dipping Sauce

Recipe

Alright, stop with all the science talk, now; HOW DO YOU EVEN MADE A BOWL OF GUAC? Fair to say, I'm kinda new to this avocado salsa... It's one of those things I didn't get around eating until 2 years ago. I used to buy the pre-made dip sauce from Tesco that would cost me around RM20 per bottle, but now no more since I know how to do it from scratch. 

Ingredients:

-2 ripe avocados

-1/2 tomato, inside flesh removed and chopped finely

-1/2 red onion, chopped

-1 clove garlic, minced

-Juice of 1/2 a lime

-A fistful of coarsely chopped cilantro/coriander leaves

-A pinch of salt & pepper

Method:

1. Cut the avocado by height and remove the seed.

2. Use a spoon and scoop out the avocado flesh and mash it up using a fork.

3. Mix in onion, garlic, tomatoes and cilantro.

4. Squeeze in 1/2 of a lime.

5. Taste and adjust salt & pepper accordingly

buruk gila plating aku, haha