Tag: guacamole

Why avocados turn brown — and how chemistry can stop it

Infographic on avocado browning. Avocados contain compounds called phenols. Exposure to oxygen converts phenols to compounds called quinones. The enzyme polyphenol oxidase speeds up this process. The polymeric compounds causing the brown colouration are melanin pigments. Leaving the stone in the avocado or in guacamole doesn’t slow browning as it doesn’t block oxygen. Covering with clingfilm can block oxygen and delay browning. Adding lemon or lime juice, or chilling the avocado, can also delay browning, as it inhibits the activity of the polyphenol oxidase enzyme.
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Anyone who’s ever purchased an avocado will testify that, after taking several days to reach the point of perfect ripeness, they remain at that point for an incredibly short amount of time before morphing into a brown, sludgy mess. As if to confound this problem, if you do catch them at the optimum ripeness, they turn brown incredibly quickly after being cut open if not eaten straight away. As always, chemical processes at work are to blame for this occurrence.

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