Aloe Vera gel browns quickly similar to the way avocado does when exposed to the air.
How to store Aloe:
Set a leaf in upright in a glass with cut side down for 15 minutes to allow sap to drain. Discard the sap. Cut leaf in half horizontally. Scoop out the gel with a spoon and place in a jar, seal and store in fridge. To keep it from browning, open a vit. E gelcap and add to gel. Use as needed.
Whole aloe vera leaves may also be wrapped then frozen.