Citrus stops apples from browning, not bananas.

Citrus stops apples from browning, but bananas are a different story — you’re better off keeping them whole.

The browning is just oxidation. Lemon or lime juice creates an acid barrier on cut apples, and that works great. A quick toss in a little citrus juice (or even orange juice) will keep apple slices pale for hours. Dilute it with a splash of water if you don’t want them too tart. Salt water works too, but then your apples taste like pretzels unless you rinse them, which defeats the purpose for a lunch box.

Bananas are stubborn because they brown from the inside out, and the enzyme reaction isn’t stopped by surface acid. You can brush the cut end with lemon, but it only buys you a little time and adds an odd flavor. The real trick: pack bananas whole. If you need slices, wait and slice them at lunch, or pack a whole banana and let the kid peel it themselves. A slightly green banana also holds up better than a fully ripe one.

Don’t overthink it — citrus-toss the apples, leave the banana alone.