Recipe(tried): How to keep lettuce from browning (RE: lemon juice and lettuce)

I agree with Patsy about the lemon juice wilting the lettuce. Lemon juice and vinegar are chemically similar (acid), and if you've ever added vinegar-based dressing to your salad too long before serving, you've seen how quickly it wilts.

The browning on lettuce is actually RUST. Yep, rust. Lettuce contains a lot of iron. Iron, when combined with moisture and oxygen, creates rust. Try this: if you need less than an entire head of lettuce, cut away what you need BEFORE washing it. Place the remainder -- unwashed, and therefore DRY -- into a plastic food storage bag. Press the cut surface against the bag, twist the bag as if to close and squeeze or suck out as much air as you can; now, close the bag with a twist-tie or one of those neat bag clips that looks like a barrette. The idea here is to keep as much air as possible away from that cut edge, where the iron in the lettuce has been "exposed". Then refrigerate as usual.

By the way, the browning (rust) is unattractive but harmless.