I worked food service most of the way through college: ran a dish room, did pot washing, iced line, grill line helper, etc., but never cooked.
Anyway, what I always used on the stuff that I couldn't get clean otherwise was the degreaser that we cleaned the dish machine with! But I wore boy's jeans and chambray shirts every day when I ran the dish room for a reason, the blue helped hide the stains AND since I was tiny and I'm short, the boys' clothes helped keep the expense of 3 pairs of jeans and 8 shirts every semester to a minimum.
We use Sun & Earth, buy it in bulk from the company online. It's got a lemon/citrus scent and since DH and I are both scent sensitive and it doesn't bug us, that's a hit. YOu can buy their laundry soap concentrated, and that's what we do now. We used to buy the 5 gallon container. Now we just get concentrate and add water.
If I was working foodservice again, I"m not sure I'd dilute the soap!
Also, lately, I've been presoaking things with Biz and that has taken a lot of the previously "permanent" stains out of our clothes. We got a bucket w/ a hole and plug in the bottom last year that DH uses to wash his bike duds as they can't go through the washer, and I use that.
IHTH!
Judi