Full-text search is case-insensitive. Everything else (String search and exact matches through the Titan index) are case-sensitive. So you can either use a full-text index:
.has("classification", CONTAINS, "Food")
...or a custom filter function (which will be very slow):
.filter { "food".equals(it.getProperty("classification").toLowerCase()) }
Another option is to simply add another property, in your case classfification_lc for example. Create a composite index over this property, then store the lowercase value of classification in it and use it for exact match queries:
.has("classification_lc", "food")
Cheers,
Daniel