The Glucose test strips were originally developed to test for glucose levels in urine for educational purposes (not medical diagnosis). Other uses include osmosis experiments where a glucose/starch solution is used to demonstrate the concept in a classroom setting.
The strips will also detect glucose levels in food, however, there are several things to consider:
1) The enzyme used to detect the glucose is specific for glucose sugar. Other sugars will not be detected by the test strip.
2) While exclusive for glucose sugar, other chemicals can interfere. The best (or worst) example is Vitamin C. The strips will not work well with foods high in Vitamin C.
3) In order for the enzyme to work properly, the solution being tested may need to sit for up to 3 hours to allow mutarotation to occur. (In most natural settings, the mutarotation has already occurred.)