I am a retired biochemistry/human nutrition college professor. I am "trying" to prepare our team (7th graders) for the exam portion by using modifications of my lecture notes that I used in my college lecture courses. I started with a discussion of the definition of a nutrient and the chemical/nutrient composition of food, followed by discussions of the structure and function of water, simple sugars (mono- and disaccharides), followed by oligo- and polysaccharides, amino acids and proteins, and lipids. These discussions involved numerous Power Point slides (the students each got a hard copy of the slides). I then cover the concept of energy derived from the macronutrients, grain structure and composition, gluten formation, aspects of baking with flour (including leavening agents), and end up with a few slides discussing chemical assay of protein, sugar, starch and lipid. Whether I have been able to get all, or any, of this information in an understandable manner to the kids remains to be seen. The challenge is getting the college level information down to a 7th grade level!
I hope this helps some out there who are wondering how to prepare, and where to start, for the Food Science portion.