The molecular composition and structure of food is often very poorly understood so relating chemistry to food properties is hard. Courses in food chemistry offer detail on the important reactions but the following “big picture” questions can help identify the important chemical features of a real food.
- Consider all parts of the food separately first (e.g., pizza base, sauce, cheese) then look at how they interact. Interactions will largely be diffusion of liquid oil or water and molecules dissolved in them. How is mass transfer controlled in the packaged food?
- Can anything grow in the food? Unless the food is sterile or dry expect microbial growth of some kind. Think about what the bugs eat and what they poop (esp. toxins, acids).
- How closely related is the food to living tissue? Unless there has been a thermal process there will likely be some residual enzyme activity. Look for polyphenol oxidase in plants causing browning or for catabolic enzymes. Even if the enzymes have been inactivated now, did they get time to affect the product chemistry during processing? How much of the native biological structures are still intact (meat = lots, ketchup = some, mayonnaise = none).
- What is the pH? How does that affect the charges on molecules present? Can acid+heat hydrolyze anything?
- What phases are present? Very often fat will be present in an emulsion, air as a foam, or sugar or ice crystals as a sol. If the food is clear it is probably either a solution or a clear glass.
- Is the food solid? If there is lots of water (or liquid oil) present it is probably a gel; look for gelling agents (polysaccharides or proteins; if there is little water present it is probably biological tissue, a glass or possibly a densely-packed suspension.
- Do you expect flavor or color changes during storage? Possibly some sort of radical oxidation process is responsible. Look for oxidizable materials (polyunsaturated fatty acids, most colors, many vitamins and phytochemicals). Try to work out how oxidation is being controlled (limiting oxygen availability, blocking light, binding metals, scavenging radicals). Remember you need very little reaction on a molar basis to get big changes in properties.
- Is the food cooked? Look for the causes and effects on Maillard browning, starch gelatinization (if enough water), protein denaturation (if above critical temperature).