Can you be more specific about the spectrometry method? Mass spectrometry, optical spectrometry?

Because the opacity of the food sample will make it difficult to use any optical method directly, I think you will need to use a separation method to analyze the amount of product formed by the enzyme, separating the product from the food material. For example, you might be able to pellet the food material in a centrifuge and measure the product in the clarified supernatant. Or you might use an organic extraction or a filtration. This depends on the nature of the food, the enzyme reaction, and the substrate and products of the enzyme reaction.

You'll need to assay the enzyme activity after extraction using its relevant assay, which depends very much on the enzyme