Cooking Minimally Changes Isotopic Ratios in Fish

A preliminary study on the influence of cooking on the C and N isotopic composition of multiple organic fractions of fish (mackerel and haddock)

Authors:

Fernandes et al

Abstract:

Stable isotope analysis represents the principal scientific technique used in the reconstruction of ancient human diet. Characterisation of human diet requires that the isotopic baseline is established, i.e. the isotopic signals of consumed food groups. However, cooking may alter the bulk isotopic signal of food groups through the selective loss of macronutrients or biochemical components with different isotopic signals. In this study, we investigate the influence of cooking on the stable isotope values of raw flesh of two fish species (mackerel, with a high fat content, and haddock, having a low fat content) using three potential prehistoric cooking methods. The fish were boiled in a pot, grilled beside an open fire, and steamed in hot sand. Cooking times and temperatures were monitored. Stable isotope ratios (δ13C and δ15N) were measured on multiple fractions (bulk flesh, lipids, lipid-extracted flesh, water-extracted flesh, water-soluble compounds, and fish-bone collagen) before and after cooking. The results show that, for some fractions, cooking modified the composition, but changes in isotopic values relative to raw fish were in general less than 1‰. The results also show that isotopic signals of fish-bone collagen were not significantly altered during cooking, and confirm previous findings that showed significant isotopic offsets between fish-bone collagen and edible fish fractions.