Work Package 7: “Burial Bioarchaeology” focuses on uncovering additional information about who was given a gypsum burial based on their surviving remains. One technique we are using to learn more about the diets of these past people is stable isotope analysis. Corrie Hyland, our Post-Doctoral Research Associate for Work Package 7, is currently working in the BioArCh labs at the University of York, extracting protein (collagen) from the bones of people and animals from Roman Yorkshire. This material will be used for stable carbon, nitrogen and sulfur isotope analysis to explore the dietary history of people found in gypsum burials.
Why extract protein from bone?
Archaeological scientists, like Corrie, extract proteins from bone because the chemical signatures of the food you eat are reflected in the collagen in your bones. You are what you eat! Bone collagen resists degrading over time, and we have methods to remove contaminants which may have come from the soil the bones were buried in. Our Yorkshire Roman period samples had to survive for over 1800 years before we had the chance to study them today!
How do we extract protein from bones?
First, we remove any dirt from the surface of the bone by abrading it with a shot blaster. We only need about 0.5 g of bone so we use a small saw to cut off a piece of the bone.
The method we use to extract the collagen protein from bone involves three major steps and is often referred to as the Acid-Base-Acid method (ABA).
Acid: The first step is to remove the rigid mineral parts of the bone by dissolving the sample in a mild acid over several days. After this stage, the bone is no longer hard and becomes soft and bouncy like rubber.
Base: The second step is to remove any potential contaminants that have entered the bone from the burial environment. We use a mild base to remove these “humic acid” contaminants. Humic acid appears as dark brown or black solutions at this stage.
Acid: During the third step, we use a low level of heat and a very weak acid to melt the collagen into a consistent gelatin. This step of the procedure is often referred to as gelatinisation.
Now that the collagen is a liquid gelatin, we can use special filters to remove any final contaminants.
The final stage is drying the collagen using a freeze dryer to ensure the collagen has a fluffy consistency similar to cotton candy or packing foam.
In this form, we can weigh the collagen into small tin capsules. These tin capsules of fluffy collagen are then analysed to produce the stable carbon and nitrogen isotope ratios that give us insights into the diets of people and animals in the past.
