Should spices such as turmeric, coriander (or others) be included while cooking or added afterwards? How does heat affect the nutritional quality of spices?

In many traditional Indian and Asian cuisines, spices found in the form of a seed (for example, coriander seed, mustard seed, peppercorn, or cumin seed) are often added to cooking oils at the start of the heating process and allowed to “pop” in the oil. Powdered spices are added at different points in the cooking process, but never before the dish has been completely cooked.

I have only been able to find one research article (not published in MEDLINE) that measured nutritional changes in cooked versus uncooked turmeric. Although it shows improved antioxidant ability from cooking, I would not expect this finding to be typical. I’ve seen research, for example, on turmerin, one of the water-soluble peptides in turmeric, which has demonstrated antioxidant ability. I would assume that a certain percentage of turmerin could be lost in the same way as other water-soluble nutrients. In many traditional Indian and Asian cuisines, spices found in the form of a seed (for example, coriander seed, mustard seed, peppercorn, or cumin seed) are often added to cooking oils at the start of the heating process and allowed to “pop” in the oil. Powdered spices are added at different points in the cooking process.

I have only been able to find one research article (not published in MEDLINE) that measured nutritional changes in cooked versus uncooked turmeric. Although it shows improved antioxidant ability from cooking, I would not expect this finding to be typical. I’ve seen research, for example, on turmerin, one of the water-soluble peptides in turmeric, which has demonstrated antioxidant ability. I would assume that a certain percentage of turmerin could be lost in the same way as other water-soluble nutrients.

I would expect there to be trade-offs between cooked versus uncooked spices. These trade-offs might be unique to each particular spice. In general, however, I would expect fresh spices to have the most plentiful nutrient content, and I would expect there to be some significant nutrient losses from either the cooking or drying of fresh spices. Once a spice has already been dried, however, I would expect there to be less of an additional nutrient loss with cooking. In general, I would also expect more nutrient loss from the cooking or drying of leafy herbs than whole seeds.