The main component of squid ring is protein, which is rich in collagen. When squid rings are heated during cooking, the collagen in them will be denatured. Denaturation refers to the structural change of protein under heat or other external conditions, which leads to the loss of its original structure and morphology.
After the collagen in the squid ring denatured, the original milky white color became transparent. This is because the denatured collagen has lost its original tissue structure, which causes light to be transmitted in a transparent form instead of being scattered or absorbed.
Therefore, when you cook frozen squid rings, it is normal that they become transparent, which is related to the denaturation of collagen during cooking.