Project: Interaction between antemortem physiology and postmortem biochemical processes in the white shrimp (Litopenaeus vannamei) muscle and its impact in quality, technological interrelation, and shelf life

One of the problems of marketing fresh-whole shrimp is the development of dark spots on the shrimp’s body caused by melanin, the same pigment in hair. The process is called melanization. It was traditionally assumed that the spots are due to postmortem activation of an enzyme called phenol oxidase (PO), which occurs once the organism dies. However, it is now known that phenol oxidase does not resist freezing, and frozen and defrosted shrimp melanize faster than those that are not frozen, involving another molecule in the presence of melanin.

This molecule is a transport protein, hemocyanin (Hc), similar to vertebrate hemoglobin. When Hc comes into contact with enzymes, such as digestive enzymes, it acquires the function of PO. Because Hc is more abundant than the real PO, once converted it has more capacity to produce melanin.

Non-melanized shrim (left) and melanized shrimp (right).

The reason for our interest in studying how Hc converts to PO is to eventually find ways to avoid and decrease melanization, and thus extend shelf life of this important sea product.

The science that studies the biological processes to modify and obtain benefits is called Biotechnology.

Even though it is possible to use chemical compounds, called food additives, such as “metabisulfites” to reduce melanization, these compounds are prohibited in countries where Mexican whole-fresh shrimp is imported. This is why we need to find biotechnological alternatives.

The general objective of this research is to evaluate intrinsic and extrinsic factors that convert Hc in PO. This is a collaboration agreement between CIBNOR and CIAD in Hermosillo.