Question

When pre-rigor fish are frozen, the following ions are released into sarcoplasmic reticulum at high concentration causing thaw rigor

• A. \(Mg^{2+}\)
• B. \(Ca^{2+}\)
• C. \(Na^{+}\)
• D. \(Cl^{-}\)

Hint:

Muscle contraction, relaxation, and post-mortem rigor are biochemically regulated by the intracellular concentration of calcium (\(Ca^{2+}\)) ions.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Thaw rigor is an extreme form of muscle contraction that occurs when fish muscle frozen in the pre-rigor state is thawed.
It is driven by a sudden release of calcium ions in the presence of high residual ATP.

Step 2: Detailed Explanation:
When fish are frozen immediately post-harvest (pre-rigor), the muscle tissue retains a high concentration of ATP.
During the freezing process, ice crystal formation damages cellular membranes, including the sarcoplasmic reticulum.
Upon thawing, this damaged sarcoplasmic reticulum releases a flood of calcium ions (\(Ca^{2+}\)) into the sarcoplasm.
The high concentration of \(Ca^{2+}\), combined with the available ATP, triggers a sudden, uncontrolled activation of actomyosin ATPase, resulting in severe muscle contraction and high drip loss.

Step 3: Final Answer:
The ion released that initiates this severe thaw rigor is \(Ca^{2+}\).