lautnusantara.com The freezing and thawing processes are critical stages in frozen shrimp processing that significantly affect quality, particularly the texture and chemical properties of the shrimp meat.

Quality degradation in frozen shrimp occurs largely due to physical and chemical damage during the freeze-thaw process, not due to the activity of microorganisms, which are inhibited by low temperatures.

1. Changes in Shrimp Meat Texture

• Changes in texture are the most visible and noticeable impact on consumers, leading to a decrease in shrimp demand.

A. During Freezing

• Ice Crystal Formation: When shrimp are frozen, the water contained in the muscle cells (meat) turns into ice crystals. If the freezing process is slow (for example, using a chest freezer), the ice crystals formed will be large and sharp.
• Muscle Fiber Damage: These large ice crystals damage and puncture the muscle cell walls, causing structural damage to the protein.

B. During Thawing

• Increased Drip Loss: This is a major textural issue. The damage to muscle fibers that occurs during freezing causes the shrimp meat protein to lose its effective water-holding capacity. When shrimp is thawed, the previously frozen water cannot be reabsorbed by the muscle tissue, so it escapes as fluid (drip) visible on the packaging.
• Meat Softening: This fluid loss (drip) causes the shrimp meat to become soft, less elastic, and less dense (flabby). Good quality shrimp should have a compact and elastic texture.
• Shrinkage: The loss of fluid during drip loss also causes the shrimp to lose weight and volume.

2. Chemical Quality Changes

• Chemical changes during freezing and re-thawing affect the nutritional value and stability of shrimp proteins.

A. Protein Denaturation

• Cause: Protein denaturation is a change in the structure of proteins (actin and myosin) that occurs due to the high concentration of solutes between ice crystals and freezing temperatures (although slowly).
• Impact: Denaturation reduces protein solubility and makes the protein unable to retain water, which contributes to drip loss and a decrease in texture. The longer the shrimp is stored frozen, the higher the level of denaturation.

B. Reduced Nutritional Content

• Protein and Minerals: When drip loss occurs during thawing, the released liquid carries with it dissolved nutritional components, such as dissolved proteins and minerals. As a result, the nutritional content of thawed shrimp will be slightly lower than when fresh.

C. Formation of Black Spots (Melanosis)

• Although not caused solely by thawing, the enzymatic activity that causes black spots (melanosis) can continue to occur slowly at frozen temperatures. Temperature fluctuations during freezing and re-thawing can accelerate this oxidation reaction.

Efforts to Maintain Quality

To minimize this quality loss, several things must be considered during the freezing and re-thawing process:

• Rapid Freezing: Use the Individual Quick Freezing (IQF) method or other rapid freezing methods at very low temperatures (around -35°C to -40°C) to produce small ice crystals and minimize cell damage.
• Glazing: Coating frozen shrimp with a thin layer of ice (glaze) to prevent dehydration (freezer burn) and oxidation during frozen storage.
• Best Thawing Method: Re-thawing should be done slowly at cold temperatures (e.g., in a refrigerator at 4°C) or by immersion in cold running water. Thawing at room temperature should be avoided as it accelerates protein denaturation and microbial growth.
• Use of Soaking: Soaking shrimp before freezing in a salt or phosphate solution (e.g., Sodium Tripolyphosphate/STPP) can increase the water-holding capacity of the protein, which has been shown to reduce drip loss after thawing.

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