Quality Changes in Kuruma Prawn during Frozen and Ice Storage

Kuruma prawn Penaeus japonicus was kept frozen at —20°, —30°, —40°, —50°, —60° and — 80°C for 9 months or stored in ice for one week. At due time intervals, the muscle was analyzed for changes in various parameters such as water holding capacity, tyrosine content, protein composition, etc. During frozen storage at —20° and — 30°C, expressible drip increased from 22% at the start to 41 % after 9 months, and tyrosine content from 5 mg/100 g at the start to 15 mg/100 g after 7 months. The pH of muscle showed a little increase. In contrast, all the parameters did not change significantly at or below — 40°C. Muscle protein composition remained roughly constant during frozen storage up to 9 months irrespective of temperatures adopted; 48-63% myofibrillar, 29-36% sarcoplasmic, and 2-12% alkali-soluble plus stroma proteins. One-week ice storage gave results similar to those obtained during frozen storage at —20° and — 30°C. The pH of muscle increased sharply from 7.0 at the start to around 7.9 after one week. From these results, it was concluded that —40°C is reasonable to keep the quality unchanged for a long-term storage, though — 20°C is low enough for a short-term storage up to a few months.