Freeze-chilling and gas flushing of raw fish fillets

Abstract

Freeze-chilling involves freezing and frozen storage followed by thawing and chilled storage. Trials with whiting and mackerel fillets/portions (Part 1) indicated no difference in odour scores (raw samples) between freeze-chilled and chilled samples; however, freeze-chilled salmon portions were inferior to chilled in terms of odour. Fresh fillets received the highest acceptability scores as cooked samples followed by frozen, chilled and freeze-chilled fillets. Freshness indicators were the same for the three species. Freeze-chilled fillets had the highest free fatty acid and peroxide values but the levels were low and did not influence sensory response. The effects of the four treatments on the colour and texture of the raw fillets were small in practical terms and typical shelf-lives in the chill phase of the freeze-chill process were 3 to 5 days. In Part 2, modified atmosphere packaging (MAP) was combined with freezechilling to further extend the shelf-life of raw whiting, mackerel and salmon fillets/portions. Typical shelf-lives in the chill phase for the freeze-chilled fillets were 5 (whiting and mackerel) and 7 (salmon) days. Good manufacturing practice coupled with HACCP and careful tempering (thawing) are essential for the successful freeze-chilling of raw fish fillets. Packs should be labelled ‘previously frozen’ for consumer information. It is concluded that freeze-chilling with MAP is a suitable technology for extending the shelf-life of raw fish fillets.