Elsevier

LWT

Volume 108, July 2019, Pages 283-288
LWT

Effect of freezing-thawing on weight loss, melanosis, and microbial growth in mildly cooked snow crab (Chionoecetes opilio) clusters

https://doi.org/10.1016/j.lwt.2019.03.083Get rights and content

Highlights

  • Freezing-thawing affected weight loss, melanosis and microbial growth in crab clusters.

  • Melanosis was severe in frozen-thawed compared to clusters refrigerated immediately.

  • Melanosis was the dominant shelf-life limiting factor.

  • Mild cooking is not recommended unless measures to reduce melanosis are adopted.

Abstract

Different mild cooking treatments of snow crab clusters in combination with immediate refrigeration (IR) or freezing-thawing before refrigeration (FBR) have been performed. The clusters were cooked in either fresh or salted (5 g NaCl/100 ml) water at two temperature/time conditions (87 °C/430 s and 96 °C/148 s) both targeting a core temperature of 81 °C in the largest cluster leg. The freezing-thawing affected quality parameters such as weight loss, melanosis and microbial growth (total viable psychrotrophic counts (TVC) and Pseudomonas spp.) during refrigeration. During refrigeration, FBR clusters showed a higher weight loss compared to the IR clusters, and the development of melanosis in the FBR clusters was faster and more severe compared to the IR clusters. Melanosis was also affected by the cooking treatments as the clusters cooked in water at 96 °C obtained better visual quality scores compared to those cooked in water at 87 °C (P < 0.05). In the FBR clusters, the levels of TVC were lower compared to the IR clusters. In summary, melanosis was the dominant shelf-life limiting factor irrespective of freezing-thawing and cooking combinations. Application of such combinations in processing of snow crabs is therefore not recommended unless measures to reduce melanosis are adopted.

Introduction

Snow crab (Chionoecetes opilio) is widely distributed in the North Pacific, the Arctic, the Northwest Atlantic, and in the Barents Sea (Siikavuopio et al., 2017). Its commercial fishery is rapidly growing under the increasing demand for snow crab products, especially in the EU, USA, Japan, and South Korea (Norwegian Seafood Council, 2019). In 2018, 2697 tons of snow crabs were captured in Norway (Norwegian Fishermen's Sales Organization, 2019).

Nowadays, the entire volume of snow crabs landed in Norway is processed into cooked and frozen clusters, i.e., sections of four walking legs and one claw attached to a shoulder (Lian et al., 2018; Norwegian Fishermen's Sales Organization, 2019). Usually, the crabs are processed on-board close to the locations of capture. Upon arrival at the destination market, the clusters are either thawed or kept frozen when displayed at points of sale (Lorentzen et al., 2018).

Cooking of snow crab clusters is usually conducted in boiling water to a target core temperature of at least 91–92 °C in the largest leg of the cluster (Lorentzen et al., 2018). However, it may be desirable to apply milder cooking conditions to reduce the risk of overcooking, which is often associated with a lower yield and a poorer eating quality (Martínez-Alvarez, López-Caballero, Gómez-Guillén, & Montero, 2009). Also, reducing total processing time and saving of energy costs are important drivers for a milder cooking treatment.

Freezing of seafood is an effective long-term preservation method. However, freezing and frozen storage may lead to denaturation and aggregation, especially of myofibrillar proteins, resulting in changes in textural attributes, such as reduced juiciness and water holding capacity (Burgaard, 2010). The extent of this quality loss depends on the rate of freezing, duration of frozen storage, speed of thawing, storage temperature, and temperature fluctuations during storage (Boonsumrej, Chaiwanichsiri, Tantratian, Suzuki, & Takai, 2007). In shrimp and other shellfish, loss of quality during frozen storage is predominately caused by oxidation, denaturation of proteins, sublimation, and ice recrystallization (Löndahl, 1991). These quality losses often lead to off-flavors, rancidity, dehydration, weight loss, loss of juiciness, and toughening (Bhobe & Pai, 1986).

From time to time, snow crab clusters may develop dark blue spots (i.e., melanosis), that can appear shortly after slaughtering (Lian et al., 2018), leading to product rejection by consumers (García-Carreño, Cota, & Navarrete del Toro, 2008). The occurrence of melanosis is linked to the presence of enzymatic phenoloxidase (PO) activity in crab tissues including the hemolymph (Gonçalves & de Oliveira, 2016; Lindberg, Siikavuopio, Øverbø, Lorentzen, & Whitaker, 2017). Melanosis is a potential challenge in snow crabs and other crustaceans, especially in the context of mild cooking treatments (Manheem, Benjakul, Kijroongrojana, & Visessanguan, 2012), as they contain PO enzymes that are highly thermostable (D90 = 3.3–12.0 min) (Huang et al., 2014; Williams, Mamo, & Davidson, 2007).

Psychrotrophic microorganisms such as Pseudomonas spp., Moraxella, Achromobacter and Acinetobacter spp. have been reported to be major contributors to spoilage in blue crab (Callinectes sapidus) (Alford, Tobin, & McClesky, 1942), Dungeness crab (Cancer magister) (Lee & Pfeifer, 1975) and edible crab (Cancer pagurus) (McDermott et al., 2018) during refrigerated storage. During freezing, microorganisms suffer damage which may cause inactivation (Lund, 2000) or death. Death rates are high at the start of freezing, followed by lower inactivation rates during frozen storage. At the same time, microbial growth does not occur at temperatures below −8 °C (Farkas, 2007).

Quality parameters related to the frozen storage of raw mud crab (Scylla serrata) (Mishra & Dora, 2008) as well as raw (Paparella & Tatro, 1971) and cooked blue crab (Webb, Tate, Thomas, Carawan, & Monroe, 1976) have been reported. To our knowledge, corresponding studies for cooked snow crab clusters have not been published. Thus, different mild cooking treatments of snow crab clusters in combination with either immediate refrigeration (IR) or freezing-thawing before refrigeration (FBR) was performed. The clusters were evaluated for weight loss, melanosis, and microbial growth during refrigeration.

Section snippets

Raw material

In March 2017, male snow crabs were harvested using snow crab pots in the Barents Sea (75°30.372 N-33°14.957 E) at depths from 230 to 350 m and stored live onboard in holding tanks. The crabs were transported to the Aquaculture Research Station in Tromsø (Norway) and immediately placed in 6 m3 tanks containing seawater at 3 °C. After a week, the snow crabs were transported live in a dry state, in polystyrene boxes covered with gel ice (Cold Inc., Oakland, CA, USA), from the Research Station to

wt change after cooking and after freezing

Weight change after cooking varied among the four cooking treatments (Table 1). The weight change of “87 °C/430 s” with and without 5% NaCl differed significantly (P < 0.05). In the corresponding “96 °C/148 s” with and without 5% NaCl, the weight change did not differ significantly (P > 0.05), showing that the effect of salt was only present in water at 87 °C. However, the salt content in the leg meat was on average equal to 1.65 ± 0.15%, and it did not differ significantly (P > 0.05) between

Conclusion

The freezing-thawing clearly affected the quality parameters of mildly cooked clusters of snow crab. The weight loss during refrigeration was significantly higher in frozen-thawed clusters compared to the clusters that were refrigerated immediately after cooking. However, neither drip loss or thawing/drip loss was influenced by the different temperature/time conditions of mild cooking.

The freezing-thawing delayed the microbial growth during storage at 4 °C, as suggested by the lower levels of

Declaration of interest

None.

Acknowledgment

This work was partly funded by Nofima and the Bionær program of The The Research Council of Norway (SnowMap, grant number 267763). The authors would like to thank Svein Kristian Stormo and Heidi Nilsen, Nofima, for useful input to the experiment and proof-reading.

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