Elsevier

LWT

Volume 78, May 2017, Pages 8-15
LWT

Water uptake and cooking losses in Octopus vulgaris during industrial and domestic processing

https://doi.org/10.1016/j.lwt.2016.11.087Get rights and content

Highlights

  • Natural octopus has mean moisture and protein of 80.7 and 16.6 g/100 g, respectively.

  • Octopus soaked in freshwater or additives solutions show significant weight gains.

  • Cooking losses significantly higher in freshwater or additives soaked octopus.

  • Moisture/Protein ratio of the octopus muscle can be used to determine water uptake.

  • Fraudulent addition of water occurs in commercial deep-frozen octopus.

Abstract

In view of references to adulteration by water addition and low yield of Octopus vulgaris after cooking, moisture and protein baseline contents and the kinetic of water uptake following processing and cooking were characterized in raw octopus from the Portuguese coast. Water addition and cooking losses were also evaluated in commercial products. Moisture and protein content and moisture/protein (M/P) ratio of unprocessed octopus (n = 265) were 80.7 g/100 g, 16.6 g/100 g and 4.9, respectively. Onboard and on land industrial processing were simulated by soaking in freshwater (1, 4 and 16 h), in 50 g/L sodium tripolyphosphate and 20 g/L citric acid (16 h). Freshwater soaked octopus increased in weight up to 17% after 4 h and M/P ratio to 7.3. Soaked samples for 16 h lost between 14% and 36% more weight after cooking. Citric acid induced one of the highest level of water uptake and the highest water loss after cooking. M/P ratio correlation with weight changes showed that can be used to follow water uptake after landing and industrial processing. Analysis of commercial samples evidenced that consumers are being defrauded. Commercial products showed weight increases up to 50.8% and cooking losses, in general, 20% higher than in unprocessed samples.

Introduction

The common octopus (Octopus vulgaris) is the most important octopus species commercially harvested worldwide being typically marketed fresh, dried salted and frozen (Barbosa & Vaz-Pires, 2004). In Southern European countries, the common octopus is one of the most important fishery resources in terms of value. For example in 2013 in mainland Portugal, octopus landings accounted for 15 percent (€37.6 million) of the total official first sale revenue generated by fisheries and were second only to sardines (16 percent; €39.7 million) (INE, 2014). Octopus is highly appreciated mainly in Mediterranean, South American and Oriental countries and product demand commands high prices throughout the distribution chain. The species sustains artisanal as well as industrial fisheries.

The majority of seafood fraud is related to supplying something different and of inferior quality to the product expected by the consumers, wholesaler, retail markets and food service establishments included. Thus, the perception associated to seafood quality may decrease whenever a product is replaced or another of inferior quality is purchased. In addition, these abusive practices may have a detrimental effect on the consumer's demand for specific seafood products and induce significant economic losses to those conforming to good manufacturing practices. It is therefore of the utmost importance to have reliable products in the market that answer consumer's wishes and expectations.

Media reports regarding food fraud and in particular seafood counterfeit have increased in the last years. Likewise, a diversity of incidents to defraud the general public, restaurants, retailers and other seafood business have been reported (Johnson, 2014; Lou, 2015, Mariani et al., 2014). Driven by the high prices attained octopus is now also under the radar of the media (Coelho, 2013, Deco, 2016) and based on a general public opinion regarding the low yield of these products after cooking, suspicion regarding an excessive water addition that could be deemed adulteration and result in economic fraud for the buyer have been raised (Coelho, 2013, Deco, 2016). However, no scientific information or technical report has been published to date on the water uptake by octopus or on the effect of these weight gains on the cooking yield.

Being an expensive seafood product, octopus is susceptible to abusive industrial processing, both by fishermen and by seafood processors, namely induced water uptake by soaking the individuals in freshwater or in additive solutions. To this effect, advantage is taken of an issue common to cephalopods in general and octopus in particular which is the passive uptake of water into the tissues by osmosis. In fact, according to Wells and Wells (1989) octopus tissues are considerably hyperosmotic compared with the sea water in which it lives and osmotic uptake over the general body surface is likely, and therefore something which the species have to counteract in life. Though not openly spoken or reported, it is generally known among octopus’ fishermen in the South of Europe that placing the octopus immediately after capture in freshwater for 3–4 h increases the weight between 15 and 20%, without significant effects on visual appearance that could be detrimental to price formation at first sale.

The following industrial processing of octopus involves canning or mostly freezing practices. In the processing of frozen octopus the industry frequently uses different additives, such as polyphosphates, citric acid, sodium citrates (approved in the EU) and sodium carbonates (not approved in the EU in unprocessed fishery products, Regulation (EC) No. 1333/2008) to retain moisture and flavor in the products, to prevent oxidation and freezer burns and also to extend shelf life. Providing they are properly used, authorized additives can be valid technological means for aiding seafood processing and maintaining product quality. Nevertheless, excessive or abusive use of these products in seafood is linked to excessive water uptake and economic fraud. As an example of similar high priced products like, Atlantic sea scallops or shrimp are known to absorb excessive water after prolonged soaking in a polyphosphates-water solution (Otwell, 1992, Rippen et al., 1996). Using this type of abusive processing the excess of water uptake falsifies the product's total weight and value when seafood prices are charged for the extra water. For this reason fishery products submitted to a water uptake process are mandatorily accurately labelled to identify this treatment, both in Europe and in the USA. Further and specifically in relation to added water, EU Regulation (EU) n° 1169/2011 (on the provision of food information to consumers) considers in Annex VI (mandatory particulars accompanying the name of the food), that in the case of fishery products and prepared fishery products which have the appearance of a cut, joint, slice, portion, filet or of whole fishery products, the name of the food shall include an indication of the presence of added water if the added water makes up more than 5% of the weight of the finished product.

This empiric knowledge regarding octopus behavior in what concerns water uptake needs a systematic study supported also by baseline studies of the proximate composition of unprocessed octopus samples. As such and taking into account that no scientific information is available regarding the water uptake of octopus, it is the objective of this study (i) to establish baseline data for the composition of octopus in an attempt to better define the moisture and protein content of raw O. vulgaris specimens, (ii) study the kinetic of water uptake, (iii) demonstrate the changes of weight, moisture and protein content in octopus as a consequence of processing with freshwater and additives (polyphosphates; citric acid) and cooking, and (iv) evaluate the quality of commercially available deep-frozen octopus products of the local retail marked, both in terms of added water and cooking losses.

Section snippets

Raw material, processing and sampling

The study was done with octopus (Octopus vulgaris) captured over several months during the years of 2014, 2015 and 2016 in a total of 265 samples from three different areas of the Portuguese coast: Olhão (south) captured in 07–12/2014; 03/2015, Peniche (west) captured in: 10/2014; 02, 11/2015; 02/2016 and Matosinhos (north) captured in: 04, 08/2015; 06/2016. These areas were selected on account of the presence of considerable cephalopod fishing activity (with clay pots and traps), but also

Results and discussion

In South European countries it is common practical knowledge among the octopus fishing value chain, namely those involved in the capture and industrial processing, that octopus is a species that can be increased in weight by the uptake of water. This deviation from processing GMP having as sole objective the weight increase has been surrounded by a certain secrecy and is obviously not declared by the fishermen or processors. When octopus is sold deep-frozen industrial processors list in the

Conclusion

Octopus is a very sensitive species and highly susceptible to weight gain when immersed in water. A weight gain higher than 16% can occur after a 4 h soaking period in freshwater. Considering that in general the time between octopus capture and landing coincides with the interval in which the highest uptake of water occurs (4–16 h), consumers may therefore be at risk of abusive practices, if fresh products are not processed with GMP at all the steps of the fishing industry value chain.

Acknowledgements

This study was supported by the National Project POLQUAL – Valorization and promotion of quality of octopus from the Portuguese coast (PROMAR 31-03-01-FEP-173). Bárbara Teixeira was supported by a postdoctoral grant from the Portuguese Foundation for Science and Technology (SFRH/BPD/92929/2013).

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