Is raw better? A multiple DNA barcoding approach (full and mini) based on mitochondrial and nuclear markers reveals low rates of misdescription in sushi products sold on the Italian market

Highlights

• A two years-survey was carried out on sushi products sold in Italy at retail level.

• 185 sushi samples were collected and subdued to DNA barcoding analysis.

• A low misdescription rate (3.3%) was found.

• Results reflect a proper training of FBO towards labelling.

Abstract

New dietary habits have favored an ever growing popularity of Eastern country cooking style and in particular of sushi. Even though the Reg. (EU) 1379/2013 does not apply to restaurants and caterers, the Reg. (EU) 1169/2011 establishes that all the information they provided to the final consumer have to meet the transparency requirements as regards the description of the ingredients used for the preparation of food. The present study aimed at performing a molecular based survey to identify the seafood species used in the sushi preparations at the retail level. A total of 185 samples were collected from sushi venues and supermarkets and DNA barcoding, followed by a pairwise divergence and Neighbor Joining clustering analysis, was applied in order to verify the information declared at purchase. Rather than to a proper training of Food Business Operators working at the catering level, the low mislabeling rate found in this study (3.4%) could be ascribed to the standardization of the products sold in ethnic restaurants. In fact, the common practice of proposing standardized menus always relying on the same species of fish could limit the risk of mislabeling occurrence.

Introduction

Ethnic foods are increasingly present in Western dietary habits as a result of last decades' trade globalization, innovation in conservation technologies, improvement of transportation networking and increasing migrations phenomena that contribute to the crossing and overlapping of different food spheres (Stano, 2015). Sushi, literally ‘seasoned rice’, is a typical Japanese bite-sized food prepared with acidified rice and various toppings and fillings based on seafood, seaweed and vegetables. This product has become increasingly popular among European consumers thanks to its nutritional properties and refined presentation (Mouritsen, 2009), perfectly matching the consumer appeal for a “high culinary aesthetic”. Subsequently, the promotion of prepackaged ready to eat sushi, also available in supermarkets, contributed to the product accessibility (Hsin-I Feng, 2012). Finally, the increasing business around sushi has been boosted following the diffusion firstly in the United States and later in Europe of low cost sushi bars and take-away venues, generally owned by people of not-Japanese origin (Cwiertka, 2005, Hsin-I Feng, 2012). In Italy, for example, sushi bars and wok-sushi are mainly managed by Chinese restaurateurs (Mudu, 2007). In these venues strong limits in hygiene management procedures and products traceability have been found, leading to lack of conformities in health and commercial requirements (Armani et al., 2015a, Guidi et al., 2010).

A great variety of seafood is currently used for sushi making, including: tuna, salmon, swordfish, yellowtail, white muscle fishes (e.g. sea bass, gilt head seabream), preserved fish (e.g. smoked eel, smocked mackerel), octopus, squid, shrimps or prawns, scallop and flying fish roes (Mouritsen, 2009). Sushi based specialties are generally presented to the final consumer with the phonetic translation of the original Japanese script using Latin alphabet (Stano, 2015) together with a brief description of the ingredients. In particular, the name of the seafood category (e.g. “shrimp” “tuna”) and not the specific official denomination is usually reported (authors’ note).

The EU fishery and aquaculture products' market is regulated by Reg. (EU) 1379/2013, which introduced specific requirements for a common organization of the market and establishes traceability and labeling rules both for caught and farmed seafood, integrating the mandatory provisions of Reg. (EU) 1169/2011 on food labeling. The Regulation applies to pre-packed and non-prepacked products sold along the supply chain and at retail level even including restaurants and caterers (Chapter I, Art. 5, g). However, restaurant owners are not required to detail all label information on their menus during administration to the final consumer, except for specific indications concerning allergens and mandatory information on specific products (raw fish and cooked crustaceans) that fully fall within the scope of Reg. (EU) 1379/2013 (Art. 35). Restaurateurs are nonetheless required to maintain and make available all the information for the authorities or the consumers at their request (D’Amico, Armani, Gianfaldoni, & Guidi, 2016). Therefore, all information provided to the consumer have to meet the transparency requirements defined by the EU Reg. (EU) 1169/2011 as regards the general description of the product.

Recent studies pointed out restaurants and catering activities as a potential weak link of the traceability system with respect to seafood mislabeling (Bérnard-Capelle et al., 2015, Vandamme et al., 2016, Warner et al., 2013). Mislabeling and misrepresentation of seafood have major consequences for both consumers and producers in terms of human health risk and economic losses. Moreover, they can affect the conservation status of overfished or endangered species. Finally, they can foster illegal, unreported and unregulated (IUU) fishing (Helyar et al., 2014, Jacquet and Pauly, 2008, Mariani et al., 2015).

Molecular biology methods based on sequencing, particularly the DNA barcoding approach, have proven as effective tools in fish species identification. Mitochondrial DNA genes, have emerged as near-universal markers for this purpose (Armani et al., 2016, Clark, 2015). At present the COI gene is the most targeted and exploited mitochondrial marker, thanks also to the ever improving international molecular identification system FISH-BOL (www.fishbol.org) and to the continuous updating of the reference sequences databases (Hanner et al., 2011, Ward, 2012). However, nuclear genes can also represent alternatives target for species discrimination and phosphoenolpyruvate carboxykinase (PEPCK) and sodium–potassium ATPase a-subunit (NaK) have been successfully applied in phylogenetic studies within Penaeoidea providing a useful instrument for the classification of these species (Ma et al., 2009, Tsang et al., 2008). Finally, the application of COI Mini DNA Barcoding protocols (Armani et al., 2015a, Armani et al., 2015b) or the selection of alternative genes, such as the 16S rRNA gene (Armani et al., 2016), represent a useful approach.

Barcoding techniques applied from 2009 to these days to investigate seafood labeling at the retail level (restaurant, grocery stores, take away venues) (Table 1), pointed out divergent results on the species substitution rate on the European and US market. From these studies a lower rate of frauds of the European market with respect to the US is evident. Given the few studies available on sushi products at the European level, conducted particularly in the UK, France and Belgium (Vandamme et al., 2016, Bérnard-Capelle et al., 2015; Oceana, 2015) and the lack of similar studies in Italy, a two years-survey was carried out on sushi products, in particular nigiri (fish topped rice ball), hosomaki and uramaki (fish filled rice roll), directly purchased from restaurants, self-services, take-away bars and grocery markets located in four different provinces in Tuscany (Pisa, Florence, Leghorn and Lucca). The aim was to verify the authenticity of the products and assess the level of misdescription by a multiple DNA barcoding approach (full and mini) based on mitochondrial and nuclear markers. Results will also provide data on the rate of species substitution at the end point of the seafood chain.