Improvement of gastronomical properties of duck Foie gras by high hydrostatic pressure
Introduction
Foie gras is a popular French dish, which is prepared from the liver of specially fattened geese or ducks. It is considered as a delicacy in cuisine, with a high added value, and its flavour is described as rich, buttery and delicate. Fresh foie gras, due to its particularities and higher quality, is the type mostly used in restaurants, and economically the most important for supplier industry.
Due to its high fat content, its preparation must be delicate and accurate and the contact with heat during cooking needs to be brief. If not, fat melts and its appreciated characteristics vanish. In fact, the technological yield is the principal quality trait and it is evaluated by the loss of fat during cooking (Théron et al., 2011). This fat loss constitutes a recurring problem for cooks and their customers because it influences the uniformity and appearance of the finished product.
To offer a high-quality product, there are some culinary techniques that assure a good texture and slightly extend in shelf life. A good example for foie gras treatment in restaurants is sous-vide cooking (French words for “under vacuum”) (Armstrong and McIlveen, 2000; Baldwin, 2012), developed by the catering industry to prepare food reducing the microbiological risk that appears during manipulation (Sebastiá et al., 2010). Beyond microbial safety, the sous-vide process has been established by chefs to assure optimal texture and flavour of the cooked product (Keller, 2008). In restaurants, the final product obtained by this method is also valuable because of its unique flavour and texture. However, this technique usually requires a huge and specialised control of the process (packaging, internal temperature, time …) to obtain the desired result and it is a long time-consuming process.
Thus, new tendencies looking for novel techniques and technologies to improve the appearance and texture of dishes have been accomplished, taking advantage of the discoveries and advances in science to impact the chemical behaviour of proteins, starches and fats. In fact, the continuous search for new transformation tools have characterised this field in the last decades.
The application of HPP is already accepted as a food treatment for a variety of reasons. Among other motives, HPP is known to respect covalent bonds (Cheftel, 1992), thus it can retain food quality and natural freshness while extending microbiological shelf-time (Cheftel, 1995). In a classical pressurization process product does not reach high temperatures (max. 25-30 °C) and consequently, high pressure processing is appropriate for decontamination of food products sensitive to heat, as foie gras is. HPP has already demonstrated to be useful to reduce microbial load of other heat sensitive product as meat and fish refrigerated products (Hayman et al., 2004; Hurtado et al., 2000; Lamballerie-Anton et al., 2002) while maintaining their sensory quality. Furthermore, the applications of this technology are wide, beyond microbial decrease. For example, high hydrostatic pressure can be used for functional protein modification (Bajovic et al., 2012; Cheftel and Culioli, 1997; Messens et al., 1997), increase bioactive compounds and micronutrients bioaccessibility and bioavailability (Barba et al., 2015), the reduction of bitterness on juices and for food texturization (Dumoulin and Hayashi, 1998).
There are some previous studies focused on the effect of high pressure in entire foie gras (duck liver) (André et al., 2015; Ballestra et al., 1999; Cruz et al., 2003; El Moueffak et al., 1996, 2001). However, these authors focused their study on the combination of pressure with mild temperature (50-60 °C) intended for microbial inactivation. Thus, there is still a lack in the study of the potentiality of HPP, applied at temperatures under 30 °C, in quality and cooking behaviour modifications in this product after treatment.
Accordingly, this work is focused on the study of effect of high-pressure processing (HPP) at low temperatures in culinary properties and behaviour of the final foie gras product, which is of interest to offer a high-quality basis material to restaurants and interested industry. In order to obtain a product with distinctive properties, the effect of the raw material, pressure and time of treatment on the final product quality are discussed in relation to the obtained texture, evidence of structural modifications and behaviour in expert cooking and sensory tests.
Section snippets
Foie gras preparation
Raw duck fatty livers from Mulard ducks were supplied by two different authorized manufacturers with different production methods in Spain, immediately after slaughter.
Bleeding and deveining of livers were carried out in a water circulatory bath (Roner Compact, ICC, Barcelona, Spain) with accurate controlled temperature at 30 °C by immersion in a mixture (1:1 v/v) of distilled water and full fat pasteurized milk and 5% (p/v) of fine salt: Briefly, liver lobes were separated, extremes were cut
Effect of raw material on product quality after pressure treatment
Preliminary tests were carried out to evaluate the behaviour of foie gras from different origins (different production methods) after high pressure treatment, to check the suitability of the technology for obtaining a top-quality product from the sensory point of view. Two different foie gras production methods were tested: Traditional production at small scale with controlled natural feeding (called A) and intensive production (codified as B). Samples were subjected to different pressure
Conclusions
French “foie gras” is a coveted dish with a high added value. Due to its high price, fat loss during cooking constitutes a frequent problem affecting the profitability of the product for the restaurants and consumers, also disturbing the uniformity of the finished product and its sensorial characteristics. As it has been proved in this work, high hydrostatic pressure can be used for improvement of the characteristics and the preservation of high-quality products. From a gastronomical point of
Acknowledgements:
This work was possible thanks to the funding from the Basque Government thought the projects “TECALFUT: Tecnologías para el Desarrollo de los Alimentos del Futuro” and “GATACA: Innovación Gastronómica derivada de la interacción Ciencia-Tecnología-Cocina”.
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2019, World's Poultry Science Journal