Pumpkin oil addition and encapsulation process as methods to improve oxidative stability of fish oil

Highlights

• Sensory properties of fish oil limit its possible application into functional foods.

• Encapsulation of fish oil with pumpkin oil enhances it oxidative stability.

• Pumpkin oil brings tocopherols, squalene, phytosterols and carotenoids to the blend.

• Rice protein use to blend oil coating significantly reduces fishy odour and flavour.

Abstract

Although seafood is an important part of a healthy and balanced diet, many humans do not consume the recommended amounts of fish or other marine products possibly due to the fishy smell and taste of the products. The aim of this study was to compare the sensory properties and oxidative stability of capsules made of fish liver oil rich in eicosapentaenoic (EPA, 20:5n-3) and docosahexaenoic (DHA, 22:6n-3) acids with capsules made of blend of fish liver oil and thick and dark green pumpkin oil with a nutty aroma and high content of native antioxidants. Sensory quality and oxidative stability of capsules prepared using different coating materials (maltodextrin, whey, sunflower and rice proteins and guar gum) were compared. Blending fish liver oil with pumpkin oil diminished the share of EPA and DHA in the prepared blend, but enriched it in tocopherols, carotenoids, squalene and enhanced almost to 2-fold the oxidative stability. Further growth of oxidative stability (by almost 5-fold) was observed after encapsulation process. Blended oil encapsulated with rice proteins had the least intense fishy and rancid odours and fishy flavour.

Introduction

According to European Food Safety Authority (EFSA), the recommended daily intake of long chain (LC) n-3 fatty acids (mainly EPA and DHA) for healthy adults should be 250 mg for normal function of the heart, brain and maintenance of normal vision, and 2 g or 3 g a day for maintenance of normal blood triglyceride levels, and normal blood pressure (http://ec.europa.eu/nuhclaims/). However, recent review of clinical trials by Petsini, Fragopoulou, and Antonopoulou (2018) showed that EPA and DHA intake varies between 0.03 and 5 g per day, and that triglycerides, high-density lipoprotein and platelet aggregation tended to ameliorate when daily intake exceeds 1 g per day. Additionally, enhanced intake of n-3 fatty acids improves the n-3/n-6 fatty acids balance, disturbed by the widespread intake foods rich in linoleic acid (cereal-based products, poultry, eggs, majority of plant oils, etc.).

Natural sources of LC n-3 PUFAs are marine oils, primarily cold-water fish such as herring, tuna, mackerel, salmon, halibut and oyster (Turchini, Nichols, Barrow, & Sinclair, 2012). One g of LC n-3 PUFAs can be found in 45–60 g of herring, 60–90 g of sardines, 60–135 g of salmon, or 90–106 g rainbow trout (Gogus & Smith, 2010). LC n-3 PUFAs can also be produced by tissue desaturases and elongases from the precursorα-linolenic acid (ALA), but conversion efficiency is estimated at only 8–20% for EPA and 0.5–9% for DHA (Weylandt et al., 2015). Although some plant products like flax, chia and perilla seeds and oils (Ciftci, Przybylski, & Rudzińska, 2012; Dąbrowski, Konopka, & Czaplicki, 2018; Tańska, Roszkowska, Skrajda, & Dąbrowski, 2016) are abundant with ALA (ca. 60% of fatty acids) desired daily intake of these products in order to provide the required amount of precursor may exceed recommended fat content (20–35% of energy from fat), or in the case of chia products recommended daily intake (2 g of oil or 15 g of seeds) (Regulation (EU) 2015/2283).

Although seafood is considered to be an important part of a healthy and balanced diet, many humans do not consume the recommended amounts of fish and other marine products (Christenson, O'Kane, Farmery, & McManus, 2017; Petsini et al., 2018). Fishy smell and taste are on the top of barriers to consumption (Annunziata & Vecchio, 2013; Christenson et al., 2017), followed by texture, presence of bones and dislike of touching, preparing or cooking seafood (Birch & Lawley, 2012). The global organisation for EPA & DHA Omega-3s (GOED) has conducted surveys in nine countries about the main reasons consumers do not try to get more EPA and DHA in their diets (Ismail, Bannenberg, Rice, Schutt, & MacKay, 2016). It has been found that between 7% and 23% of non-users, depending on the country, say the fishy flavour is a barrier to trying an n-3 product (Ismail et al., 2016). So, in population of non-vegans and non-vegetarians, which do not tolerate taste and smell of marine food, delivery of LC n-3 fatty acids could be realised by application of encapsulation to fish oils. Application of encapsulation can protect highly susceptible EPA and DHA against oxidation, which diminishes the risk of nutritional value decrease and harmful compound accumulation. Equally important is the fact that encapsulation may mask the fishy odour and flavour (Ghorbanzade, Jafari, Akhavan, & Hadavi, 2017). It is an important feature of fish oils capsules, since numerous studies indicated key role of sensory characteristics affecting acceptance of functional foods by consumers (Annunziata & Vecchio, 2011, 2013; Urala & Lähteenmäki, 2007; Verbeke, 2006). Unpleasant fish oil smell can also be masked by mixing with selected active agents (e.g. United State Patent US4853247A) or by mixing fish oil with other oils rich in aromas, like pumpkin oil (Poehlmann & Schieberle, 2013). The pumpkin seed oil is thick and dark green with a pleasantly nutty aroma and has a complex flavour that combines nutty, woody and green fruity tones with noticeable roasted notes (https://www.finestfoodage.com/en/oele/kuerbiskern, Poehlmann & Schieberle, 2013).

There are many techniques of encapsulation, but the most frequently used ones are based on spray-drying (Ghorbanzade et al., 2017; Kaushik, Dowling, Barrow, & Adhikaric, 2015). Typically different blends of protein (gelatine, casein or caseinate, whey protein, soy protein, wheat protein, corn protein, egg white powder, etc.), carbohydrates, gums and their derivatives (maltodextrin, highly branched cyclic dextrin, tapioca starch and waxy maize, methylcellulose, derivatised starch/glucose syrup, chitosan, gum Arabic, beta-cyclodextrin, etc.) with other compounds like lactose, trehalose or lecithin are used as wall materials (Kaushik, Dowling, Barrow, & Adhikari, 2015). Although gelatine and whey proteins are predominantly used, plant-derived preparations can be inexpensive alternatives. While various protein isolates and concentrations of cereal grains, oilseeds and pulses are easily commercially available, to the best of our knowledge this is the first study investigating sunflower and rice proteins in the process of fish oil encapsulation.

The aim of this study was to compare the sensory properties and oxidative stability of capsules made of pure fish liver oil rich in EPA and DHA and capsules made of fish liver oil mixed with pumpkin oil, characterised by the nutty aroma and high content of native tocopherols and carotenoids with antioxidant properties. Sensory and stability properties of prepared capsules were also analysed according to composition of capsules wall materials (maltodextrin, whey, sunflower and rice proteins and guar gum). Encapsulation process was conducted using spray-drying technique.