Elsevier

Food Chemistry

Volume 279, 1 May 2019, Pages 389-400
Food Chemistry

Impact of Nannochloropsis sp. dosage form on the oxidative stability of n-3 LC-PUFA enriched tomato purees

https://doi.org/10.1016/j.foodchem.2018.12.026Get rights and content

Highlights

Abstract

Microalgae are a sustainable alternative source of n-3 LC-PUFA that can be incorporated into the food chain either via the incorporation of the (intact or disrupted) biomass or by the incorporation of the oil extracted from the biomass. However, the impact of the dosage form on the enrichment of food products with n-3 LC-PUFA and their oxidative stability has never been described before. This study aims to contribute more insight on the impact of the dosage form of the photoautotrophic microalga Nannochloropsis in enriched tomato puree. Three different dosage forms of Nannochloropsis were compared to commercial fish oil and analyzed for their amount of n-3 LC-PUFA, lipid oxidation products, antioxidants and free fatty acids. Tomato purees supplemented with dosage forms derived from Nannochloropsis showed higher oxidative stability than those supplemented with commercial fish oil. The highest oxidative stability was observed for purees supplemented with Nannochloropsis biomass irrespective of whether it was pre-disrupted.

Introduction

Omega-3 poly-unsaturated fatty acids are getting more and more attention since their health benefits have been proven in the areas of brain development and in the prevention of cardiovascular diseases (Calder, 2014). Mainly long chain poly-unsaturated fatty acids (n-3 LC-PUFA), eicosapentaenoic acid (EPA, C20:5 n-3) and docosahexaenoic acid (DHA, C22:6 n-3) are associated with these health benefits whereby an intake of 250 mg n-3 LC-PUFA is recommended daily (FAO, 2010). The potential of photoautotrophic microalgae has already been shown in model systems as an alternative sustainable n-3 LC-PUFA source (Gheysen, Bernaerts et al., 2018). These microalgae are photosynthetic unicellular organisms and the primary producers of n-3 LC-PUFA. They are well known for their limited competition with agriculture and their high growth rate. Moreover, microalgae fit in a vegetarian, and even vegan, diet (Ryckebosch, Bruneel, Muylaert, & Foubert, 2012).

Microalgae can be incorporated into the food chain in different ways: direct incorporation of the whole biomass, direct incorporation of the oil extracted from the biomass and indirect use (microalgal oil or biomass) as an animal feed supplement to enrich animal derived products (Buono, Langellotti, Martello, Rina, & Fogliano, 2014). In previous research, heterotrophic microalgae were always incorporated in food products as oil, while photoautotrophic microalgae were incorporated as intact biomass (Gheysen, Matton, & Foubert, 2018). However, different dosage forms of the same microalga, all resulting in an increased n-3 LC-PUFA content, may each have their own advantages and disadvantages. The use of whole biomass also implies the incorporation of endogenous antioxidants present in the microalgal biomass (Goiris et al., 2012). This may help to increase the oxidative stability of the n-3 LC-PUFA, which are highly susceptible to lipid oxidation due to their large amount of unsaturated bounds (Schaich, Shahidi, Zhong, & Eskin, 2013). The whole biomass can be added as intact biomass or the cells can be (partially) disrupted (e.g. by high pressure homogenization) to promote the liberation of n-3 LC-PUFA and therewith increase the bioaccessibility (Skrede et al., 2011). However, a lower integrity of the cell may also result in a reduced oxidative stability. The economic impact of the supplementary disruption unit operation should be taken into consideration as well (Chacón-Lee & González-Mariño, 2010). Oil extracted from the biomass is another dosage form of n-3 LC-PUFA derived from microalgae. This method may lead to a more straightforward procedure for acquiring novel food status compared to the whole biomass, as some compounds are removed during extraction. On the other hand, the endogenous carotenoids are partially lost by the extraction (Ryckebosch et al., 2014) and the n-3 LC-PUFA present in the oil is not encapsulated anymore. It is hypothesized that this will lead to reduced oxidative stability. Additionally, an expensive extraction step is required to obtain this dosage form (Mercer & Armenta, 2011). To the best of our knowledge, no studies have focused on the impact of dosage form of n-3 LC-PUFA rich microalgae on the oxidative stability of enriched food products. The aim of this study was therefore to investigate this using a tomato puree as a food product.

Previous research in the addition of microalgae to food products has only targeted a small range of products, mainly carbohydrate-rich (bread, pasta, biscuits) and protein-rich (dairy, meat, fish and egg products) food products (Gheysen, Matton, & Foubert, 2018). However, fruit and vegetable based products are essential in a healthy diet as they contain high value compounds like fibers and antioxidants (Darmon, Darmon, Maillot, & Drewnowski, 2005) and are therefore interesting food products to enrich with n-3 LC-PUFA. Gheysen, Bernaerts et al. (2018) already used microalgae as a source of n-3 LC-PUFA in acidic model systems, simulating fruit and vegetable based products. In this study, photoautotrophic microalgal biomass low in free fatty acids (FFA) has been shown to be a potential alternative source of n-3 LC-PUFA with a good oxidative stability. Incorporation of microalgae in real food products also implies the exposure to food processing steps of different intensities. Although this may have a diverse influence on the different microalgal dosage forms used, no research concerning the impact of different processing steps on food products supplemented with photoautotrophic microalgae have been published.

The aim of this study was thus to investigate in-depth the potential of photoautotrophic microalgae as an alternative source of n-3 LC-PUFA in real vegetable based products, and especially consider the impact of different microalgal dosage forms. Three dosage forms of the microalga Nannochloropsis sp. (intact biomass, disrupted biomass and oil) were added to a tomato puree. Nannochloropsis sp. was selected as microalgae because of its potential shown by Gheysen, Bernaerts et al. (2018) and the presence of a tough cell (wall). The presence of the aliphatic non-hydrolysable biopolymer algaenan leads to this tough cell (wall) (Balduyck et al., 2017) and offers the possibility of creating a clear difference between intact and disrupted biomass. The effect of the different microalgal dosage forms, added in an amount to reach a standardized concentration of n-3 LC-PUFA, was investigated in the amount of n-3 LC-PUFA present and in the oxidative stability in the enriched tomato puree. The impact of the dosage forms was also compared to that of fish oil, as the main commercial source of n-3 LC-PUFA. Furthermore the impact of mechanical (HPH) and thermal processing was studied for the different dosage forms as well.

Section snippets

Materials and methods

Solvents used for lipid extraction, determination of n-3 LC-PUFA, FFA, carotenoids, phenolic compounds, ascorbic acid, tocopherols and the measurement of primary oxidation products (chloroform, methanol, ethanol, toluene, hexane, dichloromethane, acetonitrile and ethyl acetate) were HPLC grade and purchased from Carl Roth (Karlsruhe, Germany) or Biosolve (Valkenswaard, The Netherlands).

Characterization of the dosage forms of Nannochloropsis

Three different dosage forms of Nannochloropsis were studied. Intact biomass referred to the biomass as such without further pre-treatment before the incorporation in the tomato puree. Disrupted biomass was pre-treated by a high-pressure homogenization (4 passes at 100 MPa) in order to (partially) disrupt the cell (wall) integrity. The difference in cell (wall) integrity between the intact and disrupted biomass was expressed as the extraction efficiency, which is the extraction yield obtained

Conclusions

The first observed difference between the dosage forms was a lower practicality in handling of Nannochloropsis oil. Stickiness to equipment during mixing and high pressure homogenization resulted in large physical losses. Based on this result, the use of Nannochloropsis oil as n-3 LC-PUFA is not recommended from an economic point of view.

The n-3 LC-PUFA derived from all investigated sources were stable throughout high pressure homogenization, pasteurization and sterilization when incorporated

Acknowledgements

The research presented in this paper was financially supported by the Research Foundation – Flanders, Belgium (FWO SB PhD fellowship L. Gheysen 1S 270 16N and T. Bernaerts 1S 099 16N) and KULeuven (IOF-KP Vegetalgae). We thank Céline Dejonghe for the support with the enriched puree preparation. The authors sincerely thank Åsa Jerlhagen (KU Leuven KULAK, Kortrijk, Belgium) for revising the language of the manuscript.

Conflict of interest

The authors have declared no conflict of interest.

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