The changes in the release level of polyunsaturated fatty acids (ω-3 and ω-6) and lipids in the untreated and water-soaked chia seed

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Highlights

  • Soaking Chia seed in water for 24 h improves extractability of ω fatty acids.

  • Soaking Chia seed in water for 24 h enhances the ω6:ω3 ratio.

  • Phosphatidylcholines, diacylglycerols, and triacylglycerols were major lipid classes.

  • Major identified lipids mainly present in the endosperm of Chia seed.

Abstract

Despite recent studies on health benefits of chia seed owing to its high content of ω-3 fatty acids, little work has been conducted on extractability of its nutrients. We examined the effect of soaking chia seed in water on the extractability of its omega fatty acids and lipids. State-of-the-art mass spectrometry techniques including GC-MS, LC-MS, and MALDI-MSI were utilized to identify and determine the spatial distribution of omega fatty acids and lipids in chia seed. Results showed that 24 h soaking in water improves the extractability of omega fatty acids and the ω-6:ω-3 ratio. Increase in the release levels of triacylglycerols and diacylglycerols and reduction in the release levels of phosphatidylcholines are envisaged to be the result of cell wall weakening and consequently availability of lipids for extraction. Results of MALDI-MSI show that highly abundant lipid species are mainly localised in the chia seed endosperm rather than its mucilage.

Introduction

Increasing interest in maintaining a healthy human lifestyle has prompted recent investigations on novel functional foods such as chia seed with significant nutritional and disease prevention characteristics (Loaiza, López-Malo, & Jiménez-Munguía, 2016; Patel, 2015). Chia seed is an exciting superfood which could potentially reduce risks of chronic diseases such as cardiovascular disorders, diabetes, inflammatory diseases and nervous system disorders due to its unique functional and nutritional properties (Muñoz, Cobos, Diaz, & Aguilera, 2013).

Chia (Salvia hispanica L.) is an annual oleaginous plant which originated from Central and Southern America and belongs to the Lamiaceae family (Anacleto et al., 2016). Chia seed was historically cultivated and consumed by Central American civilizations and formed one of the main ingredients of their diet (Anacleto et al., 2016). Today, chia seed is a popular gluten-free grain that is widely used as whole seed, oil, and flour in various food products such as multigrain bread, cereals and nutritional bars (de Falco, Amato, & Lanzotti, 2017). Chia seed contains considerable quantities of carbohydrates (42.12 g/100 g), fat (30.74 g/100 g), dietary fibre (34.4 g/100 g) and protein (16.54/100 g) (DARS, 2018; Carrillo et al., 2018). In addition, it contains antioxidants, minerals and vitamins (de Falco et al., 2017; Marité et al., 2018). In 2009, the European Parliament considered chia seed as a novel food ingredient and recognized its marketing as a healthy nutritional element at a commercial level (Parker, Schellenberger, Roe, Oketch-Rabah, & Calderón, 2018). In addition, the Food and Drug Administration (FDA) approved chia seed as a safe novel food which is exempt from food and safety regulations (Mohd Ali et al., 2012).

Chia seed is rich in polyunsaturated fatty acids (PUFAs) including α-linolenic acid (ALA, 18:3 ω-3; 50–67%) and linoleic acid (LA, 18:2 ω-6; 12–20%) and a monounsaturated fatty acid (MUFA), oleic acid (OA, 18:1 ω-9; 7.2–10%) (de Falco, Fiore, Bochicchio, Amato, & Lanzotti, 2018; Orona-Tamayo, Valverde, & Paredes-López, 2017). Unlike OA that can be synthesized in mammalians, LA cannot be converted into ALA due to the lack of ω-3 (or Δ-12/Δ-15) desaturases enzymes in the human and animal bodies (Glick & Fischer, 2013). Therefore, only a diet which is rich in in omega-fatty acids (FAs), can supply these essential fatty acids (EFAs) to the human and animal bodies. Chia seed can act as a potential ω -3 supplement (Johnson & Bradford, 2014).

Reports in the literature show that unhealthy eating habits in the modern diet have caused an enormous increase in the accumulation of saturated and unsaturated FAs such as ω-6 in the human body which leads to an unacceptable ratio of ω-6:ω-3 FAs (being 20:1 instead of 1:1) (Simopoulos, 2016). The ω-6:ω-3 ratio in chia seed is 0.27–0.32 (being <1), better than other popular oil crops such as olive (13.17), canola (2.18) and soybean (7.50) (Castejón & Señoráns, 2018; Ciftci, Przybylski, & Rudzińska, 2012). Chia seed being rich in ω-3 FAs and with a preferable ω-6:ω-3 ratio could potentially contribute to rebalancing this ratio and enhance general well-being by reducing the risk of degenerative diseases (Simopoulos, 2008).

PUFAs are vital in brain and nervous system development, development of eyes in fetus and in defeating cardiovascular diseases, cancer and coronary heart disease (Bourre, 2004). In addition, ω-3 PUFAs have an important function as secondary messengers involved in signaling, and have anti-inflammatory, antiviral, anti-fungal and antibiotic-like properties (e.g. LA kills Staphylococcus aureus) (Bourre, 2004; Johnson & Bradford, 2014; Ruxton, Reed, Simpson, & Millington, 2004). Today, the primary sources of ω-3 supplements are fish oils, where ω-3 FAs usually comprise 30% to 50% of total FAs (Surette, 2008). However, several health-related researches have expressed concerns about the sustainability of the fish industry, both wild and farm fish, as they are not likely to meet the increasing demand for producing enough ω-3 FAs (Lenihan-Geels, Bishop, & Ferguson, 2013). Consequently, the attention of many researchers has turned to the investigation of biosynthesis, health benefits and functional roles of ω-3 FAs derived from various plant species.

Perhaps the bioavailability and digestibility of the PUFAs are the most crucial factors that need to be considered in the development of functional foods. To the best of our knowledge, there is no evidence that shows consuming untreated chia seed could lead to an adequate release of omega FAs in the human digestive system. It is envisaged that due to the small size of the chia seed and the hardness of the seed coat, the human digestive system might not be successful in extracting PUFAs from the untreated seed without mechanical intervention. However, pre-treatment and/or pre-cooking methods such as soaking in water or grinding might improve the bioaccessibility of PUFAs. Therefore, here we investigated the difference in the amount of total FAs and lipids when chia seed is soaked in water compared to the untreated chia seed. The effect of the extreme acidic condition that may exist in the stomach during the digestion on the extractability of the chia seed's omega-FAsand lipids was determined.

Section snippets

Reagents and materials

Chemicals including hydrochloric acid (HCl), ammonium formate (CH5NO2), ammonium hydroxide (NH4OH), and butylated hydroxytoluene (BHT) were purchased from Sigma-Aldrich (Sydney, Australia). GC-MS derivatization reagent Meth-PrepTM II (0.2 N methanolic solution of m-trifluoromethylphenyl trimethylammonium hydroxide) was purchased from Grace Davison Discovery (Victoria, Australia) and GC-MS internal standards (ISTDs) including fatty acid methyl ester mix (Supelco 37 FAME Mix), C19 nonadecanoic

Calibration standards

Calibration standards with different concentrations (Supelco 37 FAME Mix) were prepared for the identification and comparison of the retention times and mass spectra (unique qualifier ions) as previously described in (Jayasinghe & Anthony Dias, 2013). The concentration (pmol.mg-1) of the detected compounds from seed extracts were measured based on the regression formula obtained from the calibration standards.

GC-Q-MS conditions

Samples were reconstituted in 25 μL of 2:1 v/v chloroform:methanol and 5 μL of

Sample preparation for MALDI-MSI

Dry chia seeds and seeds soaked in water for 2 h were embedded in SCEM matrix in the stainless-steel embedding container for matrix assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) (SolariX™ XR technology, Bruker®, USA). An isopropanol:dry ice slurry was used for making SCEM frozen block containing chia seeds. A Leica CM1860 cryotome (Leica Biosystems, Mount Waverly, VIC, Australia) was used for sectioning and mounting the samples as described in (Boughton &

Total fatty acid analysis using GC-MS

The concentration of total of FAs in chia seed w/o treatment was measured using GC–MS. Fig. 1 shows the amount of ω-9, ω-6, and ω-3 FAs in the control group and the effect of three treatments on the extractability of the total FAs. The low concentration of FAs in Fig. 1 compared to the reported values in the literature (Ayerza (h) & Coates, 2011) are due to the extraction method used in this study. This allowed us to clearly see the effect of soaking on the extractability of FAs; whilst a

Conclusion

In this work, several metabolomics approaches were used to investigate the extractability, lipid content, and spatial distribution of lipids and omega FAs in chia seed and its mucilage. The focus was the effect of soaking chia seed in water on the extractability of lipids and total FAs, especially ω-3 PUFAs. The GC-MS results demonstrated that soaking chia seed in water for 24 h can improve the extractability of FAs, especially ω-3 FAs, in contrast to dry chia seed. In addition, this treatment

Conflict of Competing Interest

The authors confirm that there is no conflict of interest.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Acknowledgement

The authors would like to thank Metabolomics Australia (School of BioSciences, The University of Melbourne, Australia), which is a National Collaborative Research Infrastructure Strategy initiative under Bioplatforms Australia Pty Ltd. (http://www.bioplatforms.com), for access to GC-MS, LC-MS and MALDI-FT-ICR-MS instrumentation.

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