Optimization and validation of methods for the determination of lipid composition in macroalgal matrices – characterization of undervalued red and brown macroalgae species

Abstract

Red and brown macroalgae are a natural source of bioactives, like polyphenols, carotenoids and polyunsaturated fatty acids (PUFA), with several industrial applications, including food and feed. Polar lipids (PL), such as glycolipids (GL), are an important fraction of macroalgae lipids standing out due to their antiviral, antioxidant, anti-inflammatory and antimicrobial activities. The present work aimed to optimize and validate an analytical protocol, based on an HPTLC (High Performance Thin Layer Chromatography) method, for the characterization of macroalgae lipid classes. Two extraction protocols were considered: Folch and Bligh and Dyer. The lipid composition of two red (Asparagopsis armata and A. taxiformis) and brown algae (Treptacantha abies-marina and Cystoseira humilis) were studied, along with the effect of drying conditions: sun and shade. Total lipid (TL) content ranged between 1.89-2.43% dw, in C. humilis (shadedried, Folch) and A. armata (shade-dried, Bligh and Dyer), respectively. Both shade-dried Asparagopsis (Folch method) were the exception, showing higher contents: 3.15 and 3.20% dw (A. armata and A. taxiformis, respectively). The PL were globally the most abundant, especially in A. taxiformis (74.3 to 88.1% of TL, sun- and shade-dried, respectively). Among PL, monogalactosyldiacylglycerol (MGDG) was predominant, while triacylglycerols (TAG) and diacylglycerols (DAG) were predominant in non-polar lipids. The highest PUFA contents were observed in brown macroalgae, leveraged by high contents of arachidonic acid (ARA, 20:4 n-6), representing 14.0-17.4% of total fatty acids (FA) (sun-dried Cystoseira and shade-dried Treptacantha, respectively). Red algae, instead, contained mainly saturated fatty acids. The brown algae FA profile of PL highlighted phospholipids as the fraction with the highest PUFA amounts (40.7 and 43.5%, for Cystoseira and Treptacantha, respectively), where ARA accounted nearly 50% of total PUFA. Considering the ARA benefits including antitumoral activity and reduction of farmed fish larval stress, both C. humilis and T. abies-marina may be beneficial if incorporated in food and feed formulations.