Perspectives on processing of high value lipids using supercritical fluids

Highlights

• Processing of high value lipids using supercritical extraction and fractionation technologies set to grow further.

• Ultra-high pressure CO₂ extraction greatly increases solubility and extraction rate of seed oils and carotenoids.

• Propane and DME viable alternative extraction solvents for high value lipids and particularly phospholipids.

• Advances in supercritical chromatography will make a broader range of highly pure fatty acids and carotenoids possible.

Abstract

Opinions regarding the state-of the-art, issues and future perspectives for the processing and production of high value lipids using supercritical fluids are discussed including examples from New Zealand. The categories of high value lipids discussed are seed oils, marine neutral lipid extracts and polyunsaturated omega-3 fatty acid concentrates, carotenoid-rich extracts, and phospholipid-rich extracts. Commercial production of carotenoid-rich extracts has been a growth area, particularly astaxanthin-rich oleoresin produced from the micro-algae Haematococcus pluvialis. The main research and development trends observed in the processing of feed streams to produce these high value lipid products are the use of ultra-high pressures for CO₂ extraction, the use of propane and dimethyl ether as alternative extraction solvent, and semi-preparative supercritical chromatography to produce omega-3 concentrates. New product opportunities include phospholipid concentrates from marine and dairy materials, EPA and/or DHA-rich oils and concentrates from GM-modified seeds, and a broader range of carotenoid-rich extracts obtained from microalgae.

Introduction

Lipids are one of the three main macronutrients critical in the human diet, the others being proteins and carbohydrates. There appears to be no standard definition for a lipid, but common features of definitions include not water soluble, fat or oil-like, and of biological origin. Lipids are further categorized as being either neutral lipids and complex lipids. Neutral lipids are generally considered to encompass partial to full glycerides, wax esters, free fatty acids, free fatty alcohols, carotenoids, sterols, tocopherol and lignin-type antioxidants and biologically-derived hydrocarbons. Complex lipids include phospholipids, glycolipids, ceramides, cerebrosides and gangliosides. There are four main classes of high value lipids that are discussed herein. These are: high value seed oils; marine neutral lipid oils including omega-3 concentrates; carotenoid-rich oleoresins; and complex lipid-rich extracts. The state of the art in supercritical processing of these high value lipids was reviewed in 2009 [1]. Here, we present our opinions on the current state of the art including some recent research and development activity and commercial products, a discussion of the issues and gaps in knowledge that are hindering further commercial exploitation; and possible future perspectives. Each category of high value lipid is discussed with regard to these parameters. The possible future perspectives are shown schematically in Fig. 1 with respect to current and possible future extraction solvents, noting however that supercritical CO₂ is still the preferred solvent unless the alternative solvent offers a substantial technical and economic benefit.