Enzymatic synthesis of a b-sitosterol ester in bio-based solvents was compared with conventional solvents. Limonene and p-cymene gave higher initial reaction rates than n-hexane, and comparable conversions after 24 hours (75%). Importantly, a solvent-free system yielded the highest conversion (88%).Due to their structural similarities, b-sitosterol has been proven to reduce absorption of cholesterol in the gut. 1-4 However, in order to use phytosterols as food additives, their properties need to be improved. b-Sitosterol has poor solubility in both water and fat. 5 A high melting point also makes b-sitosterol unsuitable for formulation into foods that require refrigeration. 5 Esterication of b-sitosterol with a food grade fatty acid is a common method used to improve these characteristics. b-Sitosterol esters are now frequently used as natural hypo-cholesterolemic food additives. 6,7 Classically, phytosterols would be reacted with food grade fatty acids or fatty esters via acid catalysed esterication or base catalysed transesterication. 8,9 These reactions are performed at high temperatures which is energy intensive and can cause degradation of the product or lead to by-product formation. In most cases, a post-reaction workup dilutes the catalyst into a low concentration acidic or basic aqueous phase. Catalyst reuse is not possible without extensive drying, and as such neutralisation and disposal is oen carried out instead. 8,9 As the b-sitosterol esters need to be a food-grade product, sufficient purication must be carried out to meet regulatory barriers. 10 Alternatively, the lipase-catalysed esterication of b-sitosterol with fatty acids has been reported for industrial use (Scheme 1). 11 Many lipases have been studied in this reaction giving varying yields based on the nature of the enzyme and of the substrates employed. 12-23 In this work we consider the use of bio-based solvents to complement bio-catalysis. Bio-based solvents are wholly or partially produced from biomass feedstocks. 24 They can be equivalent to conventional solvents (e.g. bio-ethanol) or neoteric molecules. 25 To the best of the authors' knowledge, the lipase-catalysed sterol esterication has not been reported in a range of biobased solvents. 26 Herein, the lipase catalysed esterication of b-sitosterol was investigated in green and sustainable bio-based solvents to give a nutraceutical product. Three readily available lipases were selected for initial studies and the most active enzyme was subsequently used for kinetic studies in a range of bio-based solvents. The objective was to test a range of solvents with dissimilar properties in order to examine and understand the relationship between solvent properties and reaction efficiency.Lipase from C. rugosa and lipase from C. antarctica, CAL-A and CAL-B were investigated. C. rugosa and CAL-A were selected due to their high performance for this type of reaction in the literature, while CAL-B was selected due to its broad applicability. 17,19,20 An enzyme-free control experiment was also ...

This mini-review assesses supercritical carbon dioxide (scCO2) extraction and high-pressure carbon dioxide pre-treatment technologies for valorisation of corn stover agricultural residues with particular focus on showing how these can aid in the creation of a holistic biorefineries. Corn stover is currently the largest source of agriculture residues in the USA, as such there is significant potential for exploitation to yield valuable chemicals. ScCO2 extraction could lead to the recovery of a variety of different chemicals which include flavonoids, sterols, steroid ketones, hydrocarbons, saturated fatty acids, unsaturated fatty acids, fatty alcohols, phenolics and triterpenoids. Importantly, recent studies have not only demonstrated that supercritical extraction can be utilized for the recovery of plant lipids for use in consumer products, including nutraceuticals and personal care, but the processing of treated biomass can lead to enhanced yields and recovery of other products from biorefinery processes. Despite the great potential and opportunities for using scCO2 and high-pressure systems in a biorefinery context their real-world application faces significant challenges to overcome before it is widely applied. Such challenges have also been discussed in the context of this mini-review.