Synthesis, characterisation and physicochemical properties of hydrophobically modified inulin using long-chain fatty acyl chlorides

Abstract

A B S T R A C TA series of inulin derivatives were synthesized in aqueous solution using acyl chlorides with varying alkyl chain length (C10-C16). They were characterised using a number of techniques including MALDI TOF-MS, 1 H NMR and FTIR and their degree of substitution determined. The solution properties of the hydrophobically modified inulins were investigated using dye solubilisation and surface tension and it was confirmed that the molecules aggregated in solution above a critical concentration (critical aggregation concentration, CAC). The value of the CAC was found to be reasonably consistent between the different techniques and was shown to decrease with increasing hydrophobe chain length. It was found that the C10, C12 and C14 derivatives formed stable oil-inwater emulsions and the emulsion droplet size decreased with increasing alkyl chain length. The C16 derivative was not able to produce stable oil-in-water emulsions; however, it was able to form stable water-in-oil emulsions. The fact that the derivatives are able to form micellar-like aggregates and stabilise emulsions makes them suitable candidates for the encapsulation and delivery of active compounds with potential application in food, cosmetic, personal care and pharmaceutical formulations.

Potential applications of hydrophobically modified inulin as an active ingredient in functional foods and drugs - A review

“…This graft copolymer has widely been used as an emulsifier due to the multipoint attachment of its particles or droplets and high degree of hydration, with more than 97 % purity of the end product ( Exerowa et al, 2007 , 2009b ; Exerowa & Platikanov, 2009 ; Gotchev et al, 2007 ; Nestor et al, 2007 ; Stevens, Meriggi, Booten et al, 2001 ; Tadros, 2017 ). Consequently, several authors have documented the modification of inulin by esterification, etherification, and carboxymethylation using fatty acid methyl esters (FAMEs), fatty acid acyl chlorides, alkyl epoxides, and alkyl isocyanates or by alkenyl succinic anhydrides, mainly in organic solvents and environmentally friendly aqueous solvents ( Exerowa, Gotchev, Gotchev et al, 2009 ; Exerowa & Platikanov, 2009 ; Morros, Infante, & Pons, 2012 , 2011 ; Morros et al, 2010a ; Morros, Levecke, & Infante, 2010 ; Nestor et al, 2007 ; Stevens, Meriggi, Booten et al, 2001 , 2001b ; Gotchev et al, 2011; Khristov & Czarnecki, 2010 ; Zhu et al, 2018 ; Hartzell, Maldonado-Gómez, Yang, Hutkins, & Rose; Han et al, 2015 , 2017 ; Kokubun et al, 2013 ). Thus, it is important to divide the chemical modification reactions of inulin based on the types of anhydride and types of reaction medium, which will be discussed below.…”

“…Normally, the high reaction efficiency is very desirable. Furthermore, the same research group has produced different types of HMI derivatives ( Han et al, 2017 ) and alkenylated inulin samples (OSA, DDSA, TDSA, HDSA, and ODSA) ( Han et al, 2015 ). The former derivatives were synthesized using fatty acid acyl chlorides with varying alkyl chain lengths (C10-C16), while the latter samples were formed using alkenyl succinic anhydrides (ASAs) with a wide range of alkenyl chain lengths (C8-C18) in aqueous solution.…”

“…DS 2 C 16 was unable to form O/W emulsions; however, it could form W/O emulsions. Han et al (2017) Inutec®SP1 Inutec®SP1 was formed by carbamoylation using dodecyl isocyanate in an aprotic solvent to obtain inulin dodecyl carbamate. HMI emulsions were prepared using three stages.…”

“…Moreover, Khristov and Czarnecki (2010) and Gotchev et al (2011) revealed that the size of the loops of inulin molecules at the interface depended on the alkyl chains attached to it. Furthermore, the experimental results regarding the stabilization of emulsions motivated the interrogation of O/W and W/O emulsions, which were prepared through varying concentrations of oils ( Han et al, 2017 ). The stability of the emulsions was evaluated for several inulin derivatives, which were synthesized with various alkyl chain lengths (C 10 -C 16 ).…”

“…Moreover, various types of inulin derivatives have been produced by the reaction of inulin with fatty acid methyl esters (FAMEs), fatty acid chlorides, alkyl epoxides, and alkyl isocyanates ( Exerowa & Platikanov, 2009 ; Exerowa, Gotchev, Gotchev et al, 2009 Gotchev et al, 2011; Khristov & Czarnecki, 2010 ; Stevens, Meriggi, & Booten, 2001 , 2001b ). In consideration of environmental issues with the development of industrialization, a green methodology has been established to synthesize different types of inulin derivatives with varying alkenyl chain lengths and varying degrees of substitution (DSs) by using alkenyl succinic anhydrides in an aqueous environment under mild alkaline conditions ( Han, Ratcliffe, & Williams, 2015 ; Han, Ratcliffe, & Williams, 2017 ; Kokubun, Ratcliffe, & Williams, 2013 ; Kokubun, Ratcliffe, & Williams, 2015 ; Kokubun et al, 2018 ; Morros, Levecke, & Infante, 2010 ; Morros, Levecke, & Infante, 2011 ). It was revealed that these types of inulin derivatives adsorbed at the liquid-liquid interface, solid-liquid interface, and air-water interface and produced micellar-like structures in the solution above a critical concentration.…”