Solvent-free lipase-catalyzed synthesis of long-chain starch esters using microwave heating: Optimization by response surface methodology

Enzymatic acylation of starch

Starch a cheap, abundant and renewable natural material has been chemically modified for many years. The popular modification acylation has been used to adjust rheological properties as well as deliver polymers with internal plasticizers and other potential uses. However the harsh reaction conditions required to produce these esters may limit their use, especially in sensitive applications (foods, pharmaceuticals, etc.). The use of enzymes to catalyse acylation may provide a suitable alternative due to high selectivities and mild reaction conditions. Traditional hydrolase-catalysed synthesis in non-aqueous apolar media is hard due to lack of polysaccharide solubility. However, acylated starch derivatives have recently been successfully produced in other non-conventional systems: (a) surfactant-solubilised subtilisin and suspended amylose in organic media; (b) starch nanoparticles dispersed in organic medium with immobilised lipase; (c) aqueous starch gels with lipase and dispersed fatty acids. We attempt a systematic review that draws parallels between the seemingly unrelated approaches described.

Biosysthesis of corn starch palmitate by lipase Novozym 435

Esterification of starch was carried out to expand the usefulness of starch for a myriad of industrial applications. Lipase B from Candida antarctica, immobilized on macroporous acrylic resin (Novozym 435), was used for starch esterification in two reaction systems: micro-solvent system and solvent-free system. The esterification of corn starch with palmitic acid in the solvent-free system and micro-solvent system gave a degree of substitution (DS) of 1.04 and 0.0072 respectively. Esterification of corn starch with palmitic acid was confirmed by UV spectroscopy and IR spectroscopy. The results of emulsifying property analysis showed that the starch palmitate with higher DS contributes to the higher emulsifying property (67.6%) and emulsion stability (79.6%) than the native starch (5.3% and 3.9%). Modified starch obtained by esterification that possesses emulsifying properties and has long chain fatty acids, like palmitic acid, has been widely used in the food, pharmaceutical and biomedical applications industries.

Deciphering role of amino acids for the stability of Staphylococcus aureus lipase (SAL3)

Lipase from Staphylococcus aureus (SAL3) has been gaining attention because of its potential application in detergent industries against its thermostability and pH stability. It has been also used in synthesis of starch oleate recently. Protein engineering of SAL3 will give insight in development of better lipase for industrial applications. The present work aims at bringing out the role of amino acid residues in the stability of SAL3 using prosa2003 (Protein Structure Analysis) program. 127 amino acid residues were identified as structurally/strategically important for stability of the protein among the modeled 386 residues and further categorized into four classes. In the first class, 47 positions are predicted at which substitution of any one of these 47 positions by any other amino acids will lead to destabilization of the protein. The second class comprises of 33 positions which can be mutated by one corresponding amino acid without affecting the stability of the protein. The third class comprises of 21 positions which can be mutated by two corresponding amino acids without affecting the stability of the protein. The fourth class comprises of 26 positions which can be substituted by three corresponding amino acids without affecting the stability of the protein. Further five residues Glu9, Glu136, Phe286, Lys305 and Leu358 are identified in which substitution by any amino acid does not affect protein stability. Hence mutation can be carried out at these positions in the direction of increasing protein stability. In conclusion, this study prefigures well as a prototype for mutation and protein engineering studies of SAL3.