Development of biocatalyst systems for transformation of sucrose into value added bioproducts

Abstract

Considering the drawbacks associated with overconsumption of caloric and cariogenic sucrose, it is desirable to develop enzymatic processes for transformation of sucrose into value added bioproducts. The present doctoral research revealed novel enzyme variants with desirable catalytic properties to convert the caloric and cariogenic sucrose sugar into value-added bioproducts. A novel gene encoding amylosucrase (Asmet) was cloned from the metagenome of a warm water habitat. The gene was expressed and characterized for transglycosylation of sucrose into turanose, a non- cariogenic isomer of sucrose exhibiting low-glycaemic response and suppressive effect on lipid accumulation. The maximum sucrose to turanose conversion yield of about 47% was achieved. Asmet enzyme molecules were immobilized onto iron nanoparticles, which resulted into recyclable nano-biocatalyst for turanose production. Further, Asmet transglycosylation activity was also exploited for the biosynthesis of another glycosylated product, arbutin, from hydroquinone and sucrose. Arbutin is a pharmaceutical molecule for decreasing hyperpigmentation in melanocytes. The maximum hydroquinone to and#945;-arbutin conversion yield of about 70% was achieved. A novel gene for trehalose synthase (TreM) was cloned from an extreme temperature aquatic habitat metagenome. The gene was expressed in a heterologous host. TreM was characterized for transglycosylation of sucrose and maltose into the rare sugars, trehalulose and trehalose, respectively. Trehalulose is a low-glycaemic and antioxidant isomer of sucrose. Trehalose is a cryoprotectant molecule with moderate glycaemic index and low insulin response. The maximum sucrose to trehalulose bioconversion was 90%, and maltose to trehalose was 74%. Both the functional sugars are useful in food and pharmaceutical industries. Furthermore, by employing levansucrase from Leuconostoc sp. the transformation of sucrose was done into levan, a prebiotic and antimicrobial polymer of D-fructose.