Enzymatic oxidation of polygalactomannans from the seeds of leguminous plants and characterization of an aerogel obtained from fenugreek as a versatile delivery system

Plant polysaccharides are used in a growing number of applications, in their native or in chemically and/or biochemically modified forms. We have previously described TEMPO-mediated oxidation with laccase of polygalactomannans (PGM) from: locust bean (Ceratonia siliqua), tara (Caesalpinia spinosa), guar (Cyamopsis tetragonolobus), sesbania (Sesbania bispinosa) and fenugreek (Trigonella foenum-graecum). Upon laccase/TEMPO oxidation, viscosity of all PGM's increases many folds and structured, elastic, stable gels are formed, which can be degraded by hydrolysis with a ?-mannanase. This phenomenon appears to be directly related to the galactose content of PGM, which follows the decending order fenugreek > sesbania > guar > tara > locust bean > cassia. Thus, it is more pronounced in the case of fenugreek with a Gal : Man ratio of 1 : 1. Indeed, upon laccase/TEMPO oxidation in aqueous solution, fenugreek viscosity increases over fifteen-fold and a strong elastic gel is generated. Native and oxidized PGM were characterized by 1D and 2D NMR spectroscopy and by rheology. When the enzymatic oxidation is followed by lyophilization, a water-insoluble aerogel is obtained, which is capable of absorbing water up to 40 times its own weight and was characterized by: elemental analysis, SEM, IR, NMR, water uptake properties. If the procedure is carried out in the presence of lysozyme, the muraminidase enzyme becomes entraped in the aerogel and can be gradually released in an active form, as confirmed by biochemical and microbiological tests. The entrapment/release of other molecules in under study. We propose that this original "delivery system", composed of an enzymaticall-modified polysaccharide from renewable source, might be a versatile delivery device of active principles for the protection of food and non food products in various type of conditions and packagings.