The role of hydroxypropyl methylcellulose structural parameters on the stability of emulsions containing Spirulina biomass

Hydroxypropylmethyl cellulose (HPMC) samples with varying degrees of substitution of methoxy groups (DS), mass molar substitutions of hydroxypropoxy groups (MS) and molecular weights were used in combination with Arthrospira platensis, a nutritious microalgae, as oil in water emulsion stabilizers. The HPMC samples presented DS ranging from 1.37 to 2.00, MS ranging from 0.23 to 0.85 and average molecular weights (M-w) of 2.5 x10(5) g/mol and 6.7 x10(5) g/mol. Crude extracts of Spirulina were prepared in buffers at pH 6 (CE6) and pH 8 (CE8) by sonication and part of the extracts was centrifuged (CCE6 or CCE8). All extracts contained protein (50%), lipids and phycocyanin and presented mean zeta-potential ranging from - (16 +/- 2) mV to - (20 +/- 2) mV, mean diameter ranging from (108 +/- 52) nm to (306 +/- 68) nm and interfacial activity. The HPMC with the highest values of DS, MS and molecular weight led to the lowest O/W interfacial tension. The combination of CE6 (at 10 g/L) and four different types of hydroxypropyl methylcellulose (HPMC) at concentration range from 0.3 to 1.0 wt% increased substantially the emulsion stability, although the.-potential values decreased one order of magnitude. Particularly, the HPMC (at 1.0 wt%) with the highest values of DS, MS and molecular weight led to the most stable emulsions, due to (i) chains segments arrangements at the interface, (ii) favorable interactions between microalgae proteins and lipids and HPMC chains segments at the O/W interface and (iii) the increase of the emulsion continuous phase viscosity.