Association of anionic polysaccharides and starches to vehiculate anthocyanins

Ionotropic gelation is a technique for producing of hydrogels that allows encapsulating sensitive substances to ensure their functional properties. Negatively charged biopolymers chains, as anionic polysaccharides, form gels in the presence of cations, providing a three-dimensional structure. The addition of other polysaccharides in the network, such starch, can resulting to changes in the gel characteristics, modulating its properties and; thus, its end-use. This work aimed to develop microgels formed from the combined addition of anionic polysaccharides (gellan gum (GG) or alginate (AG)) and different starches (corn (CS), potato (PS) or phosphated (PPS)) to vehiculate anthocyanins. To prepare the microgels, the anionic polysaccharides (1% w/w) (GG or AG) were solubilized in deionized water, for 20 min, at 90 ºC, followed by the addition of starch (CS, PS or PPS) (1% w/w). The mixture remained for 20 more minutes at 90 ºC for the gelatinizing the starch granules. After that, the solutions were cooled until 40 ºC, and anthocyanin extract (0.5% w/w) was added. The systems were atomized in calcium chloride solution (150 mM), for gelation. The rheological behavior of the solutions was evaluated and the microgels were analyzed according their ability to retain anthocyanin (EE), particle size distribution, and morphology. The microgels prepared with AG showed smaller D3,2 in comparison with GG, independently of the starch source, which was associated to the smaller consistency index (k) found for AG, that facilitated the formation of droplets during the atomization process. Furthermore, the addition of starch in the biopolymeric network was determinant for the particle size, once larger starch granules, as PS, resulted in larger microgels (> D3,2) for both AG and GG. Considering the microscopies, microgels containing PS presented better distribution of amylose and amylopectin molecules in the network; while microgels with CS and PPS exhibited evident remaining starch granules located on the surface of the particles. This fact probably contributed to small irregularities observed in the particle surface for those formulations. Regarding the entrapment of anthocyanin, it was found that alginate microgels presented higher EE (≥ 84%) than gellan microgels (< 81%). Such result could be explained by interactions between anthocyanin and alginate that increased the solution viscosity before the atomization. In general, results showed that microgels produced with alginate were better than gellan gel formulations, once the smallest size of particles can be associated with lower sensory perception of structures when added to foods. In addition, alginate microgels provided better retention of the bioactive compound, without differences between the different starches. Considering the characteristics of the different starches evaluated in the present work, as the greater availability of corn starch or the lower retrogradation of the phosphated one, the hydrogels produced allow the application in different foods. Thus, as both anionic polysaccharides have similar properties, what will define the microgel application is the starch.