Structural effects of microalgae additives on the starch gelatinisation process

This work presents a detailed structural characterisation of the starch gelatinisation process and the effect of the addition of three microalgae species, Nannochloropsis gaditana sp., Scenedesmus almeriensis and Spirulina, by means of an advanced approach consisting of temperature-resolved simultaneous SAXS/WAXS experiments, combined with DSC. Furthermore, regular and high amylose corn starch were utilised to evaluate the impact of the amylose content. The presence of microalgae has been seen to limit water accessibility towards the interior of starch granules, reducing granule swelling and, thus, hindering the arrangement of amylopectin helices into highly ordered crystalline structures. As a result, more heterogeneous lamellar structures, with reduced apparent crystallinity, are attained. Despite the existence of lipidic compounds in the three microalgae species, the tough cell walls in Nannochloropsis and Scenedesmus impede their release towards the aqueous medium. In contrast, the weak cell walls in Spirulina are disrupted by stirring, allowing cell components to be released. The diffused lipids form helical inclusion complexes with the amylose chains and promote the crystallisation of V-type structures. The presence of amylose-lipid complexes counteracts the limited water swelling effect and results in the formation of more crystalline and homogeneous lamellar structures. This result is relevant for the food industry due to the potential of Spirulina to affect the processability and nutritional characteristics of starch-based products.Synchrotron experiments were performed at NCD beamline at ALBA Synchrotron with the collaboration of ALBA staff (2016021658 project). M.J. Fabra, Marta Martinez-Sanz and L.G. Gómez-Mascaraque are recipients of a Ramon y Cajal (RYC-2014-158), Juan de la Cierva (IJCI-2015-23389) and predoctoral (call 2013) contracts from the Spanish Ministry of Economy, Industry and Competitiveness, respectively.Peer reviewe