Microalgae as new sources of starch: Isolation and characterization of microalgal starch granules

Starch is a very important biopolymer used in the modern society. It is a basic element of our diet (35% of daily calories in UE and USA). Moreover, it is widely used in the non-food industries. Indeed, the market of the non-food applications is nowadays growing and it includes chemical additives, bulking agents, and bioplastics productions (e.g. Mater-Bi by Novamont). The key starch features for industrial applications are: size and shape distributions of starch granules, crystallinity, amylose-amylopectin ratio, thermal properties. These features are critical to address the starch processing in the industrial production. Nowadays the main sources of small starch granules that fulfil the industrial requirements are maize, wheat, rice, oats, and amaranth. However, the reduced availability of arable lands and the increase of food demand ask for alternative sources for starch not in competition with food cultures. Microalgae are considered a novel highly efficient starch producers. Their starch content can reach the 40%W. They do not require arable land and fresh water for their cultivation. Nevertheless, limited information is available in literature about physico-chemical characterization of microalgal starch. Therefore, additional analysis about molecular weight, crystallinity, and amylose fraction are required to validate the potential industrial applications of this starch type. The present contribution reports a study on starch granules present in the microalga Chlorella sorokiniana. The granules were isolated and a preliminary physico-chemical characterization was carried out. The microalgal starch was characterized by small granules of about 1 μm with a narrow size distribution (key feature for some applications). The molecular weight of microalgal starch is comparable with that of plantstarch sources. The amylose content and crystallinity pattern were similar to cereal starch. Moreover, the high gelatinization temperature of 110 °C makes these granules suitable for system requiring high processing temperature such as for biodegradable materials