The effect of drying, cell disruption and storage on the sensory properties of Nannochloropsis sp.

Adding microalgae into food could strongly influence the flavor of the final product which is the key factor for consumer acceptation. To assist food processors in the development of tasteful food products containing microalgae, it is necessary to understand the impact of processing and storage on the flavor of freshly harvested microalgae biomass. In this study, the effect of commonly used drying techniques (freeze-drying, spray drying and thin-layer oven drying) and cell disruption (high pressure homogenization) on the sensory quality of fresh Nannochloropsis sp. biomass was investigated. Furthermore, the impact of storage on the flavor properties of intact (non-disrupted) and disrupted Nannochloropsis paste was examined. Sensory evaluation by a trained panel indicated that the flavor of Nannochloropsis was not affected by freeze-drying. Whereas thin-layer oven drying at 60 °C resulted in a strong bitter taste and a musty odor. This odor is positively correlated with volatile organic compounds (VOCs) including Strecker aldehydes that arise from the Strecker degradation in the course of the Maillard reaction. Spray drying reduced the odor intensity and grassy odor of Nannochloropsis which could be attributed to the loss of several VOCs including esters, saturated alcohols and dimethyl sulfide. Furthermore, cell disruption of Nannochloropsis using high pressure homogenization resulted in intense grassy and fish oil odors features due to high amounts of fatty acid-derived unsaturated aldehydes, ketones and alcohols. Finally, dark storage of fresh intact and disrupted Nannochloropsis paste at ambient temperature strongly impacts the volatile profile due to the rapid formation of several VOCs, which negatively impact the palatability of the Nannochloropsis biomass. Our results provide the basis to be applied in downstream food processing of harvested Nannochloropsis biomass in order to maintain or optimize the flavor properties for specific food products.