Bio-accessibility of Lipids from Chlorella Vulgaris

Greta Canelli, Carmen Tarnutzer, Lukas Neutsch, Roberta Carpine, Sabrina TevereFrancesca Giuffrida, Christoph Boltena, Alexander Mathys

ETH Zürich, Institute of Food, Nutrition and Health, Switzerland; ETH Zürich, Institute of Food, Nutrition and Health, Switzerland ; ZHAW, Campus Grüental, Switzerland; ZHAW, Campus Grüental, Switzerland; ZHAW, Campus Grüental, Switzerland; Nestec SA; SOCIETÉ DES PRODUITS NESTLÉ; ETH Zürich, Institute of Food, Nutrition and Health, Switzerland

Microalgae are emerging as alternative, vegan source of polyunsaturated fatty acids, protein and micronutrients. Microalgae producing ω3-PUFAs can be grown heterotrophically without light on low-cost substrates. Chlorella spp. contains up to 27% ALA in the lipid fraction. Microalgae lipids are usually used upon extraction. For food supplements or ingredients, whole biomass can be also consumed as such. For example, dried biomasses of Chlorella spp. are commercially available as source of protein and healthy lipids. However, bioaccessibility of lipids, as well as other nutrients, in the whole microalgae cell has not been extensively studied. Bioaccessibility is strictly related to cell wall composition and structure. The cell wall consists of a matrix of glycoprotein and polysaccharides resistant to digestion and whose composition depends on species and growth stage. Downstream treatments could be used to enhance the nutrient bioaccessibility. Enzymatic hydrolysis with chitinase, lysozyme, pectinase, sulfatase, β-glucuronidase, and laminarinase was reported to have a positive effect on cell wall degradation. Moreover, enzymatic treatment of the cell wall has major advantages over mechanical treatments, such as low energy requirements, and mild and pollutant free processing conditions (Baudelet et al., 2017). Also, enzymatic treatments do not cause a temperature stress, preserving the quality of ω3-PUFAs.

The fatty acid profile of five commercial Chlorella spp. biomasses was evaluated and compared to the C. vulgaris grown in our lab. All biomasses showed a good (5:1) to ideal (1:1) ω6:ω3 ratio. Lipid bioaccessibility was measured through INFOGEST protocol, resulting in less than 7% for commercial biomasses.
Regarding the effect of growth phase, this was studied in C. vulgaris (CCALA 256) grown in heterotrophic controlled conditions in a 16 L fermenter, for seven days, reaching concentrations of 7.1 ± 0.3 g/L. ALA accounted for 20% ± 2% in C. vulgaris total fatty acids.

Results showed that lipids were more bioaccessible in stationary compared to exponential phase.

To increase the bioaccessibility, a treatment with chitinase and lysozyme on C. vulgaris biomass was performed. A 10% increase in both protein and lipid bioaccessibility was reached.

This research shows how harvesting time influence lipid productivity and bioaccessibility and that downstream treatments are needed to increase the bioaccessibility of nutrients in microalgae biomasses.