High-pressure treatment of the green and orange Dunaliella salina biomass: effect on particle size distribution, small amplitude oscillatory shear rheology, and microstructure.

Dunaliella salina, a halophilic microalga, is well known for its ability to produce β-carotene and has significant commercial applications. The actively growing green culture turns to orange color due to photosensitization, during which there is a significant reduction in chlorophyll content (chlorophyll A and B: 16.04 and 2.80-1.70, 0.21 mg/g dry basis, respectively) with an increase in carotenoids (α- and β-carotenes: 1.60 and 4.81 mg/g dry basis). This change has been accompanied by a considerable variation in protein content (green: 34.27% and orange: 18.57%) and ash content (green: 38.37% and orange: 58.11%). To avoid extreme heat sensitivity, high-pressure (HP) processing, a nonthermal technology, has been applied to pigment-rich Dunaliella. This research aimed to examine the effects of HP treatment (300-600 MPa/15 min) on the rheological, structural, and particle size distribution of Dunaliella in two consecutive cell growth stages (e.g., green and orange). Oscillatory rheology data displayed a distinct protein denaturation at 57.87 °C for untreated green cells, whereas orange cells did not. Conversely, several denaturation peaks appeared in the HP-treated orange cell suspensions, and those peaks remained unaffected by pressure treatment. Isothermal heating exhibited liquid-like behavior for green cells, whereas the solid-like behavior was evident for orange cells. PSD displayed a shift of unimodal to bimodal distributions of Dunaliella cells after the HP treatment. Orange cells exhibited PSD parameters of Dv