Effects of thermal disinfection and autoclave sterilisation on the quality of microalgae concentrates

Abstract

Microalgae concentrates are important for hatchery operations but have been found to contain high concentrations of bacteria. Therefore, this study investigated the effects of four thermal disinfection and sterilisation treatments, low-temperature long-time (LTLT; 62–65°C, 30 min), high-temperature short-time (HTST; 72–75°C, 15 s), ultra-high-temperature (UHT; 120–150°C, 1–3 s) and high-temperature high-pressure (HTHP; 121°C, 0.2 MPa, 15 min), on concentrates of the microalgae, Chaetoceros gracilis, Chlorella vulgaris (fortified with eicosapentaenoic acid and docosahexaenoic acid) and Nannochloropsis oculata. The concentrates had reduced bacterial counts following LTLT, HTST and UHT and were completely sterilised by HTHP. Furthermore, cell dispersibility was retained in all treatment groups except HTHP-treated C. gracilis. Rotifers that were cultured with HTHP-treated C. vulgaris and N. oculata experienced significant population increases, whereas the survival rate and growth of Artemia nauplii significantly improved when supplied with HTHP-treated N. oculata, indicating that HTHP enhances the digestibility of this microalga. HTHP did not affect the total lipid content and fatty acid composition of the microalgae. These results suggest that HTHP-treated C. vulgaris and N. oculata could be used for the nutritional enrichment of rotifers and Artemia, while avoiding the risk of bacterial contamination, and would have an increased shelf life at room temperature.