The ratio of diester to monoester astaxanthin was determined as it presents an indication of asthaxanthin degradation because monoesters are reported to degrade more rapidly than diesters (Miao et al., 2013). It was slightly higher in the freeze-dried (0.163±0.002) than spray-dried (0.148 ± 0.001) powder on week 0 (Table 4). Among the spray-dried samples, the ratio remained similar for the ones stored at −20 °C and 4 °C and vacuum-packed during the 20 weeks of storage.