Thermal stability of astaxanthin in oils for its use in fish food technology

Astaxanthin is one of the inputs that most influences the final prices of salmonids on the market and is unstable due to its sensitivity to various factors, such as temperature, which cause the loss of its bioactivity during feed processing and storage. Dilocarcinus pagei is a native crab that is commonly found in fish culture ponds and presents an attractive reddish-brown coloration. The objectives of the present study were to evaluate this crab as a natural source of astaxanthin and to assess how the stability of this pigment was affected by different vegetable oils (soy and sunflower) and butylhydroxytoluene (BHT) presence over a range of temperatures used in feed processing technology like extraction, cooking, extrusion and storage. Individuals of D. pagei were collected and homogenized. Carotenes were extracted from different samples using acetone. The extractions were analyzed using High-Performance Liquid Chromatography (HPLC). The percentages of remaining astaxanthin dissolved in soy and sunflower oils with or without BHT (0.1%) were estimated before and after being incubated at 50 degrees C. Astaxanthin dissolved in both oils with BHT were exposed to different temperatures between 25 degrees C and 180 degrees C. Samples were taken at different intervals of time and astaxanthin was measured at lambda max490 nm by a spectrophotometer. The degradation rate of astaxanthin at each temperature in both oils was estimated. The results showed that D. pagei would be an alternative as a natural source of astaxanthin since its concentration values (231.5 mu g/g dry matter) are similar to those present in other species commercially exploited. The two-ways Analysis of variance (ANOVA) showed that the presence of BHT (P = 0.03) and the oils (P < 0.01) used as dissolvent affect the percentages of remaining astaxanthin independently of the oil used (P = 0.06). The astaxanthin degradation rates in sunflower were higher than those in soy oil at all tested temperatures, being significantly different (P < 0.05) at temperatures from 25 degrees C to 120 degrees C but not at 180 degrees C. The activation energies calculated for soy oil was 88.7 kJ/mol while for sunflower oil, it was 85.5 kJ/mol. Astaxanthin was more stable in soy oil than in sunflower oil. Moreover, commercial soy oil is a cheap ingredient and a good source of unsaturated fatty acids (omega 3, omega 6 and omega 9). Thus, soy oil would be recommended as a solvent to extract the pigment.