Green Valorization of Parapenaeus longirostris By-Products Through Ultrasound-Assisted Extraction of Astaxanthin with Extra Virgin Olive Oil: Application in Functional Trahanas with Enhanced Stability and Consumer Acceptability

Astaxanthin, a potent antioxidant, has attracted growing interest for its applications in the food, pharmaceutical, and cosmetic industries. This study aims to optimize the green extraction of astaxanthin from shrimp ( Parapenaeus longirostris ) by-products using ultrasound-assisted extraction (UAE) with extra virgin olive oil (EVOO) as a sustainable solvent, and explore its application in trahana fortification, a traditional Greek fermented cereal-based product. Response Surface Methodology (RSM) was applied to optimize astaxanthin extraction conditions (extraction time, liquid-to-solid (L/S) ratio, and ultrasound amplitude). Fatty acid analysis was performed with gas chromatography (GC-FID), and sensory analysis was conducted using a 7-point hedonic scale for sensory attributes. The optimal UAE conditions for astaxanthin, determined by RSM, were 228 min extraction time, a 65:1 liquid-to-solid ratio, and 41% ultrasound amplitude, predicting 83.50 μg astaxanthin/g by-product. At the optimal conditions, the experimentally obtained yield of 76.75 ± 1.17 μg astaxanthin/g by-product fell within the 95% confidence interval of the predicted value. The enriched trahanas retained nutritionally relevant levels after cooking (46.35 ± 0.60 μg astaxanthin per 60 g serving). Accelerated storage testing at 65 °C for six days was used to assess the thermal stability of astaxanthin in enriched trahanas. Based on first-order degradation kinetics and Arrhenius-based extrapolation of literature-derived activation energy values, astaxanthin retention above 80% at 25 °C was estimated to be maintained for approximately 27–51 days. Thereafter, progressive degradation is expected, with the estimated half-life ranging from 85 to 159 days. GC-FID analysis revealed favorable incorporation of bioactive lipids, including omega-3 fatty acids (EPA and DHA). Sensory evaluation demonstrated enhanced consumer acceptability, with enriched samples scoring significantly higher in appearance, aroma, and overall acceptance compared to traditional trahanas. These findings highlight UAE as an efficient and environmentally friendly strategy for recovering astaxanthin from seafood by-products and for developing functional cereal-based foods that align with sustainability. This work demonstrates the effective use of extra virgin olive oil as a green extraction solvent that also serves as a nutritional carrier, enabling the enrichment of trahanas with astaxanthin. The approach ensures both nutritional stability and consumer acceptability, providing a practical pathway for the development of sustainable, functional cereal-based foods.