Valorisation of sea buckthorn pomace by optimization of ultrasonic-assisted extraction of soluble dietary fibre using response surface methodology

Sea buckthorn pomace is a valuable industrial waste/by-product obtained after juice production that contains bioactive, health-promoting dietary fibres. This pomace finds usage as animal feed or simply discarded, owed to the lack of appropriate handling or processing facilities. The present study was aimed to evaluate the effects of green extraction technologies such as ultrasonicassisted extraction on the yield of soluble dietary fibre (SDF) from sea buckthorn pomace. Response surface methodology (RSM) coupled with Box–Behnken design (BBD) was applied for optimization of SDF yield. The effects of sonication temperature (60–80^◦ C), sonication power (100–130 W) and extraction time (30–60 min) on the yield of SDF were also investigated. Furthermore, colour measurement and hydration properties of sea buckthorn pomace powder (STP) and dietary fibre fractions (SDF and insoluble dietary fibre, IDF) were also investigated. From the RSM results, the optimal sonication temperature (67.83^◦ C), sonication power (105.52 W) and extraction time (51.18 min) were identified. Based on this, the modified optimum conditions were standardised (sonication temperature of 70^◦ C, sonication power of 105 W and extraction time of 50 min.). Accordingly, the yield of SDF obtained was 16.08 ± 0.18%, which was close to the predicted value (15.66%). Sonication temperature showed significant effects at p ≤ 0.01, while sonication power and extraction time showed significant effects at p ≤ 0.05 on the yield of SDF. The result on colour attributes of STP, SDF and IDF differed (L* (STP: 54.71 ± 0.72, IDF: 72.64 ± 0.21 and SDF: 54.53 ± 0.31), a* (STP: 52.35 ± 1.04, IDF: 32.85 ± 0.79 and SDF: 43.54 ± 0.03), b* (STP: 79.28 ± 0.62, IDF: 82.47 ± 0.19 and SDF: 71.33 ± 0.50), and ∆E* (STP: 79.93 ± 0.50, IDF: 74.18 ± 0.30 and SDF: 68.40 ± 0.39)). Higher values of hydration properties such as the water holding, swelling and oil holding capacities were found in SDF (7.25 ± 0.10 g g⁻¹, 7.24 ± 0.05 mL g⁻¹ and 1.49 ± 0.02 g g⁻¹ ), followed by IDF (6.30 ± 0.02, 5.75 ± 0.07 and 1.25 ± 0.03) and STP (4.17 ± 0.04, 3.48 ± 0.06 and 0.89 ± 0.03), respectively. Based on our results, response surface methodology is recommended to be adopted to optimize the ultrasonic-assisted extraction to obtain maximum yield of SDF from sea buckthorn pomace. These results can be of practical usage while designing future functional food formulations using sea buckthorn pomace.