An Integrated Approach for the Valorization of Sea Bass (Dicentrarchus labrax) Side Streams: Evaluation of Contaminants and Development of Antioxidant Protein Extracts by Pressurized Liquid Extraction

Abstract

In this study, the presence of As, Hg, Cd, Pb, and mycotoxins in sea bass side streams (muscle, head, viscera, skin, and tailfin) was evaluated as a preliminary step to assess the effect of an innovative extraction technique (Pressurized Liquid Extraction; PLE) to obtain antioxidant protein extracts. Then, a response surface methodology-central composite design was used to evaluate and optimize the PLE extraction factors (pH, temperature, and extraction time) in terms of total protein content and total antioxidant capacity (TEAC and ORAC). Heavy metals were found in all samples while DON mycotoxin only in viscera, both far below the safe limits established by authorities for fish muscle tissue and fish feed, respectively. The selected optimal PLE extraction conditions were pH 7, 20 °C, 5 min for muscle, pH 4, 60 °C, 15 min for heads, pH 7, 50 °C, 15 min for viscera, pH 7, 55 °C, 5 min for skin, and pH 7, 60 °C, 15 min for tailfins. Optimal PLE conditions allowed increasing protein content (1.2-4.5 fold) and antioxidant capacity (1-5 fold) of sea bass side stream extracts compared to controls (conventional extraction). The highest amount of protein was extracted from muscle while the highest protein recovery percentage was found in viscera. Muscle, head, and viscera extracts showed higher antioxidant capacity than skin and tailfin extracts. Moreover, different SDS-PAGE patterns were observed among samples and a greater quantity of protein fragments of lower molecular weight were found in optimal than control extracts.

Keywords: SDS-PAGE; antioxidant capacity; heavy metals; mycotoxins; pressurized liquid extraction; protein; sea bass; side streams.

Figure 1

Scheme of sea bass side stream sample preparation.

Figure 2

Main effects of each independent variable (pH, temperature, time) of Pressurized Liquid Extraction for each response (total protein content and total antioxidant activity (TEAC and ORAC)) in extracts from seabass muscle (a–c), head (d–f), viscera (g–i), skin (j–l), and tailfins (m–o).

Figure 3

Estimated response surface by plotting desirability versus pH (4–10), temperature (20–60 °C), and 15 min of extraction time for each sea bass side stream (M: Muscle, H: Head, V: Viscera, S: Skin, T: Tailfin). Desirability is based on the joint response of the different responses analyzed (total protein content and total antioxidant capacity by TEAC and ORAC assays).

Figure 4

Total protein content in control extracts and optimal PLE extracts from sea bass muscle, head, viscera, skin, and tailfin side streams. PLE: Pressurized Liquid Extraction. Results are expressed as mean ± standard deviation (n = 2). Different lowercase letters in the bars indicate statistically significant differences (p < 0.05) among samples.

Figure 5

Molecular weight distribution of protein fraction of sea bass side stream extracts. SDS-PAGE electrophoresis patterns (A) and grouping of band areas by molecular weight ranges (B). MW: Molecular weight standard. C: Control extract. Opt: Optimal extract.

Figure 6

Total antioxidant capacity (TEAC and ORAC) in control extracts and optimal PLE extracts from sea bass muscle, head, viscera, skin, and tailfin side streams. TEAC: Trolox equivalent antioxidant capacity. ORAC: Oxygen radical absorbance capacity. PLE: Pressurized Liquid Extraction. Results are expressed as mean ± standard deviation (n = 3 for TEAC and n = 6 for ORAC). Different lowercase letters in the bars indicate statistically significant differences (p < 0.05) among samples.