Abstract
Rising trends in fish filleting are increasing the amount of processing by-products, such as skins of turbot, a flatfish of high commercial value. In line with circular economy principles, we propose the valorization of turbot skins through a two-step process: initial gelatin extraction described for the first time in turbot, followed by hydrolysis of the remaining solids to produce collagen hydrolysates. We assayed several methods for gelatin extraction, finding differences in gelatin properties depending on chemical treatment and temperature. Of all methods, the application of NaOH, sulfuric, and citric acids at 22 °C results in the highest gel strength (177 g), storage and loss moduli, and gel stability. We found no relation between mechanical properties and content of pyrrolidine amino acids, but the best performing gelatin displays higher structural integrity, with less than 30% of the material below 100 kDa. Collagen hydrolysis was more efficient with papain than alcalase, leading to a greater reduction in Mw of the hydrolysates, which contain a higher proportion of essential amino acids than gelatin and show high in vitro anti-hypertensive activity. These results highlight the suitability of turbot skin by-products as a source of gelatin and the potential of collagen hydrolysates as a functional food and feed ingredient.
Highlights
Turbot (Scophthalmus maximus) is a flatfish of high commercial value, currently produced for the most part in aquaculture farms, mainly in China and Europe [1]
We report for the first time the valorization of skin, generated as waste in the filleting of aquaculture turbot, as a source for the production of gelatin and collagen derivatives, following the principles of sustainability and bioeconomy
The application of different treatments and chemicals on fish skin leads to significant differences in the amount and characteristics of gelatin extracted, in line with previous reports on other fish [12,13,14]
Summary
Turbot (Scophthalmus maximus) is a flatfish of high commercial value, currently produced for the most part in aquaculture farms, mainly in China and Europe [1]. Turbot has been traditionally marketed as a whole fish, but processing companies are increasingly filleting this species driven by consumer demand for convenience food. As this practice expands, so will the amount of waste generated, which needs to be handled to avoid environmental problems and enhance resource efficiency, in line with the principles of the blue economy. Because of the limited access to turbot by-products so far, very few works have focused on the valorization of this species. Another work obtained antioxidant peptides, this time from the discarded skin of turbot, through fermentative processes [3]. Collagen is one of the main components of fish skin, and instead of extensive protein breakdown, valuable gelatin can be obtained from this by-product through mild hydrolysis [4]
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