Differential impacts of post-harvest hydrothermal treatments on chemical composition and in vitro digestibility of two brown macroalgae (Fucales, Phaeophyceae), Ascophyllum nodosum and Fucus vesiculosus, for animal feed applications

Abstract

This study tested the hypothesis that post-harvest hot water blanching improves the chemical composition, mainly mineral and carbohydrate contents, and in vitro digestibility of two predominant brown macroalgae, Ascophyllum nodosum (AN) and Fucus vesiculosus (FV), as feed ingredients for monogastric and ruminant animals. Low-temperature water blanching (LTB; 40 °C for 5 min) had minor impacts on macroalgal chemical composition and in vitro digestibility. Conversely, high-temperature water blanching (HTB; 80 °C for 5 min) effectively reduced total ash and specific elements, including sodium, potassium, iodine, and arsenic, by ~ 25–73% compared to unblanched algal biomass (more prominently in FV). The HTB raised total sugar contents by ~ 25% in FV, markedly elevating uronic acids (~ 60%) and glucans (~ 33%). However, HTB reduced mannitol (> 50%) and enhanced total polyphenol extractability in both macroalgae. The HTB diminished ~ 8% of in vitro dry matter or organic matter digestibility and 26% of crude protein (CP) digestibility of both macroalgae for monogastric animals and of FV for ruminants (particularly of CP by ~ 42%). Those reduced digestibilities were associated with enriched fibre, uronic acids, total polyphenols, and declined mannitol in the HT-blanched macroalgal biomass. Our findings suggest that hot-water blanching can be an efficient technique to optimise the elemental composition of two fucoid algae, but the altered sugar and complex carbohydrate compositions may impair their digestibility. Future studies should identify appropriate post-harvest processing techniques for brown macroalgae that can optimise both nutritional composition and digestibility along with favourable impacts on feed utilisation and animal performance.