Aquatic weeds as novel protein sources: Alkaline extraction of tannin-rich Azolla

Paul Brouwer; Klaas G J Nierop; Wouter J J Huijgen; Henriette Schluepmann

doi:10.1016/j.btre.2019.e00368

Aquatic weeds as novel protein sources: Alkaline extraction of tannin-rich Azolla

Biotechnol Rep (Amst). 2019 Aug 11:24:e00368. doi: 10.1016/j.btre.2019.e00368. eCollection 2019 Dec.

Authors

Paul Brouwer^{1

2}, Klaas G J Nierop², Wouter J J Huijgen³, Henriette Schluepmann¹

Affiliations

¹ Molecular Plant Physiology, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands.
² Department of Earth Sciences, Organic Geochemistry, Utrecht University, Princetonlaan 8a, 3584 CB Utrecht, the Netherlands.
³ Biomass & Energy Efficiency, Energy Research Centre of the Netherlands (ECN), Westerduinweg 3, 1755 LE Petten, the Netherlands.

Abstract

The aquatic weed Azolla is a potential protein crop due to its prolific growth and high protein content, supported entirely by nitrogen-fixing symbionts. Alkaline protein extraction at pH 8 followed by acid precipitation allowed recovery of 16-26% of the biomass nitrogen, while at pH 10.5 nitrogen recovery improved to 35-54%. This pH effect was typical of ferns of the family Salviniaceae, and may be explained by high concentrations of condensed tannins (CTs) in the biomass that precipitate protein at mild pH. Two approaches were tested to increase protein yield and reduce protein binding by CTs. Pre-extraction with aqueous acetone (70 v/v%) removed 76-85% of the CTs and subsequent alkaline extraction at pH 12.5 and 95 °C recovered 38% of the biomass nitrogen. Extraction with 1.5% of PEG as a CT-binding agent, also permitted to recover 38% of the nitrogen, under milder conditions of pH 8 and 45 °C.

Keywords: AAs, BSA; Alkaline extraction; Aquatic weeds; Azolla; CT, NAA; Condensed tannins; PEG, PVPP; Protein; RT, THM, UV/VIS.