The effects of processing on the in vitro antimethanogenic capacity and concentration of secondary metabolites of Asparagopsis taxiformis

The macroalga Asparagopsis taxiformis is an effective antimethanogen in ruminants due to the presence of bromoform. To date, research on the effects of A. taxiformis on methanogenesis has used freeze-dried material without an understanding of alternative post-harvest processing methods. Therefore, A. taxiformis was processed using a factorial design based on rinsing (unrinsed/dip rinsed/submerged), freezing (frozen/not frozen) and drying (freeze-dried/kiln-dried/dehydrated) to determine the effects on methane (CH 4 ) production in in vitro rumen fermentations and the concentration of bromoform in the biomass of A. taxiformis . The most effective treatment group, which completely inhibited the production of CH 4 , consisted of treatments that, regardless of rinsing, were frozen and then freeze-dried. Of these, the unrinsed treatment had the highest concentration of bromoform (4.39 ± 0.07 mg g −1 dry weight (DW)) and the rinsed treatments had concentrations between 2.0 and 3.2 mg g −1 DW. The next most effective group consisted of treatments that were unrinsed, and kiln-dried or dehydrated without freezing. These also completely inhibited the production of CH 4 but had lower concentrations of bromoform (between 1.0 and 2.0 mg g −1 DW). Importantly, all other treatments inhibited CH 4 by