Plant secondary metabolites (PSMs) can potentially reduce ruminal methane formation. However, related to differences in their molecular structures, it is not yet clear what causes an anti-methanogenic effect. In an in vitro system simulating rumen fermentation, we investigated the impact of eight compounds with distinct chemical characteristics (gallic and salicylic acids, tannic acid, catechin, epicatechin, quercetin, rutin, and salicin) when added to a basal feed (maize silage) at a concentration of 12% of the feed dry matter. After 48 h of incubation in buffered rumen fluid, methane production was significantly lowered by quercetin (43%), tannic acid (39%) and salicylic acid (34%) compared to the control (maize silage alone) and without changes in total volatile fatty acid production during fermentation. No other PSM reduced methane formation as compared to control but induced significant differences on total volatile fatty acid production. The observed differences were related to lipophilicity, the presence of double bond and carbonyl group, sugar moieties, and polymerization of the compounds. Our results indicate the importance of distinct molecular structures of PSMs and chemical characteristics for methane lowering properties and volatile fatty acid formation. Further systematic screening studies to establish the structure–function relationship between PSMs and methane reduction are warranted.

This study investigated the year-round metabolomic variation in Fucus serratus (FS) and F. vesiculosus (FV) collected monthly from Danish coastal water around Aarhus Bay. Untargeted high-resolution liquid chromatography–mass spectrometry profiling (LC-HRMS), combined with multivariate data analysis and temporal clustering analysis, revealed that species identity was the primary driver of metabolic separation, followed by seasonal variation. FS showed higher levels of hydrolyzable tannins, flavonoid derivatives, aromatic amino acids, and glutamine-rich peptides, whereas FV was enriched in complex phlorotannins, tricarboxylic acid cycle intermediates, and carnitine derivatives. Temporal analysis identified recurring seasonal patterns across both species, including spring increases in amino acids, purine metabolites, and osmolytes; mid-summer peaks in mannitol and sulfated derivatives; and late-autumn elevations in phenolic compounds and betaine-type osmolytes. Despite apparent interspecific differences, several metabolite groups exhibited similar seasonal dynamics, suggesting shared physiological strategies associated with growth activation in spring, metabolic adjustment during summer to possible increased grazing pressure, and nutrient reallocation prior to winter. These findings provide a comprehensive, high-resolution view of seasonal metabolomic patterns in Fucus spp., offering new insights into their biochemical ecology and supporting the targeted utilization of these species for applications requiring specific metabolite profiles. Finally, this study contributes to the creation or expansion of metabolomic libraries for HRMS specific to Fucus seaweeds.

The simultaneous determination of bromine and iodine in biological and feed-related samples by inductively coupled plasma mass spectrometry (ICP-MS) is challenged by matrix effects, analyte carryover, and the potential loss of volatile halogen species during sample preparation. This study aimed to develop and validate a sensitive and robust ICP-MS method for determining total bromine and iodine in total mixed ration (TMR), milk, urine, feces, ileum, and duodenum. Samples were prepared using a common alkaline extraction procedure with tetramethylammonium hydroxide (TMAH) followed by centrifugation, filtration, and matrix-specific dilution. Bromine and iodine were measured in SQ-KED and TQ-O₂ acquisition modes. Matrix-specific dilution, additional washing between samples, and the introduction of 0.5% ammonium hydroxide (NH₄OH) as a rinse solution alongside the existing 0.2% TMAH wash effectively reduced analyte carryover and improved signal stability. Matrix-matched spike-recovery experiments yielded recoveries of 95.7–110.7%, with relative standard deviations of 0.4–5.5% and the majority below 2.5%. Limits of detection (LODs) ranged from 0.01 to 0.25 µg/L, while matrix-dependent lower limits of quantification (LLOQ) ranged from 1.0 to 2.0 µg/L for bromine and from 0.2 to 1.0 µg/L for iodine. Among the evaluated approaches, ⁸¹Br TQ-O₂ and ¹²⁷I SQ-KED yielded the overall recoveries closest to 100% across the matrices included in the real-sample analysis and were therefore selected for reporting these results. Bromine and iodine in digested TMR samples remained stable during 30 days of storage at 5 °C. Application to samples from a dairy-cow feeding experiment demonstrated the method’s suitability for detecting treatment-associated differences in bromine and iodine concentrations. The method provides a practical and reliable analytical workflow for determining total bromine and iodine across diverse biological and feed-related matrices.