Animal feeds may contain exogenous compounds that can induce toxicity when ruminants ingest them. These toxins are secondary metabolites originating from various sources including plants, bacteria, algae and fungi. Animal feed toxins are responsible for various animal poisonings which negatively impact the livestock industry. Poisoning is more frequently reported in newly exposed, naïve ruminants while ‘experienced’ ruminants are observed to better tolerate toxin-contaminated feed. Ruminants can possess detoxification ability through rumen microorganisms with the rumen microbiome able to adapt to utilise toxic secondary metabolites. The ability of rumen microorganisms to metabolise these toxins has been used as a basis for the development of preventative probiotics to confer resistance against the poisoning to naïve ruminants. In this review, detoxification of various toxins, which include plant toxins, cyanobacteria toxins and plant-associated fungal mycotoxins, by rumen microorganisms is discussed. The review will include clinical studies of the animal poisoning caused by these toxins, the toxin mechanism of action, toxin degradation by rumen microorganisms, reported and hypothesised detoxification mechanisms and identified toxin metabolites with their toxicity compared to their parent toxin. This review highlights the commercial potential of rumen inoculum derived probiotics as viable means of improving ruminant health and production.

In this study, avocado leaves were dried by five different drying treatments: oven‐drying at 50 and 100 °C, microwave‐drying, ambient air‐drying, and freeze‐drying. Investigation showed that oven‐drying and ambient air‐drying of leaves caused decrease in antioxidant properties while microwave‐drying and freeze‐drying preserved them. Polyphenol oxidase (PPO) and peroxidase (POD) activities decreased notably after drying in oven at 50 and 100°C, microwave, ambient air and blanching at 100°C. However, increase in PPO was observed in freeze‐dried leaves. Chlorogenic acid and rutin present in leaves showed varying decrease in drying processes except microwave‐drying, and freeze‐drying. Cellular antioxidant assay revealed reduced antioxidant activity in all drying treatments except for microwave‐drying. Factors that affected changes in antioxidant properties by various drying processes were identified and discussed. Microwave‐drying was considered to be the best drying method for avocado leaves as phenolic compounds were preserved and PPO and POD activities were deactivated. Practical applications Avocado leaves are used as herbal tea in traditional medicine and are reported to have medicinal properties such as antioxidant, anti‐viral, and anti‐inflammatory. Processing of fresh herbal tea leaves are required to preserve phenolic compounds and quality of the tea leaves. This study represents a comprehensive study on the effects of different drying treatments on the antioxidant activity using both in vitro and in vivo analysis and enzymatic changes of avocado leaves. The optimum drying condition found in this study will be beneficial to the tea processing industry.

Beneficial properties of herbal tea leaves can be affected by oxidase enzymes activity on harvesting, as these enzymes utilize phenolics as the main substrate. The purpose of this study was to investigate whether there is any correlation between the oxidase enzymes activity and the degree of phenolic degradation. Eight herbal tea leaves underwent ambient air‐drying process and their total phenolic content change as well as polyphenol oxidase and peroxidase enzyme activity change for each fresh leaf were determined after ambient air‐drying. Results showed that except for two plants, polyphenol oxidase activity had a positive linear correlation with total phenolic degradation (y = 1.929x + 21.082; R2 = 0.8909), but peroxidase activity showed no such relationship. Plants with rosmarinic acid as their main phenolics, showed a much better correlation. Practical applications The process of preserving herbal tea leaves for their bioactivities by drying is crucial for the purpose of commercialization. Herbal industries have been using, among others, air‐drying method as a means of preservation because of its cost effectiveness. However, the presence of oxidase enzymes may lead to degradation of beneficial compounds. In our study, by identifying the correlation between oxidase enzyme activity for both polyphenol oxidase and peroxidase with that of total phenolic degradation, we are able to understand the actual effect of oxidase enzymes on phenolics degradation. Hence, through the correlation and solely based on its oxidase enzyme activity, mainly polyphenol oxidase, we could determine whether air‐drying will be suitable for a particular herbal tea leaf. This will result in a much faster and efficient decision in choosing a preserving method for the herbal tea leaf.