With its foul smell and low recognition threshold, p-cresol is the most persistent and significant contributor to the odor from dairy operations. It can be produced from tyrosine directly from a lyase-mediated elimination reaction or formed by the decarboxylation of 4-hydroxyphenylacetate, an oxidation metabolite of tyrosine. Our recent study has shown that rutin effectively reduced p-cresol production in the rumen through competitive inhibition of 4-hydroxyphenylacetate decarboxylation. However, whether rutin or rutin-rich ingredients could suppress p-cresol formation in the incubation of dairy excreta or manure remains unknown. In this study, buckwheat stover (leaf and stem), was evaluated based on its rich rutin content (~ 3 mg/g dry weight). A batch of fresh dairy excreta (a mixture of feces and urine was mixed with 4 treatments, i.e., untreated control; 0.2 mg/g rutin; 6% fine buckwheat stover (&lt; 0.5 mm particle size); 6% rough buckwheat stover (2 mm particle size), and incubated anaerobically for 14 days. Small aliquots of incubation samples were collected on day 0, 1, 2, 4, 7, and 14 of incubation, and analyzed by liquid chromatography-mass spectrometry-based quantitative analysis for tyrosine metabolites. The results showed that p-cresol in the mixture was quickly decreased by buckwheat stover during the first 2 days of co-incubation and remained low afterwards while the buckwheat-elicited increase of 4-hydroxyphenylacetate mainly occurred on day 7 and 14 of co-incubation. Interestingly, pure rutin did not decrease p-cresol, but increased 4-hydroxyphenylacetate. Overall, our preliminary results indicated that buckwheat stover could be effective for suppressing p-cresol production in the anaerobic incubation of dairy excreta, which warrants additional investigations on mechanisms and applications.

Buckwheat stover inhibits decarboxylation of p-hydroxyphenylacetate to p-cresol in anaerobic incubation of dairy excreta

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