Understanding methane reducing tannins in enteric fermentation using grape marc as a model tannin source - Department of Agriculture Ref No 01200.007

Summary

Grape marc has been thoroughly tested for the presence of agrochemicals, tannins, nutritive profile and other compounds of interest to methanogenesis. The agrochemical survey highlighted iprodione as an area of further research, with high concentrations found in some unprocessed samples.

Grape marc tannin was found to vary greatly in concentration and composition across the processing chain with skin only and seed only samples giving rise to the biggest compositional variations.

Objectives

The objective of this project is to reduce Australia's agricultural methane emissions through:

• Quantifying grape marc compositional variation, including a survey of potential agrichemical residues and any other harmful or toxic chemical compounds, with a specific view to generating information about tannin levels and types in grape marc.
• Conducting in vitro screening of grape marc samples with known tannin variations, in partnership with DPI Victoria through project(B. CCH. 6460), This will determine how tannin variations (level and type/complex) effect methane emissions.
• Based on the findings of the tannin and marc characterisation work and the results of in vitro screening, conduct in vivo assessment of grape marc as a feed additive, This will be completed in partnership with DPI Victoria through project B.CCH.6460.
• Characterising grape marc tannins and elucidating to what extent they are the active ingredients responsible for reducing ruminant emissions -this could guide improvements across all agricultural feedstocks.

Key findings

In vitro experiments highlighted the roles of both fat and tannin in reducing methanogenesis, although fat was also closely related to loss of fermentation efficiency. Small tannin was found to be more effective at reducing methane production, with extractable tannin reducing methane without inhibiting fermentation.

Marc parcels that have undergone limited or no extraction will be beneficial due to the presence of small, extractable tannin, but also readily fermentable sugars. However, marc with limited processing needs to be screened for the presence of agrochemical residues.

Benefits to industry

Grape marc must be applied under the correct conditions, with reductions in total feed energy contributing to productivity losses that overshadow any anti-methanogenic potential.

The use of grape marc feeding to achieve reductions in methane should be done during times of low energy requirements, such as the summer-autumn feed gap, during times of drought, or when a feed supplement of equivalent energy is being replaced.

For marc to be used effectively on-farm a number of issues need to be addressed such as preservation of tannin and methods for handling that prevent mould formation.

MLA action

MLA continues to conduct research, development, and adoption activities into supplement and additive technologies that have potential to reduce enteric methane, without any loss of productivity, via the Emissions Avoidance Partnership.

Future research

The supplementation of grape marc into high energy feeds has shown to result in reductions in fermentation performance or animal productivity. When grape marc is used in a lower energy ration, the effect of tannin and fat can be better observed. Additional feeding studies should be undertaken using low energy control diets, during the summer-autumn feed gap, or when animals are being fed at or just above maintenance. It is likely that the role of grape marc in feeding systems is during one of these scenarios, and that the extent of anti-methanogenic effect would be maximised.

The logistics of using grape marc on farm needs to be better understood. Large scale storage and transportation methods, as a well as ways to limit mould formation all while preserving the anti-methanogenic properties of marc. As oxidative conditions are known to be responsible for degradation of tannin, methods for anaerobic long term storage must be the focus of future research, especially when the production of grape marc is limited to such a small window from February to April.

Related resources

• MLA's CN30 overview
• Hixson, J.L., Bindon, K.A. and Smith, P.A., 2015. Evaluation of direct phloroglucinolysis and colorimetric depolymerization assays and their applicability for determining condensed tannins in grape marc. Journal of agricultural and food chemistry, 63(45), pp.9954-9962
• Hixson, J.L., Durmic, Z., Vadhanabhuti, J., Vercoe, P.E., Smith, P.A. and Wilkes, E.N., 2018. Exploiting Compositionally Similar Grape Marc Samples to Achieve Gradients of Condensed Tannin and Fatty Acids for Modulating In Vitro Methanogenesis. Molecules, 23(7), p.1793.