Abstract
Two protein tanning methods were evaluated to contribute to the withdrawal of formaldehyde as a tanning agent of meals for feeding ruminants. The experimental materials were two fractions of rapeseed and sunflower meals collected at the positive electrode of an electrostatic separator, presenting high contents in proteins and phenolic compounds. The objective was to make phenolics and proteins interact without addition of exogenous tannins. Treatment CH incubated a meal fraction:water mixture (1:2, w:w) for 48 h at 50 °C. Treatment FR incubated a meal fraction:water mixture (1:10, w:w) at pH 9.0 for 48 h at 4 °C. Microbial proteolysis on meal fractions were quantified during 24 h rumen batch fermentations with cellulose and starch as nitrogen-free energy sources. The net production of ammonia tended to be reduced by treatment FR mostly on rapeseed, corresponding to an 8% saving of rapeseed meal proteins degradable in the rumen. When untreated, the sunflower fraction decreased methane production by 50%, while treatments restored the fermentation pattern. Cold alkaline treatment could be considered to protect meal proteins from degradation by rumen micro-organisms.
Highlights
Among the sources of dietary amino acids available to ruminants in Europe, rapeseed and sunflower cakes have been promoted for 50 years as alternatives to imported soybean meal (Grenet and Demarquilly, 1970; Richardson et al, 1981)
The lowering of the rumen degradability of proteins, initially obtained by toasting (Grenet and Demarquilly, 1970), mainly uses tanning with formaldehyde, which reacts with about ten amino acids, mainly asparagine, glutamine, lysine and arginine, to form methylene bonds that cause protein reticulation (Barry, 1976; Verite et al, 1977; Antoniewicz et al, 1992). These bonds are hydrolysed when transiting from the rumen content at neutral pH to the abomasum acid medium. This industrial process was considered safe for the animal because the free formaldehyde fraction is rapidly metabolised in the rumen to carbon dioxide (Puigserver et al, 2004), growing social demand for more natural farming practices and the risks associated with the handling of formaldehyde during tanning have prompted the search for tanning agents of plant origin, in the continuity of pioneering work on chestnut wood hydrolysable tannins (Zelter et al, 1970)
Our study aims at quantifying the impact of two pretreatments – hot or cold and alkaline – on the rumen degradability of proteins in rapeseed and sunflower meal fractions enriched in proteins and phenolic compounds
Summary
Among the sources of dietary amino acids available to ruminants in Europe, rapeseed and sunflower cakes have been promoted for 50 years as alternatives to imported soybean meal (Grenet and Demarquilly, 1970; Richardson et al, 1981). The lowering of the rumen degradability of proteins, initially obtained by toasting (Grenet and Demarquilly, 1970), mainly uses tanning with formaldehyde, which reacts with about ten amino acids, mainly asparagine, glutamine, lysine and arginine, to form methylene bonds that cause protein reticulation (Barry, 1976; Verite et al, 1977; Antoniewicz et al, 1992). Laguna et al (2018) evaluated several dry separation techniques on their ability to isolate proteinenriched or phenolic-enriched meal fractions in advance of more selective processes They established that electrostatic separation made it possible to collect on the positive electrode fractions with protein and phenolic contents higher than in initial cakes by 50–55% and 80–100% for rapeseed and sunflower respectively. The results were partially displayed as a poster at the International Rapeseed Congress held in Berlin in 2019
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