Protection of protein from ruminal degradation by alkali‐induced oxidation of chlorogenic acid in sunflower meal
The efficient utilization of dietary crude protein (CP) is crucial in ruminant nutrition, both for an optimal supply of nitrogen (N) to ruminal microbes and amino acids to the animal and for reducing environmental pollution from ruminant husbandry. However, excessive microbial CP degradation in the rumen decreases the efficiency of protein utilization in the small intestine (Calsamiglia, Ferret, Reynolds, Kristensen, & van Vuuren, 2010). Thus, ruminants would benefit from ruminally undegraded CP (RUP) sources that escape degradation but can be hydrolysed and the released amino acids be absorbed post‐ruminally. Previous attempts aiming at the preparation of high‐RUP sources include, but are not limited to, the use of polymeric coatings, heat, addition of ionophores, treatment of proteins with chemicals such as formaldehyde or different acids and the addition of secondary plant metabolites (Antoniewicz, van Vuuren, van der Koelen, & Kosmala, 1992; Patra & Saxena, 2009; Wu & Papas, 1997; Yu, Goelema, Leury, Tamminga, & Egan, 2002). However, some phytogenic additives may cause adverse effects such as decreased feed intake due to sensory effects. The use of formaldehyde and other chemicals has raised safety concerns. Heat treatment facilitates Maillard reactions, which can be poorly controlled and may lead to decreased intestinal digestibility and, finally, bioavailability of some amino acids. Therefore, alternative approaches for the preparation of feedstuffs with elevated RUP concentrations are needed. A promising approach may be using naturally occurring compounds in feedstuffs such as chlorogenic acid (CQA) in solvent‐extracted sunflower meal (SFM). Sunflower meal is the co‐product resulting from solvent extraction of sunflower oil from the seeds and contains 400–500 g/kg CP (dry matter basis) (Lomascolo, Uzan‐Boukhris, Sigoillot, & Fine, 2012). Therefore, SFM is an economically interesting source of nutrients (González‐Pérez, Merck, & Vereijken, 2002). The highest protein yields are usually obtained by alkali extraction, whereas the presence of CQA in the meal gives rise to the formation of chlorogenic o‐quinones due to oxidation. The CQA quinones are electron acceptors that readily react with nucleophiles, such as thiols and amino groups in proteins (Rawel, Meidtner, & Kroll, 2005; Weisz, Schneider, Schweiggert, Kammerer, & Carle, 2010). Interactions between CQA quinones and SFM protein may lead to the formation of covalent reaction products, thereby protecting SFM protein from ruminal degradation. It is not known whether the covalent reaction products are persisting in the abomasum and small intestine.
In the present study, SFM was subjected to alkaline treatment to investigate the influence of reactions between SFM protein and CQA quinones on ruminal degradation in order to enhance the content of RUP. For this purpose, response surface methodology was applied with pH, reaction time and drying temperature of the resulting SFM as independent numerical variables. This approach allows the identification of variables significantly influencing the reaction between CQA and SFM protein and of interactions between these variables and a multivariate optimization of the process. The resulting SFM was subjected to fractionation of feed CP according to the Cornell net carbohydrate and protein system (CNCPS) as a basis for estimating RUP. To estimate the intestinal digestibility of the treated SFM, a three‐step in vitro method was applied.