1697 Research Article Received: 28 January 2009 Revised: 8 April 2009 Accepted: 20 April 2009 Published online in Wiley Interscience: 4 June 2009 (www.interscience.wiley.com) DOI 10.1002/jsfa.3643 In vitro gas production profiles and fermentation end-products in processed barley, maize and milo Arash Azarfar, a* Kuenga Namgay, b Wilbert F Pellikaan, b Seerp Tamminga b and Antonius FB van der Poel b Abstract BACKGROUND: An experiment was carried out to establish whether using a pre-compacting device (expander) changes the contribution of dry matter (DM) and degradative behaviour of grains of barley, maize and milo pre-processed by grinding over the different DM fractions (non-washable (NWF), insoluble washable (ISWF) and soluble washable (SWF) fractions). Samples of the entire concentrate ingredients (WHO ingredients) and their different fractions (NWF, ISWF and SWF) were subjected to three processes (Retsch-milled (R), expander-treated (E) and expander-pelleted (EP) samples) and their fermentation characteristics were evaluated using an in vitro gas production technique. RESULTS: The E process increased the size of the NWF and decreased that of the SWF compared with the R process. The ISWF of R samples was very rich in starch. The maximum fractional rate of substrate degradation and maximum rate of gas production were higher in EP samples than in R samples (P < 0.05). In maize and milo the E and EP processes shifted the pattern of fermentation towards a more glucogenic fermentation, as represented by a lower non-glucogenic/glucogenic ratio (NGR). In all grains the ammonia concentration (NH 3 -N) and branched chain ratio (BCR) of E and EP samples were significantly (P < 0.05) lower than those of R samples. CONCLUSION: It is concluded that the E and EP processes have the potential to synchronise the fermentation of dietary proteins and carbohydrates and shift the pattern of fermentation towards a more glucogenic fermentation. c  2009 Society of Chemical Industry Keywords: cereal grains; expander; expander-pelleting; gas production; fermentation INTRODUCTION Processing of cereal grains is a well-known concept to ruminant nutritionists and the feed industry. Various feed-processing methods that are deemed beneficial to animals are widely used in feed industries around the world. Expander processing is one such technique in feed manufacturing, which involves heat, pressure and shear. The major parameters characterising the expander pro- cess are temperature (80 – 130 ◦ C), moisture content of the product (180 – 300 g kg −1 ), residence time (5 – 15 s) and shear force. 1 Expander processing may improve the nutritive value of feeds for ruminants by increasing available energy/protein, which, with appropriate diets and feeding regimes, contributes to synchronising nutrient supply. 2–4 Subjecting cereal grains to such a hydrothermal process increases the degree of starch gelatinisation and makes the starch granule more accessible for both bacterial attachment and ruminal fermentation. 5 Moreover, expander treatment and the ensuing pelleting process involve shear forces that may affect the size of particles. Therefore processing of feeds may change their degradability in ruminants either by changing the degradation rate or by changing the distribution of feed dry matter (DM) over the different fractions (washable, potentially degradable and undegradable fractions) in whole feeds. 4,6 The in situ technique is a very common procedure that is often used to characterise ruminal degradation of unprocessed as well as processed feeds. This technique fractionates feed material into a washable (W) fraction, a potentially degradable (D) fraction and an undegradable (U) fraction and gives information on the fractional degradation rate of the D fraction. The in situ technique cannot measure the rate at which the W fraction of protein and starch is actually degraded. Therefore assumptions are made regarding the part of it that escapes rumen fermentation. 7 This means that a great deal of information is available on the degradative behaviour in the rumen of starches, proteins and cell walls present in the D fraction but not in the W fraction. Since the W fraction quantitatively constitutes an important part of feedstuff DM (up to 500 g kg −1 DM), 8 characterising its degradative behaviour is of great importance. The combination of ∗ Correspondence to: Arash Azarfar, Faculty of Agriculture, University of Lorestan, PO Box 465, Khorramabad, Iran. E-mail: Arash.Azarfar@gmail.com a Faculty of Agriculture, University of Lorestan, PO Box 465, Khorramabad, Iran b Wageningen Institute of Animal Sciences, Animal Nutrition Group, Department of Animal Sciences, Wageningen University, Marijkeweg 40, PO Box 338, NL-6700 AH Wageningen, The Netherlands J Sci Food Agric 2009; 89: 1697–1708 www.soci.org c  2009 Society of Chemical Industry