Investigating the effect of processing with autoclave and centrifuge methods on the nutritional value of dried rumen fluid using spray drying method

Introduction: Slaughterhouse rumen fluid contains microbial proteins, volatile fatty acids, microorganisms, vitamins and minerals. Rumen fluid has a very diverse population of bacteria and other microorganisms. Rumen bacteria have a thick bacterial polysaccharide (BPS) coating, so this fluid contains hundreds of bacterial polysaccharide molecules. Rumen fluid activity does not appear to be highly dependent on the diet. Bacterial polysaccharides are potent antigens and remain active even after autoclaving (Muscato et al., 2002). On the other hand, it contains high levels of ammonia and phosphorus, which, when disposed of in slaughterhouses, cause environmental pollution. Its nutrients cause eutrophication when excreted in soil and waterways. It is therefore important to find consistent uses of ruminal fluid (Trit and Schuchardt, 1992). The benefits of recycling these wastes are firstly reducing environmental pollution and secondly producing a feed source for ruminants (Mundal et al., 2013.( Muscato et al. (2000) suggested the autoclave method at 121°C for 40 minutes to destroy pathogenic microorganisms in the rumen fluid, which prevents the transfer of pathogens and disease-causing agents to healthy animals. Centrifugation can also be used to reduce odors and suspended substances. One of the methods that makes it easier to transport, store, check, and mix and distribute the rumen liquid in small amounts in the feed formulation is to dry it. Spray drying has recently been used to dry biologically active compounds (Tribizenk et al. 1997). It is a simple, fast, and economical technique for obtaining powder from a solution or a liquid suspension (such as an enzyme suspension) (Bajsic and Kranjsevik 2001). This method is widely used in the pharmaceutical and dairy industries to dry milk, whey, antibiotics, vitamins, and enzymes (DeVos et al. 2010). Spray drying changes the liquid to a solid form and causes transport, storage, easy examination, and uniform mixing and distribution in food formulations in small amounts (Tan et al. 2005). Therefore, this research will investigate the effect of processing with autoclave and centrifuge methods on the nutritional value of dried rumen liquid using a spray dryer.
Materials and methods: The rumen fluid was taken from the slaughterhouse to the laboratory and was smoothed using a 4-layer linen cloth. From an unprocessed rumen fluid sample, one sample was autoclaved at 121°C for 40 minutes to prevent pathogen transmission, another sample of rumen fluid was centrifuged for 10 minutes at a speed of 1000 rpm to separate the suspended material and reduce its odor. The other sample was first autoclaved and then centrifuged. Finally, all samples were dried by spray drying method. Therefore, experimental treatments include: 1- fresh rumen fluid (FRF); 2- fresh rumen fluid dried by spray drying method (SFRF); 3- fresh rumen fluid autoclaved and dried by spray drying method (SAFRF); 4 - Fresh rumen fluid centrifuged and dried by spray drying method (SCFRF); 5- Fresh rumen fluid was autoclaved, centrifuged and dried by spray drying method (SCAFRF). AOAC (2000) method was used to determine the chemical composition (percentage of dry matter, crude protein, ether extract and ash) in the tested samples. The method of Agarwal et al. (2000) was used to determine the concentration of carboxymethylcellulase, microcrystalline cellulose, amylase and filter paper activity. A gas chromatography device (Varian Inc., Walnut Creek, Canada) was used to measure the concentration of volatile fatty acids in it. The concentration of macro and micro elements and heavy metals, after removing ash from the samples, was determined with an inductively coupled plasma emission spectrometer (Genesis model, manufactured by Spectro, Germany).
Results and discussion: There is a statistically significant difference between fresh rumen liquid and rumen liquid autoclaved and centrifuged and dried by spray drying method in terms of chemical compounds (P<0.01). So far, there is no report about the processes of autoclaving and centrifugation on the chemical composition of dried rumen fluid. In a report, they reported 5.83, 15.52, 5.17, and 11 percent of moisture, crude protein, ether extract, and ash in the dried digestate of slaughtered sheep, respectively (Sakaba et al., 2017). Although the increase in the percentage of dry matter and crude protein is not important for a feed additive in livestock, but this increase shows that these processes did not reduce the chemical compounds of the rumen liquid. The activity of carboxymethylcellulase, avisalase, amylase and filter paper enzyme activity was the highest in rumen liquid dried by spray drying method (P<0.01) and the lowest in rumen liquid autoclaved, centrifuged and dried by spray drying method. In this research, autoclaving was used to destroy pathogenic microorganisms in rumen fluid and centrifugation was used to remove suspended substances and reduce odor. It is expected that by autoclaving at 121°C for 40 minutes, the activity of enzymes will decrease to zero due to their protein nature, but the autoclaved treatments had more enzyme activity than the centrifuged one, and even with autoclaving and centrifugation, the activity of polysaccharides degrading enzymes have not reached zero. The concentration of volatile fatty acids was significantly affected by autoclave and centrifugation processes. In this research, centrifugation increased the concentration of volatile fatty acids in several cases and even autoclaving did not have a statistically significant difference with fresh rumen fluid in several cases The concentration of mineral elements was significantly affected by the treatments .By using autoclave and centrifuge methods, the concentration of most measured minerals increased significantly. Yu et al. (2013) reported that the rumen fluid is rich in mineral elements and can be used as an additive, so by autoclaving and centrifuging, the concentration of most mineral elements increases, and on the other hand, pathogenic microorganisms and suspended substances and odor also decreases.
Conclusion: According to the obtained results, the autoclaving process was effective in eliminating the pathogenic microorganisms of the rumen fluid. With centrifuge-autoclave processes, the various enzymes were still active. The use of the centrifugation process was more effective than autoclave in maintaining the concentration of volatile fatty acids. Also, autoclave processing reduced the concentration of volatile fatty acids that have a low boiling point, and the simultaneous use of these two processes increased the concentration of most volatile fatty acids compared to fresh rumen fluid. Also, using these two processes, the concentration of most of the macro and micro elements increased. Therefore, centrifugation and autoclaving are recommended to remove suspended substances, reduce odor, and also eliminate pathogenic microorganisms in the rumen fluid.