Effects of different levels of slow-release non-protein nitrogen on bioconversion of potato waste by rumen microorganisms

Introduction: Daily, large amounts of rumen contents are produced as waste in slaughterhouses, which are not used and released into the environment, which causes environmental issues and problems. Potato (Solanum tuberosum) is one of the crops with high production throughout the world a large amount of which is removed from the consumption cycle as waste during different stages, and if not used correctly, it can cause environmental pollution. The main method of using potato waste is to use it in fresh or dried form to feed domestic animals. Although drying waste potatoes for use in animal feed seems like a good idea, but its high cost has made this uneconomical. Therefore, it is necessary to transform potato waste into a sustainable product that has a higher economic value. Compared to other processing methods, bioconversion is a new and desirable method for agricultural waste management. Ruminal fluid, as a rich source of enzymes, can be used in the bioconversion of agricultural waste. The microbial population present in the rumen is a rich source of new enzymes that have a high potential for industrial use. Various studies using different methods, such as the use of Saccharomyces yeasts and Lactobacillus species for the biological conversion of potato waste to ethanol, producing biogas from solid potato waste in a two-step process anaerobic digestion, fermentation of potato waste by mixed culture to produce lactic acid, enzymatic hydrolysis of potato pulp to produce glucose and ethanol and using Various bacterial species have been used for the biological conversion of potato pulp into cellulose. The objective of this study was to investigate the effect of different levels of slow-release non-protein nitrogen on the bioconversion of potato waste by ruminal microorganisms.
Materials and methods: Potato waste was collected from potato storage stocks and after cleaning the waste materials, it was boiled and then grated before incubation. The required rumen fluid was obtained from the slaughterhouse and after being filtered with a four-layer cheesecloth, it was added to the glass bottles of the rumen digestion simulator apparatus (DaisyII) and immediately transferred to the apparatus and incubated at 39 degrees Celsius for 24 hours. Experimental groups were: 1) 400 ml of rumen fluid + 200 g of waste potato (N0), 2) 400 ml of rumen fluid + 200 g of waste potato + 1.5 g of nitrogen from a slow-release nitrogen source (N1.5), 3) 400 ml of rumen fluid + 200 grams of waste potatoes + 3 grams of nitrogen from a slow release nitrogen source (N3) and 4) 400 ml of rumen fluid + 200 grams of waste potatoes + 4.5 grams of nitrogen from a slow release nitrogen source (N4.5). After the end of the incubation time, the samples were removed from incubation bottles, and after filtering and separating the solid and liquid parts from each other for further tests. The liquid portion of the incubation medium was analyzed for protozoa count, volatile fatty acids, ammonia nitrogen, and hydrolytic enzymes and compared to the fresh initial rumen fluid used for the incubation. The resulting data were analyzed in the form of a completely randomized design using SAS software (2003). Means were shown as Least Squares (LSMEAN) along with standard error and mean comparisons at a significance level of five percent.
Results and discussion: Protozoa count in the liquid portion of the incubation medium was affected by the experimental groups. Rumen fluid had the highest number of protozoa and supplementing the culture medium with a non-protein nitrogen source had a decreasing effect on the protozoa population. The activities of carboxy-methyl cellulase, alpha-amylase, microcrystalline cellulose, and filter-papers enzymes were affected by the levels of supplementation from slow-release non-protein nitrogen sources and the highest carbohydrate-degrading activities were recorded at 1.5 gr nitrogen supplementation per 100 gr potato waste (P<0.05). The level of urease and protease enzyme activity was also affected by different levels of non-protein nitrogen sources and 4.5 grams of nitrogen from non-protein nitrogen sources showed the highest level of activity. Supplementing the incubation medium increased its ammonia concentration and the highest value was observed at 4.5 grams of slow-release non-protein nitrogen level (P<0.05). For all enzyme activities, initial fresh rumen fluid had the lowest activities. Volatile fatty acid production was affected by supplementation with non-protein nitrogen levels and the amount of volatile fatty acids in the liquid phase of the incubation medium showed the highest values with 3 grams of non-protein slow-release nitrogen supplementation.
Conclusion:
Based on the results of the present study, the addition of slow-release non-protein nitrogen to the incubation medium of potato waste with rumen liquid microorganisms significantly increases their power in the biotransformation of potato waste. Also, the liquid part of the culture medium can be considered as a source of enzymes and acids for use on an industrial scale due to the increased activity of hydrolytic enzymes and volatile fatty acids that are the product of the fermentation process. The use of the processed rumen fluid resulting from this incubation as a source of enzymes and nutrients in feeding livestock and poultry will be an environmentally friendly method, in this way, the rumen fluid of slaughterhouses and potato waste will be used with proper management methods. Therefore, the results of the present study, rumen liquid microorganisms along with a non-protein nitrogen source can be used in the bioconversion of potato waste more effectively to increase its nutritional value and produce a liquid rich in volatile fatty acids as well as a source of favorable enzyme activities.