Nitrogen-containing Substances Research Articles

Endogenous proteins in terminal ileal digesta of adult subjects fed a casein-based diet

Although there are several published estimates of the endogenous amino acid composition of ileal digesta in humans, to our knowledge, there are no systematic studies of ileal digesta endogenous proteins. We determined the nature and composition of endogenous nitrogen-containing substances lost from the upper digestive tract of humans. Digesta were collected from the terminal ileum for a period of 8 h by using a nasoileal tube in 6 adult subjects fed a single meal that contained 22% of casein as the only source of nitrogen. The total nitrogen that passed the terminal ileum was 39.3 mg/g native digesta dry matter. Of this amount, 86% was proteinaceous, ~60% was bacterial protein, ~7% was soluble-free protein, ~15% was mucin protein, and ~5% was protein from intact mucosal cells. For nonprotein nitrogen, ~5% of the total nitrogen was ammonia, and ~4% of the total nitrogen was urea. Bacterial and human mucosal cellular DNA nitrogen were collectively ~0.5% of the total nitrogen. Approximately 30% of the nonprotein nitrogen (4% of the total nitrogen) remained unidentified. This amount was assumed to include free amino acids, RNAs, amines, and the tetrapyrroles bilirubin and biliverdin. Bacterial nitrogen, combined with ammonia and urea nitrogen, represented >68% of total ileal nitrogenous losses. Findings are presented on the endogenous nitrogen-containing compounds that left the terminal ileum. Of particular significance is the observation that mucin was the most abundant truly endogenous component within the terminal ileal digesta. Bacterial protein, which was strictly nondietary rather than endogenous, contributed the highest proportion, by far, of nondietary protein, the result of which makes a significant contribution to published estimates of ileal endogenous amino acids and protein. The high concentration of bacterial protein and the presence of ammonia and urea nitrogen indicate potentially substantial microbial activity within the human distal small intestine.

Effects of cultural medium and conditions on the proliferation and hypoglycemic activity of Saccharomyces pastorianus no. 54

A yeast strain of Saccharomyces pastorianus no. 54 with hypoglycemic activity was isolated from soils of a winery. The aims of this study were first to investigate the effects of the cultivation conditions on proliferation and hypoglycemic activity of this yeast using the assay model of the differentiated 3T3-L1 adipocytes, and then, to confirm in vivo the hypoglycemic activity of cultured yeast by oral administration in streptozotocin (STZ)-induced diabetic mice. Among 7 diluted fruit juice samples the diluted strawberry juice (1.74 g/L reducing sugar content) was chosen as the basal medium. After investigation of the effects of addition of various substances, including 1% of 5 different sugars and glycerol, 0.1% of 6 nitrogen-containing substances, and 1 ppm of 7 growth factors, the diluted strawberry juice added with 1% glucose, 0.1% yeast extract and 1 ppm aspartic acid was optimized at 20 °C with initial pH value of 6.0 for cultivating S. pastorianus no. 54 in flask. The scale-up system of a 5-L fermentor was further established by using the same medium with initial pH 6.0 and being incubated at 20 °C with an aeration rate of 1.2 vvm for 96 h. The hypoglycemic activity of yeast cells cultivated in fermentor was 3.11 times of that in flask. Oral administration of the cultured yeast at a dosage of 130 mg/kg body weight/day for 6 days could significantly reduce the plasma glucose content in STZ-induced diabetic mice and keep their body weights in the normal range.

Features of nitrogen metabolism in fishes

Presence in water is easily metabolized nitrogen-containing substances is a vital condition for the existence of food organisms in ponds used for fish reproduction. At the same time, the end products of nitrogen metabolism—ammonia, nitrites and nitrates are always displayed the body of fish into the environment, adding to the total number of these compounds dissolved in water. Ammonia, nitrite and nitrate anions are formed during biological processes, as well as man-made origin, have toxic properties and are considered as environmental factors that may limit fish productivity of reservoirs. The results of a brief review of the literature showed that the features of nitrogen metabolism in fish are actual direction of research, both theoretical science and in practical fish farming. Published the results of studies of amino acid metabolism in fish suggest that, firstly, the processes responsible for the neutralization and the release of ammonia from the body of fish, as well as ontogenetic aspects of the dynamics of formation and emission of ammonia is not fully understood. Meanwhile, several authors stressed the importance of this area of interest for the formation of science-based ways to improve the efficiency of plant breeding in fish culture. Secondly, endogenous nitrite, being the product of oxidation of the molecule nitric oxide and its transport form, the norm are always present in fish. However, the mechanisms responsible for maintaining the stability of the concentration of nitrite in the internal environment of fish, not well understood. Also, in our opinion, of interest to determine the physiological rules of nitrites and nitrates in the body of various species, depending on the seasons and stages of ontogeny. Thirdly, the literature pays much attention to the toxic properties of nitrite in water biocenosis. Certainly, the analysis of the manifestation in fish tissue-specific toxic effects of nitrites and their derivatives—an important area of research. Nevertheless, we can not exclude that it may be quite promising analysis of the incorporation of exogenous nitrite as a substrate exist in fish of the physiological mechanisms re-synthesis of nitric oxide. This kind of “interference” of endogenous and exogenous nitrite-anions are not causing serious structural damage to organs and tissues, however, can cause substantial damage to the practical fish farming, causing changes in the level of regulatory mechanisms of fish at the most critical stages: when working with manufacturers, the incubation of eggs, and larvae rearing and wintering fish.

The change of polyphenolic composition and tyrosol content of the wine as an effect of sur lie method

While keeping wines on the fine lees the composition of nitrogen-containing substances, including the amino acid concentration, changes as a result of the autolysis of yeasts. During the course of former experiments, it was proven that yeasts were able to reduce the polyphenolic composition of wines. As part of the research for the present publication, the change of polyphenolic content in ‘Chardonnay’ wines kept on the lees was analysed. In addition the quantity of tyrosol, required for the forming of simple phenolics, was examined. The results proved that yeasts reduced the quantity of polyphenolics. In addition, due to the increased amino acid concentration, yeasts reduced the quantity of tyrosol that is derived from the amino acid called tyrosine.

Effect of Replacing Soybean Meal with Lupin Seed-based Meal in Chicken Diet on Performance, Carcass Value and Meat Quality

The main objective of this experimental study was to determine how diets containing lupin meal affect the performance indicators, carcass value, and chemical composition of breast and thigh muscles in broiler chickens. The diets tested in experimental groups E1 and E2 differed as follows: in group E1, one third of nitrogen-containing substances (NSs) from extracted soybean meal was replaced with NSs from lupin meal; in group E2, two thirds were replaced compared to the control group. The replacement of soybean meal with lupin meal in experimental diets failed to produce any significant effect on the average live weight of chickens on Day 42 of the fattening period compared to the control group. The replacement of soybean meal with lupin meal resulted in decreased average weight of carcass and breast muscles and in decreased yield of breast muscles. Differences between the control group (C) and group E2 were significant (P &#x2AAC 0.01). Chickens in group E2 also showed a significant increase (P &#x2AAC 0.01) in the yield of the heart and stomach compared to the control group. The differences in weight and yield of thigh muscles between the control group and the experimental groups (E1 and E2) were not significantly affected. As far as chemical composition is concerned, chickens receiving the lupin-containing feed showed a significant (P &#x2AAC 0.01) increase in the ash content in breast muscles. On the contrary, in thigh muscles in group E2, the ash content decreased significantly (P &#x2AAC 0.01). The content of calcium showed an increasing trend in both breast and thigh muscles in both experimental groups. In contrast, the content of magnesium in chicken muscles in both experimental groups decreased. These differences were significant (P &#x2AAC 0.01) only in thigh muscles. Our results show that lupin seed is a suitable substitute for NSs contained in soybean extracted meal. It is considered optimal to replace up to one third of NSs contained in soybean meal with lupin seed. Higher inclusion rate of lupin meal in diets may reduce the growth intensity of chickens, particularly the yield of breast muscles. Due to substantial inter-varietal differences, it is necessary to optimize individual nutrients, particularly amino acids when formulating lupin-containing diets.

Geochemical analysis of Lake Bant sediments to ascertain inorganic and organic indicators for warfare residues

The immediate time period after the Second World War (1945–1946) was characterised by an urgent need to dispose large amounts of ammunition residues. Although the environmental relevance of explosives released to soils is intensively investigated, to date, their fate and effects in marine ecosystems are not well known. Surface sediments from Lake Bant, Germany, for which deposition of an enhanced amount of ammunition after World War II has been reported, were analysed to identify organic and inorganic indicators for warfare residues. Additionally, samples of ammunition residues collected from the Wadden Sea, Germany, were analysed in order to obtain information on the long-term behaviour of explosives in undamaged ammunition left in the aquatic environment and to obtain first insights into the spectrum of organic substances which are possibly released to the aquatic environment by such ammunition residues. Inorganic analyses comprising determination of major elements (energy dispersive X-ray fluorescence) and heavy metals (ICP-OES, graphite furnace AAS and LA-ICP-MS) were applied to surface sediment samples from Lake Bant as well as to metal coatings of ammunition samples. Organic constituents of sediment samples, corresponding pore water and ammunition fillings were analysed by a Gas chromatographic/mass spectrometer-based non-target screening approach. Analyses of lake sediment samples depicted a complex pattern of pollution dominantly derived from petrogenic and sewage sources. Comparing the spatial distribution of petrogenic contaminants with petroleum-related emissions sources present till 1945 at Lake Bant, it is likely that the detected petrogenic contamination represents dominantly war-related residues. Contamination from ammunition residues was not clearly evident in the sediment samples. However, indicative nitrogen-containing compounds potentially reflecting ammunition impact were obtained from analyses of pore water samples. The presence of dibenzylamine, N-nitroso dibenzylamine and diethylamino benzopyranone might give evidence that nitrogen-rich compounds have been released by dumped ammunition. Additional investigation of ammunition samples from the same time period derived from the Jade Bay indicated a high-preservation potential and consequently long-term preservation for explosives in undamaged ammunition residues. War-related residues in sediments of Lake Bant have to be appointed dominantly to petroleum-related emission sources, whereas ammunition residues currently do not contribute significantly. However, the identification of specific nitrogen-containing organic substances in the corresponding pore water pointed to the assumption that (1) pore water might be an appropriate compartment to follow the environmental fate of ammunition constituents in surface water systems and (2) an extended bioavailability has to be presumed for explosive derivatives. Furthermore, based on the observed preservation of ammunition fillings, the corrosion and decomposition of ammunition shells might lead to the emission of unaltered explosives even decades after their deposition in aquatic environments. However, the information on their environmental stability and fate in surface waters is still limited. Since the knowledge on the environmental fate of ammunition residues in the aquatic environment comprising their stability as well as their potential harmful effects is very low, further investigations on the long-term behaviour of ammunition residues in subaquatic sediments and the corresponding water body is recommended.

Inter‐laboratory comparison of elemental analysis and gas chromatography/combustion/isotope ratio mass spectrometry. II. δ15N measurements of selected compounds for the development of an isotopic Grob test

An inter-laboratory exercise was carried out by a consortium of five European laboratories to establish a set of compounds, suitable for calibrating gas chromatography/combustion/isotope ratio mass spectrometry (GC-C-IRMS) devices, to be used as isotopic reference materials for hydrogen, carbon, nitrogen and oxygen stable isotope measurements. The set of compounds was chosen with the aim of developing a mixture of reference materials to be used in analytical protocols to check for food and beverage authentication. The exercise was organized in several steps to achieve the certification level: the first step consisted of the a priori selection of chemical compounds on the basis of the scientific literature and successive GC tests to set the analytical conditions for each single compound and the mixture. After elimination of the compounds that turned out to be unsuitable in a multi-compound mixture, some additional oxygen- and nitrogen-containing substances were added to complete the range of calibration isotopes. The results of delta(13)C determinations for the entire set of reference compounds have previously been published, while the deltaD and delta(18)O determinations were unsuccessful and after statistical analysis of the data the results did not reach the level required for certification. In the present paper we present the results of an inter-laboratory exercise to identify and test the set of nitrogen-containing compounds present in the mixture developed for use as reference materials for the validation of GC-C-IRMS analyses in individual laboratories.

Flavouring Group Evaluation 85: Consideration of miscellaneous nitrogen-containing substances evaluated by JECFA (65th meeting) - Scientific Opinion of the Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food

Flavouring Group Evaluation 85: Consideration of miscellaneous nitrogen-containing substances evaluated by JECFA (65th meeting) - Scientific Opinion of the Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food

Interaction between Insulating Paper and Transformer Oil: Bacterial Content and Transport of Sulfur and Nitrogen Compounds [Feature Article

There were variations between different insulating papers, but all contained significant amounts of sulfur. The sulfur showed little migration and it is therefore less likely that transformer paper will contribute, in a significant degree, to the amount of sulfur found in transformer oil in service. Thermally upgraded qualities of transformer paper are treated with different nitrogen-containing compounds. Therefore, the clear increase of nitrogen content in oil exposed to thermally upgraded paper suggests that migration from transformer paper can contribute considerably to the amount of nitrogen-containing substances found in transformer oil in service.

LC-DAD-MS (ESI+) Analysis and Antioxidant Capacity of Crocus sativus Petal Extracts

In this study, various fractions isolated from the petals of Crocus sativus were assessed at first for their phenolic content both qualitatively and quantitatively and secondly for their antioxidant activity. The phytochemical analysis was carried out by LC-DAD-MS (ESI (+)) whereas the antioxidant potential was evaluated by applying two methodologies, the DPPH. radical scavenging activity test and the Co(II)-induced luminol chemiluminescence procedure. According to data obtained from these antioxidant tests, the diethyl ether, ethyl acetate and aqueous fractions demonstrated the strongest antioxidant capacity. Interestingly, the major constituents identified in these fractions correspond to kaempferol, quercetin, naringenin and some flavanone and flavanol derivatives glycosylated and esterified with phenylpropanoic acids. In addition, the presence of some nitrogen-containing substances, as well as other phenolics and phenylpropanoic derivatives was also traced. The identification and structural elucidation of all substances isolated in this study was achieved by both comparing available literature data and by proposed fragmentation mechanisms based on evaluating the LC-DAD-MS (ESI (+)) experimental data. The quantitative analysis data obtained thus far have shown that Crocus sativus petals are a rich source of flavonoids. Such a fact suggests that the good antioxidant capacity detected in the various fractions of Crocus sativus petals could be attributed to the presence of flavonoids, since it is already known that these molecules exert antioxidant capability. The latter, along with the use of Crocus sativus in food and pharmaceutical industry is discussed.

Characterization of Puff-by-Puff Resolved Cigarette Mainstream Smoke by Single Photon Ionization−Time-of-Flight Mass Spectrometry and Principal Component Analysis

Soft single photon ionization-time-of-flight mass spectrometry (SPI-TOFMS) and principal component analysis (PCA) were applied for the characterization and discrimination of the chemical patterns of all individual cigarette puffs from the 2R4F University of Kentucky research reference cigarette. The SPI-TOFMS was connected to a smoking machine, and 10 cigarettes were smoked under defined smoking conditions. A total of 41 detected mass signals could be clearly assigned to smoke constituents (e.g., unsaturated hydrocarbons, aromatic species, sulfurous compounds, and nitrogen-containing substances). For further analysis, the on-line recorded mass signals were added up for each cigarette puff resulting in a single summed mass spectrum for each puff. The so-achieved puff-by-puff resolved yields were additionally normalized by the corresponding total ion signal, which eliminated the influences of varying amounts of burnt tobacco. These values were incorporated into a PCA to find differences and similarities in the chemical patterns of the individual cigarette puffs. In addition, absolute (without normalization) and normalized puff resolved yields were used to clarify occurring trends. Thereby, it was shown that the chemical pattern of the first cigarette puff was very unique, whereby extraordinary high yields of unsaturated hydrocarbons are mainly responsible for this. Depending on the smoking procedure, the chemical pattern of the second puff can also be separated from the first and the third puff. In this case, nitrogen-containing substances play an important role. Puffs three to eight show only small but observable differences. These changes are greater influenced by oxygen-containing and sulfurous smoke constituents. The findings reveal that the overall chemical patterns of machine-smoked cigarette puffs vary quite a lot during the smoking process. This lets us assume that the burden of hazardous compounds for the human smoker also differs from puff to puff.

Inter‐laboratory comparison of elemental analysis and gas chromatography combustion isotope ratio mass spectrometry (GC‐C‐IRMS). Part I: δ13C measurements of selected compounds for the development of an isotopic Grob‐test

This study was directed towards investigating suitable compounds to be used as stable isotope reference materials for gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) calibration. Several compounds were selected from those used in the 'Grob-test' mixture. Oxygen- and nitrogen-containing substances were added to these compounds to allow the mixture to be used as a possible multi-isotopic calibration tool for 2H/1H, 13C/12C, 15N/14N and 18O/16O ratio determinations. In this paper we present the results of delta13C measurements performed by the consortium of the five laboratories taking part in this inter-calibration exercise. All the compounds were individually assessed for homogeneity, short-term stability and long-term stability by means of EA-IRMS, as required by the bureau communitaire de reference (BCR) Guide for Production of Certified Reference Materials. The results were compared then with the GC-C-IRMS measurements using both polar and non-polar columns, and the final mixture of selected compounds underwent a further certification exercise assessing limits of accuracy and reproducibility under specified GC-C-IRMS conditions.

Investigation, by single photon ionisation (SPI)–time-of-flight mass spectrometry (TOFMS), of the effect of different cigarette-lighting devices on the chemical composition of the first cigarette puff

Soft single-photon ionisation (SPI)-time-of-flight mass spectrometry (TOFMS) has been used to investigate the effect of different cigarette-lighting devices on the chemical composition of the mainstream smoke from the first cigarette puff. Lighting devices examined were a Borgwaldt electric lighter, a propane/butane gas lighter, a match, a candle, and the burning zone of another cigarette. To eliminate the effects of the different masses of tobacco burnt by use of the different lighting methods a normalisation procedure was performed which enabled investigation of changes in the chemical patterns of the resulting smoke. When another cigarette was used as the lighting device, elevated levels of ammonia and other nitrogen-containing substances were observed. These are high in the sidestream smoke of the cigarette used for lighting and would be drawn into the mainstream smoke of the cigarette being lit. In contrast, smoke from the cigarette lit by the electric lighter contained slightly higher normalised amounts of isoprene. Lighting the cigarette by use of a candle resulted in larger amounts of substances, e.g. benzene, which most probably originated from thermal decomposition of wax. The composition of the first puff of smoke obtained by use of the three lighting methods with open flames (gas lighter, match, and candle) was usually similar whereas the composition of the smoke produced by use of the electric lighter and the cigarette as the lighter were more unique. The chemical patterns generated by the different lighting devices could, however, be separated by principal-component analyses. Two additional test series were also studied. In the first the cigarette was lit with an electric lighter, then extinguished, the ash was cut off, and the cigarette was re-lit. In the second the cigarette was heated in an oven to 80 degrees C for 5 min before being lit. These treatments did not result in changes in the chemical composition compared with cigarettes lit in the ordinary way.

Testing of Two Varieties of Lupin Seeds as Substitutes for Soya Extracted Meal in Vegetable Diets Designed for Young Broilers

The main aim of this experiment was to verify the suitability of two Polish varieties of dehulled lupin seed (the low-protein SONET variety and the high-protein JUNO variety) as protein components to replace 50% of soya extract meal in feeding mixtures designed for the feeding of young broilers. The results of this experiment demonstrate that suitable treatment of lupin seed (dehulling) may significantly increase its nutritional value. Dehulling provides a product (core) in which the level of nitrogen-containing substances is by 27% higher than that in the original seed, providing an important protein component to be added in feeding mixtures for chickens. The experiment has also shown that production performance depends on the particular Lupinus variety used. Chickens fed on the JUNO variety seed (Group E1) reached a live weight of 2.332 kg on Day 40, which is comparable with the control group of chickens (2.337 kg; Group C). However, chickens in Group E2 fed on the SONET variety seed had a conclusively lower average weight (2.280 kg) (P < 0.05). Feed consumption per kg of weight gain at this level of average live weight was as follows: 1.89 kg (Group C), 1.85 kg (Group E1), and 1.93 kg (Group E2). The results confirm the suitability of dehulled lupin seed as a substitute for soya extract meal. When designing the composition of feeding mixtures one has to know the exact nutritional composition of the particular lupin variety. One important finding from a nutritional point of view is that the seed of the Lupinus genus is a major source of the amino acid arginine, which is often deficient in the feeding mixtures.

The fate of organic nitrogen in photocatalysis: an overview

Photocatalytic processes taking place on TiO2 have been widely employed and investigated. However, nitrogen-containing substances have not received the same attention as other substrates. Mineralization of such compounds is expected to lead to the formation of N2 gas, ammonium and/or nitrate ions through photooxidative and/or photoreductive pathways. Herein, we will focus the attention on how the chemical structure may influence both the ratio and the extent of formation of the inorganic nitrogen. This review will consider heteroaromatic compounds, containing two or three-nitrogen in the ring, and small molecules, that could be formed as intermediate during the degradation of more complex substrates (i.e. pesticides), such as amino-alcohols, and molecules containing amide groups and nitriles. The fate final of the nitrogen in all these structures has been rationalized on the basis of the nature of N–N and C–N bonds in which the organic nitrogen is involved.

Automatic calibration of the spectrometric channels in a device for detecting explosives

The calibration of the energy scale of a device which is a spectrometer and is to be used for detecting explosives in various objects (baggage of airline passengers, mail, briefcases, cases, and others) is examined. The work is based on the method of neutron-radiation analysis. In the present case the calibration is of fundmental importance because the nitrogen sensitivity of the device is low. A brief description of a working model, the basic characteristics, the background spectrum of capture radiation with a sample of nitrogen-containing substance, and an example of a calibration curve are presented. The method of check sums and its advantages are examined. It is shown that it can be used in setups for detecting explosives.

Nitrogen Pool in Northern-Taiga Larch Forests of Central Siberia

The pools of nitrogen in different blocks of forest ecosystems and its cycle in the soil are considered. It is shown that the bulk of nitrogen concentrates in the soil and dead organic matter (necromass) of an ecosystem. The nitrogen pool of forest litters and soils consists by 83-93% of the inert compounds that cannot be involved in the biological cycle. Mineralization of organic nitrogen-containing substances in the litters and soils usually yields ammonium as an end product. The amount of nitrogen mineralized over the growing season is partially expended for annual plant increment (30-65%) and immobilization (12-17%), with its large proportion being found in the soil.

Quantitative determination of protein of bacterial origin on the basis ofd-aspartic acid andd-glutamic acid content

In recent decades several methods have been developed for determination of the proportion of nitrogen-containing substances passed from the rumen into the abomasum, or small intestine, which are of microbial origin. Recently, when examining thed-amino acid content of foodstuffs, particularly milk and milk products, it was observed that, in addition tod-alanine (d-Ala,d-glutamic acid (d-Glu) andd-aspartic acid (d-Asp) can also be detected in similar quantities, primarily in products which have links with bacterial activity. This gave rise to the idea of examining the diaminopimelic acid (DAPA),d-Glu, andd-Asp content of bacteria extracted from the rumen of cattle, and that of chyme from the same cattle, to establish whetherd-Asp andd-Glu can be used to estimate protein of bacterial origin.

Evaluation of the sealed‐tube low‐temperature combustion method for the 13C/12C and 2H/1H ratio determinations of cellulose nitrate

AbstractTraditionally‐suggested combustion time of 1 h at 550°C) with the sealed‐tube combustion method for determining the 13C/ 12C ratio of cellulose nitrate or other nitrogen‐containing components could produce large negative deviation up to 1°. Three types of cellulose are used to ascertain possible causes. The presence of nitrous oxide (N2O) formed during combustion is most likely responsible for this deviation. Prolongation of the combustion time (at least 5 h at 550°C) and intimate contact between copper oxide and organic matter can greatly improve the analysis precision and effectively reduce this deviation to an acceptable level. Regardless of scattered carbon isotope data, hydrogen isotope data are all reproducible within 2° when this method is coupled with the high temperature uranium reduction method. Thus, care should be taken for determining carbon and nitrogen isotope compositions of nitrogen‐containing substances using the low temperature sealed‐tube combustion method.

A NEW METHOD FOR THE QUANTITATIVE DETERMINATION OF PROTEIN OF BACTERIAL ORIGIN ON THE BASIS OF D-ASPARTIC ACID AND D-GLUTAMIC ACID CONTENT

In the past years several methods have been developed for the determination of the proportion of the nitrogen-containing substances of microbial origin passed from the rumen into the abomasum or the small intestine. Recently, on examining the D-amino acid content of foodstuffs, particularly milk and milk products, it has been observed that, in addition to D-Ala, D- glutamic acid (D-Glu) and D-aspartic acid (D-Asp) can also be detected in similar quantities, primarily in products which have links with bacterial activity. This gave rise to the idea of examining the diaminopimelic acid (DAPA), D-Glu and D-Asp content of bacteria extracted from the rumen of cattle and that of chyme from the same cattle, in order to determine the type of relation existing among these three components, and to establish whether D-Asp and D-Glu can be used in the estimation of protein of bacterial origin. On determination of the DAPA, D-Asp and D-Glu content by means of amino acid analyser and high performance liquid chromatography of duodenal chyme from five growing bulls and of ruminal bacteria from the same bulls, the following values were established. For chyme (and, in brackets, for ruminal bacteria) r value calculated by means of linear regression was 0.78 (0.76) between DAPA and D-Asp, and 0.70 (0.81) between DAPA and D-Glu. The r values between the crude protein content of ruminal bacteria and the markers examined were found to be the following: DAPA, 0.74; D-Asp, 0.73; D- Glu, 0.61. In the model experiment performed for the re-obtaining of values for protein of bacterial origin the theoretical values were determined on the basis of D-Asp and D-Glu and values approximately 10% higher than the theoretical value on the basis of DAPA. It is therefore recommended that in addition to DAPA these other two amino acids be included among the bacterial protein markers.