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Protein and amino acids
Published in Geoffrey P. Webb, Nutrition, 2019
This 6.25 figure is an approximation and more precise values may be used for some foods. Some foods may contain non-protein nitrogen but in most cases this is largely amino acid and so would not produce any dietetic error. The Kjeldahl method can also be used to estimate the nitrogen content of urine and if this is multiplied by 6.25 it indicates how much protein has been broken down to produce this amount of nitrogen. Sweat and faeces can also be analysed for nitrogen to give a complete picture of protein losses by catabolism or direct protein loss in faeces.
Microalgae for Human Nutrition
Published in Gokare A. Ravishankar, Ranga Rao Ambati, Handbook of Algal Technologies and Phytochemicals, 2019
Mariana F.G. Assuncao, Ana Paula Batista, Raquel Amaral, Lília M.A. Santos
Microalgae as a source of protein dates back to the 1950s, when an increase in the world’s population and the prediction of an insufficient protein supply led to the search for new sources of this macronutrient (Spolaore et al., 2006). The high protein content detected in some microalgal species compared with conventional foods (Table 16.1) is the main reason to consider these organisms as an alternative source of protein (Becker 2004). However, many of the published values on the protein content of microalgae are an estimation of crude protein, a measurement used to evaluate food and feed (Becker 2004). These calculations are based on the hydrolysis of the algal biomass and the evaluation of the total nitrogen (N) released. The application of an N-to-P (nitrogen-to-protein) conversion factor universally used for food labeling (N × 6.25) allows the calculation of total protein (Becker 2004; Wells et al., 2017). This conversion factor assumes that the protein source contains 16% of N, but it overlooks the content of nonprotein nitrogen in structural proteins found in microalgal cells, which are not nutritionally interesting: bioactive peptides, free amino acids, nucleic acids and ammonia (Lourenço et al., 2004; Tibbetts et al., 2015). Nevertheless, microalgae are still in line as a food source since only ~10% of the nitrogen detected in their biomass consists of nonprotein nitrogen (Arthrospira [Spirulina] 11.5% and Dunaliella 6%) (Becker 2004; Becker 2007). Some studies suggest the use of an overall mean N-to-P conversion factor of 4.78 since microalgae have nonprotein nitrogen in different amounts depending on the species, the cultivation method and the growth phase (Lourenço et al., 2004).
Infrared analyzers for the measurement of breastmilk macronutrient content in the clinical setting
Published in Expert Review of Molecular Diagnostics, 2020
Cristina Borràs-Novell, Ana Herranz Barbero, Victoria Aldecoa-Bilbao, Georgina Feixas Orellana, Carla Balcells Esponera, Erika Sánchez Ortiz, Oscar García-Algar, Isabel Iglesias Platas
We have reviewed the relevant literature assessing the performance of human milk analyzers against classical laboratory methods and other information that could be relevant toward clinical applicability. Overall, most authors conclude that infrared milk analyzers are accurate and reliable for measuring macronutrients, specifically crude protein, and total fat, when compared to reference methods, despite some differences. For measuring protein with the MIRIS HMA, correlation and precision were good [3,5,8,15], but the difference with reference methods oscillated between small [3,8] and very high [5,12]. It is important to note that infrared technology was originally developed for the dairy industry. It measures crude protein and it does not differentiate nonprotein nitrogen (i.e. urea, small peptides, amino acids, or nucleotides). In bovine milk, the amount of nonprotein nitrogen is less than 5%, but in human milk is usually between 20% and 30% and can be up to 50% [13]. Therefore, the mentioned discrepancies might be due to the presence of high percentage of nonprotein nitrogen in human milk [74]. Moreover, the use of different conversion factors can result in variability because the true value will depend on the particular amino acid sequence of the protein. The concentration of samples can also have an influence on the accuracy of the measurements [8].
The rumen microbiome: a crucial consideration when optimising milk and meat production and nitrogen utilisation efficiency
Published in Gut Microbes, 2019
Chloe Matthews, Fiona Crispie, Eva Lewis, Michael Reid, Paul W. O’Toole, Paul D. Cotter
The composition of milk is important in milk processing as it affects the quality of the product produced and the economic output of the dairy industry.106 Milk composition is an important factor with respect to milk processability. Key components are milk protein fractions, i.e., casein, whey and non-protein nitrogen (NPN), and minerals, with the most important being calcium, phosphorus and sodium. NPN refers to any compound that is not a true protein but can be converted into protein in the rumen following microbial synthesis.107 NPN is currently wasteful with regard to the processing of milk, thus a push towards having a larger proportion of casein or whey, relative to NPN, in the milk would mean more profitability for the processors per kg of milk produced. A high milk protein quality is key to maintaining thermal stability and gelation during processing.108 Urea is the most available NPN and is quickly broken down by bacterial ureases to form ammonia.109 The ammonia that is formed is important for bacterial growth, as it is used for amino acid synthesis, required for optimum growth. However, when ammonia is produced in high concentrations in the rumen, a certain amount is reabsorbed back into the bloodstream, converted back into urea in the liver and excreted through the kidneys and passed out as urine. It should be noted that urea may play an important role in low protein diets, compensating for the low concentrations of dietary protein in the diet, making urea utilization higher in comparison to that of high protein diets.
The estimation of protein equivalents of total nitrogen in Chinese CAPD patients: an explanatory study
Published in Renal Failure, 2022
Chunyan Su, Tao Wang, Peiyu Wang, Xinhong Lu, Wen Tang
The classical NB was calculated with the equation NB = NI – TNA = NI – DN – UN − FN. Nonprotein nitrogen appearance (NPNA) was calculated by subtracting total protein loss (TPL)/6.25 from TNA. The PNA was calculated as TNA multiplied by 6.25 and PNPNA (the protein equivalent of NPNA) as 6.25 NPNA. The UNA was calculated from the sum of urea nitrogen output in urine and dialysate. Total miscellaneous nitrogen (Nmc) was calculated by subtracting protein nitrogen (Npr) and urea nitrogen appearance (UNA) from total nitrogen output in urine and dialysate: Nmc = DN + UN – UNA − Npr.