Comparison of three methods for calculating protein content of foods

Heidelbaugh, N. D.; Huber, C. S.; Bednarczyk, James.; Smith, Malcolm; Rambaut, P. C.; Wheeler, Harry Ogden

doi:10.1021/jf60200a006

Cited by 52 publications

(68 citation statements)

References 4 publications

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“…37 According to this method, it is possible to calculate the amount of crude protein (CP) in the sample by multiplying the percent nitrogen (N) by a conversion factor (6.25) (Eq. 2).…”

Section: General Methodsmentioning

confidence: 99%

Extraction and physico-chemical characterization of a versatile biodegradable polysaccharide obtained from green algae

Alves

Caridade

Mano

et al. 2010

Carbohydrate Research

113

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“…37 According to this method, it is possible to calculate the amount of crude protein (CP) in the sample by multiplying the percent nitrogen (N) by a conversion factor (6.25) (Eq. 2).…”

Section: General Methodsmentioning

confidence: 99%

Extraction and physico-chemical characterization of a versatile biodegradable polysaccharide obtained from green algae

Alves

Caridade

Mano

et al. 2010

Carbohydrate Research

113

View full text Add to dashboard Cite

“…This included TAA measurements which were not originally used to determine protein content but were reported along with nitrogen and/or protein content. Second, N-protein factors were also calculated just for TAA data as this method is considered the most accurate method for determining protein (Heidelbaugh et al 1975). These N-protein factors were calculated only from the 5th to 95th percentile as not to represent extreme values and were used to determine seaweed-specific N-protein factors for an applied use and for correlations with internal N content.…”

Section: Ecologicalmentioning

confidence: 99%

“…N-protein conversion factors are based on the quantification of total amino acids which is considered to be the most accurate way of determining protein (Heidelbaugh et al 1975). Conversion factors have been calculated using two different methods.…”

Section: Introductionmentioning

confidence: 99%

The protein content of seaweeds: a universal nitrogen-to-protein conversion factor of five

et al. 2015

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A global drive to source additional and sustainable biomass for the production of protein has resulted in a renewed interest in the protein content of seaweeds. However, to determine accurately the potential of seaweeds as a source of protein requires reliable quantitative methods. This article systematically analysed the literature to assess the approaches and methods of protein determination and to provide an evidence-based conversion factor for nitrogen to protein that is specific to seaweeds. Almost 95 % of studies on seaweeds determined protein either by direct extraction procedures (42 % of all studies) or by applying an indirect nitrogen-to-protein conversion factor of 6.25 (52 % of all studies), with the latter as the most widely used method in the last 6 years. Meta-analysis of the true protein content, defined as the sum of the proteomic amino acids, demonstrated that direct extraction procedures underestimated protein content by 33 %, while the most commonly used indirect nitrogen-to-protein conversion factor of 6.25 over-estimated protein content by 43 %. We therefore determined whether a single nitrogen-to-protein conversion factor could be used for seaweeds and evaluated how robust this would be by analysing the variation in this factor for 103 species across 44 studies that span three phyla, multiple geographic regions and a range of nitrogen contents. An overall median nitrogen-to-protein conversion factor of 4.97 was established and an overall mean nitrogen-to-protein conversion factor of 4.76. We propose that the overall median value of 5 be used as the most accurate universal seaweed nitrogen-to-protein (SNP) conversion factor.

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“…In this study we assume that the actual concentrations of protein in the samples are calculated from the sum of amino acid residues (Tables 1 and 2), a widely accepted procedure since the 1970s (Heidelbaugh et al, 1975). After acid hydrolysis, all proteins are destroyed, even those associated with other macromolecules and biological membranes.…”

Section: Amino Acid Profile Non-protein Nitrogen and Protein Contentmentioning

confidence: 99%

An evaluation of methods for extraction and quantification of protein from marine macro- and microalgae

2005

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Comparison of data of protein content in algae is very difficult, primarily due to differences in the analytical methods employed. The different extraction procedures (exposure to water, grinding, etc.), protein precipitation using different amounts of 25% trichloroacetic acid and quantification of protein by two different methods and using two protein standards were evaluated. All procedures were tested using freeze-dried samples of three macroalgae: Porphyra acanthophora var. acanthophora, Sargassum vulgare and Ulva fasciata. Based on these results, a protocol for protein extraction was developed, involving the immersion of samples in 4.0 mL ultra-pure water for 12 h, followed by complete grinding of the samples with a Potter homogeniser. The precipitation of protein should be done with 2.5:1 25% TCA:homogenate (v/v). The protocol for extraction and precipitation of protein developed in this study was tested with other macroalgae (Aglaothamnion uruguayense, Caulerpa fastigiata, Chnoospora minima, Codium decorticatum, Dictyota menstrualis, Padina gymnospora and Pterocladiella capillacea) and microalgae (Amphidinium carterae, Dunaliella tertiolecta, Hillea sp., Isochrysis galbana and Skeletonema costatum). Comparison with the actual protein content determined from the sum of amino acid residues, suggests that Lowry's method should be used instead of Bradford's using bovine serum albumin (BSA) as protein standard instead of casein. This may be related to the reactivity of the protein standards and the greater similarity in the amino acid composition of BSA and algae. The current results should contribute to more accurate protein determinations in marine algae.

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Comparison of three methods for calculating protein content of foods

Cited by 52 publications

References 4 publications

Extraction and physico-chemical characterization of a versatile biodegradable polysaccharide obtained from green algae

Extraction and physico-chemical characterization of a versatile biodegradable polysaccharide obtained from green algae

The protein content of seaweeds: a universal nitrogen-to-protein conversion factor of five

An evaluation of methods for extraction and quantification of protein from marine macro- and microalgae

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