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Cited by 60Food Nutrient Composition and Product DevelopmentMilk Quality and Mastitis in Dairy CowsMembrane Separation Technologies

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Comparative study of the most commonly used methods for total protein determination in milk of different species and their ultrafiltration products

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Hueso, Diego, Fontecha, Javier, Gómez-Cortés, Pilar·2022·Frontiers in Nutrition
DOI 10.3389/fnut.2022.925565PMC PMC9513457
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Abstract

Milk ultrafiltration is a widely used membrane filtration process that allows the recuperation of whey proteins in a concentrate high in total solids, which can later be transformed in multiple healthy dairy products with great prospects for the food industry. Protein content is a decisive factor for the technological performance of milk concentrates and currently, the ISO standard method for its determination is Kjeldahl, which is time-consuming and requires specific instrumentation. For this reason, the use of rapid methods to quantify protein would greatly facilitate the monitoring of the milk ultrafiltration process. In this study, the bicinchoninic acid assay (BCA), the detergent compatible Bradford assay and the Dumas method were compared to Kjeldahl protein determination to select a quick and accurate methodology suitable for milk of different species and its ultrafiltration products (retentates and permeates). The protein content obtained from Bradford assay and Dumas method in origin milk and retentate samples was consistent with Kjeldahl values. In contrast, BCA protein levels were significantly different when compared to Kjeldahl and no method was proved to be suitable for protein determination in permeate samples. The use of sodium dodecyl sulfate was also examined to improve protein measurements without success. In comparison with the official method, Bradford assay quantitatively provided the best results, and it would be recommended for a quick, economic and easy determination of total protein content in milk and retentate samples.

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Figure 1 SDS-PAGE analysis of cow milk (1), cow milk retentate (2), cow milk permeate (3), goat milk (4), goat milk retentate (5), goat milk permeate (6), sheep milk (7), sheep milk retentate (8) and sheep milk permeate (9). MW, Molecular weight standard; αLA, α-lactalbumin; βLG, β-lactoglobulin; BSA, bovine serum albumin.
Figure 1 SDS-PAGE analysis of cow milk (1), cow milk retentate (2), cow milk permeate (3), goat milk (4), goat milk retentate (5), goat milk permeate (6), sheep milk (7), sheep milk retentate (8) and sheep milk permeate (9). MW, Molecular weight standard; αLA, α-lactalbumin; βLG, β-lactoglobulin; BSA, bovine serum albumin.CC BY · PubMed Central
Figure 2 Comparison of protein levels in milk (g / 100 mL) obtained by Kjeldahl official reference method with the contents determined by the bicinchoninic acid assay (BCA), the detergent compatible Bradford assay and the Dumas method. (A) Cow's skimmed milk, (A') cow's whole milk, (B) goat's skimmed milk, (B') goat's whole milk, (C) sheep's skimmed milk, and (C') sheep's whole milk. Different shades of gray indicate different ultrafiltration processes. P-value: *** = P < 0.001; ** = P < 0.01; * = P < 0.05; ns = P > 0.05.
Figure 2 Comparison of protein levels in milk (g / 100 mL) obtained by Kjeldahl official reference method with the contents determined by the bicinchoninic acid assay (BCA), the detergent compatible Bradford assay and the Dumas method. (A) Cow's skimmed milk, (A') cow's whole milk, (B) goat's skimmed milk, (B') goat's whole milk, (C) sheep's skimmed milk, and (C') sheep's whole milk. Different shades of gray indicate different ultrafiltration processes. P-value: *** = P < 0.001; ** = P < 0.01; * = P < 0.05; ns = P > 0.05.CC BY · PubMed Central
Figure 3 Comparison of protein levels in milk retentate (g / 100 mL) obtained by Kjeldahl official reference method with the contents determined by the bicinchoninic acid assay (BCA), the detergent compatible Bradford assay and the Dumas method. (A) Cow's skimmed retentate, (A') cow's whole retentate, (B) goat's skimmed retentate, (B') goat's whole retentate, (C) sheep's skimmed retentate, and (C') sheep's whole retentate. Different shades of gray indicate different ultrafiltration processes. P–value: *** = P < 0.001; ** = P < 0.01; * = P < 0.05; ns = P > 0.05.
Figure 3 Comparison of protein levels in milk retentate (g / 100 mL) obtained by Kjeldahl official reference method with the contents determined by the bicinchoninic acid assay (BCA), the detergent compatible Bradford assay and the Dumas method. (A) Cow's skimmed retentate, (A') cow's whole retentate, (B) goat's skimmed retentate, (B') goat's whole retentate, (C) sheep's skimmed retentate, and (C') sheep's whole retentate. Different shades of gray indicate different ultrafiltration processes. P–value: *** = P < 0.001; ** = P < 0.01; * = P < 0.05; ns = P > 0.05.CC BY · PubMed Central

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References 36 · Cited by 60

Research works printed but not linked: 36

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Metadata

Authors
Hueso, D., Fontecha, J., & Gómez-Cortés, P.
Affiliations
Instituto de Investigación en Ciencias de la Alimentación (ES)
ORCID
Venue
Frontiers in Nutrition
Publisher
Frontiers Media SA
Published
2022-09-13
Volume
9
Pages
925565-925565
ISSN
2296-861X (ISSN-L)
DOI
10.3389/fnut.2022.925565
PMC
PMC9513457
OpenAlex
W4296588744
Cited by
60
References
36
Citations by year
2026: 17 · 2025: 19 · 2024: 15 · 2023: 7 · 2022: 2
FWCI
5.85
Type
journal article
Language
en
Open access
Licence
Locations
  • Frontiers in Nutrition (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • DIGITAL.CSIC (Spanish National Research Council (CSIC)) (submittedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
Consejo Superior de Investigaciones Científicas
Topics
  • Life Sciences › Agricultural and Biological Sciences › Food Science › Food Nutrient Composition and Product Development
  • Life Sciences › Agricultural and Biological Sciences › Animal Science and Zoology › Milk Quality and Mastitis in Dairy Cows
  • Physical Sciences › Environmental Science › Water Science and Technology › Membrane Separation Technologies
Keywords
total protein determination, whey protein concentrate, permeate, Bradford assay, bicinchoninic acid assay, Dumas method, Kjeldahl method, sodium dodecyl sulfate

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Hueso, D., Fontecha, J., & Gómez-Cortés, P. (2022). Comparative study of the most commonly used methods for total protein determination in milk of different species and their ultrafiltration products. Frontiers in Nutrition. https://doi.org/10.3389/fnut.2022.925565