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Sigma's Non-specific Protease Activity Assay - Casein as a Substrate
Published on: September 17, 2008
Development of a biosensor immunoassay for the quantification of alphas1-casein in milk
Stéphanie Muller-Renaud1, Didier Dupont, Philippe Dulieu
1INRA, Unité de Recherches en Technologie et Analyses Laitière, Place du Champ de Foire, F-39800 POLIGNY, France.
Insights
A new immunoassay accurately measures intact alphas1-casein (alphas1-CN) in milk using surface plasmon resonance (SPR). This rapid, reusable biosensor assay avoids quantifying degraded proteins, offering precise results for raw milk analysis.
Area of Science:
- Analytical Chemistry
- Biochemistry
- Food Science
Background:
- Accurate quantification of intact alphas1-casein (alphas1-CN) is crucial for milk quality assessment.
- Existing methods may not differentiate intact alphas1-CN from its degradation products.
- Development of rapid and specific analytical techniques is needed.
Purpose of the Study:
- To develop and validate a novel immunoassay for quantifying intact alphas1-casein in milk.
- To utilize an optical biosensor based on surface plasmon resonance (SPR) for enhanced specificity.
- To enable rapid, precise, and reliable analysis of alphas1-CN in raw milk samples.
Main Methods:
- A two-step sandwich immunoassay employing two specific anti-alphas1-CN antibodies.
- Surface plasmon resonance (SPR) optical biosensor technology for detection.
- Calibration using a reference milk powder with known alphas1-CN concentration.
Main Results:
- The assay specifically quantifies intact alphas1-CN, excluding degradation products.
- Achieved a detection limit of 0.87 microg/ml with low variation coefficients (2.86% intra-assay, 5.31% inter-assay).
- Sample analysis time was under ten minutes, with a reusable antibody surface for over 150 determinations.
- Applied to raw milk, yielding concentrations from 8.8 to 12.06 mg/ml in 48 samples.
Conclusions:
- The developed SPR-based immunoassay provides a sensitive, specific, and rapid method for intact alphas1-CN quantification in milk.
- This technique offers a valuable tool for milk quality control and research without sample pre-treatment.
- The assay's robustness and reusability make it suitable for routine analysis.
Abstract:
An immunoassay to quantify alphas1-casein (alphas1-CN) in milk using an optical biosensor, based on surface plasmon resonance (SPR) measurement, has been developed. The assay consists of a two-step sandwich strategy, with two anti-alphas1-CN antibodies directed against each extremity of the molecule. This strategy permits only intact alphas1-CN to be quantified and not its degradation products. The calibration curve was obtained using a reference milk powder with a known alphas1-CN concentration. Analysis time per sample was less than ten minutes. The antibody-coated surface could be used for more than 150 determinations. Detection limit was established at 0.87 microg/ml and the intra- and inter-assay variation coefficients were 2.86 and 5.31%, respectively. The method was applied to raw milk to quantify intact alphas1-CN, with no pretreatment of the sample. An initial analysis of 48 milk samples permitted alphas1-CN concentrations ranging from 8.8 to 12.06 mg/ml to be obtained.
