Whey protein testing

The detection methods of whey protein mainly include the following:

1. Determination of total protein content
Kjeldahl nitrogen determination method:
Principle: By determining the nitrogen content in the sample, the protein content is calculated. This method is based on the assumption that the nitrogen content of protein is constant, but it cannot distinguish different types of proteins.
Operation steps: After the sample is digested, it is heated and distilled in an alkaline solution to allow ammonia to evaporate and be absorbed by the boric acid solution, and then titrated with a hydrochloric acid standard solution to calculate the nitrogen content.
Colorimetry:
Principle: Quantify the protein content by the color change of the reaction between protein and dye.
Example methods: Such as the biuret method and the Lowry method. These methods are relatively simple, but may not be as accurate as the Kjeldahl nitrogen determination method.
2. Amino acid analysis
High-performance liquid chromatography (HPLC):
Principle: Separate and quantify the amino acids after hydrolysis of whey protein by using the difference in the distribution coefficient between the stationary phase and the mobile phase, and quantify them by the detector.
Application: Separate and quantify the amino acids after hydrolysis of whey protein to comprehensively evaluate the quality of protein.
Gas chromatography (GC):
Principle: After converting the sample into gas, the different adsorption and desorption capabilities of different gases on the chromatographic column are used for separation and quantification.
Application: Although not as commonly used as HPLC, it can also be used for amino acid analysis in certain specific cases.
III. Purity detection
SDS-PAGE gel electrophoresis technology:
Principle: Different migrations occur in the gel according to the different mass-to-charge ratios of proteins to achieve protein separation.
Application: Separate and analyze the ratios of different protein components (such as β-lactoglobulin, α-lactalbumin, etc.) in whey protein to determine the purity of the protein.
Reversed-phase high-performance liquid chromatography (RP-HPLC):
Principle: Use reverse phase chromatographic columns to separate proteins and quantify them through detectors.
Application: Detect different components of whey protein to confirm its purity.
IV. Detection of other components
Fat detection:
Method: Soxhlet extraction is usually used to determine the fat content in the sample.
Carbohydrate detection:
Method: The total sugar determination or liquid chromatography can be used to determine the lactose and other sugars in the sample.
5. Moisture and ash detection
Moisture detection:
Method: Use the drying method to determine the moisture content by heating the sample and measuring the mass loss.
Ash detection:
Method: Use the high-temperature burning method to heat the sample to a certain temperature and then determine the residual inorganic matter (ash) to reflect the mineral content in the sample.
6. Microbial detection
Method: Detect the total number of bacteria, salmonella, Staphylococcus aureus, and other pathogenic bacteria in the sample to ensure the safety and hygiene standards of the product. Common methods include plate counting method, etc.
7. Heavy metal detection
Method: Use atomic absorption spectroscopy (AAS) or inductively coupled plasma mass spectrometry (ICP-MS) to detect the heavy metal content in whey protein to ensure that it meets food safety standards.
8. Allergen detection
Method: Use enzyme-linked immunosorbent assay (ELISA) and other methods to quantitatively analyze allergen proteins in dairy products.
9. Solubility and water absorption test
Solubility test:
Method: By dissolving whey protein in water or other solvents, observing its dissolution degree and time, and evaluating its solubility under different conditions.
Water absorption test:
Method: Testing the performance of whey protein after absorbing water is very important for the production of soluble whey protein powder.
X. Denaturation detection
Method: Use differential scanning calorimetry (DSC) or infrared spectroscopy (IR) to analyze the denaturation of whey protein to ensure its stability during processing.
In summary, the detection methods of whey protein cover many aspects from protein content, and amino acid composition to microbial safety, heavy metal residues, etc. The selection of these methods should be based on comprehensive considerations such as the purpose of the test, sample type, detection accuracy, and cost.