Products Questions & Answers
Q: Are these tests for protein content and digestibility intended for liquid or powdered samples?
A: Nutri-Test and Digest-Pro are designed to quantify protein content and protein digestibility in powdered samples, not in liquid samples containing dissolved proteins. The tests were developed for powdered food and feed ingredients such as insect-, algae-, animal-, plant-based, and novel proteins (e.g., dried distillers’ grains with solubles (DDGS), soybean meal, fish meal, rapeseed meal, pea protein, insect meal, whey and milk powders, beef extract, maize flour, chickpea flour, peptone, and single-cell proteins, etc.). However, the tests can also be used for food products - for example, protein-rich bars, cookies, bakery products, cereals, pasta, meat analogues, dairy powders, pet foods, and feed pellets - which need to be dried and homogenised prior to analysis.
Q: How do these tests differ from Bradford, Lowry, and BCA (Bicinchoninic Acid) assays, as well as SDS-PAGE and Native PAGE methods for protein analysis?
A: Nutri-Test and Digest-Pro are fundamentally different because they provide the total protein content in dried powdered samples and the in vivo protein digestibility of those samples. In contrast, Bradford, Lowry, and BCA assays quantify protein content in liquids or buffer solutions and require dissolution and solubilization of proteins, making them unsuitable for powdered samples. Similarly, SDS-PAGE and Native PAGE also require proteins to be solubilized and primarily quantify molecular weights of the proteins and their type if compared to a standard, rather than total protein content or digestibility.
Q: Are there similar tests for total protein content on the market? How do they compare to the current methods?
A: No, Nutri-Test and Digest-Pro are the only tests available to quantify protein content in powdered food and feed samples. Currently, total protein content is determined using certified Kjeldahl and Dumas methods, both of which require expensive equipment and involve laborious procedures. Moreover, these methods rely on measuring total nitrogen and applying conversion factors, which can introduce inaccuracies. In contrast, our tests require only simple laboratory equipment and consumables, allow high-throughput analysis, and provide results as accurate as the Kjeldahl and Dumas methods, but at a lower cost per sample.
Q: Are there similar tests for protein digestibility on the market? How do they compare to the current methods?
A: No, Digest-Pro is the only test available to quantify protein digestibility in food and feed samples. Otherwise, animal trials with piglets are required to determine in vivo protein digestion.
Q: How does it work? What is the basic principle of the tests?
A: Both tests are based on digestion and comparison to standard samples. The protein content method relies on the digestion of proteins in an acidic environment. The protein digestibility test simulates a two-step physiological digestion of protein-containing ingredients: first, gastric digestion with gastric enzymes, followed by intestinal digestion using an intestinal enzyme mixture. The resulting amino acids are quantified using spectrophotometric analysis with a dye.
Q: How is protein digestibility presented? What is protein digestibility?
A: Digest-Pro is based on in vitro digestion of proteins, which mimics intestinal digestion in a test tube. The results from this in vitro digestion are then converted to in vivo protein digestibility, a parameter that is traditionally determined using lengthy and laborious animal trials.
Digest-Pro also allows the calculation of additional parameters that quantify protein quality, such as PDCAAS (Protein Digestibility-Corrected Amino Acid Score) and DIAAS (Digestible Indispensable Amino Acid Score). To determine these, either a tabulated amino acid profile for your samples or an HPLC-DAD amino acid analysis is required. For a first approximation, amino acid data can be sourced from literature if the sample is typical. Our protocol provides step-by-step guidance for all required calculations.
Q: Can you provide amino acid profiling for my samples to determine PDCAAS and DIAAS?
A: Yes, we can. Please contact us for a quotation.
Q: What is the difference between Nutri-Test and Digest-Pro?
A: Nutri-Test is an assay for the determination of protein content only, whereas Digest-Pro is a 2-in-1 test that allows measurement of both protein content and protein digestibility. Both tests include reagents for 50 assays (run in duplicates).
Q: What is in the tests?
A: The tests contain all the required reagents, standards, and a manual to perform the analyses.
Q: What other equipment or consumables are required to conduct the tests?
A: Basic laboratory reagents such as HCl, NaOH, acetic acid, distilled water, and pH paper or strips (or a pH meter), as well as micro UV-Vis cuvettes (or 96-well plates), acid-resistant glass vials, syringes, pipettes, filters, an oven, and a UV-Vis spectrophotometer or plate reader, will be required for the analysis. A water bath may be used for heating, and centrifugation can facilitate the separation of solids.
Q: Does it come with a Material Safety Data Sheet (MSDS)?
A: Yes, the MSDS is available for download upon purchase of the kit.
Q: Can you send the test protocol so that we can evaluate the suitability of the tests for our lab?
A: We cannot share the protocols prior to purchase. The tests have been designed for easy implementation in a basic laboratory setting. The tests will include: preparation of reagents by weighing and mixing; heating (up to 90-110 °C) either without mixing or preferably with mixing/shaking (using an oven for static heating, or a water bath or shaking incubator for combined heating and mixing); separation of solids from liquids by centrifugation, filtration, or both; pH determination using pH paper strips; dilutions using Gilson pipettes (10–10,000 µL). Absorbance is measured at 570 nm using a spectrophotometer (with 1.5 mL microcuvettes) or a plate reader (96-well plate). Although 6M HCl and 10M NaOH are required, they can be prepared safely without the need for a fume hood.
Q: Are your tests certified?
A: No, our tests are not certified yet; however, they are validated against the certified Dumas and Kjeldahl methods. Currently, there is no officially certified in vitro method for measuring protein digestibility in food or feed, and in vivo digestibility is determined only via animal trials. PDCAAS can be determined based on amino acid analysis and in vitro digestion; however, the challenge with in vitro tests is the variability in reaction conditions, which can reduce accuracy. Our Digest-Pro is an optimised method that uses a set of standards to overcome key challenges in determining protein digestibility.
Q: How accurate are the test kits?
A: Both test kits use a wet-chemistry-based method with UV-Vis analysis, so they share common sources of error. The precision of the UV-Vis measurement (the final step involving dye quantification) is typically <1% when performed correctly. The main contributors to overall uncertainty are procedural errors-such as inaccuracies in dilutions, sample transfers between vessels, and sample heterogeneity between duplicates or triplicates-which largely determine overall precision.
The measurement range for protein content determination is 0-100 wt% protein, although accuracy decreases below 10 wt%. Overall accuracy is within 5-7% error, comparable to the Dumas method (typically 5-6% variation between laboratories). Repeatability for duplicate or triplicate measurements is typically 3–5% RSD for both Nutri-Test (crude protein) and Digest-Pro (digestibility).
Q: How much sample is required?
A: The method was developed for a sample size of 100 mg per analysis; however, it can be downscaled to 50 mg if needed.
Q: What is the sample pre-prep procedure? Does the sample need to be wet or dry?
A: The sample should be in its original form. Note that grinding and particle size can affect the digestibility of proteins, although they have less impact on the measured protein content. The samples should be air-, oven-, or freeze-dried, preferably with a moisture content of approximately 5-7 wt.%. Protein content is expressed as % dry weight (d.w.), and overall, the moisture content must be taken into account for higher accuracy. We do advise drying the samples in an oven at 60 - 80 °C until they reach a constant weight and ensuring they have a uniform particle size of at least 0.5 - 1 mm.
Q: I struggle with the analysis and calculations. Can you help?
A: Certainly! We provide ongoing support to our customers. Write to us at info@novatica-tech.com, and we will get back to you as soon as possible.