NIR vs. Kjeldahl

Protein is a critical parameter across the food, beverage, and feed industries. However, the best solution for obtaining protein varies across the production cycle. In this blog, we propose Kjeldahl and near-infrared (NIR) spectroscopy methods for protein determination, with arguments for which technology is the best fit based on factors such as:

  • Application scope
  • Variation in sample type
  • Automated throughput
  • Speed
  • Unattended operation
  • Compliance
  • Start-up costs
  • Eco-friendliness

You can read foundational principles about Kjeldahl or NIR in earlier blog posts. Here, we will dive right into the practical discussion of selecting the best solution for your lab.

Round 1: You have a lot of different applications

Fat, protein, moisture, ash, starch, lactose… if the list of parameters you’re measuring looks like a shopping list, then NIR may be a good fit for your lab or production area. BUCHI NIR offers a variety of products to provide fast and easy analysis of a broad range of sample properties. Qualitative (e.g. product quality or conformity or to flag adulteration) and quantitative (e.g. %-fat) methods are possible.

Round 1: NIR: 1 Kjeldahl: 0

Round 2: Your samples are constantly changing

If your samples and/or formulation are relatively consistent, then NIR is a great method. Calibrations are easily updated when small changes occur. However, if samples or sample formulations are a moving target, NIR calibration becomes impractical. For those situations, Kjeldahl is the better choice. Acid digestion and steam distillation can be applied for the determination of various N-containing products, and changing matrices or highly heterogeneous samples are easily handled by Kjeldahl.

Round 2: NIR: 0 Kjeldahl: 1

Round 3: Automation & high throughput are critical

High throughput can be generated by a short sequence of multiple samples or by a high degree of parallelization. Kjeldahl is a slower technique than NIR, but can digest 20 samples at once. Following digestion, 20 samples can be distilled and titrated in parallel. With continuous operation, 120 samples can be processed by Kjeldahl in a 9-hour workday when used in combination with the autosampler.

The BUCH Kjel Line and Dist Line systems offer automated distillation and titration without the autosampler.

At-line (benchtop) NIR systems like the BUCHI NIRMaster or ProxiMate require one-at-a-time sampling with manual sample changes between measurements. Although measurement times are fast (< 60 seconds). Approximately 190 samples can be measured for all calibrated properties within a 9-hour period.

On-line NIR offers a continuous stream of real-time measurement data with no sample handling required. With process control system integration, it is the clear winner when automation and throughput are deemed most critical.

Round 3: On-line NIR: 1 At-line NIR & Kjeldahl: 0

Round 4: Data collection is rate-limiting

A rapid method is required to increase sampling frequency, enabling better quality control across food and beverage production, as well as feed and forage ingredients, pre-mix, and finished products.

At-line NIR products for the food industry, like the IP-69 ProxiMate, provide a hygienic, easy-to-use measurement solution for the control room or plant floor. With various accessories like glass or plastic dishes and transflectance adapters, the ProxiMate can collect data for solids, liquids, powders, gels, and pastes. Calibrated properties are measured simultaneously, with measurement times under 1 minute.

For even more rapid data collection, in-line or on-line NIR measurement systems are available. These systems are integrated into hoppers, conveyor belts, mixers or other processing equipment to provide real-time data and process control capabilities.

Round 4: NIR: 1 Kjeldahl: 0

Round 5: Unattended operation is required

With the use of Kjeldahl autosampler, unattended operation is possible during sample distillation or digestion runs, while NIR requires manual sample changing. On the other hand, on-line NIR offers completely unattended operation.

Round 5: NIR: 1 Kjeldahl: 1 It’s a draw

Round 6: You need to show compliance

Kjeldahl is the most established reference method for protein determination in food, beverage, feed, and forage. It often serves as the primary reference method for NIR calibrations. Plus, it is compliant with a plethora of national and international regulations, including AOAC, ISO, DIN, LFGB, and many more.

You can find application notes presenting compliant Kjeldahl methods for a variety of sample matrices using our Application Finder.

Round 6: NIR: 0 Kjeldahl: 1

Round 7: Start-up cost is an issue

The BUCHI Kjeldahl portfolio offers entry-level Kjeldahl products through highly sophisticated, fully-automated systems, allowing us to meet a variety of budgets. The BUCHI ProxiMate is an affordable at-line NIR solution that has low start-up costs and calibration costs where a BUCHI or INGOT quick start calibration package is offered. Some examples of quick start applications include:

  • Meats & seafood
  • Feed & pet food
  • Milk & dairy
  • Milling & bakery
  • Confectionery
  • Ready-made meals
  • Oils & fats

Once an NIR method is operational, it out-performs Kjeldahl with respect to low running costs, as no consumables are required for routine sampling.

Round 7: NIR: 0 Kjeldahl: 1

Round 8: You want to go green

While a variety of more eco-friendly Kjeldahl consumables options are available, using acids in digestion makes Kjeldahl less green than NIR, which produces no emissions and requires no solvents or catalysts. Moreover, analysts avoid contact with chemicals using NIR.

Round 8: NIR: 1 Kjeldahl: 0


Looking back on the discussion points above, this match-up looks like a technical draw. As an opponent, each technique has advantages that put competition on the ropes. Looking for compliance, unattended operation, and automation? Put Kjeldahl in your corner. If your ideal solution is a master of multitasking with incredible speed and agility, then place your bets on NIR. At the end of the day, only you can decide what advantages can be exploited to achieve the objectives defined by your workplace and workflow.

Dig deeper into BUCHI solutions using the links below:

As always, contact us if you want to speak with an expert on NIR or Kjeldahl!

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