Monitoring the Color of Roasted and Cooked Nuts Using On-Line Spectrophotometric Instrumentation


Posted on March 7, 2018

Nuts have served as an important food source across the world for thousands of years. While the consumption of wild nuts is believed to have been common in a number of ancient cultures, nuts were also “one of the earliest cultivated foods,” playing an important part in the move toward agricultural societies and serving as a stable nutrient source for early civilizations.1 In some cultures, the value of nuts was so great that they came to be regarded as sacred symbols and spiritual nourishment.

Today, it can be easy to forget the critical historical and cultural roles nuts have played. However, they still serve as a desirable food source due to their delicious taste and nutritional value, making them attractive to both health-conscious consumers and those craving a treat. In fact, the popularity of some nuts, particularly almonds, is growing due to the spread of vegetarianism and veganism as well as changing perceptions of the healthiness of fat.2

But while nuts are widely sought after, producers must take steps to ensure the best taste, quality, and visual appeal in order to attract and keep customers. This requires rigorous quality control protocols that can detect undesirable raw materials and incorrect processing, particularly in roasted and cooked nuts. Spectrophotometric color measurement plays an essential role in the implementation of such quality control measures, providing operators with the critical information necessary to create the best possible products.

How and When to Measure the Color of Roasted and Cooked Nuts

The color of nuts can be an important indicator of taste, quality, and correctness of processing. However, visual assessment of color is not sufficient for reliable evaluation. Instead, spectrophotometers are necessary to produce reliable, objective color data that can be used to determine conformation to color standards. But nut color is not necessarily meaningful or efficient at all stages of processing. As such, integrating spectrophotometric instrumentation at the most critical points of processing will yield the best results. Let’s take a look at the appropriateness of color measurement at various stages of processing:

  • Before cleaning: Color measurement at this stage is not particularly useful, due to the impact of a variety of external factors with no effect on the quality of the nut.
  • After cleaning: Color measurement may yield more meaningful data at this point because shell discoloration could potentially indicate compromised quality. However, color data may not reliably correlate with quality, making color measurement of limited use.
  • After blanching: Depending on the specific product and use of byproducts, the color impact of blanching may or may not be valuable to assess.
  • After roasting: Measuring the color of nuts after roasting is an invaluable part of the quality control process, as color data will provide important information about correctness of processing. For example, unwanted color variation can indicate improper roasting temperature or roasting time, allowing operators to take corrective action. Color analysis after roasting is also critical to optimizing sensory appeal, including taste and overall appearance.
  • After flavoring and coating: Color should always be measured after the addition of flavorings and coatings to ensure adherence to visual standards. The color of flavorings and coatings themselves may also be measured prior to application to determine quality and prevent costly errors.

In addition to spectrophotometric color measurement, some researchers are also experimenting with using spectral data to create optical sorting systems of raw nuts. However, such systems are not yet in widespread use.

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