Analysing apple chip production using NIR spectroscopy

Dried snack foods such as apple chips are becoming increasingly popular as a convenient alternative to fresh fruit. In order to meet the demand for variety, food manufacturers are coating such snack foods with fruit and vegetable powders to enhance taste and sensory appeal.

A new study from the University of Illinois explores the drying process of coated and uncoated apple chips using near-infrared (NIR) spectroscopy to measure moisture content in real time.

The purpose of coating is to make dried apple chips more functional and nutritional, as well as more appealing to eat, explains Ragya Kapoor, graduate student in Food Science and Human Nutrition (FSHN) at U of I and lead author on the paper.

“The idea is to get school-aged children to include apple chips in their diet. We use a cranberry powder coating to make the apple slices more attractive in terms of colour and taste,” Kapoor said. “We dip the apple slices in a liquid-based solution for 60 seconds twice, and then conduct the hot air-drying operation.”

The researchers check the moisture content at various points throughout the drying process with miniature NIR spectroscopy to ensure the chips are dry enough.

NIR technology offers advantages compared to standard monitoring techniques, said Mohammed Kamruzzaman, assistant professor in the Department of Agricultural and Biological Engineering (ABE) at U of I and co-author on the paper.

“In traditional methods, you take samples from the production for lab analysis. The process takes at least 24 hours, the samples are destroyed, and some analyses require harsh chemicals,” Kamruzzaman said.

In contrast, NIR spectroscopy takes a few seconds, does not require the removal of samples, and uses no chemicals. “Traditional lab techniques need experts to handle the equipment and interpret the data. NIR is easy to use, and almost anyone can handle the instrument and take the measurement with just a few minutes of training. And the equipment is small and portable.”

NIR works by scanning the product with invisible light, Kamruzzaman explains.

“With our eyes we can see the size, shape and colour of food, but we cannot see the nutritional composition. The near-infrared light reads the chemical bonds in the food, so you can analyse any biological matter and determine features such as moisture content, protein, fat, fibre, or carbohydrates. The NIR spectroscopy will give you many data points; we extract the data and use machine learning to interpret the results,” he states.

“The combination of NIR spectroscopy and machine learning is very powerful.”

University of Illinois graduate students Ragya Kapoor, Food Science and Human Nutrition, and Amir Malvandi, Agricultural and Biological Engineering. Image credit: College of ACES, University of Illinois.

Kapoor, Kamruzzaman, and study co-authors Amir Malvandi, graduate student in ABE, and Hao Feng, professor of food and bioprocess engineering at U of I, had two main research goals. They wanted to explore edible coating on apple slices and test the use of NIR spectroscopy to monitor the drying process for coated versus uncoated slices.

“The moisture content is different for coated and uncoated samples, and we wanted to see how drying behaviour differs for them. We found that with NIR technology we are able to differentiate between the two samples based solely on the difference in their composition,” Kapoor explains.

The results showed that the miniature NIR spectroscopy was able to monitor the drying process and discriminate between the coated and uncoated apple slices and drying times, primarily by the differences in sugar and water absorption bands.

As the NIR allows the user to see the product’s changing moisture content in real time, the researchers said the process can be used to enhance production efficiency.

“You can continuously monitor the drying process, observe the amount of dry matter, and decide the right time to stop,” Kamruzzaman said.

The paper, “Real-time moisture monitoring of edible coated apple chips during hot air drying using miniature NIR spectroscopy and chemometrics”, is published in LWT – Food Science and Technology.

Top image credit: ©stock.adobe.com/au/klio_l