"Zapping" Lentils Makes Them More Nutritious and Greener To Process

Processing red lentils with a specialized combination infrared microwave system—a countertop device that allows heating by microwave and radiant heat simultaneously—the USask research team was able to substantially improve how easily these lentils could be digested.

“The process makes these macromolecules—starch and protein—more accessible to enzymes in our bodies,” said Mehdi Foroushani, USask doctoral student and first author on the study published in the journal Food Chemistry Advances.

By tweaking the amount of moisture in the lentils, and the amounts of microwave and infrared energy, the research team was able to make more than 96 per cent of the starch digestible, and more than 85 per cent of the protein digestible, measured by how quickly the product dissolves in vitro. In raw lentils, less than 69 per cent of starch is digestible and less than 80 percent of protein is digestible.

To better understand what happened at the molecular level and examine it in the finest detail possible, the research team analyzed the lentil samples using USask’s Canadian Light Source synchrotron.

“Starch has a smooth surface,” said USask doctoral student Tahereh Najib, co-author of the study. “We make it kind of rough, so it’s more accessible by enzymes and the starch can be better broken down.”

More than two million tonnes of lentils are produced on average each year in Canada, the world’s biggest producer, with the majority produced in Saskatchewan. Lentils are harvested, cleaned, and graded before packaging or further processing. Most are cooked and consumed as a whole grain, but a growing volume of lentils is dried and turned into a powder to isolate proteins from starches and used as a food additive.

“Our process takes 200 per cent less drying time,” said USask College of Engineering researcher Dr. Venkatesh Meda (PhD), principal investigator on the study. “The unique nature of this energy method is that there is no input of chemicals used for drying, there is no output in terms of release of greenhouse gases.”

In microwaving, heat is generated from the center of the lentil and radiates outward—moisture and heat escape to the outside environment. By simultaneously roasting the surface of the lentils with infrared heat, the research team was able to increase the overall efficiency and better seal in the microwave heat.

“By having more plant-based alternative food ingredients in our diet, one can also reduce our environmental footprint by fulfilling our need for proteins from plant sources,” said Meda.

The ideal setting of lentil moisture, microwave energy intensity, and infrared roasting depends largely on how the lentil flour will be used.

“Modified lentil flour can be a great source of plant-based ingredients for our dietary and nutritional needs, and our kitchen and food processing operations,” said Meda. “Lentil flour serves as an additive or substitution to our food system to not only make the food nutritious but also preserve its acceptable texture.”

The USask-processed lentils have not yet been assessed or approved for official trials involving human or animal consumption, for which a commercial kitchen is required. While the texture may be acceptable, how does the zapped lentil flour taste?

“At home we have been using it, and the aroma has improved to ‘acceptable,’ and not deteriorated compared to any other commercial variety,” said Meda. “We’re happy to report there is not much loss in any of the sensory qualities: colour, texture, aroma.”

Currently, the lentil flour is processed in very small batches—only 50 grams. The next steps in the research involve improving the flavour, scaling up to process larger amounts of lentils, applying the process to other legumes and oilseeds, and examining whether the technique could also improve seed quality for germination.

Reference: Heydari MM, Najib T, Meda V. Investigating starch and protein structure alterations of the processed lentil by microwave-assisted infrared thermal treatment and their correlation with the modified properties. Food Chem Adv. 2022;1:100091. doi:10.1016/j.focha.2022.100091

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