Where others only see waste or animal feed, Dr. Rocío Morales sees an unused resource for a healthy plant-based diet, namely pea shells. Rich in fibers such as cellulose, hemicellulose, and pectin, the shells accumulate when peas are processed to produce starch. In Germany alone, 30,000 tons of pea shells are discarded annually in starch production. Researchers are interested in are the skins of each pea rather than the husk or pod. According to the German Nutrition Society (Deutsche Gesellschaft für Ernährung - DGE), dietary fiber prolongs our feeling of satiety, slows the rise in blood sugar, and lowers cholesterol and the risk of high blood pressure. The DGE recommends 30 grams of dietary fiber per day for adults.
Dr. Rocío Morales, who researches under the direction of Professor Dr. Stephan Drusch at the Department of Food Technology and Food Material, has been exploring ways to process the dietary fiber in pea shells for human nutrition as the shells cannot simply be added to other foods such as milk, yogurt, baked goods, or vegan rillettes. "Cellulose and hemicellulose, for example, are not water-soluble. If unprocessed pea shells were added to milk, they would settle to the bottom after a short time and the milk couldn't be sold, despite being so fiber-rich," says Morales. Additionally, cellulose consists of long fibers which feel like sand in your mouth when consumed. Last but not least, it is essential that the foods enriched with these fibers do not taste like peas. The creamy consistency of yogurt, the smooth consistency of milk, the elastic texture of bread, or the familiar taste of each food cannot be affected by the fiber.
In order to part of a fiber-rich plant-based diet, the technofunctional properties of the pea fibers such as viscosity and their ability to bind to water must be fundamentally improved. To achieve this, the fibers must be broken up and the cellular wall broken down. This is a highly complex undertaking and anything but trivial. Morales experimented with two methods: one using only high-pressure homogenization and another combining high-pressure homogenization with an enzymatic pretreatment of the pea shells, using the enzymes cellulase, hemicellulase, and pectinase. In this pre-treatment, the enzymes cut open the cell walls of the peas enabling them to break down more easily. The shells are then homogenized under high pressure. This is key to using the pea shells as a food ingredient as it allows good water binding and contributes to the desired consistency and stability, for example in dairy products, without sediment forming.
"The aim of our research was to break down the pea fiber particles, improve the fibers' ability to bind to water, and thus increase the viscosity of suspensions where we added the prepared pea fibers. We were able to achieve this using a combination of enzymatic pretreatment and mechanical high-pressure homogenization. The combination of cellulase and hemicellulase was most effective and allowed us to adapt the viscosity to the special conditions of each food. This means the viscosity of smoothies or drinkable yogurt is different than that of a vegetarian spread," explains Morales. Results also showed that the enzymatic pretreatment reduced the energy needed during high-pressure homogenization.
However, before pea shells can be used as a food ingredient, more university and industrial research is needed to improve their taste and industrial-scale applicability in food production.
The research project "Pea Fibre 2.0 - Novel approaches in increasing added value and for optimizing technological-functional and nutritive properties of fibre-rich by-products arising from processing procedures" was funded with 280,000 euros over three years by the Federal Ministry of Food and Agriculture through its Protein Crop Strategy. The TU team collaborated with Universität Hamburg in the project.
Author: Sybille Nitsche