CHAMPAIGN, Ill. — Food scientists at the University of Illinois Urbana-Champaign identified the optimal fermentation conditions for pulses ― the dried edible seeds of legumes ― that increased their antioxidant and antidiabetic properties and their soluble protein content.
Using the bacteria Lactiplantibacillus plantarum 299v as the microorganism, the team fermented pulses obtained from varying concentrations of black bean, black-eyed pea, green split pea, red lentil and pinto bean flours. While the outcomes differed among the samples after fermentation, overall, their antioxidant activity increased by up to 83% and their capacity to regulate Type 2 diabetes markers increased up to 70%, the team found. Fermentation also increased the amount of soluble protein.
"Red lentil and green split pea exhibited the greatest improvements in antioxidant scavenging activity and protein solubility," said Elvira Gonzalez de Mejia , a professor of food science and the corresponding author of the paper. "And they showed the greatest modulation of two enzymes that improve insulin metabolism."
Lp299v is a probiotic strain "containing microorganisms that support gut health," said first author Andrea Jimena Valdés-Alvarado, an Illinois graduate student. "After fermentation, it remains in the digestive process. It will not only preserve the fermented product that you're consuming, it will also produce these peptides or amino acids that are more easily absorbed than the intact protein in the pulses."
Among other benefits, Lp299v reduces inflammation, boosts immunity and enhances iron absorption, according to the study, which was co-written by Erick Damián Castañeda-Reyes, then a postdoctoral student at Illinois.
Valdés-Alvarado presented some of the findings at the American Chemical Society Conference held in San Diego, California, in April, and she will present the final results during the Institute of Food Technologists' annual conference, to be held in Chicago in July.
The team, which published the findings in the journal Antioxidants, said there is an urgent need for research on the nutritional properties of plant-based diets and their potential to prevent chronic diseases such as cardiovascular disease and Type 2 diabetes.
"Up to 70% of the protein demands of the global population are met by plant-based foods,"de Mejia said. "Products like legumes, pulses and cereals are gaining increasing attention as an alternative for animal-based proteins. And the U.S. Department of Agriculture's Dietary Guidelines for Americans 2020-2025 suggests the consumption of beans, peas, chickpeas and lentils as part of a healthy diet."
Dave Luthria, a research chemist with the USDA, provided the raw samples of the five pulses, and the team used statistical software to find the optimal fermentation conditions for each to maximize their antioxidant potential, according to the study.
Valdés-Alvarado said these conditions included differing lengths of time, concentrations of flour and strains of bacteria. "The final products were all very different," she said. "If you change just one of these conditions, it will totally change your outcome."
After grinding each of the pulses into flour, the team dispersed them in distilled water and stirred in α-amylase, a pancreatic enzyme that breaks down starch into simple sugars and promotes fermentation by providing readily available carbohydrates for the bacteria.
For optimization, the flour suspensions in water were pasteurized to reduce the native microorganisms and diluted to concentrations of 3% and 9%. The researchers added Lp299v to initiate fermentation in the samples in the treatment group and then fermented the groups of samples for differing lengths of time ― 8, 16 or 24 hours.
After incubation, soluble compounds were extracted and subjected to further analysis. The team found that each sample's scavenging efficiency ― which is important in bodily processes such as blood circulation and controlling inflammation ― increased by 57% to 83%. Scavenging activity was lowest with the red lentils, black eyed peas and pinto beans, and highest with the black beans and green split peas.
In addition, they found that the concentrations of phenols and bioactive peptides increased. However, the length of fermentation affected the phenolic composition of the red lentil samples and had varying effects on their antioxidant capacity ― increasing, decreasing or holding it stable ― depending on the assay used, they reported.
While the amount of soluble protein increased significantly in the red lentils and green split peas after fermentation, it decreased significantly in the black beans and pinto beans, according to the study.
The researchers also tested the impact on cells' uptake of glucose and on enzymes that are crucial in regulating blood glucose. As they hypothesized, fermentation decreased the activity of both dipeptidyl peptidase-IV ― an enzyme that inactivates hormones that control blood sugar ― by 40% to 70%, and that of α-glucosidase ― a digestive enzyme involved in breaking down complex carbohydrates ― by 30% to 60%.
"These findings are important and have the potential for informing continued work on fermentation and strategies for improving the functional properties of health-promoting foods," de Mejia said. "These pulses contain between 18% and 25% good-quality proteins that can be used alone or as ingredients in other food products. We need to find adequate processing conditions and motivate the food industry to use them in dairy beverages or meat substitutes."
Additionally, de Mejia said it is vital to explore the sustainability of plant-based diets in light of global problems with food insecurity, shortages of natural resources and climate change. The legumes used in the study could become important crops for Illinois agriculture producers or the food industry in the future, she said.
The work was funded by the USDA's Research, Education and Economics Agricultural Research Service, Pulse Crop Health Initiative.
