Exploration of Purified Pulse Starches for Food and Health

Pulses play a significant health role in the human population, specifically some pulses contribute to low postprandial glycemic response. Although the commercial utilization of pulse protein is rapidly growing due to the demand for alternative meat protein, healthy food choices, and the need for clean label foods, commercial pulse protein production generates approximately 35-60 percent starch. The utilization of commercially produced pulse starch from pulse protein production poses a demand for starch utilization. Consequently, the innovative development of novel functional food ingredients for human health will promote the application of unused starch. Therefore, this study purified starch using the wet-milling method, characterized and investigated the functions of pulse starches from commonly consumed pulses on food and health with a potential application as an alternative healthy ingredient. Starches were isolated and characterized from adzuki, baby lima, black bean, black-eyed pea, cranberry bean, field pea, garbanzo, great northern bean, large lima, lentil, light red kidney bean, navy bean, Nigerian honey bean, pink bean, pinto, small red bean, small white bean, and whole moth. The laboratory purified pulse starches were comparable in color, residual lipids, residual fiber, and total protein, morphology, amylose and amylopectin ratio, oil absorption capacity, water absorption capacity, water absorption and solubility indexes, swelling power, bulk density, turbidity, least gelation concentration, pastin properties, and thermal properties to corn and rice starch. Pulse starches had a different granular morphology under light and scanning electron microscope (no surface pores) compared to corn and rice. Pulse starches had higher bulk density (0.81 - 0.95 g/mL) and higher amylose (28 - 41 w/w). Similarly, pulse starches had comparable/better water and oil absorption capacities, water absorption index, water solubility index, turbidity, solubility, least gelation concentration, swelling power, pasting, and gelatinization profile when compared to starch from corn. Pulse starches showed a rapid retrogradation due to the higher amylose content and crystallinity. These two properties contributed to a higher percentage of slowly digestible starch (SDS) and resistant starch (RS) in pulse starches. The applicability of pulse starch was tested by incorporating garbanzo starch for making fortified bread. The fortified bread with garbanzo starch showed an increase in SDS and RS contents. The resistant starch content of purified pulse starches was characterized after upper-GI digestion and fecal fermentation studies. Pulse-resistant starches fermented differently with fecal samples from three healthy donors. To the best of our knowledge, this study is the first to report the use of pulse RS from pulse starches as a fermentable substrate by gut microbiota. Pulse RS significantly promoted the growth of specific endogenous microbiota (Bacteroides) and caused a significant reduction in phylum Firmicutes. The findings suggest that pulse starch as a novel food ingredient with slowly digestible properties and resistant starch that promotes beneficial gut microbiota.