Comparison of drying methods to produce bean flours with cellular integrity: Effect on digestive, techno-functional...

This study investigated the impact of different drying methods during cellular bean flour production on their microstructural and functional properties. Cellular flours were made by milling beans after hydrothermal treatment, followed by (i) freeze-drying, (ii) drying after water-alcohol exchange, or (iii) air-drying. The different drying methods did not yield substantial differences in microstructure, with all cellular flours consisting of a comparable high fraction of intact cells. All cellular flours showed a retarded in vitro starch digestion and lower thickening potential when compared to open-cell flour (i.e., flour made from uncooked beans), due to starch bioencapsulation by the intact cell walls. Overall, differences between cellular flours produced with different drying methods were limited. The freeze-dried cellular flour showed a slower initial starch hydrolysis and a lower thickening potential than the other cellular flours, indicating the possible occurrence of some physical collapse during freeze-drying. Furthermore, compared to open-cell flour, all cellular flours showed a reduction in volatile compounds originating from lipid oxidation due to enzyme inactivation during hydrothermal treatment, which is part of cellular flour preparation. These lipid oxidation products are associated with the often low-appreciated characteristic beany flavor, suggesting that cellular flour might be less associated with the typical beany off-flavor of pulses. Cellular flours made with air-drying showed a further reduction of several volatile compounds compared to freeze-dried flour or flour made after water-alcohol exchange, due to the possible occurrence of secondary oxidation reactions and volatilization of present volatiles. In general, this study showed the restricted impact of using different drying methods during cellular flour production on the functional properties of the flour. These results confirm industrial viability of pulse cellular flours, for which air-drying would be a promising drying option.