Changes in the macrocomponents and microstructure of white bean seeds upon mild hydrothermal treatment

The mild hydrothermal treatment (water bath at 40°C/24 h) of three Polish bean varieties (Phaseolus vulgaris and Phaseolus coccineus) with different sizes of seeds: the small-seed variety Raba, the medium-seed variety Aura, the large-seed variety Eureka, had a significant effect on the microstructure of the cross-sections of bean cotyledons. The first 3 hours were decisive with almost all physical and chemical parameters investigated in the study. After this time, the highest water binding or water holding capacities were observed. The tendency to a distinct decrease in the resistant starch fraction was observed especially in the large and medium bean seeds (Phaseolus sp.), based on the comparison before and after the processing. It seems that the too high dietary fibre content determined in the study resulted from exceptional sorption properties while the especially high increase in the insoluble fraction of dietary fibre (IDF) was observed during this mild hydrothermal treatment. This suggests the possibility of the occurrence of hydrophilic domains in dietary fibre. Although it cannot be explained explicitly, distinct differences were found in both fractions of dietary fibre in the varieties examined. The results obtained indicate that the conditions of the mild hydrothermal treatment can affect the nutritional and non-nutritional components of bean seeds which play an important role in the human gastrointestinal tract as both food products and diet components.