Effects of Hydrothermal Processing Duration on the Texture, Starch and Protein In Vitro Digestibility of Cowpeas, Chickpeas and Kidney Beans

Abstract

Legumes are a vital candidate in the fight for food security as a sustainable and nutritious food source. The current study systematically investigated the effects of hydrothermal processing of varying durations (15–120 min) on the texture, starch and protein digestibility of cowpeas (Vigna unguiculata), chickpeas (Cicer arietinum) and kidney beans (Phaseolus vulgaris). Texture analysis and in vitro oral-gastro-intestinal digestion of each legume was combined with kinetic modelling to explore the rate and extent of their changes observed during hydrothermal processing. All three legumes showed rapid initial texture decay in the first 30 min of processing. Chickpeas showed the fastest rate of texture degradation with processing duration, whereas texture degradation of kidney bean was slower but reached the lowest hardness value among all beans when processed up to 120 min. The rate of starch and protein digestion increased with prolonged processing duration, whilst showing an inverse relationship with texture values. The extent of starch digestion continually increased with processing duration for all three legumes, whereas the extent of protein digestion decreased after 60 min in cowpeas. This study systematically demonstrated how choosing different processing times can modulate the rate of texture degradation, starch and protein digestion in legumes. The findings of this study can aid consumers and manufacturers on optimal processing to achieve the desired texture or modulate starch and protein digestibility.

Utilizing Hydrothermal Processing to Align Structure and In Vitro Digestion Kinetics between Three Different Pulse Types

“…These observations are in line with previously reported hardness changes [ 25 ] with longer softening times for kidney beans reported as compared to CP. As hardness degradation of pulses during cooking mostly involves simultaneous phenomena, namely starch gelatinization, and middle lamellae pectin solubilization with the latter being the rate-determining process [ 5 ], previous studies have linked different softening susceptibilities to intrinsic differences in dietary fiber, CW (polymer composition) and more specifically to differences in the amount and/or composition of middle lamellae pectin [ 25 , 52 ]. Specifically, fast cooking times for beans were associated with a lower dietary fiber content, thinner CW, and higher seed weight [ 52 ].…”

“…All three ICC fractions reached similar extents of starch digestion (81–91%). Progression of starch digestion was quantitatively evaluated by kinetic modeling using a fractional conversion model (Equation (4)) to estimate final levels of starch digestion ( starch f , %) and reaction rate constant ( k , min −1 ) as previously described for other pulses ( Table 2 ) [ 17 , 25 , 31 ].…”

“…Kinetic modeling of experimental data was carried out using SAS version 9.4 (SAS Institute, Inc., Cary, NC, USA). Hardness evaluation, starch, and protein digestion kinetics in the small intestinal phase were modeled using a fractional conversion model (Equation (4)), previously used to describe hardness degradation [ 5 , 21 , 25 , 42 ] and in vitro starch and protein digestion in pulses [ 24 , 31 ]. Using kinetic modeling, the reaction rate constant of digestion or hardness decay ( (min −1 )) and the final digested starch or protein concentration or final hardness ( C f ) were estimated: where and are hardness value or digested starch or protein (%) at 0 min and t min cooking or digestion, respectively; is the residual hardness or final concentration of digested starch or protein at extended cooking or digestion times; and denotes the estimated reaction rate constant (min −1 ).…”

“…Strong evidence exists that the process-induced levels of pectin thermosolubilization determine the permeability of the CW for digestive enzymes [ 21 , 22 , 23 ], and by this modulate starch digestion (in beans) [ 21 ]. Literature suggests that CW properties are likely to govern enzymatic penetration through the CW, such as CW thickness, density, and composition, as well as the size, and the number of CW ‘pores’ [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Depending on the botanical source plant cells differ in their composition, especially their non-cellulosic polysaccharides [ 29 ], CW permeability [ 22 ] as well as starch to protein ratios [ 30 ].…”

“…The emerging interest in pulses has resulted in a major body of evidence demonstrating similarities in terms of process-induced softening (microstructure) and retarded digestion kinetics of pulses as a group [ 25 , 32 , 33 , 34 ] when compared to, e.g., cereals. However, most insights gained at the level of processing and digestion have been established on common beans, and ICC [ 5 , 18 , 28 , 35 ].…”