Impact of Thermal Treatment on the Starch-Protein Interplay in Red Lentils: Connecting Molecular Features and Rheological Properties

Abstract

Thermal treatments are widely applied to gluten-free (GF) flours to change their functionality. Despite the interest in using pulses in GF formulations, the effects of thermal treatment at the molecular level and their relationship with dough rheology have not been fully addressed. Raw and heat-treated red lentils were tested for starch and protein features. Interactions with water were assessed by thermogravimetric analysis and water-holding capacity. Finally, mixing properties were investigated. The thermal treatment of red lentils induced a structural modification of both starch and proteins. In the case of starch, such changes consequently affected the kinetics of gelatinization. Flour treatment increased the temperature required for gelatinization, and led to an increased viscosity during both gelatinization and retrogradation. Regarding proteins, heat treatment promoted the formation of aggregates, mainly stabilized by hydrophobic interactions between (partially) unfolded proteins. Overall, the structural modifications of starch and proteins enhanced the hydration properties of the dough, resulting in increased consistency during mixing.

Pasta from Red Lentils (Lens culinaris): The Effect of Pasta-Making Process on Starch and Protein Features, and Cooking Behavior

“…Pre-treatment of raw material was effective in decreasing the white specks and may be ascribed to the improved hydration properties and dough-forming capacity of heat-treated red lentils compared to the raw (untreated) sample, as a result of both starch gelatinization and protein denaturation [ 10 ]. This pre-treatment also affected the yellowness, which was twice that of pasta obtained with the same process from untreated materials.…”

“…Flours from raw (R) and heat-treated (HT) red lentils ( Lens culinaris ; starch: 51%; protein: 22%) were provided by an Italian mill. Raw material characterization was reported in previous work [ 10 ].…”

“…The suspension was then centrifuged (13,000× g for 10 min) to remove the precipitated undigested proteins. Soluble peptides were quantified by reading the absorbance of the supernatant at 280 nm versus a blank consisting of phosphate buffer and TCA [ 10 ].…”

“…Ground samples (50 mg) were suspended in 6 mL of 50 mM sodium phosphate, 0.1 M NaCl, pH 7.0, containing 0.2 mM DTNB, and incubated for 1 h g at 25 °C under shaking. The suspensions were then centrifuged (13,000× g for 15 min, 20 °C), and the number of accessible thiols (µmol -SH/g pasta) were calculated from the absorbance of the clear supernatant at 412 nm (ε = 13,600 M −1 cm −1 ) read against a DTNB blank [ 10 ].…”

“…As for gluten-free cereals, gelatinization of pulses can occur either during the pasta-making process (e.g., in the extrusion-cooking process) or even before (i.e., by using pre-gelatinized flours) [ 9 ]. In a recent study, it was found that pre-gelatinization modified both starch and protein organization in red lentils [ 10 ]. However, up to about 40% of gelatinized starch does not impact the cooking quality of pasta produced on a lab scale, but might negatively impact the nutritional properties of cooked pasta by decreasing its resistant starch content and increasing the starch hydrolysis index [ 11 ].…”