Analyzing Cooking Efficiency of Gradoli Purgatory Beans: Effects of Dehulling, Malting, and Monovalent Carbonates

Abstract

Legumes, rich in protein, fiber, and micronutrients, are increasingly popular in pulse-based and gluten-free foods despite global consumption stagnating at 21 g/day due to taste, low protein digestibility, anti-nutrients, and long cooking times. Bean resistance to cooking causes textural defects like the hardshell and hard-to-cook phenomena. The pectin-cation-phytate hypothesis explains why soaking beans in sodium salts reduces cooking time by enhancing pectin solubility in water. Gradoli Purgatory beans (GPB), from Italy's Latium region, were malted, reducing phytic acid by 32% and oligosaccharides by 63%. This study evaluated the hardness of cooked GPB seeds in various conditions, including decorticated or malted states, using a modified standard method. Cooking at 98 °C for 7-75 min on an induction hob with a water-to-seed ratio of 4 g/g was tested. Soaking was applied before cooking for conventional seeds only, followed by texture analysis. Conventional GPBs were adequately cooked if their cotyledons disintegrated upon pressing, requiring a force peak of 250 to 220 N and cooking times of 52 to 57 min. Malted, decorticated, and split GPBs cooked similarly to raw decorticated and split ones, with times of 32 and 25 min, respectively. Faster cooking was due to bean coat removal and splitting, not chemical changes. Sodium or potassium carbonate/bicarbonate at 1-2 g/L improved cooking efficiency, with 2 g/L of sodium carbonate reducing cooking time to 13 min. Higher concentrations caused non-uniform cooking. Cooking malted, decorticated, and split GPBs in sodium-carbonated water reduced greenhouse gas emissions from 561 to 368 g CO_2e/kg, meeting the demand for eco-friendly and nutritionally enhanced plant protein sources.

Keywords: Gradoli Purgatory beans; bean softening kinetics; carbon footprint of bean cooking; decorticated beans; malted and dehulled beans; optimal cooking time; sodium or potassium carbonate/bicarbonate; texture profile analysis.

Figure 1

Flowchart of the production processes for malting, dehulling, and splitting the cotyledons of Gradoli Purgatory beans.

Figure 2

Lateral (a) and front (b) view pictures of the 100 kg pilot-scale malter used in this work.

Figure 3

Effect of cooking time (t_C) on the experimental hardness H₁ of GPBs in various forms: 16 h pre-soaked (●, −); unsoaked, decorticated, and split (○, - - -); malted, decorticated and split (▲, - - -). The continuous, dotted, and broken lines were plotted using Equation (1) and the empirical coefficients listed in Table 3. The horizontal broken line represents the H₁ value that indicates the beans are adequately cooked.

Figure 4

Images of pre-soaked GPBs subjected to the pinch test after cooking for 20 to 75 min.

Figure 5

Effect of cooking time (t_C) on the first peak hardness (H₁) of malted, decorticated, and split GPBs cooked in tap water (○, ^____, 0 g/L) or with different concentrations (c_Si) of (a) sodium (●, - - -, 1 g/L NaHCO₃; ☐, ^{_ . _ . _}, 1 g/L Na₂CO₃; ■, ^{_ _ _}, 2 g/L NaHCO₃; ▲, ^{_ . . _ . . _}, 2 g/L Na₂CO₃) or (b) potassium (●, - - -, 1 g/L KaHCO₃; ☐, ^{_ . _ . _}, 1 g/L K₂CO₃; ■, ^{_ _ _}, 2 g/L KaHCO₃; ▲, ^{_ . . _ . . _}, 2 g/L K₂CO₃) salt solutions. The different lines were plotted using the regression equations listed in Table 3, while the horizontal broken lines indicate the range of H₁ values representing chewable cooked beans.

Figure 6

Effect of the molar concentration (C_i) of monovalent cations (●, Na⁺; △, K⁺) in cooking water on optimal cooking time (OCT) of malted and decorticated Gradoli Purgatory beans. The broken line was plotted using Equation (7).

Figure 7

Photos of malted, decorticated, and split GPBs cooked in tap water containing 4 g/L of Na₂CO₃ for 15 min (a) and submitted to the pinch test (b).

Figure 8

Electric energy (E_S) consumed by the induction hob to cook about 750 g of GPBs (pre-soaked in 3 L tap water for 16 h) versus cooking time (t_C). The broken lines were plotted using Equation (8) or Equation (9).