Improving the Nutritional Quality of Pallar Bean Varieties (Phaseolus lunatus L.) Through the Cooking Process ^†

Abstract

This study evaluated the effect of two cooking methods on food quality indicators in eight varieties of lima bean (Phaseolus lunatus L.), a species that in its raw state is characterized by high hardness and elevated levels of antinutritional compounds. After washing and soaking in distilled water (1:4 grain/water ratio, 3 h), two cooking methods were applied: autoclaving at 121 °C (steam cooking) and boiling in an open system at 91 °C, until reaching a defined hardness endpoint. Both cooking techniques significantly reduced grain hardness, from 2975 to 427.26 kgf in variety V3 (Torta IM. 003 red). Protein content increased up to 33.48% in V5 (Torta IM. 006 cream-black), while protein digestibility reached 89% in V1 (Pallar PE. 001), with steam cooking showing superior results. Likewise, non-nutritional components predominant in raw grains were more effectively reduced by steam cooking. The findings highlight varietal differences in response to processing and confirm steam cooking as the most efficient method to enhance nutritional quality and minimize non-nutritional components in P. lunatus. These results provide relevant insights for improving the use of P. lunatus in human nutrition.

1. Introduction

Legumes are considered one of the most environmentally sustainable food groups, with lower greenhouse gas emissions, land use, energy demand, eutrophication, and acidification per serving compared to many other foods [1]. Nutritionally, legumes are primarily composed of carbohydrates, with a low fat content [2]. The dominant carbohydrate is starch, which, unlike cereal starch, is mostly slow-digesting. This property makes legume starch particularly beneficial, as it helps reduce glycemic response and moderates insulin levels in the blood [3]. Beyond starch, beans provide dietary fiber that contributes to the prevention of chronic and degenerative diseases, including diabetes, obesity, cancer, and cardiovascular conditions [4]. The Pallar bean (Phaseolus lunatus L.) is currently recognized as a sustainable source of protein with considerable economic potential, making it a viable option for improving the environmental sustainability of agricultural systems. However, like other pulses, Pallar beans contain non-nutritional compounds such as phytic acid, tannins, trypsin inhibitors, and hydrogen cyanide. These compounds can interfere with normal nutrient absorption, in some cases affecting health, and can be partially or totally eliminated by traditional or industrial processing methods such as soaking, cooking, roasting, and hulling [5]. This study evaluated the effect of two cooking techniques, one using steam and the other using water, in an open system, on the texture components and nutritional and non-nutritional compound content of eight varieties of Pallar beans.

2. Materials and Methods

2.1. P. lunatus Varieties

Eight varieties of beans were used in the research, one of which was Pallar bean variety with white beans. The rest were single-color or two-color varieties maintained by independent researcher Eduardo Peralta Idrovo in Alangasí, Quito.

2.2. Grain Preparation Bean

Raw: rains with 35% moisture content were dried at 60 °C for 3 h in a forced-air oven (Memmert, Büchenbach, Germany) in order to reduce the moisture content to 11%. Some of the dried grains were stored whole, while others were ground in a Retsch mill ZM 200 (Fisher Scientific S.L., Schwerte, Germany) equipped with a 0.5 μm sieve. The whole and ground grains were stored in airtight glass jars and kept at 4 °C until analysis.

Steam and open system with water cooking: The beans were washed and soaked for 3 h in distilled water at a ratio of 1:4 (beans/water). The water was then changed, and, in steam cooking, the beans were cooked in an autoclave at 121 °C. In the open system with water, the beans were cooked at 91 °C. In both methods, the beans were cooked until they reached a defined point. Some of the cooked beans were used for texture determinations, while others were dried at 60 °C in a forced-air oven and ground in a Retsch mill equipped with a 0.5 μm sieve. The ground beans were stored in airtight glass jars at 4 °C until analysis.

2.3. Analysis

Texture: The instrumental texture of the grains in their raw and cooked states was evaluated using the TA.XT2i texturometer (Stable Micro Systems, Godalming, UK), equipped with Texture Expert software. The analysis was performed using uniaxial compression tests (puncture tests), employing a cylindrical stainless steel probe (type P/2 or P/36, depending on the size of the grain). The operating conditions were as follows: uniaxial compression (puncture test), with cylindrical probes (P/2 or P/36), pre-test speed (1.0 mm/s), test speed (0.5 mm/s), post-test speed (1.0 mm/s), with a penetration depth of 75% of the grain height, trigger force 5 g, and test temperature (20–25 °C) [6].

Protein: The methodology of the AOAC (955.39) cited by Martini et al. [7] was used to assess the crude protein (total N × 5.7).

Protein digestibility: This was determined according to Hsu et al. [8].

Non-nutritional components: Trypsin inhibitors: The methodology from [9] was used. Alkaloids: The methodology cited by Cid-Gallegos et al. [10] was used. Saponins: The analysis was performed using the methodology reported by Mhada et al. [11]. Nitrates: This analysis was performed according to Parks et al. [12]. Oxalates: The methodology reported by Karamad et al. [13] was used. Glucosinolates: The ISO 9167 method according to Sun and Chen [14] was applied. Urease activity: UA was determined using the AACC methodology (22–90), according to Toklu et al. [5]. Tannins: The AOAC (1984) methodology, according to Parks et al. [12], was used to determine tannins.

2.4. Statistical Analysis

All analyses were performed in triplicate, and the results are expressed as the mean ± SD. The data were analyzed using factorial analysis of variance, ANOVA I, A × B. The factors were the states of the beans (raw, cooked in an open pot, and steamed) (Factor A) and the bean varieties (Factor B), giving a total of 72 experimental units. Tukey’s significance test (post hoc) was applied to determine significant differences at the 5% level. The analyses were performed using Statgraphics statistical software, version 16.1.03.

3. Results and Discussion

3.1. Effect of Cooking on the Texture of P. lunatus

Steam cooking and cooking in open system reduced the hardness of the cotyledons and the force required to break them, while elasticity increased in most varieties (

Table 1. Effect of cooking on the texture of varieties of P. lunatus L.

	Raw Grain			Steam-Cooked			Open-System Cooked
Variety	Hardness (gf)	Fracturabilility (gf)	Elasticity (mm)	Hardness (gf)	Fracturability (gf)	Elasticity (mm)	Hardness (gf)	Fracturability (gf)	Elasticity (mm)
Pallar PE. 001 (V1)	3260.07 ± 0.01 e	1649.85 ± 0.01 e	0.41 ± 0.04 a	747.45 ± 0.03 f	1602.18 ± 0.59 a	0.39 ± 0.01 b	2372.74 ± 0.05 b	716.02 ± 0.05 f	0.70 ± 0.05 a
Torta IM. 002 red-white (V2)	4441.13 ± 0.01 b	2975.19 ± 0.0 5 d	0.17 ± 0.012 e	741.794 ± 0.02 g	503.61 ± 0.01 d	0.02 ± 0.00 g	1987.84 ± 0.05 e	2089.51 ± 0.04 a	0.20 ± 0.01 e
Torta IM. 003 red (V3)	4437.92 ± 0.03 c	4512.50 ± 0.01 a	0.23 ± 0.06 c	1420.98 ± 1.29 c	427.26 ± 0.72 g	0.33 ± 0.01 c	2251.68 ± 0.01 c	958.12 ± 0.01 c	0.44 ± 0.01 b
Torta IM. 005 white-black big (V4)	4192.04 ± 0.01 d	3383.25 ± 0.02 b	0.19 ± 0.01 d	1464.93 ± 1.01 b	436.82 ± 0.01 f	0.76 ± 0.02 a	2128.60 ± 0.01 d	847.89 ± 0.01 d	0.43 ± 0.06 c
Torta IM. 006 cream-black (V5)	4685.08 ± 0.01 a	3091.04 ± 0.01 c	0.06 ± 0.02 f	2729.92 ± 0.01 a	442.73 ± 5.02 e	0.03 ± 0.01 g	1325.14 ± 0.02 g	430.51 ± 0.03 h	0.04 ± 0.05 g
Torta IM. 007 black-white (V6)	1278.25 ± 0.05 h	610.44 ± 0.05 h	0.03 ± 0.01 g	1054.16 ± 0.26 e	514.43 ± 0.01 c	0.10 ± 0.00 f	1233.21 ± 0.02 h	624.61 ± 0.05 g	0.03 ± 0.04 g
Torta IM. 008 pink-heather (V7)	2714.42 ± 0.01 f	1167.22 ± 0.01 f	0.18 ± 0.01 de	1399.42 ± 2.01 d	629.015 ± 0.01 b	0.29 ± 0.03 d	2581.52 ± 0.01 a	1299.54 ± 0.01 b	0.15 ± 0.01 f
Torta IM. 010 black (V8)	1472.70 ± 0.01 g	841.70 ± 0.03 g	0.27 ± 0.01 b	699.63 ± 0.17 h	426.99 ± 0.18 h	0.12 ± 0.00 e	1472.70 ± 0.05 f	841.70 ± 0.01 e	0.27 ± 0.02 d

Different letters in the same column indicate significant differences (p ≤ 0.05). Mean value ± SD (n = 3).

). All varieties showed a considerable decrease in hardness when cooked with steam, starting with V2, whose hardness decreased by 83%, V1 (77%), V3 (68%), V4 (65%), V8 (52.44%), V7 (48%), V5 (42%), and V6 (17.53%). The force required to fracture or break the steam-cooked beans decreased by 52–83%, while in those cooked in open system, fracturability decreased by 29–57%. Elasticity increased between 15% in V2 variety to 126% in V4 variety, while in V7 decrease by 17%. In steam-cooked beans, an increase was recorded in V1 (5%) and V4 (300%), while V8 and V2 varieties showed a decrease of 55% and 88%, respectively.

3.2. Protein Content and Digestibility

The protein concentration of steam-cooked P. lunatus increased compared to raw beans, which could be due to the decrease in non-nutritive compounds in cooked beans and the solubilization of some proteins. In the open system, V1, V3, and V7 showed higher protein concentrations than those cooked with steam, a result that correlated (r² = 0.94) with the greater loss of tannins and trypsin inhibitors in these varieties when they were cooked with steam. Digestibility increased from 5.25 to 19.54% with the application of steam and from 4.54 to 13.79% by cooking the grains in an open system (

Table 2. Effect of cooking method on protein content and digestibility of P. lunatus varieties.

Variety	Raw Grain		Steam-Cooked		Open-System Cooked
	Protein	PD	Protein	PD	Protein	PD
Pallar PE. 001 (V1)	18.35 ± 0.03 g	84.57 ± 0.09 a	21.85 ± 0.03 g	89.01 ± 0.18 a	23.92 ± 0.77 abc	88.41 ± 3.40 a
Torta IM. 002 red-white (V2)	25.38 ± 0.29 b	74.08 ± 0.63 d	29.17 ± 0.00 b	88.56 ± 0.27 a	24.79 ± 0.00 abc	84.30 ± 0.18 bc
Torta IM. 003 red (V3)	25.67 ± 0.00 a	79.05 ± 0.36 bc	27.71 ± 0.00 c	88.56 ± 0.27 a	29.78 ± 0.03 a	84.94 ± 0.27 b
Torta IM. 005 white-black big (V4)	23.63 ± 0.29 c	79.96 ± 0.18 ab	27.13 ± 0.00 e	81.95 ± 0.18 b	18.29 ± 0.09 c	82.04 ± 0.27 c
Torta IM. 006 cream-black (V5)	21.00 ± 0.00 f	75.07 ± 0.18 bcd	33.48 ± 0.06 a	84.67 ± 0.18 b	25.96 ± 0.29 bc	84.39 ± 0.27 bc
Torta IM. 007 black-white (V6)	22.46 ± 0.29 d	74.89 ± 0.18 cd	25.96 ± 0.29 f	83.76 ± 0.18 b	26.54 ± 0.00 ab	76.16 ± 0.36 d
Torta IM. 008 pink-heather (V7)	21.79 ± 0.09 e	77.24 ± 0.18 bcd	27.42 ± 0.00 d	82.76 ± 0.27 b	29.46 ± 0.29 ab	83.22 ± 0.72 bc
Torta IM. 010 black (V8)	22.31 ± 0.06 h	78.15 ± 0.36 bcd	27.71 ± 0.00 c	82.49 ± 0.00 b	27.48 ± 0.06 ab	78.24 ± 0.45 d

Different letters in the same column indicate significant differences (p ≤ 0.05). Mean value ± SD (n = 3). Total protein content (g/100 g dw), PD = protein digestibility (%).

).

3.3. Effect of Cooking on Non-Nutritional Compounds

Trypsin inhibitors (TIs): These compounds interfere with protein digestion by inhibiting the action of the enzyme trypsin. The loss of TI in steam-cooked P. lunatus grains varied between 5 and 10% in V4 and V7, while in V1, V2, and V3, a decrease of 10–14% was recorded, and in V5, V6, and V8, a loss of 17% was recorded (

Table 3. Non-nutritional compounds of P. lunatus L. in raw, steam-cooked, and open-system conditions.

Raw Grain
	T	AT	S	AU	O	G	N	IT
Pallar PE. 001 (V1)	504.80 ± 11.30 c	0.0015 ± 0.00 h	0.046 ± 0.02 g	0.040 ± 0.00 c	1.24 ± 0.11 b	68.19 ± 0.16 e	0.51 ± 0.02 h	1.51 ± 0.01 g
Torta IM. 002 red-white (V2)	167.70 ± 7.11 h	0.0159 ± 0.00 a	0.096 ± 0.03 e	0.050 ± 0.00 b	0.70 ± 0.02 f	67.71 ± 0.32 f	1.18 ± 0.06 e	1.67 ± 0.00 e
Torta IM. 003 red (V3)	379.57 ± 5.88 e	0.0134 ± 0.0005 b	0.113 ± 0.04 b	0.057 ± 0.01 a	0.92 ± 0.02 e	80.10 ± 0.32 c	0.76 ± 0.03 g	1.62 ± 0.00 f
Torta IM. 005 white-black big (V4)	471.85 ± 15.56 d	0.0102 ± 0.0002 g	0.055 ± 0.02 f	0.012 ± 0.00 e	0.90 ± 0.00 e	66.92 ± 0.48 g	1.23 ± 0.04 d	1.73 ± 0.00 d
Torta IM. 006 cream-black (V5)	921.94 ± 4.32 a	0.0104 ± 0.0005 f	0.113 ± 0.04 b	0.034 ± 0.00 d	1.06 ± 0.07 c	60.41 ± 0.64 h	5.03 ± 0.03 a	1.84 ± 0.02 c
Torta IM. 007 black-white (V6)	890.87 ± 22.66 b	0.0109 ± 0.0010 e	0.111 ± 0.04 c	0.010 ± 0.01 e	1.24 ± 0.11 b	77.72 ± 0.16 d	3.56 ± 0.06 b	1.85 ± 0.01 c
Torta IM. 008 pink-heather (V7)	243.03 ± 5.88 g	0.0114 ± 0.0005 d	0.101 ± 0.04 d	0.07 ± 0.01 f	1.35 ± 0.00 a	93.44 ± 0.16 a	1.57 ± 0.02 c	1.88 ± 0.00 b
Torta IM. 010 black (V8)	356.97 ± 11.42 f	0.0124 ± 0.0005 c	0.121 ± 0.04 a	0.030 ± 0.01 d	1.01 ± 0.11 d	92.17 ± 0.64 b	0.99 ± 0.06 f	1.91 ± 0.02 a
Steam-cooked
Pallar PE. 001 (V1)	16.11 ± 0.21 h	0.000 ± 0.000 d	0.014 ± 0.01 f	0.03 ± 0.001 a	0.563 ± 0.11 c	24.20 ± 0.32 b	0.19 ± 0.01 h	1.368 ± 0.01 g
Torta IM. 002 red-white (V2)	96.13 ± 3.05 c	0.008 ± 0.001 a	0.044 ± 0.02 b	0.010 ± 0.001 d	0.450 ± 0.001 d	0.38 ± 0.32 g	0.46 ± 0.02 c	1.479 ± 0.03 e
Torta IM. 003 red (V3)	74.48 ± 6.52 e	0.007 ± 0.001 b	0.024 ± 0.01 c	0.030 ± 0.035 b	0.675 ± 0.001 b	27.46 ± 0.24 a	0.28 ± 0.03 f	1.412 ± 0.03 f
Torta IM. 005 white-black big (V4)	67.89 ± 1.42 g	0.007 ± 0.001 b	0.022 ± 0.01 e	0.010 ± 0.001 d	0.563 ± 0.11 c	0.14 ± 0.08 h	0.33 ± 0.02 e	1.612 ± 0.01 c
Torta IM. 006 cream-black (V5)	260.92 ± 2.31 a	0.007 ± 0.001 b	0.023 ± 0.01 d	0.030 ± 0.001 b	0.450 ± 0.001 d	11.18 ± 0.54 d	0.59 ± 0.03 b	1.568 ± 0.04 d
Torta IM. 007 black-white (V6)	180.88 ± 2.07 b	0.002 ± 0.001 c	0.044 ± 0.02 b	0.030 ± 0.001 b	0.945 ± 0.04 a	0.46 ± 0.24 f	1.06 ± 0.05 a	1.571 ± 0.01 d
Torta IM. 008 pink-heather (V7)	71.65 ± 4.31 f	0.007 ± 0.001 b	0.014 ± 0.01 f	0.007 ± 0.012 e	0.563 ± 0.11 c	6.34 ± 0.24 e	0.22 ± 0.03 g	1.720 ± 0.01 a
Torta IM. 010 black (V8)	84.84 ± 4.31 d	0.007 ± 0.001 b	0.055 ± 0.02 a	0.020 ± 0.001 c	0.563 ± 0.11 c	15.15 ± 0.16 c	0.36 ± 0.08 d	1.632 ± 0.05 b
Open-system-cooked
Pallar PE. 001 (V1)	316.47 ± 11.47 b	0.005 ± 0.01 d	0.034 ± 0.01 a	0.023 ± 0.01 b	0.233 ± 0.01 d	42.992 ± 1.42 e	0.403 ± 0.24 g	1.52 ± 0.05 g
Torta IM. 002 red-white (V2)	108.38 ± 11.41 h	0.011 ± 0.001 a	0.034 ± 0.01 a	0.010 ± 0.001 c	0.225 ± 0.01 f	41.510 ± 0.16 f	0.647 ± 0.08 e	1.58 ± 0.01 f
Torta IM. 003 red (V3)	163.94 ± 11.76 f	0.007 ± 0.01 c	0.013 ± 0.01 d	0.03 ± 0.02 a	0.47 ± 0.02 a	50.24 ± 0.16 c	0.51 ± 0.02 f	1.50 ± 0.01 g
Torta IM. 005 white-black big (V4)	156.40 ± 13.05 g	0.009 ± 0.001 b	0.034 ± 0.01 a	0.01 ± 0.001 c	0.23 ± 0.01 e	40.16 ± 0.24 g	0.83 ± 0.02 c	1.66 ± 0.01 e
Torta IM. 006 cream-black (V5)	36.62 ± 5.88 a	0.006 ± 0.01 d	0.014 ± 0.001 d	0.02 ± 0.001 b	0.23 ± 0.01 e	38.49 ± 0.64 h	1.68 ± 0.02 a	1.70 ± 0.01 d
Torta IM. 007 black-white (V6)	269.40 ± 16.31 c	0.008 ± 0.01 b c	0.018 ± 0.01 c	0.02 ± 0.01 b	0.45 ± 0.01 b	47.94 ± 0.40 d	1.30 ± 0.04 b	1.78 ± 0.01 c
Torta IM. 008 pink-heather (V7)	174.29 ± 7.47 e	0.007 ± 0.001 c	0.02 ± 0.01 b	0.01 ± 0.001 c	0.23 ± 0.01 e	68.82 ± 0.16 b	0.66 ± 0.03 d	1.80 ± 0.04 b
Torta IM. 010 black (V8)	238.32 ± 9.92 d	0.009 ± 0.01 b	0.034 ± 0.01 a	0.01 ± 0.001 c	0.25 ± 0.02 c	70.57 ± 0.32 a	0.66 ± 0.03 d	1.84 ± 0.02 a

Different letters in the same column indicate significant differences (p ≤ 0.05). Mean value ± SD (n = 3). T = tannins (mg/100 g), TA = total alkaloids (g/100 g), S = saponins (g/100 g), AU = urease activity (g/100 g), O = oxalates (mg/100 g), G = glucosinolates (mg/100 g), N = nitrates (g/100 g), IT = trypsin inhibitors (g/100 g).

). In open system with water, V1, V4, V6, V7, and V8 showed a 5% loss, and in V2, V3, and V5, the decrease ranged from 5 to 10%.

Total alkaloids (TAs): The alkaloid content in raw bean grains showed significant differences (p < 0.05) between varieties. V1 had the lowest concentration (0.0015 g/100 g dw), while V2 and V3 had higher alkaloid contents (0.016–0.013 g/100 g dw). The loss of alkaloids in V4, V5, and V7 cooked with steam varied between 28–38%, while in V1, V2, V3, and V8, losses between 38–70% were recorded. In open system, V1, V2, V4, V6, V7, and V8 showed alkaloid losses between 10–40%, while in V3 and V5, losses fluctuated between 42–50%.

Nitrates (N): Nitrates can be converted into nitrites and nitrosamines, which are potentially toxic. The nitrate content in raw bean grains showed significant differences (p < 0.05) between varieties. When cooked with steam, the nitrate content varied between 0.19–0.59 g/100 g, representing a loss of 55 to 67% in V1, V2, V3, and V8. In V4 and V6, the loss of nitrates reached 95%. In open system with water, nitrates varied between 0.40–1.68 g/100 g, representing a decrease between 10–40% in V1, V3, V4, and V8.

Oxalates (O): The content of these compounds in P. lunatus did not show a significant difference according to cooking with steam or in an open system (p > 0.05), but it varied substantially with respect to raw grains. The steam cooking system showed a greater effect on the decrease in oxalates, with values ranging from 0.45 to 0.94 mg/100 g dw, after cooking in an open system, the O contents ranged from 0.22 to 0.47 mg/100 g dw (Table 3).

Glucosinolates (G): The G content in raw grains showed significant differences (p < 0.05) between varieties. V1, V2, V4, and V5 showed values between 60–70 mg/100 g, while V7 and V8 had higher concentrations (90–95 mg/100 g dw). V5 and V7 cooked with steam showed a 95% decrease compared to raw grains. V1, V2, V3, and V8 showed a lower loss (55–67%). V7 and V8 showed losses between 22–28% when beans were cooked in open system, while in V1, V2, V3, V4, V5, and V6, losses reached values between 34–42%.

Urease activity (UA): The UA in the raw grain of P. lunatus showed significant differences (p < 0.05) between varieties. A notable decrease (90%) in UA through steam cooking was recorded in V7, while in V1, V3, V4, V5, and V8, the loss varied between 11.76–47.36%. In open cooking system, V4, V6 and V7 showed losses between 10–40%, in contrast V1, V2, V3, V5 and V8 recorded losses between 42–85%.

Tannins (T): The tannin content in raw P. lunatus beans varied significantly (p < 0.05) between varieties. V2 and V7 showed the lowest concentrations (167 and 243 mg/100 g), and the highest concentrations (921 and 890 mg/100 g dw) were found in V5 and V6. The loss of these compounds in V2 treated with steam reached 45%, while in V1, V3, V5, V6, V7, and V8, the loss ranged between 65–80%. When cooked in open system with water, V4 showed the greatest loss of tannins (85%), while in V3, V4, V5, and V6, losses ranged between 56–69%, and in V1, V2, V7, and V8, losses varied between 28–37%.

Saponins (S): The saponin content in raw grains of P. lunatus showed significant differences (p < 0.05) between varieties. V1 and V2 showed the lowest concentrations (0.046 and 0.096 g/100 g), while V3, V5, and V8 showed the highest concentrations (0.113, 0.113 and 0.121 g/100 g). Steam cooking lowered saponins to values between 0.014–0.055 g/100 g, whereas open system cooking yielded 0.013–0.034 g/100 g. Overall, these decreases show that thermal processing, especially steam, effectively removes saponins and improves the palatability of P. lunatus grains.

4. Conclusions

The varieties of P. lunatus underwent significant changes in texture as a result of the cooking technique used. The hardness of the cotyledons decreased while the elasticity increased in the steam-cooked grains, due to conditions that favored the softening and fracture of the grains. The two cooking techniques reduced non-nutritional compounds, improving protein concentration and digestibility. This effect was evident in V3 (Torta IM. 003 red) which showed 27.71% protein cooked with steam and 29.78% cooked in open system. Similarly, digestibility increased to 89.01% and 88.41% in V1 (Pallar PE. 001), cooked with steam and open system, respectively. Steam cooking is more efficient from an economic and nutritional point of view, as it promotes more sustainable and healthier preparation practices, which are relevant both at home and in the food industry.