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Effect of thermal treatments on vitality and physical characteristics of bean, chickpea and lentil
Journal of Stored Products Research 51 (2012) 86e91
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Effect of thermal treatments on vitality and physical characteristics of bean, chickpea and lentil Alessandro Miceli a, *, Claudia Miceli b a b
Dipartimento dei Sistemi Agro-Ambientali, Università di Palermo, Viale delle Scienze 4, 90128 Palermo, Italy INRAN e Istituto Nazionale di Ricerca per gli Alimenti e la Nutrizione - Settore Sementiero, Viale Regione Siciliana Sud-Est 8669, 90121 Palermo, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Accepted 5 August 2012
Thermal disinfestation treatments are relatively easy to apply, leave no chemical residues and may have some fungicidal activity. However, temperature and time combinations required to kill insect pests may meet or exceed those that reduce the viability of seeds, nutrients content, shelf life or technological characteristics. The aim of this study was to investigate the effect of thermal treatments (different temperature and time combinations) on physical and biological characteristics of bean, chickpea and lentil. Seed samples of common bean, chickpea and lentil were treated at low (12, 24 or 48 h at 18 C) or high (30, 60 or 90 min at 60 C) temperature. Seed germination, mean germination time, physical characteristics: solids loss, electrolytes leached and firmness after cooking, were determined. The use of thermal treatments for disinfesting seeds of bean, chickpea and lentil represent a physical technique of pest control that can be harmless for seeds destined for crop production (especially for organic farming) or to be stored in germplasm banks. Moreover, thermal treatments can be applied also to grain legumes used as food by humans, with no significant effect on lentils and with a reduction of cooking time for chickpeas. Beans should be treated only with cold treatments and for no more than 24 h. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Cicer arietinum L. Lens culinaris Medik. Phaseolus vulgaris L. Seed disinfestation Postharvest treatments Cooking quality
1. Introduction Legumes, along with cereals, have been widely used by humans since early times and play an important role in the traditional diets of many regions throughout the world. Early farmers highly appreciated legumes for their nutritive value and long-term storability. Among the plant species, legume seeds contain a moderately high amount of dietary proteins thus providing the major vegetal source of these nutrients. Their use as food is still limited as protein quality in grain legumes does not reach the same level as in animal products due to the unbalanced amino acid composition (low amounts of sulphur-containing amino acids), the low protein digestibility and the presence of several anti-nutritional factors (Barampama and Simard, 1994; Bressani and Elias, 1980; Norton et al., 1985). Legumes have a high caloric content and are a good source of carbohydrates, dietary fibre, vitamins (especially B-group) and minerals such as K, Zn, Ca and Mg (Meiners et al., 1976; Reyes-Moreno and Paredes-Lopez, 1993). They also contain a variety of micronutrients and phytochemicals that can play an important role in human metabolism. Legumes are usually cooked
* Corresponding author. Tel.: þ39 091 23862219; fax: þ39 091 23862240. E-mail address: [email protected] (A. Miceli). 0022-474X/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jspr.2012.08.001
before being used in the human diet. This improves the protein quality by destruction or inactivation of the heat labile antinutritional factors (Chau et al., 1997; Wang et al., 1997; Vijayakumari et al., 1998) but causes considerable losses in soluble solids, especially vitamins and minerals (Barampama and Simard, 1995). The increase of prosperity in Western countries resulted in an increase in the consumption of meat and other sources of proteins, reducing the use of legumes and their dietary role. Long cooking time is another factor responsible for wider under-utilization of legume seeds. This characteristic is mainly due to genetic and structural factors but may also be determined by seed age and storage conditions. Another major problem for production and storage of legumes is infestation by insect pests occurring in the field or during processing and marketing. In fact, grain legumes suffer heavy quantitative and qualitative losses during storage from the attack of stored product insects. Damage to stored grains and grain products may amount to 5e10% in temperate and 20e30% in tropical zones (Nakakita, 1998), and has approached 50% as reported by Caswell (1981) for cowpeas infested by Callosobruchus maculatus (F.). Weevils may attack the seeds during the cropping period in the fields and young larvae are already infesting dry legumes at the harvest. Without a disinfestation treatment immediately after
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harvest, the development of juvenile instars and the emergence of a new generation can cause serious damage to seeds during the storage period. Damaged seeds with emergence holes do not meet quality standards for human consumption in developed countries. Just a few kernels hosting hidden post-embryonic stages can communicate a bad odour to the entire lot of seeds during cooking (Dupuis et al., 2006). To increase the quality and availability of grain legumes for human consumption, it is often necessary to reduce pest-associated storage losses by applying control measures soon after harvesting. The eradication of infesting pests in stored food around the world is primarily dependent on chemical fumigants like methyl bromide (MeBr) and phosphine. Although effective, they have had undesirable effects on other insect species or non-target organisms, and may have a negative impact on the environment and human health. The ban of methyl bromide since 2005 in developed countries and from 2015 in developing countries (UNEP, 2006) and the increase of insect resistance to phosphine (Benhalima et al., 2004) have emphasized the need to develop practical alternatives to chemical fumigants for control of insect pests in legumes with minimum impact on product quality and environment. In addition, the rising popularity of organic products increases the need for non-chemical postharvest insect control methods. Thermal treatments at high or low temperatures have been investigated extensively as MeBr alternatives for disinfesting stored grains (Casagrande and Haynes, 1976; Loi and Festante, 1989; Kitch et al., 1992; Krishnamurthy et al., 1992; Chinwada and Giga, 1996; Chauhan and Ghaffar, 2002; Dosland et al., 2006; Dupuis et al., 2006; Loganathan et al., 2011). For most stored-product pests, prolonged exposure to temperatures less than 13 C or higher than 35 C is lethal. The more extreme the temperature, the more quickly insects die, with death occurring in a few minutes at 20 or 55 C (Fields, 1992). Thermal disinfestation treatments are relatively easy to apply, leave no chemical residues and may have some fungicidal activity. However, temperature and time combinations required to kill insect pests may meet or exceed those that reduce the viability of seeds, nutrients content, shelf life or technological characteristics (cooking time, texture, hardness and colour after processing, etc.). The aim of this study was to investigate the effect of thermal treatments (different temperature and time combinations) on physical and biological characteristics of bean, chickpea and lentil.
2. Material and methods 2.1. Legumes and thermal treatments Plants of Cicer arietinum L. (Chickpea), Lens culinaris Medik. (Lentil) and Phaseolus vulgaris L. (Bean) were grown in Sicily and seeds were harvested during spring and summer 2010. Once collected, sample seeds from a batch of homogeneous seeds were randomly selected and measured. Average seed weight was 52.4, 48.2 and 7.1 g per 100 seeds respectively for bean, chickpea and lentil. Seven samples of about 200 g for each legume were stored in sealed metal boxes under ambient conditions until thermal treatments were performed. Each sample was treated at low (18 C) or high (60 C) temperature. Heat treatments were made by placing the boxes in a hot air oven at 60 1 C to maintain the seeds at this temperature for 30, 60 or 90 min. Cold treatments were performed placing the boxes into a freezer at 18 1 C for 12, 24 or 48 h. At the end of each treatment, the seeds were brought naturally to ambient temperature and stored in this condition until further analysis. One box for each legume was kept at room temperature as a control test. Each treatment was replicated three times.
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2.2. Seed vigour and germination For each species and treatment, four replicates of 50 seeds were placed in Petri dishes on germination paper with 10 ml of distilled water. Seeds were allowed to germinate at 20 1 C in the dark until the end of the test as stated by official seeds analysis methods (9 days for beans, 8 days for chickpeas and 10 days for lentils) (ISTA, 2006). Germination was considered to have occurred when the radicles were 5 mm long. The seedlings with short, thick and spiral formed hypocotyls and a stunted primary root were considered as abnormally germinated (ISTA, 2006). The number of germinated seeds was recorded every 24 h and mean germination time (MGT) was calculated to assess the rate of germination according to the P following formula: MGT ¼ (g$d)/G where g is the number of seeds germinated on day d and G is the total number of germinated seeds at the end of germination analysis. 2.3. Physical properties Samples of 10 g (weighed exactly) were counted and transferred to measuring cylinders where 50 ml of distilled water were added. Seed volumes were obtained after subtracting 50 ml from the total volume of seeds and water. The cylinders were then covered with aluminium foil and left at room temperature (20 C) for 18 (bean and chickpea) or 12 h (lentil). After soaking, the seeds were drained, blotted dry with filter paper and weighed. As for dry seeds, swollen seed volume was measured in a graduated cylinder. From these data, weight, volume and density (as g per cubic cm) were calculated for dry and soaked seeds. Seed weight and volume were reported as weight and volume of 1000 seeds in order to average out the small variations occurring at single seed level. Hydration capacity, hydration index, swelling capacity and swelling index were calculated according to Saha et al. (2009). Hydration capacity and hydration index were determined by using the following formulas: Hydration capacity per seed (g seed1) ¼ Ws Wd/N; Hydration index ¼ Ws Wd/Ws where Ws is the weight of soaked seeds (g), Wd is the weight of seeds before soaking (g) and N is the number of seeds. Swelling capacity and swelling index were determined by using the following formulas: Swelling capacity per seed (ml seed1) ¼ Vs Vd/N; Swelling index ¼ Vs Vd/Vs where Vs is the volume of soaked seeds (ml), Vd is the volume of seeds before soaking (ml) and N is the number of seeds. After soaking, the soak water was collected. Electrolytes leached into the soaking water were quantified by assessing electrical conductivity (EC) with a digital conductivity meter (Conductivity meter 524, Crison Instruments S.A.) in mS cm1 (Hentges et al., 1991). Soluble solids content (SSC) of the soak water was determined with a digital refractometer (MTD-045nD, Three-In-One Enterprises Co., Ltd.) and expressed as Brix. 2.4. Cooking quality The effect of thermal treatments on legume seeds was evaluated by testing also the “degree of cooking” estimating the hardness of cooked seeds after a fixed cooking time (Nasar-Abbas et al., 2008). Seeds of bean, chickpea and lentil (10 g), soaked as reported before, were transferred in beakers (100 ml capacity) covered with aluminium foil containing 50 ml of distilled water (ratio 1:5). Beakers were then placed in a hot air oven (105 C) for 120, 90 or 60 min, respectively for chickpea, bean and lentil, followed by cooling at room temperature (20 C) for 30 min. Seed hardness was measured using a digital penetrometer (mod. 53205, TR Snc.) equipped with a flat 2 mm diameter steel punch. Ten cooked beans, chickpeas or lentils were punched individually for each treatment
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and the mean peak force was calculated in Newtons per seed (N seed1). The cooking water of each treatment was collected and leached electrolytes and soluble solid content were determined as reported before. 2.5. Statistical analysis A completely randomized design was performed. For each legume, data represent the mean of three replicate samples for each treatment. Statistical analyses were performed using ANOVA and the means were separated according to Duncan’s Multiple Range Test at a significance level of 0.05. 3. Results and discussion 3.1. Bean (Table 1) Germination percentage was very high (>97.5%) and was not affected by thermal treatments. MGT of non-treated seeds was 5.25 days. The treatments at 18 C for 24 or 48 h increased seed vigour reducing MGT by about 0.5 day; also hot treatments reduced the average germination time especially when seeds were treated for 60 min (4.82 days). Considering the 1000-seed lots, weight loss was significantly greater for those treated at 18 C for 12 or 14 h and at 60 C for 60 min. The volume of seeds slightly decreased when treated at 60 C, while the reduction was markedly greater for seeds treated at 18 C, and reached about 50 ml less for those treated for 24 h. The soaking of the beans for 18 h almost doubled the seed weight. There was no effect of thermal treatments on hydration capacity and hydration index. The soaked beans had a similar swelling capacity ranging from 0.44 to 0.50 ml seed1, while the swelling index was significantly affected by thermal treatments. The beans treated at 18 C for 18 or 24 h had a swelling index of respectively 1.26 and 1.21 followed by the beans treated at 60 C for 90 min (1.17), while all the other samples almost doubled their initial volume after soaking (1.08).
At the end of the soaking time, the electrolytes leached from beans had a significantly higher EC in the soak water of the treated seeds than in that of non-treated seeds (319.50 mS cm1). Solids loss was not influenced by temperature nor by time of treatment; EC was on average 495.06 and 509.78 mS cm1 respectively for cold and hot treatments. Soluble solids loss was very low, with an average content of 0.52 Brix and did not vary significantly among treatments. After cooking, the leaching of electrolytes in all samples was about ten times greater than in soaking water. Solids loss in cooking water amounted to an EC of 3.93 mS cm1 for non-treated beans, while all treated samples had a higher EC (4.25 mS cm1 on average) with no significant difference due to time and temperature of treatments. Soluble solid content of cooking water of non-treated beans was 2.10 Brix. Only the shortest treatment at 18 C did not differ from control, while all the other samples had a higher soluble solids loss during cooking. Bean hardness after cooking was markedly influenced by thermal treatments. All the treated samples were harder than nontreated seeds (1.57 N seed1) or those treated for 12 h at 18 C (1.80 N seed1). Increasing the time of cold treatments increased up to 10 times the resistance to punching of seeds (48 h at 18 C: 18.42 N seed1). The effect of a hot treatment was greater. After 30 min at 60 C seed hardness was 10.18 N seed1 and increased to 26.35 N seed1 when seeds were treated for 90 min. Our results showed that hot treatments and cold treatments of longer duration promoted the hard-to-cook phenomenon that can occur in many legumes and has been investigated by many authors (Burr et al., 1968; Hentges et al., 1991). The increase in seed hardness after cooking seems to be due to structural and biochemical modifications that occur during seed ageing and can be accelerated by storage conditions (temperature and relative humidity) and water activity of the bean (Aguilera and Rivera, 1992; Nasar-Abbas et al., 2008). Hardness of many common bean varieties increases even after medium term storage (3e6 months) at 30e35 C (Del Valle and Stanley, 1995; Reyes-Moreno et al., 1994). Many authors reported that the beans with the hard-to-cook phenomenon are characterized by a water absorption rate lower than soft beans (Burr et al., 1968; Varriano-Martson and Jackson, 1981). It can presumed that a similar pattern could have been induced by the
Table 1 Effect of thermal treatments on viability and physical characteristics of bean seeds. Thermal treatments
Germination (%) M.G.T (d) 1000 seeds weight (g) 1000 seeds volume (ml) 1000 soaked seeds weight (g) 1000 soaked seeds (ml) Density (g ml1) Hydration capacity (g seed1) Hydration index Swelling capacity (ml seed1) Swelling index Soaking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Cooking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Firmness (N seed1)
Non-treated
12 h at 18 C
24 h at 18 C
48 h at 18 C
300 at 60 C
600 at 60 C
900 at 60 C
97.50 a 5.25 a 537.62 a 437.62 a 1042.79 a 912.28 a 1.23 a 0.51 a 0.94 a 0.47 a 1.08 a
98.75 a 5.08 ab 508.68 b 407.02 bc 994.74 a 848.25 a 1.25 a 0.49 a 0.96 a 0.44 a 1.08 a
98.75 a 4.76 b 510.26 b 389.91 c 992.11 a 881.58 a 1.31 a 0.48 a 0.94 a 0.49 a 1.26 a
98.75 a 4.73 b 526.32 ab 412.28 b 1029.83 a 912.28 a 1.28 a 0.50 a 0.96 a 0.50 a 1.21 a
100.00 a 5.09 ab 526.14 ab 422.37 ab 1028.6 a 871.05 a 1.25 a 0.50 a 0.95 a 0.45 a 1.06 a
98.75 a 4.82 b 517.46 b 422.37 ab 1010.7 a 879.39 a 1.23 a 0.49 a 0.95 a 0.46 a 1.08 a
97.50 a 5.08 ab 524.56 ab 421.05 ab 1028.07 a 912.28 a 1.25 a 0.50 a 0.96 a 0.49 a 1.17 a
319.50 b 0.57 a
547.67 a 0.53 a
478.67 a 0.50 a
493.00 a 0.50 a
496.00 a 0.50 a
501.67 a 0.50 a
531.67 a 0.53 a
3.93 b 2.10 c 1.57 d
4.19 a 2.30 bc 1.80 d
4.30 a 2.67 ab 3.96 c
4.22 a 2.57 ab 18.42 ab
4.32 a 2.77 a 10.18 b
4.18 a 2.50 ab 21.31 a
4.27 a 2.67 ab 26.35 a
Means within a row followed by different letters are significantly different at P < 0.05 (Duncan Multiple Range Test). Analysis of the percentage values was performed on corresponding angular values.
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thermal treatments tested in this study, even if no differences were noticed in hydration and swelling coefficient probably because the seeds had already reached a saturation threshold after 18 h soaking. In fact, many authors reported that the rate of water absorption in beans reaches a saturation rate after 12 h regardless of storage conditions or ageing (Berrios et al., 1999; Sefa-Dedeh and Stanley, 1979; Hsieh et al., 1993). The negative effect of thermal treatments on bean seeds is confirmed also by the increase of electrical conductivity of soaking and cooking water of the treated seeds. It is well known that solids loss in damaged or aged seeds is higher than young and intact seeds, and that it is due to loss of membrane integrity and to changes of intercellular spaces and adhesion areas between cotyledon cells (Berrios et al., 1998). Hincks et al. (1987) showed a high correlation between electrolyte leakage, determined by the conductance of the leachate, and seed hardness after cooking. Our trials confirmed this observation. 3.2. Chickpea (Table 2) Thermal treatments did not change chickpea seed vitality. Germination percentage of non-treated seeds was 96.25. Treating seeds at 60 C for 90 min slightly reduced germination (90.0%) while no effect was recorded with the other time temperature combinations. Mean germination time (MGT) was 3.57 days for non-treated seeds; thermal treatments had no effects on MGT. Average seed weight was not modified significantly by thermal treatments, while both hot and cold treatments caused a reduction of the 1000 seed volume in longer treatments. The seeds treated at 18 C for 12 h significantly increased in volume (412.70) by about 40 ml 1000 seeds1. Increasing the cold treatment to 24 h, the volume of seeds reduced approximately by 30 ml 1000 seeds1. This may be due to volume variations of the water inside seeds when temperature drops under 4 C. A shorter cold treatment may determine an increase of water volume inside the seeds, while in longer cold treatments the water inside the seeds reaches a lower temperature and thus a lower volume, reducing the whole-seed volume. The density of untreated seeds was 1.34 g ml1, and did not change significantly with heat treatment. The treatment at low temperature for 12 h gave the lowest density (1.18 g ml1) which
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then tended to increase, reaching the highest density (1.38 g ml1) in seeds treated at 18 C for 48 h. After 18 h of soaking, seed weight almost doubled for every treatment, while their volumes increased differently. Nevertheless no significant difference was recorded among soaked seeds of different treatments. These trends are confirmed by hydration and swelling capacity testing. The swelling index of treated samples was not significantly different from non-treated seeds. Differences were found among treatments, especially cold treatments that ranged between 1.08 (12 h at 18 C) and 1.51 (48 h at 18 C). These data indicate that even if the samples absorbed the same amount of water and reached a similar final volume after soaking, the increase in volume was different and seemed determined by the effect of thermal treatments on seed volume. We can then argue that the capacity to imbibe water was substantially affected by osmotic potential of the seeds and that this was not affected by thermal treatments. Moreover, many authors reported that the differences in hydration and swelling capacity of legume seeds tend to decrease reaching a saturation threshold, after 12 h of soaking (Berrios et al., 1999; Hsieh et al., 1993; Sefa-Dedeh and Stanley, 1979). The analysis of soak water at the end of soaking time may give some information on seed integrity and on damages due to thermal treatments by evaluating soluble solids loss and electrolytes leached. Solids loss is an indication of seed deterioration (Ching and Schoolcraft, 1968; Parrish and Leopold, 1978) and is directly proportional to the EC of the soaked water (Nasar-Abbas et al., 2008). The EC of soak water of chickpeas decreased as the treatment time increased for both cold or hot treatments. The EC of the soaking water of non-treated seeds (1388.8 mS cm1) was significantly higher than the conductivity of the soaking water from chickpeas treated for 12 h at 18 C (1189.3 mS cm1) or for 90 min at 60 C (1161.0 mS cm1). Electrolytes leached in water during cooking were twice the amount in soak water and with no significant differences among control and thermal treatments. Cooking also increased the amount of soluble solids loss, perhaps due to the hydrolysis of polysaccharides, but with no differences among treatments (2.48 Brix on average). Hardness of chickpeas after cooking was significantly influenced by thermal treatments. The puncture force required for non-treated
Table 2 Effect of thermal treatments on viability and physical characteristics of chickpea seeds. Thermal treatments
Germination (%) M.G.T. (d) 1000 seeds weight (g) 1000 seeds volume (ml) 1000 soaked seeds weight (g) 1000 soaked seeds (ml) Density (g ml1) Hydration capacity (g seed1) Hydration index Swelling capacity (ml seed1) Swelling index Soaking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Cooking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Firmness (N seed1)
Non-treated
12 h at 18 C
24 h at 18 C
48 h at 18 C
300 at 60 C
600 at 60 C
900 at 60 C
96.25 a 3.57 a 493.65 a 371.42 bc 980.87 a 898.41 a 1.34 ab 0.49 a 0.99 a 0.53 a 1.44 ab
97.50 a 3.85 a 487.30 a 412.69 a 974.60 a 857.14 a 1.18 b 0.49 a 1.00 a 0.44 a 1.08 b
96.25 a 3.98 a 498.73 a 409.52 ab 1004.04 a 902.38 a 1.22 ab 0.51 a 1.01 a 0.49 a 1.21 ab
96.25 a 3.73 a 472.01 a 343.43 c 943.93 a 859.30 a 1.38 a 0.47 a 0.99 a 0.52 a 1.51 a
93.75 a 3.67 a 485.71 a 380.95 bc 982.54 a 873.02 a 1.28 ab 0.50 a 1.02 a 0.49 a 1.29 ab
96.25 a 3.78 a 498.73 a 363.49 c 1003.96 a 919.84 a 1.38 a 0.51 a 1.01 a 0.56 a 1.54 a
90.00 b 3.99 a 476.69 a 359.30 c 958.08 a 860.03 a 1.33 ab 0.48 a 1.01 a 0.50 a 1.40 ab
1388.84 ab 0.87 a
1443.33 a 0.87 a
1285.19 bc 0.90 a
1189.26 c 0.93 a
1471.27 a 0.90 a
1261.04 c 0.90 a
1295.33 bc 0.88 a
2.72 a 2.40 a 2.14 a
2.70 a 2.40 a 1.99 ab
2.76 a 2.63 a 1.71 cd
2.61 a 2.40 a 1.52 d
2.75 a 2.53 a 1.86 bc
2.64 a 2.40 a 1.58 d
2.72 a 2.57 a 1.29 e
Means within a row followed by different letters are significantly different at P < 0.05 (Duncan Multiple Range Test). Analysis of the percentage values was performed on corresponding angular values.
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Table 3 Effect of thermal treatments on viability and physical characteristics of lentil seeds. Thermal treatments
Germination (%) M.G.T. (d) 1000 seeds weight (g) 1000 seeds volume (ml) 1000 soaked seeds weight (g) 1000 soaked seeds (ml) Density (g ml1) Hydration capacity (g seed1) Hydration index Swelling capacity (ml seed1) Swelling index Soaking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Cooking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Firmness (N seed1)
Non-treated
12 h at 18 C
24 h at 18 C
48 h at 18 C
300 at 60 C
600 at 60 C
900 at 60 C
93.33 a 2.64 d 70.71 a 55.33 a 135.03 a 116.47 a 1.28 a 0.06 a 0.91 a 0.06 a 1.11 a
98.67 a 2.99 c 69.87 a 56.18 a 133.15 ab 112.32 a 1.25 a 0.06 ab 0.91 a 0.06 a 1.00 a
98.67 a 3.47 a 69.53 a 57.26 a 133.82 a 111.85 a 1.21 a 0.06 a 0.93 a 0.05 a 0.95 a
96.00 a 3.21 b 70.25 a 57.87 a 133.61 a 115.71 a 1.22 a 0.06 ab 0.90 a 0.06 a 1.01 a
97.33 a 3.22 b 69.31 a 52.97 a 132.62 ab 114.16 a 1.31 a 0.06 ab 0.91 a 0.06 a 1.16 a
98.67 a 3.08 bc 67.51 a 54.31 a 128.14 b 109.82 a 1.25 a 0.06 b 0.90 a 0.06 a 1.03 a
97.33 a 2.99 c 70.45 a 52.51 a 133.43 ab 110.48 a 1.34 a 0.06 ab 0.89 a 0.06 a 1.11 a
1735.00 a 1.10 ab
1653.33 ab 1.00 bc
1668.67 ab 1.00 bc
1604.00 ab 0.97 c
1688.00 ab 1.13 a
1499.67 b 0.93 c
1689.00 ab 1.02 ac
2.63 ab 2.47 a 1.36 a
2.63 ab 2.40 a 1.24 a
2.52 b 2.17 b 1.42 a
2.67 a 2.47 a 2.51 b
2.63 ab 2.53 a 1.09 a
2.67 a 2.53 a 1.48 a
2.59 ab 2.43 a 1.24 a
Means within a row followed by different letters are significantly different at P < 0.05 (Duncan Multiple Range Test). Analysis of the percentage values was performed on corresponding angular values.
seeds was 2.14 N seed1. Treated seeds decreased their hardness after cooking with increasing treatment duration. The reduction of puncture force was greater for high temperature treatments, differing significantly from controls even for the shorter treatments (30 mine1.86 N seed1) and reached the lowest hardness (1.29 N seed1) among treated samples in chickpeas treated for 90 min at 60 C. The reduction of the hardness of cooked chickpeas due to thermal treatments may lead to a reduction of cooking time. Many grain legumes, among these is chickpea, suffer from the hardto-cook tendency due to storage conditions or seed ageing (ReyesMoreno et al., 2001). Hincks et al. (1987) showed a positive correlation between EC of leachate and final cooked texture. Our data on chickpea confirm this correlation: short treatments and nontreated samples had higher values of EC in soak water and higher hardness after cooking, while longer thermal treatments determined a reduction of EC of soak water and a correlated reduction of seed texture after cooking (r ¼ 0.999, P 0.01). 3.3. Lentil (Table 3) The germination percentage of lentil seeds in every treated sample was greater than the non-treated sample (93%). Mean germination time of the treated seeds was higher than the non-treated lentils (2.64 d). The cold treatment slowed the germination speed, especially for longer durations (3.47 de24 h at 18 C; 3.21 de48 h at 18 C), while hot treatment was more effective on MGT for the 30 min treatment (3.22 d). The weight and the volume of lentil seeds were not influenced by thermal treatments with average values of about 70 g and 55 ml for 1000 seeds and a density of 1.27 g ml1 on average. Even after soaking for 12 h the seed weight and volume did not change as a result of thermal treatments. Hydration and swelling capacity were similar to controls. Solid loss in soaking water was higher than in beans or chickpeas, probably due to the different volume/area ratio. The EC of soaking water was 1735.0 mS cm1 for non-treated lentils and slightly lower for treated seeds, with the lowest value (1499.7 mS cm1) recorded for lentils treated for 60 min at 60 C. The EC of cooking water was similar to those of chickpeas, and did not differ significantly from treated or non-treated lentils. Soluble solids content of soaking water showed a decreasing trend in longer treatments. SSC was higher in cooking water but
only the samples treated for 24 h at 18 C was significantly lower than control. Lentils have shorter cooking time than other legumes and suffer less from the hard-to-cook characteristic due to ageing and suboptimal storage conditions. For lentils, as for other legumes, there is a relationship between water absorption, solid loss and cooking time (Pirhayati et al., 2011). Nevertheless, thermal treatments did not modify these characteristics. For cooking quality of lentil, the pedological characteristics of soil and the mineral metabolism of the growing seed are more influential than storage temperature (Bhatty, 1995). 4. Conclusions Biological and physical characteristics such as germination, vigour, water absorption, solids loss and electrolytes leached and cooking quality, were studied on bean, chickpea and lentil seeds treated at high or low temperature. Pest control of stored seeds can be achieved by thermal treatments at low (18 C) or high (60 C) temperature. Their efficacy depends on duration and on how quickly seeds reach the target temperature (Casagrande and Haynes, 1976; Dupuis et al., 2006; Fields, 1992; Chinwada and Giga, 1996). It is, therefore, of technical relevance to know how thermal treatment can affect grain legumes used for seed or as food. The data collected show that the exposition of legume seeds to extreme temperatures (18 C for 48 h; 60 C for 90 min) did not compromise viability, but may affect their vigour. In fact, mean germination time changed for each legume. Chickpea was not influenced by thermal treatments but bean and lentil were affected. Treated seeds of lentil had slowed germination while treated beans germinated faster. Thermal treatments may also determine structural modification of the tissues and may affect physical characteristics and cooking of grain legumes. These alterations were observed by the variations of solutes leached into soaking water that corresponded to variations in hardness after cooking. The legumes studied in this work, reacted in different ways to thermal treatments, probably due to differences in structural and morphological characteristics of the seeds. Firmness after cooking was reduced in chickpeas as thermal treatments increased, while beans showed the hard-to-cook phenomenon especially when treated at 60 C and at the longest cold treatment.
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The use of thermal treatments for disinfesting seeds of bean, chickpea and lentil represent a physical technique of pest control that can be harmless for seeds destined for reproduction (especially for organic farming) or to be stored in germplasm banks. Moreover, thermal treatments can be applied also to grain legumes used as human food, with no significant effect on lentils and with a reduction of cooking time for chickpeas. Beans, however, should be treated only with cold treatments and for no more than 24 h. References Aguilera, J.M., Rivera, R., 1992. Hard-to cook defect in black beans: hardening rates, water imbibitions and multiple mechanism hypothesis. Food Research International 25, 101e108. Barampama, Z., Simard, R.E., 1994. Oligosaccharides, antinutritional factors, and protein digestibility of dry beans as affected by processing. Journal of Food Science 59, 833e838. Barampama, Z., Simard, R.E., 1995. Effect of soaking, cooking and fermentation on composition, in-vitro starch digestibility and nutritive value of common beans. Plant Foods for Human Nutrition 48, 349e365. Bhatty, R.S., 1995. Comparisons of good- and poor-cooking lentils. Journal of the Science of Food and Agriculture 68, 489e496. Benhalima, H., Chaudhry, M.Q., Mills, K.A., Price, N.R., 2004. Phosphine resistance in stored-product insects collected from various grain storage facilities in Morocco. Journal of Stored Products Research 40, 241e249. Berrios, J.D.J., Swanson, B.G., Cheong, W.A., 1998. Structural characteristics of stored black beans (Phaseolus vulgaris L.). Scanning 20, 410e417. Berrios, J.D.J., Swanson, B.G., Cheong, W.A., 1999. Physico-chemical characterization of stored black beans (Phaseolus vulgaris L.). Food Research International 32, 669e676. Bressani, R., Elias, L.G., 1980. Nutritional value of legume crops for humans and animals. In: Summerfield, R.J., Bunting, A.H. (Eds.), Advances in Legume Science. Royal Botanical Gardens, Kew, Richmond, London, pp. 135e155. Burr, H.K., Kon, S., Morris, H.J., 1968. Cooking rates of dry beans as influenced by moisture content and temperature and time of storage. Food Technology 22, 336e338. Casagrande, R.A., Haynes, D.L., 1976. A predictive model for cereal leaf beetle mortality from sub-freezing temperatures. Environmental Entomology 5, 761e769. Caswell, G.H., 1981. Damage to stored cowpea in the northern part of Nigeria. Samaru Journal of Agricultural Research 1, 11e19. Chau, C.F., Cheung, P.C., Wong, Y.S., 1997. Effect of cooking on content of amino acids and antinutrients in three Chinese indigenous legume seeds. Journal of the Science of Food and Agriculture 75, 447e452. Chauhan, Y.S., Ghaffar, M.A., 2002. Solar heating of seeds e a low cost method to control bruchid (Callosobruchus spp.) attack during storage of pigeonpea. Journal of Stored Products Research 38, 87e91. Ching, T.M., Schoolcraft, I., 1968. Physiological and chemical differences in aged stored seeds. Crop Science 8, 407e411. Chinwada, P., Giga, D.P., 1996. Sunning as a technique for disinfesting stored beans. Postharvest Biology and Technology 9, 335e342. Del Valle, J.M., Stanley, D.W., 1995. Reversible and irreversible component of bean hardening. Food Research International 28, 455e463. Dosland, O., Subramanyam, Bh., Sheppard, K., Mahroof, R., 2006. Temperature modification for insect control. In: Heaps, J. (Ed.), Insect Management for Food Storage and Processing, second ed. American Association of Cereal Chemists, St. Paul, MN, pp. 89e103. Dupuis, A.S., Fuzeau, B., Fleurat-Lessard, F., 2006. Feasibility of French beans disinfestations based on freezing intolerance of post-embryonic stages of Acanthoscelides obtectus (Say). In: Lorini, I., et al. (Eds.), Proceedings of the 9th International Working Conference on Stored Products Protection, Campinas (Brazil). Brazilian Post-harvest Association (ABRAPOS), pp. 956e965. Fields, P.G., 1992. The control of stored-product insects and mites with extreme temperatures. Journal of Stored Products Research 28, 89e118.
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Hentges, D.L., Weaver, C.M., Nielsen, S.S., 1991. Changes of selected physical and chemical components in the development of the hard-to-cook bean defect. Journal of Food Science 56, 436e442. Hincks, M.J., McCannell, A., Stanley, D.W., 1987. Hard to cook defect in black beans. Soaking and cooking processes. Journal of Agriculture and Food Chemistry 35, 576e583. Hsieh, H.M., Pomeranz, Y., Swanson, B.G., 1993. Composition, cooking time, and maturation of Azuki (Vigna angularis) and common beans (Phaseolus vulgaris). Cereal Chemistry 69, 244e248. ISTA, 2006. International Seed Testing Association. ISTA Handbook on Seedling Evaluation, third ed. Kitch, L.W., Ntoukam, G., Shade, R.E., Wolfson, J.L., Murdock, L.L., 1992. A solar heater for disinfesting stored cowpeas on subsistence farms. Journal of Stored Products Research 28, 261e267. Krishnamurthy, T.S., Muralidharanm, M., Muthu, M., 1992. Disinfesting grain with solar heat. Appropriate Technology 18, 15e16. Loganathan, M., Jayasa, D.S., Fields, P.G., White, N.D.G., 2011. Low and high temperatures for the control of cowpea beetle, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in chickpeas. Journal of Stored Products Research 47, 244e248. Loi, G., Festante, G., 1989. The influence of high and low temperatures on the mortality of adults of Acanthoscelides obtecus (Say) (Coleoptera Bruchidae). Frustula Entomologica (Pisa) 10, 181e185. Meiners, C.R., Derise, N.L., Lau, H.C., Crews, M.G., Ritchey, S.J., Murphy, E.W., 1976. The content of nine mineral elements in raw and cooked mature dry legumes. Journal of Agriculture and Food Chemistry 24, 1126e1130. Nakakita, H., 1998. Stored rice and stored product insects. In: Rice Inspection Technology Manual. A.C.E. Corporation, Tokyo, Japan, pp. 49e65. Nasar-Abbas, S.M., Plummer, J.A., Siddique, K.H.M., White, P., Harris, D., Dods, K., 2008. Cooking quality of faba bean after storage at high temperature and the role of lignins and other phenolics in bean hardening. LTW 41, 1260e1268. Norton, G., Bliss, F.A., Bressani, R., 1985. Biochemical and nutritional attributes of grain legumes. In: Summerfield, R.J., Roberts, E.H. (Eds.), Grain Legume Crops. Collins, London, pp. 73e114. Parrish, D.J., Leopold, A.C., 1978. On the mechanism of aging in soybean seeds. Plant Physiology 61, 365e368. Pirhayati, M., Soltanizadeh, N., Kadivar, M., 2011. Chemical and microstructural evaluation of ‘hard-to-cook’ phenomenon in legumes (pinto bean and small-type lentil). International Journal of Food Science and Technology 46, 1884e1890. Reyes-Moreno, C., Paredes-Lopez, O., 1993. Hard-to-cook phenomenon in common beans: a review. Critical Reviews of Food Science and Nutrition 33, 227e286. Reyes-Moreno, C., Paredes-Lopez, O., Barradas, I., 1994. A fast laboratory procedure to assess the hard to cook tendency of common bean varieties. Food Chemistry 49, 187e190. Reyes-Moreno, C., Rouzaud-Sandez, O., Milan-Carrillo, J., Garzon-Tiznado, J.A., Camacho-Hernandez, L., 2001. Hard to cook tendency of chickpea (Cicer arietinum L.) varieties. Journal of the Science of Food and Agriculture 81, 1008e1012. Saha, S., Singh, G., Mahajan, V., Gupta, H.S., 2009. Variability of nutritional and cooking quality in bean (Phaseolus vulgaris L.) as a function of genotype. Plant Foods for Human Nutrition 64, 174e180. Sefa-Dedeh, S., Stanley, D.W., 1979. Textural implications of the microstructure of legumes. Food Technology 33, 77e83. UNEP (United Nations Environmental Programme), 2006. Handbook for the Montreal Protocol on Substances that Deplete the Ozone Layer. Nairobi, Kenya: Secretariat of the Vienna Convention for the Protection of the Ozone Layer & the Montreal Protocol on Substances that Deplete the Ozone Layer. Varriano-Martson, E., Jackson, M., 1981. Hard to cook phenomenon: structural changes during storage and imbibition. Journal of Food Science 46, 1379e1385. Vijayakumari, P., Siddhuraju, P., Pugalenthi, M., Janardhanan, K., 1998. Effect of soaking and heat processing on the levels of antinutrients and digestible proteins in seeds of Vigna aconitifolia and Vigna sinensis. Food Chemistry 63, 259e264. Wang, N., Lewis, M.J., Brennan, J.G., Westby, A., 1997. Effect of processing methods on nutrients and anti-nutritional factors in cowpea. Food Chemistry 58, 59e68.
Contents lists available at SciVerse ScienceDirect
Journal of Stored Products Research journal homepage: www.elsevier.com/locate/jspr
Effect of thermal treatments on vitality and physical characteristics of bean, chickpea and lentil Alessandro Miceli a, *, Claudia Miceli b a b
Dipartimento dei Sistemi Agro-Ambientali, Università di Palermo, Viale delle Scienze 4, 90128 Palermo, Italy INRAN e Istituto Nazionale di Ricerca per gli Alimenti e la Nutrizione - Settore Sementiero, Viale Regione Siciliana Sud-Est 8669, 90121 Palermo, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Accepted 5 August 2012
Thermal disinfestation treatments are relatively easy to apply, leave no chemical residues and may have some fungicidal activity. However, temperature and time combinations required to kill insect pests may meet or exceed those that reduce the viability of seeds, nutrients content, shelf life or technological characteristics. The aim of this study was to investigate the effect of thermal treatments (different temperature and time combinations) on physical and biological characteristics of bean, chickpea and lentil. Seed samples of common bean, chickpea and lentil were treated at low (12, 24 or 48 h at 18 C) or high (30, 60 or 90 min at 60 C) temperature. Seed germination, mean germination time, physical characteristics: solids loss, electrolytes leached and firmness after cooking, were determined. The use of thermal treatments for disinfesting seeds of bean, chickpea and lentil represent a physical technique of pest control that can be harmless for seeds destined for crop production (especially for organic farming) or to be stored in germplasm banks. Moreover, thermal treatments can be applied also to grain legumes used as food by humans, with no significant effect on lentils and with a reduction of cooking time for chickpeas. Beans should be treated only with cold treatments and for no more than 24 h. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Cicer arietinum L. Lens culinaris Medik. Phaseolus vulgaris L. Seed disinfestation Postharvest treatments Cooking quality
1. Introduction Legumes, along with cereals, have been widely used by humans since early times and play an important role in the traditional diets of many regions throughout the world. Early farmers highly appreciated legumes for their nutritive value and long-term storability. Among the plant species, legume seeds contain a moderately high amount of dietary proteins thus providing the major vegetal source of these nutrients. Their use as food is still limited as protein quality in grain legumes does not reach the same level as in animal products due to the unbalanced amino acid composition (low amounts of sulphur-containing amino acids), the low protein digestibility and the presence of several anti-nutritional factors (Barampama and Simard, 1994; Bressani and Elias, 1980; Norton et al., 1985). Legumes have a high caloric content and are a good source of carbohydrates, dietary fibre, vitamins (especially B-group) and minerals such as K, Zn, Ca and Mg (Meiners et al., 1976; Reyes-Moreno and Paredes-Lopez, 1993). They also contain a variety of micronutrients and phytochemicals that can play an important role in human metabolism. Legumes are usually cooked
* Corresponding author. Tel.: þ39 091 23862219; fax: þ39 091 23862240. E-mail address: [email protected] (A. Miceli). 0022-474X/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jspr.2012.08.001
before being used in the human diet. This improves the protein quality by destruction or inactivation of the heat labile antinutritional factors (Chau et al., 1997; Wang et al., 1997; Vijayakumari et al., 1998) but causes considerable losses in soluble solids, especially vitamins and minerals (Barampama and Simard, 1995). The increase of prosperity in Western countries resulted in an increase in the consumption of meat and other sources of proteins, reducing the use of legumes and their dietary role. Long cooking time is another factor responsible for wider under-utilization of legume seeds. This characteristic is mainly due to genetic and structural factors but may also be determined by seed age and storage conditions. Another major problem for production and storage of legumes is infestation by insect pests occurring in the field or during processing and marketing. In fact, grain legumes suffer heavy quantitative and qualitative losses during storage from the attack of stored product insects. Damage to stored grains and grain products may amount to 5e10% in temperate and 20e30% in tropical zones (Nakakita, 1998), and has approached 50% as reported by Caswell (1981) for cowpeas infested by Callosobruchus maculatus (F.). Weevils may attack the seeds during the cropping period in the fields and young larvae are already infesting dry legumes at the harvest. Without a disinfestation treatment immediately after
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harvest, the development of juvenile instars and the emergence of a new generation can cause serious damage to seeds during the storage period. Damaged seeds with emergence holes do not meet quality standards for human consumption in developed countries. Just a few kernels hosting hidden post-embryonic stages can communicate a bad odour to the entire lot of seeds during cooking (Dupuis et al., 2006). To increase the quality and availability of grain legumes for human consumption, it is often necessary to reduce pest-associated storage losses by applying control measures soon after harvesting. The eradication of infesting pests in stored food around the world is primarily dependent on chemical fumigants like methyl bromide (MeBr) and phosphine. Although effective, they have had undesirable effects on other insect species or non-target organisms, and may have a negative impact on the environment and human health. The ban of methyl bromide since 2005 in developed countries and from 2015 in developing countries (UNEP, 2006) and the increase of insect resistance to phosphine (Benhalima et al., 2004) have emphasized the need to develop practical alternatives to chemical fumigants for control of insect pests in legumes with minimum impact on product quality and environment. In addition, the rising popularity of organic products increases the need for non-chemical postharvest insect control methods. Thermal treatments at high or low temperatures have been investigated extensively as MeBr alternatives for disinfesting stored grains (Casagrande and Haynes, 1976; Loi and Festante, 1989; Kitch et al., 1992; Krishnamurthy et al., 1992; Chinwada and Giga, 1996; Chauhan and Ghaffar, 2002; Dosland et al., 2006; Dupuis et al., 2006; Loganathan et al., 2011). For most stored-product pests, prolonged exposure to temperatures less than 13 C or higher than 35 C is lethal. The more extreme the temperature, the more quickly insects die, with death occurring in a few minutes at 20 or 55 C (Fields, 1992). Thermal disinfestation treatments are relatively easy to apply, leave no chemical residues and may have some fungicidal activity. However, temperature and time combinations required to kill insect pests may meet or exceed those that reduce the viability of seeds, nutrients content, shelf life or technological characteristics (cooking time, texture, hardness and colour after processing, etc.). The aim of this study was to investigate the effect of thermal treatments (different temperature and time combinations) on physical and biological characteristics of bean, chickpea and lentil.
2. Material and methods 2.1. Legumes and thermal treatments Plants of Cicer arietinum L. (Chickpea), Lens culinaris Medik. (Lentil) and Phaseolus vulgaris L. (Bean) were grown in Sicily and seeds were harvested during spring and summer 2010. Once collected, sample seeds from a batch of homogeneous seeds were randomly selected and measured. Average seed weight was 52.4, 48.2 and 7.1 g per 100 seeds respectively for bean, chickpea and lentil. Seven samples of about 200 g for each legume were stored in sealed metal boxes under ambient conditions until thermal treatments were performed. Each sample was treated at low (18 C) or high (60 C) temperature. Heat treatments were made by placing the boxes in a hot air oven at 60 1 C to maintain the seeds at this temperature for 30, 60 or 90 min. Cold treatments were performed placing the boxes into a freezer at 18 1 C for 12, 24 or 48 h. At the end of each treatment, the seeds were brought naturally to ambient temperature and stored in this condition until further analysis. One box for each legume was kept at room temperature as a control test. Each treatment was replicated three times.
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2.2. Seed vigour and germination For each species and treatment, four replicates of 50 seeds were placed in Petri dishes on germination paper with 10 ml of distilled water. Seeds were allowed to germinate at 20 1 C in the dark until the end of the test as stated by official seeds analysis methods (9 days for beans, 8 days for chickpeas and 10 days for lentils) (ISTA, 2006). Germination was considered to have occurred when the radicles were 5 mm long. The seedlings with short, thick and spiral formed hypocotyls and a stunted primary root were considered as abnormally germinated (ISTA, 2006). The number of germinated seeds was recorded every 24 h and mean germination time (MGT) was calculated to assess the rate of germination according to the P following formula: MGT ¼ (g$d)/G where g is the number of seeds germinated on day d and G is the total number of germinated seeds at the end of germination analysis. 2.3. Physical properties Samples of 10 g (weighed exactly) were counted and transferred to measuring cylinders where 50 ml of distilled water were added. Seed volumes were obtained after subtracting 50 ml from the total volume of seeds and water. The cylinders were then covered with aluminium foil and left at room temperature (20 C) for 18 (bean and chickpea) or 12 h (lentil). After soaking, the seeds were drained, blotted dry with filter paper and weighed. As for dry seeds, swollen seed volume was measured in a graduated cylinder. From these data, weight, volume and density (as g per cubic cm) were calculated for dry and soaked seeds. Seed weight and volume were reported as weight and volume of 1000 seeds in order to average out the small variations occurring at single seed level. Hydration capacity, hydration index, swelling capacity and swelling index were calculated according to Saha et al. (2009). Hydration capacity and hydration index were determined by using the following formulas: Hydration capacity per seed (g seed1) ¼ Ws Wd/N; Hydration index ¼ Ws Wd/Ws where Ws is the weight of soaked seeds (g), Wd is the weight of seeds before soaking (g) and N is the number of seeds. Swelling capacity and swelling index were determined by using the following formulas: Swelling capacity per seed (ml seed1) ¼ Vs Vd/N; Swelling index ¼ Vs Vd/Vs where Vs is the volume of soaked seeds (ml), Vd is the volume of seeds before soaking (ml) and N is the number of seeds. After soaking, the soak water was collected. Electrolytes leached into the soaking water were quantified by assessing electrical conductivity (EC) with a digital conductivity meter (Conductivity meter 524, Crison Instruments S.A.) in mS cm1 (Hentges et al., 1991). Soluble solids content (SSC) of the soak water was determined with a digital refractometer (MTD-045nD, Three-In-One Enterprises Co., Ltd.) and expressed as Brix. 2.4. Cooking quality The effect of thermal treatments on legume seeds was evaluated by testing also the “degree of cooking” estimating the hardness of cooked seeds after a fixed cooking time (Nasar-Abbas et al., 2008). Seeds of bean, chickpea and lentil (10 g), soaked as reported before, were transferred in beakers (100 ml capacity) covered with aluminium foil containing 50 ml of distilled water (ratio 1:5). Beakers were then placed in a hot air oven (105 C) for 120, 90 or 60 min, respectively for chickpea, bean and lentil, followed by cooling at room temperature (20 C) for 30 min. Seed hardness was measured using a digital penetrometer (mod. 53205, TR Snc.) equipped with a flat 2 mm diameter steel punch. Ten cooked beans, chickpeas or lentils were punched individually for each treatment
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and the mean peak force was calculated in Newtons per seed (N seed1). The cooking water of each treatment was collected and leached electrolytes and soluble solid content were determined as reported before. 2.5. Statistical analysis A completely randomized design was performed. For each legume, data represent the mean of three replicate samples for each treatment. Statistical analyses were performed using ANOVA and the means were separated according to Duncan’s Multiple Range Test at a significance level of 0.05. 3. Results and discussion 3.1. Bean (Table 1) Germination percentage was very high (>97.5%) and was not affected by thermal treatments. MGT of non-treated seeds was 5.25 days. The treatments at 18 C for 24 or 48 h increased seed vigour reducing MGT by about 0.5 day; also hot treatments reduced the average germination time especially when seeds were treated for 60 min (4.82 days). Considering the 1000-seed lots, weight loss was significantly greater for those treated at 18 C for 12 or 14 h and at 60 C for 60 min. The volume of seeds slightly decreased when treated at 60 C, while the reduction was markedly greater for seeds treated at 18 C, and reached about 50 ml less for those treated for 24 h. The soaking of the beans for 18 h almost doubled the seed weight. There was no effect of thermal treatments on hydration capacity and hydration index. The soaked beans had a similar swelling capacity ranging from 0.44 to 0.50 ml seed1, while the swelling index was significantly affected by thermal treatments. The beans treated at 18 C for 18 or 24 h had a swelling index of respectively 1.26 and 1.21 followed by the beans treated at 60 C for 90 min (1.17), while all the other samples almost doubled their initial volume after soaking (1.08).
At the end of the soaking time, the electrolytes leached from beans had a significantly higher EC in the soak water of the treated seeds than in that of non-treated seeds (319.50 mS cm1). Solids loss was not influenced by temperature nor by time of treatment; EC was on average 495.06 and 509.78 mS cm1 respectively for cold and hot treatments. Soluble solids loss was very low, with an average content of 0.52 Brix and did not vary significantly among treatments. After cooking, the leaching of electrolytes in all samples was about ten times greater than in soaking water. Solids loss in cooking water amounted to an EC of 3.93 mS cm1 for non-treated beans, while all treated samples had a higher EC (4.25 mS cm1 on average) with no significant difference due to time and temperature of treatments. Soluble solid content of cooking water of non-treated beans was 2.10 Brix. Only the shortest treatment at 18 C did not differ from control, while all the other samples had a higher soluble solids loss during cooking. Bean hardness after cooking was markedly influenced by thermal treatments. All the treated samples were harder than nontreated seeds (1.57 N seed1) or those treated for 12 h at 18 C (1.80 N seed1). Increasing the time of cold treatments increased up to 10 times the resistance to punching of seeds (48 h at 18 C: 18.42 N seed1). The effect of a hot treatment was greater. After 30 min at 60 C seed hardness was 10.18 N seed1 and increased to 26.35 N seed1 when seeds were treated for 90 min. Our results showed that hot treatments and cold treatments of longer duration promoted the hard-to-cook phenomenon that can occur in many legumes and has been investigated by many authors (Burr et al., 1968; Hentges et al., 1991). The increase in seed hardness after cooking seems to be due to structural and biochemical modifications that occur during seed ageing and can be accelerated by storage conditions (temperature and relative humidity) and water activity of the bean (Aguilera and Rivera, 1992; Nasar-Abbas et al., 2008). Hardness of many common bean varieties increases even after medium term storage (3e6 months) at 30e35 C (Del Valle and Stanley, 1995; Reyes-Moreno et al., 1994). Many authors reported that the beans with the hard-to-cook phenomenon are characterized by a water absorption rate lower than soft beans (Burr et al., 1968; Varriano-Martson and Jackson, 1981). It can presumed that a similar pattern could have been induced by the
Table 1 Effect of thermal treatments on viability and physical characteristics of bean seeds. Thermal treatments
Germination (%) M.G.T (d) 1000 seeds weight (g) 1000 seeds volume (ml) 1000 soaked seeds weight (g) 1000 soaked seeds (ml) Density (g ml1) Hydration capacity (g seed1) Hydration index Swelling capacity (ml seed1) Swelling index Soaking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Cooking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Firmness (N seed1)
Non-treated
12 h at 18 C
24 h at 18 C
48 h at 18 C
300 at 60 C
600 at 60 C
900 at 60 C
97.50 a 5.25 a 537.62 a 437.62 a 1042.79 a 912.28 a 1.23 a 0.51 a 0.94 a 0.47 a 1.08 a
98.75 a 5.08 ab 508.68 b 407.02 bc 994.74 a 848.25 a 1.25 a 0.49 a 0.96 a 0.44 a 1.08 a
98.75 a 4.76 b 510.26 b 389.91 c 992.11 a 881.58 a 1.31 a 0.48 a 0.94 a 0.49 a 1.26 a
98.75 a 4.73 b 526.32 ab 412.28 b 1029.83 a 912.28 a 1.28 a 0.50 a 0.96 a 0.50 a 1.21 a
100.00 a 5.09 ab 526.14 ab 422.37 ab 1028.6 a 871.05 a 1.25 a 0.50 a 0.95 a 0.45 a 1.06 a
98.75 a 4.82 b 517.46 b 422.37 ab 1010.7 a 879.39 a 1.23 a 0.49 a 0.95 a 0.46 a 1.08 a
97.50 a 5.08 ab 524.56 ab 421.05 ab 1028.07 a 912.28 a 1.25 a 0.50 a 0.96 a 0.49 a 1.17 a
319.50 b 0.57 a
547.67 a 0.53 a
478.67 a 0.50 a
493.00 a 0.50 a
496.00 a 0.50 a
501.67 a 0.50 a
531.67 a 0.53 a
3.93 b 2.10 c 1.57 d
4.19 a 2.30 bc 1.80 d
4.30 a 2.67 ab 3.96 c
4.22 a 2.57 ab 18.42 ab
4.32 a 2.77 a 10.18 b
4.18 a 2.50 ab 21.31 a
4.27 a 2.67 ab 26.35 a
Means within a row followed by different letters are significantly different at P < 0.05 (Duncan Multiple Range Test). Analysis of the percentage values was performed on corresponding angular values.
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thermal treatments tested in this study, even if no differences were noticed in hydration and swelling coefficient probably because the seeds had already reached a saturation threshold after 18 h soaking. In fact, many authors reported that the rate of water absorption in beans reaches a saturation rate after 12 h regardless of storage conditions or ageing (Berrios et al., 1999; Sefa-Dedeh and Stanley, 1979; Hsieh et al., 1993). The negative effect of thermal treatments on bean seeds is confirmed also by the increase of electrical conductivity of soaking and cooking water of the treated seeds. It is well known that solids loss in damaged or aged seeds is higher than young and intact seeds, and that it is due to loss of membrane integrity and to changes of intercellular spaces and adhesion areas between cotyledon cells (Berrios et al., 1998). Hincks et al. (1987) showed a high correlation between electrolyte leakage, determined by the conductance of the leachate, and seed hardness after cooking. Our trials confirmed this observation. 3.2. Chickpea (Table 2) Thermal treatments did not change chickpea seed vitality. Germination percentage of non-treated seeds was 96.25. Treating seeds at 60 C for 90 min slightly reduced germination (90.0%) while no effect was recorded with the other time temperature combinations. Mean germination time (MGT) was 3.57 days for non-treated seeds; thermal treatments had no effects on MGT. Average seed weight was not modified significantly by thermal treatments, while both hot and cold treatments caused a reduction of the 1000 seed volume in longer treatments. The seeds treated at 18 C for 12 h significantly increased in volume (412.70) by about 40 ml 1000 seeds1. Increasing the cold treatment to 24 h, the volume of seeds reduced approximately by 30 ml 1000 seeds1. This may be due to volume variations of the water inside seeds when temperature drops under 4 C. A shorter cold treatment may determine an increase of water volume inside the seeds, while in longer cold treatments the water inside the seeds reaches a lower temperature and thus a lower volume, reducing the whole-seed volume. The density of untreated seeds was 1.34 g ml1, and did not change significantly with heat treatment. The treatment at low temperature for 12 h gave the lowest density (1.18 g ml1) which
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then tended to increase, reaching the highest density (1.38 g ml1) in seeds treated at 18 C for 48 h. After 18 h of soaking, seed weight almost doubled for every treatment, while their volumes increased differently. Nevertheless no significant difference was recorded among soaked seeds of different treatments. These trends are confirmed by hydration and swelling capacity testing. The swelling index of treated samples was not significantly different from non-treated seeds. Differences were found among treatments, especially cold treatments that ranged between 1.08 (12 h at 18 C) and 1.51 (48 h at 18 C). These data indicate that even if the samples absorbed the same amount of water and reached a similar final volume after soaking, the increase in volume was different and seemed determined by the effect of thermal treatments on seed volume. We can then argue that the capacity to imbibe water was substantially affected by osmotic potential of the seeds and that this was not affected by thermal treatments. Moreover, many authors reported that the differences in hydration and swelling capacity of legume seeds tend to decrease reaching a saturation threshold, after 12 h of soaking (Berrios et al., 1999; Hsieh et al., 1993; Sefa-Dedeh and Stanley, 1979). The analysis of soak water at the end of soaking time may give some information on seed integrity and on damages due to thermal treatments by evaluating soluble solids loss and electrolytes leached. Solids loss is an indication of seed deterioration (Ching and Schoolcraft, 1968; Parrish and Leopold, 1978) and is directly proportional to the EC of the soaked water (Nasar-Abbas et al., 2008). The EC of soak water of chickpeas decreased as the treatment time increased for both cold or hot treatments. The EC of the soaking water of non-treated seeds (1388.8 mS cm1) was significantly higher than the conductivity of the soaking water from chickpeas treated for 12 h at 18 C (1189.3 mS cm1) or for 90 min at 60 C (1161.0 mS cm1). Electrolytes leached in water during cooking were twice the amount in soak water and with no significant differences among control and thermal treatments. Cooking also increased the amount of soluble solids loss, perhaps due to the hydrolysis of polysaccharides, but with no differences among treatments (2.48 Brix on average). Hardness of chickpeas after cooking was significantly influenced by thermal treatments. The puncture force required for non-treated
Table 2 Effect of thermal treatments on viability and physical characteristics of chickpea seeds. Thermal treatments
Germination (%) M.G.T. (d) 1000 seeds weight (g) 1000 seeds volume (ml) 1000 soaked seeds weight (g) 1000 soaked seeds (ml) Density (g ml1) Hydration capacity (g seed1) Hydration index Swelling capacity (ml seed1) Swelling index Soaking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Cooking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Firmness (N seed1)
Non-treated
12 h at 18 C
24 h at 18 C
48 h at 18 C
300 at 60 C
600 at 60 C
900 at 60 C
96.25 a 3.57 a 493.65 a 371.42 bc 980.87 a 898.41 a 1.34 ab 0.49 a 0.99 a 0.53 a 1.44 ab
97.50 a 3.85 a 487.30 a 412.69 a 974.60 a 857.14 a 1.18 b 0.49 a 1.00 a 0.44 a 1.08 b
96.25 a 3.98 a 498.73 a 409.52 ab 1004.04 a 902.38 a 1.22 ab 0.51 a 1.01 a 0.49 a 1.21 ab
96.25 a 3.73 a 472.01 a 343.43 c 943.93 a 859.30 a 1.38 a 0.47 a 0.99 a 0.52 a 1.51 a
93.75 a 3.67 a 485.71 a 380.95 bc 982.54 a 873.02 a 1.28 ab 0.50 a 1.02 a 0.49 a 1.29 ab
96.25 a 3.78 a 498.73 a 363.49 c 1003.96 a 919.84 a 1.38 a 0.51 a 1.01 a 0.56 a 1.54 a
90.00 b 3.99 a 476.69 a 359.30 c 958.08 a 860.03 a 1.33 ab 0.48 a 1.01 a 0.50 a 1.40 ab
1388.84 ab 0.87 a
1443.33 a 0.87 a
1285.19 bc 0.90 a
1189.26 c 0.93 a
1471.27 a 0.90 a
1261.04 c 0.90 a
1295.33 bc 0.88 a
2.72 a 2.40 a 2.14 a
2.70 a 2.40 a 1.99 ab
2.76 a 2.63 a 1.71 cd
2.61 a 2.40 a 1.52 d
2.75 a 2.53 a 1.86 bc
2.64 a 2.40 a 1.58 d
2.72 a 2.57 a 1.29 e
Means within a row followed by different letters are significantly different at P < 0.05 (Duncan Multiple Range Test). Analysis of the percentage values was performed on corresponding angular values.
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Table 3 Effect of thermal treatments on viability and physical characteristics of lentil seeds. Thermal treatments
Germination (%) M.G.T. (d) 1000 seeds weight (g) 1000 seeds volume (ml) 1000 soaked seeds weight (g) 1000 soaked seeds (ml) Density (g ml1) Hydration capacity (g seed1) Hydration index Swelling capacity (ml seed1) Swelling index Soaking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Cooking water: Electrical conductivity (mS cm1) Soluble solids content ( Brix) Firmness (N seed1)
Non-treated
12 h at 18 C
24 h at 18 C
48 h at 18 C
300 at 60 C
600 at 60 C
900 at 60 C
93.33 a 2.64 d 70.71 a 55.33 a 135.03 a 116.47 a 1.28 a 0.06 a 0.91 a 0.06 a 1.11 a
98.67 a 2.99 c 69.87 a 56.18 a 133.15 ab 112.32 a 1.25 a 0.06 ab 0.91 a 0.06 a 1.00 a
98.67 a 3.47 a 69.53 a 57.26 a 133.82 a 111.85 a 1.21 a 0.06 a 0.93 a 0.05 a 0.95 a
96.00 a 3.21 b 70.25 a 57.87 a 133.61 a 115.71 a 1.22 a 0.06 ab 0.90 a 0.06 a 1.01 a
97.33 a 3.22 b 69.31 a 52.97 a 132.62 ab 114.16 a 1.31 a 0.06 ab 0.91 a 0.06 a 1.16 a
98.67 a 3.08 bc 67.51 a 54.31 a 128.14 b 109.82 a 1.25 a 0.06 b 0.90 a 0.06 a 1.03 a
97.33 a 2.99 c 70.45 a 52.51 a 133.43 ab 110.48 a 1.34 a 0.06 ab 0.89 a 0.06 a 1.11 a
1735.00 a 1.10 ab
1653.33 ab 1.00 bc
1668.67 ab 1.00 bc
1604.00 ab 0.97 c
1688.00 ab 1.13 a
1499.67 b 0.93 c
1689.00 ab 1.02 ac
2.63 ab 2.47 a 1.36 a
2.63 ab 2.40 a 1.24 a
2.52 b 2.17 b 1.42 a
2.67 a 2.47 a 2.51 b
2.63 ab 2.53 a 1.09 a
2.67 a 2.53 a 1.48 a
2.59 ab 2.43 a 1.24 a
Means within a row followed by different letters are significantly different at P < 0.05 (Duncan Multiple Range Test). Analysis of the percentage values was performed on corresponding angular values.
seeds was 2.14 N seed1. Treated seeds decreased their hardness after cooking with increasing treatment duration. The reduction of puncture force was greater for high temperature treatments, differing significantly from controls even for the shorter treatments (30 mine1.86 N seed1) and reached the lowest hardness (1.29 N seed1) among treated samples in chickpeas treated for 90 min at 60 C. The reduction of the hardness of cooked chickpeas due to thermal treatments may lead to a reduction of cooking time. Many grain legumes, among these is chickpea, suffer from the hardto-cook tendency due to storage conditions or seed ageing (ReyesMoreno et al., 2001). Hincks et al. (1987) showed a positive correlation between EC of leachate and final cooked texture. Our data on chickpea confirm this correlation: short treatments and nontreated samples had higher values of EC in soak water and higher hardness after cooking, while longer thermal treatments determined a reduction of EC of soak water and a correlated reduction of seed texture after cooking (r ¼ 0.999, P 0.01). 3.3. Lentil (Table 3) The germination percentage of lentil seeds in every treated sample was greater than the non-treated sample (93%). Mean germination time of the treated seeds was higher than the non-treated lentils (2.64 d). The cold treatment slowed the germination speed, especially for longer durations (3.47 de24 h at 18 C; 3.21 de48 h at 18 C), while hot treatment was more effective on MGT for the 30 min treatment (3.22 d). The weight and the volume of lentil seeds were not influenced by thermal treatments with average values of about 70 g and 55 ml for 1000 seeds and a density of 1.27 g ml1 on average. Even after soaking for 12 h the seed weight and volume did not change as a result of thermal treatments. Hydration and swelling capacity were similar to controls. Solid loss in soaking water was higher than in beans or chickpeas, probably due to the different volume/area ratio. The EC of soaking water was 1735.0 mS cm1 for non-treated lentils and slightly lower for treated seeds, with the lowest value (1499.7 mS cm1) recorded for lentils treated for 60 min at 60 C. The EC of cooking water was similar to those of chickpeas, and did not differ significantly from treated or non-treated lentils. Soluble solids content of soaking water showed a decreasing trend in longer treatments. SSC was higher in cooking water but
only the samples treated for 24 h at 18 C was significantly lower than control. Lentils have shorter cooking time than other legumes and suffer less from the hard-to-cook characteristic due to ageing and suboptimal storage conditions. For lentils, as for other legumes, there is a relationship between water absorption, solid loss and cooking time (Pirhayati et al., 2011). Nevertheless, thermal treatments did not modify these characteristics. For cooking quality of lentil, the pedological characteristics of soil and the mineral metabolism of the growing seed are more influential than storage temperature (Bhatty, 1995). 4. Conclusions Biological and physical characteristics such as germination, vigour, water absorption, solids loss and electrolytes leached and cooking quality, were studied on bean, chickpea and lentil seeds treated at high or low temperature. Pest control of stored seeds can be achieved by thermal treatments at low (18 C) or high (60 C) temperature. Their efficacy depends on duration and on how quickly seeds reach the target temperature (Casagrande and Haynes, 1976; Dupuis et al., 2006; Fields, 1992; Chinwada and Giga, 1996). It is, therefore, of technical relevance to know how thermal treatment can affect grain legumes used for seed or as food. The data collected show that the exposition of legume seeds to extreme temperatures (18 C for 48 h; 60 C for 90 min) did not compromise viability, but may affect their vigour. In fact, mean germination time changed for each legume. Chickpea was not influenced by thermal treatments but bean and lentil were affected. Treated seeds of lentil had slowed germination while treated beans germinated faster. Thermal treatments may also determine structural modification of the tissues and may affect physical characteristics and cooking of grain legumes. These alterations were observed by the variations of solutes leached into soaking water that corresponded to variations in hardness after cooking. The legumes studied in this work, reacted in different ways to thermal treatments, probably due to differences in structural and morphological characteristics of the seeds. Firmness after cooking was reduced in chickpeas as thermal treatments increased, while beans showed the hard-to-cook phenomenon especially when treated at 60 C and at the longest cold treatment.
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