Chickpea lines with colored testa (seed coat) contain high levels of polyphenolic compounds that exhibit high levels of antioxidant activity. However, common processing procedures, such as soaking and cooking, may decrease the levels of these bioactive compounds and subsequent overall antioxidant activity. Here, the effects of soaking, cooking and steaming processes were examined in relation to total phenolic content (TPC), total flavonoid content (TFC) and ferric reducing ability of plasma antioxidant activity (FRAP AA) of colored chickpea seeds. All processing steps significantly reduced TPC, TFC and FRAP AA in all of the tested chickpea seeds. Nevertheless, soaking the seeds at room temperature (for 22 h) resulted in a smaller decrease in TPC, TFC and FRAP AA than soaking at 60℃ (for 2 h). Moreover, steaming was superior to cooking in terms of conserving polyphenol and antioxidant activity. The observed reduction in TPC was mainly due to leaching of these compounds from the seed coat into the soaking or cooking water. Based on these results, we suggest that soaking at room temperature for 22 h followed by steaming for 1 h is the best method for retaining TPC, TFC and FRAP AA of colored chickpea.
Chickpea (Cicer arietinum L.) is an annual grain legume (pulse crop) that is extensively cultivated for human consumption. Chickpea is cultivated throughout the world, including the Mediterranean basin, the Near East, Central and South Asia, East Africa, South and North America, and Australia. It is the second-most important pulse crop in the world (after dry bean), covering 15% (10.2 million ha) of the area dedicated to pulse cultivation and accounting for 14% (7.9 million tons) of pulse production worldwide (FAOSTAT http://faostat.fao.org/default.aspx). In Israel, chickpea is the main pulse crop, pp. it is grown on about 6000 to 10,000 ha spread throughout the country. Chickpea seeds vary in size, shape and color [
Polyphenols are common constituents of foods of plant origin and are major antioxidants in the human diet. These compounds possess diverse biological properties which provide a number of benefits, including antioxidant, apoptotic, antiaging, anticarcinogenic and anti-inflammatory activities, cardiovascular protection, and improvement of endothelial function. Polyphenols also inhibit angiogenesis and cell-proliferation activity (reviewed by [
The amounts of polyphenols, flavonoids and antioxidant activity vary greatly among different legumes [20, 23]. In previous studies with chickpea, for example, we found that isolated hulls from a colored chickpea line contain large amounts of polyphenols and flavonoid compounds that exhibit high levels of antioxidant activity [
Two desi lines (731 with black color and 668 with red color) and one kabuli line (cv. Zehavit, a commercial Israeli kabuli cultivar, with beige color) of chickpea were used in this study. All desi-type lines were purchased from the National Germplasm Resources Laboratory (USDA-ARS, Beltsville, MD, USA). Seeds of all these lines were produced in our laboratory.
Samples (2 g seeds per sample) of each chickpea line were used to determine the effects of soaking time and temperature on TPC, TFC and FRAP AA. Seeds of each line were soaked at room temperature (25˚C) in about 10 ml of tap water in 20-ml glass vials for 2, 6 and 22 h, or in a water bath at 60˚C for 1, 2 and 6 h. The water absorption (moisture increase) of the initially dry legumes during the course of the soaking process was evaluated by measuring seed weight at each time point. A waterabsorption curve was constructed by plotting the increase in relative seed weight against time (dry seed weight was defined as 100%). At each time point, three vials of each of the desi and kabuli lines were sampled. All samples were freeze-dried and stored at 4˚C until use (usually between 1 and 2 days).
Chickpea seeds were pre-soaked at room temperature for 22 h as described in the previous section (defined as 0 time of cooking). For the regular cooking treatment, soaked seeds were immersed in 15 ml of fresh tap water. All vial contents were brought to a boil in a 2.5-L pot containing 2 L of tap water. Samples were drawn at 60, 90 and 120 min of boiling.
Steaming was performed in a VC1002 steam cooker (Tefal, France). After pre-soaking at room temperature for 22 h, chickpea samples were placed in a plastic net on a tray inside the steam cooker covered with a lid and steamed over 1 L of boiling water under atmospheric pressure. Samples were drawn after 60, 90 and 120 min. After regular cooking or steaming, seeds were drained and cooled to room temperature. All samples were freezedried and stored at 4˚C until use (usually between 1 and 2 days).
Seed samples were ground to a fine powder in a Retsch MM301 grinder. A 0.1-g portion of the powder was extracted in a 2-ml microfuge tube with 1 ml of 50% acetone, previously found to be the best extraction solvent [
TPC in whole chickpea seeds was determined on a dry matter basis using the Folin-Ciocalteu assay [25,26] and TFC was determined using a colorimetric method [
Analyses were performed in triplicate. The data were subjected to ANOVA using JMP (Version 5.0). Tukey HSD multiple-range tests were carried out to detect significant differences between lines and between treatments. A Pearson correlation test was conducted to determine the correlation among variables. Levels of significance were defined using P ≤ 0.05.
Soaking chickpea seeds in water or alkali salts is a common cooking pretreatment that allows for shortened cooking times and reduced energy costs [
The effects of soaking conditions on TPC, TFC and FRAP AA are shown in
resulted in significantly greater reductions in TPC, TFC and FRAP AA than soaking at room temperature (Figures 2(a-f)). Temporally, when desi chickpeas were soaked at room temperature, significant reductions of 30% to 40% in TPC, TFC and FRAP AA occurred only after 22 h (Figures 2(a-f)). When these lines were soaked at 60˚C, however, significant reductions of up to 70% to 80% in TPC, TFC and FRAP AA were obtained after 1 to 6 h (Figures 2(a-f)). Analysis of the soaking water indicated that it contained about 85% of the lost TPC, and about 40% of the lost FRAP AA (data not shown). In the kabuli line (cv. Zehavit), there were small and in most cases nonsignificant reductions in TPC and TFC under room temperature soaking, and in FRAP AA under both soaking conditions (Figures 2(g-i)). However, soaking of this line at 60˚C resulted in a significant (up to 45%) reduction in TPC and a small nonsignificant increase in TFC (Figures 2(g-h)).
The effects of cooking method and duration are shown in
The levels of TPC, TFC and FRAP AA observed in this study for the dried seeds of the beige and the two colored chickpea lines were similar to our previous study [
lowing processing, due to the fact that up to 95% of the TPC, TFC and FRAP AA are lost to the soaking and cooking water. Thus, after cooking, the levels of TPC, TFC and FRAP AA in colored chickpea seeds resembled those of the beige-colored seed. This phenomenon of decreasing TPC, TFC and FRAP AA during processing has also been observed for other seed legumes, including chickpea. Our results are similar to those observed for kabuli-type seeds [
soaking and cooking water. Indeed, using this method in the preparation of humus (a chickpea dish), we were able to retain TPC, TFC and FRAP AA in the end product (Galili, unpublished data).
We found that colored chickpea lines contain high levels of phenolic material that exhibits high levels of antioxidant activity. However, soaking, cooking and steaming processes significantly affected the TPC and antioxidant activities of all of the chickpea lines tested. The observed reduction in TPC was due to the movement of polyphenols from the seed coat to the soaking or cooking water. Steaming was found to be better than regular cooking in terms of conserving polyphenols. Based on these results, the use of soaking at room temperature for 22 h in combination with steaming for 1 h is suggested to be the best way to retain the TPC, TFC and FRAP AA of colored chickpea.