The use of hydrogen peroxide for the digestion and determination of total nitrogen in chickpea (Cicer arietinum L.) and pigeonpea (Cajanus cajan L.)

The use of hydrogen peroxide as an alternative to catalysts in the determination of nitrogen in plant materials has been investigated. Nitrogen determination in leaf, stem and seed samples of chickpea and pigeonpea was carried out by three digestion procedures, using hydrogen peroxide (H₂O₂ digestion) without a catalyst, and with mercury or selenium as catalysts (catalyst digestions). The nitrogen values obtained by the three digestion procedures did not differ significantly from each other when examined by microKjeldahl (MKJ) using mercury as a catalyst, and by a Technicon auto analyser (TAA) using selenium as catalyst. The gradual addition of H₂O₂, as recommended previously, was found to be unnecessary. In view of the cost and health hazards implicated with the use of mercury and selenium for digestion, the procedure based on H₂O₂ digestion is preferable for large scale N determinations in plant tissue and seed samples of these pulse crops. The results sugest that the H₂O₂ digestion technique can be conveniently adapted for total N analysis in plant tissues and grain samples by either TAA or MKJ method.     

Nutrient Losses Due to Scarification of Pigeonpea (Cajanus cajan L.) Cotyledons

Outer layers of cotyledons of pigeonpea cultivar C 11 were successively scarified using a Tangential Abrasive Dehulling Device (TADD). Scarification for 0; 2, 4, 8, and 12 min resulted in the removal of 0, 6.7, 12.7, 25.3, and 36.9%, respectively, of powder fractions. The cotyledons and powder fractions at each level of scarification were analyzed for chemical composition, including minerals and trace elements, protein fractions, amino acid composition, and trypsin inhibitor acitivity (TIA). Protein, soluble sugars and ash of the dhal fraction (scarified cotyledons) decreased with increasing scarification time, while starch content increased. Considerable amounts of calcium (about 20%) and iron (about 30%) were removed by scarification for 4 min, but the process did not adversely affect protein quality in terms of amino acids. Trypsin inhibitors were not removed substantially by scarification.     

Nutritional quality evaluation of newly developed high-protein genotypes of pigeonpea (Cajanus cajan)

Two high-protein genotypes of pigeonpea (Cajanus cajan L), HPL 8 and HPL 40, were analysed for their nutritional quality characteristics, and the results were compared with those of normal-protein genotypes (C 11 and ICPL 211). The protein content of the high-protein genotypes was higher on average by nearly 20% but their starch content, the principal constituent of the seed, was lower by about 8%. The higher fraction (about 7%) of globulin, the major storage protein, was associated with a lower glutelin fraction in the high-protein genotypes. The amino acid composition (g per 100 g protein) of the high-protein genotypes was comparable with those of the normal-protein genotypes. However, the sulphur-containing amino acids methionine and cystine were noticeably higher (about 25%) in high-protein genotypes when results were expressed in g per 100 g sample. No large differences in true protein digestibility, biological value and net protein utilisation were observed between HP and NP genotypes. True protein digestibility was significantly increased by cooking in both whole-seed and dhal samples. The values for utilisable protein were considerably higher in high-protein genotypes, suggesting their superiority from the nutritional point of view.     

Cooking characteristics,chemical composition and protein quality of newly developed genotypes of pigeonpea (Cajanus cajan L)

Eight newly developed pigeonpea genotypes (ICPL 87, ICPL 151, ICPL 270, ICPL 366, ICPL 87051, ICPL 87063, ICPL 87067, and ICPV 1), and the two controls (BDN 2 and C 11) were analysed for cooking quality parameters and chemical composition, including amino acids and minerals. Protein quality was evaluated by determining the true protein digestibility, biological value, net protein utilisation (NPU), and utilisable protein. These genotypes differed significantly (P < 0–01) in the dhal cooking time. Sensory properties of dhal of these genotypes were found to be within the acceptable range, even though there were considerable differences among genotypes. Dhal protein, calcium, magnesium, zinc, and iron contents of these genotypes showed noticeable differences. Calcium content of ICPL 87067 was the highest (85-6 mg per 100 g) and of ICPL 87 the lowest (54-4 mg per 100 g) indicating large differences among the newly developed genotypes. No noticeable differences in sulphur-containing amino acids of these genotypes were observed. NPU was the highest (65–4%) for ICPL 366 and the lowest (56–6%) for ICPL 270 and ICPL 87067 indicating significant (P < 0–01) differences among genotypes studied.     

Physical and chemical analyses of pigeonpea (Cajanus cajan) cultivars and F1 crosses

The weight of ‘dhal’ (the edible part of the seed) from 100 whole seeds, and the hull, protein, fat, starch and soluble carbohydrate contents of 12 pigeonpea (Cajanus cajan) cultivars and the F₁ crosses were determined. The mean values for cultivars and the F₁ crosses differed in 100-seed wt, hull content (%) and protein and starch contents. Whereas 100-seed wt showed a high positive correlation with the weight of dhal, its correlation was significantly negative with hull content (%) in cultivars and protein content in the F₁ crosses.     

Methods for the estimation of protein in pigeonpea [Cajanus cajan (L.) Millsp.] and the relationship between whole grain and dhal protein contents

Protein determinations of 172 grain and dhal (decorticated dry split seed) pigeonpea samples were carried out using three methods: (a) micro-Kjeldahl (MKJ), (b) colorimetric estimation of NH₄+ with phenol hypochlorite reagents using the Technicon Auto-Analyser (TAA), and (c) dye-binding capacity (DBC) method using Acid Orange 12 dye. Protein percentages determined by the TAA and MKJ methods were highly correlated for whole-grain (0.948**) and dhal (0.967**) samples. The DBC method gave reliable results for dhal samples only. In the DBC procedure, higher protein percentages were recorded with smaller flour particles and longer mixing time, but different temperatures and durations of heating had no effect. Positive and highly significant correlations were obtained between the protein values of whole-grain and dhal samples in all the methods. Small grains gave a lower correlation between whole-grain and dhal protein content due to the observed negative correlation between grain size and percentage of seed-coat.     

In vitro Digestibility of Starch from Native and Germinated Pigeon Pea (Cajanus cajan L.)

The in vitro digestibility of native and germinated pigeon pea starches both in raw and cooked forms were investigated. The rate of digestibility (glucoamylase) was different for the two raw starches. There was a preferential utilization of low molecular weight ‘amyloses’ in the germinated samples, during in vitro enzymatic digestion of the raw granule. On acid hydrolyses, germinated samples produced lower molecular weight fragments than did raw starch, though the rate of reducing sugar released was not different. It may therefore be concluded that the size of the „amylopectin”︁ molecule is smaller in germinated starch. The easy availability of low molecular weight „amyloses”︁ may also influence the greater susceptibility of germinated starches to amylolysis even after cooking.     

Effects of isolation technique and conditions on the extractability,physicochemical and functional properties of pigeonpea (Cajanus cajan) and cowpea (Vigna unguiculata) protein isolates. I. Physicochemical properties

Physicochemical properties of pigeonpea and cowpea protein isolates were determined as a function of extraction technique and pH of the extracting medium. Protein extractability by the isoelectric point precipitation (IP) technique was positively correlated within the pH of the NaOH solution used in the pH range 8.5–12.5. The micellization (MP) technique extracted significantly (P<0.05) less protein than the IP technique when extraction pH of the NaOH was 9.5 or higher, and 10.5 or higher from cowpea and pigeonpea, respectively. The subunit composition and electrical mobility of the isolates were not affected by extraction technique and pH conditions. However, it was observed that the IP isolate extracted at pH 12.5 had the lowest proportion of hydrophilic amino acids, suggesting that the pH of the extracting medium exerted a major influence on the hydrophilicity of the isolates. Pigeonpea MP isolate exhibited significantly (P<0.05) higher exposed hydrophobicity than the IP isolates except for those extracted at pH 9.5 and 10.5. However, the cowpea MP isolate exhibited significantly lower exposed hydrophobicity than the IP isolate extracted at pH 8.5 but this was higher than the rest of the IP isolates. For IP isolates, an inverse relationship was apparent between the extraction pH and hydrophobicity. The MP isolates from both legume seeds were significantly lighter in colour than the corresponding IP isolates and, for the latter, the lightness value (L) was inversely correlated with extraction pH. Differential scanning calorimetry showed that the MP isolates exhibited higher transition enthalpy (ΔH) than the IP. For the IP isolates, ΔH decreased with increasing extraction pH.     

Resistance screening of 14 Cajanus cajan (L.) Millsp. cultivars to Callosobruchus maculatus (F.) (Coleoptera:Bruchidae)

Pigeonpea, Cajanus cajan, is a rich source of human dietary protein and carbohydrate as well as an income generator for farmers especially in developing countries. However, a major limiting factor to the viable production and post-harvest preservation of pigeonpea is infestation by the cowpea weevil, Callosobruchus maculatus. An experiment to screen for resistance in 14 newly developed C. cajan cultivars from The University of the West Indies (UWI) was conducted. The experiment compared oviposition preference based on eight parameters, namely, testa thickness, testa hardness, seed sphericity, surface area, total adult emergence, larval + pupal mortality, seed hardness and surface roughness. Four of the pigeon pea cultivars screened were resistant and could be ranked in the order of decreasing resistance as: A16 = A66PL1> A112 > A196PL2. Seed surface roughness, seed testa hardness and seed grain hardness were all found to play a major role in oviposition deterrence with seed roughness being the most effective deterrent. The results suggest that breeding for pigeonpea cultivars with rougher seed coats, harder seed testa and harder grains could enhance pigeonpea seed resistance to C. maculatus by reducing infestation and damage while in storage.     

Nutritional Quality of Vegetable Pigeonpeas [Cajanus cajan (L.) Mill sp.]: Mineral and Trace Elements

Mineral and trace elements of green and mature seed of pigeonpea genotypes were determined. Among the genotypes tested a considerable variation was observed in phosphorus, potassium and calcium of both green and mature seeds whereas the variation was small for magnesium. When consumed, green seeds are a richer source of iron, copper and zinc on a dry matter basis than the mature seed whereas there was a reverse trend for manganese. The calcium content of mature seed was significantly higher than green seed and this was attributed to the seed coat content of the mature seed.     

Proteinase inhibitors of redgram (Cajanus cajan)

Proteinase inhibitory activity of 35 varieties of redgram (Cajanus cujun L) was determined. Chymotrypsin inhibitory activity was more pronounced than trypsin inhibitory activity in all redgram varieties tested. Both trypsin and chymotrypsin inhibitory activities were found to be markedly reduced on germination.     

Effect of bicarbonate soaking on dehusking efficiency and composition of pigeon pea (Cajanus cajan L.) seeds and dhal

Soaking pigeon pea seeds in 6% sodium bicarbonate solution for 1 h, followed by oven-drying to 10% moisture improved dehusking efficiency from 66% in untreated seeds, or 71% in water-soaked seeds similarly dried, to 94% yield of dhal. Treatment reduced gum and pectin content, increased enzyme activity, but caused losses in protein and starch content of the dhal.     

Physicochemical properties of rice flour as affected by alkaline soaking and washing treatments

Effects of alkaline [NaOH, saturated Ca(OH)₂ and/or limewater] soaking and subsequent washing (with water vs. without washing) treatments on physicochemical properties of rice flour were investigated. Alkaline soaking treatment generally caused a loss of granule angularity but some birefringence was observed for unwashed alkali-soaked flour granules. After soaking, protein content of the flours significantly (P < 0.05) decreased but swelling power significantly (P < 0.05) increased compared to the control (soaked in water). The washed flours had lower protein content than unwashed flours (3.77–6.87% vs. 5.26–7.87%). The NaOH-soaking treatment yielded higher swelling power and solubility, respectively, for unwashed and washed flours. Alkaline soaking increased breakdown but decreased pasting temperature, trough viscosity, final viscosity and setback of the paste compared to the control. Compared to the control, hardness of soaked flour paste was lower due to lower final viscosity and setback. Overall, physicochemical properties of rice flour could be modified by alkali-soaking and washing treatments.     

Storage of mung bean (Vigna radiata [L.] Wilczek) and pigeonpea grains (Cajanus cajan [L.] Millsp) in hermetic triple-layer bags stops losses caused by Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Dry mung bean and pigeonpea grains that had sustained some insect damage but fumigated before the start of the experiment were stored in triple-layer hermetic bags (Purdue Improved Crop Storage (PICS™ bags) or woven polypropylene (PP) bags for 6 months. Some of the bags were artificially infested with cowpea bruchid Callosobruchus maculatus (F.) (PICS1, PP1) while others were not (PICS0, PP0). In an additional trial, PP bags containing the grains were treated with Actellic Super^® dust before being artificially infested (PP1Ac). Moisture content, live adult C. maculatus count, grain damage, weight loss, and seed germination were determined on a monthly basis. At six months, moisture contents of grain stored in PICS and PP bags remained below 12%. Storage in PICS bags halted multiplication of C. maculatus, and the initial damage level and weight of grains did not change. Conversely, in the PP bags, C. maculatus populations increased massively and seed damage reached 71.8 ± 1.9%, 76.9 ± 0.4%, and 60.3 ± 0.6% corresponding to weight losses of 14.5 ± 0.1%, 16.5 ± 0.2% and 12.5 ± 0.1% in PP0, PP1 and PP1Ac, respectively, in mung beans. With the pigeonpeas, seed damage reached 55.1 ± 0.6%, 95.7 ± 0.4% and 75.8 ± 0.9%, corresponding to weight losses of 13.0% ± 0.3%, 26.2 ± 0.2% and 13.5 ± 0.1%, in PP0, PP1 and PP1Ac, respectively. PICS bags are an effective tool for preserving mung beans and pigeonpeas against C. maculatus attack, and their performance is superior to that of Actellic Super^® dust.     

Nutritional Quality of Vegetable Pigeonpeas [Cajanus cajan (L.) Millsp.]: Dry Matter Accumulation, Carbohydrates and Proteins

Since average dry matter accumulation of green pigeonpea seeds intended for use as a vegetable was 65.6% of the total in matured seeds, green seeds were collected prior to physiological maturity. Green seed contained less starch and more dietary fiber than did mature seed. Flatulence causing oligosaccharides were present in a lower amount in green seed. Trypsin inhibitor activity (TIA) was more in mature seed whereas green and mature seed differed little in chymotrypsin inhibitor activity (CIA). The mean value for in vitro protein digestibility (IVPD) of green seed was more than that of mature seed. The green seed had a greater amount of tryptophan and threonine and the sulphur containing amino acids, methionine and cystine. It is concluded that the green seeds of pigeonpea genotypes are nutritionally better than their mature seeds.     

Effects of isolation technique and conditions on the extractability,physicochemical and functional properties of pigeonpea (Cajanus cajan) and cowpea (Vigna unguiculata) protein isolates. II. Functional properties

The functional properties of pigeonpea and cowpea protein isolates were determined as a function of extraction technique and pH conditions of the extraction medium. The isolates extracted using the micellization technique (MP) showed significantly (P<0.05) higher solubility than those extracted using the isoelectric point precipitation technique (IP) and, for the latter, solubility was negatively correlated with the extraction pH. The MP isolates exhibited significantly higher water absorption than the isoelectric isolates extracted at pH 8.5 but lower than the isolates extracted at pH 11.5 and 12.5. Cowpea MP exhibited higher oil absorption than the IP but pigeonpea MP was lower in this property than the IP extracted at pH 8.5 and higher than those extracted at pH 9.5–11.5. The MP isolates exhibited better emulsifying properties than the corresponding IP isolates and this property was drastically impaired at extraction pH 12.5. Pigeonpea MP exhibited lower foam expansion than the IP isolates except for the isolate extracted at pH 12.5, but was higher in foam stability. Cowpea MP showed higher foam expansion than the IP isolates which decreased with increasing extraction pH for the latter, but foam stability was only slightly affected. The MP isolates exhibited better gelation properties than the IP isolates extracted at pH above 9.5 and the least gelation concentration increased with increasing extraction pH. The solubility and exposed hydrophobicity best predicted the whipping properties, emulsion stability, and least gelation concentration of the isolates.     

Chemical and nutritional quality changes in germinating seeds of Cajanus cajan L.

Changes in the chemical constituents and nutritive quality of germinating seeds of pigeon pea, Cajanus cajan L. were studied in seeds that were germinated for 0, 1, 2, 3, 4 and 5 days. The differently germinated seeds were analysed for proximate composition, mineral elements, structural carbohydrates, calorific value, nutritive and non-nutritive matter and certain antinutritional factors. Germination significantly altered the nutrient composition of the seed, causing marked increase in calorific value. Crude protein, soluble carbohydrate, cellular and organic cellular contents, cellulose, lignin, non-nutritive matter, total oxalate and phytic acid contents of the seed were negatively correlated with germination, whereas the reverse was the case with the seed's contents of fat, crude fibre, total ash, soluble ash, acid-insoluble ash, cell wall carbohydrate, hemicellulose, iron, manganese, calcium, magnesium, copper, phosphorus, food energy, digestible energy, tannins, total phenolics and trypsin inhibitory activity. It was concluded that the increased contents of tannins, total phenolics and trypsin inhibitory activity of the seed during the progressive germination might limit its nutritive quality.