The Effect of Processing on the Antinutrients in Selected Legumes in Botswana
Keywords:legumes, protein, antinutrients, processed, unprocessed
Edible legumes particularly grain legumes or pulses are important sources of protein in many developing countries. However, this protein may not be available for digestion because of antinutritional factors such as condensed tannins, enzyme inhibitors, and others. Two local varieties of cowpeasVignaunguiculata (tswana and black-eyed) were obtained from the Botswana Agricultural Marketing Board in Gaborone, Botswana. Processed and unprocessed samples of Tylosemaesculentum (marama) and the two local cowpea varieties were analysed for condensed tannins and trypsin inhibitors. The marama beans were roasted in an oven at 80 ÂºC for 30 minutes, and the cowpeas were boiled for one hour.Condensed tannin was measured using the butanol-HCl method. For the condensed tannin contents, the results (%) for the unprocessed samples were: marama 0.381, black-eyed 0.111 and tswana 0.381 respectively. After processing, the condensed tannin results (%) were: marama 0.223, black-eyed 0.050 and tswana 0.032. After processing, the condensed tannin contents (%) were reduced by 41%, 55% and 92% for marama, black-eyed and tswana beans, respectively.The trypsin inhibitor activity was determined using benzoyl-DL-arginine-p-nitranilide hydrochloride method. The trypsin inhibitor activities (TIU/g dry matter) for the raw legumes were: marama 27.8, black-eyed17.4, and tswana 17.3. After roasting of the marama bean and boiling of the cowpeas, the following results were obtained:marama 26.4, black eye 8.4 and tswana 8.0. The decrease in trypsin inhibitor activity was reduced by 5%, 52% and 54% for marama, black-eyed and tswana beans respectively. The results showed that processing reduced the antinutrients in the legumes studied by varying amounts. In order to benefit from the high protein contents in these legumes, they have to be well cooked in order to reduce or completely destroy the antinutrients. This would improve on the digestibility of the protein in these legumes. The cultivation and increased consumption of these legumes would positively contribute to food security in the southern Africa region.
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