Effect of cooking methods on time and nutrient retention of pigeon pea (Cajanus cajan)

Abstract

Protein malnutrition is widespread among the rural poor in developing countries and legumes serve as a major source of dietary protein where animal protein is very expensive. Pigeon pea is an important legume with high amount of protein, but its consumption is limited due to its hardness and time-consuming process of cooking. This study was carried out to determine effect of cooking methods on time and nutrient retention of pigeon pea as a means of promoting dietary diversity. Pigeon pea seeds were purchased from Oja Oba market in Ado-Ekiti, Ekiti State, Nigeria, cleaned, sorted, and divided into five portions. One portion was labelled as raw sample. The second portion was washed and cooked with distilled water on an electric cooker at 300ºC for 2 hours and labelled as Sample 2. The third portion was washed and cooked at 3000C for two hours, with decanting and replenishing the water, and labelled as sample 3. The fourth portion was washed and pressure-cooked with distilled water at 300ºC for 1hour and labelled as Sample 4; while the fifth portion was pressure-cooked at 300ºC for 45 minutes, decanting and replenishing the water, cooked for 15 minutes, then labelled as sample 5. The five samples were analysed in triplicates for proximate, minerals and selected vitamins composition using standard methods of AOAC. Raw pigeon pea contained 11.9g moisture, 22.1g crude protein, 3.4g fat, 3.4g ash, 59.0g carbohydrates, 47.76mg sodium, 1025.63mg potassium, 100.25mg calcium, 377.87mg phosphorus, 13.01mg iron, 11.95mg zinc, and yielded 315.8kcal energy/100g sample. Boiling, and decanting the boiling water, and pressure cooking led to significant reduction in all macronutrients (p<0.05), the reduction being most pronounced in samples with cooking water decanted. Pressure-cooked samples retained more macronutrients with highest retention recorded in pressure-cooked sample without decanting the water (p<0.05). Boiling without decanting the water had highest retention of minerals, followed by pressure-cooked sample without decanting the water, while boiled sample with decanted water retained least minerals. Pressure cooking the pigeon pea significantly reduced cooking time (p<0.05), thereby reducing cost of electricity. Pigeon pea is a good source of protein, energy, potassium, calcium, phosphorus, iron and zinc, and can contribute significantly to meeting nutrient needs of consumers; hence, its consumption should be encouraged as a means of dietary diversity among the populace where it is available.

Keywords: Protein malnutrition, Pigeon pea, Cooking methods, Nutrient retention, Micronutrient potential

Afr. J. Food Agric. Nutr. Dev. 2019; 19(3): 14708-14725