Effect of storage conditions and pre-processing treatments on physical, cooking and nutritional properties of two common bean varieties in Kenya

Abstract

Common beans (Phaseolus vulgaris) are highly nutritious and widely consumed in Kenya. They are goodsources ofnutrients such as proteins, vitamins, minerals, complex carbohydrates and polyunsaturated free fatty acids. The objective of this study was to determine effects of storage conditions (25 ˚C and 75% RH,45 ˚C and 75%RH and 35 ˚C and 83% RH) and pre- processing treatments on the physical, cooking and nutritional quality in the common beans. The tropical climate ambient conditions of 25˚C and 75% RH were the control and the conditions of 45 ˚C and 75% RH and 35 ˚C and 83% RH) were the accelerated conditions of storage.Two common bean varieties harvested in the same season, Rose coco (GLP 2) and Red Kidney (GLP 24) were obtained from KenyaAgricultural and Livestock Research Organization(KALRO), Thika. The beans were subjected to a combination of varying temperature (25 ˚C, 35 ˚C and 45 ˚C) and relative humidity (75% RH and 83% RH) storage conditions in incubation chambers for a maximum storage period of six months. The desired levels of relative humidity were maintained by use of saturated salt solutions of sodium chloride and potassium chloride for 75% and 83% RH respectively. Beans from each treatment condition were sampled at different time intervals after which analysis of physical properties, cooking properties and nutritional properties were performed. Soaking pretreatment in deionized water, sodium carbonate, and calcium chloride and subsequent cooking were carried out to determine their effects on nutritional and cooking properties.For physical properties; dimension,weight and densitycharacteristics were not significantly differentfor both bean varieties during the storage period.However, colour characteristics differed significantly. Soaking characteristics: hydrationand swelling coefficientfor both varieties decreased significantlywhile leached solutes and electrical conductivity increased. Cooking profiles for Rose coco and Red kidney revealed that under the accelerated conditions of storage, cooking time increases with increased storage time.The pre-processing treatment of Na2CO3 shortened the cooking time significantlywhile soaking in 0.1M CaCl2 resulted in beans that did not cook within 5hrs.The pre-processing treatment of Na2CO3and deionized water also reduced the levels of antinutrients in the beans such as phytates and tannins. In both varieties; crude protein and mineral content did not have significant change while significant decrease was observed for moisture uptake, protein digestibility and phytates. On the other hand, tannins had a significant increase. From this study, the accelerated storage conditions of (35 ˚C and 45 ˚C) and relative humidity (75% RH and 83% RH) caused development of the HTC defect as was evident from some of the physical, cooking and nutritional properties. In conclusion, the results of this study revealed that storage at elevated temperature and RH led to the development of the HTC defect. Soaking pre-treatments for beans not only reduces the cooking time but also reduces the antinutrients content. Breeding for bean varieties without the HTC trait should be done and these varieties passed onto other stakeholders in the bean value chain for utilization. Key words: Common bean, storageconditions,hard to cook defect