Peter K. Kinyanjui

Hydration properties and texture fingerprints of easy- and hard-to-cook bean varieties.

The objective of this study was to understand the factors that affect the hydration and cooking profiles of different bean varieties. During this study, nine bean varieties were classified as either easy-to-cook (ETC) or hard-to-cook (HTC) based on a subjective finger pressing test and an objective cutting test. Rose coco, Red haricot, and Zebra beans were classified as ETC, while Canadian wonder, Soya fupi, Pinto, non-nodulating, Mwezi moja, Gwaku, and New mwezi moja were HTC. The effect of different soaking (pre)-treatments on the cooking behavior and/or water absorption of whole or dehulled beans was investigated. Dehulling, soaking in high pH and monovalent salt solutions reduced the cooking time of beans, while soaking in low pH and CaCl2 solutions increased the cooking time. Moisture uptake was faster in ETC and dehulled beans. Soaking at high temperatures also increased the hydration rate. The results point to pectin-related aspects and the rate of water uptake as possible factors that influence the cooking rate of beans.

Extraction and characterization of pectic polysaccharides from easy- and hard-to-cook common beans (Phaseolus vulgaris)

The occurrence of the hard-to-cook (HTC) defect in legumes is characterized by the inability of cotyledons to soften during the cooking process. This phenomenon may be influenced by pectin properties. The objective of this study was to characterize the pectic polysaccharides comprised in the alcohol insoluble residue (AIR) extracted from easy-to-cook (Rose coco) and hard-to-cook (Pinto) common beans. This would provide an insight in the relationship between the pectin properties and HTC defect. The AIR was extracted from raw, half-cooked hard, half-cooked soft and fully-cooked bean samples. Subsequently, it was fractionated into water-, chelator- and Na2CO3-soluble pectin fractions and a hemicellulose fraction. For the AIR and the pectin fractions, determination of the galacturonic acid content, neutral sugars, degree of methylesterfication (DM), degree of acetylation (DAc) and molar mass (MM) distribution was performed. Results on the pectin fractions, MM distribution and pectin content profile, revealed that Rose coco pectin generally showed higher pectin solubility than Pinto. Neutral sugar profiles indicated that Pinto contained higher amounts of branched pectin (i.e. arabinans) than Rose coco. There was no difference between the DM of Pinto and Rose coco, however, the DAc was higher in Rose coco. In conclusion, the differences in pectin structure and solubility properties between easy- and hard-to-cook common beans might contribute to the differences in their cooking behavior.

Detailed analysis of seed coat and cotyledon reveals molecular understanding of the hard-to-cook defect of common beans (Phaseolus vulgaris L.).

The hard-to-cook (HTC) defect in legumes is characterized by the inability of cotyledons to soften during the cooking process. Changes in the non-starch polysaccharides of common bean seed coat and cotyledon were studied before and after development of the HTC defect induced by storage at 35°C and 75% humidity for 8months. Distinct differences in the yields of alcohol insoluble residues, degree of methoxylation (DM), sugar composition, and molar mass distribution of non-starch polysaccharides were found between the seeds coat and cotyledons. The non-starch polysaccharide profiles, both for seed coats and cotyledons, significantly differed when comparing HTC and easy-to-cook (ETC) beans. In conclusion, differences in the structure, composition and extractability of non-starch polysaccharides between the ETC and HTC beans confirmed the significant role of pectin polysaccharides in interaction with divalent ions in the HTC development, which consequently affect their cooking behaviors.

Arsenic Levels in the Environment and Foods Around Kisumu, Kenya

The objective of this study was to determine the level of arsenic in the environment and in foods consumed around Kisumu, and compare these levels with the recommended WHO maximum limits. Arsenic was determined in water samples from Lake Victoria, River Nyamasaria, tap water as well as in the soil samples. It was also determined in staple foods including maize, beans, fish and vegetables. Arsenic content in the samples was determined using Atomic Absorption Spectrophotometry. The results showed that arsenic content in the water and soil ranged from 0.00 to 8.30 ng/100 ml and 12.39 to 24.36 � g/100 g, respectively, and the mean arsenic levels in all water and soil samples were within the safe WHO limits for arsenic. The arsenic content in the maize and bean samples ranged from 5.21 to 7.03 � g/100 g. The arsenic content in the vegetables and fish ranged from 2.89 to 7.34 and 4.31 to 7.66 � g/100 g, respectively. The arse- nic content in all the food samples were also within the safe WHO arsenic limits. However, there were variations in arse- nic contents between the species of fish studied. The arsenic content was significantly higher in soil samples in compari- son to water samples (p<0.05). Overall the arsenic levels in all the food, water and soil samples were within the maximum WHO safe limits. It is recommended that continuous monitoring of arsenic levels of water, soil and foods be put in place since there could be seasonal variations in their levels.