| Abstract | Dry beans are one of the least expensive protein sources for resources poor people and considered as a major source of this important nutrient in many less developed countries. Dry beans are extensively consumed in the central rift valley and souther parts of Ethiopia. However, protein indigestibilty is a common problem with these dry beans. This is attributed to the presence of phytate, trypsin inhibitors (protease inhibitors), polyphenols, lectins and saponins. Some of these also diminish the bioavailabilty of trace elements and proteins. Several studies have been reported on the nutritional and antinutritional composition of dry beans from diffrent agro-ecological zones and localities. Processing methods to reduce or remove unwanted components from beans also reported. However, there is a continued need to carry out this type of work with new varieties that are released principally on the basis of yields, rate of maturity and resistance to disease and draw some over all conclusions taking into account nutritional aspects as well. Detailed information on the proximate composition and physico-chemical properties, antinutritional composition, functional properties and pasting characterization of bean starch are needed. The effects of processing on the removal of undesirable antinutritional compounds using simple and cost-effective processing options for use in developing countries in order to make best use of their nutritional value of the beans are necessary. This study was initiated to quantify the nutritional and cooking quality (texture of cooked beans), antinutrients and recommended processing methods to remove/reduce antinutritional and flatulence-causing factors and increase protein digestibility. The first phase of the study consisted of the physico-chemical properties and chemical composition of eight varieties of dry beans obtained from Ethiopia. The nutrition related parameters studied were moisture, ash, crude protein, crude lipid, crude fiber, crude fat, total carbohydrates, total energy, mineral content and physico-chemical properties. The physicochemical properties analyzed included density, 100-seed mass, water hydration capacity, swelling capacity, hydration index, swelling index, swelling and hydration coefficient, cooking time, color and cooked texture. Protein content ranged between 17.96 and 22.07 g/100 g with significant differences among improved varieties. Crude fat ranged 1.27- 3.02 g/100 g, crude fiber 4.66-5.95 g/100 g, ash 2.86-4.26 g/100 g,· carbohydrates 56.53- 61.56 g/100 g, moisture content 9 .08-11.00 g/100 g and lipid 0.67-1.19 g/100 g, respectively. Energy values of the seeds were 1320.01-1375.74 kJ/100 g (DM), which are comparable to those of other dry beans. Mineral contents of the seeds showed greater variation. Calcium was the most abundant 1929.77 mg/kg whereas zinc was low 28.22 mg/kg. Large variations existed between varieties in cooking time, swelling capacity, hydration capacity, unhydrated seeds and hardness. In the second phase of study, the content and composition of antinutrients, raffinose family oligosaccharides, sucrose and in-vitro protein digestibility of the eight improved varieties of Phaseolus vulgaris (L) were determined. Stachyose was the predominant α-galactosides in all dry bean samples but verbascose, fructose, glucose and maltose (present in many bean types) were not detected in all the seed samples. The concentrations observed for the raffinose family oligosaccharides, sucrose, antinutrients and in-vitro protein digestibility varied significantly (P < 0.05). Dry bean varieties mean values for raffinose, stachyose, α-galactosides, sucrose, trypsin inhibitor, tannins, phytic acid, Zn, ash, saponins and lectins were 3.14 mg/g, 14.86 mg/g, "17.99 mg/g, 24.22 mg/g, 20.68 TUlx10^3/g, 17.44 mg catechin equivalent/g, 20.54 mg/g, 2 1.78 mg/kg, 3.53 g/100g, 1.01 g/100g and 4.75 g/kg PHA (P vulgaris lectin) on dry weight basis respectively. Statistical analyses of data confirmed that in- vitro protein digestibility and undesirable factors were influenced by variety (genotype). Many correlations between antinutrients and in-vitro protein digestibility of dry beans were observed. Dry bean starch from improved varieties was isolated by wet-milling process and pasting behavior, functional and physico-chemical properties of bean flour and starch were studied. The functional and physical properties of flour and starch including, swelling power and solubility pattern, color, pH, water and oil absorption capacity, apparent viscosities of bean starch-water suspension were examined. Pasting behavior of bean flour and starch extracts were evaluated and presented in RVA profiles. Results of analyses for pasting behavior, functional and physico-chemical properties indicated that significance differences (P < 0.05) among bean varieties were existed. The factors which influence the pasting characteristics resulting to decrease in paste viscosities (peak viscosity, trough and final viscosity) of starch compared to bean flour can be attributed to inherent starch granular type of different varieties and presence of minor but important components like proteins, lipids, etc. On the basis of the swelling power of the improved bean flour and starch isolates, they can be categorized to be in the group of highly restricted-swelling starch. This characteristic is desirable for the manufacture of value added products such as noodles and composite blends with cereals. The uses of starch from improved bean varieties to impart viscosity to local processed foods have remarkable potential in the context of East and Great Lakes Regions of Africa where bean consumption of such products are increasing. In the third phase of the work, the effects of processing methods such as soaking, autoclaving, germination, cooking, (and their combinations), microwave heating, natural and controlled fermentation on the reduction/elimination of antinutrients, flatus-producing compounds and the improvement of in-vitro protein digestibility of selected dry bean varieties grown in Ethiopia were studied. These experiments were done with three varieties (Roba, Awash, Beshbesh) of haricot bean chosen from the previous study consider to have high, medium and low antinutritional factors naturally. The influence of soaking, autoclaving, germination, cooking and their combinations, on the reduction/elimination of antinutrients (trypsin inhibitors, phytic acid, lectins, saponins, and tannins), flatus-producing compounds (α-galactosides) and the improvements of in-vitro protein digestibility of three selected Phaseolus vulgaris varieties were studied. Soaking in water and sodium bicarbonate solution produced a reduction in total α-galactosides ( 40-48%) and other antinutrients but did not affect lectins and caused only 9-18% reduction of trypsin inhibitor activity in all bean varieties. Soaking along with autoclaving, however, brought about a larger reduction in total α-galactosides (74-80%) for all bean varieties. In contrast, trypsin inhibitors, lectins and saponins decreased drastically to undetectable amounts by the heating process due to their heat-sensitive nature. Germination had less effect on the reduction of the heat-sensitive antinutrients. For example, soaking and sprouting processes were less effective than cooking/autoclaving processes in reducing trypsin inhibitor, saponin and lectin concentrations. Germination was more effective in reducing stachyose, raffinose, phytic acid and tannins. Raffinose and stachyose were reduced to undetectable levels after 48-hours of germination. Furthermore, unlike all other processes germination increased the sucrose content up to 73% for Awash bean variety. In-vitro protein digestibility of dry beans varied from 80. 7 to 94.2%, 71.1 to 84.1 % and 65.6 to 80.1 % for Roba, Awash and Beshbesh varieties respectively after ge1mination of pre-soaked bean seeds with subsequent autoclaving. These results showed that certain heat-sensitive antinutritional factors were removed by cooking or autoclaving while others were removed by the metabolic activity during germination. A combination of these methods (germination followed by heat treatment) gave the best results in this study and many antinutritional factors were reduced to undetectable levels. The effects of microwave heating on antinutrients, raffinose family oligosaccharides, sucrose, in-vitro protein digestibility and solubility of 3 selected varieties of whole common bean (Roba, Awash and Beshbesh) were evaluated. The increase of in-vitro protein digestibility as a consequence of microwave heating depends on the extent of heating. The best in-vitro protein digestibility due to reduced antinutrients was obtained with three minutes exposure at 1.18 KW power and 2450 MHZ. Protein solubility, tannins and trypsin inhibitor activity of treated whole bean samples decreased as microwave time increased. The total protein of common beans was not affected as a consequence of microwave heating. The results indicate that microwave heating can be used to effectively reduce some antinutrients and improve protein quality. It should be remembered that microwave heating devices which are common in the developed world can not be afforded by a large portions of the developing world. In any case this method was not found to be the most effective method for removal of antinutritional and flatulence-producing factors. Dry beans (Phaseolus vulgaris) were also subjected to natural (endogenous micro flora on the seeds) and controlled fermentation (a mixed strain culture containing Lactobacillus acidophilus, Bifidobacterium , Streptococcus thermophillus) and then assessed for flatus-producing compounds, antinutrients and in-vitro protein digestibility. Results showed an important decrease in raffinose oligosaccharides and antinutritional components. A natural lactic fermentation of ground pulse dry beans produced significant increase (P < 0.05) in invitro protein digestibility. Appreciable improvement in in-vitro protein digestibility was observed along with an increment in fermentation time due to the reduction of antinutrients during fermentation. For all varieties of dry beans, raffinose concentration reduced prominently to undetectable level after 96 h of natural fermentation (NF). The concentration of stachyose (the main α-galactosides in raw bean) for all varieties diminished remarkably after 48 and 96 h of NF (47-62% and 92-95%; respectively). In controlled fermentation (CF), however only 15-20% was removed after 96 h. CF does not have much effect on the reduction of the α-galactosides content of the flours during fermentation as the microbes chosen did not produce extra cellular enzymes required for their hydrolysis. The microbial flora present on the beans naturally is more effective than the fermented milk forming probiotic strains/bacteria used in this study. As mentioned earlier a combination of germination and subsequent heat treatment .(autoclaving) yielded the most promising result in reducing/eliminating antinutritional and flatulence-causing factors. It also improved the in-vitro protein digestibility of dry beans which is as an indicator for protein quality. Alternatively, NF of Phaseolus vulgaris bean flour provides an inexpensive method by which consumers can obtain good quality protein and seems to be more effective than CF in reducing the flatulence-producing factors and to reduce/eliminate some important antinutritional factors. Among all the bean varieties studied in this work, Roba exhibited better protein nutritional and cooking quality, low antinutrients concentration and obtained higher protein digestibility under different processing treatments. A review of many processes including literature data was carried out. The levels of antinutritional factors and the extent of reduction by processing are different and difficult to compare. The combination of germination and autoclaving which reduced antinutritional factors to undetectable levels has not been reported earlier. However, there is a need for establishing the threshold levels at which these antinutrients cause deleterious effects which can help determines the goals to be achieved in such studies. The results of this work can be used in the preparation of bean-based processed food products including infant diets or as a formula for undernourished children and other value-added products to combat the widely prevailing protein energy malnutrition (PEM) problem in developing countries especially in East and Great Lakes regions of Africa. |