Thiamin retention in extruded cowpea, mungbean, defatted soybean and air classified mungbean products was studied by a least squares regression equation using process temperature, screw speed, buffer pH and moisture content as the major independent variables, The increase in process temperature, pH and screw speed variables effected the decrease of thiamin retention values, while the increase in moisture content increased retention. The heat generation due to increase of stress force caused by increased screw speed presumably resulted in the thiamin retention values which were lower than expected. .The carbohydrate and protein of the feed material flours protected the thiamin during the thermoplastic extrusion process.
Available lysine (AL) losses in extruded cowpea (ECP) and in extruded mung bean (MB) proteins from commercial legumes, were predicted by a least squares regression equation using process temperature, screw speed, buffer pH and moisture content as the major independent variables. The destruction of AL depended strongly on the process temperature, moisture content, screw speed and pH. Total sugars released increased with increased process temperature and moisture content of the products and when screw speed and pH were decreased. The average total sugars was 16.25 mg/g of sample in ECP and EMB products. Reducing sugars were released in a quadratic function wih total sugars. Contour-maps show that the AL retention value could be improved if either the concentration of total or reducing sugars in the products is lowered.
Materials and methods
Raw materialsCowpea (CP) [Vigna sinensis (L.) Wilczek] and mung bean (MB) [Vigna rudiuta (L.) Wilczek] were obtained from the open market at Divisioria in Manila. These dried samples were contained in rice bags and stored in a cold room ( 10°C) until used. Methodology statistical analysis were described in part I of this series (Pham & del Rosario, 1984).The preparation of samples, experimental design, extrusion processing and
Determination of available lysine (AL)The freeze dried samples were analysed for AL and moisture content. AL was determined using the fluorodinitrobenzene (FDNB) procedure of Carpenter (1960) with the modifications proposed by Booth (1971). This involved reaction of the samples with FDNB to form the dinitrophenyl (DNP)-lysine derivative and hydrolysing the sample with 6.1 M HC1 for 16 hr. After refluxing, the samples were filtered and two aliquots were taken from each sample. One aliquot was extracted with ether to remove any excess FDNB or DNP and used as a control. The methyl chloroformate derivative of lysine was formed in the second aliquot and the compound extracted with ether. The absorbance of both extracts was read at 435 nm against water. No correction factor was applied in the calculation of AL.
Determination of total sugarsTotal sugars were extracted from the extruded samples by the procedure of Chiang & Johnson (1977). A 5 g sample was extracted with 50 ml of 80% hot ethanol and agitated for 15 min with a magnetic stirrer at room temperature. The suspension was then centrifuged at loo00 rev/min for 10 min. The supernatant was decanted and the residue was re-extracted under the same conditions to insure complete extraction of soluble carbohydrates. The total sugar content in the combined supernatant was determined by the anthrone method (McReady et ul., 1950).
Determination of reducing sugarsreaction with 3,5-dinitrosalycyclic acid and phenol (Borel, Hosteller & Deuel, 1952).Reducing sugars were determined from the extracted solution of total sugars by
Results and discussion
Available lysineThe €-amino group of lysine is free to react like any free amino group in a system. Thus, it could be used as an indicator for the reaction undergone by the ...
The effect of process temperature, screw speed, moisture content and pH on the protein properties of cowpea (CP), mung bean (MB), defatted soybean (DSB) and air classified mung bean (ACMB) were studied. At high process temperature and low moisture content, increased screw speed resulted in decreased nitrogen solubility index (NSI). Water absorption capacity (WAC) measurement reflected differences in the composition of the raw materials. WAC values increased with pH, screw speed and process temperature and with decreased moisture content for high protein containing ACMB and DSB products, while with low protein containing CP and MB products, WAC values decreased at high moisture content. The insolubilized protein of the extruded products was resolubilized by sodium dodecyl sulphate (SDS) and dithiothreitol (DTT) reagents in a pH 7.6 buffer indicating the presence of both non-covalent interactions and disulphide bonds. During the extrusion process, the decrease in solubilities of extruded products can either be due to the formation of non-covalent interactions and of new disulphide bonds.
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