University of Khartoum

A Biophysical Study on Total Proteins of the Traditionally Fermented Roselle (Hibiscus sabdariffa L.) Seed “Furundu”

A Biophysical Study on Total Proteins of the Traditionally Fermented Roselle (Hibiscus sabdariffa L.) Seed “Furundu”

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Title: A Biophysical Study on Total Proteins of the Traditionally Fermented Roselle (Hibiscus sabdariffa L.) Seed “Furundu”
Author: Ahmed Yagoub, Abu El-Gasim
Abstract: Furundu, is a meat substitute derived from traditional fermentation of karkade (Hibiscus sabdariffa L.) seed. It is prepared by cooking the seeds in boiling water and then naturally fermented for 9 days. Karkade seed (raw and cooked) and furundu ferments of 3, 6 and 9 days were analyzed for physicochemical and functional properties of their total proteins in order to study the changes encountered during fermentation process. Furundu fermentation was found to cause significant changes in karkade seed major nutrients. It significantly increased fat, fibre and ash contents of the cooked seeds, but significantly decreased total protein and carbohydrates due to changes in dry matter composition. These major changes were reflected in nonprotein nitrogen (NPN), soluble carbohydrates and starch contents as well as in total acidity (TA), fat acidity (FA) and pH. Furundu preparation reduced NPN of karkade seed from 1.35 to 0.86% at the preheating stage, while fermentation significantly increased NPN by about 57%. Soluble carbohydrates (11.07%) and starch (18.3%) were significantly reduced in furundu product to values of 5.6% and 17.6%, respectively. Total polyphenols and phytic acid were also reduced. The increase in TA and FA coupled with a decrease in pH, indicate microbial hydrolysis of the major nutrients; proteins, carbohydrates and fats. Structural changes in karkade seed proteins were also noticed in the reduced in vitro digestibility of the seed proteins upon cooking from 77.8 to 69.8%. Fermentation significantly increased the value to 82.7% at the 6th day thereafter significantly decreased it, retaining the initial value by the end of the process. Changes in physicochemical and functional properties of karkade seed proteins due to furundu fermentation were observed. Nitrogen solubility index of the karkade seed proteins (22.87% w/w of the total N) was decreased upon cooking to 17.90%, then it significantly increased with fermentation up to the 6th day (20.40), thereafter significantly decreased (15.54%) by the end of the process. The N solubility of karkade, raw and cooked seeds, and furundu samples were tested in the pH range 1 - 12, both in water and 1 M NaCl solution. The percent soluble N in water for karkade seed increased on both sides of pH 3.5 (isoelectric point), with maximum solubility occurred at pH 10. Cooking the seeds prior to fermentation reduced N solubility over a wide range of pH 1 - 11, accompanied with slight displacement in the isoelectric point (pH 3.75). Fermentation of the cooked karkade seed apparently improved N solubility at the pH range 2.5 - 5.5, but negatively affected the solubility at the alkaline region. Also the isoelectric point of the proteins in cooked seeds was unaffected after fermentation (i.e. pH 3.75). Karkade seed and furundu proteins extracted in 1 M NaCl solution at various pH values did not show solubility minima like those extracted in water with shift in the isoelectric points to more acid pH. Cooking reduced salt-soluble proteins along the profile, while fermentation did not show improvement. Furundu fermentation increased both the reduced apparent viscosity and thermal aggregation ability of the karkade seed proteins upon cooking, restoring the initial values. Variations in protein fractions were found during furundu preparation. Albumin plus globulin as well as prolamin fractions significantly decreased, while glutelins and insoluble proteins increased during fermentation. The water absorption capacity of the fermented furundu (2.63 ml/g flour) was higher than that of karkade seed (2.42 ml/g flour), but the fat absorption of the raw seed (3.54 ml/g flour) remained unchanged during the course of fermentation. Cooking of the karkade seed before fermentation significantly reduced the foaming capacity from the initial value of 46.5% to 29.0%, which was then raised to 53.8% by the end of fermentation. Emulsification capacity, emulsifying activity and emulsion stability were all improved in furundu product. SDS-PAGE pattern suggest a decrease in the molecular size of karkade seed proteins due to furundu fermentation; indicating high susceptibility to proteolysis. The results were explained on the basis of surface properties and physicochemical properties of karkade seed proteins.
Description: 178 Pages
URI: http://khartoumspace.uofk.edu/handle/123456789/10600
Date: 2015-05-12


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