Optimization of extraction of dietary fibre from Ulva lactuca and its application in fish sausage

Abstract

This study was conducted to optimize extraction conditions of dietary fibre from Ulva lactuca and to evaluate its functional properties. Response surface methodology was adopted following Box-Behnken design to determine the optimal conditions of three independent variables namely concentration of the enzyme, time of enzyme hydrolysis and temperature of enzyme hydrolysis for five response variables namely yield, total dietary fibre, water holding capacity, oil holding capacity and swelling capacity. The models obtained by RSM produced a satisfactory fit to the data with respect to dietary fibre extraction. The results revealed that the optimum extraction conditions were 0.95 per cent, 60 degree celsius and 63.82 min. for enzyme concentration, hydrolysis temperature and hydrolysis time, respectively. Under this optimal condition, the yield, TDF, WHC, OHC and SWC were 22 per cent; 91.36 per cent; 11.14 g per g; 1.24 g/g and 12.47 ml/g, respectively. Structural pattern and surface morphology were evaluated using Fourier-transformed infrared spectroscopy analysis and scanning electron microscopy analysis. The SEM image of dietary fibre showed irregular, uneven and intact surface morphology. The results showed that RSM can optimize the extraction of dietary fiber from U. lactuca. Dietary fibre fortified fish sausage were prepared with 1-5 per cent level of dietary fibre from seaweed. Sausage fortified with 1per cent level of dietary fibre gives better consumer acceptability based on textual and sensory evaluation. The SEM image of sausages developed with dietary fibre showed that there is a variation in the network of dietary fibre and protein matrix in control and fibre incorporated sample. It indicates the stable structural interaction between dietary fibre and fish protein. The results of the study demonstrate that dietary fibre extracted from U. lactuca under optimized condition has good functional properties and can be incorporated at 1 per cent level in pangasius fish sausage.