Extraction, modification, and characterization of native litchi seed (Litchi chinesis Sonn.) starch

Litchi seeds, because of their high starch content, have the potential to serve as a valuable non-conventional source of starch with various applications. This study aimed to optimize the extraction of native litchi seed and its modification using citric acid. Response surface methodology was used to determine the optimal combination of the independent variables extraction temperature (30-60 °C), and extraction time (4-20 h), to obtain the maximum starch yield (%). Starch was then modified chemically with citric acid concentrations of 20% and 40% to investigate its effect on physicochemical, morphological, and functional properties.

The second-order polynomial model effectively described the experimental data, demonstrating a satisfactory fit for the observed results. The optimized condition with the highest starch recovery (212.4 g kg^-1 ) was found to have an extraction temperature of 30 °C and an extraction time of 11 h. It was observed that an increase in concentration of citric acid resulted in a decrease in amylose content, swelling power, and solubility, and the water absorption capacity of modified starch increased. The scanning electron microscopy (SEM) micrographs showed that citric acid modification resulted in surface irregularities, whereas the shape and size of granules remained unaffected. Not much difference was observed in the X-ray diffraction (XRD) pattern of modified starch except for the decrease in the intensities of peaks. An effect on the thermal properties of modified starch was also observed.

The results of the study reveal that extraction temperature and extraction time are critical factors, exerting a significant effect on the extraction yield of starch. Furthermore, modified starches with improved functional properties can serve as novel and versatile sources of starch in various food and non-food sectors. © 2023 Society of Chemical Industry.