Preparation and characterization of biopolymer based on mango seed starch

Abstract

The conventional plastics derived from petroleum-based materials have caused environmental problems. For this reason, the biodegradable polymer such as starch has been utilized to produce biodegradable plastics. Currently, the efforts are underway in extracting starch from mango seeds as a promising biopolymer. As such, a comparison between distillation, alkaline, sedimentation and centrifugation starch extraction method were investigated. In this work, the composition analysis, physicochemical, morphological, functional and thermal properties of the extracted starch were investigated. From the analysis, the extracted starch from all extraction methods exhibited 7.43 to 14.33 % moisture content, 0.21 to 0.25 % ash content, 74.56 to 91.72 % starch yield, and 21.22 to 21.99 % amylose content. Moreover, the extracted starch revealed oval to cuboidal shape granules with average diameter ranges from 13.80 to 19.91 µm under Scanning Electron Microscope (SEM) and categorized as an A-type starch evidenced by the X-ray diffractograms. The Fourier Transform Infrared (FT-IR) spectra presented the appearance of -OH, C-H and C-O peaks, hence confirmed the presence of starch. Moreover, the thermal behaviour of the extracted starch suggested its’ capability to form starch-based film. The analytical hierarchy process (AHP) was utilized to enhance the selection process of suitable starch extraction method for packaging application. Based on the AHP method, the distillation method was found to be the most suitable method. In order to develop the films, the extracted starch was modified by adding glycerol as plasticizer and citric acid as crosslinking agent. The mango seed starch was incorporated with various amount of glycerol (5 to 30 wt. %) and citric acid (2 to 10 wt. %) via solution casting method, producing starch-based films. The optimum blend ratio of starch, glycerol and citric acid on physical, mechanical, thermal and biodegradability properties of fabricated films were studied. From the analysis, mango seed starch (GTPS) film reached an optimum condition at 5 wt. % glycerol and 4 wt. % citric acid. The maximum tensile strength was obtained at 3.30 MPa. The results were correlated to morphological structure observed under SEM, in which the mango seed starch granules were fused into homogeneous phase in the presence of glycerol and citric acid. Furthermore, thermal stability of thermoplastic starch (TPS) was improved since the adhesion between starch, glycerol and water in TPS was enhanced with addition of citric acid, as proven in thermogravimetric (TG) curve. The FT-IR spectra showed the appearance of ester-carbonyl band which indicate the successful crosslinking of TPS with citric acid. The film samples were subjected to soil burial and their extent of degradation was identified by the greater weight loss, diminished in size as well as the presence of microorganisms observed under SEM. Therefore, the mango seed is confirmed to be a promising source of starch, and compatible with plasticizer and crosslinking agent for producing biodegradable films.