Physicochemical characteristics of autochthonously-fermented prawn shell chitosan and its effects on drought-stress Solanum melongena L.

Water deficiency in urban farming negatively impacts crop growth and productivity. Chitosan, a well-known growth stimulant and stress mitigator, can mitigates these deleterious effects. Thus, a convenient household method for producing chitosan from prawn shell waste and the drought-stress mitigating function of the synthesised chitosan on a plant model (Solanum melongena L.) were demonstrated in this study. Prawn shell waste was autochthonously fermented for 14 days in sugarcane molasses with varying salt concentrations (2.5%, 5.0%, and 7.5% w/v). Physicochemical characteristics of autochthonously-fermented prawn shell chitosan (AFC) was evaluated by FTIR, XRD and elemental analyser. Microfloral profile in different fermentation conditions i.e. without salt (sample A) and with salt (sample B) was elucidated by New Generation Sequencing (NGS) method. The growth promoting and stress mitigating of AFC were evaluated on Solanum melongena L. plants which were subjected to a 10-day drought-stress. The optimum characteristics of AFC was observed in fermentation with 5% (w/v) salt as shown by 73.9% degree of acetylation (DD) by FTIR, 96.81% crystallinity by XRD and a favourable carbon/nitrogen ratio (7.28%) by elemental analyser. Commercial chitosan, for comparison, displayed 78.47 %DD, 6.49% carbon/nitrogen ratio, and 84.54% crystallinity. Microfloral profiling showed initial Weissella dominance in fermentation without salt (22.48%), before shifting to Lactiplantibacillus after 14 days. Meanwhile, microfloral profile with 5% w/v salt presence showed Weissella dominance (19.84%) on day 1, but eventually succeeded by Lactococcus (27.03%) after 14 days. AFC improved plant growth and development of drought-stressed Solanum melongena L. plant by 8.5% as compared to commercial chitosan. AFC also increased phenolic content by 11.6%, chlorophyll content by 10.6% to 96.5%, and reduced hydrogen peroxide levels by 29.5% as compared to commercial chitosan, indicating its drought stress alleviation. In conclusion, AFC showed comparable physicochemical properties to commercial chitosan and demonstrated comparable functionalities to commercial chitosan in enhancing plant growth and mitigating drought stress effects. This research demonstrated environmental sustainability practice in terms of converting waste (prawn shell) into useful products whilst contributing to food security.