Effect of E’ Food Grade Preservatives and Preservation Methods on Physiochemical Characteristics, Microbial Population and Antioxidant Activity of Nipa Palm (Nypa fruticans Wurmb) Sap and Its Docking Study

• Main Author: Dayang Nur Athirah, Binti Abg Mohd Preudrus
• Format: Thesis
• Language: English; English; English
• Published: University of Malaysia Sarawak Institutional Repository 2025
• Subjects: QD Chemistry
• Online Access: http://ir.unimas.my/id/eprint/49580/

Nipa palm (Nypa fruticans) trees is one of the mangrove plants that grows wildly in coastal areas. Many products could be obtained from the tree, including nipa -sap (air nira), -syrup and -sugar (Gula Apong). Hence, it has a vast economic potential for Sarawak. However, its sap has a short shelf-life, which could contribute to low yield and bad quality of Gula Apong. This study aims to enhance the shelf-life of the sap in terms of controlling the pH, sugar content, organic acids content and its microbial growth using E’ food grade preservatives − potassium sorbate and sodium metabisulfite. Different preservation methods were tested, applying preservatives before (pre-tapping) and after sap collection (post-tapping), and in solid (effervescent granules) or liquid (aqueous neutralizing solution) forms. The study was conducted at two locations: Kampung Pinggan Jaya (Site I, using plastic bottle) and Pusa (Site II, using bamboo vessel). Samples treated with effervescent granules (Sample X, Y, M and N) were collected at both sites, while samples treated with neutralizing aqueous solution (Sample A and B) were collected at Site I. The preservation methods tested were introducing the preservative during pre-tapping (Sample X, M and A); the preservative was added into the empty bottle before the tapping begins and post-tapping (Sample Y, N and B); the preservative was added after the sap has been collected. Changes in physical appearance has been evaluated using sensory evaluation method, meanwhile pH and sucrose content were measured on-site at every one-hour interval. Due to the remote location of Site II, further analysis could not be conducted. Only on-site experiments, such as pH, sensory evaluation, and sucrose content, were performed at Site II. The results showed that pre-tapping treatments preserved more sucrose (Sample X: 112.0 ± 0.4 g/L, Sample M: 110.0 ± 0.5 g/L, Sample A: 150.0 ± 0.1 g/L) than post-tapping treatments (Sample Y: 116.0 ± 0.4 g/L, Sample N: 105.0 ± 0.3 g/L, Sample B: 145.0 ± 0.4 g/L) after 24 hours of storage. Further analysis showed that treated samples (both pre- and post-tapping) exhibited lower glucose and fructose concentrations compared to their controls. Sample A showed the lowest reducing sugar concentration (51.8 ± 2.4 g/L), followed by Sample B (51.3 ± 2.0 g/L), Sample X (67.6 ± 2.8 g/L) and Sample Y (63.6 ± 2.5 g/L). Sample A (0.95 g/L) and Sample B (0.97 g/L) had lower concentration of lactic acid compared to Sample X (1.15 g/L) and Sample Y (1.08 g/L). Sample A (0.08 g/L) and Sample B (0.07 g/L) also had lower acetic acid levels compared to Sample X (0.12 g/L) and Sample Y (0.09 g/L). The control sample experienced a rapid decline in RSA, dropping from 32.39 ± 0.31% at 8 hours to just 9.33 ± 0.36% at 24 hours. Pre-tapping samples (X and A) maintained higher antioxidant activity, with Sample X showing 37.32 ± 1.27% at 8 hours and 29.39 ± 2.57% at 24 hours, and Sample A showing 48.91 ± 0.99% at 8 hours and 45.38 ± 1.30% at 24 hours. In contrast, post-tapping samples (Y and B) showed lower antioxidant retention, with Sample Y at 32.55 ± 7.93% at 8 hours and 22.52 ± 6.34% at 24 hours, and Sample B at 39.95 ± 1.07% at 8 hours and 30.46 ± 0.81% at 24 hours. The study on antimicrobial activity showed that the pre-tapping treatments were more effective at reducing bacterial counts than post-tapping treatments. Sample A had the lowest bacterial counts, ranging from 1.47×103 CFU/mL at 10⁻¹ to TFTC at 10⁻⁶, showing the highest antimicrobial activity. This antimicrobial effect was comparable to the activity of VCO or its active compound, lauric acid, which was used as a reference for evaluating antimicrobial efficacy in the treated sap. Overall, the results suggested that the aqueous preservative reacts faster as it is already dissolved, which leads to a faster reaction rate compared to effervescent granules preservatives. Docking simulations showed that potassium sorbate binding strongly with glucose oxidase through hydrophobic interactions, with the most stable conformation showing a binding affinity of -4.9 kcal/mol.