Impact of Longkong Pericarp Extract on the Physicochemical Properties of Alginate-Based Edible Nanoparticle Coatings and Quality Maintenance of Shrimp (Penaeus monodon) during Refrigerated Storage

**Background:** Shrimp is highly perishable due to its high moisture and nutrient content, leading to rapid quality deterioration during storage. Synthetic preservatives pose health concerns, driving interest in natural alternatives. Longkong pericarp extract (LPE) is rich in polyphenols with known antimicrobial and antioxidant properties. Alginate (ALG) is a GRAS polysaccharide that forms strong gels and is widely used as an edible coating material. This study aimed to develop LPE-enriched alginate-based nanoparticle coatings and evaluate their efficacy in maintaining the quality of black tiger shrimp during 14 days of refrigerated storage.

**Methods:** Longkong pericarps were dried at 40 °C, ground, and extracted with absolute ethanol at 40 °C for 4 hours. Four coating treatments were prepared: T1 (basic ALG coating without LPE or ultrasonication), T2 (ALG nanoparticle coating with 0.5% LPE), T3 (ALG nanoparticle coating with 1.0% LPE), and T4 (ALG nanoparticle coating with 1.5% LPE). A control (C) used distilled water. Nanoparticle formation was achieved via ultrasonication at 210 W, 20 kHz for 10 min. Coating solutions were characterized for pH, viscosity, turbidity, whiteness index, particle size, and polydispersity index. Shrimp were coated by immersion, stored at 4 °C for 14 days, and analyzed every 2 days for weight loss, pH, polyphenol oxidase (PPO) activity, total and reactive sulfhydryl content, carbonyl content, peroxide value (PV), TBARS, p-anisidine value (AnV), totox value, TVB-N, and microbial counts (TVC, LAB, Enterobacteriaceae, psychrotrophic bacteria).

**Key Results:** Coating pH ranged from 6.1 to 7.1, decreasing with increasing LPE concentration (T4: 6.2, control: 7.1). T1 had the highest viscosity; NP-ALG-LPE coatings (T2–T4) showed no significant viscosity differences. Turbidity decreased with ultrasonication but increased with LPE concentration. Whiteness index decreased with LPE addition. Particle sizes of NP-ALG-LPE coatings ranged from 218 to 260 nm. PDI was lower for ultrasonicated coatings. Weight loss increased in all samples over storage; T4-coated shrimp had the lowest weight loss at day 14. pH of control reached 7.6 (unacceptable limit) by day 6, while coated shrimp remained below this threshold throughout storage. T4 showed the lowest PPO activity. Total and reactive sulfhydryl content decreased in all samples but least in T4. Carbonyl content increased in all samples; T3 and T4 had significantly lower carbonyl content than T2 at end of storage. PV remained below the acceptable limit of 18–20 meq/kg for all samples; T4 had the lowest PV. TBARS values were below 1–2 mg MDA/kg for all groups; T4 showed the lowest TBARS. AnV and totox values followed similar trends, with T4 showing the lowest values. TVB-N of control reached 58.4 mg N/100 g on day 14, while NP-ALG-LPE-coated samples remained within the acceptable limit of 30–35 mg N/100 g. TVC of control reached 23.15 log CFU/g on day 14; T4 had the lowest TVC. LAB counts were reduced by 2, 2.16, 2.67, and 3.15 log CFU/g for T1, T2, T3, and T4, respectively, compared to control. T4 had the lowest Enterobacteriaceae and psychrotrophic bacteria counts.

**Clinical Implications:** This study demonstrates that alginate-based nanoparticle coatings enriched with 1.5% longkong pericarp extract can effectively maintain shrimp quality during 14 days of refrigerated storage by reducing moisture loss, inhibiting enzymatic browning, retarding protein and lipid oxidation, and suppressing microbial growth. The findings support the use of natural plant extracts in nanotechnology-enhanced edible coatings as a viable alternative to synthetic preservatives in the seafood industry, potentially improving food safety and reducing reliance on chemical additives.