Chamuang (Garcinia cowa Roxb.) Leaf Extract and Selected Non-thermal Processing Technologies for Inhibition of Melanosis and Quality Changes of Pacific White Shrimp (Litopenaeus vannamei) during Refrigerated Storage

Abstract

Inhibition of Pacific white shrimp (PWS) polyphenoloxidase (PPO) with Chamuang leaf extract (CLE) was studied. CLE was rich in polyphenolic glycosides, in which chrysoeriol 6-C-glucoside-8-C-arabinopyranoside and 2-feruloyl- sinapoylgentiobiose were dominant. It also contained organic acids including hydroxycitric acid and oxalosuccinic acid. CLE with copper chelation activity could inhibit PPO in a dose dependent manner. PWS treated with 1% CLE had the lower melanosis score than 1.25% sodium metabisulfite (SMS) treated sample and the control throughout the refrigerated storage of 12 days at 4 °C (p<0.05). Lower total volatile base (TVB) and thiobarbituric acid reactive substances (TBARS) along with lower counts of microbial (mesophile, psychrophile) and spoilage bacteria (Pseudomonas, Enterobacteriaceae and H2S-producing bacteria) were obtained with 1% CLE treatment than the control and SMS treated sample during entire storage of 12 days at 4 °C. When pulsed electric field (PEF) at varying specific energy densities (54 483 kJ/kg) and pulse numbers (200-600) was applied on PWS, PPO activity in cephalothorax was decreased as both parameters increased (p<0.05). Shrimp treated with PEF at highest level (PEF-T3) (483 kJ/kg, 600 pulses) had lower melanosis score than other samples, packaged in polystyrene trays and wrapped with shrink film, during 10 days of storage at 4 °C (p<0.05). Highest shear force values were noticed for the PEF-T3-treated sample at Day 10 (p<0.05). Microstructural gaping between shrimp muscle fibers was higher in PEF-T3. No protein degradation was observed for all samples. Lower total viable count (TVC) and psychrophilic bacterial count (PBC) in shrimp were obtained when PEF-T3 was implemented. After 10 days, higher sensory scores of PEF-T3-treated samples were attained, compared to others (p<0.05). The combined effect of PEF treatment applied on PWS before soaking in CLE at different concentrations (0.5 and 1%) for 30 min was investigated. Sample pre-treated with PEF and soaked with 1% CLE (PEF-1 CLE) showed lower melanosis score than that with 1.25% SMS treatment, PEF treated sample or those soaked in CLE without prior PEF and the control during storage of 10 days (p<0.05). PEF-1 CLE sample showed lower TVB, PV and TBARS, but high sensory scores than others (p<0.05). Lower increases in mesophile, psychrophile and spoilage bacterial counts were obtained in PEF-1 CLE. Chrysoeriol 6-C-glucoside-8-C-arabinopyranoside and veranisatin-C were found in PEF-1 CLE sample and were plausibly involved in keeping quality of shrimp. The effects of PEF and 1% CLE treatment on PWS packed under various modified atmospheres (MAP) including absolute N2, Ar or CO2 were studied. Lower melanosis score was evidenced in PEF pre-treated shrimp, followed by soaking in 1% CLE and packing under CO2-MAP (PEF-CLE-CO2) than the control and other treated samples during storage at 4 °C (p<0.05). PEF-CLE-CO2 showed lower pH, protein carbonyl content (PCC), TVB, peroxide value (PV) and TBARS, but exhibited higher likeness scores (p<0.05).. Spoilage and lactic acid bacterial (LAB) counts were less than 3 log CFU/g, which was lower than those of other samples at day 10 (p<0.05). Oxidation of fatty acids (EPA and DHA) was prevented in PEF-CLE-CO2 than the control and other treated samples (p<0.05). Volatile compounds in PEF-CLE-CO2 sample were negligible, compared to the control which was abundant in 3-methyl-1- butanol. The impact of high voltage cold atmospheric plasma (HVCAP) using dielectric barrier discharge (DBD) was implemented on PWS pre-soaked in 0.5 or 1% CLE solutions. Lower melanosis scores were found in the samples treated with 1% CLE and HVCAP in the presence of Ar and air (80:20) than the control and other samples throughout the storage of 15 days at 4 °C (p<0.05). Chemical quality changes in HVCAP treated PWS along with 1% CLE packaged in Ar and air MAP (CP-Ar/Air-1 CLE sample) were not significantly found at day 15. Microbiological and spoilage bacterial counts were less or equal to 5 log CFU/g meat in CP-Ar/Air-1 CLE sample, which were lower than the control and other treated samples at day 15 (p<0.05). CP- Ar/Air-1 CLE sample also exhibited higher likeness scores for all the tested attributes. Lipid and protein oxidation of HVCAP treated sample was prevented by 1% CLE, irrespective of gas composition. The effects of PEF pre-treated PWS were soaked in CLE solutions (1 or 2%), followed by HVCAP (under Ar + Air at 80:20) for 10 min, were elucidated. Least melanosis scores were attained in the samples pre-treated with PEF-T2 (800 pulses) and CLE (2%) prior to HVCAP (PEFT2-CLE2-Ar/Air-CP), compared to the control, during 18 days at 4 °C (p<0.05). The lowest microbial load and spoilage bacteria count (≤ 5 log CFU/g meat) were attained in PEFT2-CLE2-Ar/Air-CP sample (p<0.05). PEFT2-CLE2-Ar/Air-CP sample showed higher quality and likeness scores were noted in PEFT2-CLE2-Ar/Air-CP sample for all the attributes. Oxidation of polyunsaturated fatty acids and proteins was alleviated by CLE treatment. Effect of vacuum impregnation (VI) assisted penetration of CLE (1 or 2%) was studied at vacuum pressure of 5 kPa with various vacuum times (VT; 7.5-15 min) and restoration times (RT, 15-22.5 min) towards PEF treated PWS prior to MAP (Ar/Air; 80:20). Least melanosis scores were attained in samples pre-treated with PEF, VT-2 (15 min) and CLE (2%) (PEF-VI2-CLE2-MAP) than the control during 18 days, at 4 °C (p<0.05). Lower microbial load and spoilage bacteria counts were attained in PEF-VI2-CLE2-MAP sample (p<0.05). PEF-VI2-CLE2-MAP sample showed higher quality and likeness scores of all attributes when HVCAP was applied to treat PWS which were penetrated with CLE (1 or 2%) with the aid of VI (VT: 15, RT: 15 min) under Ar/Air (80:20) atmosphere for 10 min. Least melanosis scores and microbial load were attained in sample 2% CLE with the aid of PEF and VI and exposed to HVCAP (PEF-VI-CLE2-HVCAP) than the control during 18 days at 4 °C (p<0.05). This sample also showed lower lipid oxidation, pH, TVB and PCC than others (p<0.05). Higher likeness scores of all attributes were noted in aforementioned sample. Thus, shelf-life of PWS could be extended by the combination of non-thermal processes along with CLE up to 18 days.