Impact of high-pressure processing on hemolymph, color, lipid globular structure and oxidation of the edible portion of blood clams.

Impact of high-pressure processing (HP-P) on hemolymph and lipid globular structures of the edible portion (EP) of blood clams (BC) was investigated. HP-P above 400 MPa decreased heme iron content, while upsurged non-heme iron content. Increasing pressure induced gaps and abnormal hemocyte cell arrangements. However, HP-P at 300 MPa improved and maintained total hemocyte counts, the heme iron content, and a*-value in BC-EP. For lipid globular structures, the mean diameter drastically decreased when an HP-P pressure of 600 MPa was employed. HP-P at higher pressure induced lipid oxidation, along with decreases in monounsaturated and polyunsaturated fatty acids as well as increases in thiobarbituric acid reactive substances and peroxide value. FTIR spectra displayed a reduction in phosphate groups and cis double bonds in lipids from HP-P treated BC, compared to controls. Therefore, HP-P at 300 MPa is recommended for preparing ready-to-cook BC with less tissue damage and lipid oxidation.

Impact of Prior Pulsed Electric Field and Chitooligosaccharide Treatment on Trypsin Activity and Quality Changes in Whole and Beheaded Harpiosquillid Mantis Shrimp during Storage in Iced Water.

Harpiosquillid mantis shrimp (Harpiosquilla raphidea) (HMS) without and with beheading pretreated with pulsed electric field (PEF) (15 kV/cm, 800 pulses, 5 min) were soaked in chitooligosaccharide (COS) solution at varying concentrations (0, 1 and 2%, w/v) for 20 min and stored for 3 days in iced water. Changes in the trypsin activity, color, texture, protein pattern, TCA soluble peptide content, histological images, protein secondary structure and microbial load were monitored during the storage. The beheaded HMS pretreated with PEF and soaked in 2% COS solution showed the maximum efficacy in inhibiting trypsin activity and proteolysis, thus retaining muscle proteins, especially myosin heavy chain, actin and troponin T as well as shear force up to day 3. Pronounced muscle destruction in the whole HMS was displayed by a decreased mean grey index and fiber gapping. Such changes were lowered by the beheading and PEF/2% COS treatment (2% COS-BH). Nevertheless, no marked change in the secondary structure including α-helix, ß-sheets, ß-turns and random coil were observed among any of the samples. The microbiological analysis revealed that the total viable count (TVC) was below 6 log CFU/g till day 2 in all samples. Nonetheless, the 2% COS-BH sample had the lowest psychrophilic bacterial count and Enterobacteriaceae count at day 3, compared to the others. Thus, the combination of the prior PEF and 2% COS treatment of beheaded HMS could effectively inhibit proteases, retard the microbial growth and maintain the quality of HMS stored in iced water.

Rapid quality deterioration of harpiosquillid mantis shrimp (Harpiosquilla raphidea) during iced storage.

Changes in physicochemical, textural, microbial, and sensory quality of harpiosquillid mantis shrimp (Harpiosquilla raphidea) (HMS) during 10 days of iced storage were studied. Weight and cooking losses were increased during storage (p < 0.05). Drastic decrease in myosin heavy chain was found after 2 days of storage. Increases in total volatile basic nitrogen, trimethylamine, peroxide value, and thiobarbituric acid reactive substances with coincidentally augmented pH were found during the storage (p < 0.05). For microbiological analyses, total viable counts exceeded the limit at day 6. Melanosis score increased with a decreased L* value as storage time increased. Rapid decreases in hardness, springiness, cohesiveness, gumminess, and chewiness were associated with pasty and softened texture, which was supported by looser arrangement of muscle fiber along with gapping. This was reconfirmed by lowered shear force. Based on the quality evaluation, HMS could maintain the freshness and quality for not longer than 2 days in ice.