Effect of Freeze-Thaw Cycles on the Freshness of Prepackaged Penaeus vannamei

The effect of temperature fluctuations on the freshness of shrimp in simulated trays was investigated by setting a freeze-thaw (F-T) cycle of 12 h after freezing at -20 °C and thawing at 1 °C under refrigeration. The results showed that the shrimp's physicochemical properties deteriorated to different extents with the increase in F-T cycles. The total colony count of shrimp was 6.07 lg CFU/g after 21 cycles, and the volatile saline nitrogen content reached 30.36 mg/100 g, which exceeded the edible standard. In addition, the sensory quality and textural properties (hardness, elasticity, chewiness, and adhesion) declined to different degrees with increased F-T cycles. LF-NMR and protein property measurements showed that F-T cycles resulted in reduced water holding capacity and protein denaturation, which were the main factors leading to the deterioration of shrimp quality. Furthermore, flavor changes were analyzed using an electronic nose sensor to establish a freshness model. The W1W, W1S, W2S, and W5S sensors were correlated with the quality changes in shrimp and used as the main sensors for detecting the freshness of Penaeus vannamei. As a result, to better maintain the overall freshness, temperature fluctuations should be minimized in sales and storage, and fewer than 8 F-T cycles should be performed.

Effects of different cooking methods on the proximate composition and physical properties of Brown shrimp (Metapenaeus dobsonii) during cooking and freezing cycle

Present study aimed to evaluate the changes in proximate composition and physical attributes in brown shrimp (Metapenaeus dobsonii) exposed to different methods of cooking followed by freezing. For this, three different grades (100/200, 200/300, and 300/500 numbers per kg) of brown shrimp were cooked at 90°C till the core temperature of the product reaches 85°C using hot water, steam, and microwave (400W) techniques. The changes in yield, cooking loss, proximate composition, textural, and colour profile were assessed for cooked shrimps. The cooking loss was higher for larger grades of shrimp, whereas shrimp cooked using hot water exhibited the highest cooking loss. Lowest cooking loss was observed for microwave-cooked shrimp. Moisture content decreased after cooking whereas protein, fat, ash, and calorie content increased. After cooking, different grades of shrimp showed an increase in their lightness (L*), redness (a*), and yellowness (b*) values. The smaller grade shrimp exhibited lower value for cohesiveness, hardness, chewiness, and gumminess. Different cooking techniques yielded cooked shrimp of varying hardness values.

The Quality and Bacterial Community Changes in Freshwater Crawfish Stored at 4 °C in Vacuum Packaging

Crawfish can be easily spoiled due to their rich nutrition and high water content, which is difficult to preserve. In this study, the dominant spoilage organisms in crawfish which were stored at 4 °C in vacuum packaging were identified by high-throughput sequencing technology; after sequencing the full-length 16S rRNA gene, the changes in the bacterial community structure, diversity and quality (texture, flavor, etc.) were analyzed. Our results reflected that the specific spoilage organisms (SSOs) of crawfish were Aeromonas sobria, Shewanella putrefaciens, Trichococcus pasteurii and Enterococcus aquimarinus, since their abundances significantly increased after being stored for 12 days at 4 °C under vacuum conditions. At the same time, the abundance and diversity of the microbial community decreased with storage time, which was related to the rapid growth of the dominant spoilage organisms and the inhibition of other kinds of microorganisms at the end of the spoilage stage. Function prediction results showed that the gene which contributed to metabolism influenced the spoilage process. Moreover, the decline in texture of crawfish was negatively correlated to the richness of SSOs; this may be because SSOs can produce alkaline proteases to degrade the myofibrillar protein. On the contrary, the unpleasant flavor of crawfish, resulting from volatile flavor compounds such as S-containing compounds and APEOs, etc., is negatively correlated to the richness of SSOs, due to the metabolism of SSOs by secondary metabolites such as terpenoids, polyketides and lips, which can lead to decarboxylation, deamination and enzymatic oxidation. These results are very important to achieve the purpose of targeted inhibition of crawfish spoilage at 4 °C in vacuum packaging.

Effect of pressure cooking alone and in combination with other treatments on shrimp allergic protein, tropomyosin

Shrimp allergen, tropomyosin is a highly heat stable allergen a common causative of shrimp allergy in sensitive individuals. Effect of house hold pressure cooking on immunogenicity of shrimp allergen, topomyosin from Metapenaeus dobsoni was investigated in both shrimp extract and peeled shrimp by extending the time of pressure cooking to 5, 10 and 20 min. Soaked shrimps in salt, baking soda, papain and acetic acid along with pressure cooking was also investigated. In the case of extracts, IgE activity was significantly (p < 0.05) decreased and the tropomyosin band was absent in the immunoblott using pooled sera of shrimp sensitive individuals. While in the case of whole peeled shrimp, IgE activity was significantly (p < 0.05) increased and the tropomyosin band was retained in the immunoblott analysis which indicates the retention of allerginicity in the peeled shrimp. Although pressure cooked shrimp after soaking in acetic acid didn't show significant (p > 0.05) difference to that of without soaking, the tropomyosin band was observed to be very faint or absent in SDS PAGE and immunoblott analysis which indicated the effective reduction in allegenicity of whole peeled shrimp.

Functional properties and preservative effect on Penaeus vannamei of chitosan films with conjugated or incorporated chlorogenic acid

The chlorogenic acid-grafted-chitosan conjugates (CA-g-CS) with three grafting ratios were synthesized. Then the CA-g-CS conjugated films (CA-g-CS I, CA-g-CS II, and CA-g-CS III) and the CA-CS incorporated films (CA-CS I, CA-CS II, and CA-CS III) with equivalent chlorogenic acid content were prepared, respectively. The physical, mechanical, and biological properties of CA-g-CS conjugated and CA-CS incorporated films were evaluated. Further, the CA-g-CS III and CA-CS III were chosen to evaluate their preservative effect on shrimp. Compared with CS film, CA-g-CS conjugated and CA-CS incorporated films showed enhanced opacity and water solubility, changed thickness and water vapor permeability, and reduced moisture content, tensile strength and elongation at break. Conjugation or incorporation of CA enhanced antioxidant and antibacterial activities of CS films, and these activities increased with the increasing of CA content. CA-g-CS III showed better preservative effect on shrimp than CA-CS III in terms of weight loss, pH value, total volatile basic nitrogen, total bacterial count and sensory score of shrimp during storage. Therefore, CA-g-CS conjugated films exhibited better bioactivities and preservative effect on shrimp than CA-CS incorporated films. Compared with incorporation, conjugation of CA with CS is a more efficient way to improve properties of CS film.

Inhibition of Enterococcus faecalis Growth and Cell Membrane Integrity by Perilla frutescens Essential Oil

Some plant essential oils were reported to have antimicrobial activity and have the potential to replace chemical preservatives in food industry. In this study, the antibacterial activity and possible mechanism of Perilla frutescens essential oil (PEO) were evaluated using Enterococcus faecalis R612-Z1 as the target strain. The minimum inhibition concentration of PEO against E. faecalis was 0.5 μL/mL. The PEO solutions at the concentrations higher than minimum inhibition concentration had varying degrees of bactericidal effects against E. faecalis. With the addition of PEO, the cell membrane integrity was destroyed, the cell membrane potential was decreased, and the intracellular adenosine triphosphate loss was increased. By testing the bacterial counts and total volatile basic nitrogen contents in chicken breast meat, PEO can significantly inhibit the growth of E. faecalis. The results showed that PEO can be used as an effective natural food preservative during food storage.

Effect of electron beam irradiation on the biochemical, microbiological and sensory quality of Litopenaeus vannamei during chilled storage

The effects of electron beam irradiation (0, 2.5, 5.0, 7.5 and 10 kGy) on the quality characteristics of vacuum packed headless vannamei stored under chilled condition (2 °C) was assessed. The total volatile base nitrogen, non protein nitrogen content, peroxide value and thiobarbituric acid reactive substances showed an increasing trend during storage. Texture analysis indicated that shrimp irradiated at above 2.5 kGy dose had a lower hardness than control. L* value showed a decreased trend during storage (51.87-13.89). Moreover, b* and a* value showed a gradual increase during storage. The total viable count was lower in the irradiated sample than control. A similar trend also observed for psychrophilic, pseudomonas and H₂S former count. There is a significant (p < 0.05) reduction in Brochothrix thermosphacta and lactobacillus count in the irradiated sample. Based on the microbial and sensory analysis control had a shelf life up to 12th day. However, electron beam irradiated sample had extended shelf life of 15-23 days with respect to dose level.

Effect of low-temperature preservation on quality changes in Pacific white shrimp, Litopenaeus vannamei: a review

Shrimp has been widely accepted as an excellent resource for white meat due to its high-protein and low-fat content, especially low cholesterol. However, shrimps are highly perishable during preservation and retailing procedures due to the activities of enzymatic proteolysis, lipid oxidation, and microbial degradation. With increasing knowledge of and demands for safety, nutrition, and freshness of shrimp products, energy efficient, quality, maintained, and sustainable preservation technologies are needed. Low-temperature preservation, a practical processing method for improving the shelf life of food products, is widely used in the aquatic industry. This review focuses on the effects of low-temperature preservation on the quality changes in Litopenaeus vannamei. It considers physicochemical properties, sensory evaluation, melanosis assessment, and microbiological analysis. The perspectives of non-protein-based techniques on quality analysis of shrimps during preservation are also discussed. © 2019 Society of Chemical Industry.

Localization of trypsin-like protease in postmortem tissue of white shrimp (Litopenaeus vannamei) and its effect in muscle softening

Fluorescein-isothiocyanate (FITC) labeled trypsin-like protease was prepared and injected into the hepatopancreas of white shrimp. Different segments of the injected shrimp were analyzed with a fluorescence microscope during storage. FITC-trypsin-like protease can be detected in the first segment of shrimp muscle at day 4, while it cannot be observed in the second segment until day 6. The results showed that trypsin-like protease can migrate from hepatopancreas to the tail portion. Texture profile analysis showed that soybean trypsin inhibitor retarded the softening of the shrimp muscle. The rheological results revealed that the content of myosin heavy chain (MHC) in shrimp muscle was decreased with the extended storage time. Proteomics analysis displayed that trypsin-like protease accelerated the metabolism of postmortem muscle. It can be concluded that trypsin-like protease migrated from the hepatopancreas to the muscle tissue, degraded myofibrillar protein, deteriorated the muscle texture, and eventually leaded to the softening of white shrimp.