Shelf Life Of Shrimp Research Articles

The Role of Gelatin-Based Film Coating Combined with Orange Peel Essential Oil on the Quality of Refrigerated Shrimp

In this study, application of gelatin-based film coating combined with essential oil obtained from orange (Citrus sinensis (L.) Osbeck) peel on the quality of deep water pink shrimp (Parapenaeus longirostris Lucas 1846) was aimed. Gelatin film (GF) and gelatin film incorporated with orange peel essential oil (GF+EO) were used for film coating. Thickness and microstructure of the films, nutritional composition (protein, moisture, lipid, ash and free amino acid content), sensory and melanosis evaluation, chemical [Sulphur dioxide (SO2), pH, total volatile base nitrogen (TVB-N), trimethylamine nitrogen (TMA-N), thiobarbituric acid (TBA), peroxide value (PV), free fatty acid (FFA)], physical (color) and microbiological [total viable counts (TVC), total psychotropic bacteria (PB), total coliform bacteria (TCB) and Enterobacteriacea (EB) ] were carried out for 15 days. As a result, gelatin film coatings were effective on the quality and shelf life of shrimps than the control group. Gelatin films were more effective on melanosis than control and the essential oil protected the shrimp’s quality more than the other groups. According to the sensorial and microbiological analysis results, control group samples (C) have 7 days’ shelf life while gelatin group samples (GF) have 12 days, and gelatin film with orange peel essential oil coated group samples (GF+EO) have 15 days.

Freshness assessment of shrimp Metapenaeus affinis by quality index method and estimation of its shelf life

ABSTRACT This study aimed to develop a Quality Index Method (QIM) for ice stored Metapenaeus affinis, and estimate its shelf life of shrimp during 12 days of storage analyzing periodically microbiological (total mesophilic (TMC), psychrotrophilic (PTC), physicochemical (TVB-N, TMA, pH, TBARS and FFA), and sensory (Quality Index Method protocol) characteristics. Partial least squares (PLS) regression was used to correlate the QIM attributes, and linear regression analysis was used to check the variables as a function of storage time. Principal component analysis (PCA) was used for interpreting physicochemical and bacteriological quality parameters. The QIM scheme was developed based on 18 demerit points, in which zero indicates total freshness. From the integration of sensory, microbiological, and physicochemical data, it was possible to estimate that the shelf life of ice stored Metapenaeus affinis is 9 days.

Changes in sensory, physicochemical, and microbiological properties of fresh captured tropical pink shrimps (Penaeus duorarum notialis) inoculated with Lactobacillusplantarum Lp6SH, Lactobacillus rhamnosus Yoba, and their cell‐free culture supernatants during storage at 4°C

AbstractThis study was conducted to evaluate the biopreservative potential of Lactobacillus plantarum Lp6SH (Lp6SH), Lactobacillus rhamnosus Yoba (LrYoba) and their cell‐free supernatants (CFS) on whole captured tropical pink shrimps (Penaeus duorarum notialis) during storage at 4°C for 8 days. Shrimps were inoculated with strains Lp6SH, LrYoba, their supernatants, sodium metabisulfite (2%) and stored at 4 ° C for 8 days. Sensory evaluation, physicochemical, and microbiological analyses were performed daily. Lp6SH, CFS of Lp6SH, and CFS of LrYoba were able to prolong the sensory shelf life up to 8 days. The total volatile basic nitrogen (TVBN) concentration was lower than the acceptable value at the end of the storage period. All the treatments reduced the number of total aerobic bacteria and fungi, and maintained the coliforms count for 2 days. Strain Lp6SH reduced the number of Staphylococci for 4 days. Based on the threshold values, the microbiological shelf life of shrimps was between 2 and 6 days at 4°C. L. plantarum Lp6SH and the CFS of L. rhamnosus Yoba could be used as natural preservatives to replace the use of sodium bisulfate in prolonging the microbiological and sensory shelf life of captured whole shrimps.Practical applicationsMicrobial spoilage of raw fresh shrimps and black spots formation constitute substantial economic losses as well as serious public health problem. Due to the harmful effects of chemical preservatives, attention is paid nowadays to the search for fresh shrimp preservation methods that could obviate the use of chemicals and prevent blackspot formation. In this respect, the results of this study supported that Lactobacillus plantarum Lp6SH strain and the cell‐free supernatant of Lactobacillus rhamnosus Yoba are suitable biopreservatives that could be used to increase the safety, prevent melanosis, and extend the sensory shelf life of captured whole shrimps stored under refrigeration. After studies for their application at large scale, the fishermen and food industries can use the bacterial suspension and the cell‐free supernatant as spray or immersion solutions for the treatment of shrimps (or other seafood) prior to freezing.

Farklı Esansiyel Yağların Vakum Paketlenmiş ve Soğukta Depolanmış Karidesler Üzerinde Duyusal ve Kimyasal Etkileri

The aim of this study was to increase shelf life of shrimps [Penaeus semisulcatus, (De Hann 1844)] found commonly in the mediterranean and aegean sea, by treating with different essential oils. Treated and vacuum packeged shrimp were examined as chemical and sensory within 0, 4, 8, 12, 16, 20, 24, days of refrigerated storage. At the limit of the pH acceptability, 8. days for control, 20. for carvacrol and 24. for thymol and eugenol groups, according to Total Volatile Basic Nitrogen (TVBN) values, 8. days for control, 16. for carvacrol, 20. for thymol and eugenol groups, regarding to Trimethylamine–Nitrogen (TMAN) values, 8.days for control, 16. for carvacrol, 20. for tymole and eugenol groups were completed the shelf life. The control extended the shelf life 8. for appearance and odor, 4. days for taste. Carvacrol group reached the shelf life 20. for apparence and odor, 16. for taste evaluation. The shelf life of eugenol group was at 24. for apparence, odor and 20. days for taste. In the respect to apperance and odor, taste, the tymole used group completed shelf life at 24. days. The result of sensory evaluation showed the similar shelf life related days with pH, TVBN, TMAN values. Tymole was advised for consumer due to higher sensory evaluation. It has been determined that there was not a study like this one on shrimp at literature in Turkey.

Effect of layer-by-layer antimicrobial edible coating of alginate and chitosan with grapefruit seed extract for shelf-life extension of shrimp (Litopenaeus vannamei) stored at 4 °C

The effect of a layer-by-layer (LbL) electrostatic deposition coating of alginate and chitosan with grapefruit seed extract was investigated on the shelf life of shrimp (Litopenaeus vannamei) stored for 15 days under refrigeration (4 °C). The shrimp were periodically analyzed for changes in microbiological parameters (total aerobic mesophilic bacteria and total aerobic psychrotrophic bacteria counts), chemical parameters, melanosis, and sensory characteristics. The chitosan–alginate coating had the advantage of reducing the bacterial count by 2 log CFU in combination with the antimicrobial activity of the grapefruit seed extract. The bilayer coating reduced the off-flavor of shrimp during the storage period by preventing the odor of acetic acid that was used to dissolve chitosan. In conclusion, chitosan and chitosan–alginate treatments could prolong the shelf life of shrimp.

Antimicrobial and antioxidant effects of a hydroxypyridinone derivative containing an oxime ether moiety and its application in shrimp preservation

In order to explore the potential of a novel tyrosinase inhibitor, namely the hydroxypyridinone derivative (5-hydroxy-1-octyl-4-oxo-1,4-dihydropyridine-2-carbaldehyde O-ethyl oxime, HPO), for shrimp preservation, six bacterial isolates from shrimp (Penaeus vannamei) (S1, S2, S3, S5, S6 and S7) were investigated. These bacteria were identified as Shewanella amazonensis, Shewanella haliotis, Microbacterium oxydans, Photobacterium damselae, Staphylococcus haemolyticus and Bacillus cereus. The antimicrobial effect of HPO on these bacteria was evaluated by an inhibition zone test, together with minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) assays. The results indicated that HPO possessed a stronger inhibitory effect than kojic acid. The antioxidant activity of HPO was evaluated by determining its 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide anion radical scavenging ability. The preservation effect on shrimp (Penaeus vannamei) of HPO was assessed by determining the quality indicators of the shrimp during the storage, including total bacterial count, pH value, total basic volatile nitrogen content, thiobarbituric acid reactive substances (TBARS) and by sensory evaluation. It was found that treatment of shrimp with HPO effectively extended the shelf life to 10 days at 4 °C. In the same assay, the shelf life of shrimps treated with 4-hexylresorcinol, kojic acid, and the control group was found to be 10, 6, and 4 days, respectively. The treatment of shrimps with HPO in combination with 0.1% citric acid further extended its shelf life to 12 days. Clearly, HPO could be applied as a shrimp preservative due to its potent anti-browning, antimicrobial and antioxidant activities.

Shelf life extension of Pacific white shrimp (Litopenaeus vannamei) using chitosan and ε-polylysine during cold storage

In this study, we examined the effects of an ε-polylysine (PL) and chitosan (CH) coating on the quality of shrimp under refrigeration. Pacific white shrimp (Litopenaeus vannamei) were coated with PL, CH, or CH + PL and stored at 4 °C for 15 days. The quality of shrimp was measured by observing changes in microbiota, pH, total volatile basic nitrogen (TVB-N), and sensory characteristics. Among the coating films, the CH + PL coating most effectively inhibited the growth of mesophilic and psychrotrophic bacteria, Pseudomonas spp., and H2S-producing bacteria. This coating increased the shelf life of shrimp by decreasing the amount of mesophilic and psychrotrophic bacteria, with inhibition greater than three log cycles on the ninth day of storage. In addition, the CH and CH + PL coatings effectively suppressed the formation of TVB-N compared with that in the control by 43% and 30%, respectively. The pH of all treated samples increased slowly compared with that of the control, but no significant difference was observed. Sensory quality was similar to microbial and physicochemical properties, and the acceptability of all treated samples gradually decreased.

Spoilage of refrigerated Litopenaeus vannamei: eavesdropping on Acinetobacter acyl-homoserine lactones promotes the spoilage potential of Shewanella baltica.

Shewanella baltica and Acinetobacter are among the predominant spoilage bacteria in refrigerated shrimp (Litopenaeus vannamei). S. baltica are incapable of producing acyl-homoserine lactone (AHL) quorum sensing signals, but can respond to environmental AHLs. In this paper, Acinetobacter was found to produce three AHLs, i.e. N-butanoyl-l-homoserine lactone (C4-HSL), N-(3-oxohexanoyl)-l-homoserine lactone (O-C6-HSL) and N-(3-oxooctanoyl)-l-homoserine lactone (O-C8-HSL), according to thin-layer chromatography using the bioreporter Agrobacterium tumefaciens A136. The agar diffusion and β-galactosidase assays revealed that S. baltica could eavesdrop on these three AHLs from Acinetobacter. Eavesdropping on Acinetobacter AHLs especially C4-HSL was found to boost the growth of S. baltica particularly under nutrient limiting conditions (up to 40-fold increase) in the co-culture experiments. The azocasein assay revealed that S. baltica produced fourfold more extracellular proteases in response to Acinetobacter AHLs. As demonstrated by the biofilm crystal violet staining assay and confocal laser scanning microscopy, eavesdropping also decreased the biofilm-forming capacity of Acinetobacter. By inoculation of S. baltica and Acinetobacter onto surface-sterilized shrimp, eavesdropping was found to endow a growth advantage to S. baltica in vivo, resulting in a 0.5day shortened shelf life of shrimp according to total volatile basic nitrogen levels and sensory analysis. Overall, the AHL-dependent eavesdropping increased the spoilage potential of S. baltica, providing a fresh perspective on the spoilage process of refrigerated L. vannamei, and this may inspire the development of novel preservation techniques in the future to further reduce post-harvest loss of shrimp.

Quality assessment of shrimps preserved with orange leaf essential oil incorporated gelatin

Assessment of edible gelatin coating solution enriched with essential oil obtained from orange (Citrus sinensis (L.) Osbeck) leaves on the quality and shelf life of cold stored deep water pink shrimp (Parapenaeus longirostris Lucas 1846) was studied. Gelatin (G) and 2% orange leaf essential oil incorporated gelatin (G+OL) solution, which was selected after antimicrobial and antioxidant analysis, were used for coating. Microstructure characterization of the gelatin films was done by Scanning Electron Microscopy. Sensory and melanosis, microbiological [total viable counts (TVC), psychrotrophic bacteria counts (PBC), Enterobacteriaceae (EB)], chemical [sulphur dioxide (SO2), pH, total volatile base nitrogen (TVB-N), trimethylamine nitrogen (TMA-N), thiobarbituric acid (TBA), peroxide value (PV)] and physical (color) analysis were carried out for control and coated samples and shelf-life was determined throughout the storage period of 14 days.The results indicate that the edible gelatin coating solutions enriched with orange leaf essential oil has noticeable effects on the quality and shelf life of shrimps when compared to control group. It was determined that edible gelatin coating solutions used were effective in all groups particularly on melanosis which may occur in shrimps and edible gelatin coating solutions with orange leaf essential oil preserved the quality of shrimp better.

Effect of Citrus wilsonii Tanaka extract combined with alginate-calcium coating on quality maintenance of white shrimps (Litopenaeus vannamei Boone)

The combined effect of Citrus wilsonii extract and alginate-calcium film coating on microbiological, chemical and sensory changes of white shrimps (Litopenaeus vannamei) was studied over 6 days of storage at 4 °C. A specific spoilage microorganism Lysinibacillus sphaericus S1 was isolated from local shrimp samples, which could cause the appearance of orange spoilage spots. The methanol extract of C. wilsonii exhibited significant antimicrobial activity against L. sphaericus S1, as well as several other food-borne pathogens. GC–MS analysis showed a high percent of furandione and furfural compounds in the extract. The extract with edible alginate-calcium coating was effective in delaying the quality deterioration of the shrimps stored at 4 °C. Total viable count of the treated shrimps was more than 10 times lower than the negative untreated control. The lower rate of the increase in pH and total volatile base nitrogen (TVB-N) was also observed in shrimps treated with the extract compared to the control group shrimps. After 6 days of refrigerated storage, shrimps treated with the extract combined with coating had the significant higher sensory score for odor, color and texture. The results suggest that the methanol extract from C. wilsonii may be promising to be developed as a new eco-friendly preservative that might be applied to extend the shelf life of shrimps maintaining good quality.

Novel Multifunctional Hydroxypyridinone Derivatives as Potential Shrimp Preservatives

In order to develop a new efficient method for the prolongation of shrimp shelf life, two novel hydroxypyridinone derivatives ((S)-2-amino-N-((S)-1-(((5-hydroxy-4-oxo-1,4-dihydropyridin-2-yl)methyl)amino)-1-oxo-3-phenylpropan-2-yl)-3-phenylpropanamide (2) and (S)-(5-hydroxy-4-oxo-1,4-dihydropyridin-2-yl)methyl 2-(benzyloxycarbonyl)-3- phenylpropanoate (3)) possessing strong tyrosinase inhibitory activity were investigated to explore their potential as shrimp preservatives. Their antimicrobial activities were evaluated by a disk diffusion method. Inhibition zone assays indicated that both 2 and 3 possess a stronger inhibitory effect than kojic acid. The minimum inhibition concentrations (MICs) of compound 3 against Bacillus subtilis, Staphylococcous aureus, Escherichia coli, Salmonella spp., and Pseudomonas aeruginosa were determined to be 32, 32, 32, 8, and 16 μg/mL. Both 2 and 3 were also found to possess antioxidant activity. The IC50 values of 2 and 3 for scavenging DPPH radical were measured to be 2.93 and 2.37 mg/mL, respectively. At 4 mg/mL, 2 and 3 were determined to have total antioxidant capacity of 2.43 and 2.72 U/mL, respectively. Compound 3 was further investigated for efficacy in shrimp preservation by sensory evaluation, determination of total volatile basic nitrogen (TVB-N), pH, and total bacterial count. The treatment with 3 was found to extend the shelf life of Penaeus vannamei Boone to 10 days at 4 °C, while the shelf life of shrimp treated with 4-hexylresorcinol, kojic acid, and the control group was 9, 6, and 4 days, respectively. Compound 3 could find application in the food industry, as a shrimp preservative, due to its protective properties.

The effect of high-pressure treatment on functional components of shrimp ( Litopenaeus vannamei ) cephalothorax

Abstract High-pressure (HP) technology has been applied to extend the shelf life of shrimps by inhibiting enzymes with PPO activity or microorganisms. However, there is very little information on its effect on relevant compounds from a nutritional or functional point of view, such as fatty acids, α-tocopherol, astaxanthin, and hemocyanin, which constitutes the main objective of the present work. Shrimp cephalothoraxes were HP processed at 200, 400, or 600 MPa/18 °C/15 min or three consecutive 5 min cycles. It was found that hemocyanin was partially denatured at pressures up to 400 MPa, resulting in lower PPO activity, and it was totally denatured at 600 MPa, although 20% residual PPO activity remained. Astaxanthin, α-tocopherol, and total antioxidant activity were stable whichever HP treatment was applied, whereas 600 MPa caused a slight reduction of eicosapentaenoic acid (C20:5n3, EPA) and docosahexaenoic acid (C22:6n3, DHA). Despite this reduction, the ω -6/ ω -3 fatty acids ratio was very low (1). Industrial relevance Shrimps are high-value fishery products with a very short shelf life under refrigeration, mainly because of microbial growth and development of melanosis. Thermal treatment is effective for extending shelf life, but it affects the nutritional quality of shrimps through degradation of bioactives such as polyunsaturated fatty acids, tocopherols, or astaxanthin, which are mainly located in the cephalothorax. High pressure is a non-thermal processing technology that has been proved to extend shrimp shelf life, but very little information can be found on its effect on the above-mentioned compounds as well as on the melanosis-inducing hemocyanin. Such basic knowledge is very important for industrial application of high-pressure technology to extend the shelf life of shrimps.

Acerola Fruit as a Possible Antimelanotic Agent in White Shrimp (Litopenaeus vannamei)

This study aimed to testify acerola’s inhibitory activity on melanosis in farmed white shrimp (L. vannamei). Shrimp samples underwent immersion in different treatments (control group (C), metabisulphite solution group (M), and acerola solution group (A)). Quality Index Method (QIM) was used to measure the shrimp shelf life, during 21 days, where microbiological, chemical, and sensory analyses were performed at each 3 days. Groups C and A exceeded the limit of mesophilic bacterial count within 15 days of storage, and for M the period was 18 days. As for the psychrophilic bacteria, C and A both crossed the limit on day 12 and M on the 15th day. Group M had the highest TVBN and pH means, followed by A and lastly C. Yet, TMA analysis showed highest values in group C, second A, and finally M. Sensory analysis determined the shelf life of groups C, M, and A as 10.5, 14.6, and 12.3 days, respectively. There were not many significant differences between the groups in all analyses; hence, dipping shrimp in acerola solutions would not suffice to inhibit melanosis formation. Further studies are needed to fully determine acerola’s antimelanosic potential.

Effect of Delayed Icing on the Quality of White Shrimp (Litopenaeus vannamei) during Chilled Storage

The effect of delayed icing on the quality of Litopenaeus vannamei was assessed by chemical, microbiological and sensory evaluation. Shrimps were divided into three lots. One lot was immediately iced and the other two lots were subjected to delayed icing after keeping in ambient conditions (30 ± 2C) for 2 and 4 h, respectively. White shrimp had a moisture content of 77.21%, protein 18.80%, ash 1.47% and fat 1.30% on wet weight basis. Total volatile basic nitrogen, trimethylamine, thiobarbituric acid and K value showed increasing trend during chilled storage. It was observed that there is a significant (P < 0.05) decrease in the hardness of shrimp meat during storage. Sensory evaluation indicated that the shelf life of white shrimp iced immediately after catch and 2 h delayed iced was approximately 9 days, whereas 4 h delayed iced sample had shortened shelf life of 6 days. Practical Applications Shrimp is one of the most traded and consumed aquatic product worldwide. Shrimps are rich in protein, containing very little fat and have significant cholesterol content. Shrimp is more prone to deterioration because of its high content of free amino acids and other soluble nonprotein nitrogenous substances that can serve as easily digestible nutrients for microbial growth. Chilled or iced preservation helps in delaying or reducing the bacterial growth, preventing browning and prolonging the shelf life of shrimp. Delayed icing of the catch at the site results in downgrading of the shrimp. The present study provides information about a baseline investigation of the shelf life and quality of Pacific white shrimp due to delayed icing. It can be useful to quantify the quality and shelf life of fresh shrimp prior to the application of preservative treatments to extend the shelf life.

Effects of Tea Polyphenols on the Quality and Shelf Life of Shrimp during Cold Storage

Effects of Tea Polyphenols on the Quality and Shelf Life of Shrimp during Cold Storage

Effect of nano-SiO2-LDPE packaging on biochemical, sensory, and microbiological quality of Pacific white shrimp Penaeus vannamei during chilled storage

A novel nano-SiO2 modified low density polyethylene (NSLDPE) packaging was prepared by blending LDPE with nano-SiO2 in this study. Its effect on the quality of Pacific white shrimp Penaeus vannamei during 8-day storage at (4 ± 1) °C and compared NSLDPE with existing LDPE were investigated. The effect of NSLDPE packaging on the shrimp was compared with normal LDPE by analyzing the microbiological and physicochemical indices. Results showed that shrimp packaged in NSLDPE packaging possessed higher sensory evaluation score and stronger water holding capacity. NSLDPE packaging inhibited the polyphenoloxidase activity and melanosis occurrence and reduced the contents of thiobarbituric acid reactive substances, total volatile base nitrogen and K value by 25.48, 8.09, and 22.22 % at the end of storage when compared with LDPE packaging, respectively. Additionally, NSLDPE packed shrimps remained the commercial acceptability for 8 days, while the total viable counts of control reached to a limiting level for shrimp processing (1 × 106 CFU g−1) after 6 days. NSLDPE packaging delayed the deterioration by improved gas barrier, inhibited endoenzyme activity, antimicrobial effect, and extended the shelf life of shrimp by nearly 33 %. Therefore, NSLDPE packaging should be recommended as a promising alternative method to maintain the quality of Pacific white shrimp.

The effects of Aloe vera (Aloe barbadensis) coating on the quality of shrimp during cold storage.

Green tiger shrimp (Penaeus semisulcatus) is an important aquaculture species worldwide. Its perishable nature, however, needs preservation methods to ensure its quality and shelf life. In this study, the effects of Aloe vera coating on the quality and shelf life of shrimps during cold storage were investigated. Shrimp samples were dipped in aqueous solutions containing 25%, 50%, 75%, and 100% Aloe vera gel before storage at 4°C for 7days. Drip loss, pH, TBA, TVB-N, and texture of both the control and treated shrimp samples were analyzed periodically. There were significant differences between coated shrimps and the control group in all parameters evaluated. Aloe vera at 75% and 100% concentrations was able to prevent lipid oxidation and drip loss properly; however, coatings containing 25% Aloe vera did not have the desired effects on these characteristics. Shrimps coated with higher concentrations of Aloe vera had better textural properties during cold storage. Results also indicated the positive effects of Aloe vera coating on the sensory quality of shrimp.

Impact of the O2 Concentrations on Bacterial Communities and Quality of Modified Atmosphere Packaged Pacific White Shrimp (Litopenaeus Vannamei)

The importance of spoilage-related bacteria in fresh Pacific white shrimp (Litopenaeus vannamei) under different modified atmospheres (MAs) at 4 °C and the effect of O2 were demonstrated in the current study. The changes of bacterial communities in MA-packed shrimp during cold storage were studied by a combined method of plate counts with isolation and identification. Three gas mixtures were applied: 80% CO2 /5% O2 /15% N2, 80% CO2 /10% O2 /10% N2 and 80% CO2 /20% O2, and unsealed packages of shrimp were used as the control. In addition, the TVB-N, pH, whiteness index, and sensory scores were also determined to evaluate the quality changes of shrimp. MA packaging effectively inhibited the increase of total psychrotrophic bacteria counts and H2 S-producing bacteria counts by about 1.7 and 2.1 log cycles, respectively. The growth of Gram-negative spoilage bacteria in shrimp, including Shewanella spp., Aeromonas spp., and Pseudomonas spp., was inhibited by MA packaging, but the growth rate of Gram-positive bacteria such as lactic acid bacteria (LAB) and Brochothrix spp. were less affected by MA as effectively as Gram-negative bacteria. In comparison with the MA-packaged samples, the counts of H2 S producers in shrimp under a CO2 -enriched atmosphere with 20% O2 were slightly lower than the count in samples under an atmosphere with 5% O2 . However, MA with 20% O2 led to higher concentrations of TVB-N, and lower whiteness values and sensory scores. The shelf life of shrimp under 80% CO2 /10% O2 /10% N2 has been prolonged by > 6 d in comparison with the control according to the sensory scores.

3‐Hydroxypyridinone‐l‐phenylalanine conjugates with antimicrobial and tyrosinase inhibitory activities as potential shrimp preservatives

SummaryTo explore the potential of novel tyrosinase inhibitors, 3‐hydroxypyridinone‐l‐phenylalanine conjugates, as shrimp preservatives, compounds 1 and 2 were evaluated for the antimicrobial activity, and compound 2 was investigated for the shrimp preservative efficacy. It was found that they both possess a stronger antibacterial effect than kojic acid against two Gram‐positive bacteria and three Gram‐negative bacteria. The minimum inhibitory concentrations (MICs) of compound 2 against Escherichia coli, Staphylococcous aureus, Salmonella gallinarum, Vibrio parahaemolyticus and Bacillus subtilis were determined as 18.5, 37, 148, 37 and 295 μg mL−1, respectively, whereas MICs of kojic acid against the same 5 bacterial strains were determined to be 355, 178, 1420, 1420 and 355 μg mL−1, respectively. It has also been demonstrated that treatment with compound 2 improves the sensory properties, retards the growth of spoilage bacteria, decreases the total volatile basic nitrogen (TVB‐N) and increases the pH of Penaeus vannamei Boone, thereby extending the shelf life to 10 days. In contrast, the shelf life of shrimp treated with kojic acid and the control group was 7 and 6 days, respectively. Clearly, 3‐hydroxypyridinone‐l‐phenylalanine conjugates could find application as shrimp preservatives by inhibiting melanosis and by preventing the growth of bacteria during the storage.

Effects of gamma irradiation on chemical, microbial quality and shelf life of shrimp

In the present study the combined effect of gamma irradiation (1, 3 and 5kGy) and storage at two temperatures: refrigeration (+4°C) and frozen (−18°C), on the shelf-life extension of fresh shrimp meat was investigated. The study was based on microbiological and physicochemical changes occuring in the shrimp samples. Total volatile base nitrogen values and trimethylamine values for irradiated shrimp samples were significantly lower than non-irradiated samples at both storage temperatures, and the rate of decrease was more pronounced in samples irradiated at the higher dose (p<0.05). Thiobarbituric acid values for irradiated shrimp samples were significantly higher than non-irradiated samples at both storage temperatures (p<0.05). pH values of shrimp samples were affected significantly by both irradiating dose and storage temperatures (p<0.05). Microbial counts for non-irradiated shrimp samples were higher than the respective irradiated samples at both storage temperatures (p<0.05). The results revealed that irradiation at high dose (5kGy) might enhance lipid oxidation, although the growth of microorganisms and protein oxidation was inhibited.