The present study was conducted aiming at establishing chemical quality parameters to assess ice stored mullet (0℃ ± 1℃) through the evaluation of nucleotide (adenosine monophosphate [AMP], inosine [HxR] and hypoxanthine [Hx]) degradation, biogenic amine (histamine [HI], putrescine [PU], cadaverine [CA] and tyramine [TI]) quantification and mesophilic and psychrotrophic bacteria count monitoring. The microbial load of 7 log CFU·g–1 established as maximum acceptable limit was attained after the 20th day of ice storage. IMP concentration declined during the storage period to levels below the detection limit. HxR content increased only up to time T3 and then declined. Hx level increased during all the storage period. CA and HI content increase was not observed, on the other hand, PU and TI contents significantly increased (p < 0.05) at time T5. We concluded that IMP and Hx concentrations can be adequate parameters to assess mullet quality under the study conditions. HxR proved to be adequate to evaluate the freshness of mullet in the first days of storage while the amines, PU and TI, can be used to assess loss of quality. Mullet obtained in conditions similar to those of the present study and maintained at 0℃ ± 1℃ can be consumed up to the 20th storage day.
Fish per capita consumption has increased worldwide during the past five decades [
Fish spoilage process begins with the action of endogenous enzymes from the muscle tissue or enzymatic activity of the viscera. The catabolites formed during this autolytic process, favor bacterial growth [
The products originated from nucleotide degradation have been used as quality indicators [
In this context, due to the need of establishing reliable parameters for quality assessment and acknowledging the importance of mullet (Mugil platanus) as an alternative fish resource to substitute the traditional resources the capture and yield of which are declining in Brazil, especially in the Rio de Janeiro State [
A total of 25 mullet specimens with weight ranging from 389.3 to 660.7 grams were acquired, immediately after capture, directly from fishing boats in the Municipality of Maricá (RJ) (22˚57’36.1”S, 42˚41’48.5”W) from May to August, 2012. The mean ambient water temperature was 23˚C ± 1˚C. The capture was performed with the aid of nets in hygienic conditions and avoiding fish stress. The specimens were sacrificed by hypothermia in cold water and ice. Then, the fish were transported to the analysis’ laboratory in expanded polystyrene isothermal boxes with ice within two hours from the moment of the harvest. There, they were individually washed in tap water and packed in plastic containers with ice (0˚C ± 1˚C) with a fish/ice ratio of 1:2. The fish were maintained in these conditions for 24 days, period in which the analyses were performed.
A 25g aliquot sample was collected on alternate days, under sterile conditions and homogenized with 225 mL of 0.1% Saline Peptone Water (SPW) in a Stomacher (SEWARD-Stomacher 80) type homogenizer to prepare a 10-1 solution. Other dilutions were obtained from this one as the results were obtained. The Aerobic Heterotro- phic Mesophilic Bacteria Count (AMHBC) and Psychrotrophic Heterotrophic Bacteria Count (APHBC) were carried out by the methodology described by the American Public Health Association [
Nucleotide extraction was performed according to the methodology used by Andrade et al. [
Based on AMP, IMP, HxR and Hx concentrations, the values Ki [
Biogenic amine extraction was conducted according to AOAC methodology [
The parameters of bacterial growth (lag phase and generation time) were determined using the DMfit 2.0 computer program based on predictive microbiology and idealized by Baranyi and Roberts [
The correlation between the quality indices based on nucleotide concentration with storage time was assessed by the determination of Pearson’s coefficient (R). Variance analysis (ANOVA) was used to verify the differences of nucleotide and biogenic amine content among storage times. To help result interpretation, the data obtained (from day 0 to day 24) were grouped into five periods of time, according to Rodrigues et al. [
All the analyses were performed using the GraphPad Prism version 6.00 for Windows (GraphPad Software, San Diego, California, USA), considering a significance of 5%.
The means of the Aerobic Mesophilic Heterotrophic Bacteria Count (AMHBC) and Aerobic Psychrotrophic He- terotrophic Bacteria Count (APHBC) are represented in
Mean of Aerobic Mesophilic Heterotrophic Bacteria Count (AMHBC) and Aerobic Psychrotrophic Heterotrophic Bacteria Count (APHBC) of mullet (Mugilplatanus) stored at 0˚C ± 1˚C for 24 days
. Results of Aerobic Mesophilic Heterotrophic Bacteria Count (AMHBC) and Aerobic Psychrotrophic Heterotrophic Bacteria Count (APHBC) growing parameters in mullet (Mugilplatanus) stored under refrigeration at 0˚C ± 1˚C for 24 days
Initial Count (log∙CFU∙g−1) | lag (days) | g (hour) | Stationary phase Count (log∙CFU∙g−1) | Shelf life (days) | |
---|---|---|---|---|---|
AMHBC | 2.2 | 7.6 | 22.6 | 7.2 | 20 |
APHBC | 1.9 | 2.7 | 13.8 | 11.5 | - |
Initial count: Bacteria count in log CFU∙g−1; Lag: lag phase in days; g: generation time in hours; Stationary phase count: Bacteria count at the beginning of the stationary phase in log CFU∙g−1.
The content of AMP, IMP, HxR and Hx over the different mullet storage times at 0˚C ± 1˚C obtained by HPLC is represented in
The values Ki, G and H calculated from AMP, IMP, HxR and Hx concentration in mullet samples stored in ice (0˚C ± 1˚C) are represented in
Concentrations of adenosine monophosphate (AMP), inosine monophosphate (IMP), inosine (HxR) and hypoxanthine (Hx) in mullet (Mugilplatanus) kept at 0˚C ± 1˚C for differ- rent storage times: T1 (0 to 4th storage day), T2 (5th to 9th storage day), T3 (10th to 14th storage day), T4 (15th to 10th and T5 (20th to 24th storage days). Mean concentrations (n = 8). Standard deviations are indicated by bars. Different letters indicates the statistically significant differences of values between storage time (p < 0.05)
Mean Ki, G and H values in mullet (Mugilplatanus) kept at 0˚C ± 1˚C for different storage times: T1 (0 to 4th storage day), T2 (5th to 9th storage day), T3 (10th to 14th storage day), T4 (15th to 10th and T5 (20th to 24th storage days). Mean concentrations (n = 8). Standard deviations are indicated by bars. Different letters indicates the statistically significant differences of values between storage time (p < 0.05)
intermediary products of ATP degradation to IMP, because in some species this process occurs very fast impairing the identification of those compounds. G value showed high correlation (R = 0.92) with storage time with a significant increase (p < 0.05) during the initial storage times (T1 ~ 26%, T2 ~ 69% and T3 ~ 90%). From T4 its increase was not significant (p > 0.05), reaching at time T5 ~ 104%. G value, according to Burns et al. [
The content of the biogenic amines derivatizated with AQC researched by HPLC in mullet stored on ice (0˚C ± 1˚C) is shown in
The nucleotides IMP, HxR and Hx and the biogenic amines PU and TI are potential compounds for use as
Mean of histamine (HI), putrescine (PU), cadaverine (CA) and tyramine (TI) concentrations in mullet (Mugilplatanus) kept at 0˚C ± 1˚C for different storage times: T1 (0 to 4th storage day), T2 (5th to 9th storage day), T3 (10th to 14th storage day), T4 (15th to 10th and T5 (20th to 24th storage days). Mean concentrations (n = 8). Standard deviations are indicated by bars. Different letters indicates the statistically significant differences of values between storage time (p < 0.05)
chemical parameters to assess the quality of mullet stored at 0˚C ± 1˚C. The IMP and Hx showed high correlation with quality loss of mullet, as well as the PU and TI, while HxR proved to be adequate to evaluate mullet freshness during the first days of storage. The results obtained show that mullet can be consumed up to the 20th storage day, when obtained in similar conditions as in the present study and kept at the same storage conditions (0˚C ± 1˚C).
The authors are grateful for the financial support from the Carlos Chagas Filho Research Support Foundation of the State of Rio de Janeiro (FAPERJ), processes numbers E-26/112.620/2012 and E-26/112.620/2012. S.C.S. Andrade was supported by the Coordination for the Improvement of Higher Education (CAPES).