Quantitative and qualitative changes in added phosphates in cod (Gadus morhua) during salting, storage and rehydration

Analysis of added phosphates in hake fillets by ion-exchange chromatography: A case study of false positives induced by nucleotides coelution

This study aimed to optimize an ion-exchange chromatography method for an accurate quantification of phosphates. Coelution of nucleotides was detected following the quantification of small amounts of di- and trimetaphosphates in hake fillets. In some samples, triphosphates were added to the glaze ice, therefore, defrosting waters (glaze ice + drip loss of fillets) should be analyzed for an effective assessment of the use of phosphates in seafood. Even low amounts of adenosine 5'-diphosphate (ADP) and inosine 5'-monophosphate (IMP) triggered false positive results for P₂O₇^4- and P₃O₉^3-. Keeping the initial isocratic conditions for longer was crucial for the separation of ADP from P₂O₇^4- and of IMP from P₃O₉^3-. The improved method showed that in general, hake fillets did not have diphosphates, and trimetaphosphates were residual. Triphosphates were clearly added in only four defrosting waters, and in most of the remaining ones, diphosphates and trimetaphosphates contents corresponded to false positive results.

Effect of salting procedures on quality of hake (Merluccius hubbsi) fillets

The influence of salting procedures on the proximate analysis, mechanical parameters, and color of hake (Merluccius hubbsi) was investigated. Three procedures were comparatively evaluated: dry salting (DS), mixed salting (MS) and brining (BS). MS samples had the highest fat content, a considerable protein content and an equilibrium salt content similar to BS. MS samples had a great water loss, as DS method, but hardness and other mechanical parameters were similar to that obtained with BS, i.e. significantly lower than DS. All samples showed color parameters significantly different as compared to fresh hake, turning more red-orange as the salting time increased. Lightness diminished, a∗ values increased and b∗ values did not show a clear trend throughout the salting time. Principal component analysis (PCA) described the relationship between some variables (z_NaCl, color, and mechanical parameters) with salting time. High Pearson's correlation coefficients were found between z_NaCl and hardness, springiness, cohesiveness and a∗ parameter (r = 0.76, p < 0.001; r = 0.93, p < 0.0001; r = 0.95, p < 0.001 and r = 0.93, p < 0.0001, respectively). Luminosity was negatively correlated with z_NaCl (r = -0.87, p = 0.0001). The correlation curves showed nonlinear relationships (R²_adj between 83.7 % and 97.4 %), which could be used to predict quality attributes of hake fillets as a function of salting time. This work contributed to know the effect of different salting procedures on the quality attributes of a species widely available in the Southwest Atlantic Ocean.

Quality of Frozen Hake Fillets in the Portuguese Retail Market: A Case Study of Inadequate Practices in the European Frozen White Fish Market

The overall quality of frozen hake fillets in the Portuguese market was evaluated. Physical, biochemical, microbiological, and sensory analysis in 20 brands revealed several non-conformities. Hake was identified in 19 brands, although two mislabeled the species. Lower net weight than labeled was evidenced in ca. one-third of brands. TVB-N in ca. one-third of the samples presented high values, although within legal limit. Almost all brands presented excessive amount of ice glaze, low levels of WHC (raw/cooked), low levels of soluble protein, and undue thaw-drip loss, thus reflecting the poor quality of fillets. Added phosphates were below the legal limit in all samples; however, they were used in glaze ice in three brands, and only labeled in one. Overall microbiological quality of frozen fillets was good, though yeasts and molds detected in six samples indicate poor hygienic conditions in some facilities. Labels comply with legal requisites, however, need improvement, namely the ‘best before’ periods. In general, packaging was efficient regarding presence of ice crystals and dehydration signs. Concerning sensory analysis of cooked fillets, 63% of the brands had bad to poor quality and 37% fair quality. Merluccius productus revealed the worst quality, namely regarding thaw drip loss, thaw drip loss protein, M/P ratio, pH and sensory evaluation. Overall results show that a significant part of the hake fillets business operators are still failing in relation with best practices.

The analytical determination of polyphosphates in food: A point-to-point comparison between direct ion chromatography and indirect photometry

Being an indirect approach, the standard method for the determination of polyphosphates (PPs) in food maybe characterized by high variability which can lead to significant errors in the final measurement. In this study, this method was validated and then compared to the ion chromatography-based approach. Method trueness and measurement uncertainty resulted comparable, while the precision of ion chromatography approach was higher. No "false positive" responses were obtained from ion chromatography analysis, while indirect photometry may cause "false positive" results (5% of analyzed samples). Regarding "false negative" results, this possibility maybe verified for all food types tested and for seafood when using indirect photometry and ion chromatography, respectively. The percentages of "false negative" samples were equal to 23.3% for indirect photometry and 10% for ion chromatography. In conclusion, the indirect photometry is a reliable method especially as "screening technique", while ion chromatography maybe used as a confirmatory technique, successfully.

Polyphosphates changes in dried salted cod (Gadus morhua) during industrial and domestic processing

Changes in added polyphosphates throughout the processing of dried salted cod in industrial environment were evaluated. As consumers purchase both dried salted cod and desalted cod, domestic and industrial desalting processes were performed. After brining, total phosphates increased to 11.6 and 16.6 g P₂O₅/kg in cod processed with 3 and 6% of polyphosphates, respectively. During dry-salting, total phosphates decreased in both cases to ca. 5 g P₂O₅/kg, suggesting that most polyphosphates were drained with the water released. Cod with polyphosphates needed 85 h extra drying time to achieve regulatory moisture levels. After desalting, total phosphates values in dry weight indicate that phosphates were not removed during this processing step. Free phosphates, and in particular triphosphate contents, were higher in cods desalted following domestic procedures, in comparison with industrial desalting. This study demonstrates that the use of polyphosphates is not recommended for the production of Portuguese dried salted cod. These additives prevent water from being removed during the drying process, increasing the costs. Moreover, in contrast to what was assumed, part of polyphosphates is retained in the final product, even after the desalting process.

Dehydration and Rehydration of Cooked Mussels

The objective of this study was to investigate different drying methods (oven-drying, vacuum-drying, and freeze-drying) applied to cooked mussels meat and the resulting rehydration and water-holding capacity. Drying curves were obtained using an online weighting system that allows continuous monitoring of sample weight during processing. The influence of the processing temperature on the drying rates and on the properties of dehydrated samples was assessed. In the studied conditions, freeze-drying presented higher drying rates and less structure alterations compared to the other drying methods investigated. The equilibrium rehydration capacity of oven-dried and vacuum-dried mussels was about 37 % lower than rehydration capacity of freeze-dried samples for the rehydration performed at 20 °C and about 21 % lower for rehydration performed at 80 °C.

Determination of polyphosphates in fish and shrimp muscles by capillary electrophoresis with indirect UV detection after phosphatase inhibition using high pressure pretreatment

A method was proposed for the determination of polyphosphates (P2O7(4-), P3O10(5-) and (PO3)3(3-)) in fish and shrimp muscles by capillary electrophoresis with indirect UV detection after phosphatase inhibition using high pressure pretreatment (HPP). Separation parameters were optimized and the effects of HPP on deactivation of enzyme were investigated. Well resolution was obtained with 10 mM adenosine 5'-phosphate (ATP) in 16 mM disodium hydrogen phosphate combining with 32 mM citric acid buffer (pH = 6.4) containing 0.1 mM cetyltrimethyl ammonium bromide, and phosphatase was effectively inhibited by HPP at 400 MPa for 10 min. Method was validated with LOD (0.23-0.33 mg g(-1)) and LOQ (0.77-1.0 mg g(-1)). Recovery of P2O7(4-), P3O10(5-) and (PO3)3(3-) in the fortified samples were in the range of 91.6-100.1%, 97.6-104.6% and 79.1-88.1%, respectively, and the corresponding RSD ranged from 1.1% to 6.8%. Finally, the method was applied in the determination of polyphosphates in food samples collected from local markets.