Improvement of Oil Valorization Extracted from Fish By-Products Using a Handheld near Infrared Spectrometer Coupled with Chemometrics.

A handheld near infrared (NIR) spectrometer was used for on-site determination of the fatty acids (FAs) composition of industrial fish oils from fish by-products. Partial least square regression (PLSR) models were developed to correlate NIR spectra with the percentage of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs) and, among them, omega-3 (ω-3) and omega-6 (ω-6) FAs. In a first step, the data were divided into calibration validation datasets, obtaining good results regarding R2 values, root mean square error of prediction (RMSEP) and bias. In a second step, all these data were used to create a new calibration, which was uploaded to the handheld device and tested with an external validation set in real time. Evaluation of the external test set for SFAs, MUFAs, PUFAs and ω-3 models showed promising results, with R2 values of 0.98, 0.97, 0.97 and 0.99; RMSEP (%) of 0.94, 1.71, 1.11 and 0.98; and bias (%) values of -0.78, -0.12, -0.80 and -0.67, respectively. However, although ω-6 models achieved a good R2 value (0.95), the obtained RMSEP was considered high (2.08%), and the bias was not acceptable (-1.76%). This was corrected by applying bias and slope correction (BSC), obtaining acceptable values of R2 (0.95), RMSEP (1.09%) and bias (-0.05%). This work goes a step further in the technology readiness level (TRL) of handheld NIR sensor solutions for the fish by-product recovery industry.

Rapid Differentiation of Unfrozen and Frozen-Thawed Tuna with Non-Destructive Methods and Classification Models: Bioelectrical Impedance Analysis (BIA), Near-Infrared Spectroscopy (NIR) and Time Domain Reflectometry (TDR).

The performances of three non-destructive sensors, based on different principles, bioelectrical impedance analysis (BIA), near-infrared spectroscopy (NIR) and time domain reflectometry (TDR), were studied to discriminate between unfrozen and frozen-thawed fish. Bigeye tuna (Thunnus obesus) was selected as a model to evaluate these technologies. The addition of water and additives is usual in the fish industry, thus, in order to have a wide range of possible commercial conditions, some samples were injected with different water solutions (based on different concentrations of salt, polyphosphates and a protein hydrolysate solution). Three different models, based on partial least squares discriminant analysis (PLS-DA), were developed for each technology. This is a linear classification method that combines the properties of partial least squares (PLS) regression with the classification power of a discriminant technique. The results obtained in the evaluation of the test set were satisfactory for all the sensors, giving NIR the best performance (accuracy = 0.91, error rate = 0.10). Nevertheless, the classification accomplished with BIA and TDR data resulted also satisfactory and almost equally as good, with accuracies of 0.88 and 0.86 and error rates of 0.14 and 0.15, respectively. This work opens new possibilities to discriminate between unfrozen and frozen-thawed fish samples with different non-destructive alternatives, regardless of whether or not they have added water.

Active naringin-chitosan films: impact of UV irradiation.

Bioactive citrus extract-chitosan films were prepared through solvent casting-evaporation method. The impact of near UV irradiation was studied to reach a better understanding of the film behavior. The antimicrobial activity of films against Listeria innocua was maintained after UV irradiation. To study the interaction between chitosan and citrus extract components, naringin (main component) was selected as the model compound. UV treatment caused modifications of the flavanone regardless of the solvent used for its dissolution, depending on the concentration of naringin in the film: the greater the concentration the lower the modification. DSC results suggested cross-links due to UV irradiation and interactions between naringin and chitosan. This was confirmed by a decrease in the naringin release from the irradiated samples. Naringin- and citrus extract-chitosan films showed an increased absorbance in the UV region compared to pure chitosan films, showing potentiality for decreasing the lipid oxidation induced by UV light in foodstuffs.

Aging properties of films of plasticized vital wheat gluten cast from acidic and basic solutions.

In order to understand the mechanisms behind the undesired aging of films based on vital wheat gluten plasticized with glycerol, films cast from water/ethanol solutions were investigated. The effect of pH was studied by casting from solutions at pH 4 and pH 11. The films were aged for 120 days at 50% relative humidity and 23 degrees C, and the tensile properties and oxygen and water vapor permeabilities were measured as a function of aging time. The changes in the protein structure were determined by infrared spectroscopy and size-exclusion and reverse-phase high-performance liquid chromatography, and the film structure was revealed by optical and scanning electron microscopy. The pH 11 film was mechanically more stable with time than the pH 4 film, the latter being initially very ductile but turning brittle toward the end of the aging period. The protein solubility and infrared spectroscopy measurements indicated that the protein structure of the pH 4 film was initially significantly less polymerized/aggregated than that of the pH 11 film. The polymerization of the pH 4 film increased during storage but it did not reach the degree of aggregation of the pH 11 film. Reverse-phase chromatography indicated that the pH 11 films were to some extent deamidated and that this increased with aging. At the same time a large fraction of the aged pH 11 film was unaffected by reducing agents, suggesting that a time-induced isopeptide cross-linking had occurred. This isopeptide formation did not, however, change the overall degree of aggregation and consequently the mechanical properties of the film. During aging, the pH 4 films lost more mass than the pH 11 films mainly due to migration of glycerol but also due to some loss of volatile mass. Scanning electron and optical microscopy showed that the pH 11 film was more uniform in thickness and that the film structure was more homogeneous than that of the pH 4 film. The oxygen permeability was also lower for the pH 11 film. The fact that the pH 4 film experienced a larger and more rapid change in its mechanical properties with time than the pH 11 film, as a consequence of a greater loss of plasticizer, was presumably due to its initial lower degree of protein aggregation/polymerization. Consequently, the cross-link density achieved at pH 4 was too low to effectively retain volatiles and glycerol within the matrix.

Properties of aged montmorillonite-wheat gluten composite films.

The properties of new and aged glycerol-plasticized vital wheat gluten films containing < or =4.5 wt % natural or quaternary ammonium salt modified montmorillonite clay were investigated. The films were cast from pH 4 or pH 11 ethanol/water solutions. The films, aged for < or =120 days, were characterized by tensile testing, X-ray diffraction, and transmission electron microscopy. In addition, water vapor permeability (11% relative humidity) and the content of volatile components were measured. The large reduction in the water vapor permeability with respect to the pristine polymer suggests that the clay platelets were evenly distributed within the films and oriented preferably with the platelet long axis parallel to the film surface. The film prepared from pH 11 solution containing natural clay was, as revealed by transmission electron microscopy and X-ray diffraction, almost completely exfoliated. This film was consequently also the strongest, the stiffest, and the most brittle and, together with the pH 11 film containing modified clay, it also showed the greatest decrease in water vapor permeability. The large blocking effect of the clay had no effect on the aging kinetics of the films. During aging, the pH 4 and pH 11 film strength and the pH 4 film stiffness increased and the pH 4 film ductility decreased at the same rate with or without clay. This suggests that the aging was not diffusion rate limited, that is, that the loss of volatile components or the migration of glycerol or glycerol/wheat gluten phase separation was not limited by diffusion kinetics. The aging rate seemed to be determined by slow structural changes, possibly involving protein denaturation and aggregation processes.