Mechanical, Barrier, Antioxidant and Antimicrobial Properties of Alginate Films: Effect of Seaweed Powder and Plasma-Activated Water.

The incorporation of natural fillers such as seaweed may potentially enhance the properties of biopolymer films. In this study, we investigated the effect of seaweed powder as a bio-filler in alginate-based films at different concentrations (10, 30, and 50%, w/w alginate) and particle sizes (100 and 200 µm) on the mechanical, barrier, antioxidant, and antimicrobial properties of alginate which are essential for food packaging applications. Initially, mechanical properties of the alginate films prepared at different temperatures were evaluated to find the optimal temperature for preparing alginate solution. The addition of seaweed powder did not have any positive effect on the mechanical properties of the alginate films. However, the barrier (water vapor transmission rate) and antioxidant properties were improved with the addition of seaweed filler regardless of concentration. In addition, selected films were prepared in plasma-activated water (PAW). The mechanical properties (tensile strength, but not elongation at break) of the films prepared with PAW improved compared to the films prepared in distilled water, while a significant decrease was observed when incorporated with the seaweed filler. The films prepared in PAW also showed improved barrier properties compared to those prepared in distilled water. The antimicrobial activity of the alginate-seaweed film-forming solution was in general more pronounced when prepared with PAW and stored at 10 °C, particularly at the highest concentration of the film-forming solution (83.3% v/v). A more pronounced inhibitory effect was observed on the Gram-positive S. aureus than on the Gram-negative E. coli, which has been attributed to the different composition and structure of the respective cell walls. This study has demonstrated the potential of seaweed filler in combination with PAW towards enhanced functionality and bioactivity of alginate films for potential food packaging applications.

Current status of biobased and biodegradable food packaging materials: Impact on food quality and effect of innovative processing technologies.

Fossil-based plastic materials are an integral part of modern life. In food packaging, plastics have a highly important function in preserving food quality and safety, ensuring adequate shelf life, and thereby contributing to limiting food waste. Meanwhile, the global stream of plastics into the oceans is increasing exponentially, triggering worldwide concerns for the environment. There is an urgent need to reduce the environmental impacts of packaging waste, a matter raising increasing consumer awareness. Shifting part of the focus toward packaging materials from renewable resources is one promising strategy. This review provides an overview of the status and future of biobased and biodegradable films used for food packaging applications, highlighting the effects on food shelf life and quality. Potentials, limitations, and promising modifications of selected synthetic biopolymers; polylactic acid, polybutylene succinate, and polyhydroxyalkanoate; and natural biopolymers such as cellulose, starch, chitosan, alginate, gelatine, whey, and soy protein are discussed. Further, this review provides insight into the connection between biobased packaging materials and innovative technologies such as high pressure, cold plasma, microwave, ultrasound, and ultraviolet light. The potential for utilizing such technologies to improve biomaterial barrier and mechanical properties as well as to aid in improving overall shelf life for the packaging system by in-pack processing is elaborated on.

Prior thermal and high-pressure processing alters the impact of high intensity ultrasound on reconstituted skim milk.

Reconstituted skim milk was subjected to heat treatment at 85 °C for 20 min or high pressure processing (HPP) at 400 or 600 MPa for 15 min with or without subsequent high intensity ultrasound (US) at 68 kHz, 500 W for 15 min at 30 °C. Untreated and treated samples were analyzed for particle size distribution, zeta potential, surface hydrophobicity, and concentration of total and surface sulfhydryl groups in addition to Native- and SDS-PAGE of serum phase upon ultracentrifugation and pH adjustment. Preceding heat- and HPP altered the impact of the subsequent US treatment, demonstrating process- and intensity-dependent exposure and burial of surface reactive sites on milk proteins respectively. US following HPP promoted sedimentation of HPP-dispersed serum casein fractions, while US following heat was directed mainly at the whey proteins originally bound to the micelles. The primary US effect on the untreated and treated milk proteins was at the molecular level.

Effects of capture-related stress and pre-freezing holding in refrigerated sea water (RSW) on the muscle quality and storage stability of Atlantic mackerel (Scomber scombrus) during subsequent frozen storage.

Crowded (stressed) and unstressed Atlantic mackerel with or without pre-freezing holding in refrigerated sea water (RSW) were stored at -19 °C for ∼12 months and analysed for nucleotide degradation (K value), muscle pH, water holding capacity (WHC), fillet firmness, cathepsin B/L like activity, lipid oxidation and fillet colour. The frozen storage showed the largest and most consistent direct effects on the quality metrics leading to increased lipid oxidation, discolouration (yellowing) and reduction on WHC and cathepsin activity. RSW treatment promoted nucleotide degradation and reduced WHC and fillet firmness in interaction with frozen storage and affected fillet colour lightness and saturation. Although showing only marginal main effects, crowding stress modified WHC, cathepsin activity and fillet firmness and colour through significant interactions with the frozen storage and RSW treatment. Further studies with larger sample sizes would be needed to elucidate their complex effects and interactions on the quality and storage stability of mackerel.

Combined Effect of Citric Acid and Polyphenol-Rich Grape Seed Extract towards Bioactive Smart Food Packaging Systems.

Alginate films (2% w·v-1) were prepared with varying concentrations (5-20% w/w) of citric acid and aqueous grape seed extract (GSE) filtrate (11.66 ± 1.32 g GAE/L) using the solvent-evaporation method. Crosslinking alginate via ester bonds (FTIR analysis) with citric acid up to 10% (w/w) led to a 33% increase in tensile strength, a 34% reduction in water vapor transmission rate (WVTR), and had no impact on elongation at break. Crosslinking alginate with citric acid in the presence of GSE increased the tensile strength by 17%, decreased WVTR by 21%, and significantly improved DPPH scavenging activity. Moreover, after incubation for 24 h at 37 °C, the film-forming solutions exhibited increased antimicrobial activity, resulting in 0.5- and 2.5-log reductions for Escherichia coli and Staphylococcus aureus, respectively, compared to the values obtained without the addition of GSE. The stronger inhibitory effect observed against Gram-positive bacteria can be attributed to the unique composition and structure of their cell walls, which creates a barrier that restricts the penetration of polyphenols into the cells. The pH adjustment of the GSE film-forming solution from 2.0 to 10.0 shifted the UV/VIS absorption spectra, resulting in a colour change from yellow to red. The findings of this study have showcased the potential of combining GSE and citric acid to enhance the functionality and bioactivity of alginate films for applications in smart food packaging.

Innovative Ultrasound-Assisted Approaches towards Reduction of Heavy Metals and Iodine in Macroalgal Biomass.

The aim of this work was to evaluate the potential of ultrasound (US), alone or in combination with mild heating and/or EDTA towards reduction of As, Cd, I, and Hg content of Laminaria hyperborea. Concentrations of As, Cd, I, and Hg of 56.29, 0.596, 7340, and <0.01 mg kg-1 of dry weight, respectively, were found in L. hyperborea blades. Treatment with US at 50 °C increased approx. 2-fold the amount of As released, although did not affect significantly the content of Cd or I, as compared to control (no US) samples. Reducing the temperature to 8 °C significantly decreased the effect of US, but heating at 80 °C did not cause a significant effect as compared to treatments at 50 °C. On the other hand, treatment with 0.1 N EDTA at 50 °C enhanced the percentage of Cd released by approximately 7-fold, regardless of sonication. In the present work, the combination of US and EDTA at 50 °C for 5 min led to a significant reduction of the As (32%), Cd (52%) and I (31%) content in L. hyperborea, thus improving the product's safety for consumers.

Impact of Plasma-Activated Water Treatment on Quality and Shelf-Life of Fresh Spinach Leaves Evaluated by Comprehensive Metabolomic Analysis.

Fresh baby spinach leaves are popular in salads and are sold as chilled and plastic-packed products. They are of high nutritional value but very perishable due to microbial contamination and enzymatic browning resulting from leaf senescence. Therefore, innovative food processing methods such as plasma-activated water (PAW) treatment are being explored regarding their applicability for ensuring food safety. PAW's impact on food quality and shelf-life extension has, however, not been investigated extensively in vegetables so far. In the present study, a comprehensive metabolomic analysis was performed to determine possible changes in the metabolite contents of spinach leaves stored in a refrigerated state for eight days. Liquid chromatography high-resolution mass spectrometry, followed by stringent biostatistics, was used to compare the metabolomes in control, tap-water-rinsed or PAW-rinsed samples. No significant differences were discernible between the treatment groups at the beginning or end of the storage period. The observed loss of nutrients and activation of catabolic pathways were characteristic of a transition into the senescent state. Nonetheless, the presence of several polyphenolic antioxidants and γ-linolenic acid in the PAW-treated leaves indicated a significant increase in stress resistance and health-promoting antioxidant capacity in the sample. Furthermore, the enhancement of carbohydrate-related metabolisms indicated a delay in the senescence development. These findings demonstrated the potential of PAW to benefit food quality and the shelf-life of fresh spinach leaves.

Synthesis of Sodium Alginate-Silver Nanocomposites Using Plasma Activated Water and Cold Atmospheric Plasma Treatment.

In this study, sodium alginate (SA)-based, eco-friendly nanocomposites films were synthesized for potential food packaging applications using silver nitrate (AgNO3) as the metal precursor, reactive nitrogen and oxygen species (RNOS) created within plasma activated water (PAW), or through cold plasma treatment (CP) as reducing agent and SA as stabilizing agent. The formation of silver nanoparticles (AgNPs) was confirmed via the absorption peaks observed between 440 and 450 nm in UV-vis spectroscopy. The tensile strength (TS) and tensile modulus (TM) of the nanocomposite films were significantly higher than those of the SA films. An increase in the TS was also observed as the AgNP concentration was increased from 1 to 5 mM. The storage modulus (G') of the nanocomposite solution was higher than that of the SA solution. The synthesis of AgNPs resulted both in a higher solution viscosity and a more marked shear-thinning effect. The synthesized AgNPs showed antimicrobial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The AgNPs were spherical in shape with an average size of 22 nm.

Effect of antioxidants on the sensory quality and physicochemical stability of Atlantic mackerel (Scomber scombrus) fillets during frozen storage.

This study aimed to evaluate the shelf-life of mechanically filleted well-fed Atlantic mackerel during frozen storage at -25 °C and effect of treatment with antioxidants (sodium erythorbate and a polyphosphate mixture) and different antioxidant application methods (dipping, spraying and glazing). Both physicochemical measurements and sensory analysis were applied. Antioxidant treatments prolonged shelf-life of mackerel. Sensory analysis indicated that untreated fillets had a shelf-life of less than 2.5 months, while all antioxidant treated fillets exceeded that. The most effective treatment, dipping fillets into a sodium erythorbate solution, yielding a shelf-life of 15 months. Physicochemical methods used to evaluate degradation of lipids in the fillets were free fatty acids (FFA), lipid hydroperoxides (PV) and thiobarbituric acid reactive substances (TBARS). They did not correlate with sensory results and might therefore be a questionable choice for evaluation of oxidation and development of rancid flavour and odour in complex matrixes such as Atlantic mackerel.

Towards the Next-Generation Disinfectant: Composition, Storability and Preservation Potential of Plasma Activated Water on Baby Spinach Leaves.

Plasma activated water (PAW) has rapidly emerged as a promising alternative to traditional sanitizers applied in the fresh produce industry. In the present study, PAW chemistry and storage stability were assessed as a function of plasma operating conditions. Increasing plasma exposure time (5, 12.5, 20 min) and power (16, 26, 36 W) led to a significant drop in pH (2.4) and higher nitrates and nitrites levels (320 and 7.2 mg/L, respectively) in the PAW. Non-detectable hydrogen peroxide concentration, irrespective of the treatment conditions, was attributed to its instability in acidic environments and the remote PAW generation mode. pH, nitrates and nitrites levels in the PAW remained unaffected after two weeks at 4 °C. The potential of PAW for microbial inactivation and quality retention was demonstrated on baby spinach leaves. Rinsing steps influenced colour development during chilled storage to a greater extent than PAW treatment itself. About 1 log reduction in total bacterial counts (5 log CFU/g) was achieved through PAW rinsing, with no variability after eight days at 4 °C (typical shelf-life at retailers). Moreover, microbial levels on PAW-treated samples after storage were significantly lower than those on control samples, thus contributing to extended product shelf-life and reduced food waste generation.

Spectral changes of Atlantic salmon ( Salmo salar L.) muscle during cold storage as affected by the oxidation state of heme.

The spectra of fresh salmon fillets change due to storage and packaging atmospheres. The aim of this study was to demonstrate the effects of heme oxidation states on spectral development in salmon fillets and to investigate the origin of a shoulder peak representing important spectral variations during storage. Hyperspectral images of fresh salmon fillets and mince with various water contents were collected during storage under different atmospheres. In addition, the absorption spectra of extracted salmon hemoglobin and its derivatives (methemoglobin and deoxyhemoglobin) were obtained. Air storage resulted in an increased similarity between spectra of methemoglobin and salmon fillets in principal component analysis. Results from the mince storage demonstrated that absorption features at the shoulder peak could be related to water content in the salmon muscle. This study established that the formation of oxidized heme is the primary source of spectral variations that occur during air storage of fresh salmon. Changes in the status of heme due to storage and packaging can influence the appearance of the underlying water absorption at the shoulder peak and create variations in the salmon spectra.

Visible/near-infrared spectroscopy detects autolytic changes during storage of Atlantic salmon (Salmo salar L.).

UNLABELLED: Visible (VIS)/near-infrared (NIR) spectroscopy was used to investigate spectroscopic changes occurring during storage of Atlantic salmon fillets with and without bacterial growth. A storage experiment was conducted for 11 d postmortem. Bacterial growth was inhibited by soaking a group of salmon fillets in 3 mM NaN3 prior to storage, while a control group retained its normal bacterial growth. Spectra were obtained by directly applying the spectroscopic probe onto the loin part of each fillet stored under conditions accelerating degradation. Principal component analysis (PCA) was used to monitor and compare spectroscopic development of the 2 groups and the results showed that VIS/NIR spectral changes occurred in the control as well as the treated group of samples within a single day after filleting. After 2 d of storage, stored samples were distinguishable from those fresh in both groups and it was only after the microbial spoilage became pronounced (8 to 9 log colony forming unit [CFU]/g) that the spectra of the spoiled control samples could be differentiated from spectra of the treated samples with no bacterial growth. Microbial growth is therefore not the only explanation for the spectral variations prior to microbial spoilage. Nonmicrobial, autolytic changes including possible changes in the physical properties are also contributing. Our results show that VIS/NIR spectroscopy can detect autolytic changes occurring in salmon muscle during the early stage of storage, independent of microbial growth. PRACTICAL APPLICATION: Important spectroscopic changes occur even when microbial growth is not apparent. This indicates that VIS/NIR spectroscopy may be used to determine the degree of freshness before microbial spoilage becomes relevant.