Nanoemulsion-Based Multilayer Films for Ground Beef Preservation: Antimicrobial Activity and Physicochemical Properties.

This study aimed to improve the physical, mechanical, and biological properties of a monolayer pectin (P) film containing nanoemulsified trans-Cinnamaldehyde (TC) by incorporating it between inner and outer layers of ethylcellulose (EC). The nanoemulsion had an average size of 103.93 nm and a zeta potential of -46 mV. The addition of the nanoemulsion increased the opacity of the film, reduced its moisture absorption capacity, and improved its antimicrobial activity. However, the tensile strength and elongation at break of the pectin films decreased after the incorporation of nanoemulsions. Multilayer films (EC/P/EC) showed a higher resistance to breaking and better extensibility compared to monolayer films. The antimicrobial activity of both mono and multilayer films was effective in inhibiting the growth of foodborne bacteria during storage of ground beef patties at 8 °C for 10 days. This study suggests that biodegradable antimicrobial multilayer packaging films can be effectively designed and applied in the food packaging industry.

Effect of pectin on the properties of nanoemulsions stabilized by sodium caseinate at neutral pH.

The effect of different concentrations of low methoxyl pectin (LMP) on lipid oxidation and physical stability of sodium caseinate (CAS) stabilized nanoemulsions under neutral pH was investigated. The addition of pectin at low concentration (≤ 0.10 wt%) had no significant effect on the average size of nanoemulsions, but a slight size increase and phase separation were observed at higher concentrations of pectin (≥ 0.25 wt%). This result suggests that LMP can not adsorb at the oil/water interfacial CAS membrane at neutral pH. However, in the presence of LMP, the physical stability of nanoemulsions against high salt concentrations and freeze-thaw cycles was significantly enhanced. Moreover, nanoemulsions containing pectin have a better ability to inhibit lipid and protein oxidation than nanoemulsions without pectin after 3 weeks, and the lowest lipid hydroperoxide content was observed for nanoemulsions containing 0.25 wt% pectin.

Effect of drying and interfacial membrane composition on the antimicrobial activity of emulsified citral.

Citral-in-water emulsions were prepared with two different essential oil concentrations of 2.5 and 5.0% (w/w), then spray-dried in the presence of the same amount of maltodextrins (20%). The microcapsules were prepared with two different emulsifier compositions: monolayer microcapsules (ML) stabilized by sodium caseinate alone and layer-by-layer microcapsules (LBL) stabilized by sodium caseinate and pectin. The encapsulation efficiency was higher for LBL microcapsules (e.g. 99.6 ±â€¯0.4% for 2.5% citral) than that for ML ones (e.g. 78.6 ±â€¯0.6% for 2.5% citral) which confirm that the additional pectin layer was able to protect citral during the spray-drying process whatever citral concentration. Furthermore, our results showed that the antibacterial activity of the obtained microcapsules significantly depends on both citral concentration and interfacial membrane composition. The presence of two layers surrounding the citral droplets may result in a progressive and controlled release of the encapsulated citral.

Spray-drying of protein/polysaccharide complexes: Dissociation of the effects of shearing and heating.

The aim of this study was to dissociate the effect of atomization from that of heating during the spray-drying of Low Methoxyl (LM) pectin/sodium caseinate complexes. The properties of these complexes were studied by measuring turbidity, particle size distribution, zeta-potential, as well as surface hydrophobicity of caseinate within the formed complexes. The results showed that the spraying step had a significant effect on the charge and the size of the complexes. In fact, the application of atomization resulted in the dissociation of caseinate/pectin aggregates especially for high pectin concentrations. Besides, the analysis of the surface hydrophobicity of caseinate indicated that complexation with high concentrations of pectin is able to protect the structure of the protein against heat denaturation. This study allowed a better understanding of the influence of atomization and heat treatment (during the dehydration step) on the molecular interactions within caseinate/pectin complexes.

Physicochemical and rheological changes of acidified camel milk added with commercial low methoxyl-pectin.

The influence of the addition of low methoxyl amidated pectin (LMA) on acid milk gels from whole camel milk (WCM) on physicochemical and rheological proprieties were studied. The zeta potential, particle size, viscosity, dynamic oscillatory rheology and isothermal titration calorimetry were monitored. The presence of LM-pectin in milk had an impact on the average size of the casein micelles and a large and dominant influence on rheological behavior during acidification. Zeta potential and viscosity of gels with 0.5% pectin were not affected. However, milk gels containing 1%, 1.5% and 2% of LM-pectin showed highest values of particle size at pH4. This modification of the structure of the casein micelles induces a significant improvement (p<0.05) on its acid gelation behavior. Therefore, the addition of pectin enhanced the rheological proprieties. Higher pectin concentration led to a strong gel with higher G' values. This result could be attributed to the formation of complexes and the mechanical spectra prove the hypothesis that pectin forms strands with caseins micelles. Isothermal titration calorimetry results showed that pectin concentration had a marked influence on the gels structure and that this polysaccharide stabilizes caseins micelles in acidified camel milk gel due to electrostatic interaction and steric repulsion.

pH-dependent complexation of lysozyme with low methoxyl (LM) pectin.

In order to understand the effect of pH on the formation of electrostatic complexes between lysozyme and low methoxyl (LM) pectin, mixtures were prepared at a fixed lysozyme concentration (0.714g.L-1) by progressive addition of LM pectin (from 0 to 4g.L-1). Turbidity analysis allowed to determine specific conditions of pH and lysozyme/LM pectin ratio for optimal complex aggregation. The intrinsic fluorescence enhancement observed upon binding of LM pectin to lysozyme was correlated with the formation of intermolecular aggregates. Conversely, the intrinsic fluorescence decrease observed at higher LM pectin amounts was correlated with the dissociation of intermolecular aggregates. UV absorption spectroscopy showed modifications in lysozyme conformation during both the aggregation phase and the dissociation phase. The role of electrostatic interactions in the formation of lysozyme/LM pectin complexes is discussed in relation to the overall structure and the charge density profile of the two biopolymers.

Complex coacervation for the development of composite edible films based on LM pectin and sodium caseinate.

Coacervation between sodium caseinate (CAS) and low methoxyl pectin (LMP) at pH 3 was investigated as a function of protein/polysaccharide ratio. The highest amount of complex coacervates was formed at a CAS/LMP ratio of 2 at which the ζ-potential value was zero and the turbidity reached its highest value. Then, the properties of films based on these complex coacervates were studied. Coacervation resulted in decreasing water content and water sorption of films as the protein concentration increased. The mechanical properties of films were highly influenced by the formation of electrostatic complexes. The highest values of Young's modulus (182.97± 6.48MPa) and tensile strength (15.64±1.74MPa) with a slight increase of elongation at break (9.35±0.10%) were obtained for films prepared at a CAS/LMP ratio equal to 0.05. These findings show that interactions between LMP and CAS can be used to develop innovative packaging containing active molecules.

Effect of emulsification and spray-drying microencapsulation on the antilisterial activity of transcinnamaldehyde.

Spray-dried redispersible transcinnamaldehyde (TC)-in-water emulsions were prepared in order to preserve its antibacterial activity; 5% (w/w) TC emulsions were first obtained with a rotor-stator homogeniser in the presence of either soybean lecithin or sodium caseinate as emulsifiers. These emulsions were mixed with a 30% (w/w) maltodextrin solution before feeding a spray-dryer. The antibacterial activity of TC alone, TC emulsions with and without maltodextrin before and after spray-drying were assayed by monitoring the growth at 30 °C of Listeria innocua in their presence and in their absence (control). Whatever the emulsifier used, antilisterial activity of TC was increased following its emulsification. However, reconstituted spray-dried emulsions stabilised by sodium caseinate had a higher antibacterial activity suggesting that they better resisted to spray-drying. This was consistent with observation that microencapsulation efficiencies were 27.6% and 78.7% for emulsions stabilised by lecithin and sodium caseinate, respectively.

Effect of a Vietnamese Cinnamomum cassia essential oil and its major component trans-cinnamaldehyde on the cell viability, membrane integrity, membrane fluidity, and proton motive force of Listeria innocua.

The antibacterial mechanism of a Cinnamomum cassia essential oil from Vietnam and of its main component (trans-cinnamaldehyde, 90% (m/m) of C. cassia essential oil) against a Listeria innocua strain was investigated to estimate their potential for food preservation. In the presence of C. cassia essential oil or trans-cinnamaldehyde at their minimal bactericidal concentration (2700 µg·mL(-1)), L. innocua cells fluoresced green after staining with Syto9® and propidium iodide, as observed by epifluorescence microscopy, suggesting that the perturbation of membrane did not cause large pore formation and cell lysis but may have introduced the presence of viable but nonculturable bacteria. Moreover, the fluidity, potential, and intracellular pH of the cytoplasmic membrane were perturbed in the presence of the essential oil or trans-cinnamaldehyde. However, these membrane perturbations were less severe in the presence of trans-cinnamaldehyde than in the presence of multicomponent C. cassia essential oil. This indicates that in addition to trans-cinnamaldehyde, other minor C. cassia essential oil components play a major role in its antibacterial activity against L. innocua cells.