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.

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.

Study of interactions between anionic exopolysaccharides produced by newly isolated probiotic bacteria and sodium caseinate.

The present study aims to evaluate the interactions between four exopolysaccharides (EPS) produced by probiotic bacteria and sodium caseinate (Cas) in order to simulate their behavior in dairy products. Complexation between the produced EPS samples and Cas was investigated as a function of polysaccharide to protein ratio. The highest turbidity and average size of complexes were formed at an EPS/Cas ratio of 3 (corresponding to 1 g/L of EPS and 0.33 g/L of Cas) as a result of the combination of individual complexes to form aggregates. Zeta potential measurements and Cas surface hydrophobicity results suggested that complex formation occurred essentially through electrostatic attractions with a possible contribution of hydrophobic interaction for EPS-GM which was produced by Bacillus tequilensis-GM. Afterwards, the effect of pH on the complexation between biopolymers was studied when EPS and Cas concentrations were maintained constant at 1 and 0.33 g/L, respectively. pH was adjusted to 3.0 and 3.5, respectively. Results showed that the highest amount and sizes of EPS/Cas complexes were formed at pH 3.5 and that EPS-GM enabled to obtain the biggest and highest amount of aggregates. Therefore, the obtained results support the fact that the simultaneous presence of EPS and Cas in dairy products results in complexes formation via electrostatic interactions depending on EPS/Cas ratio and pH of the medium.

Using complexation for the microencapsulation of nisin in biopolymer matrices by spray-drying.

The aim of this study is to investigate the potential of complexation to encapsulate nisin (5g/L concentration) using spray-drying technique and to evaluate how complexation with pectin or alginate (2g/L concentration) can preserve nisin structure and antimicrobial activity. Spray-drying of nisin-low methoxyl pectin or nisin-alginate electrostatic complexes has led to the microencapsulation of the peptide in different networks that were highly influenced by the polysaccharide type. Turbidity and particle size measurements indicated that while spray-drying promoted the aggregation of nisin-pectin complexes, it favored the dissociation of nisin-alginate aggregates to form individual complexes. Structural changes of nisin induced by complexation with pectin or alginate and spray-drying were studied by using UV-Vis absorption and fluorescence spectroscopy. The results showed that complexation with pectin or alginate preserved nisin structure as well as its antimicrobial activity during spray-drying.