Synergic antimicrobial properties of Carvacrol essential oil and montmorillonite in biodegradable starch films.

This work evaluated the synergic effect of carvacrol essential oil (EO) and montmorillonite (MMT) (named hybrid compound), incorporated in thermoplastic starch (TPS) films in different contents (4.5, 9, and 15 wt%). TPS films were characterized by FTIR, FT-Raman, DSC, XRD, and antimicrobial assay. FTIR and FT-Raman indicated new hydrogen bonds between hybrid and starch, altering the thermal properties and requiring more energy to destroy the TPS-hybrid bonds. XRD analysis showed slight crystallinity changes, and TPS-15 hybrid showed an amorphous structure that allows the diffusion of EO thought the films. TPS-hybrid films showed antimicrobial behavior against E. coli due to the synergistic effect of MMT and EO, which resulted in strong antimicrobial effects due to the destabilization and partial destruction of the bacteria cell membrane. The hybrid probably changed the E. coli cell permeability, respiration, and electron transport. TPS-15 hybrid sample presented the lowest crystallinity, facilitating the film's oil diffusion, maximizing the bacterium inhibitory effect, and acting as a biocidal agent. The results demonstrated that a hybrid compound is a good option for starch antimicrobial films for fresh food, such as fruits and vegetables.

Biomimetic Transformation of p-Menthene Glucosides into p-Cymenes and Carvotanacetone.

A biomimetic transformation of p-menthene glucosides into aromatic monoterpenoids that alluded to mechanisms for essential oil metabolism, which lines up with the precepts of molecular economy, is described. Acid treatment of (-)-(3 S,4 S,6 R)-3,6-dihydroxy-1-menthene 3- O-ß-d-glucopyranoside (1) and (-)-(3 S,4 R,5 R,6 S)-3,5,6-trihydroxy-1-menthene 3- O-ß-d-glucopyranoside (2), from Ageratina glabrata, yielded p-cymene (7) and carvacrol (9). The stable oxidized intermediates (+)-(3 S,4 S,6 R)-3,6-dihydroxy-1-menthene (3), (+)-(1 S,4 S,6 R)-1,6-dihydroxy-2-menthene (4), (+)-(1 R,4 S,6 R)-1,6-dihydroxy-2-menthene (5), (+)-(4 S,6 R)-yabunikkeol (6), (+)-(4 S)-carvotanacetone (8), (+)-(1 S,4 S,5 R,6 R)-1,5,6-trihydroxy-2-menthene (15), (+)-(1 R,4 S,5 R,6 R)-1,5,6-trihydroxy-2-menthene (16), and the new (+)-(4 S,5 R,6 S)-1(7),2-menthadiene (17) permitted establishment of the reaction mechanisms. The reactivity of the hydroxy groups of 4 and 5, as well as those of 15 and 16, was compared by acetylation reactions and supported by DFT calculations, revealing diminished reactivity in 4 and 15 due to the cis configuration of their hydroxy groups at C-1 and C-6. In addition, p-cymene (7) was detected as one of the major constituents of the essential oil of A. glabrata, which matches well with the biomimetic study.