Agriculture Reference
In-Depth Information
Among the complex constituents of citrus essential oils, the terpene citral is known
to have strong antifungal properties (Rodov and others 1995). In addition, cinnamon
oil and its active compound (cinnamaldehyde) also have been tested for their inhibi-
tory activity against
E. coli
(Friedman and others 2004a,b; Helander and others 1998).
Phenolic compounds are found in numerous plant species (Walsh 2003). These
compounds appear to be involved in the defense of plants against invading pathogens,
including bacteria, fungi, and viruses. Phenolic compounds present in teas (Friedman
and others 2005, 2006), pigmented rice brans (Nam and others 2006), and most fruits
and vegetables (Shahidi and Naczk 2004) are also reported to exhibit antimicrobial
effects (Friedman and others 2003, 2005). Some of these have been incorporated in
edible fi lms (Cagri and others 2004).
Studies on the antibacterial activity of oregano, lemongrass, and cinnamon plant
essential oils and their major components carvacrol, citral, and cinnamaldehyde in
apple pur é e fi lm-forming solutions against the foodborne pathogen
E. coli
O157 : H7
and
Salmonella enterica
show that oregano oil as well as its major component carva-
crol killed
E. coli
O157 : H7 and
S. enterica
practically on contact (3 min). The order
of antimicrobial activities was as follows: carvacrol
>
oregano
>
citral
>
cinnamalde-
hyde
cinnamon oil (Friedman and others 2004). The evaluation of the
physicochemical properties of fi lms made from apple slurries revealed no adverse
effect of the additives on water vapor permeability properties (Rojas-Graü and others
2006 , 2007a ). The antimicrobial fi lms showed good oxygen barrier properties and
their tensile strength did not differ signifi cantly from control fi lms without added
antimicrobials.
>
lemongrass
>
Physical Properties of Edible Films Containing Plant Essential Oils
The ideal characteristics of an edible fi lm would be low water vapor permeability and
high mechanical strength. The physicochemical properties of edible fi lms (e.g., color,
tensile strength, water vapor, and oxygen permeability) relate to the ability of the
coating to enhance the mechanical integrity of foods, inhibit moisture loss and oxida-
tive rancidity, and improve fi nal-product appearance (Debeaufort and others 1998). A
complete analysis of both antimicrobial and physicochemical properties is important
for predicting the behavior of antimicrobial edible fi lms in the food system (Cagri and
others 2001; McHugh and Krochta 1994b).
McHugh and others (1996) demonstrated that apple-based edible fi lms were not
very good moisture barriers and that the addition of lipids could potentially improve
the water barrier properties of fruit-based fi lms. Rojas - Gra ü and others (2006) found
that water vapor permeability decreased when the proportion of the hydrophobic
compounds increased in apple-based edible fi lms, this effect being more prominent
when oregano oil was used in the composition of the fi lms.
Adding carvacrol addition to apple purée edible fi lms resulted in signifi cant decrease
in fi lm water vapor permeability. Water vapor transfer generally occurs through the
hydrophilic portion of the fi lm; thus, water vapor permeability depends on the hydro-
philic-hydrophobic ratio of the fi lm components (Hern á ndez 1994 ). Water vapor
permeability increases with polarity, unsaturation, and degree of branching of the lipid,
but it also depends on the water absorption properties of the polar part of the fi lm
(Gontard and others 1994 ).
