Agriculture Reference
In-Depth Information
Edible Film Casting Methods
Despite the growth in research on edible fi lms, the extent of commercialization has
not progressed as signifi cantly. Manufacturing processing methods and the resultant
mechanical and water barrier properties of edible fi lms must be improved for practical
use (Arvanitoyannis and Gorris 1999). Edible fi lms are commonly produced via a
solution casting process where the fi lms are dried from 2 to 12 h. Shorter drying times
allow the formation of fi lms with no signifi cant microbial contamination. Knowledge
of critical control points is necessary to reduce the risk of microbial growth. The
quality of the starting materials, as well as the use of heat and good sanitation during
casting and drying, is necessary to ensure safety (McHugh and Olsen 2001).
Most of the edible fi lms made have been cast using ineffi cient technologies and
there is a need to develop more effi cient methodologies for the mass production of
edible fi lms. Recently, we reported signifi cant differences in physical and antimicro-
bial properties of apple- and tomato-based edible fi lms made by continuous casting
under infrared heating in a pilot plant lab coater and by a batch drying process done
overnight under ambient air (Du and others, 2008a,b). The continuous method for fi lm
casting was more suitable for large-scale production of fruit- and vegetable-based
edible fi lms than the batch method. The tendency of volatile active antimicrobial
compounds to evaporate during casting at high temperatures can be compensated by
manipulating the formulation to achieve an appropriate fi nal concentration of the
antimicrobial compound in the dried fi lms (Du and others, 2008a,b).
Antimicrobial Plant Essential Oils in Edible Films
Naturally derived biological compounds and other natural products may have applica-
tion in controlling pathogens in produce. They have varied antimicrobial and antioxi-
dant properties that can break down cellular membranes and disrupt biosynthetic
pathways of microorganisms (Benaventi-García and others 1998; Bowles and Juneja
1998; Bowles and others 1995). The use of edible fi lms as antimicrobial carriers
represents an interesting approach for the external incorporation of plant essential oils
and other phytochemicals onto food system surfaces. The agents can then diffuse into
the food to control target microorganisms. The antimicrobial activity of plant essential
oils is confi ned to a number of small terpenoid and phenolic compounds, which are
known to exhibit antibacterial or antifungal activity.
Recent studies have shown that essential oils of oregano (
Origanum vulgare
),
thyme (
Thymus vulgaris
), cinnamon (
Cinnamon casia)
, lemongrass (
Cymbopogon
citratus
), and clove (
Eugenia caryphyllata
) are among the most active antimicrobials
against strains of
Escherichia coli
(Dorman and Deans 2000; Friedman and others
2002; Hammer and others 1999; Smith-Palmer and others 1998). Although the effec-
tiveness of all these compounds has been widely reported, carvacrol (a major compo-
nent of the essential oils of oregano and thyme) appears to have received the most
attention from investigators. Carvacrol is generally regarded as safe (GRAS) and used
as a fl avoring agent in baked goods, sweets, ice cream, beverages, and chewing gum
(Fenaroli 1995). However, widespread application of plant essential oils in food
systems has been limited by the incompatibility of their strong fl avors with some
foods. Plant essential oils and their components are compatible with the sensory char-
acteristics of fruits and vegetables and have been shown to prevent bacterial growth.
