Development of edible composite coatings with antifungal activity on citrus fruits
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Valencia-Chamorro, Silvia A.Date
2009Cita bibliográfica
Valencia, S. (2009). Development of edible composite coatings with antigungal activity on citrus fruit (Ph. D. Thesis). Universitat Politècnica de València.Abstract
In the citrus industry, very important economical losses are primarily
caused by postharvest green and blue molds, caused by the pathogens
Penicillium digitatum (Pers.:Fr.) Sacc. and Penicillium italicum Wehmer. For
many years, chemical fungicides have been widely applied to control
these diseases. However, consumer concerns about prolonged and
extensive use of chemical fungicides to control citrus postharvest decay
lead researchers to look for alternative nonpolluting methods that do not
deposit harmful residues in/on fruit and contaminate the environment.
The use of edible films and coatings is an environmentally-friendly
alternative method to increase the shelf-life of many food products
including fruits and vegetables. However, very little research has been
focused on the development of edible composite coatings with the
addition of antifungal compounds as a new method to control major
fungal postharvest diseases of fresh citrus fruit.
The general objective of the present doctoral thesis was to develop
new edible composite coatings with the addition of antifungal food
additives for the control of posharvest green and blue molds on
commercially important citrus cultivars. Firstly, new hydroxypropyl
methylcellulose (HPMC)-lipid edible composite films containing food
additives or generally recognized as safe (GRAS) compounds with
antifungal properties were developed and selected according to their
capability of forming stable emulsions. Films from stable emulsions were
evaluated for their in vitro activity against P. digitatum and P. italicum and
their mechanical and barrier properties (Chapter 1). Then, selected
emulsions were used in in vivo tests to coat commercially important citrus
species and cultivars and determine their curative (fruit coated after
fungal inoculation) and preventive (fruit coated before fungal
inoculation) antifungal activity against green and blue molds (Chapter 2).
Next, the effect of the application of selected antifungal coatings on the
development of penicillium molds and the physico-chemical and sensory
quality of ‘Valencia’ oranges, and ‘Ortanique’ and ‘Clemenules’
mandarins during long-term cold storage was assessed (Chapters 3, 4,
and 5). Finally, the effectiveness of chitosan edible coatings to control
green and blue molds of ‘Valencia’ oranges and ‘Oronules’ mandarins
was determined (Chapter 6).
Summary
Only around 5% of about 470 emulsion formulations prepared by
incorporating food preservatives (mostly mineral salts, salts of organic
acids, salts of parabens) to HPMC-lipid were stable. Edible films and
coatings containing parabens, potassium sorbate (PS), sodium benzoate
(SB), and some mixtures were the most effective to inhibit the in vitro
growth of P. digitatum and P. italicum, and control in vivo the development
of green and blue molds on previously inoculated ‘Valencia’ oranges, and
‘Ortanique’ and ‘Clemenules’ mandarins (curative action). Important
differences in antifungal activity were observed between in vitro and in
vivo tests. In general, the curative activity of the coatings after incubation
at 20 ºC for 7 d was higher on oranges than on mandarins. The activity
was fungistatic rather than fungicidal. The tested coatings did not
provide any preventive activity against both molds. The lipid
composition and the properties of added food preservatives greatly
influenced the barrier and mechanical properties of selected films.
During cold storage at 5 ºC for up to 2 months, the PS+SP- and SBbased
coatings were the most effective to inhibit both molds on
‘Valencia’ oranges and ‘Ortanique’ mandarins, being the antifungal
activity higher on oranges than on mandarins. Although the coatings did
not reduce weight loss of ‘Valencia’ oranges, they did not adversely affect
the fruit physico-chemical quality. The coatings significantly reduced
weight loss and maintained the firmness of coated ‘Ortanique’ and
‘Clemenules’ mandarins. Sensory quality was evaluated as acceptable in
all cases.
Since selected HPMC-lipid edible coatings effectively reduced mold
development and preserved fruit quality during cold storage, they
showed promise as nonpolluting commercial alternatives to conventional
fungicide-amended citrus waxes. Further research should focus on the
modification of some physical characteristics of the coatings to improve
their gloss and visual aspect, and their combination with other alternative
control methods to find synergistic or complementary activities in an
integrated disease management approach.
In general, the effectiveness of chitosan-based coatings was highly
dependent on inoculum density, fruit cultivar, and storage conditions,
but it was not consistently high enough for commercial decay control.