Effects of polysaccharide-based coating conjugated with silver nanoparticles on shelf-life extension of papaya (Carica papaya L. cv. Eksotika)
Papaya is a tropical fruit that is well accepted worldwide for its good taste and nutritional content. However, like many other tropical fruits, papaya also has postharvest problems due to several reasons including short shelf life caused by disease mainly fungal infection. This problem also affe...
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| Format: | Thesis |
| Language: | English |
| Published: |
2014
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/75964/1/FSTM%202014%2031%20-%20IR.pdf http://psasir.upm.edu.my/id/eprint/75964/ |
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| Summary: | Papaya is a tropical fruit that is well accepted worldwide for its good taste and
nutritional content. However, like many other tropical fruits, papaya also has
postharvest problems due to several reasons including short shelf life caused by
disease mainly fungal infection. This problem also affects Carica papaya L. cv.
Eksotika, which is one of the popular papaya cultivars in Malaysia. In the present
study, polysaccharide-based coatings incorporated with silver nanoparticles were
used to prolong the shelf life of Eksotika papaya.
In this study, a two-factor central composite design (CCD) was used to optimize two
different edible coating formulations for coating of Eksotika papaya. The effect of
two different coating formulations, namely, chitosan-based [chitosan (0.5 – 2.5%)
and glycerol (0 – 2%)] and carrageenan-based [carrageenan (0.2 – 0.8%) and
glycerol (0 – 1%)] on texture and colour components (L, a and b values) of coated
papaya were evaluated. From the multiple response optimization analysis,
combination of 2.32% chitosan with 0.53% glycerol, and 0.78% carrageenan with
0.85% glycerol for chitosan-based and carrageenan-based coating respectively were
predicted to give desirable effect to the response variables tested, with no significant
(p > 0.05) difference between the experimental and predicted values. However,
during shelf life monitoring of the coated samples, papaya coated with the optimized
chitosan-based formulation failed to ripen. In order to overcome this, visual
observation of papaya coated with different concentrations of chitosan (0.5, 1.0, 1.5
and 2.32%) were conducted. 1% chitosan was found to successfully coat papaya
without retarding the ripening process.
Silver nanoparticles at the range of 0-80 ppm were incorporated into the chitosanand
carrageenan-based coatings to evaluate the antimicrobial properties of the
formed polysaccharide-silver nanocomposites. Chitosan alone without synergistic
interaction with silver nanoparticles was sufficient in giving bactericidal and
antifungal effects. Carrageenan on the other hand requires addition of 2.5 and 30
ppm of silver nanoparticles to give antifungal and bactericidal effects respectively.
Application of chitosan, carrageenan-silver nanocomposite and carrageenan-based
coating on Eksotika papaya were able to prolong the shelf life up to 13, 11 and 9 days at ambient condition (26±2°C;70±10% RH), respectively. During low
temperature (15±1°C; 60±10% RH) storage, the shelf life was extended up to 21
days for chitosan and carrageenan-silver nanocomposite based coating and also 17
days for carrageenan-based coating. The maximum shelf life of uncoated papaya
was 7 and 13 days at ambient and low temperature, respectively. Shelf life extension
of coated papaya was judged based on no visible fungal decay.
Physiological and physico-chemical evaluations during storage showed that there
was no significant (p > 0.05) difference between coated samples and control except
for firmness at ambient condition and also total soluble solids. The microbial counts
between coated and uncoated papaya were also found to be insignificant (p > 0.05).
Determination of silver concentration in papaya fruit coated with carrageenan-silver
nanocomposite revealed that, silver migrated through the peel and into the innermost
pulp layer of papaya during storage. Consumer acceptance test showed that scores of
all tested attributes for coated samples were above the minimum acceptable value
(>5). This indicated that the coating did not give negative visual or physical
perception towards the consumer. Hence, coating gave positive contribution on shelf
life extension of papaya especially for marketing purposes, but incorporation of
silver nanoparticles needs to be reconsidered since silver migrated into the pulp due
to the thin peel layer of papaya fruit. |
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