- Title
- Edible films and coatings for improving postharvest quality of fresh horticulture produce
- Creator
- Thakur, Rahul
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2019
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Consumer’s interest in high-quality food along with the rising environmental concerns over synthetic plastic packaging has led to the development of biodegradable edible coatings. Starch has been applied to develop edible films, however, these films have limitations in controlling the moisture migration making them not ideal for coating applications. Hydrophobic plasticizers can be combined to overcome these limitations. Among the different starches, rice starch is one of the underutilized materials for fruit coating applications. Its wide range of amylose-amylopectin ratio is suitable for making good edible films in combination with co-biopolymers and compatible plasticizers. The current study aimed to develop novel composite edible coating from rice starch, ι- carrageenan, fatty acid and glycerol for minimising water loss and extending the postharvest shelf life of selected fruits. Comparative study on the formation of edible films from the starches of eight different rice varieties showed the differences in the film properties. Of the studied starch varieties, “Reiziq” was the best source of starch for preparation of edible films with improved attributes. The films from this variety showed minimum thickness (0.08 mm), water vapour permeability (WVP) (2.7 gs_1m_1 Pa_1), solubility (43.12%) opacity(0.44%), and better mechanical properties, demonstrating the importance of selection of the source of the starch. The study concluded that starch amylose content and amylose–amylopectin associations during retrogradation play a significant role in determining the various properties of the films. However, these filmshad poor flexibility and water barrier properties. To improve the flexibility and water barrier properties of Reiziq starch films, glycerol and hydrophobic plasticizers were blended to the starch-ι-car mixture. Water barrier properties were improved with all the investigated hydrophobic plasticizers, and films prepared from rice starch-ι-car-glycerol- sucrose fatty acid (FAEs) mixture resulted in a film with better physical, mechanical, barrier and optical properties. Before applying the developed coating on the fruit surface, the concentration of ingredients (rice starch, ι-carrageenan, FAEs and glycerol) were optimised using Response surface methodology (RSM). The optimisation results showed that rice starch 2.5%, ι-carrageenan 1.5%, FAEs 2% and glycerol 1.5% are best in rendering films with desired physical, mechanical and permeability properties. The optimal coating material was then applied to different fruit including apple, plum and banana to keep or improve their postharvest quality. During storage, fruit weight loss, respiration rate, ethylene production rate, total soluble solids (TSS), titratable acidity (TA), firmness, greasiness and change in the fruit skin colour were measured. The effect of the coating treatment on changes to the bioactive profile (total phenolic content (TPC), total antioxidant capacity (TAC), flavonoid content (FC) and free radical scavenging activity) of the fruit was also analysed.The applied coating formulation was effective in reducing weight loss and maintained tissue firmness without affecting TSS, TA and the bioactive profile of the apple fruit during postharvest storage (5°C + 1 day at 20°C). A delay in skin colour change and a significant reduction in fruit greasiness was observed in the coated fruit. For the plum fruit, the rice starch composite coating was shown to be effective in reducing both weight loss (WL) and respiration rate and inhibiting the endogenous ethylene production when compared to the uncoated control fruit stored at room temperature (p < 0.05). The coating was effective in delaying ethylene biosynthesis and reducing respiration rate in case of banana fruit. Other factors, including delayed chlorophyll degradation, reduced weight loss and retention of fruit firmness for the first six days, all of which improved the commercial value of the fruit.In summary, the developed rice starch-ι-car-FAEs composite formulation has a great potential for improving the postharvest shelf life and quality of fresh horticulture commodities. However, to have better applications of the rice starch-ι-car-FAEs film,future studies are recommended to deeply elucidate the structural interaction between starch and other ingredients during the thermal (gelatinization) and post thermal (retrogradation) events. The effects of temperature and relative humidity on film properties are also needed to investigate for their effect on physical and chemical changes during storage. Finally, coating techniques and conditions (spraying or dipping) are recommended to be optimized to identify the most suitable coating formulations for specific fresh produce.
- Subject
- biopolymer; starch; films; coatings; postharvest; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1404526
- Identifier
- uon:35355
- Rights
- Copyright 2019 Rahul Thakur
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 20 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 162 KB | Adobe Acrobat PDF | View Details Download |