- Title
- Evaluation of edible coating application on ‘Valencia’ orange fruit
- Creator
- Saberi, Bahareh
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The continuous increase of consumer interest in higher quality food, in combination with the ecological and economic requirements to decrease disposal of post-user waste, has induced increasing attention to research into edible films and coatings. As a replacement to more traditional recycling procedures, edible and biodegradable polymers, that can be reverted to the biological cycle after use, have emerged. Consequently, the use of biodegradable agricultural polymers would not only resolve the environmental problems, but also present a potential new use for extra farm produce. Such films can mechanically protect foods, inhibit the contamination from microorganisms, and preserve quality loss of foods caused by mass transfer (e.g. moisture, gases, flavors, etc.). Additionally, edible films and coatings can be applied as a carrier for incorporating natural or chemical antimicrobial agents, antioxidants, enzymes or functional components such as probiotics, minerals and vitamins. The application of edible films and coatings has been studied as a good alternative for the conservation of intact, and fresh fruit and vegetables. Fruit and vegetables consist of living tissue which undergoes many physical and chemical changes due to deteriorative and synthetic biochemical processes, such as enhanced ethylene production and respiration rate, as well as consumption of sugars, lipids and organic acids accelerating the ripening process. Therefore the quality of products can be affected including flavor, textural, nutritional, and pigmentation changes during storage. The major purpose of employing edible films and coatings is to act as a semipermeable membrane against gases and vapor that preserves the produce and reduces the rate of physiological postharvest degradation; however, they can also carry additives, for example texture enhancers, antimicrobials, and antioxidants to extend the shelf life of produce after harvest. Edible films can be prepared from proteins, polysaccharides, lipids or a combination of these constituents. Starch can be used for edible films production because it can be obtained from a large number of raw materials and is a renewable and biodegradable biopolymer. Pea starch has been demonstrated to produce the films with improved physical and mechanical properties in comparison with films prepared from other starches due to high amount of amylose. The development of pea starch film with improved functions affects its application. Hypothesis and Aims: In the current study, we hypothesized that development of novel edible films made of pea starch will be an improved alternative to substitute the common commercial waxes used for coating in the citrus industry for extending the orange fruit shelf-life. The optimized formulations of pea starch and other ingredients used to improve the physical, mechanical and barrier properties of films will maintain physical, sensorial and quality properties of the fruit during simulated commercial storage conditions. Overall, the aims of this study were: Aim 1: To develop pea starch films: (A) To determine the moisture barrier, color, mechanical, and structural properties of pea starch film affected by different concentrations of glycerol as plasticizer and environmental relative humidity (RH). (B) To develop a new type of edible film made of pea starch and guar gum in the presence of glycerol, and to examine the mechanical and water barrier properties of the resulting composite films as a function of guar gum and glycerol concentrations using a mixture experimental design. (C) To study the influence of different plasticizers (glycols, sugars and polyols) on the moisture sorption, mechanical, physical, optical, and microstructure characteristics of pea starch-guar gum (PSGG) film. (D) To investigate the alteration of physical, barrier and mechanical properties of PSGG films resulting from the incorporation of hydrophobic compounds such as shellac, emulsifier, and surfactant using response surface methodology. Aim 2: To evaluate the potential of application of films obtained from Aim 1 on ‘Valencia’ orange fruit: (A) To determine whether films have the potential to be used as an edible coating for increasing the shelf life of ‘Valencia’ orange whilst maintaining the quality of fruit during storage. The effectiveness of the best coatings formulation on gas exchange, vitamin C, total phenolic compounds, antioxidant capacity, and sensory quality of fruit were evaluated. Results: The results showed that increasing the concentration of glycerol led to improvement of the tensile strength of the pea starch films at RH < 43 %, the percent elongation as well as the deformation at break at RH < 84 %. Increasing plasticizer content and RH also resulted in films with lower Young’s modulus, lower puncture force, but higher puncture deformation. Furthermore, increasing plasticizer content led to the films with a more opaque appearance. Pea starch films prepared with 15 and 25 % glycerol had lower water vapor permeability in comparison with un-plasticized film indicating its potential application as edible films in the food and pharmaceutical industries. The physical, optical, mechanical and barrier properties of pea starch edible films were improved by optimizing concentrations of pea starch (2-3 g), guar gum (0.1-0.5 g) and glycerol (15-35%) by using Box–Behnken response surface design (BBD). The results revealed that increasing pea starch and guar gum content favored formation of a more resistant polymeric structure. The optimized conditions with the goal of maximizing optical and mechanical properties and minimizing water vapor permeability, moisture content, solubility and color were 2.5 g pea starch, 0.3 g guar gum and 25 % (w/w) glycerol based on the dry film matter in 100 mL of distilled water. The addition of various plasticizers to the PSGG film showed that the films containing plasticizers with higher functional groups had lower equilibrium moisture content at aw < 0.4. In general, a reduction in tensile strength and Young's modulus and an increase in elongation at break were detected when the molecular weight of plasticizers and relative humidity increased in all film formulations. Films plasticized with monosaccharide showed similar mechanical properties to those with sorbitol, but lower solubility and water vapor permeability (WVP), higher transparency and moisture content than the sorbitol-plasticized films. The most noticeable plasticization effect was exerted in the following order: glycerol > EG > PG > xylitol > fructose > sorbitol > mannitol > galactose > glucose > sucrose > maltitol. The incorporation of shellac as the hydrophobic compound in the PSGG film plasticized with glycerol led to a slightly increased film thickness. However, the addition of higher concentrations of shellac did not improve the moisture barrier of PSGG film owing to the poor distribution of shellac in the film structure. Film formulated with 40 % shellac, 1 % SA, and 0.3 % Tween-20 exhibited optimal functional properties. Moreover, films containing oleic acid (OA) showed not only lower thickness, WVP, moisture content, and water solubility, but also higher percentage of elongation (E), tensile strength (TS), and transparency compared with other fatty acids tested. Biocomposite pea starch-guar gum-shellac (PSGG-Sh) film containing OA was considered for the coating of oranges. The incorporation of lipid compounds into the PSGG coatings (PSGG-Sh) generally resulted in the best performance in reducing fruit respiration rate, ethylene production, weight and firmness loss, peel pitting, and fruit decay rate of the coated oranges. Fruit coated with PSGG-Sh and a single layer of PSGG coatings generally resulted in higher scores for overall flavor and freshness after four weeks at 5 °C followed by one week at 20 °C, than uncoated fruit, as assessed by a sensory panel. Overall results suggested that PSGG-based edible coatings could be a beneficial substitute to common commercial waxes for maintaining quality and storability, as well as extending shelf life of citrus fruit and potentially other fresh horticultural produce. Conclusions: In conclusion, the hypothesis was supported and the aims were addressed. This study revealed that pea starch can be used to produce films with appropriate physical and mechanical properties in the presence of guar gum, various plasticizers (polyols, glycols and sugars), and hydrophobic compounds. Application of PSGG edible coatings incorporated with shellac showed great potential for preservation quality, storability and improved shelf life of ‘Valencia’ oranges at 5 °C and 20 °C. The results of this study can be further utilized for formation of biodegradable films or edible coatings and better understanding of using pea starch in the food packaging industry. The results also suggested that PSGG-based edible coatings could be a beneficial substitute to common commercial waxes for maintaining quality and extending shelf life of citrus fruit and potentially other fresh horticultural produce.
- Subject
- pea starch; edible film; biocomposite; food packaging; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1406382
- Identifier
- uon:35623
- Rights
- Copyright 2018 Bahareh Saberi
- Language
- eng
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