Edible Coatings And Films To Improve Food Quality Pdf
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Nowadays, the world's plastic production generates lot of plastic waste. Therefore, the need of reducing conventional nonbiodegradable plastic materials has encouraged the development of innovative biodegradable materials from renewable resources.
- Natural edible films and coatings applied in food: a bibliographic review
- Edible coatings and films to improve food quality
- Edible Coatings and Films to Improve Food Quality 2nd Edition 1420059629
Natural edible films and coatings applied in food: a bibliographic review
Alginate is a naturally occurring polysaccharide used in the bio industry. It is mainly derived from brown algae species. This paper reviews the most recent essential information about alginate-based edible coatings. Future trends are also reviewed to identify research gaps and recommend new research areas. The summarized information presented in this article will enable researchers to thoroughly understand the fundamentals of the coating process and to develop alginate-based edible films and coatings more readily.
The principal roles of food packaging are to protect food products from physical, chemical, and biological influences by delaying food deterioration, retaining and prolonging the beneficial effects of processing, and maintaining the quality and safety of the foods with extending shelf life [ 1 ].
Broad external influences such as the development of international food markets, legal and technological requirements, raw material availability, consumer demands, etc. A total of 1. Non-renewable, non-biodegradable packaging materials have serious environmental drawbacks. They have been considered a major source to the solid waste and environmental pollution by consumers and environment activists [ 4 , 5 ].
In order to solve this problem, companies and researchers have been working on ways to develop new packaging strategies with environmentally friendly, abundant biodegradable packaging materials made from renewable natural polymers [ 4 , 6 ].
Furthermore, the rapidly growing interest in the use of edible packaging can also be associated with a growing interest from consumers for minimally processed fresh-like foods with an extended shelf life and trend in improving the quality of food with edible barriers [ 7 ]. Edible films and coatings are thin layers of material their thickness is generally less than 0. Therefore, the materials used in the formulation should conform to the general food laws and regulations [ 10 ].
Additionally, the coatings and films should not affect the organoleptic properties of the food product negatively [ 6 ]. The coating can also be applied on individual pieces of the whole product, which have not been individually packaged due to practical arguments, such as fresh-cut melons, kiwis, strawberries, nuts, beans, pears [ 11 ].
Edible films and coatings can be used to overcome many obstacles involved in the marketing of foods [ 12 ]. These functions can be specified as retarding moisture, gas, solute and oil migration, improving structural integrity, retaining volatile flavor compounds, conveying food additives [ 12 ].
In addition, they improved the aesthetic appearance by minimizing the development of physical damage, hiding scars, and improving surface shine [ 13 , 14 ].
For instance, hot-melt paraffin waxes have been used to coat citrus fruits to retard moisture, edible collagen casings have been used for sausages to provide structural integrity and apples have been coated with wax to improve surface shine and prevent physical damage. The required features expected from edible films and coatings can be assigned by the specific characteristics of the product and changes during production, transportation, and storage periods.
Despite providing a barrier, the non-edible packaging is still essential for edible coated food products due to hygienic reasons [ 8 ]. Nevertheless, combining edible films and coatings with traditional packaging would likely reduce the non-biodegradable packaging waste of processed foods and environmental effluence [ 12 , 15 , 16 ]. Although edible coating and edible film terms have been used interchangeably or as synonyms in some sources; their application on the food products constitutes their main difference [ 9 ].
Edible films are stand-alone wrapping materials which can be cut and placed on the food product separately due to having enough integrity; on the other hand, edible coatings form a thin layer on the product directly subsequent to the application [ 8 , 9 , 17 , 18 ]. Therefore, although produced from the same gelling agent, the characteristics of edible films and coatings can be very different [ 9 ].
Alginate-based food coatings and films attracted widespread interest. A wide range of scientific research has been published in the literature. This overview summarizes the literature information with dividing into categories in a layout:. Lists of additives incorporated into the alginate-based edible films and coatings in the literature. Sums up the research findings on alginate coated fruits-vegetables, meats, poultry, seafood, cheese.
Our present study can be used as a guide for researchers both in the academy and industry who plan to work on alginate-based coatings, will select the components of their formulations, and plan their future studies and experiments. Film-forming biopolymers are generally classified according to the type of film-forming material, which form cohesive and continuous matrices [ 8 ]. These are hydrocolloids polysaccharides and proteins , lipids and composites Figure 1 [ 12 , 19 ].
Hydrocolloids are composed of hydrophilic polymers of microbial, vegetable, animal, or synthetic origin [ 15 ]. Mostly, they are large molecules with many hydroxyl groups [ 15 , 20 ]. Hydrocolloid film applications do not target to control water vapor migration due to their hydrophilic nature [ 12 ]. However, the continuous polysaccharide film can be referred to as a sacrificial moisture agent. That is, moisture evaporates from the film instead of the food surface [ 21 , 22 , 23 , 24 ].
Subsequent to the desiccation of the coating film, the food product would lose its moisture [ 24 ]. The film-forming biomaterials that have been studied extensively for the formation of edible coatings and films Donhowe and Fennema [ 12 ], Embuscado and Huber [ 25 ]. In general, polysaccharides are used as gas barriers; lipids reduce water transmission, while proteins provide mechanical stability [ 9 ].
The main disadvantages of lipid-based films and coatings are their opaqueness, fragility, and instability rancidity , on the other hand, hydrocolloid films and coatings have a more neutral taste [ 6 ]. Composites are formulated using both lipid and hydrocolloid components, which are incorporated into the formulation in order to benefit from their advantages together [ 12 ]. Composites can be formed as a bilayer or as a conglomerate [ 12 ].
Alginates are naturally occurring, indigestible polysaccharides commonly produced by and refined from various genera of brown algae mainly Laminaria hyperborean , Macrocystis pyrifera , Ascophyllum nodosum ; lesser extent Laminaria digitate , Laminaria japonica , Eclonia maxima , Lesonia negrescens , Sargassum sp.
Some bacteria such as Azotobacter vinelandii or mucoid strains of Pseudomonas aeruginosa also synthesize alginate like polymers as exopolysaccharide i. Alginate production from Marine algae [ 32 ] and A. An algal alginate structure could be separated into three fractions three uronic acid blocks : These are homopolymeric regions of M and G blocks, and alternating MG blocks containing both polyuronic acids [ 27 , 35 , 36 ]. Bacterial alginates have O-acetyl groups, while they are not present in the structure of algal alginates [ 37 ].
Additionally, bacterial alginates have higher molecular weights compared to the algal polymers [ 33 ]. The source of the alginate affects the ratio of M and G residues, which have an impact on the physical and chemical properties of the alginate, as well as the viscosity of the coating solution and thickness on the product [ 28 , 36 , 39 ]. Martinsen, et al. Alginic acid was first discovered and isolated by Dr.
Stanford in [ 35 ]. Alginates i. Alginic acid and calcium alginate are insoluble in water while sodium alginate, potassium alginate, and ammonium alginate are water-soluble polymers [ 42 , 43 ].
They have a limited solubility at low pH values [ 44 ]. The solubility of different types of alginates in numerous solvents and solutions were listed by Kimica Corporation [ 45 ]. The U. Alginate is widely used in various industries such as food, beverage, textile, printing, and pharmaceutical as a thickening agent, stabilizer, emulsifier, chelating agent, encapsulation, swelling, a suspending agent, or used to form gels, films, and membrane [ 28 , 47 ].
Sodium alginate is the most common salt of alginate [ 48 ]. It is widely well-known that alginate is polyuronide, a natural ion exchanger [ 49 ].
The charged state of alginate is beneficial for film formation. In the absence of bivalent ions, alginate can be only used to increase viscosity [ 38 ].
However, the addition of certain bivalent cation into the alginate solution leads to a gel formation through ion exchange [ 42 , 47 ]. Alginate gel formation is rather a complex process. The proportion and length of the guluronic acid block G-blocks in the polymeric chain, the capacity to bind the number of divalent ions, the type of gelling ions and gelling conditions affect strongly the hydrogel properties of alginate [ 39 , 52 , 53 , 54 ].
A higher amount of G-Blocks will create rigid and dense gels, while a higher amount of M-Blocks will build flexible, porous gels [ 54 , 55 , 56 , 57 ]. Therefore, the diffusional resistance of gels containing predominantly high polyguluronic alginate content against high-molecular-weight-compounds is high [ 56 , 57 ]. There are two types of procedures for the incorporation of gelling ions into the alginate solution to form hydrogel i.
According to Mancini and McHugh [ 53 ], gel formation by cooling of the hot solution, which contains all the components, can be evaluated as the third method to initiate the controlled alginate gelation. Due to the thermal energy that the alginate solution possesses, a calcium-induced hydrogel formation can only take place after cooling [ 53 ]. The source of calcium ions i. Allen et al. The steady-state gel strength was reached fastest by calcium chloride followed by calcium lactate and calcium gluconate [ 52 ].
On the contrary, according to the study by Chrastil [ 64 ], the gelation kinetic constants did not depend on the calcium source. However, the strength of the formed gel and the resistance against calcium diffusion are not dependent on the calcium source type [ 38 , 52 ]. Despite its high solubility, calcium chloride is not an attractive calcium source due to imparting a bitter taste on the food [ 38 ]. On the other hand, calcium gluconate and calcium lactate can be used in coating applications where the taste attributes are important [ 38 ].
In situ gelation of alginate, and strongly homogeneous structure forming are also an interest of biotechnology e. A technique to prepare homogeneous alginate gels with a slow release of calcium ions has been reported [ 65 , 66 ]. In their subsequent research, the dimensional stability swelling tendency of the gel due to an increased tendency of the carboxyl and hydroxyl groups to interact with water molecules and osmotic pressure was controlled by controlling the calcium ion concentration of the external aqueous environment, crosslinking density, and polymer concentration of the gel and chemical composition of alginate [ 68 ].
It was pointed out by Pavlath, et al. The increased concentration of the multivalent ion diminishes the dominance of the dissolution process [ 69 ]. Rhim [ 70 ] also noticed the same phenomena and added that the method of CaCl 2 treatment affected the thickness of the film, i. The degree of crosslinking affects the swelling ability of the 3D structure of the alginate in the solvent, and we end up with a decrease in the permeability to various solutes and being used in drug controlled release systems [ 71 ].
Similarly, Rhim [ 70 ] observed that an increase in the CaCl 2 concentration caused an increase in the tensile strength and a decrease in the percentage elongation at break. The literature on the effects of calcium chloride dipping alone without coating has shown that CaCl 2 can be used as an effective firming agent due to the ability of calcium to bind cell wall polymers, maintain its structure, and diminish the water solubility of pectic substances with forming calcium pectate [ 72 , 73 , 74 ].
Improvement in firmness increases with increasing concentration of CaCl 2 , however, this is independent from the dipping time [ 75 ]. The mechanical, functional, organoleptic, and nutritional characteristics of edible films and coatings can be modified with the incorporation of various natural or chemical additives [ 12 ]. The mechanical properties of biodegradable packages can be improved by the plasticization of the polymer-network with plasticizers, which are generally non-volatile and miscible with the polymer.
The primary objectives of the plasticizers are increasing the free volume or molecular mobility of polymers, decreasing the intermolecular forces, bestowing flexibility, reducing brittleness, improving tear impact resistance, and regulating the flow of the coating material [ 26 , 76 , 77 , 78 , 79 ].
Water is the most common and most effective plasticizer; still, the plasticizing effect of water in hydrophilic biopolymers is difficult due to the dependency of the environmental conditions such as relative humidity and temperature [ 6 , 8 ]. Apart from water, glycerol, sorbitol, acetylated monoglyceride, polyethylene glycol, sucrose, etc. The addition of hydrophilic plasticizers to the formulation generally promotes water vapor permeability WVP and influences the mechanical properties of the coating material [ 12 , 80 ].
Therefore, the type and the quantity of the plasticizer are very important in the designing of the edible coating formulation. Parris, et al. Glycerine and sodium lactate lead to stronger and more elastic alginate-based films compared to sorbitol, which was stiffer [ 81 ].
Edible coatings and films to improve food quality
Figure 1. Biopolymer sources Biopolymers have multiple film-forming mechanisms, including intermolecular forces such as covalent bonds e. For the resulting films or coatings to be edible, the film-forming mechanism involved in fabrication should be an appropriate food process: pH modification, salt addition, heating, enzymatic modification, drying, use of food-grade solvents, or reactions with other food-grade chemicals. The nature of edible packaging films, which is rigid and brittle, causes limitations in food applications. These film structures are brittle due to extensive interactions between polymer molecules Krochta, Mechanical properties could be improved by doping some hydrophilic and hygroscopic plasticizer which can attract water molecules, as a result of having interactions between plasticizer—biopolymer instead of between biopolymer —biopolymer.
Updated and completely revised with the latest discoveries, Edible Coatings and Films to Improve Food Quality, Second Edition is a critical resource for all those.
Edible Coatings and Films to Improve Food Quality 2nd Edition 1420059629
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Alginate is a naturally occurring polysaccharide used in the bio industry. It is mainly derived from brown algae species.
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