Advances in Edible Coating for Improving the Shelf Life of Fruits

MAMTATHAKUR1’, ISHRAT MAJID2, and VIKAS NANDA1

'Department of Food Engineering and Technology,

Sant Longowal Institute of Engineering and Technology (Deemed-to-be-University), Longowal 148106, Punjab, India

2Researcher, Department of Food Technology,

Islamic University of Science and Technology, Awantipora,

Jammu and Kashmir (India) - 192122

'Corresponding author. E-mail: This email address is being protected from spam bots, you need Javascript enabled to view it ; thakurma m ta food tech @gma i I. com

ABSTRACT

Recently, the rising consumer demand for safe and healthy foods with increased awareness about the adverse environmental impact of nonbiode- gradable packaging waste is the major drive behind the success of edible coatings. Fruits are one of the healthiest foods, but have shorter shelf-life due to its high perishable nature thus making its perseveration a great challenge. In this regard, the application of edible coatings is the best approach that is applied as a protective covering to control the gas and water exchange and retain the glossiness of fruits. Recently, the new trend of incorporating active compounds like antioxidants, nutraceuticals, antimicrobials, antibrowning agents, etc., into the edible coatings is getting attention because of the unproved functionality. The novel herbal coatings are developed few years ago to meet the needs of consumers to get the natural chemical-free fresh fruits. This chapter discusses the potential of several edible coating materials, like proteins, polysaccharides, lipids, and their composite, in the quality improvement and shelf-life extension.

INTRODUCTION

Fruits are an indispensable constituent of the human diet and are in huge demand recently mainly for inherent functional ingredients and crisp freshlike quality. They are rich in essential minerals, vitamins, flavonoids, dietary fibers, flavor components, and antioxidants thus making fruits quite sensitive commodity to the biotic and abiotic distresses. Fruits are highly perishable living entities that use oxygen and produce carbon dioxide. During the respiration process, carbohydrates and other substrates, including organic acids, proteins, and fats, are metabolized and once metabolized, they cannot be replenished after the fruit or vegetable has been detached from the plant (DeEll et al., 2010). The quality factors of fresh produce, such as texture, color, appearance, flavor, nutritional value, and microbial safety, are measured by plant variety, ripening stage, maturity stage preharvest, and postharvest conditions (Lin and Zhao, 2007). The postharvest losses of fruits are a serious problem because it rapidly deteriorates them during handling, transport, and storage. It is more complicated to extend shelf-life of fruits than that of vegetables as fruits have more complicated physiology with respect to ethylene production and stages of ripeness. The fruit skin may contaminate the flesh encouraging the biochemical reactions, like off- flavor generation, browning, and texture break-down, lowering the quality and growth of pathogens and spoilage microorganisms that ultimately cause the fruit spoilage. Further, the microorganisms, insects, respiration, and transpiration are the main cause of the major quality and quantity losses in fresh fruits during the harvest for consumption (Tiwari, 2014). The harvesting alters the equilibrium between the oxygen consumption and carbon dioxide release thus enhancing the gas transfer rate due to the degeneration of cells. This results in the metabolic losses that lead toward the slight maturation and finally to the senescence of fruits. The several factors, like temperature, species, cultivar, atmospheric composition (02, CO„ and ethylene ratios), growth state, and other stress factors determine the gas transfer rate.

Regulating the respiration process of fruit tissues, their storability and shelf-life can be improved. Therefore, several teclmiques have been developed to extend the shelf-life of fruits. Controlled atmosphere storage (CAP) and modified atmosphere storage (MAP) have been used for preserving the fruits by lowering their quantity and quality losses during storage. The application of edible coatings on the fresh fruits decreases the quality and quantity losses via altering and controlling the internal environment of fruits and hence, may become an alternative to the MAP. The edible coating also ensures the negligible or minimum use of packaging materials that is helpful for maintaining the environment. The edible coating is a thin layer of edible materials that can be safely consumed without incorporating any kind of unfavorable characteristics to the foodstuff. Edible coatings regulating the respiration, ethylene synthesis, and moisture transfer, control the oxygen entrance and fasten the volatile components (Embuscado and Huber, 2009). A definite degree of respiration is offered by the edible coatings that inhibit the fruit tissues from senescence and death. Moreover, the edible coatings are known for canying the food ingredients like colorants, nutrients, antibrowning agents, antioxidants, flavors, and antimicrobial components, thus prolonging the shelf-life of fruits and improving their quality (Pranoto et al., 2005).

A wide literature is available that discusses the advantages of coating the fresh produce. But this chapter particularly focuses on the recent advances in the edible coatings with emphasis on applications to enhance the shelf- life of fruits. The biopolymers have been also discussed that has the potential to act as novel edible coatings for fruits due to their health properties, antimicrobial behavior, wettability, mechanical characteristics, and aesthetic features. The information about the trends of edible coatings as carriers of active components is also updated for improving the functionality, quality, and safety of the fruits along with sensoiy implications. In the end, the regulatory status for edible coating application has been reviewed and future potential of such coatings is provided.

EDIBLE COATING: DEFINITION, CHARACTERISTICS, AND FUNCTIONS

Recently, the increased consumers demand toward the naturally preserved food and more concern about the environmental regulations and sustainability have found a way for the use of edible coating formulations. An edible coating refers to, “a skinny layer of edible material applied on the food surface that can be eaten as a part of whole food and serves as a primary packaging of food, thus, hindering the gas exchange, moisture, and other solute transfer, respiration, and microbial growth for the extension of shelf- life” (Vargas et al., 2008; Mehyar and Han, 2011; Chiumarelli and Hubinger, 2014). Edible coatings are slightly different from the edible films in the way of their use. They are earned in the liquid form to coat the food surface only, whereas the edible films are firstly constructed as the solid sheets, placed either between the food ingredients or used to wrap the food (Falguera et al., 2011). The edible coatings are generally applied by spraying, brushing, dipping, and recently through electrospraying, producing thin and uniform coating (Andrade et al., 2012; Khan et al., 2013). The fruit surface is typically covered with the layers of a variety of edible materials, such as polysaccharides, lipids, proteins, and their derivatives, either alone or in combinations to create a semipermeable film to lower the respiration, regulating the moisture loss, and furnishing several other functions for prolonging the shelf-life. The substances employed for the synthesis of such coatings must hold the FDA approved Generally Recognized as Safe (GRAS) status due to their consumption puipose (Paviath and Orts, 2009).

The idea of edible coating is not novel, it is an age-old technique. Initially, the lipid-based coatings like waxes, including beeswax, candelilla, paraffin, camauba, rice bran, acetylated monoglycerides, and surfactants were successfully employed as fruit-coating formulations (Bourtoom, 2008; Saucedo-Pompa et al., 2009; Mladenoska, 2012; Dhall, 2013). Wax, the first ever edible coating was applied to the oranges and lemons by the Chinese in 12th and 13th centuries because according to them wax-applied fruits had longer storage life than nonwaxed ones without knowing the action of edible coating (Vargas et al., 2008). Coatings were generally applied to prevent the moisture transfer and incorporate the glossiness to the fruit surface until the mid-20th century. The other coatings were mainly composed of proteins, like zein, gelatin, gluten, etc., and polysaccharides, such as cellulose, starch, gums, and their derivatives, etc., that fulfill the necessary overall optical and mechanical characteristics. However, they are greatly sensitive to the moisture exhibiting the poor moisture barrier properties. Natural biopolymers being biodegradable and renewable substances are more preferred to compose the edible coatings than the synthetic biopolymers to substitute the short shelf-life plastics. The most frequently used biopolymer is starch due to its high availability, low price, and easy handling. The cellulose, vegetable proteins, and lipids have been examined as an edible coating in the form of cellulose/polyurethane mixtures, gluten/synthetic resin mixtures, and casein or lipid/synthetic polymer mixtures, respectively (Lin and Zhao, 2007; Azeredo et al., 2009). But most of them are unsuitable in case of the high-moisture foods as they may dissolve, swell, or decay after interacting with water (Wu, 2002).

An edible coating must remain stable under the high relative humidity and should protect the outer membrane of fruits. The thickness of edible coating must be typically less than 0.3 mm and should provide shiny appearance to fruit surface (Tharantham et al., 2003). Then characteristic properties greatly depend on the molecular structure of coating components instead of the chemical constituents and molecular size of compounds. Generally, the edible coatings must possess the properties as shown in Figure 7.1 (Bour- toom, 2008). They must be cheaper, water-resistant, nontoxic, low-viscous, reduce the gas, aroma, and water exchange, and improve the aesthetic value of fruits. Edible coatings are typically colorless, tasteless, and odorless possessing numerous functions, like mechanical properties, gas, and moisture or solute bander, appearance, water/lipid solubility, nontoxicity, etc. Their major characteristic feature is to suppress the respiration rate of the fresh fruits and protect them from postharvest injuries and environmental damages for extending the shelf-life without affecting the fruit quality and causing the anaerobiosis (Tharantharn et al., 2003; Kokoszka and Lenart, 2007).

Major properties exhibited by edible coatings

FIGURE 7.1 Major properties exhibited by edible coatings.

The efficiency of edible coatings strongly relies on the coating thickness and its kind, temperature, alkalinity, and the condition and cultivar of fruit (Dhall, 2013). The edible coatings have the following major functions that benefit the fresh produce (Pranoto et al., 2005):

1. They act as a water vapor barrier to eliminate the issues of moisture loss from the produce surface that otherwise may cause weight loss and alterations in the flavor, appearance, and texture of fruits.

  • 2. They control the gaseous transfer between the fruit surface and its environment thus retarding the respiration rate, enzymatic oxidation reactions, and decay.
  • 3. They regulate the aroma components exchange between the fruit surface and environment thus preventing the natural flavor loss and attainment of odors from surroundings.
  • 4. They protect the fruits from any kind of physical injury due to the pressure, vibrations, impact, and other similar factors.
  • 5. They may contain the functional components including the antioxidant and antimicrobial substances, nutraceuticals, nutrients, antibrowning agents, coloring and flavoring agents in order to prevent the oxidation and discoloration, lower the pathogens loads, and enhance the quality and health properties of fruits. Generally, the antimicrobial substances are directly incoiporated into the foods as a result of which their functional performance may be hindered by the compounds found in the food (Frazao et al., 2017). Therefore, the antimicrobial edible coating is more effective compared with the direct addition of antimicrobial substances because they are gradually or selectively transferred from the outer most coating layer onto the food surface, thus, retaining the higher amount at the most needful site (Valencia-Chamorro et al., 2011).
 
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