Advances in Edible Coatings for Fresh Fruits and Vegetables:

Authors R.K. Dhall,

Edible coatings are an environmentally friendly technology that is applied on many products to control moisture transfer, gas exchange or oxidation processes. Edible coatings can provide an additional protective coating to produce and can also give the same effect as modi?ed atmosphere storage in modifying internal gas composition. One major advantage of using edible films and coatings is that several active ingredients can be incorporated into the polymer matrix and consumed with the food, thus enhancing safety or even nutritional and sensory attributes. success of edible coatings for fresh products totally depends on the control of internal gas composition. Quality criteria for fruits and vegetables coated with edible ?lms must be determined carefully and the quality parameters must be monitored throughout the storage period. Color change, ?rmness loss, ethanol fermentation, decay ratio and weight loss of edible ?lmcoated fruits need to be monitored. The use of different edible coatings (polysaccharides, proteins, lipids and composite) as carriers of functional ingredients on fresh fruits and vegetables to maximize their quality and shelf life. Also includes incorporation of antimicrobials, texture enhancers and nutraceuticals to improve quality and functionality of fresh-cut fruits. Vegetables and fruits are highly perishable as they contain80–90% water by weight. If they are left without cuticle, the water quickly begins to evaporate, resulting in poor product shelf life. Major losses in quality and quantity of fresh fruits and vegetables occur between harvest and consumption. When the fruit is harvested, there is a change of the gaseous balance between the consumption of oxygen and the production of car-bon dioxide. In this new condition, the cells are not renewed, and the gas transfer rates increase, causing a metabolic loss and taking the fruit to a gradual maturation and eventual senescence. The gas transfer rate depends upon internal and external factors. The internal factors include the species, cultivar, and growth state, while the external factors include the atmospheric composition (O2,CO2, and ethylene ratios), the temperature, and other stress factors , In addition, contamination of the fruit ?esh can occur from the skin, increasing the fruit spoilage leading biochemical deteriorations such as browning, off-?avor development, and texture breakdown, decreasing the fruit quality and the risk to consumer due to pathogenic micro-organisms presence. Different types of Salmonella as well as E.coli O157:H7 have been implicated in food borne outbreaks by consumption of cantaloupe, honeydew, and watermelon. The optimum extension of the postharvest life of food products is critically dependent upon three factors:(1) reduction in desiccation, (2) reduction in the physiological process of maturation and senescence, and (3) reduction in the onset and rate of microbial growth. Several techniques like controlled atmosphere storage and modi?ed atmosphere storage have been used for preserving fruits by reducing their quality changes and quantity losses during storage. Edible coatings on fresh fruits and vegetables can provide an alternative to modi?ed atmosphere storage by reducing quality changes and quantity losses through modi?cation and control of the internal atmosphere of the individual fruit or vegetable. Edible coatings may contribute to extend the shelf life of fresh fruits and vegetables by reducing moisture and solute migration, gas exchange, respiration, and oxidative. reaction rates as well as by reducing or even suppressing physiological disorders. Edible coatings have a high potential to carry active ingredients such as ant browning agents, colorants, ?avors, nutrients, spices, and antimicrobial compounds that can extend product shelf life and reduce the risk of pathogen growth on food surface, Moreover, another important advantage of edible coating is the reduction of synthetic packaging waste because these coatings are composed of biodegradable raw material. Edible coatings are thin layers of edible material applied to the product surface in addition to or as a replacement for natural protective waxy coatings and to provide a barrier to moisture, oxygen, and solute movement for the food, re applied directly on the food surface by dipping, spraying, or brushing to create a modi?ed atmosphere. Edible and biodegradable coatings must meet several special functional requirements, for example, moisture barrier, solute or gas barrier, water/lipid solubility, color and appearance, mechanical characteristics, nontoxicity, etc. The effect of coatings on fruits and vegetables depends greatly on temperature, alkalinity, thickness and type of coating, and the variety and condition of fruit and vegetable. The functional characteristics required for the coating depend on the product matrix (low to high moisture content) and deterioration process to which the product is subjected. Fruits and vegetables continue to respire even after harvest and use up all the oxygen with in the produce, which is not replaced as quickly as by edible coating and produces carbon dioxide, which accumulates within the produce because it can-not escape as easily through coating. Eventually the fruit and vegetable will shift to partial anaerobic respiration that requires less oxygen (1–3%). With less oxygen, the production of ethylene (which accelerates ripening process) is disrupted, and physiological loss of water is minimized. Thus, fruits and vegetables remain ?rm, fresh, and nutritious for longer periods, and their shelf life almost doubles. The natural barrier on fruit and vegetable, and the type and amount of coating will influence the extent to which the internal atmosphere (oxygen and carbon dioxide) are modi?ed and the level of reduction in weight loss. The properties of edible coating depend primarily on molecular structure rather than molecular size and chemical constitution. Speci?c requirements for edible ?lms and coatings are: The coating should be water-resistant so that it remains intact and covers a product adequately, when applied, it should not deplete oxygen or build up excessive carbon dioxide. A minimum of 1–3% oxygen is required around a commodity to avoid a shift from aerobic to anaerobic respiration. It should reduce water vapor permeability. It should improve appearance, maintain structural integrity, improve mechanical handling properties, carry active agents (antioxidants, vitamins, etc.) and retain volatile ?avor compounds. It should melt above 40?C without decomposition. It should be easily emulsi?able, non-sticky, or should not be tacky, and have ef?cient drying performance. It should never interfere with the quality of fresh fruit or vegetable and not impart undesirable order. It should have low viscosity and be economical. It should be translucent to opaque but not like glass and capable to tolerate slight pressure. Fruits and vegetables that are coated include Fruits: Apple, kinnow, grapefruit, passion fruit, avocado, orange, lime, peach, and lemon. Vegetables: Cucumber, bell pepper, melons, tomato. Fresh-cut products are highly perishable, the main reason being the removal of skin (the natural protective layer) from their surface area and the physical stress they undergo while peeling, cutting, slicing, shredding, trimming, coring, etc. Fresh-cut fruits and vegetables on which coating is used commercially include Fruits: Fresh-cut apples, fresh-cut pear, and fresh-cut peach. Vegetables: Minimally processed carrot, fresh-cut lettuce, fresh-cut cabbage, minimally processed onion, fresh-cut potato, fresh-cut tomato slices, fresh-cut muskmelon, and cantaloupe