Nature has bestowed Pakistan with a versatile environment for cultivation of several varieties of fruit and vegetables. However, post-harvest losses are one of the major problems that decrease the value of food commodities for export and consumption.

Major losses in quality and quantity of fresh fruits and vegetables occur between harvest and consumption, as the overall quality is affected and shelf-life reduced by several factors including water loss, enzymatic browning, texture deterioration, senescence processes and microbial growth etc. Unfortunately, 25 to 40 per cent of harvested fruits and vegetables are lost due to poor post-harvest management resulting in  economic waste.

Many storage techniques including refrigeration, freezing, controlled atmosphere packaging, fungicides, chemical preservatives and additives have been employed to extend the shelf-life of fresh horticulture commodities. Some of these techniques are expensive, may cause chilling injury and allied safety concerns. However, in developed countries, to overcome these drawbacks, an emerging technology known as 'edible coating' has recently been introduced.

When edible coating is applied to a fruit or vegetable, it forms a transparent film that covers food items and acts as a barrier against humidity and oxygen. These coatings improve the overall food quality, extend shelf-life and uplift the economic value of packaging material through modification of gas exchange between tissues and external environment, thus delaying ripening and senescence as well as controlling discolouration and spoilage.

Edible coatings are divided into different categories on the basis of the nature of material from which they are obtained protein-based coatings, polysaccharide-based coatings and lipid and resin-based coatings.

Coatings are applied on fruit and vegetables through various methods like dipping, spraying, foaming and dripping. However, dipping is the easiest method to handle as extra material can simply be drained. A unique characteristic of edible coating is its use as a vehicle for incorporating functional ingredients such as antioxidants, flavours, colours, antimicrobials and nutraceuticals.

Extensive research on edible coatings and films has been done in recent years. Over the last decade, a growing interest in the development and use of bio-based packaging materials to prolong shelf-life and improve quality of fresh, frozen and formulated food products has been witnessed.

A research was conducted on the same lines to introduce edible coatings on apples in the Postgraduate Research Laboratory, National Institute of Food Science and Technology (NIFSAT), University of Agriculture, Faisalabad in Pakistan.

For this purpose, fresh apples were procured that were uniform in size and colour and had no physical damage or fungal infection. After thorough washing and drying, a polysaccharide-based alginate coating was applied. The coating which was prepared in the laboratory with different substances including sodium alginate, glycerol, calcium chloride, N-acetyl cysteine and sunflower oil was heated at 70 degrees centigrade until a transparent material was obtained. This formulation was spread uniformly on fruit surface and upon drying; a coating with adequate adhesion, cohesion and durability was formed. Alginate coating was applied in different concentrations on the fruit i.e. one, two and three per cent.

Physico-chemical analysis of the different treatments were performed on a weekly basis to check the shelf-life of apples including moisture and weight loss, pH, acidity, vitamin C, total soluble solids, texture, colour and sensory evaluation for up to six weeks.

Research revealed that apples containing two and three per cent alginate showed better performance than one per cent alginate. Shrivelling of skin occurred in apples without coating but the coated fruit had a fresh and shiny appearance. Alginate coating worked as a barrier to water vapour by decreasing water loss and protecting the desired texture. Loss of acidity and total soluble solids occurred less in two and three per cent alginate-coated apples.

The pH which increases with the passage of time, appeared less in the coated fruit. Physico-chemical analysis showed that three per cent alginate-coated fruits had more shelf-life than others; however, their sensory characteristics were not as appealing as thick coating reduced the taste of the fruit. On the other hand, higher sensory scores were assigned to two per cent alginate-coated fruits as compared to other treatments. Moreover, the physico-chemical analysis of two per cent alginate-coated fruits also gave better results than that of one per cent alginate-coated and controlled apples.

The overall, highest results of two per cent alginate-coated apples proved to be better compared to all other treatments. Alginate coatings preserved the quality of apples without causing any anaerobic respiration in the fruit.

Alginate coating for food preservation is a promising technology that can improve the quality of fresh products and increase their shelf-life and stability. However, polysaccharide-based coatings are hydrophilic in nature and further research is needed to reduce considerable moisture and shrivelling. In a nutshell, the innovative technique of edible coating must be adopted in Pakistan not only to increase the value of fruit and vegetables in the foreign market but also to attract local consumers.