Multifunctional Fruit Coating

About

World hunger is a mounting concern. It impacts over 800 million people, which translates to ~10.7% of the world’s population. However, ⅓ of the food produced around the globe is never consumed. Partly this owes to the food loss during the distribution phase, and partly because of arching over the best-by-date of the food in retail stores. This is particularly critical for fresh products such as fruits and vegetables since they are an integral part of our regular diet, providing us with the benefits of various nutrients and vitamins. However, the major challenge faced by the industry is that they are easily perishable with a shelf life of only a few days. Around 40−50% of the fruits and vegetables produced in the field are wasted every year before consumption. The main factors affecting the quality and post-harvest life of fruits are attributed to water loss, enzymatic browning, texture deterioration, senescence processes, and microbial growth. In an effort to reduce food shortages, this issue is often addressed by the development of genetically modified products or chemical additives and inedible coatings, which create additional health and environmental concerns. To date, different methods have been incorporated to improve the shelf life of perishable foods. A common practice to extend the shelf life is a method called fruit waxing. This artificial wax coating (including weak organic acids and their derivatives, like acetic, lactic, benzoic, and sorbic acids, aldehydes, and esters) enters the human body during consumption. Although this method prevents water loss and spoilage, and the outgrowth of microbial cells, on entering the human body, the cells fragment the preservatives into ions to maintain the physiological balance, resulting in several adverse effects, including toxic ion accumulation, membrane disruption, and essential metabolite inhibition. Other prevalent methods to increase shelf-life include refrigeration, modified atmospheric packaging (MAP) with increased concentrations of carbon dioxide, and paraffin-based active coatings. However, these methods are expensive, time-consuming, visually alter the appearance of fruits, and affect the flavor. The strategies to extend the post-harvest life of perishable products are based on reducing three factors: maturation and senescence, dehydration, and rate of microbial growth. Some other factors should also be considered, including biocompatibility, biodegradability, edibility, wash-ability, membrane forming capacity, and safety. However, to date, the practical combinations of such coating are not commercially available, and the literature has generally failed to meet the expectations on a larger scale. Our innovation to overcome these challenges can be fallen into two general categories: 1) development of edible and washable protein-based coatings through various chemical modifications that can meet the above-mentioned criteria and 2) the development of processing techniques to scale-up production. In our innovation, the coating components we select, from solvents to solutes (polymeric solution), are all from natural sources. Our multifunctional conformal edible coating is comprised mostly of animal/vegetable protein and cellulose that slows down fruit decay by retarding ripening, dehydration, and microbial invasion. Besides, while the coating is formed to make the fruit less permeable to water, prior to consumption, it can easily be washed away, unlike wax-based coatings. Our coating has a similar glossiness as the commercial inedible wax coating. Also, the edible and washable coating is made from readily available inexpensive or waste materials, making it a promising economic sustainable alternative and a solution to combat food wastage that is rampant in the world. The coating has been developed based on poly(albumen) protein and cellulose nanocrystals and can be coated conformally onto different perishable fruits as a micron-thickness coating using different approaches such as dip and spray coating. The coating successfully reduces microbial growth, respiration, and dehydration of fruits, all of which contribute to an increased shelf-life while being edible and washable. As a proof-of-concept, avocadoes, papayas, and bananas have been utilized to demonstrate the effectiveness of the coating. The coating preserves the cosmetic appearance and shelf life of the fruits for longer and is easily washed off so that the taste for consumers is not altered. We have developed the cellulose nanocrystal reinforced poly(albumen) nanocomposite coating with various biocompatible modifiers to extend the shelf-life and cosmetic appearance of fruits. To synthesize the nanocomposite coating, we start with egg whites, comprised mostly of albumen protein (~54%), and enable the dried formation of strong edible films with a moderate gas barrier property. However, poly(albumen) is very brittle owing to its random organization of denatured proteins. The addition of plasticizers, such as glycerol, reduces intermolecular forces in the protein chain and increases mobility in the protein-polymer chains and their flexibility. Therefore, an egg white plasticized with glycerol is capable of coating irregularly shaped objects like fruit without cracking. However, glycerol is hydrophilic and swells in humid environments. To prevent unwanted swelling, we incorporated a small fraction of egg yolk, which is hydrophobic and rich in fatty acids and can alleviate the susceptibility to moisture. Next, we added curcumin, which is an edible extract from turmeric that possesses antibacterial, antifungal, and antibiofilm properties. These properties reduce microbial growth on the fruit surface while also decreasing oxygen and increasing carbon dioxide in the microenvironment, which helps to maintain the fruit’s freshness. Lastly, we incorporate cellulose nanocrystals to reduce the water and gas permeance of the coating and to add mechanical reinforcement. Although our coating is based on poly-albumen protein, the coating can be extended to agricultural proteins such as soy and corn considering the allergy effect of consumers. Hence, we believe this innovation presents a promising approach to addressing the global food waste problem as an environmentally friendly, highly scalable, and low-cost freshness preserver.