Effetti dell'impiego di rivestimenti commestibili sulla qualità e shelf life della pera

Edible coatings are thought to minimize the loss and the waste of foods, like fruits or vegetables because of the specific properties that make the shelf life longer. These coatings can be applied to pears, covering the whole fruit or small packaged wedges (fresh-cut pears). In climatheric fruits, like pears, the breathing higly increases because of wounds or cuts and this casuses the worsening some characteristics, like firmness, colour, vitamin and phenolic content. Films aim to reduce these losses preserving qualitative aspects of fruits. Besides, edible coatings have some advantages because they can be directly eaten with the fruit. These substances operate to reduce the moving of oxygen, water, carbonic anhydride, to maintain flavours and to regulate antioxidant agents. Films are rarely composed by only a constituent, they are usually two or three and often an antioxidant is added to them. The compounds most used are starch, zeina of mais, soy proteins, milk and whey proteins, mashed vegetables, alginates, carrageenans, pectins and gellan; besides, the antioxidants are N-Acetylcysteine and glutathione. A team of researchers have produced edible coatings made by mashed fruits, in particular pears and apples. At film compositions they have added lipids in order to increase moisture retention. The results obtained have been great, but whey proteins have been added to realize coatings with more elasticity, transparency and resistance. Films are applied to fruits by different ways: by dipping, by thermoforming, by casting and by extrusion. They can prolong the shelf life of fruits not contained in cold stores or maintain vegetable qualities in the period before being consumed. I present two examples of studies on the use of edible films on both fresh-cut pears and whole fruit;. The first case is carried out on 'Williams' pears, kept at 25° C for 15 days. To types of films that were used are: the first made by carrageenan solution at 0.5% of concentration, the second made by alginate solution at 0.2%. The results obtained showed how coatings can really prolong the conservation of fruit, highly preserving qualitative properties (firmness, weight, soluble solids, acidity). The sodium alginate resulted more efficient than carrageenan with coated fruits without significant changes of quality. It means that it would be probably possible to extend the shelf life of fruits, in the way described, for some days preserving a good quality. The second experiment shows the results of edible coating application on fresh-cut fruit. The fruits used are ' Flor de Invierno' pears, stored at 4° C for one month and, then, cut and packaged. They were covered with three types of film, alginate, gellan and pectin, and compared with uncoated samples. The same types of edible coatings were used added with antioxidants. The applications of edible coatings to fresh-cut fruits reduces the loss of water; the addition of antioxidant is effective on more aspects, like the decrease of ethylene production, microbial deterioration and browning. The content of vitamin C and phenolics is higher and more stable in coated samples with antioxidants, preserving the beneficial functions they can have in human organism. These results are encouraging, so much that edible coatings can be applied on more products reducing the use of plastic material. It is necessary to evaluate costs and methods more efficient to produce the films because now the information about is lacking. They may also be used to maintain storage rooms at higher temperature during storage, with a saving on refrigeration.