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From Science & Research

From Science & Research Lacquer from tomato for metal cans by D.ssa Angela Montanari, coordinator of BIOCOPAC project 16-hydroxyhexadecanoic acid 16Hid Introduction HO O 10,16-dihydroxyhexadecanoic acid HO O Fig. 4: Composition of tomato cutin OH OH 16Hid-10ol OH Every year millions of tons of tomatoes are used and large amounts of tomato by-products are treated as waste. About 300 million tonnes of by-products, waste and effluent are produced in the EU each year. Tomato waste consists essentially of the fibrous parts of fruits, seeds and skins, and can constitute as much as 2.2% of the weight of the processed tomato. The cost of disposing of these wastes is over 4 €/t. Currently tomato waste is used mainly for animal feed or, once it is dried, as the substrate for the production of fertiliser and lately for the production of biogas. Now BIOCOPAC, a project funded by the EU with € 800,000 under the 7th European Framework, is to develop a biobased lacquer for the protection of metal food packaging, using a natural biopolymer, cutin, extracted from peels and skins of industrial tomato by-products. The idea for the project is based on an old patent developed by SSICA (Stazione Sperimentale per l‘Industria delle Conserve Alimentari) in the 1940. Lacquers for metal packaging The lacquers currently used are based on synthetic resins, mostly epoxy resins. However in recent years those synthetic lacquers have been the subject of several cases of alert due to problems of the migration of residues of polymerisation, monomers and oligomers, plasticizers added to the lacquering system or other additives. The object of the Biocopac project is to develop a natural based lacquer from the tomato skins. In this way Biocopac will meet the demand for sustainable 24 bioplastics MAGAZINE [03/13] Vol. 8

From Science & Research Fig. 2: Dried tomato peels Fig. 1: Separation of tomato peels and seeds from tomato waste Fig. 3: Raw cutin production and for the safeguarding of consumer health, increasing at the same time the competitiveness of the metal can industry, valorising waste produced by the food industry, reducing refuse and obtaining a product with high added value. Analysis of tomato skins Tomato samples, collected in two tomato factories (one in Italy, one in Spain) have been subject to chemical and microbiological analysis. As the lacquer will be in contact with food products, the concentration of heavy metals and pesticides have been analysed. While tin (~ 80 ppb – parts per billion) and copper (4.9-11.8 ppb) were detected, other heavy metals were at values below the quantification limit of the measuring equipment. All samples analyzed for pesticide residues presented values below the significance’s limit. Set-up of the extraction’s method The procedure of extraction of raw cutin from tomato peels consists in a treatment of skins with an alkaline solution and then cutin is separated through precipitation for successive centrifugation after a treatment with an acid solution. This procedure has shown very good results, with regard to the final product obtained, the yield and the reproducibility of the method as well as the applicability of the method even on an industrial scale. The final bioresin obtained with the extraction procedure showed a good ability to form a new bio-lacquer that is the target of Biocopac project. The method has run not only in laboratory but also in a pilot plant with large quantities and high volumes. This is an important result for the project, as regarding a future application of the patent to industries. Naturally some improvements and modifications can be even studied and applied to obtain a continuous process. Analysis of the cutin extracted The composition of tomato skins’ cutin has just been extensively studied in relation to the plant’s botany. Recently Graça [1] provided a tomato cutin consisting of n,16-dihydroxyhexadecanoic acids where the 10-isomer is largely dominant. The tomato cutin is a polyester biopolymer interesterificated. The significant proportion of secondary esters (esterification in the C-10 secondary hydroxyl) shows that the polyester structure is significantly branched. Resin’s production The experimental work, in the consecutive phase, still in progress, has examined the production of the resin. For the production of the cutin-based resin two alternative methods are currently underway: • Homopolymerization of the extracted raw cutin With the homopolymerization the cutin-based resin has been obtained from extracted cutin applying particular experimental conditions of polymerization; in this method the cutin polymerizes with itself to get a higher molecular weight resin. bioplastics MAGAZINE [03/13] Vol. 8 25

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