*5.2.2. Steel and tinplate*

210 Olive Germplasm – The Olive Cultivation, Table Olive and Olive Oil Industry in Italy

and, in Italy to a lesser degree, plastic and polycoupled ones.



*5.2.1. Glass* 

after it is sealed and the oxygen diffused through the walls



The principal used materials for olive oil packaging are represented by glass, steel, tinplate

Glass represents an ancient material used in container structure: first glass containers derived by rocks date back to 3000 BC. It is formed principally by silica obtained by sand, flint or quartz. Silica is fused at very high temperatures (about 1720 °C) to form silicated glass. In most cases, silica is mixed with variable proportions to several raw materials: e.g. sodium and potassium carbonates (which act as stabilizer and protect the glass from the water solubilisation), lead (which confers transparency and lightness) and aluminium (which increases its hardness and lastingness). Glass is neither in a solid nor in a liquid state but glassy. Its molecules are arranged in disarray but with a sufficient cohesion to give mechanical stiffness. The structural basic unit is represented by the silica-oxygen tetrahedron, in which a silica atom is surrounded by four oxygen atoms to form a tetrahedron. Big groups tend to dispose with disorder (amorphous structure) giving the glass fragile with the tendency to rupture if submitted to an excessive tension. This induces effects on its thermal resistance that is function of container type, packaging faces and exposed surface to tension (internal if warmed and external if cooled) (Robertson, 2009).

In Italy glass is the king container for the olive oil packaging. Glass bottles can have different forms and capacities and their colour can vary largely from white to green and more dark tints. In Figure 1 several size of glass bottles are presented to demonstrate the large offer in the Italian olive oil market also of aromatized oils with spices or hot pepper.

From an Italian research about the most diffused containers, 64%of olive farms use the green glass whereas only the 10% of the total chooses the transparent one (Ricci, 2007). The best containers for the olive oil are made in opaque and dark glass: it is advisable to prefer very dark ones because little light can pass through. Since the consumer appreciates also the light glass because it is transparent and so shows the oil colour, then it is advisable to supply the bottle with a paper case which can protect the product by light. Guil-Guerriero and Urdo Romacho (2009) reported a shelf life study carried out on oils produced from *Picual*, *Hojiblanca* and *Arbequina* cultivars packaged in dark and transparent glass bottles. These oils showed an increase in some parameters; the variation of peroxide value was significant in extra virgin olive oils stored in transparent glass. Similar results were observed by Del Caro et al. (2006) and Vacca et al. (2006) on *Bosana* extra virgin olive oils. Several studies


First uses of this material date back to 1700 in domestic environment. Steel is an iron/carbon alloy: the higher the carbon percentage, the higher the rupture limit.

The tinplate is a sheet of soft steel, which is more workable because of its lower carbon content, coated on both faces by tin oxides layers and on face destined to the contact with food also by organic synthetic lacquers. Tinplate container is mainly of rectangular shape; its side seam is welded and protected with a food-approved special varnish: the welding method assures a secure side seam, avoiding the dissolution of lead into the product (Tsimis & Karakasides, 2002).

The inox steel is an alloy containing 11% of chrome which reacts with oxygen originating an autopassivation condition due to the chrome oxides presence (Piergiovanni & Limbo, 2010). It is the best material for the preservation of big volumes of olive oil. Compared to glass, it has the same water resistant properties (so protects the product from oxygen, humidity and microrganisms), and major advantages, e.g. handless, cleanness, shock resistance and total light protection.

A research of Grover (1982) demonstrated that the quality of oils decreases if packed in reused tinplate containers, whereas new containers did not alter oils during the one year storage period. A more recent study confirmed that the storage of oils in stainless and dark glass appears more adequate, with respect to other packaging materials, as clear PET and clear glass (Dabbou et al., 2011).

Tin plate is used for the olive oil retail both in bigger volume size (3-5 L) and in smaller bottles (1 L). A recent study of Rababah et al. (2011) on olive oil samples stored for 60 months at light in bottles of 2.5 L denoted higher sedimentation amount in tinplate than in the other containers and a strong reduction of sensory attributes, probably due to the reaction of other components in olive oil, e.g. phenol compounds, with tinplate that negatively affected the descriptive attributes.

Packaging and Storage of Olive Oil 213

containers is developing. Contemporary trends in olive oil packaging include dark coloured glass bottles and PET bottles which have incorporated oxygen scavengers. These are used in order to prolong the shelf life of foods whose degradation kinetic depends on the partial pressure of oxygen inside the container. In particular, Del Nobile et al. (2003) confirmed that oxidation kinetics slower than that found with glass bottles can be obtained by bottling the olive oil into materials containing an oxygen scavenger. However, the slowest decay kinetics were obtained by bottling the oil in PET containers and by reducing the oxygen concentration prior to bottling to 10% of the equilibrium value. Also Gambacorta et al. (2004) studied the effect of several percentages of oxygen scavengers and of barrier resin included in PET on olive oil quality, and indicated that the materials having higher oxygen barrier properties can slow

Policoupled materials are mainly represented by a triple coupled material formed by Low Density Polyethylene (LDPE)/paper/LDPE and a thin aluminum foil between further polyethylene layers as barrier respectively to gas, light and liquids. It is a parallelepiped with rectangular section, the most known version of which is the Tetra Brik®, also named

Tetra Prisma allows an ideal storage for distributors and consumers. For the packaging of vegetable oils including olive oil is being used today in some Mediterranean countries, e.g. Spain and Greece, in the form of brick-type cartons and bag-in-box pouches. It is a very revolutionary packaging because guarantees a total and prolonged protection of olive oil chemical and physical characteristics up to two years. This material permits also to update the packaging aspect, with a more coloured, snappy and modern graphic design. Besides preserving the quality, Tetra Prisma allows the producer a major differentiation in packaging, logistic efficiency, lower probabilities of rupture during transfer and, not least, a 100% recyclable package. From the consumers point of view, the pack is indestructible, easy to take and handle. The realized cap contributes to protect from oxygen and it is for a prolonged use, with the aim to avoid the drip, the product spill after opening and to facilitate the pouring, regulating the flow and cutting the drip. In Italy, the olive oil packaged in Tetra Prisma was proposed in 2005 with opposite considerations (Soressi, 2007). Studies have been conducted also on this material type to evaluate its performance as container for oil. It is efficient in maintaining antioxidants in stored product for several months, due to its efficient barrier to light and oxygen, unlike the transparent glass and plastic materials, despite these last show a low gas permeability (Mendez & Falque, 2007).

Glass is the preferred packaging material in Italy for olive oil, and the most used bottle shape is the *marasca* type. It is chosen for three aspects: small price, the best shelf management and the functionality. The most diffused bottle volume is 0.75 L, followed by 0.5 L; the use of other volumes is very marginal. A research developed in 2005 on 48

down the quality decay kinetics of extra virgin olive oil.

**5.3. Olive oil packaging shape and size** 

*5.2.4. Policoupled material* 

Tetra Prisma.
