**9.6 Shelf life**

228 Olive Oil – Constituents, Quality, Health Properties and Bioconversions

Along with the determination of the best cultivars, the methods of harvesting and processing have been evaluated. Many types of harvesters and extractors, generally from European manufacturers, were being used throughout the industry. Hand harvesting and many types of vibrating rakes, tree shakers and accessories were unsuitable for large scale production. Larger producers investigated straddle harvesters (Fig. 3) which underwent

Processing also went through stages. Some producers tried mechanical mat presses or stone mills (Mailer & Ayton, 2004) in the early stages but these were never used for large scale production The majority of processors have installed modern two or three phase centrifugal

several modifications to make them suitable. These are used widely today.

Fig. 5. One of the early harvesting methods adopted in an Australian olive grove.

As the industry developed, a need for quality evaluation increased. Using the resources of the International Olive Oil Council, Australian laboratories were able to set up methods to determine oil quality. Many of the existing methods were time consuming, reasonably difficult to carry out and expensive. This prompted the investigation of more rapid methods such as the near infra red spectrometry (Mailer, 2004), a rapid screening analytical tool whilst more intensive, wet chemistry methods were maintained as checks where necessary. Minor compounds in olive oil were recognised as the basis of the sensory attributes, nutritional value and stability, or antioxidant capacity, of the oil. Additionally, minor compounds are used to ensure authenticity in Australian research, particularly the sterol profile. As Australian oil has a wide spectrum for each of the sterol components, which may lie outside the limits of the IOC standards, this has been an important focus for Australian scientists (Guillaume et al., 2010). Environmental effects and irrigation on polyphenols both showed a significant effect (Mailer et al 2007). The influence of frost on these compounds and the resulting changes in sensory and chemical characteristics has also been investigated (Guillaume et al., 2009). Frost is one of the most important weather related hazards for the Australian olive industry and has caused significant economic losses during the past decade. Its impact on oil quality has been significant in 2006 with more than 20 per cent of Australian

**9.4 Harvesting and processing** 

extraction mills.

**9.5 Quality analysis** 

Although oil may be acceptable when it is processed, maintaining the quality after processing became a major consideration. Two studies carried out in 2008 by the Australian Olive Association on supermarket oils (AOA Report – unpublished) included 22 oils initially and later, a further 33 oils of random brands. The reports revealed that many oils would not pass IOC tests most likely because of poor storage or old age, although some oils were clearly adulterated. The AOA and RIRDC have funded long term storage studies under extremes of temperature, light and oxygen exposure to determine potential shelf life and develop an understanding of methods used to advise marketing on potential shelf life.

Shelf life depends heavily on the type of material the oil is stored in. Although most experts would recommend the use of glass or stainless steel, often oil is stored temporarily in plastic bottles or collapsible bags. Studies on the effects of the different types of containers used for transport and sometimes for long term storage have been published (Mailer & Graham, 2009). The study reinforces that the best storage conditions for olive oil is in opaque, impervious and inert containers, stored at cool temperatures. Metallised flexible bags used for short term transport may provide reasonable protection. Storage in clear plastic, particularly in the light and at elevated temperatures, is unacceptable and results in loss of extra-virgin olive oil quality within a short period. Re-use of these containers is highly undesirable and would cause more rapid degradation.
