Olive oil was discovered by early man, as he accidentally crushed fallen olive seeds and noticed that the segregated oil moistened. Since ca. 5000 BC, people have collected and squeezed olives in stone mortars, but the Romans expedited the crushing operation with a millstone crusher, the trapetum , and improved the separation system with the introduction of presses ( Kiourellis, 2005 ). Following the fall of the Roman Empire there were no innovations in olive oil processing for many years, which continued to be based on the screw press ( Di Giovacchino, 2000 ). In 1795 the hydraulic pressing system was invented ( Balatsouras, 1986 ). Since the second half of the 20th century many technological improvements and innovations have occurred ( Kapellakis et al., 2008 ). Olive oil separators have replaced the traditional methods, and productivity has been increased with the widespread adoption of hydraulic pressing systems. The pressing process has been the most widespread method for processing olive fruit to obtain olive oil. The use of stone rollers or wheels on a slab of stone allows the grinding of olives and kneading the resulting olive paste. The olive paste was drenched with hot water, in order to achieve better separation of olive oil, and then placed in oil diaphragms. In 1960 a new process for separation of oil from olive paste was introduced, based on the density differences of the olive paste constituents (olive oil, water and insoluble solids). Separation is accomplished through a horizontal centrifuge. At the same time, the rotating wheels were replaced with metallic crushers (hammer crusher and disk crusher). In order to preserve the kneading operation that occurred using rotating wheels, a new machine was introduced: the malaxer machine. Thus, a new phase in the procedure was introduced: the malaxation phase. Malaxing is an extremely important phase in olive oil extraction. During the malaxing phase the olive paste is subjected to a slow continuous kneading, aimed at breaking off the emulsions formed during the crushing process and facilitating adequate coalescence. It is necessary to heat the olive paste at a carefully monitored temperature during malaxation in order to diminish the viscosity of the product and to stimulate its enzymic activity, therefore increasing the extraction yields. This operation facilitates high extraction yields, by helping small oil droplets to coalesce. These can be separated subsequently using a decanter centrifuge ( Di Giovacchino, 2000 ). The malaxing process determines the balance between the quality and the quantity of the oil extracted, by varying a range of parameters (time, temperature and atmosphere in contact with the olive paste), as the olive paste is gradually heated and the enzymes within are activated. All this must be done without affecting the biochemical structure of the olive paste, as this would affect the flavor, shelflife and nutritional properties of the oil ( Amirante et al., 2006 ). This operation is one of the critical points in olive oil extraction. Many studies have been carried out to investigate its influence on the olive oil quality. Nowadays the olive oil consumer asks for healthy products. There has been a large increase in demand for high-quality virgin olive oil, attributed not only to its potential health benefits, but also to its particular organoleptic properties. In fact, the sensory quality plays an important role in customer preferences ( Angerosa et al., 1998 ). The operating environment during malaxation affects the volatile and phenolic composition of virgin olive oil and, as a consequence, its sensory and healthy qualities. The sensory and health-related properties of virgin olive oil are closely linked to its volatile and phenolic composition ( Reiners and Grosch, 1998 ; Servili et al., 2002 ). The presence of these substances in the oil is the end result of various endogenous enzymatic activities activated during processing of the olive fruit ( Morales et al., 1999 ; Angerosa et al., 2001 ). Research on olive oil quality has also shown the effect of the oxygen concentration in the head space of malaxer on the activities of these enzymes and hence on the olive oil quality itself. Processing conditions strongly influence rheological properties of the olive paste. These in turn determine the behavior of the paste during the sedimentation and can thereby influence the extraction yield ( Di Renzo and Colelli, 1997 ). Extension of the malaxation time improves the yield but can damage the final quality of the product. In order to correct for this potential disadvantage modifications have to be made to the malaxing system ( Amirante et al., 2002 ). Much research has targeted the efficiency of this innovative continuous system, with many changes to the malaxer machine, aimed at improving the eventual olive oil quality ( Amirante et al., 2005, 2006, 2008a, 2008b ).

The Malaxation Process: Influence on Olive Oil Quality and the Effect of the Control of Oxygen Concentration in Virgin Olive Oil

LEONE, ALESSANDRO;
2010

Abstract

Olive oil was discovered by early man, as he accidentally crushed fallen olive seeds and noticed that the segregated oil moistened. Since ca. 5000 BC, people have collected and squeezed olives in stone mortars, but the Romans expedited the crushing operation with a millstone crusher, the trapetum , and improved the separation system with the introduction of presses ( Kiourellis, 2005 ). Following the fall of the Roman Empire there were no innovations in olive oil processing for many years, which continued to be based on the screw press ( Di Giovacchino, 2000 ). In 1795 the hydraulic pressing system was invented ( Balatsouras, 1986 ). Since the second half of the 20th century many technological improvements and innovations have occurred ( Kapellakis et al., 2008 ). Olive oil separators have replaced the traditional methods, and productivity has been increased with the widespread adoption of hydraulic pressing systems. The pressing process has been the most widespread method for processing olive fruit to obtain olive oil. The use of stone rollers or wheels on a slab of stone allows the grinding of olives and kneading the resulting olive paste. The olive paste was drenched with hot water, in order to achieve better separation of olive oil, and then placed in oil diaphragms. In 1960 a new process for separation of oil from olive paste was introduced, based on the density differences of the olive paste constituents (olive oil, water and insoluble solids). Separation is accomplished through a horizontal centrifuge. At the same time, the rotating wheels were replaced with metallic crushers (hammer crusher and disk crusher). In order to preserve the kneading operation that occurred using rotating wheels, a new machine was introduced: the malaxer machine. Thus, a new phase in the procedure was introduced: the malaxation phase. Malaxing is an extremely important phase in olive oil extraction. During the malaxing phase the olive paste is subjected to a slow continuous kneading, aimed at breaking off the emulsions formed during the crushing process and facilitating adequate coalescence. It is necessary to heat the olive paste at a carefully monitored temperature during malaxation in order to diminish the viscosity of the product and to stimulate its enzymic activity, therefore increasing the extraction yields. This operation facilitates high extraction yields, by helping small oil droplets to coalesce. These can be separated subsequently using a decanter centrifuge ( Di Giovacchino, 2000 ). The malaxing process determines the balance between the quality and the quantity of the oil extracted, by varying a range of parameters (time, temperature and atmosphere in contact with the olive paste), as the olive paste is gradually heated and the enzymes within are activated. All this must be done without affecting the biochemical structure of the olive paste, as this would affect the flavor, shelflife and nutritional properties of the oil ( Amirante et al., 2006 ). This operation is one of the critical points in olive oil extraction. Many studies have been carried out to investigate its influence on the olive oil quality. Nowadays the olive oil consumer asks for healthy products. There has been a large increase in demand for high-quality virgin olive oil, attributed not only to its potential health benefits, but also to its particular organoleptic properties. In fact, the sensory quality plays an important role in customer preferences ( Angerosa et al., 1998 ). The operating environment during malaxation affects the volatile and phenolic composition of virgin olive oil and, as a consequence, its sensory and healthy qualities. The sensory and health-related properties of virgin olive oil are closely linked to its volatile and phenolic composition ( Reiners and Grosch, 1998 ; Servili et al., 2002 ). The presence of these substances in the oil is the end result of various endogenous enzymatic activities activated during processing of the olive fruit ( Morales et al., 1999 ; Angerosa et al., 2001 ). Research on olive oil quality has also shown the effect of the oxygen concentration in the head space of malaxer on the activities of these enzymes and hence on the olive oil quality itself. Processing conditions strongly influence rheological properties of the olive paste. These in turn determine the behavior of the paste during the sedimentation and can thereby influence the extraction yield ( Di Renzo and Colelli, 1997 ). Extension of the malaxation time improves the yield but can damage the final quality of the product. In order to correct for this potential disadvantage modifications have to be made to the malaxing system ( Amirante et al., 2002 ). Much research has targeted the efficiency of this innovative continuous system, with many changes to the malaxer machine, aimed at improving the eventual olive oil quality ( Amirante et al., 2005, 2006, 2008a, 2008b ).
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11369/8739
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact