Washing the Olives
The Importance of Washing Olives Before Pressing: A Complete Review
Explore the crucial role of olive washing before pressing in the production of high-quality virgin olive oil. Discover its impact on oil quality, microbiological activity and contaminant removal.
Introduction
The production process of high-quality virgin olive oil (VOO) involves several critical steps, one of which is washing the olives before pressing. This report aims to provide an in-depth analysis of the importance of olive washing, based on peer-reviewed studies and authoritative sources such as PubMed. The objective is to examine how washing affects oil quality, the microbiological profile of olives, and the presence of contaminants such as pesticides.
Context
Washing olives is a standard practice in the olive oil industry, primarily aimed at removing dirt, dust, and other contaminants from the surface of the fruit. However, the implications of this step go beyond mere cleaning. Washing can affect the microbiological activity on the olives, the chemical composition of the oil, and the presence of pesticide residues. Understanding these effects is critical to optimizing the quality of VOO.
Microbiological Impact
Increased Microbial Load
One of the main findings in the literature is that olive washing can significantly alter their microbiological profile. A PubMed study found that immersing healthy freshly harvested olive fruits in contaminated water from an olive mill washing tank resulted in a significantly increased presence of lactic acid and enteric bacteria, fungi, and Pseudomonas on the surface of the olives. The microbial load increased by 2-3 orders of magnitude compared to hand-picked control samples. This increase in microbial activity may have several downstream effects on oil quality.
Biogenesis of Volatile Compounds
The same study also observed that the microbiological profile of olives significantly influenced the biogenesis of volatile compounds and the extraction of polyphenols and pigments from olives. These changes occurred even without any previous storage of olives. The presence of some microorganisms can lead to the formation of off-flavors and other sensory defects in oil, thus affecting its overall quality.
Chemical Composition
Ethanol Content
Another critical aspect affected by olive washing is the ethanol content in both the fruit and the oil. According to a study published in PubMed, olive washing resulted in an increase in the ethanol content in the fruit. This increase was also reflected in a higher concentration of ethanol in the oil. Ethanol is a precursor to ethyl esters, compounds that can negatively affect the sensory characteristics of oil. The study concluded that olive storage should be avoided or reduced to less than 12 hours and, if possible, olives should not be washed before storage to prevent loss of sensory characteristics and ethanol synthesis.
Phenolic Compounds
Phenolic compounds are crucial to the antioxidant properties and overall health benefits of VOO. A study on the application of a cold-pressing system to olives prior to oil extraction, published in PubMed, found that this method significantly improved the amount of oil extracted and increased its concentration of total phenols by up to 33%. Although this study did not specifically focus on washing, it does highlight the importance of processing methods in preserving phenolic content.
Pesticide Residues
Washing Effectiveness
The presence of pesticide residues in olives and their subsequent transfer to olive oil is a significant concern. A study aimed at evaluating the fate of five pesticides in olives, published in PubMed, found that olive washing could effectively reduce pesticide residues, especially if performed shortly after pesticide application. The study used gas chromatography-mass spectrometry to analyze residues and found that washing performed one day after treatment was the most effective in reducing residues, particularly for simazine. However, the fraction of pesticides not removable by washing increased with time after treatment until their degradation began in the sixth week.
Industrial Practices and Recommendations
Conservation and Processing
The industrial conditions in which olives are stored and processed can significantly affect oil quality. According to the ethanol content study (PubMed), industrial conditions resulted in more significant increases in ethanol content in oil than hand-processed olives. After 24 hours of storage, oils were classified as 'virgin' rather than 'extra virgin' due to sensory defects. This finding highlights the importance of minimizing storage time and optimizing washing practices to maintain oil quality.
Emerging Technologies
Several new and emerging technologies are being explored to improve the quality of VOO. A review in PubMed discussed the impact of technologies such as pulsed electric fields, high pressure, ultrasound, and microwave treatment on the yield, quality, and content of minor compounds and bioactive components in VOO. These technologies offer potential benefits in terms of improving the extraction process and oil quality, although their application in the context of washing and early processing stages requires further investigation.
Environmental and Economic Considerations
Valorisation of By-Products
The olive oil extraction process generates several by-products, including olive wash water (OWW) and olive mill solid waste (OMSW). A study on the complete valorization of these by-products, published in PubMed, explored the use of the microalgae Raphidocelis subcapitata to treat OWW and OOWW. The microalgal biomass was then used as a co-substrate for anaerobic co-digestion with OMSW, improving methane yield and integrating all by-products into a complete valorization system. This approach not only addresses environmental concerns but also contributes to a circular economy in the olive oil industry.
Health Benefits of By-Products
Olive pomace, a by-product of the olive oil extraction process, contains high concentrations of dietary fiber and phenolics with significant antioxidant capacity. A study on the health benefits of drum-dried olive pomace, published in PubMed, found that incorporating this by-product into a high-fat diet for mice resulted in lower weight gain and reduced body fat. The study highlighted the potential of olive pomace as a novel agricultural by-product with bioactive compounds that can be used in feed and food to provide health benefits.
Conclusion
Washing olives before pressing is a critical step that can significantly affect the quality of virgin olive oil. Although washing can effectively remove dirt and reduce pesticide residues, it also increases the microbial load on olives, which can affect the biogenesis of volatile compounds and the extraction of polyphenols and pigments. In addition, washing can lead to an increase in the ethanol content of the oil, negatively affecting its sensory characteristics. Therefore, it is recommended to minimize storage time and optimize washing practices to maintain oil quality. Emerging technologies and by-product valorization offer promising avenues to improve the sustainability and economic viability of the olive oil industry.