This study investigated the effects of water and content of solid particles, taken together as well as separately, on stability of veiled olive oil. The following oil samples were obtained through four different separation treatments: veiled, filtered, ‘solid-only’, and ‘water-only’. Changes in chemical, microbial, and sensory characteristics were evaluated during storage (240 days). A significant effect of hydrolysis was shown in veiled and ‘water only’ oils; in ‘solid-only’ oils, a slow increase of phenols was observed. A notable microbial activity, with resulting formation of volatile metabolites and sensory defects, was observed in veiled samples. Filtered oils underwent less significant changes.

Preservation of quality during storage is an important subject for extra-virgin olive oil (EVOO) producers (

Cloudy aspect of veiled extra-virgin olive oils (VEVOO) is due to the presence of micro-droplets of water and fragments of olive pulp and stone suspended/dispersed in the oil phase (

The difference between VEVOO and filtered extra-virgin olive oil (FEVOO) during storage is still a controversial and widely studied topic for the quality of olive oil (

On the other hand, in literature, improvement in shelf life because of elimination of sediment by filtration was evidenced. In VEVOO, solid particles and water micro-droplets trap microorganism, mainly yeasts, and constitute a perfect environment for microbial survival (

Given the conflicting results about the role of turbidity on the stability of VEVOOs, in this work, an original research was carried out on the different role of water and insoluble solid particles content during storage of EVOO by testing a wide spectrum of olive oil ‘turbidities’.

The present work is a part of wide study on the turbidity and stabilization of olive oil. The first contribution (

Finally, the present work aimed (i) to study the contribution of dispersed water droplets or solid particles, which, to different extent, contribute to turbidity in VEVOOs and affect the qualitative characteristics of olive oil during a simulated medium storage period, and (ii) how important the qualification of olive oil turbidity could be to plan separation techniques during crop seasons and storage of olive oil.

EVOO samples were extracted in October–November 2017 in an industrial continuous plant (TEM, Florence, Italy) in Azienda Agricola La Ranocchiaia (Florence, Italy). The plant was equipped with the following: olive cleaner, blade cutter crusher, sealed vertical malaxer (300 kg), and two-phase horizontal centrifuge (i.e., decanter). The malaxation was carried out at 18°C for 20 min.

Six different 300-kg batches of blend of olive cultivars, harvested in Tuscany, were processed on three different days in 2017: olive oils #1 and #2 were processed on October 31, 2017; olive oils #3 and #4 were processed on November 7, 2017; and olive oils #5 and #6 were processed on November 28, 2017.

Six 20-kg batches of oil from each batch of blended olive cultivars were collected at the end of ‘decanter’, immediately transferred to the laboratory, and subjected to the following four different water and solid particle separation treatments: (1) first ¼ of oil batches (5 kg of oil) were untreated, forming VO samples for this study (i.e., samples VO#1–VO#6); (2) second ¼ of oil batches (5 kg of oil) were filtered using a portable filter press (Colombo Inox 12, Rover Pompe, Padua, Italy) equipped with five filter sheets (Rover 8, 3-μm cut-off, Rover Pompe, Padua, Italy), forming FO samples for this study (i.e., samples FO#1–FO#6); (3) third ¼ of oil samples (5 kg of oil) were freeze-dried (Modulyo, Edwards, Milan, Italy), forming the ‘solid particle-only’ (SO) samples for this study, that is, freshly extracted olive oil containing solid particles only without water (i.e., samples SO#1–SO#6); and (4) last ¼ of oil samples (5 kg of oil) were filtered with glass wool using a filter aid to separate solid particles, forming ‘water-only’ (WO) samples for this study, that is, freshly extracted olive oil containing water only without solid particles (i.e., samples WO#1–WO#6).

All oil samples obtained (4 treatments × 6 different oil batches = 24 oil samples) were bottled in 0.25-L clear glass bottles with a headspace of about 8% of bottle’s volume, and immediately analyzed to measure turbidity characterization parameters (i.e., degree of turbidity, water content, water activity, solid particles content, and microbial cell count) as described in

For storage test, all olive oil samples (4 treatments × 6 different oil batches × 4 storage periods = 96 oil samples) were bottled in 0.25-L clear glass bottles with a headspace of about 8% of bottle’s volume. These were stored at room temperature (20°C) in a chamber (1.3 × 1.0 × 0.8 m) with internal walls covered with reflective material and a light intensity of 1,900 lux (Master TL-D 90 Graphica lamp, 35 W/390, Philips, Amsterdam, the Netherlands) for 12 h per day. After 45, 120, 180, and 240 days of storage, the olive oil samples were analyzed to measure FFA, PV, K232, K270, ΔK, and phenolic and volatile compounds content and sensory parameters.

The degree of turbidity was measured in nephelometric turbidity unit (NTU) using a Hach Model 2100 turbidimeter (Hach, Loveland, CO, USA). Water content, calculated as percent of water content weight/100-g olive oil sample (% w/w), was analyzed with a Karl Fischer Kit for visual water determination without titrator (37858 HYDRANAL – Moisture Test Kit, Honeywell Fluka, Bucharest, Romania). Water activity (Aw) was measured using a Rotronic Hygroskop DT hygrometer (Michell Italia Srl, Milan, Italy). The solid particles content, calculated as the difference in weight and quantified as percentage of solid particles weight/100-g olive oil sample (% w/w), was measured using the method described in literature (

The FFA (% oleic acid), PV (meq O_{2} kg^{−1}), and UV spectroscopic indices (K232, K270, and ΔK) were measured according to the official EU method (REG. 2016/2095). Extraction, identification, and determination of phenolic compounds was performed in agreement with the official IOC method (IOC/T.20/Doc.29/Rev.1; ^{®} 250-4.6 Purospher^{®} STAR RP-18E, 5 µm (250 × 4.6-mm id; Merck KGaA) equipped with a LiChroCART^{®} 4-4 Purospher^{®} STAR RP-18E, 5-µm pre-column (4 × 4 mm). Contents of phenolic compounds in oil samples were studied as total content, content of polyphenols from different family groups (sum of oleuropein and its derivates, sum of ligstroside and its derivates, phenolic acids, flavonoids, and lignans), and content of single representative compounds in EVOO (hydroxytyrosol and tyrosol). Moreover, R-index, which relates the content of the more hydrolysed phenols (hydroxytyrosol and tyrosol) to the less hydrolysed ones (oleuropein and its derivates and ligstroside and its derivates) was calculated as follows (

The content of volatile organic compounds in olive oil was determined using the combination of headspace solid phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC–MS) technique as described in literature (

The panel test was carried out according to the official IOC method (IOC/T.20/Doc.15/Rev.10;

A linear model that included two tested variables (treatment and storage period) and their interactions were used to fit the experimental data. Data were analyzed with Matlab R2017B software (MathWorks, Natick, MA, USA). A two-way mixed effect ANOVA was performed to assess significant differences (

Six olive oil samples for each treatment were used as replicated for storage study. This choice was done to understand both the behavior of unfiltered oils related to filtered oils, regardless of individual oil turbidity characteristics, and the separated role of water and solid particles during storage of unfiltered olive oils.

Immediately after production, the six VEVOO samples (VO#1–VO#6) used in this study were characterized for different ‘turbidities’ (^{-1}.

After treatments, turbidity characteristics of olive oil samples changed radically. FEVOO samples (FO#1–FO#6) were characterized by a degree of turbidity grade (10–20 NTU), water (0.04–0.05% w/w), and insoluble solids content (0.00% w/w), water activity (0.30–0.45), and microbial cell count (0.00 log CFU g^{-1}), which were statistically (^{-1} and 0.0–.7 log CFU g^{-1}, respectively.

All olive oil samples resulted from the values of chemical parameters, FFA, PV, K232, K270, and ΔK, in the ‘extra-virgin’ category during whole storage (

Mean values of chemical parameters of all olive oil samples for each separation treatment. Different superscribed letters (^{a,b,c}) in the same row indicate significant differences (^{x,y,z}) in the same column indicate significant differences (

Time (days) | St. Err. | R^{2} |
ADJ-R^{2} |
Limit value for ‘extra-virgin’ category | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|

Acidity (% oleic acid) | 0 | 0.19^{a,x} |
0.22^{b,x} |
0.16^{a,x} |
0.17^{a,x} |
0.01 | n.s. | *** | n.s. | 0.6490 | 0.6096 | |

45 | 0.18^{a,x} |
0.24^{b,x} |
0.18^{a,x} |
0.20^{a,x} |
||||||||

120 | 0.17^{a,x} |
0.25^{b,x} |
0.20^{a,x} |
0.18^{a,x} |
≤0.8 | |||||||

180 | 0.17^{a,x} |
0.24^{b,x} |
0.21^{a,x} |
0.19^{a,x} |
||||||||

240 | 0.18^{a,x} |
0.25^{b,x} |
0.16^{a,x} |
0.20^{a,x} |
||||||||

Peroxide value (meq O_{2}/kg) |
0 | 5.4^{a,x} |
6.3^{a,x} |
5.9^{a,x} |
5.8^{a,x} |
0.2 | n.s. | n.s. | n.s. | 0.1202 | 0.0216 | ≤20 |

45 | 7.6^{a,x} |
6.4^{a,x} |
7.5^{a,x} |
7.2^{a,x} |
||||||||

120 | 5.9^{a,x} |
5.9^{a,x} |
6.2^{a,x} |
7.2^{a,x} |
||||||||

180 | 7.5^{a,x} |
5.8^{a,x} |
5.4^{a,x} |
6.9^{a,x} |
||||||||

240 | 9.2^{a,x} |
7.5^{a,x} |
7.2^{a,x} |
6.3^{a,x} |
||||||||

K232 | 0 | 1.69^{a,x} |
1.68^{a,x} |
1.77^{a,x} |
1.70^{a,x} |
0.01 | ** | n.s. | n.s. | 0.5542 | 0.5042 | ≤2.50 |

45 | 1.76^{a,xy} |
1.74^{a,x} |
1.80^{a,x} |
1.79^{a,y} |
||||||||

120 | 1.79^{a,y} |
1.78^{a,y} |
1.84^{a,xy} |
1.80^{a,y} |
||||||||

180 | 1.81^{a,y} |
1.78^{a,y} |
1.82^{a,x} |
1.81^{a,y} |
||||||||

240 | 1.84^{a,y} |
1.79^{a,y} |
1.87^{a,y} |
1.87^{a,y} |
||||||||

K270 | 0 | 0.13^{a,x} |
0.15^{a,x} |
0.19^{b,x} |
0.15^{a,x} |
0.01 | ** | *** | n.s. | 0.5340 | 0.4818 | ≤0.22 |

45 | 0.15^{a,xy} |
0.16^{a,x} |
0.18^{b,x} |
0.16^{a,x} |
||||||||

120 | 0.18^{a,y} |
0.17^{a,xy} |
0.21^{b,x} |
0.17^{a,xy} |
||||||||

180 | 0.17^{a,y} |
0.17^{a,xy} |
0.20^{b,x} |
0.17^{a,xy} |
||||||||

240 | 0.18^{a,y} |
0.18^{a,y} |
0.20^{b,x} |
0.18^{a,y} |
||||||||

ΔK | 0 | –0.005^{a,x} |
–0.004^{a,x} |
–0.004^{a,x} |
–0.005^{a,x} |
0.000 | *** | ** | n.s. | 0.5215 | 0.4678 | ≤0.01 |

45 | –0.005^{a,x} |
–0.002^{b,y} |
–0.003^{ab,xy} |
–0.003^{ab,y} |
||||||||

120 | –0.002^{a,y} |
0.000^{b,z} |
–0.002^{a,y} |
–0.001^{ab,z} |
||||||||

180 | –0.002^{a,y} |
0.000^{b,z} |
–0.001^{ab,y} |
–0.001^{ab,z} |
||||||||

240 | –0.002^{a,y} |
0.000^{b,z} |
–0.002^{a,y} |
–0.001^{ab,z} |

n.s., *, **, and *** indicate significant differences by two-way ANOVA at

Microbial cell count was statistically significant for treatment. VO samples had a microbial cell count higher than FO samples; WO olive oil samples had a microbial cell count between VO and FO samples. SO olive oil samples had a microbial cell count between WO and FO samples (i.e., no significant difference than both WO and FO). No statistically significant variation occurred during storage time. However, interactions between time and treatment were statistically significant. In WO and SO olive oil samples, the microbial cell count decreased during storage, in FO samples it did not change, and in VO samples, the microbial contamination increased up to 120 days, then decreased (

Mean contents and standard error of microbial cell count in samples of virgin oil (VO; red circle), olive oil containing water only (WO; blue diamond), olive oil containing solid particles (SO; purple triangle), and filtered oil (FO; green square) during storage. The R^{2} and ADJ-R^{2} values of microbial cell count were 0.8522 and 0.8356, respectively.

The content of phenolic compounds of oil samples was studied as total content, content of different family groups of polyphenols, and content of single representative compounds in EVOO, as described in literature (

Mean values of total content, content of groups, and content of single representative phenolic compounds of all oil samples for each separation treatment. Different superscribed letters (^{a,b,c}) in the same row indicate significant differences (^{x,y,z}) in the same column indicate significant differences (

Time (days) | FO#1–FO#6 | VO#1–VO#6 | SO#1–SO#6 | WO#1–WO#6 | St. Error | R^{2} |
ADJ-R^{2} |
||||
---|---|---|---|---|---|---|---|---|---|---|---|

Hydroxy tyrosol (mg/kg) | 0 | 2.7^{a,x} |
5.0^{b,x} |
6.5^{b,x} |
4.4^{ab,x} |
1.5 | *** | *** | *** | 0.7985 | 0.7759 |

45 | 3.1^{a,x} |
14.3^{b,y} |
8.1^{ab,x} |
8.4^{ab,xy} |
|||||||

120 | 4.7^{a,x} |
20.0^{b,yz} |
9.4^{ab,x} |
11.7^{ab,y} |
|||||||

180 | 4.7^{a,x} |
20.0^{b,yz} |
9.1^{ab,x} |
13.5^{ab,y} |
|||||||

240 | 5.9^{a,x} |
27.9^{b,z} |
15.4^{ab,y} |
17.5^{ab,y} |
|||||||

Tyrosol (mg/kg) | 0 | 2.4^{a,x} |
2.9^{a,x} |
3.1^{a,x} |
3.1^{a,x} |
0.6 | *** | *** | *** | 0.7504 | 0.7224 |

45 | 2.8^{a,x} |
5.4^{a,x} |
3.5^{a,x} |
3.6^{a,x} |
|||||||

120 | 3.0^{a,x} |
7.9^{b,xy} |
4.2^{ab,xy} |
4.6^{ab,x} |
|||||||

180 | 2.9^{a,x} |
10.2^{b,y} |
3.8^{ab,xy} |
4.1^{a,bx} |
|||||||

240 | 4.1^{a,x} |
11.8^{b,y} |
5.4^{ab,y} |
7.1^{ab,y} |
|||||||

Sum of oleuropein and its derivates (mg/kg) | 0 | 290.9^{a,x} |
369.5^{b,x} |
437.9^{c,x} |
384.8^{bc,x} |
13.9 | n.s. | *** | n.s. | 0.6646 | 0.6270 |

45 | 248.5^{a,x} |
307.8^{b,x} |
427.5^{c,x} |
346.1^{bc,x} |
|||||||

120 | 307.3^{a,x} |
308.4^{a,x} |
438.8^{b,x} |
278.3^{a,x} |
|||||||

180 | 298.5^{a,x} |
282.6^{a,x} |
425.6^{b,x} |
326.8^{a,x} |
|||||||

240 | 325.9^{b,x} |
286.6^{a,x} |
444.9^{c,x} |
343.5^{b,x} |
|||||||

Sum of ligstroside and its derivates (mg/kg) | 0 | 152.4^{a,x} |
181.4^{a,x} |
149.7^{a,x} |
163.7^{a,x} |
6.7 | n.s. | *** | n.s. | 0.3822 | 0.3129 |

45 | 101.4^{a,x} |
198.6^{b,x} |
186.4^{b,x} |
173.5^{b,x} |
|||||||

120 | 132.6^{a,x} |
178.3^{ab,x} |
206.4^{b,x} |
149.4^{ab,x} |
|||||||

180 | 138.1^{a,x} |
176.3^{ab,x} |
229.9^{b,x} |
161.3^{ab,x} |
|||||||

240 | 156.2^{a,x} |
178.7^{ab,x} |
214.8^{b,x} |
178.5^{ab,x} |
|||||||

Total contents (mg/kg) | 0 | 548.4^{a,x} |
701.2^{c,x} |
724.6^{c,x} |
671.5^{b,x} |
20.3 | n.s. | *** | n.s. | 0.6179 | 0.5751 |

45 | 445.5^{a,x} |
655.1^{b,x} |
732.7^{c,x} |
644.6^{b,x} |
|||||||

120 | 543.6^{a,x} |
646.6^{b,x} |
769.6^{c,x} |
556.2^{a,x} |
|||||||

180 | 543.3^{a,x} |
638.5^{b,x} |
778.5^{c,x} |
609.2^{b,x} |
|||||||

240 | 597.6^{a,x} |
637.7^{b,x} |
798.0^{c,x} |
676.2^{b,x} |

n.s., *, **, and *** indicate significant differences by two-way ANOVA at

The total phenolic content was statistically significant (

Significant interactions between storage period and treatment (^{–1} and 5 mg kg^{–1}, respectively, in all samples. During the 240 days of storage, the contents increased statistically in all samples except FO samples. VO samples had content of hydroxytyrosol and tyrosol statistically (

The contents of hydroxytyrosol, tyrosol, oleuropein, and ligstroside and their derivates were used to calculate R-index (R-index = [hydroxytyrosol + tyrosol]/[oleuropein and its derivates + ligstroside and its derivates]), a useful marker of the hydrolysis of secoiridoids (

Mean value, standard error of R-index in samples of virgin oil (VO; red circle and line), olive oil containing water only (WO; blue diamond and line), olive oil containing solid particles (SO; purple triangle and line), and filtered oil (FO; green square and line) during storage. The R^{2} and ADJ-R^{2} values of R-index were 0.8343 and 0.8157, respectively.

The ratio of oxidized form of phenolic compounds to not oxidized form (OX:not OX) during storage period (

Mean value and standard error of phenolic oxidized–not oxidized form ratio (OX:not OX) in virgin oil VO (red circle), olive oil containing water only WO (blue diamond), olive oil containing solid particles SO (purple triangle), and filtered oil FO (green square) samples during storage. The R^{2} and ADJ-R^{2} of OX/not OX were 0.1957 and 0.1055, respectively.

The content of volatile compounds in olive oil samples was studied as described in literature (

Some statistically significant differences (

Mean contents and standard error of lipoxygenase (LOX) pathway volatile compounds in virgin oil VO (red circle), olive oil containing water only WO (blue diamond), olive oil containing solid particles SO (purple triangle), and filtered oil FO (green square) samples during storage. Only compounds statistically significant different (^{2} and ADJ-R^{2} values for LOX pathway volatile compound are as follows: 1-hexanol, R^{2} = 0.5003, ADJ-R^{2} = 0.4442; E-2-hexenol, R^{2} = 0.6473, ADJ-R^{2} = 0.6077; Z-3-hexenol, R^{2} = 0.7068, ADJ-R^{2} = 0.6740; 1-peten-3-one, R^{2} = 0.5996, ADJ-R^{2} = 0.5547; and E-2-penten-1-ol, R^{2} = 0.7460, ADJ-R^{2} = 0.7175.

The same statistically significant difference was also determined in 3-methyl-butanal, 2-octanol, and 2-nonanone unpleasant volatile compounds related to ‘fusty’ defect (

Mean contents and standard error of volatile compounds related to ‘fusty’ defect in virgin oil VO (red circle), olive oil containing water only WO (blue diamond), olive oil containing solid particles SO (purple triangle), and filtered oil FO (green square) samples during storage. Only compounds statistically significant different (^{2} and ADJ-R^{2} values for ‘fusty’ defect volatile compounds are as follows: 3-methyl-butanal, R^{2} = 0.4201, ADJ-R^{2} = 0.3551; 2-octanol, R^{2} = 0.7852, ADJ-R^{2} = 0.7611; and 2-nonanone, R^{2} = 0.5197, ADJ-R^{2} = 0.4659.

The main effect of treatment and storage period and their interactions were not statistically significant for the unpleasant volatile compounds related to ‘rancid’ defect.

The sensory attributes were evaluated and a significant (

Mean values of sensory attributes and defects of all oil samples for each separation treatment. Superscribed different letters (^{a,b,c}) in the same row indicate significant differences (^{x,y,z}) in the same column indicate significant differences (

Time (days) | FO#1–FO#6 | VO#1–VO#6 | SO#1–SO#6 | WO#1–WO#6 | St. Err. | R^{2} |
ADJ-R^{2} |
||||
---|---|---|---|---|---|---|---|---|---|---|---|

0 | 0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
0.16 | *** | *** | * | 0.4908 | 0.4337 | |

45 | 0.28^{a,x} |
0.68^{b,xy} |
0.00^{a,x} |
0.05^{a,x} |
|||||||

120 | 0.75^{a,xy} |
1.96^{b,yz} |
0.38^{a,x} |
0.59^{a,x} |
|||||||

180 | 1.08^{a,y} |
1.79^{b,y} |
1.73^{b,y} |
0.53^{a,x} |
|||||||

240 | 0.60^{a,xy} |
2.23^{c,z} |
1.39^{b,y} |
0.61^{a,x} |
|||||||

0 | 0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
0.06 | *** | n.s. | n.s. | 0.2023 | 0.1129 | |

45 | 0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
|||||||

120 | 0.63^{a,y} |
0.78^{a,y} |
0.50^{a,y} |
0.66^{a,y} |
|||||||

180 | 0.00^{a,x} |
0.30^{b,xy} |
0.08^{a,x} |
0.00^{a,x} |
|||||||

240 | 0.00^{a,x} |
0.39^{b,xy} |
0.10^{a,x} |
0.00^{a,x} |
|||||||

0 | 0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
0.09 | *** | *** | ** | 0.6216 | 0.5792 | |

45 | 0.00^{a,x} |
0.55^{b,xy} |
0.08^{a,x} |
0.00^{a,x} |
|||||||

120 | 0.00^{a,x} |
1.03^{b,y} |
0.12^{a,xy} |
0.08^{a,x} |
|||||||

180 | 0.17^{a,y} |
1.08^{b,y} |
0.19^{a,y} |
0.14^{a,x} |
|||||||

240 | 0.15^{a,y} |
1.32^{b,y} |
0.14^{a,xy} |
0.12^{a,x} |
|||||||

0 | 0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
0.00^{a,x} |
0.26 | *** | *** | n.s. | 0.5960 | 0.5507 | |

45 | 0.65^{ab,x} |
1.33^{b,y} |
0.83^{ab,x} |
0.00^{a,x} |
|||||||

120 | 1.70^{a,y} |
3.18^{c,z} |
2.36^{b,y} |
0.43^{a,xy} |
|||||||

180 | 1.57^{a,xy} |
3.14^{c,z} |
2.38^{b,y} |
0.82^{a,y} |
|||||||

240 | 1.65^{a,xy} |
3.25^{c,z} |
2.42^{b,y} |
0.95^{a,y} |
|||||||

0 | 3.40^{a,y} |
3.37^{a,y} |
3.12^{a,y} |
3.57^{a,z} |
0.19 | *** | *** | n.s. | 0.5339 | 0.4816 | |

45 | 2.98^{a,xy} |
2.33^{a,xy} |
2.63^{a,xy} |
3.03^{a,xy} |
|||||||

120 | 2.31^{b,x} |
1.03^{a,x} |
1.83^{a,x} |
1.97^{b,x} |
|||||||

180 | 2.48^{b,x} |
1.18^{a,x} |
1.16^{a,x} |
2.65^{b,xy} |
|||||||

240 | 2.51^{b,x} |
1.05^{a,x} |
1.01^{a,x} |
2.11^{b,x} |
|||||||

0 | 3.42^{a,z} |
3.30^{a,z} |
2.80^{a,y} |
n.d. | 0.27 | - | - | - | 0.7410 | 0.7119 | |

45 | 2.85^{a,y} |
2.03^{a,y} |
2.72^{a,y} |
n.d. | |||||||

120 | 1.93^{b,x} |
0.47^{a,x} |
2.27^{b,xy} |
n.d. | |||||||

180 | 2.99^{b,y} |
1.68^{a,y} |
1.95^{b,x} |
n.d. | |||||||

240 | 2.58^{b,xy} |
1.12^{a,xy} |
1.90^{b,x} |
n.d. | |||||||

0 | 4.96^{a,z} |
4.53^{a,z} |
4.90^{a,z} |
n.d. | 0.39 | - | - | - | 0.8327 | 0.8139 | |

45 | 3.53^{b,y} |
2.73^{a,y} |
3.93^{b,y} |
n.d. | |||||||

120 | 1.78^{b,x} |
0.63^{a,x} |
2.63^{b,x} |
n.d. | |||||||

180 | 3.40^{b,y} |
1.21^{a,x} |
3.08^{b,x} |
n.d. | |||||||

240 | 2.75^{b,xy} |
1.05^{a,x} |
2.97^{b,x} |
n.d. |

n.s., *, **, and *** indicate significant differences by two-way ANOVA at

The negative ‘fusty’ and ‘winey’ defects, both related to microbial activity, and ‘rancid’ defect, related to oxidation, showed significant (

Mean contents and standard error of the ‘fusty’, ‘winey’, and ‘rancid’ defect scores in virgin oil VO (red circle), olive oil containing water only WO (blue diamond), olive oil containing solid particles SO (purple triangle), and filtered oil FO (green square) samples during storage. The R^{2} and ADJ-R^{2} for each sensory attribute are reported below: ‘fusty’, R^{2} = 0.4908, ADJ-R^{2} = 0.4337; ‘winey’, R^{2} = 0.6216, ADJ-R^{2} = 0.5792; ‘rancid’, R^{2} = 0.5960, ADJ-R^{2} = 0.5507.

The bitterness and pungency attributes significantly (

The experimental data highlighted that water and solid particles had some specific roles to play in the quality evolution of EVOO during storage. The obtained results demonstrated that two degradation phenomena, hydrolysis and microbial activity, were faster in VO samples than in FO, WO, and SO samples.

The presence of water micro-droplets dispersed in oil matrix increased the water/oil exchange surface, and the hydrolysis reaction occurred to a significant extent (XENAKIS

The ‘fusty’ and ‘winey’ sensory defects and their related volatile compounds were strictly connected to the microbial activity. The microorganism cell count in VO samples was higher than in FO, SO, and WO samples during storage; the microbial survival was due to the favorable environment of VO samples, starting with water activity of >0.6 (

The microbial activity was also helped by the content of solid particles. Our results highlight that water has to be combined with solid particles for microbial growth. WO and SO samples were not good for microbial survival, and only VO samples had favorable conditions for microbial growth (

The content of solid particles could be involved in promoting the transfer of phenols transfer from solid particles to oil. The SO samples were able to show the above effect, thanks to both absence of water and slow hydrolytic phenomena of phenolic compounds. The significant higher contents of both total phenolic compounds and sum of oleuropein and its derivatives in SO samples (

Derived from the experimental results, following are the other functions of water and solid particles in the quality evolution of EVOO during storage, although they had some uncertain aspects.

The water content seemed to promote the LOX enzymatic pathway, which is responsible for ‘fruity’ positive sensory attributes. The content of C5 and C6 volatile compounds of LOX pathway was higher in VO samples than in FO and WO samples (

The water content also seemed to protect EVOO against negative oxidative phenomena during storage. The OX:not OX ratio of phenolic compounds (

In this study, an original approach was carried out to understand the significance of VO in terms of preservation of EVOO quality during storage. A clear effect of water content on hydrolytic phenomena and microbial activity was evidenced. Effect of content of solid particles to promote microbial activity was also demonstrated, potentially resulting in the loss of EVOO quality.

The results of the present study asserted that the recommended technique to avoid significant degradation during storage was to quickly filter freshly produced olive oil. However, an immediate filtration is not always possible as veiled olive oil is the product sought for bottling by producers. Therefore, A qualification of oil turbidity, based on separate measurement of water and insoluble solids contents, is suggested during different processing steps of olive oil chain, such as VO storage in mills, VO supply and storage in oil blenders, and transportation and distribution of veiled EVOO. It follows that, for olive oil producers, the qualification of veiled olive oil in potentially different combinations of water and solid contents (i.e., high–high, high–low, low–high, or low–low) could be useful to plan and control both water/solid separation techniques and storage of oil.

Lorenzo Guerrini, Alessandro Parenti, and Bruno Zanoni did conceptualization; Carlotta Breschi and Lorenzo Guerrini curated the data. Formal analysis was done by Carlotta Breschi, Ferdinando Corti, and Luca Calamai. Funding acquisition was done by Alessandro Parenti and Bruno Zanoni. Methodology was done by Luca Calamai and Paola Domizio; and software handling was done by Carlotta Breschi and Lorenzo Guerrini. Supervision was carried out by Alessandro Parenti and Bruno Zanoni. Original draft was written by Carlotta Breschi and Lorenzo Guerrini; and the final writing—review and editing—was done by Lorenzo Guerrini, Alessandro Parenti, and Bruno Zanoni.

This study was supported by the AGER 2 Project, Grant No. 2016-0174, COMPETiTiVE—Claims of Oliveoil to IMProvE The marketValuE of the product.

The authors declare no conflict of interest.