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Influence of Irrigation Management and Ripening on Virgin Olive Oil Quality and Composition
Chapter 6
Influence of Irrigation Management and Ripening on Virgin Olive Oil Quality and Composition Giuseppe Fregapane, Aurora Gómez-Rico and Maria Desamparados Salvador Departamento de Tecnología de Alimentos, Universidad de Castilla – La Mancha, Spain
6.1 Introduction
6.2 Irrigation management
The olive tree is generally grown under rainfed conditions, especially in Castilla – La Mancha, a region with limited water resources. Nevertheless, since irrigation increases the yield of the olive orchard, even with a low amount of water, there is increasing interest in irrigated agriculture. This has led to a situation in which some of the traditional olive groves and the majority of the new ones are being adapted to irrigation techniques. However, a satisfactory compromise between the amount of water applied and the improvement in the production of the olive crop and characteristics of virgin olive oil must be reached. Some recent research has shown differences in the chemical makeup and sensory characteristics of virgin olive oil from irrigated and rainfed olive trees (Aparicio and Luna, 2002). The chemical components most influenced by irrigation are the phenolic compounds which affect both the oxidative stability and the sensory characteristics, especially the bitterness attribute, showing in both cases an inverse relationship with the amount of water applied to the olive trees (D’Andria et al., 1996; Motilva et al., 1999, 2000; Tovar et al., 2001). This aspect is important in olive cultivars that produce virgin olive oils with high bitterness and pungency, like the Cornicabra variety in Castilla – La Mancha and therefore just the right level of irrigation could enhance its sensory characteristics. To optimize sustainable irrigation conditions in the Cornicabra olive cultivar grown in Castilla – La Mancha, a region where aquifers are over-exploited, and to study the effect of different irrigation management and ripening on the composition of Cornicabra virgin olive oil, different irrigation treatments (based on 100% crop evapotranspiration, ETc, also known as the FAO method, 125 FAO, two different regulated deficit irrigation strategies and rainfed) were applied to a traditional olive orchard (Cornicabra cv).
The experimental olive orchard of Cornicabra cv., located in Ciudad Real (Spain), is constituted by three hundred 50-year-old trees (spaced 12 12 m2) structured in a randomized complete block design with four different irrigation treatments (Table 6.1): rainfed (RF) conditions, regulated deficit irrigation (RDI), FAO and 125 FAO. Rainfed conditions were used as a control to compare the results obtained with the irrigation treatments. In FAO treatment the water requirements were calculated using a methodology based on the crop evapotranspiration (ETc) proposed by the United Nations Food and Agriculture Organization. In 125 FAO treatments a total irrigation dosage 25% higher than the FAO treatment was applied. For regulated deficit irrigation (RDI), a maximum of 75 mm of water was established since in many Spanish irrigated olive areas there is a legal limit of 100 mm. Two different strategies were evaluated. In 2003 (RDI-1), water was applied throughout the entire season with different rates of application (10% FAO in May and June, 4% FAO in July and August and 18% FAO in September); whereas in 2004 (RDI-2), based on the results obtained during the previous crop season, water was applied only from the beginning of August, when the oil starts to form in the fruit, for the purpose of investigating which RDI treatment is more effective in achieving similar olive production and olive oil quality to that obtained by the FAO method while considerably reducing the total amount of water applied. The total water applied in 2003/04 for the different irrigation treatments was: 56 mm for RDI-1, 148 mm for FAO and 206 mm for 125 FAO; and in 2004/05: 60 mm for RDI-2, 124 mm for FAO and 154 mm for 125 FAO. More detailed data on the irrigation management have been previously reported (Gómez-Rico et al., 2006, 2007).
Olives and Olive Oil in Health and Disease Prevention. ISBN: 978-0-12-374420-3
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Section | I The Plant and Production
Table 6.1 Key facts of irrigation management. This table lists the key facts of irrigation management describing the basic characteristics of the different irrigation treatments studied in the Cornicabra olive orchard. 1. Irrigation management in olive orchard increases the olive and olive oil production 2. Water applied to olive trees may affect virgin olive oil quality and composition 3. According to the irrigation methodology proposed by the FAO (Food and Agriculture Organization), the total water requirements of olive trees is calculated by subtracting the effective precipitation from the crop evapotranspiration (ETc) 4. ETc is calculated using the effective crop coefficient (Kc), the reference crop evapotranspiration (ETo), and a reducing coefficient (Kr) 5. The regulated deficit irrigation (RDI) is based on a lower dose of water to the olive orchard than the 100% ETc, established according to the weather and phenological stage of the trees, assuring an adequate water status during full bloom and oil accumulation in the fruit 6. The olive trees in rainfed (RF) condition only receive the effective precipitations and therefore are used to determine the ‘highest water stress’ situation 7. Olive trees are generally irrigated by compensating drippers placed around the trees
Olive fruit samples from rainfed and irrigation treatment trees were harvested throughout ripening, from immature stage to normal harvest period for the Cornicabra variety (from the beginning of November to the middle of January). The influence of fruit ripening and irrigation management on the production of the olive grove, which was significantly lower under rainfed conditions than under irrigation (about 35%), and the characteristics and composition of the olive fruit have been discussed elsewhere (Gómez-Rico et al., 2007).
6.3 Virgin olive oil quality indices Free acidity, given as % of oleic acid, peroxide value (PV) expressed as milliequivalents of active oxygen per kilogram of oil (meq O2 kg1), and K232 and K270 extinction coefficients calculated from absorption at 232 and 270 nm, were measured following the analytical methods described in European Regulation EEC 2568/91 and subsequent amendments. The observed free acidity ranging from 0.09 to 0.20%, and peroxide value, from 1.7 to 3.4 meqO2 kg1, of the different types of virgin olive oils (VOO) studied in this assay
in the crop season 2003/04 were considerably lower than the upper limit of 0.8% as oleic acid and 20 meqO2 kg1, respectively, established by EU legislation for extra virgin olive oil. Moreover, these two quality indices were not influenced by irrigation, since no statistically significant differences in oil from rainfed and irrigation treatments in the crop season 2003/04 were obtained. This was also observed by Tovar et al. (2001) in virgin olive oils from Arbequina cultivar, Dettori and Russo (1993) in Leccino, Nociara and Ogliarola Salentina cultivars and Patumi et al. (1999) in Nocellara del Belice and Ascolana Tenera cultivars. On the contrary, in crop 2004/05 a statistical difference for free acidity and peroxide value was indeed obtained between RF and the irrigation treatments due to the higher degree of fruit damage as a consequence of the olive fly attack. Nevertheless, the values of free acidity and the peroxide value of the olive oil obtained from partially damaged fruit were not high from an olive oil quality point of view: a maximum acidity of 0.4% and a 5.4 peroxide value were observed.
6.4 Sensory characteristics All the virgin olive oils obtained using the different irrigation treatments of the trees were classified as ‘extra virgin’ oil by means of the organoleptic evaluation as reported in Table 6.2. Sensory evaluation was assessed by an International Olive Oil Council-recognized panel of assessors from the Protected Designation of Origin ‘Montes de Toledo’ (Toledo, Spain) according to Annex XII of Regulation EC 796/2002 (amending ECC 2568/91). Sensory attributes affected by irrigation were ‘bitterness’, ‘pungency’ and ‘fruitiness’, according to what has previously been described for other olive cultivars (Salas et al., 1997; Tovar et al., 2001, 2002). As is known, the intensity of sensory pungency and especially bitterness are related to the phenol content in the olive oil, which, as expected, was higher in oils obtained under rainfed conditions. In all cases, a slight decrease in the intensity of these positive attributes was observed, more marked in the case of bitterness, by increasing the amount of water delivered through irrigation. This observation is very relevant from the olive quality and marketing point of view since, although bitterness is a positive sensory attribute in virgin olive oil, a high level of bitterness could cause consumers to reject the oil. A high level of bitterness is a typical characteristic of the Cornicabra variety virgin olive oils’ sensory profile, and therefore the use of irrigation could produce a desirable descent in the intensity of this attribute and hence increase consumer preference. However, in the 2004/05 crop season no statistically significant differences were obtained in the positive sensory attributes, including bitterness, between the olive oils obtained under rainfed and irrigation conditions.
Chapter | 6 Influence of Irrigation Management and Ripening on Virgin Olive Oil Quality and Composition
Table 6.2 Virgin olive oil organoleptic evaluation as affected by the different irrigation treatments and the ripeness index of the fruits. Ripeness Index
Grade
2003/2004
Sensory attributes
K225
Fruity
Bitterness
Pungency
RF
2.7 0.3a,x
Extra Virgin
6.1 0.2b,x
8.2 0.4b,w
7.8 0.3a,w
0.78 0.01c,x
RDI-1
2.8 0.4a,x
Extra Virgin
6.2 0.5b,w
8.0 0.3b,wx
8.0 0.3a,wx
0.67 0.07b,x
FAO
3.1 0.3a,x
Extra Virgin
5.5 0.1b,w
7.7 0.5ab,w
7.7 0.3a,w
0.66 0.04b,yz
125 FAO
2.8 0.2a,w
Extra Virgin
4.9 0.3a,w
7.2 0.3a,wx
7.6 0.3a,w
0.56 0.07a,xy
RF
3.7 0.2a,y
Extra Virgin
5.4 0.2ab,w
8.5 0.2c,w
8.4 0.2ab,w
0.77 0.01c,x
RDI-1
3.8 0.3a,y
Extra Virgin
6.2 0.3b,w
8.3 0.2c,x
8.5 0.1b,w
0.64 0.07b,wx
FAO
4.0 0.4a,y
Extra Virgin
5.5 0.2ab,w
7.7 0.3b,w
8.0 0.2ab,w
0.56 0.04ab,x
125 FAO
3.9 0.1a,y
Extra Virgin
5.3 0.2a,w
6.9 0.4a,w
8.0 0.2a,w
0.49 0.08a,wx
RF
5.7 0.4b,z
Extra Virgin
5.4 0.3ab,wx
8.3 0.2a,w
8.1 0.2ab,w
0.66 0.05c,w
RDI-1
5.4 0.5ab,z
Extra Virgin
6.2 0.1b,w
7.5 0.5a,w
7.7 0.1a,x
0.57 0.03b,w
FAO
5.5 0.3ab,z
Extra Virgin
5.0 0.3a,w
7.7 0.3a,w
7.9 0.2a,w
0.46 0.03a,w
125 FAO
4.9 0.1a,z
Extra Virgin
6.0 0.1b,x
8.0 0.3a,x
8.0 0.2b,w
0.41 0.09a,w
RF
2.8 0.2b,w
Extra Virgin
6.4 0.3a,w
7.6 0.2a,w
8.0 0.3a,w
0.66 0.09a,w
RDI-2
2.3 0.1a,w
Extra Virgin
6.0 0.2a,x
7.4 0.5a,w
7.9 0.6a,wx
0.70 0.00a,x
FAO
2.5 0.2ab,w
Extra Virgin
5.6 0.4a,w
6.7 0.3a,w
7.5 0.2a,w
0.67 0.00a,x
125 FAO
2.4 0.1a,w
Extra Virgin
5.2 0.6a,w
7.3 0.2a,w
7.7 0.3a,w
0.60 0.00a,y
RF
3.4 0.0a,x
Extra Virgin
5.5 0.2ab,w
7.0 0.5a,w
7.4 0.5a,w
0.60 0.08a,w
RDI-2
3.4 0.0a,x
Extra Virgin
4.9 0.4a,w
7.0 0.3a,w
7.1 0.3a,w
0.60 0.03a,x
FAO
3.4 0.0a,x
Extra Virgin
5.5 0.2ab,w
6.9 0.4a,w
7.6 0.2a,w
0.59 0.03a,x
125 FAO
3.5 0.1a,x
Extra Virgin
5.5 0.5b,w
6.6 0.3a,w
7.4 0.2a,w
0.50 0.02a,x
RF
4.1 0.1a,y
Extra Virgin
6.0 0.4a,w
7.4 0.3ab,w
7.6 0.4a,w
0.59 0.12b,w
RDI-2
4.2 0.0a,y
Extra Virgin
5.4 0.3a,wx
7.6 0.2b,w
8.2 0.2a,x
0.57 0.01b,w
FAO
4.2 0.0a,y
Extra Virgin
5.4 0.3a,w
7.4 0.3b,w
7.5 0.3a,w
0.54 0.01ab,w
125 FAO
4.2 0.0a,y
Extra Virgin
5.9 0.2a,w
6.6 0.4a,w
7.4 0.3a,w
0.36 0.04a,w
2004/2005
Sensory attributes affected by irrigation were ‘bitterness’, ‘pungency’ and ‘fruitiness’. In all cases, a slight decrease in the intensity of these positive attributes was observed, more marked in the case of bitterness, by increasing the amount of water delivered through irrigation. RF, rainfed; RDI, regulated deficit irrigation; FAO, Food and Agriculture Organization method. Different letters within a column (a–c) indicate significant differences (p 0.05) with respect to irrigation treatment in each sampling. Different letters within a column (w–y) indicate significant differences (p 0.05) with respect to ripeness index for each treatment.
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Olive oil bitterness can also be measured by the instrumental K225 parameter called bitterness index (GutiérrezRosales et al., 1992). In the 2003/04 crop, a great decrease in the bitterness index was observed as the water dose applied to olive trees increased (Table 6.2), varying from 0.77 to 0.49 respectively for RF and 125 FAO for the sampling close to a ripeness index of 4.0. However, in the 2004/05 crop no statistically significant differences were obtained.
Section | I The Plant and Production
were observed between the irrigation treatments studied. However, Tovar et al. (2002) reported significant increases in the -tocopherol values in Arbequina VOO as the irrigation doses applied in the trees increased. On the other hand, these rises did not imply changes in the oxidative stability of the oils.
6.6.1 Total Phenol Content 6.5 Fatty acid composition Fatty acid composition is performed according to the European Regulations EEC 2568/91 and subsequent amendments, corresponding to the AOCS Method Ch 2-91. In both crop seasons studied and in all irrigation treatments studied, the palmitic acid content slightly decreased as fruit ripened, i.e. from 10.4% down to 9.1% and from 11.4% to 9.7% respectively for RF and FAO irrigation treatments; whereas oleic and linoleic acids showed an opposite trend, i.e. the oleic acid content varied from 78.4% to 79.5% and the linoleic acid from 3.7% to 4.6% under the FAO conditions. The increase in oleic acid content is due to the triacylglycerols’ active biosynthesis which takes place throughout fruit ripening, involving a fall in the relative percentage of the oil’s palmitic acid content. On the other hand, the increase in linoleic acid content is due to the transformation of oleic acid into linoleic acid by the oleate desaturase activity which is active during triacylglycerol biosynthesis (Sanchez and Harwood, 2002). The content of the other fatty acids remained practically unchanged during fruit ripening. In the 2003/04 crop, rainfed olive oils always showed a statistically significant higher content in oleic acid, whereas olive oils from irrigated trees had a higher content in palmitic and linoleic acids. As a consequence, the unsaturated/ saturated and MUFA/PUFA ratios were significantly higher in oils obtained in rainfed conditions, in line with the results obtained by Salas et al. (1997). However, these changes are very slight and do not possess any nutritional value relevance.
6.6 Natural antioxidants content The values of the -tocopherol and total phenol content and the oxidative stability of the virgin olive oils obtained from the different treatments studied are shown in Table 6.3. Phenolic compounds were quantified by HPLC at 280 nm using syringic acid as internal standard and the response factors determined by Mateos et al. (2001), and described in GomezAlonso et al. (2002). Tocopherols were evaluated following the AOCS Method Ce 8-89. Oxidative stability was evaluated by the Rancimat Method (Laübli and Bruttel, 1986). The -tocopherol content decreased slightly during ripening, whereas insignificant differences in its concentration
The total phenol content of the oils was significantly affected by the irrigation such that as the water dose applied to olive trees increased, the amount of the phenolic compounds in the virgin olive oil obtained decreased significantly (Table 6.3). For example, in crop 2003/04 in the case of rainfed virgin olive oil samples the total phenol content decreased from 1700 mg kg1 to 900 mg kg1 through fruit ripening, whereas for olive oil samples under FAO treatment, the phenol content decreased from 1080 to 650 mg kg1. Panelli et al. (1989), Salas et al. (1997), and Patumi et al. (1999, 2002) observed similar behavior for other olive cultivars like Picual, Nocellara del Belice, Kalamata and Ascolana Tenera. As was previously mentioned, the concentration of phenolic compounds affects the sensory bitterness attribute with the beneficial and important consequences earlier discussed in the case of the Cornicabra olive oil variety, as well as oxidative stability. In terms of the latter, the observed decrease in the oxidative stability does not affect the Cornicabra virgin olive oil shelf-life or quality since this is a very stable and phenol-rich olive oil variety, but could significantly reduce the shelf-life of other varieties like Arbequina, due to its naturally poor phenol content.
6.6.2 Phenolic Profile (Reprinted in part with permission from J Agric Food Chem 54 (2006) 7130–7136. Copyright 2006 American Chemical Society.) There is a considerable difference in the concentrations of secoiridoid derivatives of hydroxytyrosol and tyrosol observed in the VOO in the course of fruit ripening and under the various irrigation treatments studied. In fact the compounds most affected by irrigation scheduling of the olive grove and by ripening of the fruit were the complex phenol chemical forms, the levels of which decreased significantly in the VOO during ripening and as the water supplied increased. For example, in crop 2003/04 the 3,4-DHPEA-EDA content decreased from 770 mg kg1 to 450 mg kg1 and the 3,4-DHPEA-EA diminished from 300 mg kg1 to 170 mg kg1 in the course of fruit ripening in the rainfed (RF) VOO samples, while from RF conditions to FAO irrigation, at a ripeness index of approximately 4.0, the 3,4-DHPEA-EDA content decreased from
Chapter | 6 Influence of Irrigation Management and Ripening on Virgin Olive Oil Quality and Composition
Table 6.3 Virgin olive oil antioxidants content and oxidative stability as affected by the different irrigation treatments studied and the ripeness index of the fruits. 2003/2004
Ripeness index
-tocopherol (mg kg1)
Total phenols (mg kg1)
Oxidative stability (h)
RF
1.5 0.5a,w
283 64a,x
1719 130c,y
–
RDI-1
1.8 0.6ab,w
284 59a,w
1354 42b,y
–
2.5 0.4
b,w
125 FAO
2.0 0.3
ab,v
RF
FAO
a,w
222 25
a,x
a,z
–
a,y
–
1076 122
273 33
968 254
2.7 0.3a,x
235 43a,wx
1380 62c,x
38.3 0.5d,x
RDI-1
2.8 0.4a,x
259 35a,w
1084 146b,x
34.0 0.4c,w
FAO
3.1 0.3a,x
212 25a,w
998 85b,yz
31.1 1.3b,x
125 FAO
2.8 0.2a,w
254 26a,wx
805 125a,xy
27.1 0.1a,w
RF
3.2 0.3a,xy
226 41ab,wx
1294 64c,x
–
b,x
–
RDI-1
3.5 0.4
FAO 125 FAO
a,xy
b,w
252 29
946 40
3.6 0.4a,xy
201 25a,w
868 78b,xy
–
3.4 0.3a,x
237 8ab,wx
699 139a,wx
–
a,y
a,wx
225 47
1364 107
c,x
38.4 0.5d,x
RF
3.7 0.2
RDI-1
3.8 0.3a,y
242 44a,w
1004 160b,x
31.9 1.3c,w
FAO
4.0 0.4a,y
204 21a,w
824 56ab,x
30.1 1.3b,x
125 FAO
3.9 0.1a,y
227 25a,w
651 124a,wx
24.6 0.4a,w
RF
5.7 0.4b,z
193 32a,w
905 189b,w
34.4 0.3b,w
RDI-1
5.4 0.5ab,z
226 31a,w
757 12ab,w
28.5 3.2ab,w
FAO
5.5 0.3ab,z
202 11a,w
654 108a,w
24.3 0.5a,x
125 FAO
4.9 0.1a,z
233 19a,w
536 124a,w
22.2 3.4a,w
RF
2.8 0.2b,w
298 17b,w
1019 216a,w
29.8 2.2a,w
RDI-2
2.3 0.1a,w
250 7a,w
905 10a,x
32.5 2.0a,w
FAO
2.5 0.2ab,w
272 10ab,x
877 11a,x
30.3 0.9a,x
125 FAO
2.4 0.1a,w
271 19ab,w
724 38a,x
28.7 1.0a,x
RF
3.4 0.0a,x
280 14b,w
921 183b,w
29.7 2.5a,w
RDI-2
3.4 0.0a,x
238 11a,w
691 11ab,w
28.2 1.6a,w
FAO
3.4 0.0a,x
263 2b,wx
724 57ab,w
28.5 1.6a,wx
125 FAO
3.5 0.1a,x
238 3a,w
551 14a,wx
25.5 0.1a,x
RF
4.1 0.1a,y
269 12b,w
818 224b,w
27.2 3.4b,w
RDI-2
4.2 0.0a,y
226 3a,w
739 51b,w
27.4 1.1b,w
FAO
4.2 0.0a,y
241 8ab,x
679 19b,w
23.9 1.8ab,w
125 FAO
4.2 0.0a,y
241 17ab,w
423 102a,w
18.3 3.6a,w
2004/2005
The total phenol content in VOO decreased clearly as the irrigation dose applied in olive trees increased; as expected a similar behavior was observed in the oxidative stability of the oils. RF, rainfed; RDI, regulated deficit irrigation; FAO, Food and Agriculture Organization method. Different letters within a column (a–d) indicate significant differences (p 0.05) with respect to irrigation treatment in each sampling. Different letters within a column (w–z) indicate significant differences (p 0.05) with respect to ripeness index for each treatment. Reprinted with permission from Food Chemistry 100 (2007) 568–578. Copyright 2007 Elsevier Science.
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Section | I The Plant and Production
Figure 6.1 Evolution of hydroxytyrosol and its complex secoiridoid forms, and of tyrosol and its derivatives, in the course of fruit ripening as affected by irrigation management in crop season 2003/04. The complex phenols were not affected in the same way by irrigation, since the secoiridoid derivatives of hydroxytyrosol decreased more than those of tyrosol. , rainfed; , regulated deficit irrigation, RDI-1; , FAO; , 125 FAO. Reprinted with permission from J Agric Food Chem 54 (2006) 7130–7136. Copyright 2006 American Chemical Society.
676 mg kg1 to 388 mg kg1 and the 3,4-DHPEA-EA from 258 mg kg1 to 123 mg kg1. Tovar et al. (2001) observed similar behavior for the Arbequina cultivar, since the levels of secoiridoids diminished as the irrigation dose of olive trees increased. As far as the 2004/05 crop season is concerned, although the levels of complex phenols in the VOO samples were lower, the trend was similar to that of the previous crop season. It is important to note that the differences in phenol contents between the oils from FAO and the second regulated deficit irrigation (RDI-2) strategy were not statistically significant; this indicates that the RDI scheduling employed in the second crop season (RDI-2), where water was applied from the beginning of August only, produced a VOO with a phenolic composition more similar to that of oil from FAO-treated olives than that from olives grown under RDI-1 water scheduling of the previous year. Indeed, the phenolic and volatile composition related to the quality of VOO comparable to FAO management was achieved with less demand in water supply. Moreover, the complex phenols were not affected in the same way by irrigation, since the secoiridoid derivatives of hydroxytyrosol decreased more than those of tyrosol, as clearly shown in Figure 6.1. This is very important, since hydroxytyrosol and its complex derivative forms are known to possess much greater antioxidant activity and organoleptic influence than the tyrosol group (Baldioli et al., 1996; Gennaro et al., 1998). These results were similar to those reported by Tovar et al. (2001, 2002) for the Arbequina variety.
6.7 Volatile compounds 6.7.1 Evolution Along Fruit Ripening Figure 6.2 depicts the evolution of the main volatile compounds found in Cornicabra virgin olive oil in the course of fruit ripening as affected by RF and FAO irrigation conditions in crop season 2003/04. Solid phase microextraction (SPME) followed by GC is used to analyze the volatiles (Vichi et al., 2003). In all the Cornicabra VOO samples analyzed, the major volatile component was the C6 aldehyde fraction, the content of which decreased as ripening progressed. For example, the E-2-hexenal content ranged between 4.2 mg kg1 and 2.6 mg kg1 (as internal standard; IS) over fruit maturation for VOOs under RF conditions and between 8.0 mg kg1 and 3.5 mg kg1 for those under FAO scheduling; the amount of hexanal was lower and varied between 1.10 mg kg1 and 0.45 mg kg1 over fruit ripening under RF conditions and between 0.90 mg kg1 and 0.50 mg kg1 under FAO treatment. These compounds, which are responsible for the positive green sensory notes in VOO, are produced through the LOX pathway that takes place during crushing of the olive fruit and olive paste malaxation and are incorporated into the oily phase (Sanchez and Harwood, 2002). Aparicio et al. (1998) reported similar behavior, but other researchers (Angerosa et al., 2001) have shown that during olive ripening the amount of volatile compounds, especially E-2-hexenal, increased up to a maximum
Chapter | 6 Influence of Irrigation Management and Ripening on Virgin Olive Oil Quality and Composition
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Figure 6.2 Evolution of main volatile compounds in virgin olive oils under rainfed conditions and FAO irrigation scheduling in the course of fruit ripening in crop season 2003/04. A great fall of C6 aldehydes in VOO along the fruit maturation, as well as a higher content of E-2-hexenal, hexan-1-ol and Z-3-hexen-1-ol in VOO from FAO methodology rather than in rainfed conditions is observed. (open circle), E-2-hexenal; , hexanal; , Z-3hexen-1-ol; , hexan-1-ol; , E-2-hexen-1-ol. Reprinted with permission from J Agric Food Chem 54 (2006) 7130–7136. Copyright 2006 American Chemical Society.
concentration, which occurred when fruit skin color turned from yellow-green to purple; beyond that point the volatile content decreased. With respect to the evolution of C6 alcohols, there was a significant decrease in E-2-hexen-1-ol content, while hexan-1-ol and Z-3-hexen-1-ol increased slightly during fruit ripening. It is worth noting that this observed increase was statistically significant in VOO from olives under FAO and 125 FAO treatments, which received the highest irrigation doses. A similar trend was observed in the crop season 2004/05. As regards C6 esters such as hexyl-acetate and Z-3-hexyl-acetate, these were present in very small amounts in Cornicabra VOO, indicating that there was also little activity of the alcohol acyl transferase.
6.7.2 Effect of Irrigation The volatile compounds most affected by the irrigation were E-2-hexenal, Z-3-hexen-1-ol and hexan-1-ol, in the sense that the increase in the water applied to the olive trees produced an increase in these volatiles, mainly in oils from fruits whose ripeness index was higher than 2.5–3.0. RDI-1 resulted in a VOO with a similar volatile composition to those from FAO treatment. On the other hand, the total volatile levels in VOOs produced under RDI-2 conditions were higher than in VOOs produced under FAO conditions and similar to the levels found in VOOs produced under 125 FAO conditions. It is therefore very important to note that the VOOs produced by the second RDI strategy were richer in volatile compounds than those produced
under FAO conditions, but with a considerable reduction in the total amount of water used in the olive grove.
Summary points The quality indices are generally not influenced by irrigation, since no statistically significant differences in oil from rainfed and irrigation treatments are observed. l The different water stress levels in olive trees affect not only the total amount of phenolic and volatile compounds in the VOO but also their profile. l The total polar phenol content, which affects the sensory bitterness in the oils, decreases significantly as the amount of supplied water increases. l Complex phenols are not affected in the same way by irrigation, since the secoiridoid derivatives of hydroxytyrosol decreased more than those of tyrosol. l The volatile compounds most affected by the irrigation are E-2-hexenal, Z-3-hexen-1-ol and hexan-1-ol; the increase in the water applied to the olive trees produces an increase in these volatiles. l The selection of an optimal irrigation treatment for traditional Cornicabra olive orchards in Castilla – La Mancha calls for the establishment of a suitable compromise between olive production, virgin olive oil characteristics and water consumption. l The best irrigation treatment is regulated deficit irrigation (RDI), and apparently better results are obtained applying water only from the beginning of August when the accumulation of oil begins in the fruit. l
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References Angerosa, F., Mostallino, R., Basti, C., Vito, R., 2001. Influence of malaxation temperature and time on the quality of virgin olive oils. Food Chem. 72, 19–28. Aparicio, R., Morales, M.T., 1998. Characterization of olive ripeness by green aroma compounds of virgin olive oil. J. Agric. Food Chem. 46, 1116–1122. Aparicio, R., Luna, G., 2002. Characterisation of monovarietal virgin olive oil. Eur. J. Lipid Sci. Tech. 104, 614–627. Baldioli, M., Servili, M., Peretti, G., Montedoro, G.F., 1996. Antioxidant activity of tocopherols and phenolic compounds of virgin olive oil. J. Am. Oil Chem. Soc. 73, 1589–1593. D’Andria, R., Morelli, G., Martuccio, G., Fontanazza, G., Patumi, M., 1996. Valutazione della produzione e della qualita’dell’olio di Giovanni piante di olivo allevate con diversi regimi idrici. Italus Hortus 3, 23–31. Dettori, S., Russo, G., 1993. Influencia del cultivar y del régimen hídrico sobre el volumen y la calidad del aceite de oliva. Olivae 49, 36–43. Gennaro, L., Piciola Bocca, A., Modesti, D., Masella, R., Coni, E., 1998. Effect of biophenols on olive oil stability evaluated by thermogravimetric analysis. J. Agric. Food Chem. 46, 4465–4469. Gómez-Alonso, S., Salvador, M.D., Fregapane, G., 2002. Phenolic compounds profile of Cornicabra virgin olive oil. J. Agric. Food Chem. 50, 6812–6817. Gómez-Rico, A., Salvador, M.D., La Greca, M., Fregapane, G., 2006. Phenolic and volatile compounds of extra virgin olive oil (Olea europea L. cv. Cornicabra) with regards to fruit ripening and irrigation management. J. Agric. Food Chem. 54, 7130–7136. Gómez-Rico, A., Salvador, M.D., Moriana, A., Pérez, D., Olmedilla, N., Ribas, F., Fregapane, G., 2007. Influence of different irrigation strategies in a traditional Cornicabra cv. olive orchard on virgin olive oil composition and quality. Food Chem. 100, 568–578. Gutiérrez-Rosales, F., Perdiguero, S., Gutiérrez, R., Olías, J.M., 1992. Evaluation of bitter taste in virgin olive oil. J. Am. Oil Chem. Soc. 69, 394–395. Laübli, M.W., Bruttel, P.A., 1986. Determination of the oxidative stability of fats and oils by the Rancimat method. J. Am. Oil Chem. Soc. 63, 792–795. Mateos, R., Espartero, J.L., Trujillo, M., Ríos, J.J., León-Camacho, M., Alcudia, F., Cert, A., 2001. Determination of phenols, flavones
Section | I The Plant and Production
and lignans in virgin olive oil by solid-phase extraction and highperformance liquid chromatography with diode array ultraviolet detection. J. Agric. Food Chem. 49, 2185–2192. Motilva, M.J., Romero, M.P., Alegre, S., Girona, J., 1999. Effect of regulated déficit irrigation in olive oil production and quality. Acta Hort. 474, 377–380. Motilva, M.J., Tovar, M.J., Romero, M.P., Alegre, A., Girona, J., 2000. Influence of regulated deficit irrigation strategies applied to olive trees (Arbequina cultivar) on oil yield and oil composition during the fruit ripening. J. Sci. Food Agric. 80, 2037–2043. Panelli, G., Famiani, F., Servili, M., Montedoro, G.F., 1989. Agro-climatic factors and characteristics of the compostion of virgin olive oils. Acta Hort. 286, 477–480. Patumi, M., d’Andria, R., Fontanazza, G., Morelli, G., Giori, P., Sorrentino, G., 1999. Yield and oil quality of intensively trained trees of three cultivars of olive under different irrigation regimes. J. Hort. Sci. Biotech. 74, 729–737. Patumi, M., d’Andria, R., Marsilio, G., Fontanazza, G., Morelli, G., Lanza, B., 2002. Olive and olive oil quality after intensive monocone olive growing (Olea europaea L., cv. Kalamata) in different irrigation regimes. Food Chem. 77, 27–34. Salas, J., Pastor, M., Castro, J., Vega, V., 1997. Influencia del riego sobre la composición y características del aceite de oliva. Grasas y Aceites 48, 74–82. Sanchez, J., Harwood, J.L., 2002. Byosinthesis of triacylglycerols and volatiles in olives. Eur. J. Lipid Sci. Tech. 104, 564–573. Tovar, M.J., Romero, M.P.J., Motilva, M.J., 2001. Changes in the phenolic composition of olive oil from young trees (Olea europaea L. cv. Arbequina) grown under linear irrigation strategies. J. Agric. Food Chem. 49, 5502–5508. Tovar, M.J., Romero, M.P., Alegre, S., Girona, J., Motilva, M.J., 2002. Composition and organoleptic characteristics of oil from Arbequina olive (Olea europaea L) trees under déficit irrigation. J. Sci. Food Agric. 82, 1755–1763. Vichi, S., Castellote, A.I., Pizzale, L., Conte, L.S., Buxaderas, S., LopezTamames, E., 2003. Analysis of virgin olive oil volatile compounds by headspace solid-phase microextraction coupled to gas chromatography with mass spectrometric and flame ionisation detection. J. Chromatograp. A 983, 19–33.
Influence of Irrigation Management and Ripening on Virgin Olive Oil Quality and Composition Giuseppe Fregapane, Aurora Gómez-Rico and Maria Desamparados Salvador Departamento de Tecnología de Alimentos, Universidad de Castilla – La Mancha, Spain
6.1 Introduction
6.2 Irrigation management
The olive tree is generally grown under rainfed conditions, especially in Castilla – La Mancha, a region with limited water resources. Nevertheless, since irrigation increases the yield of the olive orchard, even with a low amount of water, there is increasing interest in irrigated agriculture. This has led to a situation in which some of the traditional olive groves and the majority of the new ones are being adapted to irrigation techniques. However, a satisfactory compromise between the amount of water applied and the improvement in the production of the olive crop and characteristics of virgin olive oil must be reached. Some recent research has shown differences in the chemical makeup and sensory characteristics of virgin olive oil from irrigated and rainfed olive trees (Aparicio and Luna, 2002). The chemical components most influenced by irrigation are the phenolic compounds which affect both the oxidative stability and the sensory characteristics, especially the bitterness attribute, showing in both cases an inverse relationship with the amount of water applied to the olive trees (D’Andria et al., 1996; Motilva et al., 1999, 2000; Tovar et al., 2001). This aspect is important in olive cultivars that produce virgin olive oils with high bitterness and pungency, like the Cornicabra variety in Castilla – La Mancha and therefore just the right level of irrigation could enhance its sensory characteristics. To optimize sustainable irrigation conditions in the Cornicabra olive cultivar grown in Castilla – La Mancha, a region where aquifers are over-exploited, and to study the effect of different irrigation management and ripening on the composition of Cornicabra virgin olive oil, different irrigation treatments (based on 100% crop evapotranspiration, ETc, also known as the FAO method, 125 FAO, two different regulated deficit irrigation strategies and rainfed) were applied to a traditional olive orchard (Cornicabra cv).
The experimental olive orchard of Cornicabra cv., located in Ciudad Real (Spain), is constituted by three hundred 50-year-old trees (spaced 12 12 m2) structured in a randomized complete block design with four different irrigation treatments (Table 6.1): rainfed (RF) conditions, regulated deficit irrigation (RDI), FAO and 125 FAO. Rainfed conditions were used as a control to compare the results obtained with the irrigation treatments. In FAO treatment the water requirements were calculated using a methodology based on the crop evapotranspiration (ETc) proposed by the United Nations Food and Agriculture Organization. In 125 FAO treatments a total irrigation dosage 25% higher than the FAO treatment was applied. For regulated deficit irrigation (RDI), a maximum of 75 mm of water was established since in many Spanish irrigated olive areas there is a legal limit of 100 mm. Two different strategies were evaluated. In 2003 (RDI-1), water was applied throughout the entire season with different rates of application (10% FAO in May and June, 4% FAO in July and August and 18% FAO in September); whereas in 2004 (RDI-2), based on the results obtained during the previous crop season, water was applied only from the beginning of August, when the oil starts to form in the fruit, for the purpose of investigating which RDI treatment is more effective in achieving similar olive production and olive oil quality to that obtained by the FAO method while considerably reducing the total amount of water applied. The total water applied in 2003/04 for the different irrigation treatments was: 56 mm for RDI-1, 148 mm for FAO and 206 mm for 125 FAO; and in 2004/05: 60 mm for RDI-2, 124 mm for FAO and 154 mm for 125 FAO. More detailed data on the irrigation management have been previously reported (Gómez-Rico et al., 2006, 2007).
Olives and Olive Oil in Health and Disease Prevention. ISBN: 978-0-12-374420-3
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Section | I The Plant and Production
Table 6.1 Key facts of irrigation management. This table lists the key facts of irrigation management describing the basic characteristics of the different irrigation treatments studied in the Cornicabra olive orchard. 1. Irrigation management in olive orchard increases the olive and olive oil production 2. Water applied to olive trees may affect virgin olive oil quality and composition 3. According to the irrigation methodology proposed by the FAO (Food and Agriculture Organization), the total water requirements of olive trees is calculated by subtracting the effective precipitation from the crop evapotranspiration (ETc) 4. ETc is calculated using the effective crop coefficient (Kc), the reference crop evapotranspiration (ETo), and a reducing coefficient (Kr) 5. The regulated deficit irrigation (RDI) is based on a lower dose of water to the olive orchard than the 100% ETc, established according to the weather and phenological stage of the trees, assuring an adequate water status during full bloom and oil accumulation in the fruit 6. The olive trees in rainfed (RF) condition only receive the effective precipitations and therefore are used to determine the ‘highest water stress’ situation 7. Olive trees are generally irrigated by compensating drippers placed around the trees
Olive fruit samples from rainfed and irrigation treatment trees were harvested throughout ripening, from immature stage to normal harvest period for the Cornicabra variety (from the beginning of November to the middle of January). The influence of fruit ripening and irrigation management on the production of the olive grove, which was significantly lower under rainfed conditions than under irrigation (about 35%), and the characteristics and composition of the olive fruit have been discussed elsewhere (Gómez-Rico et al., 2007).
6.3 Virgin olive oil quality indices Free acidity, given as % of oleic acid, peroxide value (PV) expressed as milliequivalents of active oxygen per kilogram of oil (meq O2 kg1), and K232 and K270 extinction coefficients calculated from absorption at 232 and 270 nm, were measured following the analytical methods described in European Regulation EEC 2568/91 and subsequent amendments. The observed free acidity ranging from 0.09 to 0.20%, and peroxide value, from 1.7 to 3.4 meqO2 kg1, of the different types of virgin olive oils (VOO) studied in this assay
in the crop season 2003/04 were considerably lower than the upper limit of 0.8% as oleic acid and 20 meqO2 kg1, respectively, established by EU legislation for extra virgin olive oil. Moreover, these two quality indices were not influenced by irrigation, since no statistically significant differences in oil from rainfed and irrigation treatments in the crop season 2003/04 were obtained. This was also observed by Tovar et al. (2001) in virgin olive oils from Arbequina cultivar, Dettori and Russo (1993) in Leccino, Nociara and Ogliarola Salentina cultivars and Patumi et al. (1999) in Nocellara del Belice and Ascolana Tenera cultivars. On the contrary, in crop 2004/05 a statistical difference for free acidity and peroxide value was indeed obtained between RF and the irrigation treatments due to the higher degree of fruit damage as a consequence of the olive fly attack. Nevertheless, the values of free acidity and the peroxide value of the olive oil obtained from partially damaged fruit were not high from an olive oil quality point of view: a maximum acidity of 0.4% and a 5.4 peroxide value were observed.
6.4 Sensory characteristics All the virgin olive oils obtained using the different irrigation treatments of the trees were classified as ‘extra virgin’ oil by means of the organoleptic evaluation as reported in Table 6.2. Sensory evaluation was assessed by an International Olive Oil Council-recognized panel of assessors from the Protected Designation of Origin ‘Montes de Toledo’ (Toledo, Spain) according to Annex XII of Regulation EC 796/2002 (amending ECC 2568/91). Sensory attributes affected by irrigation were ‘bitterness’, ‘pungency’ and ‘fruitiness’, according to what has previously been described for other olive cultivars (Salas et al., 1997; Tovar et al., 2001, 2002). As is known, the intensity of sensory pungency and especially bitterness are related to the phenol content in the olive oil, which, as expected, was higher in oils obtained under rainfed conditions. In all cases, a slight decrease in the intensity of these positive attributes was observed, more marked in the case of bitterness, by increasing the amount of water delivered through irrigation. This observation is very relevant from the olive quality and marketing point of view since, although bitterness is a positive sensory attribute in virgin olive oil, a high level of bitterness could cause consumers to reject the oil. A high level of bitterness is a typical characteristic of the Cornicabra variety virgin olive oils’ sensory profile, and therefore the use of irrigation could produce a desirable descent in the intensity of this attribute and hence increase consumer preference. However, in the 2004/05 crop season no statistically significant differences were obtained in the positive sensory attributes, including bitterness, between the olive oils obtained under rainfed and irrigation conditions.
Chapter | 6 Influence of Irrigation Management and Ripening on Virgin Olive Oil Quality and Composition
Table 6.2 Virgin olive oil organoleptic evaluation as affected by the different irrigation treatments and the ripeness index of the fruits. Ripeness Index
Grade
2003/2004
Sensory attributes
K225
Fruity
Bitterness
Pungency
RF
2.7 0.3a,x
Extra Virgin
6.1 0.2b,x
8.2 0.4b,w
7.8 0.3a,w
0.78 0.01c,x
RDI-1
2.8 0.4a,x
Extra Virgin
6.2 0.5b,w
8.0 0.3b,wx
8.0 0.3a,wx
0.67 0.07b,x
FAO
3.1 0.3a,x
Extra Virgin
5.5 0.1b,w
7.7 0.5ab,w
7.7 0.3a,w
0.66 0.04b,yz
125 FAO
2.8 0.2a,w
Extra Virgin
4.9 0.3a,w
7.2 0.3a,wx
7.6 0.3a,w
0.56 0.07a,xy
RF
3.7 0.2a,y
Extra Virgin
5.4 0.2ab,w
8.5 0.2c,w
8.4 0.2ab,w
0.77 0.01c,x
RDI-1
3.8 0.3a,y
Extra Virgin
6.2 0.3b,w
8.3 0.2c,x
8.5 0.1b,w
0.64 0.07b,wx
FAO
4.0 0.4a,y
Extra Virgin
5.5 0.2ab,w
7.7 0.3b,w
8.0 0.2ab,w
0.56 0.04ab,x
125 FAO
3.9 0.1a,y
Extra Virgin
5.3 0.2a,w
6.9 0.4a,w
8.0 0.2a,w
0.49 0.08a,wx
RF
5.7 0.4b,z
Extra Virgin
5.4 0.3ab,wx
8.3 0.2a,w
8.1 0.2ab,w
0.66 0.05c,w
RDI-1
5.4 0.5ab,z
Extra Virgin
6.2 0.1b,w
7.5 0.5a,w
7.7 0.1a,x
0.57 0.03b,w
FAO
5.5 0.3ab,z
Extra Virgin
5.0 0.3a,w
7.7 0.3a,w
7.9 0.2a,w
0.46 0.03a,w
125 FAO
4.9 0.1a,z
Extra Virgin
6.0 0.1b,x
8.0 0.3a,x
8.0 0.2b,w
0.41 0.09a,w
RF
2.8 0.2b,w
Extra Virgin
6.4 0.3a,w
7.6 0.2a,w
8.0 0.3a,w
0.66 0.09a,w
RDI-2
2.3 0.1a,w
Extra Virgin
6.0 0.2a,x
7.4 0.5a,w
7.9 0.6a,wx
0.70 0.00a,x
FAO
2.5 0.2ab,w
Extra Virgin
5.6 0.4a,w
6.7 0.3a,w
7.5 0.2a,w
0.67 0.00a,x
125 FAO
2.4 0.1a,w
Extra Virgin
5.2 0.6a,w
7.3 0.2a,w
7.7 0.3a,w
0.60 0.00a,y
RF
3.4 0.0a,x
Extra Virgin
5.5 0.2ab,w
7.0 0.5a,w
7.4 0.5a,w
0.60 0.08a,w
RDI-2
3.4 0.0a,x
Extra Virgin
4.9 0.4a,w
7.0 0.3a,w
7.1 0.3a,w
0.60 0.03a,x
FAO
3.4 0.0a,x
Extra Virgin
5.5 0.2ab,w
6.9 0.4a,w
7.6 0.2a,w
0.59 0.03a,x
125 FAO
3.5 0.1a,x
Extra Virgin
5.5 0.5b,w
6.6 0.3a,w
7.4 0.2a,w
0.50 0.02a,x
RF
4.1 0.1a,y
Extra Virgin
6.0 0.4a,w
7.4 0.3ab,w
7.6 0.4a,w
0.59 0.12b,w
RDI-2
4.2 0.0a,y
Extra Virgin
5.4 0.3a,wx
7.6 0.2b,w
8.2 0.2a,x
0.57 0.01b,w
FAO
4.2 0.0a,y
Extra Virgin
5.4 0.3a,w
7.4 0.3b,w
7.5 0.3a,w
0.54 0.01ab,w
125 FAO
4.2 0.0a,y
Extra Virgin
5.9 0.2a,w
6.6 0.4a,w
7.4 0.3a,w
0.36 0.04a,w
2004/2005
Sensory attributes affected by irrigation were ‘bitterness’, ‘pungency’ and ‘fruitiness’. In all cases, a slight decrease in the intensity of these positive attributes was observed, more marked in the case of bitterness, by increasing the amount of water delivered through irrigation. RF, rainfed; RDI, regulated deficit irrigation; FAO, Food and Agriculture Organization method. Different letters within a column (a–c) indicate significant differences (p 0.05) with respect to irrigation treatment in each sampling. Different letters within a column (w–y) indicate significant differences (p 0.05) with respect to ripeness index for each treatment.
53
54
Olive oil bitterness can also be measured by the instrumental K225 parameter called bitterness index (GutiérrezRosales et al., 1992). In the 2003/04 crop, a great decrease in the bitterness index was observed as the water dose applied to olive trees increased (Table 6.2), varying from 0.77 to 0.49 respectively for RF and 125 FAO for the sampling close to a ripeness index of 4.0. However, in the 2004/05 crop no statistically significant differences were obtained.
Section | I The Plant and Production
were observed between the irrigation treatments studied. However, Tovar et al. (2002) reported significant increases in the -tocopherol values in Arbequina VOO as the irrigation doses applied in the trees increased. On the other hand, these rises did not imply changes in the oxidative stability of the oils.
6.6.1 Total Phenol Content 6.5 Fatty acid composition Fatty acid composition is performed according to the European Regulations EEC 2568/91 and subsequent amendments, corresponding to the AOCS Method Ch 2-91. In both crop seasons studied and in all irrigation treatments studied, the palmitic acid content slightly decreased as fruit ripened, i.e. from 10.4% down to 9.1% and from 11.4% to 9.7% respectively for RF and FAO irrigation treatments; whereas oleic and linoleic acids showed an opposite trend, i.e. the oleic acid content varied from 78.4% to 79.5% and the linoleic acid from 3.7% to 4.6% under the FAO conditions. The increase in oleic acid content is due to the triacylglycerols’ active biosynthesis which takes place throughout fruit ripening, involving a fall in the relative percentage of the oil’s palmitic acid content. On the other hand, the increase in linoleic acid content is due to the transformation of oleic acid into linoleic acid by the oleate desaturase activity which is active during triacylglycerol biosynthesis (Sanchez and Harwood, 2002). The content of the other fatty acids remained practically unchanged during fruit ripening. In the 2003/04 crop, rainfed olive oils always showed a statistically significant higher content in oleic acid, whereas olive oils from irrigated trees had a higher content in palmitic and linoleic acids. As a consequence, the unsaturated/ saturated and MUFA/PUFA ratios were significantly higher in oils obtained in rainfed conditions, in line with the results obtained by Salas et al. (1997). However, these changes are very slight and do not possess any nutritional value relevance.
6.6 Natural antioxidants content The values of the -tocopherol and total phenol content and the oxidative stability of the virgin olive oils obtained from the different treatments studied are shown in Table 6.3. Phenolic compounds were quantified by HPLC at 280 nm using syringic acid as internal standard and the response factors determined by Mateos et al. (2001), and described in GomezAlonso et al. (2002). Tocopherols were evaluated following the AOCS Method Ce 8-89. Oxidative stability was evaluated by the Rancimat Method (Laübli and Bruttel, 1986). The -tocopherol content decreased slightly during ripening, whereas insignificant differences in its concentration
The total phenol content of the oils was significantly affected by the irrigation such that as the water dose applied to olive trees increased, the amount of the phenolic compounds in the virgin olive oil obtained decreased significantly (Table 6.3). For example, in crop 2003/04 in the case of rainfed virgin olive oil samples the total phenol content decreased from 1700 mg kg1 to 900 mg kg1 through fruit ripening, whereas for olive oil samples under FAO treatment, the phenol content decreased from 1080 to 650 mg kg1. Panelli et al. (1989), Salas et al. (1997), and Patumi et al. (1999, 2002) observed similar behavior for other olive cultivars like Picual, Nocellara del Belice, Kalamata and Ascolana Tenera. As was previously mentioned, the concentration of phenolic compounds affects the sensory bitterness attribute with the beneficial and important consequences earlier discussed in the case of the Cornicabra olive oil variety, as well as oxidative stability. In terms of the latter, the observed decrease in the oxidative stability does not affect the Cornicabra virgin olive oil shelf-life or quality since this is a very stable and phenol-rich olive oil variety, but could significantly reduce the shelf-life of other varieties like Arbequina, due to its naturally poor phenol content.
6.6.2 Phenolic Profile (Reprinted in part with permission from J Agric Food Chem 54 (2006) 7130–7136. Copyright 2006 American Chemical Society.) There is a considerable difference in the concentrations of secoiridoid derivatives of hydroxytyrosol and tyrosol observed in the VOO in the course of fruit ripening and under the various irrigation treatments studied. In fact the compounds most affected by irrigation scheduling of the olive grove and by ripening of the fruit were the complex phenol chemical forms, the levels of which decreased significantly in the VOO during ripening and as the water supplied increased. For example, in crop 2003/04 the 3,4-DHPEA-EDA content decreased from 770 mg kg1 to 450 mg kg1 and the 3,4-DHPEA-EA diminished from 300 mg kg1 to 170 mg kg1 in the course of fruit ripening in the rainfed (RF) VOO samples, while from RF conditions to FAO irrigation, at a ripeness index of approximately 4.0, the 3,4-DHPEA-EDA content decreased from
Chapter | 6 Influence of Irrigation Management and Ripening on Virgin Olive Oil Quality and Composition
Table 6.3 Virgin olive oil antioxidants content and oxidative stability as affected by the different irrigation treatments studied and the ripeness index of the fruits. 2003/2004
Ripeness index
-tocopherol (mg kg1)
Total phenols (mg kg1)
Oxidative stability (h)
RF
1.5 0.5a,w
283 64a,x
1719 130c,y
–
RDI-1
1.8 0.6ab,w
284 59a,w
1354 42b,y
–
2.5 0.4
b,w
125 FAO
2.0 0.3
ab,v
RF
FAO
a,w
222 25
a,x
a,z
–
a,y
–
1076 122
273 33
968 254
2.7 0.3a,x
235 43a,wx
1380 62c,x
38.3 0.5d,x
RDI-1
2.8 0.4a,x
259 35a,w
1084 146b,x
34.0 0.4c,w
FAO
3.1 0.3a,x
212 25a,w
998 85b,yz
31.1 1.3b,x
125 FAO
2.8 0.2a,w
254 26a,wx
805 125a,xy
27.1 0.1a,w
RF
3.2 0.3a,xy
226 41ab,wx
1294 64c,x
–
b,x
–
RDI-1
3.5 0.4
FAO 125 FAO
a,xy
b,w
252 29
946 40
3.6 0.4a,xy
201 25a,w
868 78b,xy
–
3.4 0.3a,x
237 8ab,wx
699 139a,wx
–
a,y
a,wx
225 47
1364 107
c,x
38.4 0.5d,x
RF
3.7 0.2
RDI-1
3.8 0.3a,y
242 44a,w
1004 160b,x
31.9 1.3c,w
FAO
4.0 0.4a,y
204 21a,w
824 56ab,x
30.1 1.3b,x
125 FAO
3.9 0.1a,y
227 25a,w
651 124a,wx
24.6 0.4a,w
RF
5.7 0.4b,z
193 32a,w
905 189b,w
34.4 0.3b,w
RDI-1
5.4 0.5ab,z
226 31a,w
757 12ab,w
28.5 3.2ab,w
FAO
5.5 0.3ab,z
202 11a,w
654 108a,w
24.3 0.5a,x
125 FAO
4.9 0.1a,z
233 19a,w
536 124a,w
22.2 3.4a,w
RF
2.8 0.2b,w
298 17b,w
1019 216a,w
29.8 2.2a,w
RDI-2
2.3 0.1a,w
250 7a,w
905 10a,x
32.5 2.0a,w
FAO
2.5 0.2ab,w
272 10ab,x
877 11a,x
30.3 0.9a,x
125 FAO
2.4 0.1a,w
271 19ab,w
724 38a,x
28.7 1.0a,x
RF
3.4 0.0a,x
280 14b,w
921 183b,w
29.7 2.5a,w
RDI-2
3.4 0.0a,x
238 11a,w
691 11ab,w
28.2 1.6a,w
FAO
3.4 0.0a,x
263 2b,wx
724 57ab,w
28.5 1.6a,wx
125 FAO
3.5 0.1a,x
238 3a,w
551 14a,wx
25.5 0.1a,x
RF
4.1 0.1a,y
269 12b,w
818 224b,w
27.2 3.4b,w
RDI-2
4.2 0.0a,y
226 3a,w
739 51b,w
27.4 1.1b,w
FAO
4.2 0.0a,y
241 8ab,x
679 19b,w
23.9 1.8ab,w
125 FAO
4.2 0.0a,y
241 17ab,w
423 102a,w
18.3 3.6a,w
2004/2005
The total phenol content in VOO decreased clearly as the irrigation dose applied in olive trees increased; as expected a similar behavior was observed in the oxidative stability of the oils. RF, rainfed; RDI, regulated deficit irrigation; FAO, Food and Agriculture Organization method. Different letters within a column (a–d) indicate significant differences (p 0.05) with respect to irrigation treatment in each sampling. Different letters within a column (w–z) indicate significant differences (p 0.05) with respect to ripeness index for each treatment. Reprinted with permission from Food Chemistry 100 (2007) 568–578. Copyright 2007 Elsevier Science.
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Section | I The Plant and Production
Figure 6.1 Evolution of hydroxytyrosol and its complex secoiridoid forms, and of tyrosol and its derivatives, in the course of fruit ripening as affected by irrigation management in crop season 2003/04. The complex phenols were not affected in the same way by irrigation, since the secoiridoid derivatives of hydroxytyrosol decreased more than those of tyrosol. , rainfed; , regulated deficit irrigation, RDI-1; , FAO; , 125 FAO. Reprinted with permission from J Agric Food Chem 54 (2006) 7130–7136. Copyright 2006 American Chemical Society.
676 mg kg1 to 388 mg kg1 and the 3,4-DHPEA-EA from 258 mg kg1 to 123 mg kg1. Tovar et al. (2001) observed similar behavior for the Arbequina cultivar, since the levels of secoiridoids diminished as the irrigation dose of olive trees increased. As far as the 2004/05 crop season is concerned, although the levels of complex phenols in the VOO samples were lower, the trend was similar to that of the previous crop season. It is important to note that the differences in phenol contents between the oils from FAO and the second regulated deficit irrigation (RDI-2) strategy were not statistically significant; this indicates that the RDI scheduling employed in the second crop season (RDI-2), where water was applied from the beginning of August only, produced a VOO with a phenolic composition more similar to that of oil from FAO-treated olives than that from olives grown under RDI-1 water scheduling of the previous year. Indeed, the phenolic and volatile composition related to the quality of VOO comparable to FAO management was achieved with less demand in water supply. Moreover, the complex phenols were not affected in the same way by irrigation, since the secoiridoid derivatives of hydroxytyrosol decreased more than those of tyrosol, as clearly shown in Figure 6.1. This is very important, since hydroxytyrosol and its complex derivative forms are known to possess much greater antioxidant activity and organoleptic influence than the tyrosol group (Baldioli et al., 1996; Gennaro et al., 1998). These results were similar to those reported by Tovar et al. (2001, 2002) for the Arbequina variety.
6.7 Volatile compounds 6.7.1 Evolution Along Fruit Ripening Figure 6.2 depicts the evolution of the main volatile compounds found in Cornicabra virgin olive oil in the course of fruit ripening as affected by RF and FAO irrigation conditions in crop season 2003/04. Solid phase microextraction (SPME) followed by GC is used to analyze the volatiles (Vichi et al., 2003). In all the Cornicabra VOO samples analyzed, the major volatile component was the C6 aldehyde fraction, the content of which decreased as ripening progressed. For example, the E-2-hexenal content ranged between 4.2 mg kg1 and 2.6 mg kg1 (as internal standard; IS) over fruit maturation for VOOs under RF conditions and between 8.0 mg kg1 and 3.5 mg kg1 for those under FAO scheduling; the amount of hexanal was lower and varied between 1.10 mg kg1 and 0.45 mg kg1 over fruit ripening under RF conditions and between 0.90 mg kg1 and 0.50 mg kg1 under FAO treatment. These compounds, which are responsible for the positive green sensory notes in VOO, are produced through the LOX pathway that takes place during crushing of the olive fruit and olive paste malaxation and are incorporated into the oily phase (Sanchez and Harwood, 2002). Aparicio et al. (1998) reported similar behavior, but other researchers (Angerosa et al., 2001) have shown that during olive ripening the amount of volatile compounds, especially E-2-hexenal, increased up to a maximum
Chapter | 6 Influence of Irrigation Management and Ripening on Virgin Olive Oil Quality and Composition
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Figure 6.2 Evolution of main volatile compounds in virgin olive oils under rainfed conditions and FAO irrigation scheduling in the course of fruit ripening in crop season 2003/04. A great fall of C6 aldehydes in VOO along the fruit maturation, as well as a higher content of E-2-hexenal, hexan-1-ol and Z-3-hexen-1-ol in VOO from FAO methodology rather than in rainfed conditions is observed. (open circle), E-2-hexenal; , hexanal; , Z-3hexen-1-ol; , hexan-1-ol; , E-2-hexen-1-ol. Reprinted with permission from J Agric Food Chem 54 (2006) 7130–7136. Copyright 2006 American Chemical Society.
concentration, which occurred when fruit skin color turned from yellow-green to purple; beyond that point the volatile content decreased. With respect to the evolution of C6 alcohols, there was a significant decrease in E-2-hexen-1-ol content, while hexan-1-ol and Z-3-hexen-1-ol increased slightly during fruit ripening. It is worth noting that this observed increase was statistically significant in VOO from olives under FAO and 125 FAO treatments, which received the highest irrigation doses. A similar trend was observed in the crop season 2004/05. As regards C6 esters such as hexyl-acetate and Z-3-hexyl-acetate, these were present in very small amounts in Cornicabra VOO, indicating that there was also little activity of the alcohol acyl transferase.
6.7.2 Effect of Irrigation The volatile compounds most affected by the irrigation were E-2-hexenal, Z-3-hexen-1-ol and hexan-1-ol, in the sense that the increase in the water applied to the olive trees produced an increase in these volatiles, mainly in oils from fruits whose ripeness index was higher than 2.5–3.0. RDI-1 resulted in a VOO with a similar volatile composition to those from FAO treatment. On the other hand, the total volatile levels in VOOs produced under RDI-2 conditions were higher than in VOOs produced under FAO conditions and similar to the levels found in VOOs produced under 125 FAO conditions. It is therefore very important to note that the VOOs produced by the second RDI strategy were richer in volatile compounds than those produced
under FAO conditions, but with a considerable reduction in the total amount of water used in the olive grove.
Summary points The quality indices are generally not influenced by irrigation, since no statistically significant differences in oil from rainfed and irrigation treatments are observed. l The different water stress levels in olive trees affect not only the total amount of phenolic and volatile compounds in the VOO but also their profile. l The total polar phenol content, which affects the sensory bitterness in the oils, decreases significantly as the amount of supplied water increases. l Complex phenols are not affected in the same way by irrigation, since the secoiridoid derivatives of hydroxytyrosol decreased more than those of tyrosol. l The volatile compounds most affected by the irrigation are E-2-hexenal, Z-3-hexen-1-ol and hexan-1-ol; the increase in the water applied to the olive trees produces an increase in these volatiles. l The selection of an optimal irrigation treatment for traditional Cornicabra olive orchards in Castilla – La Mancha calls for the establishment of a suitable compromise between olive production, virgin olive oil characteristics and water consumption. l The best irrigation treatment is regulated deficit irrigation (RDI), and apparently better results are obtained applying water only from the beginning of August when the accumulation of oil begins in the fruit. l
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Section | I The Plant and Production
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