**3.1 Steam explosion system (SES)**

An average temperature of 200 ºC and a time of 5 minutes were used with or without acid impregnation of alperujo. The acid increases the severity of the treatment, enhancing the oxidation of the samples. A vacuum was applied to one of the treatments, with acid addition in order to diminish the possible oxidative effect of oxygen at high temperatures and pressures. The results showed (**Table 1**) an important solubilisation of the solid in all treatment. In addition, the oil was concentrated in the final solid from 8,3 up to 19,9 % with respect to the dry final solid. Despite the high level of acidity in the initial sample after the treatment, these values decreased.

K232 and K270 are simple and useful parameters for assessing the state of oxidation of olive oil. The coefficient of specific extinction at 232 nm is related to the presence of products of

New Olive-Pomace Oil Improved by Hydrothermal Pre-Treatments 259

The composition of triglycerides was determined and the results are shown in the **Table 2**. The main triglyceride peaks in all samples were oleic-oleic-oleic (OOO), oleic-oleic-palmitic

Despite the low quality of the initial oil, the relation of triglycerides was not altered by SES. As expected, in the crude olive-pomace oil obtained after SES treatment, the total content of triglycerides decreased up to 22% compared to the oil obtained from the untreated alperujo. Despite the high severity, only 22% of triglyceride composition was lost, with the rest susceptible for refining. The oxidative conditions of SES treatment were minimised using a

The great advantages of the SES application on alperujo are based, in addition to other reasons, on the solid reduction (up to 58%) and oil concentration in the final solid (up to 20%). Because the triglycerides (TG) are concentrated, their loss is not a significant or negative factor to limit the use of this system. These reasons make technically possible the extraction of the crude olive-pomace oil from one sample of alperujo treated by SES. Therefore, the application of SES to this kind of alperujo allows for the obtaining of a final solid rich in oil in a high concentration that is susceptible for further refining processes for olive-pomace oil production. However, the technical inconveniences of SES such as high temperatures and pressures or the explosive decompression make it an inadequate system

> % of total glycerides Mean ± SD

LLL 18039 0,7 ± 0,05 11076 0,6 ± 0,02 LnLO 15271 0,6 ± 0,03 5886 0,3 ± 0,01 OLL+PoLO 99759 4,0 ± 0,10 75243 3,9 ± 0,77 PLL+LnOO 62860 2,5 ± 0,15 32818 1,7 ± 0,26 POLn 23935 1,0 ± 0,07 0 0,0 ± 0,00 LOO 404446 16,1 ± 1,02 321011 16,6 ± 1,23 LOP 154422 6,2 ± 0,81 126669 6,5 ± 0,87 LPP 4000 0,2 ± 0,01 6064 0,3 ± 0,02 OOO 959632 38,3 ± 1,67 788016 40,7 ± 2,03 OOP 448959 17,9 ± 1,11 364371 18,8 ± 1,30 POP 57959 2,3 ± 0,90 39691 2,0 ± 0,11 SOO 157822 6,3 ± 1,43 108877 5,6 ± 0,95 POS 28350 1,1 ± 0,03 21116 1,1 ± 0,05 AOO 49158 2,0 ± 0,16 26398 1,4 ± 0,06

P, palmitic, Po, palmitoleic, M, margaric, S, stearic, O, oleic, L, linoleic, Ln, linolenic, and A, arachidic acids

Table 2. Triglycerides composition of crude olive-pomace oil obtained from alperujo

SES (200° C, 5 min) treated sample

> % of total glycerides Mean ± SD

Peak area

Untreated sample

Área total 2504443 1938316

Peak area

(OOP) and linoleic-oleic-oleic (LOO).

vacuum or avoiding the acid addition.

for olive-pomace oil extractors.

untreated and treated by SES.

Triglycerides

the primary stage of oxidation (hydroperoxides) and conjugated dienes, which are formed by a shift in one of the double bonds. The extinction coefficient at 270 nm is related to the presence of products of secondary oxidation (carbonylic compounds) and conjugated trienes (the primary oxidation products of linolenic acid).

The K232 values of all treated samples were lower than the untreated alperujo, unlike the K270 values in which only the sample treated with vacuum and without acid presented a similar absorbance at 270 nm. Only when vacuum and acid were applied to the SES did the value of K270 exceed the maximum concentration in ROPO (2,0), with all the K values lower than the maximum in ROPO (0,2). All these oxidised compounds diminished after the refining process.

The polar compound values that show the alteration level by the non-volatile compounds of oil are practically the same in all treatments, except when the acid and the vacuum are used simultaneously. Polar compounds provide an idea not only of oxidative reactions, but also of hydrolytic degradation, because they are partial constituents of FFA and glycerides.

Curiously, the concentration of oxidised triglycerides and polymers are lower after the SES treatments. This result could be explained by their partial solubilisation during the thermal treatment in the liquid phases that are previously separated by the oil extraction.


a % with regard to the oil sample.

Table 1. Solid reduction, oil concentration in final solid and chemical characteristics of crude olive-pomace oil treated or untreated by SES in several conditions.

The quantity of triglycerides decreased after the SES treatment, with an increased presence of diglycerides and monoglycerides as an unmistakable sign of hydrolytic degradation.

The oxidative effects do not seem to be the main cause of the COPO alteration during the SES treatment, while hydrolysis seems to be an important effect on the triglyceride loss.

the primary stage of oxidation (hydroperoxides) and conjugated dienes, which are formed by a shift in one of the double bonds. The extinction coefficient at 270 nm is related to the presence of products of secondary oxidation (carbonylic compounds) and conjugated trienes

The K232 values of all treated samples were lower than the untreated alperujo, unlike the K270 values in which only the sample treated with vacuum and without acid presented a similar absorbance at 270 nm. Only when vacuum and acid were applied to the SES did the value of K270 exceed the maximum concentration in ROPO (2,0), with all the K values lower than the maximum in ROPO (0,2). All these oxidised compounds diminished after the refining process. The polar compound values that show the alteration level by the non-volatile compounds of oil are practically the same in all treatments, except when the acid and the vacuum are used simultaneously. Polar compounds provide an idea not only of oxidative reactions, but also of hydrolytic degradation, because they are partial constituents of FFA and glycerides.

Curiously, the concentration of oxidised triglycerides and polymers are lower after the SES treatments. This result could be explained by their partial solubilisation during the thermal

> SES (200° C, 5 min, 2,5% H3PO4)

SES (200° C, 5 min, vacuum)

SES (200° C, 5 min, 2,5% H3PO4, vacuum)

treatment in the liquid phases that are previously separated by the oil extraction.

SES (200° C, 5 min)

% of solid reduction - 51,7 54,6 52,1 58,5 % of oil in final solid 8,3 17,2 18,0 16,9 19,9 Acidity (% oleic acid) 6,76 4,97 4,44 5,08 5,48 K232 5,72 4,57 3,23 5,18 5,21 K270 1,27 1,74 1,44 1,24 2,37 K -0,03 0,00 0,04 0,06 0,07

mg/g 114,3 116,59 112,81 111,37 129,87

Triglycerides a 1,61 1,25 1,34 1,41 1,36 Diglyceridesa 3,10 4,47 4,83 4,37 5,13 Monoglyceridesa 0,42 0,53 0,40 0,49 0,56 FFA (% as oleic acid) 6,10 5,28 4,49 4,66 5,73 Polymersa 0,23 0,14 0,23 0,21 0,21

Table 1. Solid reduction, oil concentration in final solid and chemical characteristics of crude

The quantity of triglycerides decreased after the SES treatment, with an increased presence of diglycerides and monoglycerides as an unmistakable sign of hydrolytic degradation.

The oxidative effects do not seem to be the main cause of the COPO alteration during the SES treatment, while hydrolysis seems to be an important effect on the triglyceride loss.

olive-pomace oil treated or untreated by SES in several conditions.

Untreated sample

Polar compounds

a % with regard to the oil sample.

Oxidised

(the primary oxidation products of linolenic acid).

The composition of triglycerides was determined and the results are shown in the **Table 2**. The main triglyceride peaks in all samples were oleic-oleic-oleic (OOO), oleic-oleic-palmitic (OOP) and linoleic-oleic-oleic (LOO).

Despite the low quality of the initial oil, the relation of triglycerides was not altered by SES. As expected, in the crude olive-pomace oil obtained after SES treatment, the total content of triglycerides decreased up to 22% compared to the oil obtained from the untreated alperujo. Despite the high severity, only 22% of triglyceride composition was lost, with the rest susceptible for refining. The oxidative conditions of SES treatment were minimised using a vacuum or avoiding the acid addition.

The great advantages of the SES application on alperujo are based, in addition to other reasons, on the solid reduction (up to 58%) and oil concentration in the final solid (up to 20%). Because the triglycerides (TG) are concentrated, their loss is not a significant or negative factor to limit the use of this system. These reasons make technically possible the extraction of the crude olive-pomace oil from one sample of alperujo treated by SES. Therefore, the application of SES to this kind of alperujo allows for the obtaining of a final solid rich in oil in a high concentration that is susceptible for further refining processes for olive-pomace oil production. However, the technical inconveniences of SES such as high temperatures and pressures or the explosive decompression make it an inadequate system for olive-pomace oil extractors.


P, palmitic, Po, palmitoleic, M, margaric, S, stearic, O, oleic, L, linoleic, Ln, linolenic, and A, arachidic acids

Table 2. Triglycerides composition of crude olive-pomace oil obtained from alperujo untreated and treated by SES.

New Olive-Pomace Oil Improved by Hydrothermal Pre-Treatments 261

(150°C, 60 min)

5687 (291)

5532 (603)

1054 (34)

2971 (5)

2472 (11)

> 460 (6)

Table 4. Total minor component composition (mg/kg ± SD) of oils from steam-treated and untreated alperujo. Numbers between parentheses indicate the standard deviation of three

For human consumption, the refining process of OPO is necessary. The refining (physical or chemical) process eliminates undesirable compounds (peroxides, degradation products, volatile compounds responsible for off-flavours, free fatty acids, etc.) but also results in the loss of valuable bioactive compounds and natural antioxidants (Ruiz-Méndez et al., 2008). The new trends of refining systems involve losing as few minor components as possible to obtain a final OPO that is rich in the minor components. The thermal treatments increase the minor component of COPO that help to obtain a final olive-pomace oil rich in interesting compounds, whose concentrations might be higher after the refining process, mainly using the new physical systems. Moreover, some of these minor components are recuperated during the refining, such as squalene, the concentration of which is increased up to 43 % after the pretreatment. After extraction, the defatted solid is lacking in phenols and then in phytoxic compounds for further bio-utilisation and rich in components like cellulose and protein.

**Figure 4** shows the main aspects of both thermal systems. The high difference between temperatures and pressures together with the absence of explosive decompression makes ST more appropriate and economically viable for industrial applications. A longer period of reaction time is necessary to treat with ST, but is easily applicable in an industrial continuous reactor. The percentage of solid reduction and, consequently, the final oil concentration show that despite the high severity difference between both treatments, there is not a significant difference in the results. Then, the new ST provides the major advantages

Thus, the positive effect of a novel thermal treatment for the extraction of crude olivepomace oil that could improve the commercial value of OPO and its bioactivities by increasing the concentrations of minor components concentration has been demonstrated. This treatment also significantly reduces the cost of oil extraction by centrifugation or solvent extraction because the starting solid is more concentrated in oil and is drier than

ST (160°C, 60 min)

> 6546 (216)

> 5880 (283)

> 1220 (124)

3124 (94)

2729 (109)

> 668 (14)

ST (170°C, 60 min)

> 6555 (298)

6389 (68)

1189 (107)

3461 (110)

3439 (171)

> 533 (20)

Components Untreated sample ST

(104)

(77)

(58)

(3)

(36)

(33)

Sterols <sup>4927</sup>

Aliphatic alcohols <sup>4065</sup>

Triterpenic alcohols <sup>992</sup>

Waxes <sup>1535</sup>

Squalene <sup>2404</sup>

Tocopherols <sup>425</sup>

of SES without technical complications.

untreated alperujo.

replicates.

#### **3.2 Effects of the new steam treatment**

The ST effect on POO composition was determined by characterisation of the fatty acid fraction. After the thermal treatment in the range of 150-170ºC for 60 min (**Table 3**), the final treated solid had an increase in oil yield up to 97%, with a reduction in solids up to 35,6- 47,6% by solubilisation. The oxidative damage was lower in the new treatment. The analysis of the polar fraction showed that oxidised triglycerides and peroxide values increased slightly and that no polymerisation reactions occurred. The hydrolytic process is shown in the diglycerides increasing from 2,5 to 6,6%, with the FFA and the unsaponifiable matter for all treatments remaining constant.


Table 3. Solid reduction, oil concentration in final solid and chemical characteristics of crude olive-pomace oil treated or untreated by ST at 150, 160 and 170ºC for one hour. a % with regard to the oil sample.

The concentration of minor components (**Table 4**) was significantly increased by ST. Sterols, aliphatic alcohols, triterpenic alcohols, and squalene increased up to 33%, 57%, 23% and 43%, respectively. In addition, the content of tocopherols increased up to 57% compared to untreated POO. This increase is due to solubilisation during the thermal treatment. The waxes level is also increased because of the high solubilisation from the external cuticle of the olive fruit and the leaves. Waxes are easily removed by the refining of COPO.

The samples of alperujo had been stored for a long time and the oil was partially extracted by centrifugation in OPO extractors just before pitting. The alperujo was chosen because its low fat concentration makes the COPO extraction economically unviable. In this condition, the initial oil has a very low quality, as previously shown in the tables. The analysed oils showed, despite the low quality of initial oil present in the alperujo studied, that the effect of thermal treatment increases slightly the values of oxidised components and hydrolytic degradation. All COPOs obtained after the thermal treatments are susceptible for a posterior refining process for OPO obtention.


The ST effect on POO composition was determined by characterisation of the fatty acid fraction. After the thermal treatment in the range of 150-170ºC for 60 min (**Table 3**), the final treated solid had an increase in oil yield up to 97%, with a reduction in solids up to 35,6- 47,6% by solubilisation. The oxidative damage was lower in the new treatment. The analysis of the polar fraction showed that oxidised triglycerides and peroxide values increased slightly and that no polymerisation reactions occurred. The hydrolytic process is shown in the diglycerides increasing from 2,5 to 6,6%, with the FFA and the unsaponifiable matter for

> ST (150° C, 60 min)

% of solid reduction - 35,6 47,1 47,6

8,1 11,8 14,3 16,0 % of oil in final solid Acidity (% oleic acid) 3,6 4,7 4,9 5,1

(meq/Kg) 8,7 9,4 10,9 12,3

Triglycerides a 0,7 1,1 1,1 1,6 Diglyceridesa 2,5 5,2 6,6 6,6

FFA (% as oleic acid) 3,3 2,8 2,9 2,8

matter (%) 2,53 3,02 2,50 2,54

the olive fruit and the leaves. Waxes are easily removed by the refining of COPO.

Table 3. Solid reduction, oil concentration in final solid and chemical characteristics of crude olive-pomace oil treated or untreated by ST at 150, 160 and 170ºC for one hour. a % with

The concentration of minor components (**Table 4**) was significantly increased by ST. Sterols, aliphatic alcohols, triterpenic alcohols, and squalene increased up to 33%, 57%, 23% and 43%, respectively. In addition, the content of tocopherols increased up to 57% compared to untreated POO. This increase is due to solubilisation during the thermal treatment. The waxes level is also increased because of the high solubilisation from the external cuticle of

The samples of alperujo had been stored for a long time and the oil was partially extracted by centrifugation in OPO extractors just before pitting. The alperujo was chosen because its low fat concentration makes the COPO extraction economically unviable. In this condition, the initial oil has a very low quality, as previously shown in the tables. The analysed oils showed, despite the low quality of initial oil present in the alperujo studied, that the effect of thermal treatment increases slightly the values of oxidised components and hydrolytic degradation. All COPOs obtained after the thermal treatments are susceptible for a posterior

ST (160° C, 60 min)

ST (170° C, 60 min)

**3.2 Effects of the new steam treatment** 

all treatments remaining constant.

Peroxide Values

Monoglyceridesa

Unsaponifiable

regard to the oil sample.

refining process for OPO obtention.

Oxidised

Untreated sample


Table 4. Total minor component composition (mg/kg ± SD) of oils from steam-treated and untreated alperujo. Numbers between parentheses indicate the standard deviation of three replicates.

For human consumption, the refining process of OPO is necessary. The refining (physical or chemical) process eliminates undesirable compounds (peroxides, degradation products, volatile compounds responsible for off-flavours, free fatty acids, etc.) but also results in the loss of valuable bioactive compounds and natural antioxidants (Ruiz-Méndez et al., 2008). The new trends of refining systems involve losing as few minor components as possible to obtain a final OPO that is rich in the minor components. The thermal treatments increase the minor component of COPO that help to obtain a final olive-pomace oil rich in interesting compounds, whose concentrations might be higher after the refining process, mainly using the new physical systems. Moreover, some of these minor components are recuperated during the refining, such as squalene, the concentration of which is increased up to 43 % after the pretreatment. After extraction, the defatted solid is lacking in phenols and then in phytoxic compounds for further bio-utilisation and rich in components like cellulose and protein.

**Figure 4** shows the main aspects of both thermal systems. The high difference between temperatures and pressures together with the absence of explosive decompression makes ST more appropriate and economically viable for industrial applications. A longer period of reaction time is necessary to treat with ST, but is easily applicable in an industrial continuous reactor. The percentage of solid reduction and, consequently, the final oil concentration show that despite the high severity difference between both treatments, there is not a significant difference in the results. Then, the new ST provides the major advantages of SES without technical complications.

Thus, the positive effect of a novel thermal treatment for the extraction of crude olivepomace oil that could improve the commercial value of OPO and its bioactivities by increasing the concentrations of minor components concentration has been demonstrated. This treatment also significantly reduces the cost of oil extraction by centrifugation or solvent extraction because the starting solid is more concentrated in oil and is drier than untreated alperujo.

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Fig. 4. Comparative scheme of two thermal pre-treatments used for alperujo utilisation.
