The results on the evolution of the texture and antioxidant activity during the processing of naturally fermented green olives are reported in the present study. The olives were brined with two different NaCl concentrations, 4 and 7%. A puncture test and a texture profile analysis (TPA) test were carried out to evaluate texture, while the antioxidant activity was assessed in consideration of the loss of absorbance of a stable radical upon reaction with a polyphenolic olive extract. The puncture test revealed both an increase and decrease in peel and flesh hardness, respectively. The olives processed with 7% NaCl concentration showed higher peel hardness than olives brined with 4% salt. The texture profile analysis did not reveal any difference between the two salt concentrations used, but showed a decrease in the value of all parameters after 30 days of brining. The antioxidant activity of the polyphenolic extract decreased significantly during processing, with a major loss after the first 30 days of processing and was higher in the 7% brined olives, than the sample treated with 4% NaCl.
According to International Olive Oil Council (
An instrumental texture analysis has been applied to Spanish style olives (Jimenez
As stated before, debittering is essential to making table olives edible. Whatever the method used, a significant loss in polyphenols occurs during the various processing steps and if we consider that polyphenols not only affect the sensory properties, but also the health promoting capacity, we can understand that differences in health properties can be found among the processing technologies used. Therefore, the health promoting capacity can be indirectly evaluated by measuring the
For the above cited reason we investigated the evolution of the texture and antioxidant activity of the polyphenolic extract during the processing of naturally fermented green olives brined at two different sodium chloride brine concentrations. The chemical-physical parameters of brine and olives were also determined.
Fruits of the “Tonda di Cagliari” cultivar were handpicked from an irrigated orchard in north Sardinia in the last decade of October at a green ripe stage and soon transferred at our lab for processing. The cultivar has been chosen because it proved to be very suitable for this kind of preparation in previous trials carried out at our lab. Selection before brining was done by discarding olives with blemishes, cuts and insect punctures as well as under or over ripe fruits. Calibration was performed with laboratory callipers and olives ranging from 17 to 21 mm in transversal diameter were considered. Replicates of 12 kg were prepared for further processing.
After careful washing with tap water to remove field dust, the olives were transferred to 20 L previously sterilized plastic containers and then processed by brining, which was carried out by preparing sterile 4 and 7% (w/w) sodium chloride solutions which were used to completely fill the containers which were finally closed after a perforated cap was placed between the olives and the top part of the container to submerge the olives in the brine. The pH of the brine was previously adjusted to 4 with lactic acid to prevent the growth of gas pockets producing
Triplicate analyses of the following parameters for each container were carried out in the brine: pH with a glass electrode, free acidity (g of lactic acid per 100 mL of brine), sodium chloride (g 100 mL-1), reducing sugars (g 100 mL-1 of brine) and phenols (mg gallic acid 100 g-1 of brine), according to Garrido-Fernández
The antioxidant activity was determined on the polyphenolic extract using the DPPH stable radical, following the method proposed by Ramadan and Morsel (
Texture analyses in fresh olives and changes during processing were monitored with a texture analyzer (mod. TA-XT2, Stable Microsystems, Surrey, UK) fitted with a 5 or 50 kg load cell. The Texture Expert program version 1.21 was used for processing data. A puncture test and a Texture Profile Analysis (TPA) were performed using twenty olives for each determination and brine concentration.
For the puncture test the olives were placed on an HDP/90 platform and punctured in the lateral face. The test was performed using an SMS P/2 needle probe and a 5 kg load cell. The test speed was 1.0 mm s-1 and the penetration depth was limited to 3 mm. The force-time curve was graphically acquired and elaborated. Three parameters were taken into account to evaluate the evolution of texture during fermentation (
Representative graph of a puncture test.
The TPA was carried out on the lateral face of whole olives in compression mode using an SMSP/75 plate. The probe speed was set at 0.5 mm sec-1, time between compressions was 5 sec and the test was stopped at 15% deformation after the auto triggering signal. A 50 kg load cell was used. Hardness, cohesiveness, gumminess, chewiness and springiness, as reported by Szczesniak (
The table olives were assessed at the end of brining (180 days) by 30 untrained judges who were asked to express their preference on the two samples. We performed a paired preference test as reported by Stone and Sidel (
Data on reducing sugars and polyphenol content on brines and olives and on the NaCl contents in the olives were subjected to one-way analysis of variance (ANOVA), with sodium chloride concentration as the group variable. Texture and antioxidant activity data were submitted to two-way ANOVA, where the factors were the sodium chloride and the days of storage. Data on sensory analysis were evaluated using the critical values table for duo-trio test and paired preference test (Stone and Sidel,
An analysis of the chemical-physical parameters in the brines and olives were carried out mainly to check the appropriate evolution of processing and to correct, at each inspection time, pH and sodium chloride values. Data obtained, in fact, were as expected and as reported in the literature (Garrido-Fernández
Evolution of some chemical parameters of the brines and olives of Tonda di Cagliari olives during 180 days of brining
Brines | Olive flesh | |||||
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NaCl (%) | Sampling Period (days) | Reducing sugars (%) | Total polyphenols (mg gallic acid 100 mL>–1) | Sodium Chloride (%) | Reducing sugars (%) | Total polyphenols (mg gallic acid 100 mL–1) |
4 | 0 | – | – | 0.12a | 1.88a | 359.2a |
7 | – | – | 0.12a | 1.88a | 359.2a | |
4 | 30 | 0.210a |
62.6a | 0.82b | 1.68a | 246.1b |
7 | 0.144b | 50.9b | 1.87a | 1.75a | 267.9a | |
4 | 60 | 0.579a | 92.7a | 1.69b | 1.46b | 183.4b |
7 | 0.406b | 76.4b | 2.81a | 1.58a | 228.2a | |
4 | 120 | 0.458a | 110.9a | 2.16b | 1.32b | 165.9b |
7 | 0.298b | 95.5b | 3.04a | 1.48a | 197.8a | |
4 | 180 | 0.324a | 135.8a | 2.86b | 1.02b | 66.5b |
7 | 0.224b | 111.6b | 3.74a | 1.25a | 80.5a |
Means followed by different letters within each column and sampling period are significantly different according to the Tukey test, significance level
As a result of the penetration test, the particular structure of the olive fruits generates a particular graph which shows a progressive increasing force during penetration up to the breaking of the peel. This maximum force (F1) has already been considered as a hardness index of the peel (Romeo
Evolution of peel break force as revealed by the puncture test during 180 days of brining of “Tonda di Cagliari” table olives. *Means statistically significant for the same period.
Evolution of peel hardness as revealed by the puncture test during 180 days of brining of “Tonda di Cagliari” table olives. *Means statistically significant for the same period.
Texture
Source of variation | Puncture test data | ||
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Peel breakForce (N) | Peel hardness (N mm–1) | Flesh hardness (N mm–1) | |
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1.317b |
0.77b | 0.846a |
|
1.378a | 0.88a | 0.871a |
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|||
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1.069d | 0.277d | 1.475a |
|
1.248c | 0.733c | 0.840b |
|
1.396b | 0.964b | 0.731c |
|
1.521a | 1.098a | 0.599d |
|
1.504a | 1.059a | 0.645cd |
Texture has been determined with a puncture test (see the Materials and Methods section).
Data with different letters within each source of variation, thesis and column differ significantly according to the Tukey test at
On the other hand, the different NaCl concentrations did not influence the flesh hardness, which, in turn, showed a significant decrease during the 180 days of brining (
Evolution of flesh hardness as revealed by the puncture test during 180 days of brining of “Tonda di Cagliari” table olives.
Representative graph of the TPA test.
Texture
Source of variation | Texture Profile Analysis Parameters | ||||
---|---|---|---|---|---|
Hardness (N) | Cohesiveness | Gumminess (N) | Chewiness (N mm–1) | Springiness | |
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|||||
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29.79a | 0.378a | 11.74a | 22.54a | 0.622a |
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29.00a | 0.379a | 11.42a | 21.50a | 0.631a |
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|||||
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56.11a | 0.438a | 24.69a | 53.65a | 0.732a |
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22.93b | 0.345c | 7.90b | 13.28b | 0.589b |
|
22.97b | 0.368bc | 8.45b | 14.58b | 0.622b |
|
21.94b | 0.381b | 8.31b | 13.66b | 0.595b |
|
23.03b | 0.362bc | 8.54b | 14.93b | 0.593b |
Texture has been determined with a TPA test (see the Materials and Methods section).
xData with different letters within each source of variation, thesis and column differ significantly according to the Tukey test at
To our knowledge, these are the very first data on texture evolution using the TPA test during the brining of green table olives using two different sodium chloride concentrations.
The DPPH test is an
Evolution of antioxidant activity of the polyphenolic extract from the flesh of “Tonda di Cagliari” green olives during 180 days of brining. All the values have been normalized considering 100% as the value of fresh olives. *Means statistically significant means for the same period.
As stated for texture evolution, no other data are present in the literature concerning the antioxidant evolution during the brining of green table olives by means of two different sodium chloride concentrations.
The panellists positively judged both samples, however, 23 judges preferred the olives brined with 4% sodium chloride, as they found the olives less salty and bitter, with respect to the 7% brined ones. This result is significant at
The use of different salt concentrations in the brining of naturally fermented green olives resulted in some chemical-physical, textural, antioxidant and sensory differences. Olives brined with the lower NaCl concentration maintained a lower polyphenol content, antioxidant activity and peel hardness during and at the end of processing, but were preferred by panellists, with respect to the olives processed with the higher NaCl concentration. Both the texture tests used on the whole olives proved to be suitable to follow the texture evolution during brining of this table olive specialty.
This research was supported by Ministero delle Politiche Agricole, Alimentari e Forestali (Mipaf), project title “Ottimizzazione delle tecnologie di trasformazione per l'ottenimento delle olive da mensa ad alto impatto sensoriale e nutrizionale”.