Assessment of Bitterness Reduction on Green Olive by Using Plant Growth Regulators

Introduction

Phytohormones regulate numerous aspects of plant growth and postharvest fruit quality [1]. Recent concepts suggest that ripening of some fruit during postharvest storages are not only deteriorative processes which was need to slow down but also useful processes in which some growth regulators play important roles such as ripening acceleration of palm, banana and olive in some extend [1, 2]. Ethylene is still considered a major influence on postharvest metabolism, the other plant hormones, the auxins, gibberellins, cytokinins, and abscisic acid, are also thought to significantly influence the aging process [3, 4, 5].

Applying different types of plant regulators such as auxin, gibberellin and its combination without giving unfavorable effects to the quality of banana was studied [1, 6]. 2,4-Dichlorophenoxyacetic acid is an auxin-like plant growth regulator. Since the 1940s, 2,4- Dichlorophenoxyacetic acid and its derivatives have been widely used during citrus postharvest handling to maintain fruit quality [7]. Green-mature banana fruit were treated with deionized water, abscisic acid, indole- 3-acetic acid and abscisic acid + indole-3-acetic acid, respectively, to investigate the role of them in fruit ripening. Results showed that abscisic acid accelerated fruit ripening, but indole-3-acetic acid delayed the process. However, treatment of abscisic acid + indole-3- acetic acid showed little difference in fruit color and firmness [1]. Palm fruit bunches were exposed to 0, 250, 500 or 1000 ppm ethylene for 24 hours. Each fruit bunch was evaluated in three separate sections: the bottom, the middle, and the top. The exogenous ethylene treatments significantly hastened palm fruit ripening, quantified by an increase in the fruit peel coloring that turns from black to reddish orange. Exogenous ethylene fumigation accelerated the ripening of oil palm fruit, increased oil yield, and decreased the free fatty acid levels [2]. Exogenous treatment with indole-3-acetic acid on the ripening of olives reported as a significant increase in the accumulation of fat and the amounts of extracted oils and a significant improvement in the extractability of phenolic content diffusible in these oils at maturity [8].

The aim of this study was to develop a new olive debittering method for table olive processing industry. Fort this aim green olives were kept in water which contain Indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid, gibberellic acid, ethephon and Signum (containing 267 g/kg boscalid and 67 g/kg pyraclostrobin) after that some physical, chemical and sensory analyzed were applied to the olives.

Analysis

pH and titratable acidity content of olives were determined according to official method TS 774 [13]. Color values of olive skin were measured with a color meter (Konica Minolta, Japan) at 23 ± 1°C. Water content of olive samples was determined in a conventional oven at 75±2°C [14]. Texture hardness of olive was measured with fruit harness tester (W.O.W FRH-5, Japan).Color and texture hardness analyses were run in 15 replicates. Absorbance value of oleuropein was determined by spectrophotometric method at 345 nm according to Mastorakis, et al. [15].

The sensory profiles of olives were assessed with sensory profile sheet used by the trained judges according to Aponte M, et al. [16]. Sensory characteristics were evaluated with 9 point scale (9: like extremely, 8: like very much, 7: like moderately, 6: like slightly, 5: neither like nor dislike, 4: dislike slightly, 3: dislike moderately, 2: dislike very much and 1: dislike extremely) by panelists. Sample preparation, serving and tasting procedures were organized according to Galán-Soldevilla and Pérez-Cacho [17]. The appearance and color attributes were assessed by the panelists on the complete sample before tasting. Odor, taste and bitterness were evaluated respectively.

Results and Discussion

Color and hardness are the important characters which highly affect the preference of consumer for table olive marketing [18]. So that these values should be controlled for developing new table olive processing methods. Color value and hardness of olive samples were given in Table 1.L value, a value, b value and hardness of green table olives were reported as 49.96‐69.56, 1.35‐17.91, 19.57‐45.47 and 434.1‐895.7 g. respectively [19]. In this study b value and hardness of olives were determined as similar but L and a color values were determined lower than Kiritsakis [19].

Water content, oleuropein absorbance value, pH and titratable acidity content of olive samples were given in Table 2. pH value, titratable acidity and water content of green olives were reported as between 2.80‐3.97, 0.59‐1.40 and 63.1-73.2 % [18, 19]. Oleuropein absorbance value of raw and processed Gemlik olives was reported as 0.57 and between 0.06-0.16 by Kumral et al whose results were lower than that was found in this study [20]. There were statistically significant differences for reduction in oleuropein absorbans value. Higher reduction was detected for ethephon treated olive samples.

Sensory characters; appearance, color, odor, taste and bitterness scores were given in Table 3. Appearance, odor and bitterness taste of green olives were reported between 8.99-9.05, 7.87-8.06 and 3.18-3.21 by using 1-11 point sensory score scale [21]. Sensory determined color acclaim value was reported between 5.6-9.0 (0-10 point score) for green olives by Ozdemir and Kurultay [22].

In this study appearance and color values were determined at higher than acceptable level (5.5) except Signum treated sample. Odor was determined as unacceptable at the end of 8 days for gibberellic acid, Signum and ethephon treated olives. Odor and taste scores were lower than López-López et al [21]. Bitterness reduction of olives was not succeeded to reduce favorable level in this experiment so that scores of taste and bitterness were lower than acceptable levels.

Conclusion

In this study, debittering of olives relies upon indigenous enzymes from raw material whose enzymes were expected to accelerated by added plant growth regulators. This practice may lead to fluctuations in the final oleuropein absorbance value and sensory bitterness scores of samples at the end of 8 days. In this study reduction of bitterness was not appropriate to suggest to producer but statistical significant reduction of oleuropein absorbance value and sensory bitterness results indicated that plant growth regulators especially enhancers has potential for develop new olive debittering methods for table olive industry. Future studies should be focus on different types, doses and conditions of ripening enhancer component to develop new olive debittering method.

Acknowledgment

Authors thanks to Ataturk Central Horticultural Research Institute (Yalova/Turkey) which supported this study.