ESTIMATION OF ‘TYTANIT’ INFLUENCE ON SELECTED QUALITY TRAITS OF STRAWBERRY FRUITS

Katarzyna Skupień¹, Jan Oszmiański^2
1 Laboratory of Plant Raw Materials Processing and Storage, Agricultural University, Szczecin, Poland
² Department of Fruit, Vegetable and Cereal Technology, Wrocław University of Environmental and Life Sciences, Poland

ABSTRACT

The objective of the study was to determine influence of titanium treatment on selected quality traits of strawberry fruits. The fruit of six strawberry cultivars (‘Dukat’, ‘Elkat’, ‘Elsanta’, ‘Kent’, ‘Selva’ and ‘Senga Sengana’) were obtained from commercial plantation localized near Szczecin. The experiment was carried out in 2004. ‘Tytanit’ spraying (Ti⁴⁺ ascorbate) was applied 3 times according to the recommendations for this treatment. Control plants remained not sprayed. The response of the cultivars to titanium was not unequivocal. Positive response was found for ‘Elsanta’, ‘Senga Sengana’, Selva’ and Kent’ berries as far as total anthocyanin content is concerned (increase by 5 - 44%). The treated fruits of ’Selva’ cultivar showed higher values of the all color parametres (L^*, a^*, b^*, C^*_, h) compared to non-treated berries whereas ‘Kent’, ‘Dukat’ and ‘Senga Sengana’ ones lower. The most stimulating effect of ‘Tytanit’ usage on fruit chemical composition was found for ‘Dukat’ berries. These fruits under titanium treatment showed higher dry weight content, higher soluble solids content, higher titratable acidity and higher soluble solids: titratable acidity ratio compared to non-treated strawberries.

Key words: strawberry, titanium, anthocyanins, fruit color, acidity, soluble solids.

INTRODUCTION

Cultivation of strawberries in Poland has played for years an important role in domestic horticulture and fruit economy. At present Poland is placed at 4-5^th position in the world at strawberry harvest [18].

Strawberries like other fruits are the source of beneficial compounds accounting for nutrition and health maintenance of humans what has been widely reviewed by others [4,5].

Yield and quality of strawberries depend on cultivar, climate and weather conditions as well as agronomic practices applied. One of the agronomic treatments aimed to stimulate fruition of strawberry plants and improve sensory attributes of fruits is usage of titanium [8]. However, in the literature there is evidence on positive effect of titanium on fruit set, there is little information on possible influence of this element on quality traits of fruits.

The aim of the study was to evaluate the influence of titanium treatment on fruit color parametres (L^*, a^*,b^*, C^* and h), dry weight content, anthocyanins, titratable acidity, soluble solids content and soluble solids:titratable acidity ratio of six strawberry cultivars (‘Dukat’, ‘Elkat’, ‘Elsanta’, ‘Kent’, ‘Selva’ and ‘Senga Sengana’).

MATERIAL AND METHODS

Plant material
The fruits of six strawberry cultivars: ‘Dukat’, ‘Elkat’, ‘Elsanta’, ‘Kent’, ‘Selva’ and ‘Senga Sengana’ (‘Senga’) cultivars were obtained in 2004 from the private plantation localized near Szczecin. Plant cultivation and protection was carried out according to the recommendations for commercial plantations. Titanium was applied in the form of ‘Tytanit’ spraying (Ti⁴⁺ ascorbate 0.02 %) 3 times, every 7 days starting with inflorescence.

‘Tytanit’ is a single-component fertilizer with 8.5 g·dm^-3 of titanium content. According to the manufacturer – Intermag [19] ‘Tytanit’ accelerates fruit and seed set, increases yield and improves its quality. Furthermore the fertilizer intensifies color of fruits, increases quantity and size of fruits and reduces plant sensitivity to the effects of disadvantageous weather conditions. Control plants for each cultivar were not sprayed. Fruits were harvested at the optimum stage of ripeness at the beginning of July. Two-kg bulk samples were collected from 0.25-0.5 ha plot mainly from third-and-fourth-year bushes.

Strawberry samples
Total anthocyanin content, fruit color assessment, were determined in cooled strawberries (kept for 24 hours at 4-6°C). Titratable acidity, soluble solids and dry weight content were estimated in strawberries packed in polyethylene bags (~300 g) and stored at -20°C for 5 days.

Fruit color assessment
The color of strawberry purée was measured with Color Quest XE (HunterLab). Fruit pulp was placed in a glass cuvette and the color was recorded using CIE L^*a^*b^* 10°/D₆₅ and CIE L^*C^*h 10°/D₆₅ color spaces. L^* indicates lightness and its value ranges from 0 (an ideal black object) to 100 (an ideal white object). In the CIE L^*a^*b^* system a^* and b^* are the chromaticity coordinates. Positive a^* value indicates the red direction, negative a^* value is the green direction, positive b^* value is the yellow direction and negative b^* value is the blue direction. C^* and h are cylindrical coordinates of the L^*C^*h color space. C^* is chroma (C^*= [a^*2 + b^*2]^1/2) and indicates the vividness or color saturation. Hue angle (h) is expressed in degrees; 0° would be +a^* (red), 90° would be +b^* (yellow), 180⁰ would be –a^* (green), and 270⁰ would be –b^* (blue). H is calculated according to the formula: tan^-1[b^*/a^*].

Anthocyanins
Aliquots (5 g) of strawberry homogenates were sonicated with acidified methanol (1 mL HCl in 1 L of methanol) for 15 min and then extracted with acidified methanol and gradually filtered through the Schott inlet (G2). The extracts were combined, made up to 50 mL and centrifuged at 8.000 × g for 5 min. Absorbance was measured in a Shimadzu UV-2401PC spectrophotometer at 510 nm. Standard curve prepared for cyanidin-3-glucoside pure chemical (ROTH) in identical conditions, was used for calculating total anthocyanin content Results were expressed as milligrams of cyanidin-3-glucoside equivalents per 100 g of fresh weight [14].

Titratable acidity
Titratable acidity was determined by titration of strawberry homogenate water extract with 0.1 mol·dm^-3 NaOH to an end point of pH 8.1 (measured with an Orion 720 A pH meter; Orion Research Incorporated, Boston, MA, USA) according to PN-90/A-75101/04.

Soluble solids
An aliquot of strawberry homogenate was squeezed through cheesecloth and soluble solids content was measured in a juice with an Abbé refractometer according to PN-90/A-75101/02.

Dry weight
Dry weight was determined with a gravimetric method (drying an aliquot of fruit tissue at 105°C to a constant weight) according to Polish standard PN-90/A-75101/03.

Statistical analysis
Except for dry weight content (in duplicate), the all measurements were carried out in three replicates. Statistical analysis was done by means of Statistica software package version 7.1 (Statsoft, Poland). The Student test for comparison the pairs of the means was used. The differences were tested at significance level p = 0.05.

RESULTS AND DISCUSSION

Color parameters
Regarding the quality of strawberries, color is one of the most important features of fresh fruit appearance. Strawberry cultivars tested in this experiment showed varied color characteristics and differential response to ‘Tytanit’ treatment (Table 1).

As far as fruit lightness is concerned, the highest L* value (38.88) was observed for Ti-treated ‘Elkat’ berries and the lowest for treated ‘Kent’ fruit (33.79). Our data obtained for strawberry purée are corroborated by the results of strawberry skin evaluation by Pérez et al. [13] and Nunes et al. [12]. The most distinct effect of ‘Tytanit’ usage on L^* values was found for ‘Elkat’, ‘Kent’ and ‘Senga’ berries. ’Elkat’ berries under titanium treatment produced significantly lighter fruits (ΔL^* increased by 2.06), whereas, the treated berries of ‘Kent’ and ‘Senga’ were significantly darker (ΔL^* decreased by 3.47 and 1.42, respectively). The fruits of other cultivars showed only negligible alterations in their brightness caused by the treatment. Maintaining or even enhancing of lightness is a positive feature for strawberries with the respect to their ‘shelf-life’ good presentation. Negative effect of titanium may be especially important for ‘Kent’ berries which develop a negative feature of getting darker and browning during ‘shelf life’. Though, the fruits simultaneously maintain good taste and flavor this adverse property strongly limits commercial attractiveness of the cultivar.

The highest a^* value (redness) was determined for treated berries of ‘Elsanta’ (26.61) and the lowest for treated fruit of ‘Kent’ cultivar (21.17). Nunes et al. [12] obtained higher a^* values (32.23 and 33.66) for strawberries from the first and the second harvest, respectively (the fruit were immediately pre-cooled and stored for one week at 1°C plus one day at 20°C). In our experiment, stimulating effect of titanium on red color intensity was observed for ‘Selva’, ‘Elkat’ and ‘Elsanta’ cultivars. The treated berries of these cultivars displayed significantly higher a^* values by 8%, 7% and 1%, respectively compared to non-treated fruit. The strongest negative influence of ‘Tytanit’ usage was observed for ‘Kent’ and ‘Senga’ cultivars – significant decrease of a^* value by 15% and 6%, respectively. The fruits of ‘Dukat’ treated with titanium had only slightly lower a^* value – by 0.6%. The changes of red color intensity for the tested cultivars were not followed by total acid content in the berries. Treated variants of ‘Selva’ and especially ‘Elkat’ cultivars were redder though their acidity was lower, while ‘Kent’ and ‘Senga’ fruits were less red with parallel higher total acid content. For the all cultivars, a negative not significant correlation was found between total anthocyanin content and a^* value for untreated fruit (r = - 0.66) and negative significant correlation for treated berries (r = – 0.88^*).

The fruits of the all cultivars presented positive b^* values indicating the yellow color direction. The b^* values ranged from 9.09 (Ti-treated ‘Kent’ berries) to 13.05 (non-treated ‘Elsanta’ fruit). ‘Tytanit’ treatment significantly increased yellow color intensity in ‘Selva’ (by 11%) and ‘Elkat’ berries (by 6%) and significantly decreased in other cultivars, except for ‘Elsanta’ (no significant changes were observed).

On the basis of cylindrical coordinates the highest C^* value (chroma) was measured for ‘Elsanta’ treated berries (29.54) and the lowest for ‘Kent’ treated fruit (23.04). Pérez et al. [13] found higher C^* values for fresh strawberry skin measurements 37.93. ‘Tytanit’ usage significantly stimulated fruit color saturation in ‘Selva’ and ‘Elkat’ cultivars, and not significantly in ‘Elsanta’ berries (by 8%, 7% and 0.7%, respectively). For these cultivars, it was concurrent with higher L^* value and intensification of red (a^*) color. Other cultivars displayed deterioration of vividness under titanium treatment and their C^* values were lower by 7% (‘Senga’) and by 1% (‘Dukat’).

Hue angle values measured for the cultivars ranged from 22.96° (‘Senga’ treated fruit) to 26.43° (‘Elsanta’ non-treated berries). The interpretation of h value is the following: the closer to value 0°, the redder color strawberries have, the closer to value 90°, the yellowier the fruits are. ‘Tytanit” treatment resulted in increase of h value only for ‘Selva’ berries (by 3%). It means that color of these fruits was more yellow. Other cultivars treated with titanium showed decline of h value by 0.3% (‘Elkat’) to 4% (‘Senga’).

Anthocyanin
The most significant function of anthocyanins is their ability to impart color to the plants or plant products in which they occur [7]. The total anthocyanin content determined for strawberries in our experiment, ranged from 24.42 (Ti-treated ‘Elkat’ berries) to 54.90 mg/100 g (treated ‘Kent’ fruit) – Table 2. The scope was narrower than that estimated by Masny et al. [9] 26.7–72.1 mg/100 g and Masny et al. [10] 16.7–62.9 mg/100 g. Kmiecik et al. [6] determined in ‘Dukat’ berries anthocyanin content 33 mg/100 g whereas, in our study, this cultivar showed 45.04 under Ti-treatment and 45.54 mg/100 g while non-treated. ‘Elsanta’, ‘Senga’, ‘Selva’ and ‘Kent’ berries showed significantly higher anthocyanin content under ‘Tytanit’ spraying by 5, 22, 29, and 44%, respectively, compared to non-treated fruits. ‘Elkat’ cultivar showed the most negative response to the treatment. For these berries significant decrease of total anthocyanins by 33% was observed. Only slight, not significant alterations were found in treated ‘Dukat’ berries – decrease by 1%. These quantitative changes of pigment content, exerted by ‘Tytanit’ usage, were reflected in anthocyanin spectra of particular cultivars (Fig. 2). Titanium may have affected the rate of fruit ripening that in turn could result in development of red color and anthocyanin content in the strawberries.

Titratable acidity

The data presenting titratable acidity, soluble solids content and titratable acidity:soluble solids ratio in the fruits of tested cultivars are listed in Table 2.

The acidity of strawberry cultivars tested in our experiment ranged from 0.627 (‘Elkat’ Ti-treated fruit) to 1.062 g citric acid/100 g (‘Dukat’ treated berries). Ayala-Zavala et al. [1] for fresh ‘Chandler’ strawberries found lower titratable acidity 0.59 mg citric acid/100 g. On the other hand, Sahari et al. [14] determined higher acidity for ‘Kordestan’ cultivar – 1.22 g citric acid/100 g. ‘Tytanit’ usage caused significant increase of titratable acidity in the fruits of ‘Senga’ (by 11%) and ‘Dukat’ (by 4%), and only slight increment in ‘Kent’ berries (by 2%). Other cultivars showed decrease of total acid content under titanium treatment. The significant decline was observed in ‘Elkat’ berries (by 26%) and ’Elsanta’ fruit (by 13%). However, not significant lowering of acidity was measured in ‘Selva’ treated berries (by 2%).

Soluble solids and dry weight content
The data on influence of Ti-treatment on dry weight content in strawberries are presented in Figure 1, whereas, the data on soluble solids content are presented in Table 2.

The highest soluble solids content was observed for ‘Kent’ non-treated fruit (10.4°Bx) whereas the lowest for ‘Dukat’ non-treated berries and ‘Selva’ treated ones (8.1°Bx, each). The range is similar compared to the data obtained by Bartczak et al. [2] 8.9–10.7°Bx and narrower than reported by Cordenunsi et al. [3] 6.0–9.0°Bx. Positive effect of titanium on soluble solids content, was found for ‘Elkat’ berries (increase by 8%) and ‘Dukat’ ones (increase by 6%). Considerable decline of soluble solids in treated fruit was determined in ‘Kent’ and ‘Selva’ berries (by 18% and 17%, respectively). ‘Elsanta’ and ‘Senga’ berries showed no reaction to titanium usage as far as soluble solids is concerned.

According to Masny et al. [10], dry weight content in strawberries amounts from 8.3% to 9.5%. In present experiment, Ti-treated ‘Elkat’ berries showed the highest dry weight content (10.21%) while the lowest was found in treated ‘Kent’ fruit (7.96%). Ti-treatment significantly increased dry weight content in ‘Dukat’ (by 8%), ‘Senga’(by 9%) and ‘Elkat’ berries (by 16%). For other cultivars; except for ‘Elsanta’ (no significant changes), significant decrease of dry weight content under Ti-treatment was observed (‘Selva’ by 12% and ‘Kent’ by 17%).

However, both traits seem to be strongly dependent on weather conditions. Our study, carried out at the same cultivars in 2003 [16] showed different relations. The highest soluble solids and dry weight content was determined in ‘Dukat’ berries (18.0°Bx and 16.68%, respectively) and the lowest in ‘Elkat’ ones (11.9°Bx and 11.85%, respectively).

Soluble solids:titratable acidity ratio
Soluble solids:titratable acidity is the more common relation used as an index of consumer acceptability and quality in fruits. Montero et al. [11] obtained for the strawberries the maximum value of the ratio at 28 days from fruit set. Saied et al. [15] determined soluble solids:titratable acid ratio for control variants of ’Elsanta’ cultivar 12.0 and ‘Korona’ 10.8. The average ratio calculated for strawberry cultivars studied by Sturm et al. [17] was 6.8.

In our study, the changes both in soluble solids content and titratable acidity of the fruits caused by titanium usage were reflected in the soluble solids:titratable acidity ratio (SS:TA) (Table 2). Ti-treated ‘Elkat’ berries showed the highest SS:TA ratio (15.8) whereas non-treated ‘Dukat berries the lowest (7.9). ‘Tytanit’ treated ‘Elkat’ berries presented the most significant increase of soluble SS:TA ratio by 45%. ‘Elsanta’ and ‘Dukat’ treated berries also displayed significant increase of soluble SS:TA ratio by 15% and 3%, respectively. Other cultivars showed significant lowering of SS:TA ratio resulting from the changes in soluble solids and total acid content caused by titanium treatment. The decline of the ratio ranged from 10% (‘Senga’) to 20% (‘Kent’).

CONCLUSIONS

‘Tytanit’ treatment exerted differential influence on quality traits of tested strawberry cultivars.

1. The positive response to ‘Tytanit’ usage was found for ‘Kent’, ‘Selva’, ‘Senga Sengana’ and ‘Elsanta’ berries as far as total anthocyanin content is concerned and for enhancing red color (a^*) of ‘Selva’, ‘Elkat’ and ‘Elsanta’ berries.

2. The treated fruits of ‘Selva’ cultivar had higher values of the all color parametres tested (L^*, a^*, b^*, C^*, h) whereas, treated berries of ‘Dukat’, ‘Kent’ and ‘Senga Sengana’ lower.

3. The berries of ‘Dukat’ cultivar under titanium treatment displayed higher values of the all chemical parameters tested (dry weight content, soluble solids, titratable acidity and soluble solids:titratable acidity ratio) while, the fruits of ‘Selva’ cultivar lower.

REFERENCES

1. Ayala-Zavala J.F., Wang S. Y., Wang C.Y., González-Aguilar G. A., 2004. Effect of storage temperatures on antioxidant capacity and aroma compounds in strawberry fruit. Lebensm.-Wiss. u-Technol. 37, 687-695.

2. Bartczak M., Lisiecka J., Knaflewski M., 2005. Jędrnosc i ekstrakt owoców truskawki (Fragaria x ananassa Duch.) uprawianej w szklarni i w polu [Firmness and soluble solid solids of strawberry (Fragaria x ananassa Duch.) grown in a greenhouse and open-field]. Zesz. Nauk. Akad. Rol. Wroc., 515, 33-37 [in Polish].

3. Cordenunsi B.R., Nascimento J.R.O., Lajolo F.M., 2003. Physico-chemical changes related to quality of five strawberry fruit cultivars during cool-storage. Food Chem. 83, 167-173.

4. Hannum S.M., 2004. Potential impact of strawberries on human health: a review of the science. Critical Rev. Food Sci. Nutri. 44, 1-17.

5. Kaur C., Kapoor H.C., 2001. Antioxidants in fruits and vegetables – the millenium’s health. Int. J. Food Sci. Tech. 36, 703-725.

6. Kmiecik W. Jaworska G., Lisiewska Z., 2000. Effect of sucrose, L-ascorbic acid and pectin on the quality of frozen strawberries. EJPAU, Food Sci. Technol. 3(2) www.ejpau.media.pl.

7. Kong J.M., Chia L.S., Goh N.K., Chia T.F., Brouillard R., 2003. Analysis and biological activities of anthocyanins. Phytochemistry 64, 923-933.

8. Laszlovszky-Zmarlicka A., Żurawicz E., 2003. Doswiadczenia z uprawa truskawek w polu na zbiór przyspieszony [Experiments on strawberry field cultivation for an earlier harvest]. Ogólnopolska Konferencja Truskawkowa, ISK Skierniewice, 26 March 2003, 73-80 [in Polish].

9. Masny A., Markowski J., Żurawicz E., 1999. Możliwosci intensyfikacji produkcji truskawek w Polsce przez hodowlę nowych odmian [Opportunities of intensification in strawberry production by breeding new cultivars]. Zesz. Nauk. AR Krak., Ses. Nauk. 351, 319-324 [in Polish].

10. Masny A., Markowski J., Żurawicz E., 2001. Ocena jakosci owoców najnowszych klonów truskawki hodowli Instytutu Sadownictwa i Kwiaciarstwa w Skierniewicach [Quality estimation of newest strawberry genotypes bred by Institute of Pomology and Floriculture at Skierniewice]. Zesz. Nauk. Inst. Sadow. Kwiac. Skiern. 9, 179-184 [in Polish].

11. Montero T.M., Mollá E.M., Esteban R.M., López-Andréu F.J., 1996. Quality attributes of strawberry during ripening. Sci. Hort. 65, 239-250.

12. Nunes M.C.N., Brecht J.K., Morais A.M.M.B., Sargent S.A., Physical and chemical quality characteristics of strawberries after storage are reduced by a short delay to cooling. Postharvest Biol. Tech., 1995, 6, 17-28.

13. Pérez A.G., Olias R., Sanz C., Olias J.M., 1996. Furanones in strawberries: evolution during ripening and postharvest shelf life. J. Agric. Food Chem. 44, 3620-3624.

14. Sahari M.A., Boostani M.F., Hamidi Z.E.,2004. Effect of low temperature on the ascorbic acid content and quality characteristics of frozen strawberry. Food Chem. 86, 357-363.

15. Saied A.S., Keutgen A.J., Noga G., 2005. The influence of NaCl salinity on growth, yield and fruit quality of strawbery cvs.‘Elsanta’ and ‘Korona’. Sci. Hort.103, 289-303.

16. Skupień K, Oszmiański J., 2004. Comparison of six cultivars of strawberries (Fragaria ananassa Duch.) grown in northwest Poland. Eur. Food Res. Technol. 219, 66-70.

17. Sturm K., Koron D., Stampar F., 2003. The composition of fruit of different strawberry varieties depending on maturity stage. Food Chem. 83, 417-422.

18. Swietlik J., 2003. Sytuacja na rynku truskawek w 2002 r., prognozy na 2003 r. oraz perspektywy produkcji truskawek po integracji z UE [Strawberry market situation in 2002, prognosis for 2003 and strawberry production perspectives after accessing EU]. Ogólnopolska Konferencja Truskawkowa, ISK Skierniewice 26 March 2003, 5-13 [in Polish].

19. www.1 – www.intermag.pl/en/produkty/nawozy_rolnicze/tytanit.html.

Accepted for print: 20.09.2007

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