The Effects of Oven Dehydration on Bioactive Compounds, Antioxidant Activity, Fatty Acids and Mineral Contents of Strawberry Tree Fruit

Abstract

In this study, the effects of oven dehydration on chemical and bioactive properties, fatty acids, polyphenolic compounds and minerals of sandal strawberry tree fruit were investigated. While total carotenoid contents of the sandal strawberry tree fruit are determined between 4.20 (120 °C) and 5.43 µg/g (70 °C), tannin amounts of the sandal strawberry tree fruit were recorded between 5.13 (control) and 6.37% (70 and 120 °C). While total phenolic contents of dehydrated sandal strawberry tree fruit were found between 444.16 (120 °C) and 665.13 mgGAE/100 g (control), total flavonoid amounts of dehydrated sandal strawberry tree fruit were recorded between 592.91 (control) and 788.71 mg/100 g (120 °C). Antioxidant activity values of fruit ranged from 4.10 (120 °C) to 7.30 mmol TE/kg (control). Both total phenolic amounts and antioxidant activity values of untreated (control) sandal strawberry tree fruit were found to be higher than dehydrated ones, and a linear relationship was determined between the total phenolic amounts of the samples and their antioxidant activities. The highest amounts of phenolic compounds (ferulic acid, resveratrol and kaempferol) were detected in strawberry tree fruit dehydrated at 70 °C, followed by the control group and fruit dehydrated at 120 °C in decreasing order. Gallic acid, 3,4-dihydroxybenzoic acid, catechin, caffeic acid and rutin were the main constituents of the strawberry tree fruit, followed by syringic acid, p-coumaric acid and ferulic acid in descending order. Palmitic, stearic and oleic acid amounts of dehydrated strawberry tree fruit oils compared to the control were observed to increase with the applied temperature, while the contents of polyunsaturated fatty acids (linoleic and linolenic) decreased. In general, the mineral content of dehydrated strawberry tree fruit increased compared to the control. Since the oil, carotenoid, total phenol and phenolic component contents of sandalwood tree fruit are higher in the sample subjected to dehydration at 70 °C, this temperature can be considered as the ideal one for drying. In addition, considering the fatty acids, heat treatment at 120 °C can be preferred.

1. Introduction

The strawberry tree (Arbutus unedo L.), known as “sandal strawberry fruit tree”, is an evergreen plant widely distributed in the Mediterranean region, especially in the Taurus Mountains [1,2,3]. In Turkey, the A. unedo tree is seen to grow on dry rocky slopes or pine forests up to 600 m above sea level. The perennial shrub plant has a height of about 7–9 m and shows resistance [2,4]. Sandal strawberry tree fruit gives orange colored fruit in autumn and naturally grows in populations or as solitary trees in Egypt, Morocco, Tunisia, Algeria, Turkey, Syria, Portugal, Spain, France, Italy, Greece, Bosnia and Herzegovina, Croatia, Serbia, the Mediterranean islands, the Canary Islands and western Asia [2,4,5,6,7,8,9]. The sandal strawberry tree fruit are generally used to produce alcoholic beverages such as wines, liqueurs, brandy, jams and marmalades. In addition, sandal strawberry tree fruit are also eaten as fresh fruit [4]. Besides being added to yoghurt in chunks or as a sweetener, they can be used to prepare confectionery, cereals, jams, jellies and marmalades, cake and pastry fillings as well as other fruit [4,10,11,12]. Although the fruit of the sandal strawberry tree is consumed as a processed product, it has been reported that it can be a good source of antioxidants when consumed as fresh fruit [13]. Sandalberry tree fruit are rich in minerals, anthocyanins, antioxidant active components, flavonoids, tannins, vitamins E, carotenoids and especially vitamin C for human health [1,9,10,14,15]. Ruiz-Rodriguez et al. [8] reported that the higher antioxidant potential of arbutus berries may be due to the activity of vitamin C and various bioactive compounds. Strawberry tree fruit and some other parts (such as root and leaf) have high antioxidant capacity and the therapeutic compounds, and these compounds are diuretic, astringent, antidiarrheal, antiasthmatic, anti-inflammatory, antidiabetic, antihypertensive and against rheumatism and gastrointestinal and renal diseases [3,16,17,18]. In addition to the important effects of heating conditions on the color, aroma, fatty acid profile and bioactive properties of parts of the plant, such as seeds, fruit and leaves, drying is one of the main heat treatment techniques used to increase the sensory properties of nuts and oil-bearing seeds [19,20,21]. While the fresh fruit are used in the production of “compote”, the dried or dehydrated fruit are used in the production of “Hoşaf”, similar to compote. Therefore, in order for the dried or dehydrated fruit to be fully rehydrated, the drying process must be very good. Many edible fruits, such as sandal strawberry tree fruit, must be collected fresh in nature and subjected to a drying process in order to preserve their shelf life and to use in the production of “Hoşaf”. Limited study has been found on the effects of dehydration or drying on the phytochemical compounds, mineral amounts and fatty acid composition of sandal strawberry tree fruit, which are not very well known by the population of Mediterranean countries in terms of nutrition and industry. The aim of this study was to determine the effect of oven dehydration on chemical and bioactive properties, fatty acids, polyphenolic compounds and minerals of sandal strawberry tree fruit pickled in Antalya, Turkey.

2. Material and Methods

2.1. Material

In this study, fully matured sandal strawberry tree (Arbutus unedo L.) fruit used as material were collected from 25 trees where they grow naturally from Kemer district of Antalya province in November 2021, and 50 fruit from each tree were randomly picked (Figure 1, Figure 2, Figure 3, Figure 4 and Figure 5). The collected fruit were brought to the laboratory in a cold environment in a polyethylene bag. Fruit was stored in the refrigerator until analysis.

2.2. Methods

2.2.1. Heat Treatment

The sandal strawberry tree fruit samples were heated in a conventional oven at 70 °C and 120 °C for 90 min. The dehydrated strawberry tree fruit were powdered (0.5 mesh) using a grinder (Sinbo Scm-2934) before analyses. Fresh samples were dried in open air at 25 °C in a 5&5 humidity environment.

2.2.2. Moisture Content

Moisture content of sandalwood fruit dehydrated at different temperatures (air, 70 °C and 120 °C) were determined by the KERN & SOHN GmbH (Balingen, Germany) electronic moisture analyzer [22].

2.2.3. Total Oil Content

Fresh sandal strawberry tree fruit were dried in an oven (70 and 120 °C) and in air (for control). Each sample was then ground and powdered in the laboratory mill. After 10 g of powdered strawberry tree fruit were added to Soxhlet cartridges, the cartridge was placed in the Soxhlet apparatus. After sufficient amount of petroleum ether (250 mL) (Merck) was added to the Soxhlet flask, extraction was carried out at 50 °C for 5 h to obtain the oil of the fruit. After the extraction, the solvent in the micella was removed under vacuum in a rotary evaporator (Germany) at 50 °C. The oil phase remaining was calculated gravimetrically (%) [22].

2.2.4. Carotenoid Content

Extraction for total carotenoid amounts of sandal strawberry tree fruit was carried out according to method described by Silva da Rocha et al. [23]. After 25 mL of acetone (Merck) was added to 2 g ground sample, the mixture was stirred by vortex for 10 min and solution was filtrated. Filtrate was transferred to a separation funnel and fractionated with 20 mL of petroleum ether. 100 mL of distilled water was used to remove the acetone. These steps were repeated twice. Whatman No. 1 covered with anhydrous sodium sulfate (5 g) for removing residual water was used to filtrate the petroleum ether layer. The volume of the extract was brought to 25 mL by petroleum ether. The absorbance of each sample was recorded at 450 nm. Carotenoid results are described as µg/g.

$$Total carotenoids \left(\mathsf{\mu }\mathrm{g}/\mathrm{g}\right)=\frac{\mathrm{A}\times \mathrm{V}\times {10}^4}{E\times \mathrm{M}}$$

A: absorbance, V: total extract volume, M: sample weight, E: extinction coefficient of β carotene in petroleum ether

2.2.5. Tannin Content

Ground sandal strawberry tree fruit samples (3 g) were stirred with 250 mL of distillated water, followed by shaking in water bath for 4 h and filtering before analysis. The extract (25 mL) was mixed with indigo solution (25 mL) and distillated water (750 mL), and then the mixture was titrated using 0.1N KMnO₄ (Merck) solution until a yellow color was obtained. Tannin is stated as % [24].

2.2.6. Extraction Procedure

Extraction was performed according to modified method reported stated by Mraihi et al. [25]. After 15 mL of methanol:water (80:20, v,v) mixture was added to 2 g ground strawberry tree fruit sample, ultrasonic bath for 30 min was applied to samples at room temperature and washed with 5 mL of hexane. After the solutions were centrifuged at 5000 rpm for 10 min, this procedure was applied twice and the supernatants were collected. After the extract solution was evaporated under vacuum in a rotary evaporator at 37 °C, the volume of the extracts was completed to 15 mL by ultrapure water. Then, the extract solution was filtered in a 0.45 µm nylon filter for analysis.

2.2.7. Total Phenolic Content

Total phenolic amounts of the sandal strawberry tree fruit were determined by Folin–Ciocalteu’s (Sigma-Aldrich) reagent (according to method reported by Yoo et al.) [26]. After 1 mL Folin–Ciocalteu was added to samples, it was vigorously mixed for 5 min. After 5 min, 10 mL of 10% (w/v) of Na₂CO₃ solution was added to the tubes, and it was stirred again and the final volume was completed to 25 mL with deionized water. After 1 h of incubation at room temperature, absorbance of the samples at 765 nm in spectrophotometer (Shimadzu UV mini 1240, Japan) was recorded in triplicate. The total polyphenol content of each samples is described as mg gallic acid equivalent (GAE)/100 g of dry weight of strawberry tree fruit.

2.2.8. Total Flavonoid Content

Total flavonoid content of sandal strawberry tree fruit extract was detected by using colorimetric method with aluminum chloride according to Hogan et al. [27]. Briefly, 1 mL extract was diluted separately with 0.3 mL of NaNO₂, 0.3 mL of AlCl₃ and 2 mL of NaOH, respectively. The mixture was kept at room temperature in dark for 15 min. The absorbance of mixture was recorded at 510 nm with a spectrophotometer (Shimadzu UV mini 1240, Japan). The results are expressed as mg catechin (CA)/g extract (dw).

2.2.9. Antioxidant Activity

Radical scavenging activity of the sandal strawberry tree fruit extracts was measured by using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) according to method described by Lee et al. [28]. Briefly, 2 mL of a methanolic solution of DPPH was mixed with extract. After the mixture was mixed vigorously, it was allowed to stand in the dark at room temperature for about 30 min. A control solution was prepared together with equal volumes of DPPH and methanol without adding the sample. Absorbance of samples for the DPPH scavenging activity was measured at 517 nm with a spectrophotometer (Shimadzu UV mini 1240, Japan). The results are described as mmol trolox/kg.

2.2.10. Determination of Phenolic Compounds

A Shimadzu-HPLC equipped with a PDA detector and an Inertsil ODS-3 (5 µm; 4.6 × 250 mm) column was applied to the analyses of phenolic compounds (Figure 4) of untreated and dehydrated strawberry tree fruit. The mobile phase was a mixture of 0.05% acetic acid in water (A) and acetonitrile (B). The flow rate of the mobile phase and the injection volume were 1 mL/min at 30 °C and 20 µL, respectively. The gradient programme was as follows: 0–0.10 min, 8% B; 0.10–2 min, 10% B; 2–27 min, 30% B; 27–37 min, 56% B; 37–37.10 min, 8% B; 37.10–45 min, 8% B. The total running time per sample was 60 min. Results obtained are described as mg/100 g(dw).

2.2.11. Fatty Acid Composition

Fatty acids were determined as methyl esters of untreated and dehydrated sandal strawberry tree fruit oils according to ISO-5509 [29] method by gas chromatography (Shimadzu GC-2010) equipped with flame-ionization detector (FID) and capillary column (Tecnocroma TR-CN100, 60 m × 0.25 mm, film thickness: 0.20µm). The temperature of injection block and detector was 260 °C. Mobile phase was nitrogen with 1.51 mL/min flow rate. Total flow rate was 80 mL/min and split rate was 1/40. Column temperature was programmed at 120 °C for 5 min and increased 240 °C at 4 °C/min and held 25 min at 240 °C. Identification was carried out compared to the retention times for fatty acid methyl esters of studied samples to the retention times of fatty acid methyl ester standards. The results are described as the weight percentage of total fatty acids.

2.2.12. Mineral Content

After sandal strawberry tree fruit were dried at 70 °C and 120 °C, they were ground in a laboratory-type mill. About 0.5 g ground strawberry tree fruit was burned by using 5 mL of 65% HNO₃ and 2 mL of 35% H₂O₂ in microwave system. Mineral content of strawberry fruit were measured by inductively coupled plasma atomic emission spectroscopy [30]. Mineral results are stated as mg/kg.

2.3. Statistical Analyses

Data of triplicate analyses were averaged and subjected to analysis of variance (JMP version 9.0). Results are pointed out as mean ± standard deviation (MSTAT C) of processes carried out on untreated and heat-treated strawberry fruit. Principal component analysis (PCA) was applied using JMP Pro 16.

3. Results and Discussion

3.1. Chemical Characteristics, Bioactive Compounds and Antioxidant Activity of Dried Strawberry Tree Fruit

Chemical characteristics, bioactive compounds and antioxidant activity of dried strawberry tree fruit dehydrated in oven at the two different temperatures (70 and 120 °C) are illustrated in

Table 1. Some chemical characteristics and bioactive compounds of untreated and dehydrated-strawberry fruit.

Process	Moisture Content (%)	Oil Content (%)	Carotenoid Content (μg/g)	Tannin Content (%)
Control	51.51 ± 0.89 a*	0.40 ± 0.00 c	4.34 ± 0.05 b	5.13 ± 0.03 b
70 °C	26.83 ± 0.32 b**	2.00 ± 0.00 a	5.43 ± 0.07 a	6.37 ± 0.01 a
120 °C	13.23 ± 0.82 c	1.34 ± 0.01 b	4.20 ± 0.05 c	6.37 ± 0.02 a
Process	Total phenolic content (mg/100 g)	Total flavonoid content (mg/100 g)	Antioxidant activity (mmol/kg)
Control	665.13 ± 15.20 a	592.91 ± 15.56 c	7.30 ± 0.01 a
70 °C	509.62 ± 13.40 b	717.95 ± 25.50 b	4.92 ± 0.00 b
120 °C	444.16 ± 19.27 c	788.71 ± 23.79 a	4.10 ± 0.01 c

* Standard deviation; ** values within each column followed by different letters are significantly different at p < 0.05.

. Results exhibited some fluctuations depending on temperatures applied compared to the control. The moisture amounts of the sandal strawberry tree fruit were determined between 13.23% (120 °C) and 26.83% (70 °C), while the oil yields of the sandal strawberry tree fruit were measured between 0.40% (control) and 2.00% (70 °C). Additionally, total carotenoid and tannin contents of the strawberry tree fruit were established from between 4.20 µg/g (120 °C) and 5.43 µg/g (70 °C) to between 5.13% (control) and 6.37% (70 and 120 °C), respectively. While total phenolic amounts of dehydrated sandal strawberry tree fruit varied between 444.16 mg GAE/100 g (120 °C) and 665.13 mg GAE/100 g (control), the total flavonoid contents of the sandal strawberry tree fruit were determined between 592.91 (control) and 788.71 mg/100 g (120 °C). Antioxidant activity values of sandal strawberry tree fruit ranged from 4.10 mmol TE/kg (120 °C) to 7.30 mmol TE/kg (control). The moisture contents of strawberry tree fruit dehydrated at different temperatures decreased significantly compared to the control, while the oil contents increase partially. Moisture and oil contents of dehydrated sandal strawberry tree fruit at 70 °C were found to be partly higher than those dehydrated at 120 °C. Both total phenolic amounts and antioxidant activity values of untreated (control) sandal strawberry tree fruit were found to be higher than dehydrated ones, and a linear relationship was determined between the total phenolic amounts of the samples and their antioxidant activities. While the tannin and total flavonoid amounts of strawberry tree fruit increase with the applied heat treatment, the total phenolic amounts and antioxidant activities of the fruit decreased when compared to the control. Significant statistical differences were observed among bioactive properties of sandal strawberry tree fruit (p < 0.05). In a previous study, Ruiz-Rodríguez et al. [8] reported that the strawberry tree fruit contained 0.30–0.78 g/100 g oil. Ruiz-Rodríguez et al. [8] detected 951 to 1973 mg/100 g (fw) total phenols in the strawberry tree fruit. In another study, Tounsia et al. [13] identified that the strawberry tree fruit contained 0.801% oil. Özcan and Hacıseferoğulları [1] reported that sandal strawberry tree fruit contained 2.1% crude oil. Oliveira et al. [6] detected that total phenolic contents of ripe, immature and intermediate strawberry tree fruit were 60, 108 and 111 mg GAE/g (dw), respectively. Total phenolic and flavonoid contents of the strawberry tree fruit changed from between 25.37 and 39.06 mg GAE/g (dw) to between 3.30 and 7.07 mg RE/g (dw), respectively [31]. The antioxidant activity (DPPH) values of strawberry tree fruit were found to be 3.33–21.08, 2.25–19.58 and 1.08–13 mg AAE/g (dw) [31]. DPPH radical scavenging activities of ripe and intermediate strawberry tree fruit were (0.25 ± 0.02 mg/mL) and (1.09 ± 0.05 mg/mL), respectively [6]. The highest radical scavenging activity values of n-hexane and methanol extracts of the strawberry tree fruit were 73.73 μg/mL and 95.25 μg/mL, respectively [32]. When the results of some chemical composition and bioactive properties of sandal strawberry tree fruit were compared with the results of the literature, some differences were detected. These differences may be due to the variety, harvest time, location, climatic conditions, applied analytical procedures and chemicals used.

3.2. The Phenolic Constituents of Untreated (Control) and Dehydrated Sandal Strawberry Fruit

The phenolic compounds of untreated (control) and dehydrated sandal strawberry tree fruit are presented in

Table 2. Phenolic compounds of untreated and dehydrated strawberry fruit samples.

Phenolic Compounds (mg/100 g)	Control	70 °C	120 °C
Gallic acid	25.63 ± 0.48 c*	26.46 ± 2.42 a	26.26 ± 0.31 b
3,4-Dihydroxybenzoic acid	12.62 ± 0.59 c**	22.09 ± 3.73 a	18.23 ± 0.73 b
Catechin	64.02 ± 2.72 c	92.23 ± 1.05 a	72.26 ± 2.72 b
Caffeic acid	6.20 ± 0.44 b	10.23 ± 2.17 a	4.78 ± 1.26 c
Syringic acid	5.74 ± 1.53 b	7.22 ± 2.51 a	5.00 ± 1.57 c
Rutin	28.58 ± 3.57 b	49.28 ± 2.43 a	23.82 ± 4.94 c
p-Coumaric acid	2.14 ± 0.93 a	2.05 ± 0.48 b	1.51 ± 0.26 c
Ferulic acid	0.91 ± 0.43 c	1.70 ± 0.07 b	5.01 ± 1.41 a
Resveratrol	0.07 ± 0.05 c	0.27 ± 0.12 a	0.20 ± 0.16 b
Quercetin	0.39 ± 0.10 c	1.05 ± 0.41 a	0.45 ± 0.24 b
Cinnamic acid	0.02 ± 0.00 b	0.03 ± 0.00 a	0.02 ± 0.00 b
Kaempferol	0.11 ± 0.03 a	0.09 ± 0.01 b	0.08 ± 0.01 c

* Standard deviation; ** values within each row followed by different letters are significantly different at p < 0.05.

. The phenolic constituents and amounts of untreated and dehydrated sandal strawberry tree fruit were identified by HPLC. Gallic acid, 3,4-dihydroxybenzoic acid, catechin, caffeic acid and rutin were the main constituents of the strawberry tree fruit, followed by syringic acid, p-coumaric acid and ferulic acid in descending order. Gallic acid and 3,4-dihydroxybenzoic acid amounts of control and dehydrated strawberry tree fruit were found from between 25.63 (control) and 26.46 mg/100 g (70 °C) to between 12.62 (control) and 22.09 mg/100 g (70 °C), respectively. Additionally, while catechin amounts of control and dehydrated fruit range from 64.00 (control) to 92.23 mg/100 g (70 °C), caffeic acid contents of sandal strawberry tree fruit were detected between 4.78 (120 °C) and 10.23 mg/100 g (70 °C). Syringic and rutin contents of untreated (control) and dehydrated strawberry tree fruit were determined from between 5.00 (120 °C) and 7.22 mg/100 g (70 °C) to between 23.82 (120 °C) and 49.28 mg/100 g (70 °C), respectively. In addition, p-coumaric acid amounts of strawberry tree fruit changed between 1.51 (120 °C) and 2.14 mg/100 g (control), while ferulic acid contents of sandal strawberry tree fruit range from 0.91 (control) to 5.01 mg/100 g (120 °C). Quercetin amounts of strawberry tree fruit samples were detected between 0.39 (control) and 1.05 mg/100 g (70 °C). The amounts of other phenolic compounds detected in untreated and heat-treated strawberry tree fruit were identified below 0.27 mg/100 g. The phenolic component contents of sandal strawberry tree fruit increased partially with the dehydration process. In addition, the highest amounts of phenolic compounds (ferulic acid, resveratrol and kaempferol) were detected in dehydrated sandal strawberry tree fruit at 70 °C, followed by the control group and fruit dehydrated at 120 °C in decreasing order. The high phenolic components of sandal strawberry tree fruit that are dehydrated at low temperature may be presumably due to the partial removal of water in the fruit and the phenolic components are not damaged much by low temperature. As a result of the significant removal of the water content of the fruit dehydrated at 120 °C, the chemical structure of the phenolic compounds may have deteriorated with the effect of dry temperature and ambient oxygen. Although the amounts of phenolic compounds decreased at 120 °C compared to 70 °C, the possible reason why the antioxidant values of the fruit dehydrated at 120 °C were found to be similar to that of the other 70 °C may be the result of Maillard reaction products formed due to excessive drying. The highest increase in dehydrated fruit compared to the control group was rutin in fruit dehydrated at 70 °C. Significant statistical differences were observed among the phenolic constituents of dehydrated sandal strawberry tree fruit compared to the control (p < 0.05). Yıldız [33] reported that strawberry tree fruit contained 47.70–186.76 mg/100 g gallic acid, 2.60–9.18 chlorogenic acid, 1.19–13.01 caffeic acid, 2.13–6.06 p-coumaric acid, 0.09–0.29 ferulic acid and 34–302 mg/100 g sinapic acid. Pimpão et al. [34] determined 117 mg/100 g gallic acid in sandal strawberry tree fruit. Ayaz et al. [10] determined 10.7 mg/g (dw) gallic acid in strawberry tree fruit. Gallic acid, protocatechin acid, (+)-catechin, phloroglucinaldehyde, ellagic acid, myricetin and quercetin were identified in strawberry tree fruit extracts obtained after enzymatic hydrolysis with hesperidinase followed by cellulose [34]. Zitouni et al. [31] identified gallic acid, catechin, chlorogenic acid, ellagic acid, syringic acid, rutin, phloridzin, vanilic acid, protocatechine acid, p-coumaric acid, ferulic acid and quercetin in strawberry tree fruit. When the differences in the phenolic contents of strawberry samples were compared with the literature data, some fluctuations were observed. The possible reason for these differences may be due to the applied heat treatment time, variety, genetic structure, fruit maturity and harvest time.

3.3. Fatty Acid Compositions of the Oils of the Untreated (Control) and Heat-Treated Sandal Strawberry Tree Fruit

Fatty acid compositions and their quantitative values of the oils of the untreated and heat-treated sandal strawberry tree fruit detected by GC are presented in

Table 3. Fatty acid composition of the oils of untreated (control) and dehydrated strawberry fruit.

Fatty Acids (%)	Control	70 °C	120 °C
Palmitic	11.91 ± 0.02 c*	20.65 ± 0.11 b	20.88 ± 0.02 a
Stearic	3.73 ± 0.07 c**	4.54 ± 0.02 b	6.32 ± 0.10 a
Oleic	27.64 ± 0.06 c	39.56 ± 0.01 b	42.17 ± 1.10 a
Linoleic	28.56 ± 0.08 a	23.67 ± 0.10 b	8.73 ± 0.05 c
Linolenic	28.16 ± 0.22 a	11.57 ± 0.20 c	21.89 ± 1.18 b

* Standard deviation; ** values within each row followed by different letters are significantly different at p < 0.05.

. Depending on fatty acid results, there are some differences in fatty acid profiles of the oils of sandal strawberry tree fruit. Palmitic, oleic, linoleic and linolenic acids were the main fatty acids of the sandal strawberry tree fruit oils. Palmitic and stearic acid contents of untreated and heat-treated strawberry oils were identified from between 11.91% (control) and 20.88% (120 °C) to between 3.73% (control) and 6.32% (120 °C), respectively. While the oleic acid contents of the oils extracted from strawberry tree fruit range from 27.64% /control) to 42.17% (120 °C), linoleic acid contents of the oils of control and dehydrated strawberry fruit were identified between 8.73% (120 °C) and 28.16% (control). Palmitic, stearic and oleic acid contents of dehydrated strawberry tree fruit oils compared to the control were observed to increase with the applied temperature, while the contents of polyunsaturated fatty acids (linoleic and linolenic) decreased. The highest decrease was detected in that of strawberry tree fruit dehydrated at 120 °C. As the unsaturated of the oils increases, the role of damage from heat treatment also increases, and it has been observed that the sensitivity of polyunsaturated fatty acids to heat is high. Palmitic acid was found as the most important saturated fatty acid in strawberry tree fruit oil. Significant statistical differences were observed among fatty acid contents of the oils extracted from dehydrated sandal strawberry tree fruit compared to the control (p < 0.05). In a previous study, Barros et al. [35] determined 6.51% α-linolenic, 21.50% linoleic and 21.01% oleic acids in the oil of strawberry tree fruit. In other study, Morales et al. [36] determined 31.26% α-linolenic, 24.26% linoleic and 24.82% oleic acids in strawberry tree fruit. When the fatty acid results in our study were compared with the literature data, some differences were observed. The fatty acid compositions of the oils extracted from sandal strawberry tree fruit were found to be high, as in the literature. These differences may be due to variety, fruit maturity, climatic factors, location and the solvent used.

3.4. The Mineral Content of Untreated (Control) and Dehydrated Sandal Strawberry Tree Fruit

The mineral content of untreated (control) and sandal strawberry tree fruit dehydrated in an oven at two different temperatures (70 and 120 °C) are illustrated in

Table 4. Mineral contents of untreated and dehydrated strawberry fruit (mg/kg).

	P	K	Ca	Mg	S	Na	Fe	Cu	Mn	Zn	B
Control	483.12 ± 17.28 c*	4877.42 ± 47.65 c	2143.81 ± 26.75 c	474.52 ± 9.28 c	196.84 ± 5.63 c	56.82 ± 1.28 b	14.01 ± 1.21 b	0.96 ± 0.12 c	2.48 ± 0.65 c	7.84 ± 0.98 a	3.40 ± 1.75 c
70 °C	702.84 ± 32.14 a**	6291.51 ± 29.87 b	3362.18 ± 12.57 a	786.65 ± 7.62 a	274.78 ± 10.23 a	56.34 ± 3.75 c	15.20 ± 1.18 a	1.96 ± 0.18 b	6.35 ± 0.89 a	5.91 ± 1.08 b	4.88 ± 1.19 b
120 °C	565.99 ± 23.09 b	6568.76 ± 11.56 a	2361.36 ± 25.71 b	596.07 ± 11.39 b	266.68 ± 8.75 b	57.75 ± 8.97 a	12.80 ± 2.76 c	4.91 ± 0.23 a	4.52 ± 0.44 b	5.87 ± 1.23 c	4.91 ± 1.05 a

* Standard deviation; ** values within each column followed by different letters are significantly different at p < 0.05.

. Significant fluctuations were observed among the amounts of mineral content depending on the temperatures applied compared to the control (p < 0.05). P and K amounts of the sandal strawberry tree fruit changed from between 483.12 (control) and 702.84 mg/kg (70 °C) to between 4877.42 (control) and 6568.76 mg/kg 120 °C), respectively. Additionally, while Mg contents of untreated and strawberry tree fruit dehydrated vary between 474.52 (control) and 786.65 mg/kg (70 °C), S amounts of the sandal strawberry tree fruit were detected between 196.84 (control) and 274.78 mg/kg (70 °C). In addition, Na and Fe contents of sandal strawberry tree fruit were identified from between 56.34 (70 °C) and 56.82 mg/kg (control) to between 12.80 (120 °C) and 15.20 mg/kg (70 °C), respectively. Additionally, Ca amounts of sandal strawberry tree fruit changed between 2143.81 (control) and 3362.18 mg/kg (70 °C). In general, the mineral content of dehydrated strawberry tree fruit increased compared to the control. This increase varied depending on the applied temperature. While the mineral content (K, Na, Cu and B) of some strawberry tree fruit samples increased in those dehydrated at 120 °C, some minerals such as P, Mg, S, Fe, Zn increased in those dehydrated at the applied temperature. Significant statistical differences were observed among the mineral contents of dehydrated sandal strawberry tree fruit compared to the control (p < 0.05). Özcan and Haciseferoğullari [1] determined 4959 Ca, 14,909 K, 1316 Mg, 701 Na and 3669 mg/kg P in strawberry tree fruit collected in Mersin (Turkey). In another study, Vidrih et al. [9] determined 118.61 K, 20.63 Na, 36.05 Ca, 9.66 Mg, 1.29 Fe, 19.99 P, 0.45 Zn, <0.99 Mn, <0.99 Cr, <0.10 Ni, <1.32 Pb and <0.10 mg/100 g Cd in strawberry fruit collected in Croatia. The macro element contents of sandal strawberry tree fruit were found to be high as in the literature. So, our results show some differences compared to the results of previous studies. These differences are probably due to harvest time, drying conditions, maturation, species, growing conditions, soil structure, location and climatic factors.

3.5. Principal Component Analysis (PCA) of Untreated (Control) and Dehydrated Sandal Strawberry Tree Fruit

Principal component analysis (PCA) was performed to determine the effects of heat treatment on phenolic compounds, which are displayed in Figure 3. PC1 explained about 65.206% of variability. PC2 showed about 34.794% of variability. The first two principal axes explained 100% of variance. PC1 was identified with cinnamic acid (0.985), quercetin (0.996), resveratrol (0.866), rutin (0.939), syringic acid (0.875), caffeic acid (0.911), catechin (0.993), 3,4-dihydroxybenzoic acid (0.897) and gallic acid (0.801), while p-coumaric acid and kaempferol were the main variables in PC2 (

Table 5. PCA results in relation to phenolic compounds of sandal strawberry tree fruit.

	PC1	PC2
Eigenvalue	7.825	4.175
Variability (%)	65.206	34.794
Cumulative %	65.206	100.000
Correlation
Gallic	0.801	−0.599
Dihyd	0.897	−0.443
Catechin	0.993	−0.116
Caffeic	0.911	0.413
Syringic	0.875	0.484
Rutin	0.939	0.341
Coumaric	0.218	0.976
Ferulic	−0.169	−0.986
Resveratrol	0.866	−0.500
Quercetin	0.996	0.089
Cinnamic	0.985	0.171
Kaempferol	−0.354	0.935

). The sample dehydrated at 70 °C was located in the positive area of both PC1 and PC2 and also contained higher amounts of phenolics and flavonoids such as quercetin, catechin, rutin, cinnamic acid, 3,4-dihydroxybenzoic acid, caffeic acid and syringic acid in comparison with other samples. Additionally, the sample dehydrated at 120°C was located in the negative area of both PC1 and PC2 and exhibited the highest amount of ferulic acid, which was located in the same area.

4. Conclusions

In this study, the effects of oven dehydration on chemical and bioactive properties, fatty acids, phenolic compounds and mineral content of pickled sandal strawberry tree fruit was investigated. Moisture and oil contents of strawberry fruit dehydrated at 70 °C were found to be partly higher than those dehydrated at 120 °C. Both total phenolic amounts and antioxidant activities of untreated (control) sandal strawberry tree fruit were found to be higher than dehydrated ones, and a linear relationship was determined between the total phenolic contents of the samples and their antioxidant values. Total carotenoid and tannin amounts of the sandal strawberry tree fruit were found from between 4.20 (120 °C) and 5.43 µg/g (70 °C) to between 5.13 (control) and 6.37% (70 and 120 °C), respectively. In general, the phenolic component amounts of strawberry tree fruit increased partially with the dehydration process. The amounts of phenolic compounds decreased at 120 °C compared to 70 °C. Gallic acid, 3,4-dihydroxybenzoic acid, catechin, caffeic acid and rutin were the main constituents of the strawberry tree fruit, followed by syringic acid, p-coumaric acid and ferulic acid in descending order. It was observed that sandal strawberry tree fruit oil is rich in oleic and linoleic acids. In general, the mineral content of dehydrated strawberry tree fruit increased compared to the control. Future studies will study the effects of different processes on the nutritional values and bioactive properties of sandal strawberry tree fruit. Since the oil, carotenoid, total phenol and phenolic component contents of sandalwood tree fruit are higher in the sample subjected to dehydration at 70 °C, this temperature can be considered as the ideal one for drying. In addition, considering the fatty acids, heat treatment at 120 °C can be preferred.