Effects of methyl jasmonate and modified atmosphere packaging on physical and mechanical characteristics of apricot fruit during cold storage

Bu calismada, metil jasmonat (MeJA) icin, 0.5 ve 1.0 mmol L-1 dozlari ile modifiye atmosfer paketleme (MAP) uygulamalarinin sogukta muhafaza suresince ‘Precoce de Thyrinthe’ kayisi cesidinin fiziksel ve mekanik ozellikleri uzerine etkileri incelenmistir. Meyveler, 0±0.5˚C ve % 90±5 oransal nemde 20 gun boyunca muhafaza edilmistir. Kayisi meyvesinin fiziksel ozellikleri olarak; geometrik ortalama cap, kuresellik, yuzey alani, agirlik, yigin hacim agirligi, meyve hacim agirligi, mekanik ozellikleri olarak; delme ve sikistirma kuvvetleri ve surtunme katsayisi incelenmistir. MAP uygulamasinin istatistiksel olarak uzunluk, genislik ve kalinlik parametreleri uzerindeki etkileri onemli bulunmustur. MeJA uygulamasinin kayisi meyvesinin boyut ozellikleri uzerinde, hasat donemine gore onemli bir farklilik meydana getirmedigi gorulmustur. Depolama suresinin boyutsal parametreler uzerine etkisi istatistiksel olarak onemli bulunmustur. Genel olarak, MAP uygulanan meyvelerde hasat donemine gore yigin hacim agirligi degerlerindeki azalmanin daha az oldugu tespit edilmistir. Depolama suresiyle ilgili olarak depolama suresi artisina gore sikistirma testi sonucu X-, Y- ve Z- ekseninden elde edilen sikistirma kuvveti sonuclarinin degisiminde azalmalar gozlenmistir. X-, Y- ve Z- eksenlerindeki delme kuvvetine etkisi MAP’siz uygulamaya gore, MAP’li uygulamada, hasat donemine gore daha dusuk duzeyde bir azalma egilimi gostermistir. Laminant ve galvaniz sac yuzeylerindeki surtunme katsayisinin, PVC, kontrplak ve lastik yuzeylerine gore daha dusuk degerler vermistir.


INTRODUCTION
Having high β-carotene and lycopene activity, apricot may prevent heart diseases. It regulates digestive conditions such as constipation and diverticulitis and is an excellent food for anemia due to its rich and valuable fiber source and high iron content (Vardi et al., 2008). However, quality losses occur after harvest due to many factors. In order to reduce these losses, growth regulators are used as a tool (Karaman et al., 2013).
Plant growth regulators are natural or synthetic compounds capable of controlling multiple physiological events within the plant, which are natural or synthetic compounds that affect fruit yield and quality, ripening process and post-harvest storage and shelf life. One of these compounds is methyl jasmonate (Öztürk 2012;Karaman et al., 2013;Öztürk et al., 2014).
Methyl jasmonate (MeJA), is an inducer of plant defense, regulation of certain cellular events such as aging, fruit ripening and ethylene synthesis and an inhibitor in cellular development, such as seed germination, pollination, and root development (Rohwer and Erwin, 2008). In a research carried out on apricot fruit (Ezzat et al., 2017), MeJA has been observed to significantly delay fruit quality losses during storage and shelf life. There are also studies reporting that MeJA has a significant effect on postharvest quality preservation in fruit species such as cherry, mango, guava and pomegranate (Gonzalez-Aguilar et al., 2003;Sayyari et al., 2011;Saracoglu et al., 2017).
Modified atmosphere packaging (MAP) is a postharvest technology used to reduce fruit quality loss during cold storage. The fruit placed in the packaging breathe carbon dioxide and use the oxygen in the environment. In this process, respiration is suppressed due to decreased oxygen and increased carbon dioxide and losses are reduced. With the spread of this method, quality losses in fresh fruit and vegetables are reduced and market value increases (Ozturk et al., 2019).
During the period until the transportation of agricultural materials to the market after harvest and post-harvest technological processes; significant changes in physical and mechanical properties are observed. Physical, mechanical and chemical properties of agricultural materials may vary depending on species and varieties, aquaculture system, environmental conditions such as light and temperature, harvest time, storage conditions and cultural processes in development regulators (Shin et al., 2008).
In this study, it was aimed to determine the effect of MeJA and modified atmosphere packaging applications on some physical and mechanical properties of 'Prococe de Thyrinthe' apricot variety during cold storage.

MATERIALS and METHODS
The material of the study consisted of fruit of 12 yearolds 'Precoce de Thyrinthe' cultivar grafted on wild apricot (Prunus armeniaca L.) grown in orchard of Malatya Apricot Research Institute in Turkey. Irrigation, fertilization, pruning and other cultural processes during the development of trees (weed, disease and pest control etc.) were regularly conducted.
The fruit were hand-harvested (19 June 2018) at a stage of uniform size and color, and the SSC content was approximately 11% and placed in 5 kg plastic box and transferred to post-harvest physiology laboratory.
The research was designed as a randomized plot with 3 replications according to factorial design. Fruit were first divided into 3 groups. The first group (1 st group) fruit (control group) were immersed only in a distilled water solution containing solvent [Triton X-100 (0.077%), Sigma-Aldrich, Germany]. The 2 nd group fruit were immersed into 0.5 mmol L -1 and 3 rd group fruit into 1.0 mmol L -1 MeJA (Sigma-Aldrich, Germany) solution for 1 minute. Then fruit were kept in the laboratory until the surface got dry. After that, the 1 st , 2 nd and 3 rd group fruit were separated into 2 and one of them was packaged in a [(code: 815-AT 10 / R), (patent no. 6190710), StePac, Xtend] modified atmosphere packaging of 65 cm height, 53 cm width, 5 kg capacity, designed especially for apricot fruit; and the other one was not exposed to any application. Each case represented a repetition and 1 kg of fruit was placed.
Finally, the fruit were pre-cooled with air cooling (4±0.5C ve 90±5% relative humidity) for 24 hours, and then the packages were closed with clips, and at 0±0.5 °C and 90±5% relative humidity stored for 20 days. In addition to fruit harvest, on the 5 th , 10 th , 15 th and 20 th days; physical properties such as geometric mean diameter, sphericity, surface area, mass, bulk and fruit densities, and mechanical properties such puncture and compressive forces and friction coefficient were determined.
All physical measurements were made on 30 fruit with 10 parallels per repetition. Fruit length, width and thickness were measured by digital caliper (Tronic, Turkey) with a precision of 0.01 mm. The fruit mass were measured with a digital scale (Radwag, Poland) with a sensitivity of 0.001 g. Geometric mean diameter (Dg), sphericity (), surface area (S) ve volume (V); calculated with the following equations (Mohsenin, 1980).
Bulk density was determined in kg m -3 by taking into account the mass of the samples by filling the fruit samples into a ¼ liter hectolitre container by heaping from a certain height (Altuntaş and Yıldız, 2007). Liquid displacement method was used to determine fruit density. Pure water was added to the tare-grade cup and the liquid displacement value was determined in terms of fruit density, fruit mass and fruit volume values in kg m -3 (Mohsenin, 1980). For mechanical measurements (fruit compaction and perforation forces), a biological material tester was used. In the tests, compression and puncture tests were carried out on the fruit shell. The tester consists of 3 main components. These are fixed plates, moving plate and data acquisition unit, PC card and computer software. The movable plate is in the form of a circular table in compression tests, and in the form of a cylindrical needle in puncture tests (Yaldız, 2014). The biological material tester used in the study consists of a draw-off dynamometer with manual movement and digital display (Sundoo, SH-50, China), a digital drawoff dynamometer and a stand with measuring scale, fixed plate and a wired computer connection. Puncture and compression tests were performed. The reading values are given in N (Newtons). In the experiments, 11.1 mm steel cylindrical table with constant compression speed in compression tests and 1.2 mm steel needle in puncture tests were used with the biological material tester. The mechanical behavior of the fruit which were punctured and compacted in 3 different axes (X-, Y-, Z-) were determined by using biological material tester on apricot fruit (F) (Figure 1). Different surfaces (PVC, rubber, plywood, galvanized sheet, laminate) were used for the friction coefficient measurements of apricot fruit. For the friction measurement of fruit, the inclined table was used. The inclined table was moved with a screw arm to allow the movement of the fruit on the different friction surfaces and the inclination angle of the inclined table was used to determine the static friction coefficient when the first movement was performed (Yaldız, 2014).
For determination of moisture content of apricot fruit, the fruit were divided into two parts and kept in the oven at 105±1° C for 24 h to reach a constant mass and moisture content (% wb) was determined according to wet base (Darıcı and Şen, 2012). The moisture content measurement value of apricot fruit harvested before the experiments was determined as 80.48% according to wet mass. Statistical analysis of the data obtained from all parameters was performed using the SPSS (V.13.0) statistical package program.

Dimensional Properties
There was no significant change in general in the dimensional properties of the fruit during cold storage. However, on day 5 measurements of storage, the length (L) value of the fruit stored in MAP and treated with MeJA was found to be significantly higher than the control fruit. When the overall means of MAP application were compared, it was found that the length, width and thickness values of fruit stored in MAP were significantly higher than those not stored in MAP (Table 1). Altuntas et al., (2012), reported that the length values of 'Fuji' apple fruit treated with MeJA before harvest were 62.56 mm to 62.52 mm; width values from 79.99 mm to 79.13 mm; the thickness values ranged from 75.45 mm to 75.56 mm. As a result of single and two applications of 0, 2000 and 4000 ppm doses 'Alar' application on 'Hasanbey' apricot cultivar 15 and 30 days after flowering, Bolat and Güleryüz (1992), determined that 'Alar' application decreased fruit length from 53.00 mm to 49.02 mm, width values of 39.50 mm to 40.94 mm. Altuntas et al., (2013), reported that MeJA applications in plum fruit (control, 1120 mg L -1 and 2240 mg L -1 ) showed that the length values decreased from 56.76 mm to 54.40 mm according to doses, and the thickness value was 46.00 mm to 44.96 mm decreased.
In this context, it can be stated that MeJA can affect the dimensional properties of the fruit. However, in our study, it was found that MeJA did not have a negative effect on dimensional properties of the fruit during storage and wasn't even different from control group in general. It is thought that the difference that occurred on the 5 th day of storage may have occurred due to the loss of water in the fruit.

Geometric mean diameter, sphericity and surface area
In Precoce de Thryinthe apricot cultivar, significant effect of MAP application on geometric mean diameter (Dg), sphericity (ϕ) and surface area (SA) was observed. In particular, a significantly higher geometric diameter, sphericity and surface area were obtained (P <0.01) from the fruit stored in MAP. However, the effect of MeJA applications on all these properties during storage was generally found to be no different from control. At the end of the storage period (day 20), the effect of MeJA application was not significant for all properties (Table 2).

Volumetric properties
When the overall averages of MAP application were evaluated, the effect of MAP on mass (M, g) and volume (V, mm 3 ) values of apricot fruit was found to be significant (P <0.01). However, the effect of MAP on bulk and fruit densities was insignificant. When the effect of MeJA applications was examined, it was observed that the values of the applications were generally at the same level as the control group.
Looking at the data obtained in the last measurement period, it was seen that the volumetric properties of the MeJA treated fruit were similar to those of the control fruit (Table 3). It was seen in our study that fruit mass and volume were better preserved in MAP treated fruit. However, the effect of MeJA applications was generally insignificant. In particular, the loss of water in fruit and the limitation of respirable products can be considered as the main reason for the losses in MAP application. Altuntas et al., (2013), stated that the effects of MeJA application on the mass value of plum fruit 0 (control), 1120 mg L -1 and 2240 mg L -1 were in the range of 70.86 g to 69.02 g. Again, in another study Altuntas et al., (2012), stated that in 'Fuji' apple cultivar, MeJA control, 1120 mg L -1 , 2240 mg L -1 and 4480 mg L -1 in post-harvest applications, fruit mass ranged between 196.53 g and 194.83 g fruit volume values were in the range of 192.93 cm 3 to 209.89 cm 3 ; with the application of MeJA, there was a 5.33% decrease in bulk density with increasing doses; bulk and fruit densities for 1120 mg L -1 and 4480 mg L -1 doses of MeJA ranged between 383.65 kg m -3 ile 364.22 kg m -3 , 967.96 kg m -3 , 954.63 kg m -3 respectively.
It was seen in our study that fruit mass and volume were better preserved in MAP treated fruit. However, the effect of MeJA applications was generally insignificant. In particular, the loss of water in fruit and the limitation of respirable products can be considered as the main reason for the losses in MAP application. Altuntas et al., (2013), stated that the effects of MeJA application on the mass value of plum fruit 0 (control), 1120 mg L -1 and 2240 mg L -1 were in the range of 70.86 g to 69.02 g. Again, in another study Altuntas et al., (2012), stated that in 'Fuji' apple cultivar, MeJA control, 1120 mg L -1 , 2240 mg L -1 and 4480 mg L -1 in post-harvest applications, fruit mass ranged between 196.53 g and 194.83 g fruit volume values were in the range of 192.93 cm 3 to 209.89 cm 3 ; with the application of MeJA, there was a 5.33% decrease in bulk density with increasing doses; bulk and fruit densities for 1120 mg L -1 and 4480 mg L -1 doses of MeJA ranged between 383.65 kg m -3 ile 364.22 kg m -3 , 967.96 kg m -3 , 954.63 kg m -3 respectively.

Compression test
In the compression tests of apricot fruit; considering the general averages of MAP application, significant differences were found only for the compression test on the X-axis. In the X-axis compression test, the value of fruit in MAP was significantly higher (P <0.05) than those not stored in MAP. The effect of MAP on the other axes (Y-and Z-) was not significant. When the effect of MeJA was examined, it was seen that the values of the applications were similar to the values of the control fruit in general (Table 4).  Altuntas et al., (2013), found that the effect of preharvest MeJA applications on the compressive force values of plum fruit changed depending on the time of harvest and the effect of MeJA applications on the Yaxis was in the range of 140 N to 129.6 N. In our study, no significant effect of MeJA in compression tests was observed. Çalışır and Aydın (2004), reported that the breaking force values of the dried black mulberry fruit ranged from 4.5 to 3.0 N at 9-77.5% moisture level and that the breaking force values decreased as a result of the compression test.

Puncture test
When the results of the puncture tests carried out in apricot fruit were examined, the puncture test values of MAP-treated fruit for all axes were found to be significantly higher than those not stored in MAP. In our study, the puncture test values of the fruit of MeJA applications were found to be similar to the control in all measurement periods (except 15 th day measurements without MAP on Y-axis) ( Table 5).
In the study, the reason why fruit stored in MAP give higher values in puncture test can be result of decrease of water loss in the fruit with MAP and as a result of this, cell wall structure's getting more resistant. Kalyoncu (2016), stated that the puncture force values of the Prunus laurocerasus fruit showed decreasing tendency in the puncture tests along the X-, Y-and Zaxis of different harvest periods. He also stated that the decrease in force values was 12.90% for length (X-) axis, 46.43% for width (Y-) axis and 24.39% for thickness (Z-) axis depending on the ripening process from the 1 st harvest period to the 3 rd harvest period.

Coefficient of friction
When the general means of MAP applications were compared, it was found that the values of fruit stored in MAP were significantly higher only on PVC friction surface than those fruit without MAP. There was no difference between friction coefficient values of MAP applications on other surfaces. When the effect of MeJA applications in the last measurement period was examined, the friction coefficient of the fruit treated with MeJA in the non-MAP group on the PVC surface was found to be significantly lower than the control group. In contrast, galvanized sheet and plywood were higher than in the control group (Table 6).
In this study, as laminate and galvanized sheet surfaces are more smooth and slippery than PVC, plywood and rubber surfaces, it was observed that it gives lower coefficient of friction. Similar to this study, Öztürk (2012), stated that in the 'Braeburn' apple cultivar, the effect of AVG applications and harvest periods on the static coefficient of friction gave a lower coefficient of friction than the plywood and rubber surface on AVG applications (0, 100 and 300 mg L -1 ); Yaldız (2014), stated that as a result of applying three different doses of 0, 100, 200 aminoethoxyvinylglycine (AVG) in the 'Santa Rosa' plum fruit in three different harvest periods, the lowest coefficient of friction was found on laminate and galvanized sheet surfaces.

CONCLUSIONS
In this study, it has been determined that modified atmosphere packaging applications have a significant effect on the preservation of dimensional properties, geometrical properties and partially volumetric properties. However, it would be a more accurate approach to state that the applied regulatory MeJA does not have a significant effect on physicomechanical properties in general. Growth regulators, including MeJA, are now widely used in agricultural production. Therefore, detailed research is needed to fully demonstrate the effect of growth regulators on physico-mechanical properties.

Declaration of competing interest
The authors declare that they have no conflict of interest.