Effect of Protected Environments on the Postharvest Quality of Strawberry (Fragaria X Ananassa) Produced in the Tropical Mountain Areas

Citation: Cucunubo Bosa PC, Vargas-Cruz J, Quintero-Arias G, Caita JF (2019) Effect of Protected Environments on the Postharvest Quality of Strawberry (Fragaria X Ananassa) Produced in the Tropical Mountain Areas. Int J Biol Instrum 2:004 Copyright: © 2019 Cucunubo Bosa PC, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. *Corresponding author: Paola Cristina Cucunubo Bosa, Research Assistant, Agricultural Engineering, Department of Civil and Agricultural Engineering, Universidad Nacional de Colombia, Colombia

When modifying the environmental conditions, it is necessary to know its effect on the postharvest quality of the fruits. The behavior of the temperature inside the high tunnel is of great importance, because it intervenes in the "metabolic activity, the absorption of water and nutrients, the gas exchange, the production and expenditure of carbohydrates and growth regulators" [13]. Additionally, an increase in temperature increases the efficiency of metabolic processes and, therefore, in crop yield [19].
Temperature is a factor that affects the chemical composition of the fruits [20], since it interferes in the formation of sugars, due to cell division and multiplication in the fruits, the alteration in the biosynthetic enzymatic activity of carbohydrates and the increase in the transpiration rate [21,22]. Likewise, it affects the color of the fruits; in the case of strawberry, the main pigment are anthocyanins, which accumulate in the vacuoles of the epidermal cells, showing tones from red to blue [23,24].
When the temperature is very low at night, there is a decrease in the content of anthocyanins that affects their antioxidant capacity [25]. The fruit coloration is measured through the color index (CI) [26], which depends on the pigmentation of the fruit surface, making it an important indicator of the quality of the strawberry. The CI values between 20 and 40 are related to tones ranging from intense to deep red [27]. Variations may occur, given the difference in the concentration of the pigments, cyanidin-3 glucoside and pelargonidin, which show magenta, crimson, pink, orange and red colors in the fruits [28].
Regarding relative humidity, the presence of high values can cause the appearance of flowering diseases that affect the formation of the fruit and later its quality [6]. Likewise, the plant responds unfavorably when the humidity of the air is high, since it restricts the gas exchanges between the stomata and the environment, limiting transpiration and, therefore, the absorption of nutrients and water [9,29,30] which affects the complete development of the plants.
Regarding radiation, it intervenes in the growth rate of the crop, which can affect the production time [31,32], the variability of the structure of the plant, the morphological development [9,11,33], the performance "as higher the amount of light intercepted by the set of levels of a plant, greater the amount of carbon assimilated" [34], the nutritional composition [35] and the quality of the fruits [10,13], due to its relationship with the photosynthetic process, the synthesis of carbohydrates [8] and secondary metabolites [33,36]. The Photosynthetically Active Radiation (PAR) captured by the plants [37] can be interpreted as the Daily Light Integral (DLI) (mol/m 2 d), since it refers to the "amount of PAR received each day as a function of light intensity (instantaneous light: μmol.m -2 .S -1 )" [38].
In crops such as kiwi, tomato and avocado, the climatic conditions under which they develop affect the postharvest quality of the fruits [7, 21,39]. For the kiwi, it has been established that fruits exposed to higher values of light intensity have a better quality, higher total soluble solids (TSS) content and higher fresh weight than those grown in low light [39]. Likewise, in tomato the TSS content increased when temperatures between 26 and 30 °C were reached and irradiation values between 50 and 170 J/m 2 s [21]. In the case of the avocado, the maturation of the fruit is affected by its exposure to the temperature ant the degree of solar exposure of the crop during the development period, since they affect the cellular structure and, therefore, the firmness of the fruits; as well as, the content of anthocyanins and chlorophyll that determine the color of the fruit [7].
On the one hand, in the case of strawberries (strawberry, raspberry, blueberry or blackberry) [40], light intensity and temperature affect the biosynthesis of anthocyanins [8, 41,42]. Likewise, radiation has an important impact on the filling quality, due to the manipulation of environmental conditions such as light [18]. An increase in phenolic compounds has been registered in fruits exposed to red light [53].
With the new market trends, the consumer looks for innovative products, safe and with high nutritional value [54], therefore, it is necessary to be competitive in the national and international market [55]. As described above, the objective of this work is to evaluate the response of the postharvest quality of the Monterrey and Albion varieties (Fragaria x ananassa), produced in a high tunnel in the Savanna of Bogotá, in order to know the potential of the product to an address the current consumers trends.

Materials and Methods
Strawberry cultivation (Fragaria x ananassa), Monterrey and Albión varieties, was established at the Marengo Agricultural Center-CAM (4° 40' 55.182" N -74° 0' 21.388" O), located in the municipality of Mosquera, Cundinamarca. For the test, a high tunnel of 40 m long, 8 m wide and 2.50 m high in its lowest part and 2.75 m in the center was used, with a plastic cover stabilized with HALS and antioxidants. 12 elevated beds of 0.5 m wide and 38 m long were installed and 130 plants of the Monterrey and Albión varieties were placed in each one, with a substrate consisting of 50% coal slag, 25% coconut fiber and 25% rice husk. During de crop cycle, drip irrigation was used, with a sheet of 100% field capacity (FC) and application of fertilizers through fertigation.

Environmental conditions
Photosynthetically Active Radiation (PAR) (μmol/m 2 s) measurements were taken, inside and outside the high tunnel with a weather station. The PAR data processed to determine the Daily Light Integral (DLI), according to the methodology described by Torres & Lopez [38]: In addition, measurements of ambient temperature (T) and relative humidity (RH) within the high tunnel were made with a Datalogger®. The data corresponding to the open field conditions were obtained from the Tibaitatá meteorological station of the Tibaitatá Research Center (4° 41' 44.189" -74° 12' 13.384"), located in the municipality of Mosquera. and quality of the fruit [43], since the uptake of incident radiation by the plant is related to the photosynthetic capacity and, therefore, to its productive performance [44]. On the other hand, a lower amount of light hours decreases the total soluble solids content and sudden changes in temperature during day and night damage the intensity of the red color [3].
In the cultivation of raspberry (Rubus idaeus), it has been established that the yields are higher in the high tunnel than in the open field [22], with values up 5.5 kg/m, while in free exposure it is only 2.5 kg/m [45]. In addition, there is greater vigorousness of the plant, less presence of pests and greater weight and quality of the fruits in the protected environment [45]. Similarly, in blackberry (Rubus Watson) there is a higher accumulated yield, a wider harvest season and higher fruits weight [46].
In Colombia, strawberry (Fragaria x ananassa) is still a crop that is developed mainly in free exposure [47]. Although the crop has been adapted to different geographical areas optimally, there is a decrease in production when it is sown at high altitudes [48], between 1.200 and 2.600 m.s.n.m [49]. Therefore, its management in a protected environment favors the yield and quality of the fruits [50,51].
La Cámara de Comercio de Bogotá [49], reports that fruit formation develops adequately at temperatures that range between 18 °C and 25 °C during the day, and at night between 8 °C and 13 °C. The deformation of the fruits is due to the presence of temperatures lower than 12 °C during the fruit setting phase and when those are lower than 10 °C the fruiting process decreases significantly [52]. Otherwise, at high temperatures the flowering is reduced and the ripening of the fruits takes place in less time, causing that it does not reach the appropriate size for the harvest [51]. Regarding relative humidity, Cámara Aranda, [51] reports recommended values between 70% and 80%.
The production of the strawberry crop in high tunnel presents favorable changes regarding the time of each phenological stage; the rate of return, with a report of up to 444.59 g/plant the first four months of harvest; fruits with greater weight, surpassing even 40 g and favoring the quality of the fruits [18]. In some varieties, including Albion, the use of plastics causes changes in performance and The data was recorded every hour during the development period.

Postharvest variables
In the Postharvest Laboratory of fruits and vegetables of the Universidad Nacional de Colombia-Bogotá Campus, the fruits collected were classified according to size as follow: • Quality 1: Fruits whose length is greater than 5 cm.
• Quality 2: Fruits whose length ranges between 3.5 cm and 5 cm.
For each sample, 6 fruits of each group were used. Then, the measured variables are described:

Dimensions
The determination of the maximum length and diameter of the fruits was made with a conventional calibrator, following the methodology described in de Colombian Technical Norm NTC 4103 [56].

Fresh weight
The fresh weight of the selected fruits was determined with a precision balance Precisa XT220A Model (0.0001 g).

Surface color
A Konica Minolta® CR-400 colorimeter was used for color measurement. Three measurements were taken around the equatorial zone of the fruit. The CIELab color space was used for reading the coordinates L, a, b. With the data obtained, the color index was determined, according to the methodology described by (Vignoni, Césari, Forte, & Mirábile [26]: Where: L: Sample brightness.
a: Zone of variation between the red and green color of the spectrum.
b: Zone of variation between the yellow and blue color of the spectrum.
From the conversion of the coordinates a, b, the angular tone and chromaticity values were obtained, as expressed below [57]:

Total Titratable Acidity (TTA)
The acid neutralization procedure was applied with 0.1 N sodium hydroxide solution (NaOH). The result obtained is expressed as percentage of citric acid and was calculated in the following way [56]: V 2 : Sample volume (5 mL).

Total Soluble Solids (TSS)
A Kikuchi® analog refractometer was used, with a reading range between 0 and 32 °Brix for the measurement of TSS, in 5 mL of juice extracted from the selected fruits.

Maturity index
The maturity index is calculated as the quotient of the TSS and TTA values [28].

Data analysis
The statistical program Statistix version 8.0 was used. The climatic conditions were analyzed by means of two independent samples normally distributed, whose significance is based on the t-Student probability distribution, P < 0.01.
The postharvest variables were studied through an analysis of variance, from a factorial experiment of two factors, which correspond to the varieties; two levels for each factor, which refer to Quality 1 and 2; 6 repetitions in random blocks; and one dependent variable, which corresponds to the postharvest variable, with a significant interaction corresponding to P < 0.05.

Environmental conditions
There are significant differences between the values of T and RH inside and outside the high tunnel, as shown in within the high tunnel. It is observed that the T in the high tunnel is higher, since the plastic coverage decreases the heat exchange with the surrounding medium [60]. In contrast, the values of T in the exterior are lower [19]. In addition, the behavior of T in the high tunnel shows a lower range of variation between maximum and minimum temperatures, hence the crop is protected against sudden changes in temperature [61], preventing plants from facing situations of thermal stress. with the external environment where maximum and minimum average T values are 17.33 °C and 9.23 °C, respectively. On the other hand, the values of RH in the high tunnel oscillate between 85.56% and 57.60%, while they vary between 91.87% and 60.78% in the open field. Figure 1. also shows the inverse relation between T and HR.

Postharvest variables of the Monterrey and Albión varieties
Fresh weight: It was established that there are statistically significant difference (P < 0.05) in the fresh weight of the fruits according to the quality of each variety, Monterrey and Albión. In Figure  3, it is observed that Quality 1 of both varieties registers values superior to those of Quality 2. In the case of the Monterrey variety, it corresponds to 53.80 g and for the Albión variety, to 48.15 g. For quality 2, fresh weight values correspond to 27.43 g and 23.77 g in Monterrey and Albión varieties, respectively.
When appreciating the diameter measurements, the average value of the fruits of Quality 1 is 4.74 cm for the Monterrey variety and 4.70 cm for the Albión variety, while for the fruits of Quality 2 it is 3.83 cm and 3.76 cm, respectively. When evaluating the dimensions of the fruits, a similar trend can be established between fresh weight and size [6,9,28]. As the fruit develops, there is a filling of it, which will cause an increase in weight [44], and in turn an increase in size [73]. This increase is largely determined by the period of development of the fruit before harvest.
Medina Bolívar, et al. [74] report that, in the case of the Albión variety, an average weight of 32 g is registered, and López Valencia, et al. [28] establish The range of variation between the maximum and minimum average values of T is 40.65% in the high tunnel and 46.76% in the open field. Give that there is less fluctuation of the T in the protected environmental, it is possible to coincide with Pérez de Camacaro, et al. [62], who reported that a more uniform behavior of the T and high values of RH, can increase the fresh weight and the size of the strawberry, since there is decrease in the respiration rate and therefore a greater accumulation of photoassimilates. Likewise, they expose that there is a greater accumulation of TSS, due to the reduction in the degradation of sugars.
According to the standards of the Cámara de Comercio de Bogotá [49] and Cámara Aranda [51], it can be observed that the conditions of T and HR in the high tunnel are close to the optimum values for the development of the strawberry crop, which makes it a good indicator for this production system.
Regarding radiation, it was determined that there are significant differences between the values of DLI (mol/m 2 d) recorded inside and outside the high tunnel, as shown in Figure 2. It can be established that the lowest values are present in the high tunnel due to the use of plastic film. The optical characteristics of plastics can alter the transmitted light spectral composition [11,63], unlike external conditions, where the incidence of radiation is direct.
In the open field, the DLI values oscillate between 13.57 mol/m 2 d and 45.05 mol/m 2 d, while in the high tunnel they are between 9.99 mol/m 2 d and 33.06 mol/m 2 d. This indicates an attenuation of 27% of the incident radiation thanks to the implementation of the plastic cover. The results may vary according to the geographical area where the production system is established. In the case of the Savanna of Bogotá, it is characterized by a high cloudiness [64], which causes a phenomenon of light scattering [65] and, therefore, the decrease in the PAR values registered inside the high tunnel. Likewise, the characteristics of roofing materials affect the registered PAR values, since the plastic film used has UV inhibitors, which indicates a restriction in the passage of solar radiation [66] towards the interior of the high tunnel.
The DLI values are higher outside than inside high tunnel and plants have a better development as the radiation values increase [67][68][69]. Consequently, it The results obtained for both varieties are similar to those obtained by López Valencia, et al. [28], who recorded that the MI for the Monterrey that the fresh weight for the Monterrey variety can reach 25 g and 20 g for the Albión variety in an open field production system. When comparing these reports with the results obtained in the high tunnel, the fresh weight of the fruits of the Quality 1 is greater in 53.53% for the Monterrey variety and up to 58.46% for the Albión variety.
This shows that fruits of higher fresh weight are obtained in the high tunnel, since there is a favorable effect of radiation. There is an incidence of the quality and quantity of light in the enzymatic activity [75], due to its relationship with the photosynthetic capacity of the plants and the production of photoassimilates for fruit filling [6].
The fruits evaluated meet the requirements of national and international regulations. In the case of the Colombian Technical Standard NTC 4103 (Chandler variety), the average fresh weight of the fruits belonging to the Extra Category corresponds to 21.8 g, which is exceeded in 59% by the Monterrey variety and in 50% by the Albión variety, in the fruits of Quality 1. Nonetheless, the fresh weight of the fruits classified in Quality 2 also meet the specifications of the Colombian standard.
In the international context, the quality of  According to Angulo Carmona [80] and Chicaiza Flores [81], this difference is due to a greater accumulation of pigments [82,83]. Although, the Monterrey variety has a less intense red, it shows the characteristic color of the fruit.
On the other hand, when analyzing the data obtained from the CIELab color space, the fruits of the Monterrey variety show higher luminosity values compared to the Albion variety. However, its epidermis shows greater variation between the yellow and blue colors of the spectrum, which has an inversely proportional relationship to the CI value and coincides with the CI value presented in Figure 5.
Although, the Albión variety has its own characteristics, it presents a more intense red color than the Monterrey variety, when contrasting the results obtained with the records of López Valencia, et al. [28], which register an IC close to 50 and 60 for the Monterrey and Albión varieties, respectively. The decrease of CI in the evaluated fruits is evident, and Albión varieties oscillates between 8 and 10, where the fruits of the Monterrey variety have the highest value of IM. If the maturity is high, the fruit has a more pleasant taste [41] for the consumer.
These varieties, are characterized by a high accumulation of TSS [28]. The analyzed fruits of the Monterrey variety register an average 7.7 °Brix, while the Albión variety reports 7.6 °Brix. The results obtained from the TSS content of the Albión variety agree with registered by Ferrucho González & Ruíz González [18], who report that same value. López Valencia, et al. [28] report TSS content between 6.5 and 7 °Brix for the Monterrey variety and between 6 and 6.5 °Brix for the fruits of the Albión obtained in an open field production system. When comparing these values with the results obtained in the high tunnel, the TSS content of the Monterrey fruits is higher up to 15.58% and for the Albión variety to 21.05%.
These results are relevant, since the TSS content may vary among fruits, according to the variety. The Cámara de Comercio de Bogotá [49] reports that the TSS can range between 6.7 and 7.28 °Brix, and ICONTEC [56] reports between 7.9 and 8.5 °Brix (Chandler variety). In the international scenario, the previous Ministry of Agriculture, Livestock and Fisheries [78] of Argentina establishes a minimum quality protocol of 7.0 °Brix, whose value is surpassed by the fruits obtained in the high tunnel in 10% for the Monterrey variety and in 8.57% for the Albión variety.
These differences can be presented due to the characteristics of each crop. Since they have a different yield, when producing a greater amount of fruit, the plant incurs an increase in the distribution of photoassimilates, which reduces the TSS content [18,79].
On the other hand, the radiation to which the plants are exposed is a determining factor. When modifying the chemical composition of the fruits through the intervention in the photoreceptor pigments, the formation and accumulation of sugars of all kinds can occur [68,20].
Color index (IC): Statistically significant differences were found (P < 0.05) between varieties, because the genotypes differ in their biochemical response capacity according to the cultivation conditions [24,25,35,36,79]. range that defines the colors from intense red to deep red. Figure 6, shows the color diagram for the Monterrey and Albión variety. The points indicate the distribution of color around the fruit: the greater the dispersion, the lower the color homogeneity in the strawberry. It can be determined that the red color is distributed more evenly in the fruits of the Albión variety, which diminishes the presence of tones that can range from pale yellow to green. In the case of the fruits of the Monterrey variety, the distribution of the red color is less homogeneous.

Conclusions
Positive results were obtained from the physical and chemical variables evaluated in fruits of the Monterrey and Albion varieties produced in a high tunnel. The highest fresh weight corresponds to the fruits classified in Quality 1 of both varieties. In comparison with the fresh weight specified in the NTC 4103 for the Extra Category, the Monterrey variety was higher by 59% and the Albion variety by, 55%. However, the weights recorded for the fruits of Quality 2 can be considered acceptable, if they are compared with the requirements of the NTC 4103.
The Monterrey variety had a higher TSS content than the Albión variety and a higher MI than the one stablished by the NTC 4103. However, both varieties show IM values similar to those stated in the standard, which is related to a pleasant taste and, therefore, to a good reception by the consumer. Regarding color, the Albion variety showed favorable results, with a more homogeneous fruit color, which makes it a more desirable variety and visually more attractive in the market. However, the fruits of the Monterrey variety show a tolerable distribution of color for commercialization. The coloring features are also favorable, as they given that it is affected by the radiation and the temperature to which the plants are exposed.
The exposure of plants to high values of solar radiation with a preponderance of short wavelengths in the light spectrum causes a greater synthesis of anthocyanins during maturation, harvest and postharvest, since is affects the expression of genes along the flavonoid pathway and the transcriptionists involved [24,36]. Likewise, temperature is a factor that effects the stability of anthocyanin, since its increase induces the loss of glycosylating sugar in the molecule and the production of colorless chalcones [42].
Identifying the incidence of these variables in the CI allows to establish that the decrease in the radiation values and the increase of the temperature in the high tunnel cause the reduction of the IC obtained in the fruits of both strawberry varieties. However, the CI obtained is within the  These indicators show that the national product does not only meets the standards of the Colombian Technical Standard, but it is also apt to compete in the international market.
The postharvest quality of the strawberry in the high tunnel for both varieties was beneficial, since fruits of greater weight and size were obtained. In addition, a high maturity ratio, high color indices and more uniform distributions were obtained, which are striking attributes for the consumer and the industry. Currently, the market demands products with high nutritional value and attractive organoleptic characteristics. Likewise, when handling varieties with different maturity and weight ratio, different consumption trends can be attended in national and international markets.
For all the aforementioned reasons, the use of high tunnels and the properties offered by plastic covers favor production in a protected environment, which increases the competitiveness of the producer, by offering good quality products. It also opens the possibility of inclusion of other technologies for greater control of the microclimate and favoring of the needs of the crop and the improvement of its quality.