Effect of pre-harvest calcium silicate on post-harvest quality of tomatoes

The present work evaluated the influence of calcium silicate on the polygalacturonase enzyme activity, respiration, ethylene, and the physicochemical characteristics on the post-harvest quality of two tomato hybrids. The experimental design was of randomized blocks, with four repetitions in protected cultivation environment. The treatments were distributed in a 2 x 5 factorial scheme, corresponding to the hybrids (Ivety and Natalia) and five doses of calcium silicate (0, 150, 300, 450 and 600 kg ha), which were applied on the same day as the pots were filled. Evaluations were carried out on the fruits, namely: ethylene production, fruit respiration, firmness, number of loculus, polygalacturonase activity, total carotenoids, lycopene, phenolic compounds, soluble solids content, pH, titratable acidity and ascorbic acid content. The application of calcium silicate provided the reduction of ethylene production and fruit respiration. Natalia hybrid showed low polygalacturonase activity, this difference being due to genetic variabilityThe increase of calcium silicate doses provided the reduction of polygalacturonase enzyme concentration due to its constitution in the cell wall. The concentrations of lycopene, phenolic compounds, soluble solids, pH, titratable acidity and ascorbic acid in the fruits increased in response to the increasing doses of calcium silicate for 'Ivety'. Hybrids present distinct behaviors on the influence of the fertilization of tomatoes with calcium silicate, which can increase the post-harvest conservation and improve the physicalchemical characteristics of tomato fruits.

The plants were vertically conducted in a single stem, using plastic ribbons up to approximately 1,90 m from the pot. During the whole cycle thinning was performed in order to keep one single stem per plant and all of them were kept with six bunches, allowing the removal of the apical bud after the third leaf above the sixth bunch.
Irrigation was done by drip irrigation four times a day according to the crop needs, being applied around 1 to 2,5 L of water per day in order to keep the substrate humidity above 80%. For this irrigation flexible tape (1,6 L h -1 ) and emitters spaced 0,50 m were used.
The volume of the solution prepared for fertigation was 20 L per application, in which 45 applications were weekly carried out and, of these, 27 applications were in the phase of full bloom and start of fruiting, applied in this initial phase a percentage between 50-60% of the total amount of macro and micronutrients fertilizers. In full fruitfulness the first and second bunch was already being harvested, in which were applied the rest of the fertilization Development, v. 9, n. 11, e74791110148, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i11.10148 7 corresponding to a percentage between 40-50% of the macro and micronutrients, being performed the fertirrigation until one week before the last harvest.
The fruits were harvested when they had 90% of red colored surface, allowing to select fruits of homogeneous size and healthy for the post-harvest quality analysis. These were performed at the Food Technology Laboratory of the Unioeste Agricultural Sciences Center, Campus Marechal Cândido Rondon. The fruits were harvested and sent to the laboratory for the analysis of respiration, ethylene production and firmness, for the other analysis the fruits were frozen.

Respiration and ethylene production
For respiration and ethylene production third and fourth bunch tomatoes (evaluated by parcel) were used, free of pathogens or any apparent defect. Three harvested fruits were allocated in hermetic plastic flasks with volume of 800 mL and silicone septum in the lid for gas sampling. After 90 minutes of bottle closure, 2,5 mL samples were collected with a gastight syringe from the inner atmosphere of the bottles and immediately injected into a gas chromatograph (Finnigan, 9001) calibrated for column (capillary) temperatures of 80 °C, injector (splitless) 100 °C, detector (flame ionization) 250 °C and methanator 350 °C.

Polygalacturonase activity
The determination of the polygalacturonase activity was performed in fruits of the third bunch, using the methodology described by Pressey and Avants (1973) homogenizing 5 g of vegetal material with 10,4 mL of distilled water. The macerate was centrifuged at 12.000 rpm for 20 minutes at 4 °C. The supernatant was discarded, and the precipitate was solubilized with distilled water and again centrifuged, the same process being repeated twice.
The supernatant was again discarded, and the precipitate was solubilized in 10,4 ml of NaCl (1 mol L -1 ), adjusting the pH with NaOH (1 mol L -1 ) to 6,0, remaining in the refrigerator for 1 hour. The extract was centrifuged, and the supernatant kept in ice. The enzyme activity was determined by incubating the extract with polygalacturonic acid solution in 100 mmol L -1 NaOAc buffer at pH 5,0 for 30 minutes at 50 °C. The reaction was stopped by the addition of PAHBAH reagent and boiling of the assay tubes for 5 minutes and then routed to ice. The Research, Society and Development, v. 9, n. 11, e74791110148, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i11.10148 8 galacturonic acid production in the reaction was determined by the Lever method (1972). The total protein of the extracts was determined by the Bradford method (1976) using BSA as standard.

Physical-chemical
Firmness was measured in opposite poles in the equatorial region of the fruit in a total of three ripe fruits of the third and fourth bunch evaluated per plot, using the texturometer (CT3 Texture Analyser, Brookfield Engineering) with a tip of 8 mm in diameter and penetration speed of 2,0 mm s -1 , which expressed the results in N. After this evaluation, the fruits were cut to count the number of loculus.
For the chemical analyses fruits were collected from all bunches, being sent to the laboratory and frozen, later they were homogenized and the analysis of soluble solids content (SS) and pH were determined by direct reading of the juice extract with the aid of a refractometer and digital pH meter, respectively. The SS content was expressed in ºBrix, the titratable acidity (TA) was determined by the titulometric method according to the methodology proposed by IAL (2008). The ascorbic acid content was determined by titration with 2,6-dichlorophenol-indophenol (DCFI) at 0.01 mol L -1 , with results expressed in mg ascorbic acid per 100 mL -1 pulp (Benassi and Antunes, 1988).
The evaluation of the pigment contents was performed with fruits from the third bunch of the plant, where the carotenoids content was performed according to the methodology the cultivation of cherry tomatoes and found reduction of ethylene production in the fruits.
Still regarding the fruits respiration (Figure 2 -B), the quadratic adjustment equation suggests a minimum respiratory rate estimate of 4,87 mg CO2 kg -1 h -1 (Figure 2 -B) for a dose of 552,24 kg ha -1 of calcium silicate.  'Ivety' showed a higher respiration rate of 6,82 mg CO2 kg -1 h -1 (Table 1). This difference between hybrids can be explained by the fact that they present a completely different genetic characteristic, where the hybrid Natalia presents the rin gene, which is an improved hybrid and present in its natural process the delayed maturation, which prolongs the post-harvest conservation (Benites et al., 2010).

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The difference in ethylene production and respiration is a characteristic that is also linked to the cell wall and consequently to the firmness of the fruits, and it did not show any difference in the interaction or factors studied alone (Table 1). This absence of significant effect may have been caused by the difference in the number of loculus or even by the ripening stage of the fruit, and the number of loculus may be modified due to the fruit size (Rodrigues et al., 2010).
Changes in the firmness of the fruit that lead to its softening during ripening involve the loss of turgidity pressure. This process occurs due to the accumulation of osmotic solutes in the apoplast because there are modifications in the simple and apoplast relationship, starch degradation and physiological changes in the composition, structure and dynamics of the cell wall (Bertin and Génard, 2018). Although firmness has not shown significant difference in the present study, it is characterized by delayed degradation in the cell wall. This absence of difference between hybrids for fruit firmness demonstrates that there was a change in the number of loculus to 'Ivety', which had more loculus ( Table 1). The number of loculus is a genetic characteristic that presents a direct correlation with the size of the fruits (Rodrigues et al., 2010).
Although there was no difference for firmness, the 'Ivety' showed the highest softness of tomato fruits, and this increase is linked to PA activity which was 21,40 µg glycose h -1 mg -1 protein (Table 1). This difference between the hybrids is related to the genetic variability between them, because the hybrid that presents the rin gene provides aspects in the alteration of ripeness, in which the fruits are firmer with less response to ethylene, which results in the structural difference of the cell wall (Benites et al., 2010).
The PA activity also showed a difference between the calcium silicate doses, providing a decrease of the PA activity with the increase of the doses (Figure 3). Calcium silicate, as a constituent of the cell wall, plays an important role in the formation of cross bridges between the pectic substances, leading to the stabilization of the fruit cell wall and the protection against the cell wall degradation enzymes, specifically pectolytic enzymes, such as PA, which breaks the glycosidic bonds between units of non-esterified galacturonic acids (Resende et al., 2004). In this way, calcium silicate interacts with these carboxylic groups without esterification, reducing their number and thus the action of PA decreases.
The reduction in the respiration and the production of ethylene according to the calcium silicate doses played an important role in the low activity of PA, providing firmer fruits. The use of silicon in fruit production increases its firmness, although it did not present a difference in the study, this increase was demonstrated in the work of Marodin et al. (2016), who worked with different sources of silicon in tomato. Islam et al. (2018) compared different ways of applying silicon to cherry tomatoes and obtained increased firmness at harvest time.
The firmness and ripeness of the fruits are closely associated, therefore, the prolongation of the firmness of the fruits is desirable to have an extension of storage. For the characteristics of fruit pigments there was no interaction between the factors studied, so the levels of total carotenoids and lycopene were evaluated separately (Table 2). The ripening of the tomato fruit is controlled by ethylene and characterized by a change of color from green to red. However, regarding photosynthetic pigments studied as total carotenoids, there was a significant difference only between hybrids (Table 2), since this Research, Society and Development, v. 9, n. 11, e74791110148, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i11.10148 13 content varies according to species and hybrid, as well as environmental factors and cultural practices before and after harvest.
Carotenoids are accessory pigments responsible for color change, pondering to come from chlorophyll degradation, causing an increase in carotenoids (β-carotenes and lycopene) and anthocyanins (xanthophylls), resulting in red and yellow colored fruits and flowers, besides being the second most important pigment in the photosynthesis process (Su et al., 2015).
Ivety' had higher lycopene content (Table 2). Among the process of decreasing the chlorophyll and xanthophyll content in tomatoes, there is a strong accumulation of lycopene, which is the main carotenoid in tomatoes, representing 71% of the total content in ripe fruits, giving the fruits a reddish color (Del Giudice et al., 2015). The lycopene content also showed a difference between doses of calcium silicate, showing the quadratic behavior during the increase in doses (Figure 4 -A).