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Fertilization strategies as a tool to modify the organoleptic properties of raspberry (Rubus idaeus L.) fruits
Scientia Horticulturae 240 (2018) 205–212
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Fertilization strategies as a tool to modify the organoleptic properties of raspberry (Rubus idaeus L.) fruits
T
Fabio Valentinuzzia, Youry Piia, Tanja Mimmoa, Gianluca Savinib, Stefano Curzelb, ⁎ Stefano Cescoa, a b
Faculty of Science and Technology, Free University of Bozen-Bolzano, Piazza Università 5, 39100, Bolzano, Italy Società Cooperativa Sant’Orsola, Via Lagorai, 131, 38057, Pergine Valsugana (TN), Italy
A R T I C LE I N FO
A B S T R A C T
Keywords: Raspberry Fertilization Firmness Sweetness index Bioactive compounds
Raspberry cultivation is increasing all over the world, being these fruits highly appreciated not only for their taste but also for their high content in bioactive compounds. However, the short shelf-life of these fruits limits their fresh consumption and industrial use to a defined time frame. For this reason, setting agronomic strategies aimed at extending the fruit shelf-life represent a prerequisite to ensure the presence of high-quality raspberries on the market for a prolonged time. Therefore, aim of this work was to assess the influence of different nutritional regimes (over-fertilization with NH4+, Si or B) on the firmness and the potential extension of the shelf-life as well as on the quality of raspberry fruits. Raspberry canes (Rubus idaeus) cv. ‘Lagorai Plus’ were grown in a high tunnel plastic greenhouse and starting from middle July to September raspberry fruits were collected. The over-fertilization with NH4+, Si or B lead to higher yields, increased colour indexes, firmness, sucrose content and sweetness indexes. Furthermore, the fertilizations led to an improved shelf-life due to a significant reduction of fruit darkening and fruit weight loss, which was particularly evident at the end of the incubation. The results of this work highlighted that the modification of the nutritional status of raspberries by adding either Si, B or NH4+ could be helpful in obtaining fruits with improved qualitative parameters. In particular, an increase in the sweetness index and firmness of fruits as well as an extension of the shelf-life could be beneficial for the attractiveness of consumer and also for the possibility of using fruits in the industrial transformations. Moreover, considering the role of Si and B in human health, the bio-fortification programs can become particularly interesting, thus opening the way for new market perspectives of these fruits in addition to the traditional ones.
1. Introduction
chronic disease and some forms of cancer (Beattie et al., 2005; Ross et al., 2007; Seeram, 2008). Moreover, beside their positive effect on human health, phenolic compounds can also considerably affect the shelf-life and postharvest quality of the berries (Hodges and DeLong, 2007; Khanizadeh et al., 2009). In fact, the seasonality of the raspberry cultivation and the fast senescence characterizing these fruits after the harvest (i.e. short shelflife) limits their fresh consumption and industrial use to a defined time frame (Han et al., 2004). Postharvest life of red raspberries represents a main issue for this fruit crop since it is only limited to a few days (generally 2–3 days from picking) (Giovanelli et al., 2014). This is mainly due to the loss of firmness and their susceptibility to fruit rot (Khanizadeh et al., 2009), caused by their structural fragility and their high respiration rate (Haffner et al., 2002). As a consequence, fresh fruits are only available in the ripening seasons and are mostly
Raspberries (Rubus idaeus L.) are cultivated in many countries worldwide, but particularly in Eastern Europe and in the USA (Giovanelli et al., 2014) having a significant economic relevance for farms (Hristov et al., 2009). As well as other berries, the global production of these fruits is increasing, being highly appreciated by consumers not only for their good taste but also for their high content in health beneficial compounds (Rao and Snyder, 2010). Indeed, many studies have shown that raspberries are a major source of antioxidants because of their high concentration in polyphenolic compounds such as anthocyanins, flavonols, catechins, ascorbic acid and ellagic acid derivatives (Beekwilder et al., 2005; Deighton et al., 2000; Moyer et al., 2002; Sariburun et al., 2010). In particular, these compounds can scavenge free radicals (Zhang et al., 2012) helping the prevention of ⁎
Corresponding author. E-mail address: [email protected] (S. Cesco).
https://doi.org/10.1016/j.scienta.2018.06.024 Received 21 March 2018; Received in revised form 17 May 2018; Accepted 9 June 2018 0304-4238/ © 2018 Elsevier B.V. All rights reserved.
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Control plants (Control) were fertigated with the following nutrient solution (NS): NO3− 6 mM, H2PO4− 1 mM, SO42- 1.5 mM, NH4+ 0.6 mM, K+ 3 mM, Ca2+ 4 mM, Mg2+ 4 mM, Fe2+ 30 μM, Mn2+ 20 μM, Zn2+ 8 μM, B 12 μM, Cu 1.75 mM, Mo 0.75 mM. For a second set of plants (+NH4+) NH4+ was added to the NS once a week, while for a third set (+Si) Si (K2SiO4 3 mM) was added to the NS during the whole growing period. The fourth set of plants (+B) was fertigated as + NH4+ and treated foliarly with 1.5 mg H3BO3 plant−1 (Wojcik, 2005) applied 4 times during the growing season (2 weeks before flowering, at flowering, 3 and 6 weeks after flowering). The solution was characterized by an average Electric Conductivity (EC) of 2000 μS cm-1 and a pH = 5.5. Harvest season started on end of July and ended in September.
consumed locally. For this reason, setting agronomic strategies aimed at extending the fruit shelf-life (increasing its conservation and storability without impacts on the nutritional value) can have an interest not only in terms of more prolonged presence in the market of high-quality raspberries, but also from the economy point of view of a specific production area. It is widely demonstrated that mineral nutrition has a thorough impact on both fruit yield and quality (Álvarez-Fernández et al., 2003; Pestana et al., 2010; Tomasi et al., 2014; Valentinuzzi et al., 2015) as well as shelf-life (Dalla Costa et al., 2011). In this respect it is interesting to mention that very recently a relationship between anthocyanins in strawberries and nitrogen (N) fertilization has been reviewed by Jezek et al., (2018). An additional example can be represented by boron (B) that, when applied in field cultivation both on soil and on leaves, not only increased tomato weight by improving fruit set, but also improved fruit firmness and shelf-life (Davis et al., 2003). Moreover, Wojcik, (2005) showed an increased berry strength in raspberries cv. Polana fertilized with B. This phenomenon was related by the authors to a possible increase in the number of berry drupelets; in fact, Robbins and Moore, (1990) observed that raspberries with a higher number of drupelets were firmer than those of a similar size with fewer large drupelets. In addition to N and B, it is also interesting the case of silicon (Si). Although its beneficial effects have been extensively proven, Si is usually omitted from the composition of nutrient solutions (Gottardi et al., 2012). Indeed, its supplementation increases significantly plant fitness with a resulting enhancement of agricultural production (Montesano et al., 2016; Savvas and Ntatsi, 2015). Furthermore, Stamatakis et al., (2003) observed an increase in total solid solutes, vitamin C and fruit firmness in tomatoes by adding K2SiO3 to the hydroponic system. Moreover, Si has shown to prolong the shelf-life of strawberry fruits (usually few days) harvested from plants supplemented with bio-available Si (Babini et al., 2012). However it should be noted that fruit yield and its quality are not exclusively related to the presence or absence of a specific nutrient/element, but also to the nutrient form supplied with the fertilizers. In this context, N represents a particular example. In fact, it is well demonstrated that a nitrate-based fertilization affects rhizosphere pH values in a totally opposite way than an ammonium-based one (Hinsinger et al., 2003). In this latter case, the ammonium-induced acidification of the soil surrounding the roots affects consistently the availability of some other nutrients (e.g Fe, Thomson et al., 1993), influencing therefore the whole nutrient acquisition process of roots. These phenomena, pretty well described for some crops such as strawberry, are still quite unknown in raspberry, particularly when fruit quality parameters are considered. Therefore, in the present work the effect of N (ammonium), B or Si availability on the firmness and an extension of the shelf-life of raspberry fruits, has been assessed. To this purpose, growth medium (ammonium) or foliar (B or Si) fertilizations were applied to the plants. At harvest, quality parameters (colour, sweetness index, sugar, organic acid contents) and the bioactive compound (phenolic compounds) concentration of raspberry fruits were assessed and related to the overall fruit quality as a function of the different nutritional treatments.
2.2. Measurement of plant growth and fruit productivity During the growing period, SPAD index of fully expanded leaves was determined using a portable chlorophyll meter SPAD-502 (Minolta, Osaka, Japan). Measurements were carried every two weeks on both basal and apical leaves (at least two per plant), and five SPAD measurements were taken per leaf and averaged. At the end of the harvest season, raspberry plants were collected separating lateral braches from the cane and fresh weight (FW) of both biomasses was measured. At harvest, total fruit yield, yield per plant (kg FW plant−1), average fruit yield (g FW) and number of discarded fruits were assessed. 2.3. Characterizazion of fruit quality Raspberry fruits were harvested once at least 80% of the fruit surface showed a red coloration. The color index (CI) to express the intensity of red color was determined using a portable tristimulus colorimeter (Chroma Meter CR-400, Konica Minolta Corp., Osaka, Japan) and calculated as CI = 100 x a/(L x b) with higher values expressing a more intense red color (Tezotto-Uliana et al., 2014). Total soluble solid contents, expressed in Brix degrees (°Bx), were determined using a digital refractometer (Atago, Tokyo, Japan) on fresh extracted fruit juice. Titratable acidity (TA) was determined as previously described (Valentinuzzi et al., 2015). Raspberry firmness was assessed on fresh fruits with a penetrometer (model PCE-FM200; PCE Instruments, Southampton, UK) equipped with a cylindrical probe 3 mm in diameter and expressed in Newton (N). 2.4. Raspberry extracts Freeze-dried raspberry samples were ball-milled (model MM400; Retsch, Haan, Germany) to obtain a homogeneous powder; the ground samples were extracted with methanol (HPLC grade, Merck, Darmstadt, Germany) using a 1:10 extraction ratio. The mixtures were then sonicated for 30 min in a thermostatic bath and centrifuged at 14000xg for 30 min at 0 °C; finally, the supernatant was collected and filtered through a 0.2 μm nylon filter (Phenomenex Inc., USA). 2.5. Organic acid and sugars analyses
2. Materials and methods The separation of both organic acids and sugars was performed by HPLC using a cation exchange column Aminex 87-H column (300 × 7.8 mm, 9 mm, Bio-Rad) using an isocratic elution with 10 mM H2SO4 as mobile phase at a flow rate of 0.6 mL min−1. Organic acids were detected at 210 nm with a Waters 2998 photodiode array detector (Waters Spa, Italy), whilst sugars were detected by a refractive index detector (Waters Spa, Italy). Standard acids and sugars were prepared as individual stock solutions and then combined to give diluted reference standards. Organic anions and sugars were identified by comparing retention times of unknowns to pure compounds. Standards were purchased from Sigma–Aldrich (St. Louis, MO, United States). Sweetness index (SI) was calculated as in Mahmood et al., (2012).
2.1. Plant growth After a storage period between −1 °C and 1.5 °C raspberry floricanes (Rubus idaeus) cv. ‘Lagorai Plus’ were transplanted at the end of May to 6.5-L pots containing coconut fiber and transferred into a high tunnel plastic greenhouse for the growing and fruiting period. 200 cane plants per treatment were utilized. The experiment was laid out in a randomized block design, with five replicates per treatment. Each block consisted of 40 cane plants and thirty centrally located plants per block were used to collect vegetative and qualitative parameters. 206
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2.6. Phenolic compounds analyses The content of total phenols of raspberry fruit extracts was determined following the Folin-Ciocalteau method (Atanassova et al., 2011; Folin and Ciocalteu, 1927), while the concentration of flavonoids and flavonols was determined by a pharmacopeia method, using rutin hydrate as reference compound (Miliauskas et al., 2004). 2.7. Elemental analysis Freeze-dried raspberry fruits were homogenized and approximately 0.3 g of each sample were acid digested with concentrated ultrapure HNO3 (650 ml L−1; Carlo Erba, Milano, Italy) using a single reaction chamber microwave digestion system (UltraWAVE, Milestone, Shelton, CT, USA). Concentrations of macro- and micronutrients were then determined by ICP-OES (Arcos Ametek, Spectro, Germany) using tomato leaves (SRM 1573a) and spinach leaves (SRM 1547) as external certified reference material. 2.8. Shelf-life assessment Qualitative analyses were carried out to assess the effect of the different treatments on fruit shelf-life at harvest (time 0) and after 2, 6 and 8 days of storage at 4 °C. Weight loss was calculated by measuring the weight of 40 raspberries per block at harvest and after 2, 5 and 8 days. The results are expressed as weight percentage respect to time 0. Color index was measured as described in paragraph 2.3 at harvest and after 2, 6 and 8 days.
Fig. 1. Yield per plant (kg) (A) and number of fruits per plant (B) of raspberry plants grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
2.9. Statistical analyses The results are presented as means of five replicates ± standard error (SE). Each replicate consisted of a pool of fruits harvested from 10 plants. Statistical analysis was performed using GraphPad Prism version 6.00 for Mac OS X, GraphPad Software, San Diego California USA. Analysis of variance (ANOVA) was carried out, and means were compared using Tukey´s test at P < 0.05.
3.2. Plant productivity In order to understand the effect of the different fertilizations on plant productivity, this was assessed by measuring the average yield per plant and the number of fruits per plant (Fig. 1). The average yield per plant was slightly increased by all the treatments with the highest fruit productivity obtained in + Si fertilized plants (+5%). The number of fruits per plant was also significantly increased by the fertilizations in + NH4+ and + Si plants.
3. Results 3.1. Plant growing parameters Table 1 shows the growing parameters used to assess the effect of the different nutrients on raspberry plants. Both cane biomass and lateral branch biomass were not significantly affected by the treatments as well as the number of lateral branches. In order to evaluate the influence of the applied treatments on the chlorophyll content of raspberry leaves, SPAD index values were measured on basal and apical leaves. As observed for the other parameters, SPAD units did not differ among treatments in both apical and basal leaves.
3.3. Fruit nutrient concentration The concentration of macro- and micronutrients (Table 2) in raspberry fruits was determined with the aim of assessing the influence of the different treatments on the fruit ionome. Regarding macronutrients,
Table 1 Primocane biomass, lateral branches biomass, number of laterals and SPAD index of both basal and apical leaves of raspberry plants grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05). +NH4+
Control
Cane biomass (g) Lateral branches biomass (g) N° lateral branches SPAD basal leaves SPAD apical leaves
+Si
+B
Mean
SE
Mean
SE
Mean
SE
Mean
SE
33.69 218.03 18.38 51.61 44.91
1.70 6.78 0.53 0.36 0.57
36.46 196.25 17.25 51.58 43.75
2.40 7.14 1.32 0.35 0.54
37.31 206.84 20.12 51.99 43.48
2.62 10.28 0.85 0.35 0.50
35.86 191.67 18.00 51.02 44.13
1.67 18.53 1.81 0.37 0.52
207
ns ns ns ns ns
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Table 2 Macro- and micronutrients concentration in raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. DW = dry weight. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05). +NH4+
Control
−1
DW) P (mg g K (mg g−1 DW) −1 Ca (mg g DW) Mg (mg g−1 DW) S (mg g−1 DW) Si (mg g−1 DW) Fe (μg g−1 DW) Mn (μg g−1 DW) Zn (μg g−1 DW) B (μg g−1 DW)
+Si
+B
Mean
SE
Mean
SE
Mean
SE
Mean
SE
1.06 6.11 1.19 1.05 0.59 0.13 31.39 31.76 15.94 56.67
0.01 0.07 0.03 0.03 0.02 0.01a 1.59 1.21b 0.61 1.25a
1.07 6.19 1.14 1.06 0.59 0.13 32.32 26.93 15.76 57.54
0.02 0.07 0.04 0.02 0.01 0.01a 1.58 1.99b 0.55 2.24a
1.07 6.08 1.09 1.02 0.61 0.17 30.92 24.75 14.78 58.18
0.01 0.07 0.04 0.01 0.01 0.01b 1.70 1.01a 0.73 2.55a
1.05 6.04 1.12 1.02 0.57 0.13 31.13 32.28 16.06 66.36
0.02 0.11 0.04 0.02 0.01 0.01a 1.04 0.78b 0.45 0.69b
ns ns ns ns ns ns ns
no significant difference could be observed among the treatments. Silicon (Si) concentration significantly increased only in + Si raspberry fruits, accordingly with the applied treatment. Considering micronutrients, Mn concentration slightly decreased in fruits harvested from plants supplied with K2SiO3, while no significant differences could be detected among the other treatments. Raspberry Fe and Zn concentration was not altered by the different treatments applied, while B concentration increased only in + B, as a consequence of foliar B application. 3.4. Fruit quality parameters Fruit quality parameters (Fig. 2) such as color index, brix degrees and firmness were determined in raspberry fruits treated with the different fertilizers. Regarding color index, this increased in all fertilized treatments as compared to control frutis. Total soluble solids concentration (expressed as °Brix) determined in raspberry juice of fruits collected from plants supplied with the four nutrients did not highlight any significant difference. On the other hand, fruit firmness was positively influenced by all the three nutrients tested with a significant increase (at least 15%) in + NH4+, +Si and + B. 3.5. Sugar concentration Fig. 3 shows the concentration of sugars in raspberry fruits harvested from plants supplemented with the different nutrients. Sucrose concentration varied significantly between control fruits and those harvested from treated plants, with the latter containing a higher concentration of sucrose. While glucose concentration was unaffected by the treatments, fructose was enhanced only in + Si fruits, while in the other fruits the concentration of this sugar was similar to that of control fruits. The altered concentration of sugars in raspberries collected from plants supplemented with the different nutrients consequently affected the sweetness of the fruits (Fig. 3D). In fact, +Si and + B raspberries had a significantly higher sweetness index compared to controls, with + NH4+ fruits having intermediate values. 3.6. Titratable acidity, organic acids and bioactive compounds Titratable acidity measured on fruit fresh juice was not significantly affected by the different treatments (Fig. 4A). Among the organic acids, citric and malic acid were the only ones detected in raspberry fruits (Fig. 4B–C). The concentration of citric acid was not significantly influenced by the treatments, even if slight differences could be observed. As well as citric acid, also the concentration of malic acid did not change among the different treatments. Regarding bioactive compounds, Fig. 5 shows the concentration of total phenols, flavonoids and flavonols in the raspberry extracts: no significant variations were
Fig. 2. Color index (A), total soluble solids (B) and firmness (C) of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
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Fig. 3. Sucrose (A), glucose (B), fructose (C) and sweetness index (D) of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
This result indicates that the N treatments have mainly as target the nutritional regimen of the whole plant, therefore affecting, in a cascade system, the yield only in the following years after the applications. In this context, it has also to be highlighted that the composition of the nutrient solution here used to supply control raspberry plants was already optimized to maximize raspberry yield and, for this reason, it has been in use for several years at the field scale. As consequence, a marked increase in fruit yield in the production cycle of treatments was not expected. Fruit colour, brix degrees and fruit firmness are important commercial parameters in determining raspberry quality (Fig. 2). Colour index, calculated to express the intensity of raspberries´ red colour was significantly increased in fruits collected from plants over-fertilized with NH4+, Si and B. Regarding Si, this result is consistent with that obtained by Figueiredo et al., (2010) who noticed an increase in the red colour of Si-treated strawberries. Similarly, also the N fertigation of strawberry plants increased the intensity of the red colour of fruit skins (Rodas et al., 2013). Besides the color index, also firmness increased in fruits supplemented with the three different nutrients (Fig. 2C). Fruit firmness is an important textural property and is of paramount importance for raspberries, since it affects the storability and the resistance to damage through handling. Former studies showed that both foliar and soil B applications increased the firmness of raspberry fruits (Wojcik, 2005) ascribing this effect to an increase in the number of drupelets. The increase of fruit firmness due to Si application was reported by Dehghani Poodeh et al., (2016), in strawberry plants and could be due to a strong bond of Si to the cellulose framework (Lewin and Reimann, 1969), thus leading to a strengthening of fruit skin. Although no significant effect on total soluble solids content (expressed as Brix degrees) was observed (Fig. 2B), a more detailed
detected among the different treatments. 3.7. Shelf-life A shelf-life assessment of raspberries harvested from plants grown in the four different conditions was carried out by evaluating the weight loss and the color index in a period of eight days (Fig. 6). Concerning weight loss, during the incubation time, raspberries supplied with the different nutrients showed a lower loss of weight following this order + B > +Si > +NH4+ > Control. Color index, evaluated to express the intensity of the red color of raspberries, showed significant differences among the treatments and during the incubation. In particular, starting from day 5, control fruits showed a darker coloration compared to raspberries harvested from nutrient supplemented plants. 4. Discussion The different treatments applied to raspberry plants did not lead to any significant increase in terms of plant biomass, branches number and SPAD units (Table 1), as also described by Kowalenko (2006) upon application of N or Si. Fruit yield on the other hand was slightly but significantly increased in all the treatments as compared to the control (Fig. 1), particularly in the Si-treated raspberry plants. Concerning this last aspect, it is interesting to note that the effect of Si in increasing the yield of different grain crops such as rice (Detmann et al., 2012) and wheat (Tahir et al., 2011), horticultural crops such as corn salad (Valerianella locusta L., Gottardi et al., 2012) but also strawberries (Miyake and Takahashi, 1986) has been widely described. In particular for N application, it should be noted that Kowalenko et al., (2000) recorded an effect on raspberry yield only after 3 years of repeated applications. 209
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Fig. 4. Titratable acidity (A), citric acid (B) and malic acid (C) of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
Fig. 5. Total phenols (A), total flavonoids (B) and total flavonols (C) content of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
analysis of sugars concentration in fruits collected from plants supplied with the different nutrients revealed an increase of sucrose concentration in + NH4+, +Si and + B fruits and fructose in + Si fruits (Fig. 3). As a consequence, the sweetness index, which is relevant for the taste perception of raspberries, was particularly increased in + B and + Si treatments as compared to controls. With respect to B, it has been already proved that this nutrient can enhance the sugar content in raspberry fruits (Wojcik, 2005) as well as in strawberries (Wójcik and Lewandowski, 2003). This effect has been ascribed to the increased formation of B-sugar complexes and, then, to their augmented transport in the phloem. Furthermore, Hajiboland et al., (2017) reported that the supplementation of Si to the nutrient solution improved several fruit quality parameters, particularly the sugar concentration. On the other hand, titratable acidity and the concentration of the two main organic acids (Fig. 4) in raspberries were not significantly influenced by the three treatments here considered. Since the ratio between sugars and organic acids (sweetness index) is an important parameter to estimate the flavor and therefore consumer acceptance of raspberries, results here presented indicate that the three treatments allow to improve this
index ensuring, consequently, a greater consumer attractiveness for these fruits. The concentration of phenolic compounds in raspberries was not significantly influenced by the treatments applied (Fig. 5). Considering the importance of these bioactive molecules in conferring nutraceutical value to raspberry fruits, it is remarkable that the supplementation of the different nutrients did not alter the composition in beneficial health compounds of fruits. Besides phenolic compounds, nutrient content of fruits are important parameters determining raspberry quality. Yet, the different nutritional regimes did not alter the composition in macroand micronutrients of raspberry fruits (Table 2), with the only exception of manganese (Mn), Si and B. Although the mechanisms are still poorly understood, the effect of Si in decreasing Mn concentration at shoot level in different plant species (Che et al., 2016) has been observed, while it is not been investigated in fruits. As expected instead, plants supplemented with either Si or B, increased the concentrations of the two elements, respectively. This is particularly important in the case of Si, since this element has beneficial effects not only for plants but 210
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was obtained with B in tomatoes (Davis et al., 2003), which has been demonstrated to have an important role in maintaining membrane stability. In conclusion, results here presented show that, with reference to the hydroponic solution currently used at the field scale for raspberry production, there still is room to improve the yield quality through the modification of the availability of some specific nutrients. The effects of these treatments on sweetness index and firmness of fruits as well as the extension of the shelf-life can be beneficial for the attractiveness of consumer and also for the possibility of using fruits in the industrial transformations. Moreover, considering the role of Si and B in human health, the bio-fortification programs can become particularly interesting, thus opening the way for new market perspectives of these fruits in addition to the traditional ones. Authors contributions Designing and performing the experiments: SCE, GS Critical discussion of the data: FV, YP, TM, GS, SCU, SCE Paper preparation: FV, YP, TM, SCE Research coordination: SCE, GS Acknowledgement This work has been financially supported by: Free University of Bozen-Bolzano (TN2023, TN2345-C). References Álvarez-Fernández, A., Paniagua, P., Abadía, J., Abadía, A., 2003. Effects of Fe deficiency chlorosis on yield and fruit quality in peach (Prunus persica L. Batsch). J. Agric. Food Chem. 51, 5738–5744. Armstrong, T.A., Spears, J.W., 2001. Effect of dietary boron on growth performance, calcium and phosphorus metabolism, and bone mechanical properties in growing barrows. J. Anim. Sci. 79, 3120–3127. Atanassova, M., Georgieva, S., Ivancheva, K., 2011. Total phenolic and total flavonoid contents, antioxidant capacity and biological contaminants in medicinal herbs. J. Univ. Chem. Technol. Metall. 46, 81–88. Babini, E., Marconi, S., Cozzolino, S., Ritota, M., Taglienti, A., Sequi, P., Valentini, M., 2012. Bio-available silicon fertilization effects on strawberry shelf-life. Acta Hortic. 934, 815–818. Beattie, J., Duthie, A.C., Duthie, Garry G., 2005. Potential health benefits of berries. Curr. Nutr. Food Sci. 1, 71–86. Beekwilder, J., Hall, R.D., De Vos, C.H.R., 2005. Identification and dietary relevance of antioxidants from raspberry. BioFactors 23, 197–205. Che, J., Yamaji, N., Shao, J.F., Ma, J.F., Shen, R.F., 2016. Silicon decreases both uptake and root-to-shoot translocation of manganese in rice. J. Exp. Bot. 67, 1535–1544. Dalla Costa, L., Tomasi, N., Gottardi, S., Iacuzzo, F., Cortella, G., Manzocco, L., Pinton, R., Mimmo, T., Cesco, S., 2011. The effect of growth medium temperature on corn salad [Valerianella locusta (L.) Laterr] baby leaf yield and quality. HortScience 46, 1619–1625. Davis, J.M., Sanders, D.C., Nelson, P.V., Lengnick, L., Sperry, W.J., 2003. Boron improves growth, yield, quality, and nutrient content of tomato. J. Am. Soc. Hortic. Sci. 128, 441–446. Dehghani Poodeh, S., Ghobadi, C., Baninasab, B., Gheysari, M., Bidabadi, S.S., 2016. Effects of potassium silicate and nanosilica on quantitative and qualitative characteristics of a commercial strawberry Fragaria × ananassa cv. ‘camarosa’’. J. Plant Nutr. 39, 502–507. Deighton, N., Brennan, R., Finn, C., Davies, H.V., 2000. Antioxidant properties of domesticated and wild Rubus species. J. Sci. Food Agric. 80, 1307–1313. Detmann, K.C., Araújo, W.L., Martins, S.C.V., Sanglard, L.M.V.P., Reis, J.V., Detmann, E., Rodrigues, F.A., Nunes-Nesi, A., Fernie, A.R., Damatta, F.M., 2012. Silicon nutrition increases grain yield, which, in turn, exerts a feed-forward stimulation of photosynthetic rates via enhanced mesophyll conductance and alters primary metabolism in rice. New Phytol. 196, 752–762. El Ghaouth, A., Arul, J., Ponnampalam, R., Boulet, M., 1991. Chitosan coating effect on storability and quality of fresh strawberries. J. Food Sci. 56, 1618–1620. Figueiredo, F.C., Botrel, P.P., Locarno, M., Guedes De Carvalho, J., 2010. Leaf spraying and fertirrigation with silicon on the physicochemical attributes of quality and coloration indices of strawberry. Cienc. e Agrotecnol. 34, 1306–1311. Folin, O., Ciocalteu, V., 1927. On tyrosine and tryptophane determinations in proteins. J. Biol. Chem. 27, 627–650. Giovanelli, G., Limbo, S., Buratti, S., 2014. Effects of new packaging solutions on physicochemical, nutritional and aromatic characteristics of red raspberries (Rubus idaeus L.) in postharvest storage. Postharvest Biol. Technol. 98, 72–81. Gottardi, S., Iacuzzo, F., Tomasi, N., Cortella, G., Manzocco, L., Pinton, R., Römheld, V., Mimmo, T., Scampicchio, M., Dalla Costa, L., et al., 2012. Beneficial effects of silicon
Fig. 6. Weight loss (A) and color index (B) of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B) collected and stored for 8 days at 4°. Data are reported as means and SE of 40 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
also for human health (Jugdaohsingh et al., 2002, 2004). For this purpose, many biofortification studies have been performed with the aim of increasing Si concentration in different plant species such as corn salad (Gottardi et al., 2012), green bean (Montesano et al., 2016) and strawberry (Valentinuzzi et al., 2018). Concerning B enrichment of edible products, no specific symptoms of B deficiency have been observed in animals and humans and no recommended dietary allowance is suggested (Rahal and Shivay, 2016); however it has been reported that ingested B through the diet helps in strengthening bone in some animals (Armstrong and Spears, 2001). Once harvested, one of the main concerns for raspberry fruits is their high perishability, resulting in a fast ripening period and senescence (El Ghaouth et al., 1991; Tezotto-Uliana et al., 2014). Therefore, we aimed at evaluating the effect of different nutrients supplementation on fruit shelf-life by measuring weight loss and colour index (CI) during a storage period of 8 days (at 0 °C and 90% RH). It is well known that during the storage a weight loss (ascribable mainly to dehydration and respiration phenomena) and a browning process of fruits, take place (Nunes and Emond, 2007) altering thus their quality. The results here presented evidenced a significant reduction of darkening in fruits of over-fertilized plants as well as a decrease in fruit weight loss, which was particularly evident at the end of the incubation with the following order: +B > +Si > +NH4+ > Control. Regarding Si, this is consistent with results reported by Zhang et al., (2017) who ascribed the fruit weight loss reduction to the deposition of Si under the cuticle and to the formation of a cuticle-Si double layer; such structural modifications strengthen the cell wall structures (Kim et al., 2002). A similar effect
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and vegetables. Proc. Fla. State Hort. Soc. 120, 235–245. Pestana, M., Gama, F., Saavedra, T., Correia, P.J., Miguel, M.G., Dandlen, S., 2010. Evaluation of Fe deficiency effects on strawberry fruit quality. Acta Hortic. 868, 423–427. Rahal, A., Shivay, Y.S., 2016. Micronutrient deficiencies in humans and animals: strategies for their improvement. Biofortification of Food Crops. pp. 217–228. Rao, A.V., Snyder, D.M., 2010. Raspberries and human health: a review. J. Agric. Food Chem. 58, 3871–3883. Robbins, J., Moore, P.P., 1990. Relationship of fruit morphology and weight to fruit strength in ‘Meeker’ red raspberry. Hortic. Sci. 25, 1988–1990. Rodas, C.L., Pereira da Silva, I., Amaral Toledo Coelho, V., Monteiro Guimarães Ferreira, D., De Souza, R.J., De Carvalho, J.G., 2013. Chemical properties and rates of external color of strawberry fruits grown using nitrogen and potassium fertigation. IDESIA 31, 53–58. Ross, H.A., McDougall, G.J., Stewart, D., 2007. Antiproliferative activity is predominantly associated with ellagitannins in raspberry extracts. Phytochemistry 68, 218–228. Sariburun, E., Şahin, S., Demir, C., Türkben, C., Uylaşer, V., 2010. Phenolic content and antioxidant activity of raspberry and blackberry cultivars. J. Food Sci. 75, C328–C335. Savvas, D., Ntatsi, G., 2015. Biostimulant activity of silicon in horticulture. Sci. Hortic. (Amsterdam) 196, 66–81. Seeram, N.P., 2008. Berry fruits: compositional elements, biochemical activities, and the impact of their intake on human health, performance, and disease. J. Agric. Food Chem. 56, 627–629. Stamatakis, A., Papadantonakis, N., Lydakis-Simantiris, N., Kefalas, P., Savvas, D., 2003. Effects of silicon and salinity on fruit yield and quality of tomato grown hydroponically. Acta Hortic. 609, 141–147. Tahir, A.M., Aziz, T., Rahmatullah, and, 2011. Silicon-induced growth and yield enhancement in two wheat genotypes differing in salinity tolerance. Commun. Soil Sci. Plant Anal. 42, 395–407. Tezotto-Uliana, J.V., Fargoni, G.P., Geerdink, G.M., Kluge, R.A., 2014. Chitosan applications pre- or postharvest prolong raspberry shelf-life quality. Postharvest. Biol. Technol. 91, 72–77. Thomson, C.J., Marschner, H., Römheld, V., 1993. Effect of nitrogen fertilizer form on ph of the bulk soil and rhizosphere, and on the growth, phosphorus, and micronutrient uptake of bean. J. Plant Nutr. 16, 493–506. Tomasi, N., Pinton, R., Dalla Costa, L., Cortella, G., Terzano, R., Mimmo, T., Scampicchio, M., Cesco, S., 2014. New “solutions” for floating cultivation system of ready-to-eat salad: a review. Trends Food Sci. Technol. 46, 267–276. Valentinuzzi, F., Mason, M., Scampicchio, M., Andreotti, C., Cesco, S., Mimmo, T., 2015. Enhancement of the bioactive compound content in strawberry fruits grown under iron and phosphorus deficiency. J. Sci. Food Agric. 95, 2088–2094. Valentinuzzi, F., Cologna, K., Pii, Y., Mimmo, T., Cesco, S., 2018. Assessment of silicon biofortification and its effect on the content of bioactive compounds in strawberry (Fragaria × ananassa cv. Elsanta) fruits. Acta Hortic in press. Wojcik, P., 2005. Response of primocane-fruiting “Polana” red raspberry to boron fertilization. J. Plant. Nutr. 28. Wójcik, P., Lewandowski, M., 2003. Effect of calcium and boron sprays on yield and quality of “Elsanta” strawberry. J. Plant. Nutr. 26, 671–682. Zhang, Z., Zhao, Z., Liu, H., Dubé, C., Charles, M.T., Kempler, C., Khanizadeh, S., 2012. Horticultural characteristics and chemical composition of advanced raspberry lines from British Columbia. J. Food, Agric. Environ. 10, 883–887. Zhang, M., Liang, Y., Chu, G., 2017. Applying silicate fertilizer increases both yield and quality of table grape (Vitis vinifera L.) grown on calcareous grey desert soil. Sci. Hortic. (Amsterdam) 225, 757–763.
on hydroponically grown corn salad (Valerianella locusta (L.) Laterr) plants. Plant Physiol. Biochem. 56, 14–23. Haffner, K., Rosenfeld, H.J., Skrede, G., Wang, L., 2002. Quality of red raspberry Rubus idaeus L. cultivars after storage in controlled and normal atmospheres. Postharvest. Biol. Technol. 24, 279–289. Hajiboland, R., Moradtalab, N., Eshaghi, Z., Feizy, J., 2017. Effect of silicon supplementation on growth and metabolism of strawberry plants at three developmental stages. New Zeal. J. Crop Hortic. Sci. 1–18. Han, C., Zhao, Y., Leonard, S.W., Traber, M.G., 2004. Edible coatings to improve storability and enhance nutritional value of fresh and frozen strawberries (Fragaria x ananassa) and raspberries (Rubus ideaus). Postharvest Biol. Technol. 33, 67–78. Hinsinger, P., Plassard, C., Tang, C., Jaillard, B., 2003. Origins of root-mediated pH changes in the rhizosphere and their responses to environmental constraints: a review. Plant Soil 248, 43–59. Hodges, D.M., DeLong, J.M., 2007. The relationship between antioxidants and postharvest storage quality of fruits and vegetables. Stewart Postharvest. Rev. 3. Hristov, S., Stoyanova, T., Minev, I., 2009. Raspberry cultivars for fruit production under mountain conditions. Acta Hortic. 825, 221–224. Jezek, M., Zörb, C., Merkt, N., Geilfus, C.-M., 2018. Anthocyanin management in fruits by fertilization. J. Agric. Food Chem acs.jafc.7b03813. Jugdaohsingh, R., Anderson, S.H.C., Tucker, K.L., Elliott, H., Kiel, D.P., Thompson, R.P.H., Powell, J.J., 2002. Dietary silicon intake and absorption. Am. J. Clin. Nutr. 75, 887–893. Jugdaohsingh, R., Tucker, K.L., Qiao, N., Cupples, L.A., Kiel, D.P., Powell, J.J., 2004. Dietary silicon intake is positively associated with bone mineral density in men and premenopausal women of the Framingham offspring cohort. J. Bone Miner. Res. 19, 297–307. Khanizadeh, S., Rekika, D., Ehsani-Moghaddam, B., Tsao, R., Yang, R., Charles, M.T., Sullivan, J.A., Gauthier, L., Gosselin, A., Potel, A.-M., et al., 2009. Horticultural characteristics and chemical composition of advanced raspberry lines from Quebec and Ontario. LWT – Food Sci. Technol. 42, 893–898. Kim, S.G., Kim, K.W., Park, E.W., Choi, D., 2002. Silicon-induced cell wall fortification of rice leaves: a possible cellular mechanism of enhanced host resistance to blast. Phytopathology 92, 1095–1103. Kowalenko, C.G., 2006. The effect of nitrogen and boron fertilizer applications on Willamette red raspberry growth, and on applied and other nutrients in the plant and soil over two growing seasons. Can. J. Plant Sci. 86, 213–225. Kowalenko, C.G., Keng, J.C.W., Freeman, J.A., 2000. Comparison of nitrogen application via a trickle irrigation system with surface banding of granular fertilizer on red raspberry. Can. J. Plant Sci. 80, 363–371. Lewin, J., Reimann, B.E.F., 1969. Silicon and plant growth. Annu. Rev. Plant Physiol. 20, 289–304. Mahmood, T., Anwar, F., Abbas, M., Boyce, M.C., Saari, N., 2012. Compositional variation in sugars and organic acids at different maturity stages in selected small fruits from Pakistan. Int. J. Mol. Sci. 13, 1380–1392. Miliauskas, G., Venskutonis, P.R., van Beek, Ta., 2004. Screening of radical scavenging activity of some medicinal and aromatic plant extracts. Food Chem. 85, 231–237. Miyake, Y., Takahashi, E., 1986. Effect of silicon on the growth and fruit production of strawberry plants in a solution culture. Soil. Sci. Plant Nutr. 32, 321–326. Montesano, F.F., D’Imperio, M., Parente, A., Cardinali, A., Renna, M., Serio, F., 2016. Green bean biofortification for Si through soilless cultivation: plant response and Si bioaccessibility in pods. Sci. Rep. 6. Moyer, R.A., Hummer, K.E., Finn, C.E., Frei, B., Wrolstad, R.E., 2002. Anthocyanins, phenolics, and antioxidant capacity in diverse small fruits: Vaccinium, Rubus, and Ribes. J. Agric. Food Chem. 50, 519–525. Nunes, C., Emond, J., 2007. Relationship between weight loss and visual quality of fruits
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Fertilization strategies as a tool to modify the organoleptic properties of raspberry (Rubus idaeus L.) fruits
T
Fabio Valentinuzzia, Youry Piia, Tanja Mimmoa, Gianluca Savinib, Stefano Curzelb, ⁎ Stefano Cescoa, a b
Faculty of Science and Technology, Free University of Bozen-Bolzano, Piazza Università 5, 39100, Bolzano, Italy Società Cooperativa Sant’Orsola, Via Lagorai, 131, 38057, Pergine Valsugana (TN), Italy
A R T I C LE I N FO
A B S T R A C T
Keywords: Raspberry Fertilization Firmness Sweetness index Bioactive compounds
Raspberry cultivation is increasing all over the world, being these fruits highly appreciated not only for their taste but also for their high content in bioactive compounds. However, the short shelf-life of these fruits limits their fresh consumption and industrial use to a defined time frame. For this reason, setting agronomic strategies aimed at extending the fruit shelf-life represent a prerequisite to ensure the presence of high-quality raspberries on the market for a prolonged time. Therefore, aim of this work was to assess the influence of different nutritional regimes (over-fertilization with NH4+, Si or B) on the firmness and the potential extension of the shelf-life as well as on the quality of raspberry fruits. Raspberry canes (Rubus idaeus) cv. ‘Lagorai Plus’ were grown in a high tunnel plastic greenhouse and starting from middle July to September raspberry fruits were collected. The over-fertilization with NH4+, Si or B lead to higher yields, increased colour indexes, firmness, sucrose content and sweetness indexes. Furthermore, the fertilizations led to an improved shelf-life due to a significant reduction of fruit darkening and fruit weight loss, which was particularly evident at the end of the incubation. The results of this work highlighted that the modification of the nutritional status of raspberries by adding either Si, B or NH4+ could be helpful in obtaining fruits with improved qualitative parameters. In particular, an increase in the sweetness index and firmness of fruits as well as an extension of the shelf-life could be beneficial for the attractiveness of consumer and also for the possibility of using fruits in the industrial transformations. Moreover, considering the role of Si and B in human health, the bio-fortification programs can become particularly interesting, thus opening the way for new market perspectives of these fruits in addition to the traditional ones.
1. Introduction
chronic disease and some forms of cancer (Beattie et al., 2005; Ross et al., 2007; Seeram, 2008). Moreover, beside their positive effect on human health, phenolic compounds can also considerably affect the shelf-life and postharvest quality of the berries (Hodges and DeLong, 2007; Khanizadeh et al., 2009). In fact, the seasonality of the raspberry cultivation and the fast senescence characterizing these fruits after the harvest (i.e. short shelflife) limits their fresh consumption and industrial use to a defined time frame (Han et al., 2004). Postharvest life of red raspberries represents a main issue for this fruit crop since it is only limited to a few days (generally 2–3 days from picking) (Giovanelli et al., 2014). This is mainly due to the loss of firmness and their susceptibility to fruit rot (Khanizadeh et al., 2009), caused by their structural fragility and their high respiration rate (Haffner et al., 2002). As a consequence, fresh fruits are only available in the ripening seasons and are mostly
Raspberries (Rubus idaeus L.) are cultivated in many countries worldwide, but particularly in Eastern Europe and in the USA (Giovanelli et al., 2014) having a significant economic relevance for farms (Hristov et al., 2009). As well as other berries, the global production of these fruits is increasing, being highly appreciated by consumers not only for their good taste but also for their high content in health beneficial compounds (Rao and Snyder, 2010). Indeed, many studies have shown that raspberries are a major source of antioxidants because of their high concentration in polyphenolic compounds such as anthocyanins, flavonols, catechins, ascorbic acid and ellagic acid derivatives (Beekwilder et al., 2005; Deighton et al., 2000; Moyer et al., 2002; Sariburun et al., 2010). In particular, these compounds can scavenge free radicals (Zhang et al., 2012) helping the prevention of ⁎
Corresponding author. E-mail address: [email protected] (S. Cesco).
https://doi.org/10.1016/j.scienta.2018.06.024 Received 21 March 2018; Received in revised form 17 May 2018; Accepted 9 June 2018 0304-4238/ © 2018 Elsevier B.V. All rights reserved.
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Control plants (Control) were fertigated with the following nutrient solution (NS): NO3− 6 mM, H2PO4− 1 mM, SO42- 1.5 mM, NH4+ 0.6 mM, K+ 3 mM, Ca2+ 4 mM, Mg2+ 4 mM, Fe2+ 30 μM, Mn2+ 20 μM, Zn2+ 8 μM, B 12 μM, Cu 1.75 mM, Mo 0.75 mM. For a second set of plants (+NH4+) NH4+ was added to the NS once a week, while for a third set (+Si) Si (K2SiO4 3 mM) was added to the NS during the whole growing period. The fourth set of plants (+B) was fertigated as + NH4+ and treated foliarly with 1.5 mg H3BO3 plant−1 (Wojcik, 2005) applied 4 times during the growing season (2 weeks before flowering, at flowering, 3 and 6 weeks after flowering). The solution was characterized by an average Electric Conductivity (EC) of 2000 μS cm-1 and a pH = 5.5. Harvest season started on end of July and ended in September.
consumed locally. For this reason, setting agronomic strategies aimed at extending the fruit shelf-life (increasing its conservation and storability without impacts on the nutritional value) can have an interest not only in terms of more prolonged presence in the market of high-quality raspberries, but also from the economy point of view of a specific production area. It is widely demonstrated that mineral nutrition has a thorough impact on both fruit yield and quality (Álvarez-Fernández et al., 2003; Pestana et al., 2010; Tomasi et al., 2014; Valentinuzzi et al., 2015) as well as shelf-life (Dalla Costa et al., 2011). In this respect it is interesting to mention that very recently a relationship between anthocyanins in strawberries and nitrogen (N) fertilization has been reviewed by Jezek et al., (2018). An additional example can be represented by boron (B) that, when applied in field cultivation both on soil and on leaves, not only increased tomato weight by improving fruit set, but also improved fruit firmness and shelf-life (Davis et al., 2003). Moreover, Wojcik, (2005) showed an increased berry strength in raspberries cv. Polana fertilized with B. This phenomenon was related by the authors to a possible increase in the number of berry drupelets; in fact, Robbins and Moore, (1990) observed that raspberries with a higher number of drupelets were firmer than those of a similar size with fewer large drupelets. In addition to N and B, it is also interesting the case of silicon (Si). Although its beneficial effects have been extensively proven, Si is usually omitted from the composition of nutrient solutions (Gottardi et al., 2012). Indeed, its supplementation increases significantly plant fitness with a resulting enhancement of agricultural production (Montesano et al., 2016; Savvas and Ntatsi, 2015). Furthermore, Stamatakis et al., (2003) observed an increase in total solid solutes, vitamin C and fruit firmness in tomatoes by adding K2SiO3 to the hydroponic system. Moreover, Si has shown to prolong the shelf-life of strawberry fruits (usually few days) harvested from plants supplemented with bio-available Si (Babini et al., 2012). However it should be noted that fruit yield and its quality are not exclusively related to the presence or absence of a specific nutrient/element, but also to the nutrient form supplied with the fertilizers. In this context, N represents a particular example. In fact, it is well demonstrated that a nitrate-based fertilization affects rhizosphere pH values in a totally opposite way than an ammonium-based one (Hinsinger et al., 2003). In this latter case, the ammonium-induced acidification of the soil surrounding the roots affects consistently the availability of some other nutrients (e.g Fe, Thomson et al., 1993), influencing therefore the whole nutrient acquisition process of roots. These phenomena, pretty well described for some crops such as strawberry, are still quite unknown in raspberry, particularly when fruit quality parameters are considered. Therefore, in the present work the effect of N (ammonium), B or Si availability on the firmness and an extension of the shelf-life of raspberry fruits, has been assessed. To this purpose, growth medium (ammonium) or foliar (B or Si) fertilizations were applied to the plants. At harvest, quality parameters (colour, sweetness index, sugar, organic acid contents) and the bioactive compound (phenolic compounds) concentration of raspberry fruits were assessed and related to the overall fruit quality as a function of the different nutritional treatments.
2.2. Measurement of plant growth and fruit productivity During the growing period, SPAD index of fully expanded leaves was determined using a portable chlorophyll meter SPAD-502 (Minolta, Osaka, Japan). Measurements were carried every two weeks on both basal and apical leaves (at least two per plant), and five SPAD measurements were taken per leaf and averaged. At the end of the harvest season, raspberry plants were collected separating lateral braches from the cane and fresh weight (FW) of both biomasses was measured. At harvest, total fruit yield, yield per plant (kg FW plant−1), average fruit yield (g FW) and number of discarded fruits were assessed. 2.3. Characterizazion of fruit quality Raspberry fruits were harvested once at least 80% of the fruit surface showed a red coloration. The color index (CI) to express the intensity of red color was determined using a portable tristimulus colorimeter (Chroma Meter CR-400, Konica Minolta Corp., Osaka, Japan) and calculated as CI = 100 x a/(L x b) with higher values expressing a more intense red color (Tezotto-Uliana et al., 2014). Total soluble solid contents, expressed in Brix degrees (°Bx), were determined using a digital refractometer (Atago, Tokyo, Japan) on fresh extracted fruit juice. Titratable acidity (TA) was determined as previously described (Valentinuzzi et al., 2015). Raspberry firmness was assessed on fresh fruits with a penetrometer (model PCE-FM200; PCE Instruments, Southampton, UK) equipped with a cylindrical probe 3 mm in diameter and expressed in Newton (N). 2.4. Raspberry extracts Freeze-dried raspberry samples were ball-milled (model MM400; Retsch, Haan, Germany) to obtain a homogeneous powder; the ground samples were extracted with methanol (HPLC grade, Merck, Darmstadt, Germany) using a 1:10 extraction ratio. The mixtures were then sonicated for 30 min in a thermostatic bath and centrifuged at 14000xg for 30 min at 0 °C; finally, the supernatant was collected and filtered through a 0.2 μm nylon filter (Phenomenex Inc., USA). 2.5. Organic acid and sugars analyses
2. Materials and methods The separation of both organic acids and sugars was performed by HPLC using a cation exchange column Aminex 87-H column (300 × 7.8 mm, 9 mm, Bio-Rad) using an isocratic elution with 10 mM H2SO4 as mobile phase at a flow rate of 0.6 mL min−1. Organic acids were detected at 210 nm with a Waters 2998 photodiode array detector (Waters Spa, Italy), whilst sugars were detected by a refractive index detector (Waters Spa, Italy). Standard acids and sugars were prepared as individual stock solutions and then combined to give diluted reference standards. Organic anions and sugars were identified by comparing retention times of unknowns to pure compounds. Standards were purchased from Sigma–Aldrich (St. Louis, MO, United States). Sweetness index (SI) was calculated as in Mahmood et al., (2012).
2.1. Plant growth After a storage period between −1 °C and 1.5 °C raspberry floricanes (Rubus idaeus) cv. ‘Lagorai Plus’ were transplanted at the end of May to 6.5-L pots containing coconut fiber and transferred into a high tunnel plastic greenhouse for the growing and fruiting period. 200 cane plants per treatment were utilized. The experiment was laid out in a randomized block design, with five replicates per treatment. Each block consisted of 40 cane plants and thirty centrally located plants per block were used to collect vegetative and qualitative parameters. 206
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2.6. Phenolic compounds analyses The content of total phenols of raspberry fruit extracts was determined following the Folin-Ciocalteau method (Atanassova et al., 2011; Folin and Ciocalteu, 1927), while the concentration of flavonoids and flavonols was determined by a pharmacopeia method, using rutin hydrate as reference compound (Miliauskas et al., 2004). 2.7. Elemental analysis Freeze-dried raspberry fruits were homogenized and approximately 0.3 g of each sample were acid digested with concentrated ultrapure HNO3 (650 ml L−1; Carlo Erba, Milano, Italy) using a single reaction chamber microwave digestion system (UltraWAVE, Milestone, Shelton, CT, USA). Concentrations of macro- and micronutrients were then determined by ICP-OES (Arcos Ametek, Spectro, Germany) using tomato leaves (SRM 1573a) and spinach leaves (SRM 1547) as external certified reference material. 2.8. Shelf-life assessment Qualitative analyses were carried out to assess the effect of the different treatments on fruit shelf-life at harvest (time 0) and after 2, 6 and 8 days of storage at 4 °C. Weight loss was calculated by measuring the weight of 40 raspberries per block at harvest and after 2, 5 and 8 days. The results are expressed as weight percentage respect to time 0. Color index was measured as described in paragraph 2.3 at harvest and after 2, 6 and 8 days.
Fig. 1. Yield per plant (kg) (A) and number of fruits per plant (B) of raspberry plants grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
2.9. Statistical analyses The results are presented as means of five replicates ± standard error (SE). Each replicate consisted of a pool of fruits harvested from 10 plants. Statistical analysis was performed using GraphPad Prism version 6.00 for Mac OS X, GraphPad Software, San Diego California USA. Analysis of variance (ANOVA) was carried out, and means were compared using Tukey´s test at P < 0.05.
3.2. Plant productivity In order to understand the effect of the different fertilizations on plant productivity, this was assessed by measuring the average yield per plant and the number of fruits per plant (Fig. 1). The average yield per plant was slightly increased by all the treatments with the highest fruit productivity obtained in + Si fertilized plants (+5%). The number of fruits per plant was also significantly increased by the fertilizations in + NH4+ and + Si plants.
3. Results 3.1. Plant growing parameters Table 1 shows the growing parameters used to assess the effect of the different nutrients on raspberry plants. Both cane biomass and lateral branch biomass were not significantly affected by the treatments as well as the number of lateral branches. In order to evaluate the influence of the applied treatments on the chlorophyll content of raspberry leaves, SPAD index values were measured on basal and apical leaves. As observed for the other parameters, SPAD units did not differ among treatments in both apical and basal leaves.
3.3. Fruit nutrient concentration The concentration of macro- and micronutrients (Table 2) in raspberry fruits was determined with the aim of assessing the influence of the different treatments on the fruit ionome. Regarding macronutrients,
Table 1 Primocane biomass, lateral branches biomass, number of laterals and SPAD index of both basal and apical leaves of raspberry plants grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05). +NH4+
Control
Cane biomass (g) Lateral branches biomass (g) N° lateral branches SPAD basal leaves SPAD apical leaves
+Si
+B
Mean
SE
Mean
SE
Mean
SE
Mean
SE
33.69 218.03 18.38 51.61 44.91
1.70 6.78 0.53 0.36 0.57
36.46 196.25 17.25 51.58 43.75
2.40 7.14 1.32 0.35 0.54
37.31 206.84 20.12 51.99 43.48
2.62 10.28 0.85 0.35 0.50
35.86 191.67 18.00 51.02 44.13
1.67 18.53 1.81 0.37 0.52
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Table 2 Macro- and micronutrients concentration in raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. DW = dry weight. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05). +NH4+
Control
−1
DW) P (mg g K (mg g−1 DW) −1 Ca (mg g DW) Mg (mg g−1 DW) S (mg g−1 DW) Si (mg g−1 DW) Fe (μg g−1 DW) Mn (μg g−1 DW) Zn (μg g−1 DW) B (μg g−1 DW)
+Si
+B
Mean
SE
Mean
SE
Mean
SE
Mean
SE
1.06 6.11 1.19 1.05 0.59 0.13 31.39 31.76 15.94 56.67
0.01 0.07 0.03 0.03 0.02 0.01a 1.59 1.21b 0.61 1.25a
1.07 6.19 1.14 1.06 0.59 0.13 32.32 26.93 15.76 57.54
0.02 0.07 0.04 0.02 0.01 0.01a 1.58 1.99b 0.55 2.24a
1.07 6.08 1.09 1.02 0.61 0.17 30.92 24.75 14.78 58.18
0.01 0.07 0.04 0.01 0.01 0.01b 1.70 1.01a 0.73 2.55a
1.05 6.04 1.12 1.02 0.57 0.13 31.13 32.28 16.06 66.36
0.02 0.11 0.04 0.02 0.01 0.01a 1.04 0.78b 0.45 0.69b
ns ns ns ns ns ns ns
no significant difference could be observed among the treatments. Silicon (Si) concentration significantly increased only in + Si raspberry fruits, accordingly with the applied treatment. Considering micronutrients, Mn concentration slightly decreased in fruits harvested from plants supplied with K2SiO3, while no significant differences could be detected among the other treatments. Raspberry Fe and Zn concentration was not altered by the different treatments applied, while B concentration increased only in + B, as a consequence of foliar B application. 3.4. Fruit quality parameters Fruit quality parameters (Fig. 2) such as color index, brix degrees and firmness were determined in raspberry fruits treated with the different fertilizers. Regarding color index, this increased in all fertilized treatments as compared to control frutis. Total soluble solids concentration (expressed as °Brix) determined in raspberry juice of fruits collected from plants supplied with the four nutrients did not highlight any significant difference. On the other hand, fruit firmness was positively influenced by all the three nutrients tested with a significant increase (at least 15%) in + NH4+, +Si and + B. 3.5. Sugar concentration Fig. 3 shows the concentration of sugars in raspberry fruits harvested from plants supplemented with the different nutrients. Sucrose concentration varied significantly between control fruits and those harvested from treated plants, with the latter containing a higher concentration of sucrose. While glucose concentration was unaffected by the treatments, fructose was enhanced only in + Si fruits, while in the other fruits the concentration of this sugar was similar to that of control fruits. The altered concentration of sugars in raspberries collected from plants supplemented with the different nutrients consequently affected the sweetness of the fruits (Fig. 3D). In fact, +Si and + B raspberries had a significantly higher sweetness index compared to controls, with + NH4+ fruits having intermediate values. 3.6. Titratable acidity, organic acids and bioactive compounds Titratable acidity measured on fruit fresh juice was not significantly affected by the different treatments (Fig. 4A). Among the organic acids, citric and malic acid were the only ones detected in raspberry fruits (Fig. 4B–C). The concentration of citric acid was not significantly influenced by the treatments, even if slight differences could be observed. As well as citric acid, also the concentration of malic acid did not change among the different treatments. Regarding bioactive compounds, Fig. 5 shows the concentration of total phenols, flavonoids and flavonols in the raspberry extracts: no significant variations were
Fig. 2. Color index (A), total soluble solids (B) and firmness (C) of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
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Fig. 3. Sucrose (A), glucose (B), fructose (C) and sweetness index (D) of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
This result indicates that the N treatments have mainly as target the nutritional regimen of the whole plant, therefore affecting, in a cascade system, the yield only in the following years after the applications. In this context, it has also to be highlighted that the composition of the nutrient solution here used to supply control raspberry plants was already optimized to maximize raspberry yield and, for this reason, it has been in use for several years at the field scale. As consequence, a marked increase in fruit yield in the production cycle of treatments was not expected. Fruit colour, brix degrees and fruit firmness are important commercial parameters in determining raspberry quality (Fig. 2). Colour index, calculated to express the intensity of raspberries´ red colour was significantly increased in fruits collected from plants over-fertilized with NH4+, Si and B. Regarding Si, this result is consistent with that obtained by Figueiredo et al., (2010) who noticed an increase in the red colour of Si-treated strawberries. Similarly, also the N fertigation of strawberry plants increased the intensity of the red colour of fruit skins (Rodas et al., 2013). Besides the color index, also firmness increased in fruits supplemented with the three different nutrients (Fig. 2C). Fruit firmness is an important textural property and is of paramount importance for raspberries, since it affects the storability and the resistance to damage through handling. Former studies showed that both foliar and soil B applications increased the firmness of raspberry fruits (Wojcik, 2005) ascribing this effect to an increase in the number of drupelets. The increase of fruit firmness due to Si application was reported by Dehghani Poodeh et al., (2016), in strawberry plants and could be due to a strong bond of Si to the cellulose framework (Lewin and Reimann, 1969), thus leading to a strengthening of fruit skin. Although no significant effect on total soluble solids content (expressed as Brix degrees) was observed (Fig. 2B), a more detailed
detected among the different treatments. 3.7. Shelf-life A shelf-life assessment of raspberries harvested from plants grown in the four different conditions was carried out by evaluating the weight loss and the color index in a period of eight days (Fig. 6). Concerning weight loss, during the incubation time, raspberries supplied with the different nutrients showed a lower loss of weight following this order + B > +Si > +NH4+ > Control. Color index, evaluated to express the intensity of the red color of raspberries, showed significant differences among the treatments and during the incubation. In particular, starting from day 5, control fruits showed a darker coloration compared to raspberries harvested from nutrient supplemented plants. 4. Discussion The different treatments applied to raspberry plants did not lead to any significant increase in terms of plant biomass, branches number and SPAD units (Table 1), as also described by Kowalenko (2006) upon application of N or Si. Fruit yield on the other hand was slightly but significantly increased in all the treatments as compared to the control (Fig. 1), particularly in the Si-treated raspberry plants. Concerning this last aspect, it is interesting to note that the effect of Si in increasing the yield of different grain crops such as rice (Detmann et al., 2012) and wheat (Tahir et al., 2011), horticultural crops such as corn salad (Valerianella locusta L., Gottardi et al., 2012) but also strawberries (Miyake and Takahashi, 1986) has been widely described. In particular for N application, it should be noted that Kowalenko et al., (2000) recorded an effect on raspberry yield only after 3 years of repeated applications. 209
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Fig. 4. Titratable acidity (A), citric acid (B) and malic acid (C) of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
Fig. 5. Total phenols (A), total flavonoids (B) and total flavonols (C) content of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B). Data are reported as means and SE of 5 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
analysis of sugars concentration in fruits collected from plants supplied with the different nutrients revealed an increase of sucrose concentration in + NH4+, +Si and + B fruits and fructose in + Si fruits (Fig. 3). As a consequence, the sweetness index, which is relevant for the taste perception of raspberries, was particularly increased in + B and + Si treatments as compared to controls. With respect to B, it has been already proved that this nutrient can enhance the sugar content in raspberry fruits (Wojcik, 2005) as well as in strawberries (Wójcik and Lewandowski, 2003). This effect has been ascribed to the increased formation of B-sugar complexes and, then, to their augmented transport in the phloem. Furthermore, Hajiboland et al., (2017) reported that the supplementation of Si to the nutrient solution improved several fruit quality parameters, particularly the sugar concentration. On the other hand, titratable acidity and the concentration of the two main organic acids (Fig. 4) in raspberries were not significantly influenced by the three treatments here considered. Since the ratio between sugars and organic acids (sweetness index) is an important parameter to estimate the flavor and therefore consumer acceptance of raspberries, results here presented indicate that the three treatments allow to improve this
index ensuring, consequently, a greater consumer attractiveness for these fruits. The concentration of phenolic compounds in raspberries was not significantly influenced by the treatments applied (Fig. 5). Considering the importance of these bioactive molecules in conferring nutraceutical value to raspberry fruits, it is remarkable that the supplementation of the different nutrients did not alter the composition in beneficial health compounds of fruits. Besides phenolic compounds, nutrient content of fruits are important parameters determining raspberry quality. Yet, the different nutritional regimes did not alter the composition in macroand micronutrients of raspberry fruits (Table 2), with the only exception of manganese (Mn), Si and B. Although the mechanisms are still poorly understood, the effect of Si in decreasing Mn concentration at shoot level in different plant species (Che et al., 2016) has been observed, while it is not been investigated in fruits. As expected instead, plants supplemented with either Si or B, increased the concentrations of the two elements, respectively. This is particularly important in the case of Si, since this element has beneficial effects not only for plants but 210
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was obtained with B in tomatoes (Davis et al., 2003), which has been demonstrated to have an important role in maintaining membrane stability. In conclusion, results here presented show that, with reference to the hydroponic solution currently used at the field scale for raspberry production, there still is room to improve the yield quality through the modification of the availability of some specific nutrients. The effects of these treatments on sweetness index and firmness of fruits as well as the extension of the shelf-life can be beneficial for the attractiveness of consumer and also for the possibility of using fruits in the industrial transformations. Moreover, considering the role of Si and B in human health, the bio-fortification programs can become particularly interesting, thus opening the way for new market perspectives of these fruits in addition to the traditional ones. Authors contributions Designing and performing the experiments: SCE, GS Critical discussion of the data: FV, YP, TM, GS, SCU, SCE Paper preparation: FV, YP, TM, SCE Research coordination: SCE, GS Acknowledgement This work has been financially supported by: Free University of Bozen-Bolzano (TN2023, TN2345-C). References Álvarez-Fernández, A., Paniagua, P., Abadía, J., Abadía, A., 2003. Effects of Fe deficiency chlorosis on yield and fruit quality in peach (Prunus persica L. Batsch). J. Agric. Food Chem. 51, 5738–5744. Armstrong, T.A., Spears, J.W., 2001. Effect of dietary boron on growth performance, calcium and phosphorus metabolism, and bone mechanical properties in growing barrows. J. Anim. Sci. 79, 3120–3127. Atanassova, M., Georgieva, S., Ivancheva, K., 2011. Total phenolic and total flavonoid contents, antioxidant capacity and biological contaminants in medicinal herbs. J. Univ. Chem. Technol. Metall. 46, 81–88. Babini, E., Marconi, S., Cozzolino, S., Ritota, M., Taglienti, A., Sequi, P., Valentini, M., 2012. Bio-available silicon fertilization effects on strawberry shelf-life. Acta Hortic. 934, 815–818. Beattie, J., Duthie, A.C., Duthie, Garry G., 2005. Potential health benefits of berries. Curr. Nutr. Food Sci. 1, 71–86. Beekwilder, J., Hall, R.D., De Vos, C.H.R., 2005. Identification and dietary relevance of antioxidants from raspberry. BioFactors 23, 197–205. Che, J., Yamaji, N., Shao, J.F., Ma, J.F., Shen, R.F., 2016. Silicon decreases both uptake and root-to-shoot translocation of manganese in rice. J. Exp. Bot. 67, 1535–1544. Dalla Costa, L., Tomasi, N., Gottardi, S., Iacuzzo, F., Cortella, G., Manzocco, L., Pinton, R., Mimmo, T., Cesco, S., 2011. The effect of growth medium temperature on corn salad [Valerianella locusta (L.) Laterr] baby leaf yield and quality. HortScience 46, 1619–1625. Davis, J.M., Sanders, D.C., Nelson, P.V., Lengnick, L., Sperry, W.J., 2003. Boron improves growth, yield, quality, and nutrient content of tomato. J. Am. Soc. Hortic. Sci. 128, 441–446. Dehghani Poodeh, S., Ghobadi, C., Baninasab, B., Gheysari, M., Bidabadi, S.S., 2016. Effects of potassium silicate and nanosilica on quantitative and qualitative characteristics of a commercial strawberry Fragaria × ananassa cv. ‘camarosa’’. J. Plant Nutr. 39, 502–507. Deighton, N., Brennan, R., Finn, C., Davies, H.V., 2000. Antioxidant properties of domesticated and wild Rubus species. J. Sci. Food Agric. 80, 1307–1313. Detmann, K.C., Araújo, W.L., Martins, S.C.V., Sanglard, L.M.V.P., Reis, J.V., Detmann, E., Rodrigues, F.A., Nunes-Nesi, A., Fernie, A.R., Damatta, F.M., 2012. Silicon nutrition increases grain yield, which, in turn, exerts a feed-forward stimulation of photosynthetic rates via enhanced mesophyll conductance and alters primary metabolism in rice. New Phytol. 196, 752–762. El Ghaouth, A., Arul, J., Ponnampalam, R., Boulet, M., 1991. Chitosan coating effect on storability and quality of fresh strawberries. J. Food Sci. 56, 1618–1620. Figueiredo, F.C., Botrel, P.P., Locarno, M., Guedes De Carvalho, J., 2010. Leaf spraying and fertirrigation with silicon on the physicochemical attributes of quality and coloration indices of strawberry. Cienc. e Agrotecnol. 34, 1306–1311. Folin, O., Ciocalteu, V., 1927. On tyrosine and tryptophane determinations in proteins. J. Biol. Chem. 27, 627–650. Giovanelli, G., Limbo, S., Buratti, S., 2014. Effects of new packaging solutions on physicochemical, nutritional and aromatic characteristics of red raspberries (Rubus idaeus L.) in postharvest storage. Postharvest Biol. Technol. 98, 72–81. Gottardi, S., Iacuzzo, F., Tomasi, N., Cortella, G., Manzocco, L., Pinton, R., Römheld, V., Mimmo, T., Scampicchio, M., Dalla Costa, L., et al., 2012. Beneficial effects of silicon
Fig. 6. Weight loss (A) and color index (B) of raspberry fruits grown in a full nutrient (Control) and a nutrient solution either supplied with NH4+ (+NH4+) or a nutrient solution supplied with K2SiO3 (+Si) or a nutrient solution supplied with NH4+ and B (+B) collected and stored for 8 days at 4°. Data are reported as means and SE of 40 replicates. The statistical significance was tested by means of ANOVA with Tukey post-test. Different letters indicates statistically different values (p < 0.05).
also for human health (Jugdaohsingh et al., 2002, 2004). For this purpose, many biofortification studies have been performed with the aim of increasing Si concentration in different plant species such as corn salad (Gottardi et al., 2012), green bean (Montesano et al., 2016) and strawberry (Valentinuzzi et al., 2018). Concerning B enrichment of edible products, no specific symptoms of B deficiency have been observed in animals and humans and no recommended dietary allowance is suggested (Rahal and Shivay, 2016); however it has been reported that ingested B through the diet helps in strengthening bone in some animals (Armstrong and Spears, 2001). Once harvested, one of the main concerns for raspberry fruits is their high perishability, resulting in a fast ripening period and senescence (El Ghaouth et al., 1991; Tezotto-Uliana et al., 2014). Therefore, we aimed at evaluating the effect of different nutrients supplementation on fruit shelf-life by measuring weight loss and colour index (CI) during a storage period of 8 days (at 0 °C and 90% RH). It is well known that during the storage a weight loss (ascribable mainly to dehydration and respiration phenomena) and a browning process of fruits, take place (Nunes and Emond, 2007) altering thus their quality. The results here presented evidenced a significant reduction of darkening in fruits of over-fertilized plants as well as a decrease in fruit weight loss, which was particularly evident at the end of the incubation with the following order: +B > +Si > +NH4+ > Control. Regarding Si, this is consistent with results reported by Zhang et al., (2017) who ascribed the fruit weight loss reduction to the deposition of Si under the cuticle and to the formation of a cuticle-Si double layer; such structural modifications strengthen the cell wall structures (Kim et al., 2002). A similar effect
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