Abstract
Saffron is one of the most appreciated, traditional, and expensive spices in the world. The objective of our study was to evaluate the effect of cooling the nutrient solution on the production, and organoleptic and commercial qualities of saffron grown in soilless culture. The nutrient solution was cooled to 4 to 5 °C whereas the control treatment was the fertigation supplied at ambient temperature. Corms were placed in a controlled cultivation chamber. The number of flowers per corms, and the weight and length of stigmas were measured. The amounts of safranal, crocin, and picrocrocin were analyzed spectrophotometrically according to the International Organization for Standardization [ISO/TS 3632-2 (2011) Normative]. Our results show that cooling of the nutritive solution increased flower production, the commercial phytochemical content, and organoleptic properties.
The cultivation of saffron (Crocus sativus L.) is one of the oldest in the world and has occurred in the region of the Orient, near the Mediterranean, since the Late Bronze Age (Zohary and Hopf, 1994). It is one of the most expensive spices used in the food industry (García-Rodríguez et al., 2017; Hosseinzadeh and Nassiri-Asl, 2012). It is also highly appreciated in many cuisines around the world, and saffron has acquired increasing interest given the health effects of its chemical components, especially from safranal, crocin, and picrocrocin (Molina et al., 2005). This species has potential medical applications, particularly those based on its antitumor and antichronic stress properties (Amin et al., 2016; Ghadrdoost et al., 2011; Naeimi et al., 2019).
The quality of saffron. Such quality is determined through the spectrophotometric quantification of picrocrocin, safranal and crocin by direct measuring of the absorbance of 1% standard aqueous solution of dried saffron at 257, 330 and 440 nm, respectively (International Organization for Standardization, 2003).
One of the factors that has proved to be important for the production of high-quality saffron is the environmental temperature at which plants are grown in terms of root and shoot growth, and flower formation (Ahrazem et al., 2015; Molina et al., 2005; Wang et al., 2021). In addition, it is well known that a markedly low temperature (≈17 °C) is the best for flower emergence or anthesis from the corm (Molina et al., 2005). This knowledge allows growers to program saffron flowering and increase production in soilless cultivation systems under controlled conditions (Gohari et al., 2013; Wang et al., 2021).
Soilless cultivation systems have been developed through chamber temperature control (Molina et al., 2010; Valero et al., 2004). However, warming the air of the entire greenhouse requires more energy than increasing the root temperature by means of circulating hot water or air through buried tubes (Elwell et al., 1985; Wang et al., 2021). Moreover, warming of the nutrient solution is even cheaper and it is always applied daily as fertigation, given that it is a mandatory action to meet the water and nutrient requirements of the crop (Urrestarazu et al., 2008).
Studies of different species have shown that plant growth is greatly influenced by root temperature (Díaz-Pérez et al., 2007; Nxawe et al., 2009; Solfjeld and Johnsen, 2006). For instance, Urrestarazu et al. (2008) reported that heating the nutrient solution in the 12- to 16-°C range was useful for increasing melon yield, and Yan et al. (2012) stated that an increase in root temperature improved nutrient uptake in cucumbers. However, little is known about the effects of increasing the nutrient solution temperature on saffron plants.
The main goal of this work was to determine the effects on yield and bioactive compound content of saffron by modifying the fertigation temperature to a develop low-cost method of obtaining high-quality saffron.
Materials and Methods
Plant growth conditions.
The experiment was carried out in controlled growth chambers located at the University of Almería, Almería, Spain, between 2019 and 2020. The corms of C. sativus were obtained from Minaya (Albacete, Spain). This is a traditional saffron-producing area in Spain under the Regulatory Council Foundation of the Protected Designation of Origen La Mancha (DOP, 2021). Before planting, corms were incubated at 25 °C (Molina et al., 2004a) for 55 d. On 25 Aug. 2019, corms were transplanted into individual 500-mL containers. The substrate used was commercial coconut fiber, which has defined physicochemical characteristics that have been described by Pozo et al. (2014).
Fertigation treatments.
Two nutrient solution temperatures were used: control, 10 to 15 °C; and cooled, 4 to 5 °C (Fig. 1). The plants were fertigated with a nutrient solution in line with the one described by Sonneveld and Straver (1994). The pH of the nutrient solutions was adjusted to 5.8 with dilute nitric acid. The nutrient solution was cooled using a refrigerator. Refrigerator, growth chamber, and substrate temperatures were controlled using an Onset Hobo Data Logger U23 Pro v2 (Onset Computer Corp., Bourne, MA). The temperatures were 5 °C inside the refrigerator, 16 °C in the culture chamber air, 16 to 17 °C in the substrate when applying the control nutrient solution, and 15 to 16 °C in the substrate when the cooled nutrient solution was supplied. The photoperiod was 16/8 h (day/night) at 16 °C, and the relative humidity was 85%.
Schematic experimental unit of saffron crop and point of sample temperature under soilless culture.
Citation: HortScience horts 56, 10; 10.21273/HORTSCI16005-21
Schematic experimental unit of saffron crop and point of sample temperature under soilless culture.
Citation: HortScience horts 56, 10; 10.21273/HORTSCI16005-21
Schematic experimental unit of saffron crop and point of sample temperature under soilless culture.
Citation: HortScience horts 56, 10; 10.21273/HORTSCI16005-21
Fertigation management was carried out according to the methodology proposed by Urrestarazu et al. (2015). The application of new fertigation was effected when the water in the growing unit reached 10% of the easily available water (Cunha-Chiamolera et al., 2017; Rodríguez et al., 2014; Urrestarazu et al., 2017). Each treatment was applied four times, and the drainage from all pots for each treatment was collected. The pH, electrical conductivity, and nitrate and potassium content of the nutrient solution and the drainage were measured using a pH-meter (Crison MM40+; Hach LPV2500.98.0002, Bizkaia, Spain), a conductivity meter (EC-Meter Crison BASIC 30, Hach), and a LAQUATwin B-742 and B-731 (Horiba, Northampton, UK), respectively. The volume was measured using a test tube graduated to one-hundredth of a millimeter.
Growth parameters.
After flowering, the number of flowers formed per corm was counted, the stigma length was measured before and after the drying process, and the dry and fresh stigma weights were measured with a resolution of 0.1 mg.
The vegetative growth of the plants (number of corms formed, and roots and leaves in the dry and fresh states) was measured after 90 d of flowering. At the end of the experiment, the corms formed per plant were classified according to diameter, and the fresh and dry weights of the leaves were also measured. Roots were rinsed in distilled water to remove substrate residue, weighed, and transferred to paper bags for drying. This was accomplished by placing the material in a convection oven (Heratherm; ThermoScientific, Waltham, MA) at 75 °C until a constant weight was achieved. This was measured using an OHAUS Adventurer Analytical Precision Analytical Balance (model AX 124/E; OHAUS, Parsippany, NJ), with a precision to four-tenths of a gram (Nájera and Urrestarazu, 2019; Urrestarazu et al., 2016).
Saffron quality analysis.
To determine the concentrations of crocin, safranal, and picrocrocin, a standard curve was used according to Khoulati et al. (2019), and the absorbance was recorded using a Helios Gamma UV-Vis Spectrophotometer (Thermo Electron Corporation, Waltham, MA).
Experimental design and statistical analysis.
The experiment was performed using a randomized complete block design, with four blocks (Petersen, 1994). The results were subjected to analysis of variance, and the comparison of means was made using Tukey’s test (P ≤ 0.05) with statistical package Statgraphics Centurion XVII (Statgraphics Technologies Inc., The Plains, VA).
Results and Discussion
Effect on growth parameters.
Flower stigmas are the main commercial product of the saffron plant (Gresta et al., 2008). When the cooled nutrient solution was applied, an improvement of 20% and 24% was found in the number of flowers formed and the dry weight of the stigmas, respectively (Table 1). Flower formation mean per corm was 50% greater than that reported by Molina et al. (2004b) under similar crop conditions. No significant effects were recorded in the remaining vegetative growth parameters. It is well known that air temperature is one of the most important factors to induce saffron flowering (Gresta et al., 2009; Molina et al., 2004a; Wang et al., 2021). Molina et al. (2004a) reported that flower emergence required the transfer of the corms from the conditions of flower formation to a markedly lower air temperature (17 °C). By applying a colder environment, greater flower production was obtained (Gresta et al., 2009). These results were similar to those reported by Urrestarazu et al. (2008) and Yan et al. (2012), who obtained significant benefits in the productivity of horticultural crops under soilless culture by means of modifying the temperature of the nutrient solution and root environment. This is because the root-zone temperature is an important factor in plant growth and water and nutrient uptake (Bode Stoltzfus et al., 1998; Marschner et al., 1996; Mozafar et al., 1993). So, the cooling of the solution is a low-cost and environmentally friendly method of increasing saffron yield.
Yield of saffron grown under soilless culture according to nutrient solution temperature.
Effect on chemical components.
Under soilless culture, the crocin, safranal, and picrocrocin contents we obtained were significantly greater than those reported by Caballero et al. (2007) (Table 2). After applying cooled fertigation, increases of 16% and 91% in safranal and crocin, respectively, were realized. However, no significant differences were found in the amount of picrocrocin. So, the fertigation temperature affects two of the main bioactive compounds of saffron.
Pigment content of saffron according to the nutrient solution temperature (measured in milligrams per gram of stigmas).
Effect on saffron quality.
Saffron quality depends on the concentration of its major metabolites according to ISO 3632/2 (International Organization of Standardization, 2011). Table 3 shows significant differences in the quality of saffron characteristics according to nutrient solution temperature as evaluated by absorption values. It is well known that the secondary metabolites (i.e., crocin, picrocrocin, and safranal) range greatly from country to country based on several factors, including climatic conditions, the harvest and drying processes, and storage (Carmona et al., 2005). The data we obtained were within the ranges reported by Carmona et al. (2005). Under cooled fertigation, absorption values for crocin, safranal, and picrocrocin increased by 16%, 52%, and 13%, respectively, thus leading to an increase in one level in the commercial ranking for two of the main bioactive compounds of saffron.
Quality characteristics of saffron according to International Organization for Standardization/TS 3632-2 (2011) Normative versus nutrient solution temperature.
The temperature of fertigation is a behavior of a eustressor according to the work by Vázquez-Hernández et al. (2019).
Conclusion
Fine-tuning the temperature of the nutritive solution increases flower production, and crocin and safranal content without affecting the growth parameters of saffron. Cooling the nutrient solution is an effective, low-cost, and environmentally friendly methodology for increasing saffron production and commercial quality based on bioactive compounds and organoleptic components.
Literature Cited
Ahrazem, O., Rubio-Moraga, A., Nebauer, S.G., Molina, R.V. & Gómez-Gómez, L. 2015 Saffron: Its phytochemistry, developmental processes, and biotechnological J. Agr. Food Chem. 63 40 8751 8764 doi: https://doi.org/10.1021/acs.jafc.5b03194
Amin, A., Hamza, A.A., Daoud, S., Khazanehdari, K., Hrout, A., Baig, B., Amphun, C.H., Adrian, T.H., Zaki, N. & Ashtiani, K.S. 2016 Saffron based crocin prevents early lesions of liver cancer: In vivo, in vitro and network analyses Recent Patents Anticancer Drug Discov. 11 1 121 133 doi: https://doi.org/10.2174/1574892810666151102110248
Bode Stoltzfus, R.M., Taber, H.G. & Aiello, A.S. 1998 Effect of increasing root-zone temperature on growth and nutrient uptake by ‘Gold Star’ muskmelon J. Plant Nutr. 21 2 321 328 doi: https://doi.org/10.1080/01904169809365406
Caballero, O.H., Pereda, M.P. & Abdullaev, F.I. 2007 HPLC quantification of major active components from 11 different saffron (Crocus sativus L.) sources Food Chem. 100 3 1126 1131 doi: https://doi.org/10.1016/j.foodchem.2005.11.020
Carmona, M., Zalacain, A., Pardo, J.E., Lopez, E., Alvarruiz, A. & Alonso, G.L. 2005 Influence of different drying and aging conditions on saffron constituents J. Agr. Food Chem. 53 10 3974 3979 doi: https://doi.org/10.1021/jf0404748
Cunha-Chiamolera, T.P.L., Urrestarazu, M., Cecílio Filho, A.B. & Morales, I. 2017 Agronomic and economic feasibility of tomato and lettuce intercropping in a soilless system as a function of the electrical conductivity of the nutrient solution HortScience 52 9 1195 1200 doi: https://doi.org/10.21273/hortsci12170-17
Díaz-Pérez, J.C., Gitaitis, R. & Mandal, B. 2007 Effects of plastic mulches on root zone temperature and on the manifestation of tomato spotted wilt symptoms and yield of tomato Scientia Hort. 114 2 90 95 doi: https://doi.org/10.1016/j.scienta.2007.05.013
DOP 2021 Azafrán de La Mancha: Denominación de Origen 21 Jan. 2021. <https://doazafrandelamancha.com/en/>
Elwell, D.L., Hamdy, M.Y., Roller, W.L., Ahmed, A.E., Shapiro, H.N., Parker, J.J. & Johnson, S.E. 1985 Soil heating using subsurface pipes: A decade of research results at OSU/OARDC Ohio Agr. Res. Dev. Ctr. 1175
García-Rodríguez, M.V., López-Córcoles, H., Alonso, G.L., Pappas, C.S., Polissiou, M.G. & Tarantilis, P.A. 2017 Comparative evaluation of an ISO 3632 method and an HPLC-DAD method for safranal quantity determination in saffron Food Chem. 221 838 843 doi: https://doi.org/10.1016/j.foodchem.2016.11.089
Ghadrdoost, B., Vafaei, A.A., Rashidy-Pour, A., Hajisoltani, R., Bandegi, A.R., Motamedi, F., Haghighi, S., Sameni, H.R. & Pahlvan, S. 2011 Protective effects of saffron extract and its active constituent crocin against oxidative stress and spatial learning and memory deficits induced by chronic stress in rats Eur. J. Pharmacol. 667 1–3 222 229 doi: https://doi.org/10.1016/j.ejphar.2011.05.012
Gohari, A.R., Saeidnia, S. & Mahmoodabadi, M.K. 2013 An overview on saffron, phytochemicals, and medicinal properties Pharmacogn. Rev. 7 1 61 66 doi: https://doi.org/10.4103/0973-7847.112850
Gresta, F., Avola, G., Lombardo, G.M., Siracusa, L. & Ruberto, G. 2009 Analysis of flowering, stigmas yield and qualitative traits of saffron (Crocus sativus L.) as affected by environmental conditions Scientia Hort. 119 3 320 324 doi: https://doi.org/10.1016/j.scienta.2008.08.008
Gresta, F., Lombardo, G.M., Siracusa, L. & Ruberto, G. 2008 Effect of mother corm dimension and sowing time on stigmas yield, daughter corms and qualitative aspects of saffron (Crocus sativus L.) in a Mediterranean environment J. Sci. Food Agr. 88 1144 1150 doi: https://doi.org/10.1002/jsfa.3177
Hadizadeh, F., Mahdavi, M., Emami, S.A., Khashayarmanesh, Z., Hassanzadeh, M., Asili, J., Shariatimoghadam, A. & Noorbakhsh, R. 2007 Evaluation of ISO method in saffron qualification Acta Hort. 739 405 420 doi: https://doi.org/10.17660/actahortic.2007.739.53
Hosseinzadeh, H. & Nassiri-Asl, M. 2012 Avicenna’s (Ibn Sina) the Canon of Medicine and saffron (Crocus sativus): A review Phytother. Res. 27 4 475 483 doi: https://doi.org/10.1002/ptr.4784
International Organization for Standardization 2003 TS 3632-1/2: Technical specification: Crocus sativus L. saffron International Organization for Standardization Geneva, Switzerland
International Organization for Standardization 2011 ISO 3632-1: Saffron (Crocus sativus L.): Specifications International Organization for Standardization Geneva, Switzerland
Khoulati, A., Ouahhoud, S., Mamira, S., Alaoui, K., Lahmass, I., Choukri, M., Kharmach, E.Z., Aserhaou, A. & Saalaoui, E. 2019 Saffron extract stimulates growth, improves the antioxidant components of Solanum lycopersicum L., and has an antifungal effect Ann. Agr. Sci. 64 138 150 doi: https://doi.org/10.1016/j.aoas.2019.10.002
Marschner, H., Kirkby, E.A. & Cakmak, I. 1996 Effect of mineral nutritional status on shoot–root partitioning of photoassimilates and cycling of mineral nutrients J. Expt. Bot. 47 1255 1263 doi: https://doi.org/10.1093/jxb/47.Special_Issue.1255
Molina, R.V., García-Luis, A., Coll, V., Ferrer, C., Valero, M., Navarro, Y. & Guardiola, J.L. 2004a Flower formation in the saffron crocus (Crocus sativus L): The role of temperature Acta Hort. 650 39 47 doi: https://doi.org/10.17660/actahortic.2004.650.2
Molina, R.V., Renau-Morata, B., Nebauer, S.G., García-Luis, A. & Guardiola, J.L. 2010 Greenhouse saffron culture: Temperature effects on flower emergence and vegetative growth of the plants Acta Hort. 850 91 94 doi: https://doi.org/10.17660/actahortic.2010.850.12
Molina, R.V., Valero, M., Navarro, Y., Garcìa-Luis, A. & Guardiola, J.L. 2004b The effect of time of corm lifting and duration of incubation at inductive temperature on flowering in the saffron plant (Crocus sativus L.) Scientia Hort. 103 1 79 91 doi: https://doi.org/10.1016/j.scienta.2004.04.008
Molina, R.V., Valero, M., Navarro, Y., Guardiola, J.L. & García-Luis, A. 2005 Temperature effects on flower formation in saffron (Crocus sativus L.) Scientia Hort. 103 361 379 doi: https://doi.org/10.1016/j.scienta.2004.06.005
Mozafar, A., Schreiber, P. & Oertli, J.J. 1993 Photoperiod and root-zone temperature: Interacting effects on growth and mineral nutrients of maize Plant Soil 153 1 71 78 doi: https://doi.org/10.1007/bf00010545
Naeimi, M., Shafiee, M., Kermanshahi, F., Khorasanchi, Z., Khazaei, M., Ryzhikov, M., Avan, A., Gorji, N. & Hassanian, S. 2019 Saffron (Crocus sativus) in the treatment of gastrointestinal cancers: Current findings and potential mechanisms of action J. Cell. Biochem. 120 10 16330 16339 doi: https://doi.org/10.1002/jcb.29126
Nájera, C. & Urrestarazu, M. 2019 Effect of the intensity and spectral quality of LED light on yield and nitrate accumulation in vegetables HortScience 54 1745 1750 doi: https://doi.org/10.21273/HORTSCI14263-19
Nxawe, S., Laubscher, C.P. & Ndakidemi, P.A. 2009 Effect of regulated irrigation water temperature on hydroponics production of spinach (Spinacia oleracea L) Afr. J. Agr. Res. 4 12 1442 1446
Petersen, G. 1994 Agricultural field experiments: Design and analysis 426 Books in soils, plants, and the environment. CRC Press London, UK
Pozo, J., Alvaro, J.E., Morales, I., Requena, J., La Malfa, T., Mazuela, P. & Urrestarazu, M. 2014 A new local sustainable inorganic material for soilless culture in Spain: Granulated volcanic rock HortScience 49 1537 1541 doi: https://doi.org/10.21273/HORTSCI.49.12.1537
Rodríguez, D., Reca, J., Martínez, J., Lao, M.T. & Urrestarazu, M. 2014 Effect of controlling the leaching fraction on the fertigation and production of a tomato crop under soilless culture Scientia Hort. 179 153 157 doi: https://doi.org/10.1016/j.scienta.2014.09.030
Solfjeld, I. & Johnsen, Ø. 2006 The influence of root-zone temperature on growth of Betula pendula Roth Trees (Berl.) 20 3 320 328 doi: https://doi.org/10.1007/s00468-005-0043-1
Sonneveld, C. & Straver, N. 1994 Nutrient solutions for vegetables and flower grow in water substrates 10th ed. Proefstation voor tuinbouw onder glas te Naaldiwjk Naaldldwjk, The Netherlands
Urrestarazu, M., Nájera, C. & Gea, M.M. 2016 Effect of the spectral quality and intensity of light-emitting diodes on several horticultural crops HortScience 51 268 271 doi: https://doi.org/10.21273/HORTSCI.51.3.268
Urrestarazu, M., Morales, I., La Malfa, T., Checa, R., Wamser, A.F. & Alvaro, J.E. 2015 Effects of fertigation duration on the pollution, water consumption, and productivity of soilless vegetable cultures HortScience 50 819 825 doi: https://doi.org/10.21273/HORTSCI.50.6.819
Urrestarazu, M., Salas, M.C., Valera, D., Gómez, A. & Mazuela, P.C. 2008 Effects of heating nutrient solution on water and mineral uptake and early yield of two cucurbits under soilless culture J. Plant Nutr. 31 3 527 538 doi: https://doi.org/10.1080/01904160801895068
Urrestarazu, M., Gallegos, V. & Álvaro, J.E. 2017 The Use of thermography images in the description of the humidification bulb in soilless culture Commun. Soil Sci. Plant Anal. 48 13 1595 1602 doi: https://doi.org/10.1080/00103624.2017.1374399
Valero, M., Molina, R.V., Navarro, Y., García, A. & Guardiola, J.L. 2004 El cultivo del azafrán con larga tradición, pero … ¿con futuro? Cuadernos de fitopatología Rev. Tec. Fitop. Entom. 21 80 47 61
Vázquez-Hernández, M.C., Parola-Contreras, I., Montoya-Gómez, L.M., Torres-Pacheco, I., Schwarz, D. & Guevara-González, R.G. 2019 Eustressors: Chemical and physical stress factors used to enhance vegetables production Scientia Hort. 250 223 229 doi: https://doi.org/10.1016/j.scienta.2019.02.053
Wang, Z., Li, X., Xu, J., Yang, Z. & Zhang, Y. 2021 Effects of ambient temperature on flower initiation and flowering in saffron (Crocus sativus L.) Scientia Hort. 279 109859 doi: https://doi.org/10.1016/j.scienta.2020.109859
Yan, Q., Duan, Z., Mao, J., Li, X. & Dong, F. 2012 Effects of root-zone temperature and N, P, and K supplies on nutrient uptake of cucumber (Cucumis sativus L.) seedlings in hydroponics Soil Sci. Plant Nutr. 58 6 707 717 doi: https://doi.org/10.1080/00380768.2012.733925
Zohary, D. & Hopf, M. 1994 Domestication of plants in the Old World 2nd ed. Clarendon Press Oxford, UK
