Sprouts are generally accepted as a pro-healthy food. They are consumed as a source of valuable macronutrients, antioxidants, microelements, and vitamins. Changing growth conditions of sprouts enables modification of their nutritional quality, as well as their safety. Thus, in order to achieve the most desirable composition of the produced sprouts, the conditions for their production are optimized. The aim of this review is to present methods currently used to modify the nutritional quality of plant sprouts. Most scientific works focus on stress conditions inducing the synthesis of secondary metabolites, mainly antioxidants. An increase in their content is achieved after application of physical (e.g., light illumination, temperature) or chemical factors (e.g., salinity stress, phytohormones, metal ions, etc). Though the application of these modifications on a larger scale is problematic. These problems include difficulties in predicting the effect of the stressor and an increased price of the obtained sprouts. However, since it is possible to enrich sprouts with valuable health-promoting substances, these methods are still considered very promising.
Key words: abiotic stress, antioxidants, sprouts biofortification, sprouts nutritional value
*Corresponding author: Magdalena Zielińska-Dawidziak, Department of Food Biochemistry and Analysis, Faculty of Food Science and Nutrition, Poznan University of Life Sciences, ul. Mazowiecka 48, 60-623 Poznań, Poland. Email: magdalena.zielinska-dawidziak@up.poznan.pl
Submitted: 8 November 2020; Accepted: 14 February 2021; Published: 1 April 2021
© 2021 Codon Publications
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0). License (http://creativecommons.org/licenses/by-nc-sa/4.0/)
Sprouts are more and more common foodstuffs, present not only in traditional Asian markets but also in other parts of the world. The fashion for healthy, low-processed and exotic food, as well as interesting sensorial features of sprouts, increased their presence on our tables significantly. EU legislation defines sprouts as a product obtained from seeds germination in water or another medium (EU, 2013). In contrast to microgreens, they are consumed as shoots and rootlets – with seeds or deseeded. They are harvested before the full expansion of cotyledon leaves and before the emergence of true leaves – usually after 2–7 days of culturing (while microgreens after 7–21 days of growing) (Kyriacou et al., 2016; Le et al., 2020). Because of the growing interest in sprout consumption, studies on their quality which is understood in terms of nutritional value and their safety are widespread.
The nutritional value of sprouts has been appreciated for years. Frequently, at the time of sprouting, no drop is observed in the content of molecules used in metabolism as a source of energy (especially lipids and sugar), despite their involvement in plant development processes (Erba et al., 2018). However, hydrolysis of macromolecules is observed, making nutrients more bioavailable and an elevated content of free sugars and amino acids may be noted (Erba et al., 2018). Research on germination suggests an increase in protein content (Erba et al., 2018; Nissar et al., 2017). However, it must be remembered that the process usually takes place in water (without additional nitrogen sources). Thus, the synthesis of proteins (hydrolytic enzymes) probably results from the rearrangement of other nitrogen-containing compounds (Bau et al., 1997). Many studies also suggest the impact of germination on dietary fiber fractions (Duenas, 2016; Masood et al., 2014), and a decreased content or activity of anti-nutritional substances (Świeca and Baraniak, 2014).
Discussion on the results regarding changes in the sprouts’ composition is concluded: the nutritional value of the obtained sprouts depends on the type of sprouted plants and applied conditions. In order to achieve the most desirable composition of the produced sprouts, the conditions for their production are optimized. Conditions that depart from the optimal usually reduce biomass production (Lim et al., 2012) but may lead to a beneficial effect on sprouts. They are referred to as stress conditions and are divided into two groups: biotic and abiotic. Biotic stress is a consequence of pathogenes’ attack (herbivores, fungi, bacteria, viruses, oomycetes, and nematodes). Abiotic stress, on the other hand, includes salinity, floods, droughts, radiation, extreme temperature, and presence of heavy metal ions and other contamination.
Stress conditions are important for the sprouting because the defense against most abiotic stressors starts in the roots (Gull et al., 2019). The defense system depends on the kind of stressors. For instance, in the case of drought plants, it shortens the shoots and starts the synthesis of compounds, adapting the plant to new osmotic pressure. Whereas in the case of heavy metal ions, plants chelate them and increase the synthesis of antioxidant compounds to detoxify them (Gull et al., 2019). Thus, due to the fact that stress induces endogenous defense mechanisms, it significantly influences the synthesis of secondary metabolites.
In the case of growing edible sprouts, which are carried with the use of special equipment (such as phytotrons or climate chambers), other methods of modifying natural conditions of plant growth are easy to apply, e.g., irradiation. At the same time, the possibility of controlled modification of growth conditions (usually by abiotic stress action) increases the interest in obtaining sprouts as a source of valuable plant metabolites. Most studies focus on decreasing anti-nutrients and the possible modification in the contents of bioactive compounds, among them antioxidants.
Modification of sprouting conditions is essential for seeds or grain germination percentage, rate, shoot and root length, fresh and dry weight, and seedling vigor (some examples are presented Table 1). These parameters depend on the seeds or grain quality, and optimum environmental conditions are variable according to their genetic nature. The most widely studied in this respect are salinity, drought, and temperature stress.
Table 1. Influence of stress factors on sprouts growth parameters.
| Effect | Stress factor | Material | Reference |
|---|---|---|---|
| Increased | |||
| Germination rate (at salt concentration <80 mM) | Salinity | Broccoli (Brassica oleracea) | Wang et al., 2019 |
| Germination strength (at both 10oC as well as 40oC) | Temperature | Edible amaranths (Amaranthus tricolor) | Ye and Wen, 2017 |
| Fresh weight Sprout length (in 30oC) |
Lignosus bean (Dipogon lignosus) | Islam et al., 2017 | |
| Fresh weight | Light | Soybean (Glicine max L.) | Xu et al., 2005 |
| Decreased | |||
| Germination percentage Germination rate |
Salinity | Maize (Zea mays L.) | Carpici et al., 2009 |
| Germination percentage, Germination rate, Root and shoot lengths, Fresh root and shoot weights. |
Sugar beet (Beta vulgaris) Cabbage (Brassica oleracea capitata L.), amaranth (Amaranthus paniculatus), pak-choi (Brassica compestris) |
Jamil et al., 2006 | |
| Radicle, root, and hypocotyl length | Mung bean (Vigna radiate) | Promila and Kumar, 2000 | |
| Dry weight | Light | Soybean (Glicine max L.) Mung bean (Vigna radiata L.) Radish (Raphanus sativus L.) Pumpkin (Cucurbita moschata) |
Mastropasqua et al., 2020 |
| Biomass | Selenium | Broccoli (Brassica oleracea), Mung bean (Vigna radiata), Onion (Allium cepa ‘Red creole’) | Arscott and Goldman, 2012 |
| Shape, length, thickness, color | Heavy metal ion | Alfalfa (Medicago sativa L.) Lentil (Lens culinaris Medik.) Lupine (Lupinus luteus) Soybean (Glicine max L.) Wheat (Triticum aestivum L.) |
Zielińska-Dawidziak et al., 2018 Zielińska-Dawidziak et al., 2014 |
These sprouting parameters usually decrease with the increase in salinity (Carpici et al., 2009; Jamil et al., 2006; Promila and Kumar, 2000), although Wang et al. (2019) proved that low salinity (<80 mM) induced growth of broccoli sprouts.
Drought also inhibits and suppresses germination (Li et al., 2013). However, this factor has little effect on the cultivation of edible sprouts, as it is usually done in hydroponic cultures.
Sprout yield and length are also influenced by temperature, which – unless optimal – can restrain germination. However, stimulation by frost or fire may be essential for some plants. Shock temperature may also promote sprouting in edible plants. And for some plants, increased temperatures may also be beneficial, as it was observed for amaranth seeds. Germination strength of the seeds improved in extreme temperatures [both in decreased (10oC) and increased (40oC)], and dried seeds tolerated ground temperature of even 70oC (Ye and Wen, 2017). It was observed that for some legumes seeds, differences in temperature between 10oC and 30oC do not affect, while the change in the temperature from ambient to 30oC increased fresh weight and sprout length of mung bean (Islam et al., 2017).
Plants in nature germinate with limited light access. Sprouts’ dry weight and length are higher in continuous dark conditions (Mastropasqua et al., 2020). However, selected light illumination may also influence sprouts growth (Xu et al., 2005).
The content of toxic elements in culture media significantly influences the efficiency of sprouting. The high concentration of many ions (especially metal ions) is usually toxic for plants; lower concentration on the other hand triggers the defense system against oxidative stress. As a consequence, reduction in germination percentage is observed, root shape and length disturbed (as it was observed during sprouting in the presence of iron, selenium, lead solutions) (Arscott and Goldman, 2012; Zielińska-Dawidziak et al., 2014, 2016, 2018).
However, research on the use of stress conditions during the growth of sprouts on their chemical composition is becoming increasingly popular. The objective is to obtain valuable pro-health substances and plants with increased nutritional quality.
There is scarce information regarding the influence of sprouting conditions on macronutrients. De novo protein synthesis and the activity of other proteins depend on many environmental conditions. They include temperature, humidity, the presence of metal ions (especially inducing oxidative stress), and concentration of phytohormones (abscisic acid, gibberellic acid, and salicylic acid).
Usually, abiotic stress (e.g., NaCl, polyethylene glycol) (Dell’Aquila and Spada, 1992) decreases protein synthesis. The expression pattern of 561 protein was studied in response to environmental disruption (Tan et al., 2013). Environmental stress induced by some metal ions also inhibits the mobilization of starch and sucrose (Scott and Jones, 1985).
Sprouts are often pointed as a source of valuable antioxidants because their high content is typical of young plants, and decreases with the age of the plant (Liu et al., 2016). Abiotic stress at the time of sprouting intensifies the synthesis of reactive oxygen species. Thus, it involves the overproduction of antioxidants (Przybysz et al., 2016; Tan et al., 2013; Zielińska-Dawidziak et al., 2018). It is obvious that antioxidant activity depends on the genus, species, and botanical variety of plants, but the content of antioxidants in sprouts may be easily modified by changing culture conditions (Table 2).
Table 2. Influence of stress factor on the activity or content of antioxidative compounds at the end of sprouting experiments.
| Effect | Stress factor | Material | Reference |
|---|---|---|---|
| Increased | |||
| Antioxidant activity | Gamma rays | Alfalfa (Medicago sativa L.) | Fan et al., 20041 |
| UV-B 300–320 nm* | Buckwheat (Fagopyrum esculentum) | Tsurunaga et al., 20132 | |
| Blue light | Chinese kale (Brassica oleracea var. alboglabra) | Qian et al., 20163 | |
| Light-emitting diode (LED) spectra (mixed wavelength) | Wheat (Triticum aestivum L.) Radish (Raphanus sativus L.) Lentil (Lens esculenta Moenh.) |
Samuolienė et al., 20112 | |
| Salt (up to 200 mM NaCl treatment) | Buckwheat (Fagopyrum esculentum) | Lim et al., 20122 | |
| Salt | Durum (Triticum turgidum L.) | Stagnari et al., 20174 | |
| Temperature (chilling down to 4oC) | Alfalfa (Medicago sativa L.), Broccoli (Brassica oleracea L.) Radish (Raphanus sativus L.) |
Oh and Rajashekar, 20094 | |
| Temperature (4oC and 40oC) | Lentil (Lens culinaris Medik.) | Świeca and Baraniak, 20144 | |
| Phenolic compounds | UV light | Fava bean (Vicia faba) | Shetty et al., 20025 |
| Blue light | Chinese kale (Brassica oleracea var. alboglabra) | Qian et al., 20166 | |
| Yellow light | Chickpea (Cicer arietinum) |
Khattak et al., 20076 | |
| Blue light Red light |
Buckwheat (Fagopyrum esculentum) | Nam et al., 20176 | |
| Light-emitting diode (LED) spectra (mixed wavelength) | Wheat (Triticum aestivum L.) Radish (Raphanus sativus L.) Lentil (Lens esculenta Moenh.) |
Samuolienė et al., 20116 | |
| Salt (25 mM NaCl) | Einkorn (Triticum monococcum L.) Emmer (Triticum turgidum L.) Durum (Triticum turgidum L.) |
Stagnari et al., 20176 | |
| Temperature (chilling down to 4oC) | Alfalfa (Medicago sativa L.) Broccoli (Brassica oleracea L.) Radish (Raphanus sativus L.) |
Oh and Rajashekar, 20096 | |
| Temperature (4oC and 40oC) | Lentil (Lens culinaris Medik.) | Świeca and Baraniak, 20146 | |
| Iron concentration | Yellow lupine (Lupinus luteus) Blue lupine (Lupinus angustifolius) |
Zielińska-Dawidziak et al., 20186 | |
| Iron concentration | Broccoli (Brassica oleracea) Radish (Raphanus sativus) Alfalfa (Medicago sativa L.) Mung bean (Vigna radiate L.) |
Przybysz et al., 20167 | |
| Flavonoids | Fluorescent light | Buckwheat (Fagopyrum esculentum) | Nam et al., 20178 |
| Temperature (4oC and 40oC) | Lentil (Lens culinaris Medik.) | Świeca and Baraniak, 20148 | |
| Iron concentration | Yellow lupine (Lupinus luteus) Blue lupine (Lupinus angustifolius) |
Zielińska-Dawidziak et al., 20189 | |
| Vitamin C | Gamma rays | Alfalfa (Medicago sativa) | Fan et al., 200410 |
| White light | Chinese kale (Brassica oleracea var. alboglabra) | Qian et al., 201610 | |
| Green light | Chickpea (Cicer arietinum L.) | Khattak et al. 200711 | |
| UV light | Soybean (Glycine max L.) | Xu et al., 200511 | |
| Iron concentration | Broccoli (Brassica oleracea) Radish (Raphanus sativus) Alfalfa (Medicago sativa L.) Mung bean (Vigna radiate L.) |
Przybysz et al., 201610 | |
| Rutin | UV-B 300–320 nm* | Buckwheat (Fagopyrum esculentum) | Tsurunaga et al., 201312 |
| Anthocyanin | UV-B 300–320 nm* | Buckwheat (Fagopyrum esculentum) | Tsurunaga et al., 201313 |
| Blue light | Chinese kale (Brassica oleracea var. alboglabra) | Qian et al., 201614 | |
| Vitamin E | Visible light | White mustard (Sinapis alba L.) | Zielińska and Kozłowska, 200315 |
| Red light | Barley sprouts (Hordeum vulgare) | Koga et al., 201315 | |
| Iron concentration (up to 20 mM FeSO4) | Soybean (Glycine max L.) | Zielińska-Dawidziak and Siger, 201215 | |
| Carotenoids | White light | Tartary buckwheat (Fagopyrum tataricum) | Tuan et al., 201316 |
| Salt (up to 100 mM NaCl) | Buckwheat (Fagopyrum esculentum) | Lim et al., 201216 | |
| Iron (10 mM FeSO4) | Soybean (Glycine max L.) | Zielińska-Dawidziak and Siger, 201216 | |
| Activity of antioxidative enzymes | Iron concentration | Broccoli (Brassica oleracea) Radish (Raphanus sativus) Alfalfa (Medicago sativa L.) Mung bean (Vigna radiate L.) |
Przybysz et al., 201617 |
| Decreased | |||
| Phenolic content | Red light Blue light Green light Fluorescent light Gamma rays |
Chickpea (Cicer arietinum) |
Khattak et al., 20076 |
| No influence | |||
| Antioxidant activity phenolic compounds and flavonoids | Iron (up to 20 mM FeSO4) | Soybean (Glycine max L.) | Zielińska-Dawidziak et al., 20181,6, 9 |
Methods of antioxidative compounds determination: Antioxidant activity 1\TRAP, 2\DPPH. 3\FRAP, and 4\ABTS; Phenolic content: 5\β-Carotene bleaching, 6\Folin-Ciocalteu and 7\spectrophotometric (Fast BlueBB); Flavonoids content: 8\Folin-Ciocalteu and 9\spectrophotometric (AlCl2); Vitamin C: 10\HPLC and 11\spectrophotometric; Rutin: 12\HPLC; Anthocyanin: 13\spectrophotometric and 14\HPLC; Vitamin E: 15\HPLC; Carotenoids: 16\HPLC; Antioxidative enzymes activity: 17\spectrophotometric.
An example may be the application of a lighting system or radiation (γ, UV) (Fan et al., 2004; Shetty et al., 2002). Properly chosen light spectra enhanced the content of the total antioxidant activity, e.g., in buckwheat, Chinese kale, pea, chickpea, wheat sprouts (Nam et al., 2017; Oh and Rajashekar., 2009; Qian et al., 2016; Samuolienė et al., 2011; Tsurunaga et al., 2013), and many others. However, it is difficult to recommend the right light wavelength or predict the acting of this factor. Nevertheless, blue light is often suggested in the above cited research.
The content of antioxidants may also be increased by the application of other abiotic stressors. Studies on stress evoked by salt concentration are frequently conducted, but they rarely concern changes in plant composition. Sometimes an increase in salt concentration induces the production of bioactive compounds while significantly reducing the growth of sprouts (Falcinelli et al., 2017). The higher content of phenolic compounds was noted for buckwheat sprouts (grown in salt concentration up to 200 mM) (Lim et al., 2012), einkorn, emmer, and durum sprouts (up to 50 mM of salt) (Stagnari et al., 2017).
Also, a change in the temperature causes differences in antioxidant concentration, which was observed after chilling broccoli, radish, and alfalfa sprouts (Oh and Rajashekar, 2009), as well as after application of heat for sprouting lentils (Świeca and Baraniak, 2014).
Usage of metal ions inducing oxidative stress enhances the accumulation of antioxidants, and it was observed in soybean, lupine (Zielińska-Dawidziak et al., 2018), broccoli, radish, alfalfa, and mung bean sprouts (Przybysz et al., 2016), among others.
Usually, phenolic compounds and flavonoids are studied, but it must be remembered that sprouts are a very good source of vitamins with a recognized high antioxidant potential (vitamin C, E, and β-carotene) (Duenas et al., 2016; Fan et al., 2004; Sim et al., 2019; Stagnari et al., 2017). The ascorbic acid content in seeds and grains is generally very low, but a different type of illumination may influence the biosynthesis of vitamin C. It was confirmed for soybean, chickpea, and kale sprouts (Khattak et al., 2006; Qian et al., 2016; Xu et al., 2005). The content of tocopherol and β-carotene was modified by the stress induced by metal ions in soybean sprouts (Zielińska-Dawidziak and Siger, 2012). Application of light illumination influenced vitamin E content in different Cruciferae sprouts (Zieliński and Kozłowska, 2003), with red light for barley sprouts (Koga et al., 2013). White light influenced carotenoids content in Tartary buckwheat (Tuan et al., 2013).
Simultaneously, this increase in some antioxidants content may modify the tart, bitter and sour flavors of sprouts (Chen and Chang, 2015). Thus, an additional change in the sprouts’ sensorial quality may be observed.
Modification of the growth conditions influence also the content of other interesting phytochemicals in sprouts (Table 3). Stress conditions (including heat treatment and salinity) may modify γ-aminobutyric acid (which acts as a neurotransmitter) content in sprouts (Benincasa et al., 2019; Guo et al., 2016; Youn et al., 2011). Reducing oxygen availability (hypoxia stress) modifies the content of γ-aminobutyric acid in response to cytosolic acidosis, which was observed for soybean (Guo et al., 2011, 2012), fava bean (Yang et al., 2013), and rice (Aurisano et al., 1995; Ding et al., 2016), and Tartary buckwheat sprouts (Guo et al., 2016).
Table 3. Influence of stress on the content of other interesting bioactive substances in sprouts.
| Effect | Stress factor | Material | Reference |
|---|---|---|---|
| Increased content | |||
| γ-Aminobutyric acid | Combined anaerobic and heat treatment (120–140oC) after sequential hydration | Wheat (Triticum L.) | Youn et al., 2011 |
| Dark cultures at 30oC, hypoxia stress | Tartary buckwheat (Fagopyrum tataricum) | Guo et al., 2016 | |
| Dark cultures at 30oC, hypoxia stress | Soybean (Glycine max L.) | Guo et al., 2011Guo et al., 2012 | |
| Glucosinolates | UVA treatment + methyl jasmonate UVB treatment +methyl jasmonate |
Broccoli (Brassica oleracea) | Moreira-Rodríguez et al., 2017 |
| Sulphur supplementation | Cabbage (Brassica oleracea), Broccoli (Brassica capitata) Radish (Raphanus sativus) | Kestwal et al., 2011 | |
| Glucose treatment | Chinese kale (Brassica oleracea var. alboglabra) Pak choi (Brassica rapa subsp. Chinensis) | Wei et al., 2011 | |
| Methionine | Cu2+, gibberellic acid, abscisic acid, desiccation | Norway maple (Acer platanoides L.) Rice (Oryza L.) Tea (Camellia sinensis L.) |
Tan et al., 2013 |
| Proline | UV treatment | Fava bean (Vicia faba) | Shetty et al., 2002 |
| Amino acids | Red and blue light illumination | Barley (Hordeum L.) | Meng et al., 2015 |
| L-DOPA | Elicitor application (Oregano extact) | ||
| UV light | Fava bean (Vicia faba) | Shetty et al., 2002 | |
| Decreased content | |||
| Glucosinolates (in shoots) | Visible light (white, red, blue) | Chinese kale (Brassica oleracea var. alboglabra) | Qian et al., 2016 |
Glucosinolates and their derivatives were also modulated in broccoli sprouts by the application of UV and phytohormones (Moreira-Rodríguez et al., 2017), sulphur supplementation (in broccoli, cabbage, and radish sprouts) (Kestwal et al., 2011), or glucose addition (in Chinese kale and pak choi sprouts) (Wei et al., 2011).
Stress also has a significant influence on methionine and proline metabolism (Shetty et al., 2002; Tan et al., 2013), thus, on the content of that essential amino acid. The stress factor may also increase the L-DOPA synthesis (an amino acid that increases the concentration of dopamine in the nervous system) (Randhir et al., 2004a; Shetty et al., 2002). Red and blue light illumination doubled the content of amino acids in barley seedlings (compared to natural sunlight) (Meng et al., 2015).
Usually, germination decreases the content of antinutrients (Boschin and Resta, 2013; Świeca and Baraniak, 2014), inhibitors among them. Some authors suggest that stress conditions activate protease inhibitors (Domash et al., 2008; Świeca and Baraniak, 2014), but with no impact on protein digestibility. Świeca and Baraniak (2014) also observed an elevated activity of α-amylase, trypsin, and chymotrypsin inhibitors in response to the impact of temperature on sprouts, but with no influence on protein digestibility and no clear impact on starch bioavailability.
The decrease in the content of many antinutrients (trypsin and amylase inhibitors, phytic acids, and lectins) may be achieved after the application of some elicitors in the growing medium. This effect was observed after using chitosan, salicylic acid, and hydrogen peroxide in a medium intended for bean sprouting (Mendoza-Sánchez et al., 2016). Khattak et al. (2007) stated the influence of blue light illumination on the decrease of phytic acid in chickpea sprouts exclusively. However, it must be remembered that the content of the phytic acid is usually lowered at the time of sprouting.
Other undesirable substances, such as alkaloids, tannins, or oligosaccharides, are leached from the seeds during soaking, owing to their water solubility. It is a traditional method of getting rid of them from seeds, especially legume seeds (e.g., lupine) (Boschin and Resta, 2013).
Examples of the observed changes in the content of anti-nutrients in sprouts growing under conditions of abiotic stress are presented in Table 4.
Table 4. Influence of stress conditions on some antinutrient content in sprouts.
| Effect | Stress factor | Material | Reference |
|---|---|---|---|
| Increased | |||
| Trypsin and chymotrypsin inhibitor activity (with no influence on protein digestibility) | Temperature (4oC and 40oC) | Lentil (Lens culinaris Medik.) | Świeca and Baraniak, 2014 |
| Trypsin inhibitor activity | Osmotic stress (NaCl) | Blue lupin (Lupinus angustifolius L.), Yellow lupin (Lupinus luteus L.), Pea (Pisumsativum L.), Barley (Hordeum vulgare L.) Rye (Secalecereale L.) |
Domash et al., 2008 |
| Decreased | |||
| Content of lectins Trypsin inhibitor activity Amylase inhibitor activity Phytic acid content |
Elicitors (chitosan, salicylic acid, hydrogen peroxide) | Dalia bean (Phaseolus vulgaris L.) |
Mendoza-Sánchez et al., 2016 |
| Phytic acid content | Blue light | Chickpea (Cicer arietinum L.) | Khattak et al., 2007 |
Modification of sprouts’ nutritional quality may also be achieved with the application of many chemicals (isolated or in mixtures) (Table 5). Examples include oregano extract, fish protein hydrolysate, peptides (e.g., lactoferrin) (Randhir et al., 2004a, b), marine protein hydrolysates (Ramakrishna et al., 2019), Saccharomyces cerevisiae and Salix daphnoides bark extracts (Gawlik-Dziki et al., 2013), tea tree extract (Viacava and Roura, 2015), H2O2 (Świeca, 2015), persimmon fruit powder (Kim et al., 2016), amino acids (e.g., phenylalanine, methionine, tryptophan, tyrosine) (Pérez-Balibrea et al., 2011; Seo et al., 2015; Świeca et al., 2014), CaCl2 and sucrose (Sim et al., 2019), glucose (Wei et al., 2011), and other saccharides (e.g., chitosan) (Lee et al., 2005; Qiang et al., 2005) or plant growth regulators (Abellán et al., 2019; Moreira-Rodríguez et al., 2017; Pérez-Balibrea et al., 2011). Enrichment of the growing medium takes place at the stage of pre-sowing treatment, and also during the further stages of sprouting. However, this modification of growth condition significantly increases the price of the obtained product. Such enrichment of the medium was successfully applied to enhance accumulations of microelements, e.g., selenium, magnesium, or iron in sprouts (Przybysz et al., 2015; Sugihara et al., 2004; Zielińska-Dawidziak et al. 2012). It is a very promising method of food fortification in deficient elements (Zielińska-Dawidziak, 2015). Control of the content of toxic elements in medium applied to sprouting is essential because their presence also induces the plant’s defense system and accumulation of these undesirable elements in sprout (Zielińska-Dawidziak et al., 2014 a and b). The necessity to use high purity solutions for the biofortification of sprouts makes their production much more expensive.
Table 5. Influence of chemical substances and natural mixtures application on sprouts composition.
| Effect | Stress factor | Material | Reference |
|---|---|---|---|
| Increased | |||
| Phenolic content | Fish protein hydrolysates | Fenugreek (Trigonella foenum-graecum) | Randhir et al., 2004a1,4,8 |
| Antioxidant and antimicrobial activity | Lactoferrin | ||
| Antioxidant activity and L-DOPA content | Oregano extract | ||
| Antimicrobial activity | Lactoferrin | Mung beans (Vigna radiate L.) | Randhir et al., 2004b4 |
| Antioxidant activity, antimicrobial activity | Oregano extract | ||
| Phenolic content | Marine protein hydrolysates | Barley (Hordeum vulgare L.) | Ramakrishna et al., 20191 |
| Phenolic content | Saccharomyces cerevisiae and Salix daphnoides bark extracts | Broccoli (Brassica oleracea L.) | Gawlik-Dziki et al., 20131 |
| Vitamin C content | Chitosan | Broccoli (Brassica oleracea L.) | Pérez-Balibrea et al., 20117,9,10 |
| Flavonoid and indole glucosinolates content | Salicylic acid, methyl jasmonate | ||
| Aliphatic glucosinolates content | Methionine | ||
| Indole glucosinolates content | Tryptophan | ||
| Antioxidant activity | Tea tree extract, Chitosan |
Lettuce (Lactuca sativa) | Viacava and Roura, 20154 |
| Vitamin C and phenolic content, unchanged antioxidant activity | Persimmon fruit powder | Soybean (Glycine max L.) | Kim et al., 20161,4,6 |
| Phenolic content and antioxidant activity | H2O2 | Lentil (Lens culinaris Medik.) | Świeca, 20151,5 |
| Flavonoids content and antioxidant capacity | Phenylalanine |
Lentil (Lens culinaris Medik.) | Świeca et al., 20151,5 |
| Antioxidant capacity | Combined UV-tyrosine treatments | ||
| Phenolic compounds | Phenylalanine and LED lights | Tartary buckwheat (Fagopyrum tataricum) | Seo et al., 20152 |
| Polyphenols, flavonoids, γ-aminobutyric acid, vitamin C, and E | CaCl2 and sucrose | Buckwheat (Fagopyrum esculentum) | Sim et al., 20192,7,9 |
| Phenolic content | Glucose | Chinese kale (Brassica oleracea) Pak choi (Brassica rapa) |
Wei et al., 20113 |
| Vitamin C | Glucose | Radish (Raphanus sativus L.) | Wei et al., 20117 |
| Vitamin C | Chitosan | Mung bean (Vigna radiate L.) | Qiang et al., 20056 |
| Iron concentration | Ferric EDTA | Broccoli (Brassica oleracea) Radish (Raphanus sativus) Alfalfa (Medicago sativa L.) Mung bean (Vigna radiate L.) |
Przybysz et al., 20169 |
| Iron concentration | FeSO4 | Yellow lupine (Lupinus luteus) Blue lupine (Lupinus angustifolius) Soybean (Glycine max L.) Alfalfa (Medicago sativa L.) Lentil (Lens culinaris Medik.) |
Zielińska-Dawidziak et al., 2012 Zielińska-Dawidziak et al., 2016 Zielińska-Dawidziak et al., 2018 |
| Content of selenium | Sodium selenite | 28 of plant species | Sugihara et al., 2004 |
| Glucosinolates | Methyl jasmonate + UV light | Broccoli (Brassica oleracea L.) | Moreira-Rodríguez et al., 20173,8,10 |
| Decreased | |||
| Phenolic and carotenoids content | Methyl jasmonate | Broccoli (Brassica oleracea L.) | Moreira-Rodríguez et al., 20173,8,10 |
Methods of antioxidative compounds determination: Phenolic content: 1\Folin-Ciocalteu, 2\HPLC and 3\FRAP; Antioxidant activity: 4\ DPPH and 5\ABTS; Vitamin C: 6\colorimetric and 7\HPLC; 8\carotenoids – HPLC; 9\flavonoids – HPLC; 10\glucosinolates – HPLC.
Application of various stress conditions usually influences microbial quality, which was not discussed here. This is an extremely significant quality problem from the perspective of introducing sprouts into the market and their shelf-life. The review did not take the application of biotic stress, also studied as a method of modification of sprouts’ chemical composition (Andini et al., 2019).
The crucial problem connected with the application of modified conditions as a way of increasing the nutritional value of sprouts is the difficulty of predicting the effect of the factor used. This may result from the genetic variation of germinated sprouts and grains. The application of light-emitting diodes and biofortification of sprouts in deficient elements are promising methods. Each of the attempts to induce abiotic stress will be associated with an increase in the cost of the sprouting process. However, such a method is still less expensive and more acceptable than genetic modification.
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