Processing and cooking effects on glucosinolates and their derivatives

CHAPTER 6

Processing and cooking effects on glucosinolates and their derivatives Nieves Baenas1, M. Elena Cartea2, Diego A. Moreno3, María Tortosa2, Marta Francisco2 1

Institute for Nutritional Medicine, Molecular Nutrition Group, University Medical Center SchleswigHosltein Campus Lübeck, Lübeck, Germany; 2Group of Genetics, Breeding and Biochemistry of Brassicas, Misión Biológica de Galicia (MBG-CSIC), Pontevedra, Spain; 3Phytochemistry and Healthy Foods Lab, Department of Food Science and Technology, CEBAS-CSIC, Murcia, Spain

Contents 6.1 Introduction 6.2 Postharvest storage and packaging conditions 6.3 Industrial nonthermal technologies 6.4 Industrial thermal technologies 6.5 Culinary treatments 6.6 Processed food ingredients enriched in GLS 6.7 Conclusions References

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6.1 Introduction The glucosinolates (GLS) are a large group of sulfur- and nitrogencontaining compounds with a common structure which comprises a b-Dthioglucose group, a sulfonated oxime moiety and a variable aglycone side chain derived from one of eight natural amino acids that determine the final chemical structure of GLS, being methionine, tryptophan, or phenylalanine the common known (Sønderby et al., 2010). The latest secondary metabolites are mainly found in the Brassicaceae family of plants. This family includes a wide range of horticultural crops, many of them with economic significance and extensively consumed as commodities and used in the industry worldwide. The principal vegetable species are Brassica oleracea (i.e., broccoli, cabbage, cauliflower, kale, Brussels sprouts), Brassica rapa (i.e., turnip, Chinese cabbage, pak choi), Brassica napus (i.e., rapeseed, leaf Glucosinolates: Properties, Recovery, and Applications ISBN 978-0-12-816493-8 https://doi.org/10.1016/B978-0-12-816493-8.00006-8

Copyright © 2020 Elsevier Inc. All rights reserved.

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rape), Raphanus sativus (radish), and Sinapis alba (mustard). In recent decades, GLS and their derived forms, isothiocyanates (ITC), have attracted the interest of scientific community because these bioactive compounds have been associated with some important human health benefits including the reduction of the risk of certain cancers and cardiovascular diseases (Traka, 2016). The seasonal and perishable nature of Brassica vegetables imposes the need of preservation to make food available for later consumption and for delivery at longer distances from the agricultural areas. Thus, before delivering to the consumer, the main Brassica food products are subjected to diverse postharvest treatments including cutting, chopping, storage, refrigeration, and packaging. Moreover, industrial nonthermal and thermal treatments are used for vegetable preservation, fresh or processed, which is expected to give beneficial effects on the vegetable properties and increasing shelf-life by avoiding growth of microorganisms (Nugrahedi et al., 2015). Finally, the domestic culinary methods are varied depending on the types of the vegetables, the local customs, and the quality attributes of intended products. All of these managing practices, processing and preparation, especially those involving heat, can considerably change the content of GLS. In this sense, it is estimated that the average loss of GLS in Brassica during processing is approximately 40% (Francisco et al., 2017). GLS are relatively stable in the plant cell. However, when Brassicaceae vegetables are processed, such as during cutting or chopping, tissues disrupt and the GLS come into contact with myrosinase (thioglucoside glucohydrolase EC 3.2.1.147), which is stored in a different vacuole in the cell (Fig. 6.1). Hydrolysis implies the enzymatic breakdown of the thioglucoside linkage with the release of glucose and an unstable aglycone, which originates a series of rearrangement products such as ITC, nitriles, thiocyanates, epithionitriles, and oxazolidines (Grubb and Abel, 2006). ITC are the most common hydrolytic products found in the cruciferous foods; however, the conditions under which hydrolysis of GLS occurs, such as the presence of epithiospecifier proteins (ESPs), thiocyanateforming proteins, and nitrile-specifier proteins, as well as the reaction conditions (pH, presence of Fe2þ, temperature, and hydration), will affect the respective proportions of the chemicals produced. GLS breakdown is under genetic control, thus, for example, the synthesis of nitriles and epithionitriles could be regulated by genetic variation at the ESPs locus, which activity specifically affects the ratio of nitrile/ITC production (Burow and Wittstock, 2009).

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Figure 6.1 Schematic illustration of the main mechanisms responsible for the glucosinolate hydrolysis during Brassicaceae vegetable processing (Grubb and Abel, 2006; Burow and Wittstock, 2009). ESP, epithiospecifier protein; GLS, glucosinolate; ITC, isothiocyanate.

Besides the health-promoting effects associated with ITC, most of the degradation products of GLS are responsible for the characteristic taste and aroma of Brassicaceae plants. Thus, when they are presented in high concentrations, they can contribute to undesirable strong taste, bitterness, or pungency, which is of extreme importance for the consumer acceptance (Fenwick and Heaney, 1983). Therefore, it becomes evident that controlling myrosinase activity during processing is of particular interest to increase the quality of the product and the accessibility and bioavailability of ITC (Miglio et al., 2008).

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Predicting the degree of GLS changes and losses after processing and the nature of their hydrolysis products formed is a difficult task because of the high number of parameters that affect the process. In general, these factors include the classes of GLS present in the plant material, storage conditions (such as temperature variations, freezing, or controlled atmosphere packaging), intensity of postharvest treatments (for instance, thermal or not thermal technologies), and cooking methods (such as chopping and the amount of cooking water used or even the temperature of the water at the start of the cooking) (Hanschen and Schreiner, 2017). This chapter focuses on the review of the effect of different postharvest industrial processing methods and culinary treatments on the GLS content in Brassicaceae foods, evaluating the optimum conditions to increase the final intake of healthy GLS and ITC by the consumer. Furthermore, the effect of new emerging processed food ingredients enriched in GLS is discussed.

6.2 Postharvest storage and packaging conditions The content of GLS in cruciferous vegetables can be significantly affected by transport and storage conditions, from harvest to consumer delivery. The main influencing parameters are the time, temperature, and the atmosphere packaging. Controlling the influence of these parameters on the preservation and bioavailability of GLS may have a big impact on the healthpromoter effects of Brassicaceae vegetables for the population. When Brassica vegetables (broccoli, Brussels sprouts, cauliflower, and cabbages) were stored at ambient temperature (12e22 C) for 7 days, there was not a significant decrease in the GLS content; however, it may be explained because of the dehydration of the tissues, being the decay visibly started in those vegetables (5%e9% loss of weight). On the other hand, after their storage for 7 days in a domestic refrigerator (4e8 C), there were found small decreases in GLS contents (11%e27%), being the losses of glucoiberin, glucoraphanin, and glucoalyssin higher than those of sinigrin, gluconapin, and progoitrin. However, weight changes of these vegetables stored at low temperatures (1%e4%) were smaller compared with the ones stored at ambient temperature (Song and Thornalley, 2007). Differences in total GLS contents after harvest also depend on the existing GLS classes. Indole GLS generally are more sensitive to storage conditions than the aliphatic or aromatic GLS (Song and Thornalley, 2007). In broccoli heads, the content of the indole glucobrassicin and 4-methoxyglucobrassicin GLS were decreased (50%) during storage

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(9 days, 85%e90% HR, 1e2 C) and the content of the indole neoglucobrassicin increased 10-fold at this time. Altogether, total indole-GLS content was decreased by 30%, no changes were found in the aromatic GLS, and an increase of aliphatic GLS was found, being mainly derived by the increase (fivefold) of glucoraphanin during storage (Fernández-León et al., 2013). Many studies have been paid much attention to the aliphatic GLS glucoraphanin, mainly present in broccoli, in which hydrolysis product, the ITC sulforaphane, has been related to health-promoter effects of Brassica consumption. Some authors showed a higher reduction of glucoraphanin in broccoli inflorescences after 5 days of storage at room temperature (85%) compared with cold storage (31%) or freeze (48%) (Rodrigues and Rosa, 1999). Rangkadilok et al. (2002) showed a 55% loss of glucoraphanin after 3 days at 20 C in open boxes, while a similar loss was found after 7 days in broccoli heads stored in plastic bags. In addition, a 50% decrease in glucoraphanin after 7 days at 20 C was found in broccoli heads, while no decrease was reported after 7 days at 4 C. In broccoli heads stored at cold temperatures (1e4 C) and high relative humidity (90%e99%) for 28 days, not deleterious effects on the levels of aliphatic GLS were found (Winkler et al., 2007). Therefore, cool temperatures (0e4 C) are essential to maintain quality, and the relative humidity appears to be a critical factor for GLS retention when storage temperatures are higher than 4 C, and then, very high relative humidity (98%e100%) is recommended to maintain cellular integrity and prevent the contact of myrosinase with the GLS (Rangkadilok et al., 2002). After harvest, also a prestorage at 0 C for 7 days before storage at 10 C for 3 days was the most favorable to maintain contents of total aliphatic, total indole, or individual GLS in broccoli heads, also delaying senescence (Rybarczyk-Plonska et al., 2016). Indeed, temperatures of 0e2 C should be used immediately after harvesting for up to 10 days in Brassicaceae species which quickly undergo microbial growth, such as the perennial wall-rocket (Diplotaxis tenuifolia), which delay would result in shelf-life reduction (Caruso et al., 2018). Freezing Brassica vegetables is also a useful method to maintain GLS content during storage. During freezing, the concentrations of bioactive molecules could be altered, and thus the potential health benefits could change. Different broccoli cultivars after industrial freezing showed an increased extractability of GLS, which could be explained because an improvement in the extraction process due to the modifications of plant cell

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membranes caused by the ice crystals (Alanis-Garza et al., 2015). However, during thawing, the enzyme myrosinase could hydrolyze GLS because of tissue disruption in the frozen vegetables, leading to the formation and loss of ITC in the plant before consumption. Therefore, a previous quick blanching step could be needed to inactivate myrosinase enzymes and avoid degradation of ITC during thawing, which contribute to the maintenance of GLS levels during consumption (blanching thermal treatment is explained and discussed in Section 6.4). The use of packaging films (with or without holes, different polymers, etc.) and modified atmosphere packaging (MAP), during storage of whole or fresh-cut cruciferous vegetables, appears to be a useful tool to extend their shelf-life, being one of their purposes to prevent myrosinase and GLS contact by tissue degradation, and therefore, reducing hydrolysis of GLS to ITC during storage. In this sense, the use of MAP with 1% O2 þ 21% CO2 provides a suitable environment for broccoli and cauliflower florets during storage, maintaining the GLS contents after 7 days at 8 C (Schreiner et al., 2007). Accordingly, broccoli heads storage with MAP at 4 C for 10 days maintained glucoraphanin concentration and total GLS content compared with day 0 samples and control air packaging samples (Rangkadilok et al., 2002). The treatment of stems of Chinese kale with 10 mL/L of 1methylcyclopropene (1-MCP), an ethylene inhibitor, at 20 C for 24 h in the dark, extended the shelf-life of these vegetables for 7 days at the same temperature, delaying yellowing and maintaining a 10% more GLS content compared with the control (Sun et al., 2012). Similar results were found in broccoli florets treated with 1-MCP (2.5 mL/L for 6 h at 20 C), where the degradation of GLS was decreased by 20% after 5 days more at 20 C (Yuan et al., 2010). The maintenance or even the increase of GLS contents during storage time depends not only on time and temperature but also on the stage of vegetables at harvest and packaging materials used, which should be optimized to avoid alterations of the whole quality of these fresh products.

6.3 Industrial nonthermal technologies During the last two decades, different nonthermal technologies, such as high pressure processing (HPP), pulsed electric fields (PEFs), ultraviolet (UV) irradiation, and ultrasounds treatments, among others, have been used for microbial inactivation in the food industry, while maintaining quality, health, and nutritional values, as well as organoleptic properties, of fresh and

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processed vegetables. In this sense, the use of nonthermal technologies as pre- or postharvest treatments in cruciferous vegetables may be a strategy to maintain their bioactive compound contents and enzymes activities, which is not possible using traditional thermal technologies, such as pasteurization (Oms-Oliu et al., 2012). Among the nonthermal processing technologies, HPP, also called high hydrostatic pressure, is the most successfully commercialized minimal processing technology for packaged food. This process eliminates food pathogens at room temperature and extends the shelf-life of plant foods circulated through the cold chain, maintaining also their health and nutritional attributes (Huang et al., 2017). In the HPP plant-derived product market, fruit beverages exhibit the fastest growth, following by fresh-cut fruits and vegetables, extending the shelf-life of all these products by inhibiting pathogen growth and without the addition of preservatives. The existing production conditions for HPP are typically a pressure from 200 to 600 MPa, duration approximately 5 min, and low or moderate temperatures (40 C). Several works have evaluated the impact of HPP on GLS and their derivative compounds, as well as on the myrosinase activity (Table 6.1). For ITC formation, the action of the myrosinase enzyme is necessary, which has been studied to be active after HPP at 100e600 MPa; however, a reduction of its activity has been observed at higher pressures (600e800 MPa). Higher concentrations of ITC were found after 600 MPa treatment compared with traditional thermal methods, such as blanching, in shredded (2e3 mm width) vacuum packed white cabbage (Alvarez-Jubete et al., 2014b). Cell permeabilization has been shown to occur during pressure treatment finding a larger proportion of GLS hydrolyzed after treatments at 400e600 MPa (Van Eylen et al., 2007). In broccoli heads, no degradation of GLS was found after 15 min of elevated pressures (300e500 MPa) at 20 C, having myrosinase only limited activity. However, when the duration (35 min) or the temperature (40 C) of the treatment was increased, more than the 80% of GLS were able to be degraded after extraction and, therefore, mainly hydrolyzed to the derivatives bioactive compounds ITC before consumption (Van Eylen et al., 2009). In broccoli sprouts, different pressures (100e600 MPa) were applied for 3 min at 30 C, showing a lower conversion from GLS into ITC in the sprouts treated at 100e300 MPa than after 400e600 MPa treatments. This effect suggests a higher decompartmentalization or cell disintegration in the sprouts tissues, as well as a possibly ESP enzymes inactivation with

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Table 6.1 Examples of nonthermal treatments used to preserve quality parameters and enhance health-promoting compound content in cruciferous vegetables. High pressure processing (HPP)

In shredded white cabbage vacuum packed, higher concentrations of isothiocyanates (6.5-fold), and therefore higher hydrolysis of GLS, were found in samples processed at 600 MPa (20e40 C) when compared with blanching, avoiding myrosinase inactivation. Fresh broccoli sprouts treated with HPP at 600 MPa, 3 min, and 30 C showed an 85% conversion of GLS hydrolyzed to ITC compared with thermally treated samples. HPP (400e600 MPa, 3 min, and 5 C) allowed glucosinolates hydrolysis up to 70% in 7-day old seedlings of Brussels sprouts compared with untreated samples. In broccoli heads, no degradation of glucosinolates after HPP at 100e500 MPa, 15 min, 20 C and degradation of 80% of total GLS after HPP at 300 MPa, 35 min, 20 C or 300 MPa, 15 min, 40 C. HPP at 300 MPa and 20 C produced some inactivation of myrosinase in broccoli florets; however, higher aliphatic and indole GLS hydrolysis were detected compared with the thermally treated samples. High HPP at 700 MPa totally inactivated myrosinase activity.

Alvarez-Jubete et al. (2014b)

Westphal et al. (2017)

Wang et al. (2016)

Van Eylen et al. (2009)

Frandsen et al. (2014)

Pulsed electric field (PEF)

Moderate PEF (4 kV/cm for 525 and 1000 ms) increased twofold glucosinolates content in broccoli flowers and stalks compared with low PEF (1 kV/cm). Moderate PEF (3e10 kV/cm) enhanced glucosinolates retention in broccoli purée compared with high PEF (20 kV/cm).

Aguiló-Aguayo et al. (2015)

Frandsen et al. (2014)

Ultraviolet light (UV)

UV-B (15 kJ/m2) treatment singled or combined with UV-C (9 kJ/m2) enhanced glucoraphanin (up to 25%) and glucobrassicin (up to 85%) content in “Bimi” broccoli by-products.

Formica-Oliveira et al. (2017)

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Table 6.1 Examples of nonthermal treatments used to preserve quality parameters and enhance health-promoting compound content in cruciferous vegetables.dcont'd

Preharvest UV-B radiation at 0.3 kJ/m2 per day for 5 days increased twofold aliphatic GLS in broccoli sprouts compared with control and higher doses (0.9e2 kJ/m2 per day).

Mewis et al. (2012)

Other technologies

Ultrasound (US) treatment while freezing immersion of red radish slices decreased the time of processing, maintained quality physical attributes, but increased volatile compounds formation, such as isothiocyanates, due to cell damage while freezing/thawing process. Application of ethylene (1000 ppm, 24 h, 20 C) increased both aliphatic and indole GLS (up to twofold) content in broccoli heads. Application of the elicitors sucrose (146 mM) and glucose (277 mM) for 5 days before harvest enhanced GLS content by 40% in different Brassicaceae sprouts. Preharvest salt stress (4 dS/m) started 5 days after transplanting cauliflowers increased the concentration of indole GLS (twofold) at harvest day. Dark conditions during 10 days after sowing enhance the content of aliphatic and indole GLS (7-fold) in Chinese cabbage sprouts compared with control in the light. Modified atmospheres packaging (MAP) at 4 C for 10 days maintained GLS content in broccoli heads. Thyme oil treatment on broccoli sprouts at sowing time enhanced GLS content at harvest day and during cold storage for 15 days, while inhibiting microbial growth.

Xu et al. (2015)

Villarreal-García et al. (2016) Baenas et al. (2014)

Giuffrida et al. (2018) Kim et al. (2014)

Rangkadilok et al. (2002) El-Awady et al. (2016)

high pressures, making the formation of ITC higher than the formation of ITC-nitriles, which have shown lower bioactive activities (Van Eylen et al., 2009; Westphal et al., 2017). In Brussels sprouts seedlings, the maximum degradation of GLS was also observed after high pressurization conditions (600 MPa), while 800 MPa resulted in almost complete inactivation of myrosinase, accompanied by a higher preservation of intact GLS (Wang et al., 2016). In addition to increase the ITC formation, HPP-treated samples

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also showed significantly higher levels of total phenolic compounds and higher antioxidant capacity when compared with thermally treated samples (Lafarga et al., 2018). This technology is very important to conserve the myrosinase activity and GLS content while reducing or eliminating foodborne pathogens on seeds or sprouts (Yishan et al., 2013), which carry a risk of disease outbreak, as temperature and humidity are ideal conditions for bacteria growing. These seed treatments could decrease the germination rate or the sprouting yield, which should be carefully studied to the different Brassica species and varieties (Neetoo and Chen, 2010). PEF treatments can lead to pasteurization at room temperatures using electrical field strengths of 10e30 kV/cm and short pulses of 1e10 ms (Table 6.1). Aguiló-Aguayo et al. (2015) optimized the PEF conditions to maximize GLS levels in broccoli florets and stalks, increasing twofold their content using 4 kV/cm for 525 and 1000 ms compared with 1 kV/cm PEF treatment (Aguiló-Aguayo et al., 2015). On the other hand, high electric field strength (20 kV/cm) in broccoli purée showed a decrease in the level of aliphatic GLS and indol-3-ylmethyl-GLS compared with the same samples treated with low electric field strength (3e10 kV/cm), suggesting that stronger PEF, independently of the number of pulses, may produce high degree of membrane permeabilization in the cells and, therefore, allowing the hydrolysis of intact GLS by myrosinase enzymes during the processing of vegetables (Frandsen et al., 2014). According to the previous results, PEF processing methods should be further studied to establish the appropriate conditions to enhance GLS concentrations in the samples after treatment, avoiding cell damage and the hydrolysis of these compounds to ITC in processing samples. The use of UV light could efficiently reduce the microbial contamination of plant foods and increase the concentration of GLS (Formica-Oliveira et al., 2017). Different authors reported that postharvest treatments with UV-B irradiation enhanced the GLS content of Brassica vegetables (Table 6.1). The exposure of broccoli sprouts to UV-B (0.3 kJ/ m2 for 5 days) led to an increase of aliphatic GLS (twofold), mainly glucoiberin and glucoraphanin, at 2 h after application, which was related to an increase in the expression of some genes related to stress response and the final step of GLS biosynthesis. In this work, also low UV-B doses induced higher glucoraphanin and glucobrassicin enhancements in broccoli sprouts regarding higher UV-B doses (Mewis et al., 2012). Also combined treatments of high UV-B (15 kJ/m2) and moderate UV-C increased the healthiness of broccoli edible florets with the highest glucoraphanin

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contents after 72 h at 15 C, which is an important attribute for the fresh market, increasingly concerned about preserving health-promoting compounds in vegetables (Formica-Oliveira et al., 2017). On the other hand, by-products from the Bimi broccoli processing industry, leaves and stalks, could be also treated with moderate UV-B (5, 10 and 15 kJ/m2), single or combined with UV-C (9 kJ/m2), to enhance their bioactive compounds, being those values compared with the edible florets (Formica-Oliveira et al., 2017). This increment in bioactive compounds also affects the content of phenolic compounds in broccoli florets after UV-C treatment (8 kJ/m2), which was correlated to an increased phenylalanine ammonia lyase activity (Lemoine et al., 2010). The effect of light treatment (fluorescent and light-emitting diode green light, LED) on shelf-life, visual quality, and bioactive compounds in broccoli florets was investigated, and the results showed that the light treatment extended shelf-life and markedly increased the GLS. After a pretreatment of 7 days at 0 C, followed by 3 days of exposure to visible light (19 mmol/m2 per second) at 10 C, significant increases (twofold) in the aliphatic GLS glucoiberin and glucoraphanin were found in broccoli heads, being indole GLS not altered (Rybarczyk-Plonska et al., 2016). The mechanisms by which light maintaining GLS content are not clear. It is possible that the response of phytochemical synthesis in broccoli florets depends on light dosage and quality, which probably is regulated by some photosynthesis or photomorphogenesis pathway. The LED green light exposure could be a useful technique in extending shelf-life and maintaining visual or nutrient quality (Jin et al., 2015), when applied in combination with refrigeration or CA during storage, transport, and distribution of cruciferous foods. Leaves of Brassicaceae plants are recognized for their nutritional value and are familiar of salads, soups, and pickles around the world. The effects of radiation processing (0.5e2 kGy) and storage on the GLS content of cabbage leaves were investigated, and sinigrin, the major GLS of cabbage, was enhanced favoring also the enhancement of allyl ITC (AITC) in the volatile oils of the irradiated vegetable. Besides extending shelf-life and safety, radiation processing can have an additional advantage in improving the nutritional quality of cabbage (Banerjee et al., 2014). Ultrasound technologies (US), based on sound waves at frequencies above 20 kHz, can be used for preservation of liquid products or solid food embedded in liquid (typical water), which generate high temperatures and pressures resulting in the cavitation phenomenon, affecting cell walls and

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membranes. This technology could be applied in a continuous process line using baths or vibrating systems (Cravotto and Binello, 2016). In this sense, US treatments have been used to secure the microbial safety of sprouts by treating broccoli seeds (150 or 175 W, with 30 kHz or 20 kHz, respectively; Jung et al., 2006). Indeed, this technology has been used as preservative treatment during the freezing processing by immersion of broccoli florets to maintain firmness (Xin et al., 2014). However, as far as we are concerned, the evaluation of GLS content in cruciferous vegetables after US processing has not been published yet. In red radish slices processed with US along with freezing immersion, it was reported that the content of sulfur-derived compounds from GLS, such as ITC, was higher compared with fresh samples, suggesting some cell damage during processing. Nevertheless, this US-freezing treatment retains a higher content of vitamin C and total phenolic compounds compared with slow freezing. In addition, this technology can minimize the time of treatment, reduce thawing time, and overall color changes due to the previous formation of smaller ice crystals inside the tissues, conserve the nutritional value, and, therefore, contribute to the retention of the final quality of the frozen vegetable (Xu et al., 2015). Other pre- or postharvest methods for cruciferous vegetables processing to enhance GLS content is the use of abiotic stresses, such as high light, salinity, wounding, or application of phytohormones, which induce the stress response of plants to produce secondary metabolites, and, therefore, the accumulation of high levels of bioactive compounds (del Carmen Martínez-Ballesta et al., 2013). Preharvest salt stress (4 dS/m) started 5 days after transplanting increased the concentration of indole GLS (twofold), total polyphenols, and ascorbic acid in a genotype-dependent way in fresh-cut cauliflower florets, at the harvest day and during storage, preserving also color and firmness degradation. Therefore, salt stress improved both organoleptic and nutraceutical profile of fresh-cut cauliflower (Giuffrida et al., 2018). The exogenous application of phytohormones, such as ethylene, salicylic acid, and methyl jasmonate, also enhances the content of individual GLS, among other bioactive compounds. These natural compounds activate plant defense mechanisms, which involve the biosynthesis of GLS, among other defense bioactive metabolites. Broccoli heads treated with ethylene (1000 ppm, 24 h, 20 C) after harvest increased glucoraphanin and 4-hydroxyglucobrassicin concentration by w50% and w200%, respectively, as compared with the control (Villarreal-García et al., 2016). On the

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other hand, in broccoli florets, ethylene (0.25%, v/v) and MeJA (250 mM) sprayed preharvest treatments only induced the levels of indole GLS (neoglucobrassicin and 4-hydroxyglucobrassicin, by w200% and w100%, respectively), indicating that genes related to indolic GLS biosynthesis are more susceptible to be induced by exogenous phytohormones rather than those playing a role in aliphatic GLS biosynthesis (Mikkelsen et al., 2003). Not only phytohormones but also other natural compounds, such as oligosaccharides, amino acids, and inorganic compounds, could be useful tools to increase health-promoting phytochemicals in Brassica vegetables as pre- or postharvest industrial treatments. In this sense, glucose (277 mM) and sucrose (146 mM) were sprayed on Brassicaceae sprouts for 5 days before harvest, showing a w40% increase of total GLS in B. napus, B. oleracea, and R. sativus species (Baenas et al., 2014). It must be emphasized that in these species, glucoraphanin and glucoraphenin, widely studied because of their healthy derived ITC, were enhanced around 30%e60% under sugar spray treatments. Therefore, the accumulation of specific GLS after treatments with abiotic stresses depends on several factors, highlighting the intensity and duration of the treatment, and the specie, variety, and developmental stage of the plant. The use of active edible coatings, such as essential oils, may represent a viable approach for achieving microbial stability and preserving quality of plant foods. Broccoli sprouts treated with thyme oil at sowing time showed a higher concentration of total GLS at harvest day, as well as intact glucoraphanin content, polyphenolic content, and seed germination index. Indeed, thyme oil also prevented GLS degradation from harvest to day 15 of storage and inhibited any fungal growth and coliform bacteria (El-Awady et al., 2016). According to the previous information, nonthermal treatments may preserve and improve the nutritive value of Brassicaceae vegetables, delivered whole, cut, or processed, thus giving opportunities to preserve health and safety attributes and develop innovative healthy food products. Studies about specific cruciferous vegetables are required to optimize processing conditions and targeted compounds content, as well as to improve the bioaccessibility and bioavailability of GLS and ITC (Barba et al., 2017).

6.4 Industrial thermal technologies Thermal treatments including pasteurization, commercial sterilization, and thermal pretreatments, such as blanching, have been used in the food

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industry since ancient times with the aim of not only delaying the inevitable deterioration of perishable foods between production and consumption but also making foods edible. They are conducted before freezing and canning to inactivate bacteria and enzymes involved in food deterioration and remove entrapped air. Thermal processing operations are conventionally classified according to the intensity of heat used: pasteurization (65e85 C), sterilization (110e121 C), and ultrahigh temperature treatment (140e160 C). In addition, Brassica vegetables are often preserved by low temperature process such as freezing. This method provides a significant extended shelf-life and has been successfully employed for long-term preservation. In this section, the effect of high and low thermal processing on GLS content will be reviewed. The effect of high temperatures on stability of bioactive components and antioxidant activity has been discussed in different Brassica vegetables (Podsedek, 2007). Oerlemans et al. (2006) studied the thermal degradation of GLS at different temperatures in red cabbage. Degradation of all the identified GLS occurred when heated at temperatures above 100 C. The indole GLS 4-hydroxyglucobrassicin and 4-methoxyglucobrassicin appeared to be most susceptible to thermal degradation, even at temperatures below 100 C. Authors also found that canning was the most severe heat treatment resulting in a substantial reduction of all measured GLS (73%), thereby having a substantial effect on the health promoting potential of the GLS in canned Brassica vegetables. Likewise, in canned broccoli, only 16% of original vitamin C was retained and a decrease of vitamin C by 66% was observed after blanching and canning of Brussels sprouts (reviewed by Podsedek, 2007). Cartea et al. (unpublished data) also studied the effects of heat treatments before canning in turnip greens and kale. GLS content was drastically reduced in both crops, after leaching, whereas the content of minerals and vitamin C was retained, and phenolic compounds and antioxidant capacity were increased in canned kales and canned turnip greens. The cooking waters resulting from the industrial processing of turnip greens and kales showed high contents of GLS 45 min after blanching, suggesting that waters, which are currently discarded in food industry, could be considered as a by-product for obtaining beverages in the form of juices or shakes. Zielinski et al. (2005) compared the effects of pasteurization (95 C for 30 min) and sterilization (1.5 atm for 30 min) on changes in rapeseed and radish sprouts. Both thermal treatment processes affected negatively the

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content of GLS, phenolic compounds, tocopherols (alpha-, beta-, gamma-, and delta-), and the antioxidant capacity in both crops, triggering sterilization higher decreases in both aliphatic and indole GLS. The effect of the pasteurization process (80 C for 10e30 min) on the content of indole-3carbinol, indole-3-acetonitrile, ascorbigen, and 3,30 -diindolylmethane was also investigated in cabbage (Ciska and Honke, 2012). Significant changes were only observed in contents of ascorbigen and 3,30 -diindolylmethane, being these compounds decreased by 20% due to thermal degradation. The effects of several industrial processing methods (glass jar, canning, vacuum sealed plastic trays, and fourth range packaging) on the contents of GLS, antioxidants (vitamin C, polyphenols), minerals, and the antioxidant capacity in turnip greens were investigated by Cartea et al. (unpublished data). GLS levels and phenolic compounds were significantly decreased after all processing methods because the thermal treatments used during blanching and sterilization process. Indeed, vacuum sealed plastic trays processing method was a good practice for the preservation of GLS, vitamin C, Fe and Ca, whereas elevated levels of phenols were observed in canned turnip greens. Commercial freezing is a feasible approach to maintain the freshness of Brassica vegetables and to extend their shelf-life. Song and Thornalley (2007) demonstrated the effect of freezing-thawing without previous inactivation of myrosinase enzyme on GLS content in different Brassica crops, being the loss of 10%e53% of individual GLS and the 33% of total GLS. During this process, significant losses of GLS can occur due to the fracture of plant cells and cellular integrity disruption, thus, the accessibility of myrosinase enzyme makes a complete GLS hydrolysis (Johnson, 2000). To avoid this GLS breakdown, as well as the loss of other quality factors, before freezing vegetables should be steamed or water blanched to inactivate enzymes that cause product deterioration. Blanching is mostly applied as pretreatment step before freezing, canning, or drying. This treatment is usually used for inactivating enzymes, especially oxidative enzymes but also myrosinase enzymes, thus, preserving color, flavor, and nutritional value. Hot water and steam are the most commonly used heating media for blanching in the industry, but microwave and hot gas blanching have also been studied. The effects of blanching and freezing on the GLS content have been widely reviewed and vary depending on the treatment conditions. It has been demonstrated that blanching process (5 min) reduces the GLS content significantly (>50%) particularly because of the mechanisms of leaching following cell lysis and diffusion, and partly due to thermal and

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enzymatic degradation (Wennberg et al., 2006). Cieslik et al. (2007) also observed a decrease by 2%e30% for total GLS levels in several Brassica vegetables (Brussels sprouts, white and green cauliflower, broccoli, and curly kale) after blanching-freezing. Likewise, Cai et al. (2016) observed that GLS levels were significantly decreased in broccoli florets after prefreezing processing, suggesting that some improvements in industrial freezing processing would be needed to attenuate the decrease in GLS content. Optimizing the industrial blanch-freezing of broccoli and cauliflower may retain the GLS content of its fresh material after frozen storage for several months and it would be a good method to preserve the beneficial attributes associated with these vegetables. For instance, blanch-frozen (105 s at 91.8 C) Brassica retained the GLS content of its fresh counterpart after storage at e20 C for up to 90 days, while the myrosinase activity was reduced by 93% (Rungapamestry et al., 2007a,b). Alanis-Garza et al. (2015) reported the effect of industrial freezing on the concentration of GLS, total phenols, and carotenoids in broccoli. Authors found that industrial freezing increased the extractability of total GLS and total carotenoids, whereas total phenols remained constant in most broccoli cultivars. Until now, the mechanism by which blanch-frozen vegetables present higher extractability of plant bioactive molecules is unclear. According to Pellegrini et al. (2010) and Alanis-Garza et al. (2015), the increase on bioactive compounds might be attributed to cell membrane disruption occurring during blanching and freezing, resulting in a greater accessibility of the compounds to extraction solvents. Freezing of vegetables can lead to the development of ice crystals within the plant matrix. These ice crystals can affect the structure of plant cell membranes, inducing modifications in their permeability and improving the extraction process of the compounds (Alanis-Garza et al., 2015; Rungapamestry et al., 2007a,b). Blanching treatments for processing Brassica vegetables before freezing often exceed the limit of the enzyme myrosinase stability, being the ITC formation totally affected, resulted blanched broccoli (2 min in water at 93 C) in a 65% reduction in sulforaphane formation (Howard et al., 1997). This thermolabile enzyme shows 90% of degradation after treatments at 80 C for 10e60 min. When the blanching protocol was modified to heat samples only to 76 C, lipoxygenase but not peroxidase and myrosinase was inactivated and 82% of the sulforaphane present in unheated broccoli remained (Matusheski et al., 2004). At 66 C, there was significantly more sulforaphane formation than in the unblanched control

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(Matusheski et al., 2004). This is attributable to the inactivation of the thermally unstable ESP, which are also present in the vegetable tissues, and can hydrolyze the GLS to the nonbioactive compound nitriles. In this sense, postharvest practices may induce the GLS breakdown to ITC over nitriles, boosting the health-promoter characteristics of cruciferous foods, being nitriles much less bioactive than ITCs, and it would be favorable to decrease the production of them (Bell and Wagstaff, 2014). A solution to achieve a greater yield of ITC after the consumption of cruciferous vegetables subjected to thermal treatments could be the use of an external source of myrosinase enzymes, such as from powdered mustard or radish seeds, improving the bioavailability of ITC, as it was found after consumption of cooked broccoli with mustard powder, being the bioavailability of sulforaphane increased by fourfold (Okunade et al., 2018).

6.5 Culinary treatments Cooking is the postharvest process that has arguably the major effect on phytochemical content in Brassica foods (Jones et al., 2006). The type and time of cooking used can also dramatically affect the GLS at the time of consumption (Miglio et al., 2008) Besides, chopping, crushing, and food preparation will stimulate the formation of anticarcinogenic ITC on hydrolysis of GLS by intervention of the myrosinase (Lafarga et al., 2018). A substantial proportion of cruciferous crop consumption is as the fresh vegetable, as a salad, and its preparation involves intensive mechanical processing (cutting or shredding). It appears obvious that the shredding intensity has a large influence on GLS content immediately after the processing. Song and Thornalley (2007) found that Brassica plants shredded finely demonstrated significant decrease in the contents of GLS up to 75% over 6 h (Song and Thornalley, 2007). In another work, the contents of GLS in chopped raw Brassica vegetables were investigated (Verkerk, Dekker and Jongen, 2001). Results demonstrated that aliphatic GLS were partially broken down in cabbage, whereas high level of indole GLS were observed for chopped cabbage and broccoli stored at room temperature. After 48 h storage, chopped white cabbage showed higher contents (15 times more) in indole GLS. Most of the aliphatic GLS contents were significantly reduced after chopping and storage. This reduction is mainly mediated by the action of myrosinase, which hydrolyzes the GLS as reported earlier. Thus, GLS levels do not necessarily decline rapidly after chopping and even induction

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can take place, but washed chopped vegetables show optimal conditions for myrosinase activity. Brassica vegetables are consumed mostly after cooking procedure involving heat (boiling, steaming, blanching, microwaving, stir-frying, and high pressure cooking) which induces significant changes in a plant’s chemical and physical composition. These changes can be both positive and negative depending on processing method and conditions (Miglio et al., 2008). In general, the nutritional quality of cruciferous foods is better preserved in little processing practices such as blanching or steaming than boiling, microwave cooking, and stir-frying process (Francisco et al., 2010; Rungapamestry et al., 2007a,b; Soares et al., 2017; Vallejo et al., 2002). Moreover, steam blanching resulted in an increased GLS content improving the health-promoting properties (Gliszczy nska-Swigło et al., 2006). Broccoli cooked in a convection steam oven at 125 C with 90% steam saturation for 8 min is characterized by the most desirable nutritive characteristics (Borowski et al., 2015). On the contrary, hot water immersion of Brassicaceae vegetables for a brief period of time (1e10 min) and using mild to high temperatures (50e100 C) decrease the GLS content (Francisco et al., 2010; Pellegrini et al., 2010; Rungapamestry et al., 2007a,b; Soares et al., 2017). During this cooking method, the heat is transferred mainly by convection of hot water into vegetable tissue (Nugrahedi et al., 2015). Because of the high temperature, myrosinase is denatured and GLS are thermally degraded, forming nitrile compounds and small amounts of ITC (Hanschen et al., 2012). However, some authors affirm that leaching is the major factor of the loss of GLS during this method. The heat transferred into the vegetable tissue will produce cell lysis, inducing the leach of both myrosinase and GLS into the cooking water. Therefore, this method leads to the highest losses in the GLS content (usually, more than 50%) (Barba et al., 2016). High pressure cooking process combines the effects of pressure and temperature to inactivate the enzymes and reduce the microbial count of product, being a milder alternative to pasteurization or sterilization (Oliviero et al., 2018). Anna Westphal et al. (2017) reported that a treated broccoli contains sixfold higher ITC concentration in comparison with raw sample. Whereas several enzymes are inactivated under high pressure treatments, myrosinase remains active, which explain the higher ITC concentration. In general, changes on GLS content are strongly influenced by processing time and temperature employed. Temperatures up to about 60 C will allow myrosinase activity, whereas higher temperatures will

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produce it denaturation (Verkerk and Dekker, 2004). Regarding treatment time, longer processing will increase cell lysis and thermal degradation and, therefore, will increase GLS losses (Nugrahedi et al., 2015). In general, steaming is one of the best thermal-processing methods to maintain high content of GLS as it avoids water leaching. Furthermore, the heating rate is lower in comparison with boiling and leads to lower rates of cell lysis and myrosinase denaturation (Conaway et al., 2001; Vallejo et al., 2002). Despite Brassica vegetables are most often consumed after heat treatments, they can also be subjected to alternative processes including fermentation or pickling (Soares et al., 2017). Fermentation is an old processing method that has formed a traditional part of the diet in many countries (Fellows, 2017). One of the most popular products among fermented Brassica vegetables is sauerkraut, which is obtained from the lactic fermentation of shredded and salted white cabbage (B. oleracea var. capitata). It is considered as the most typical dish from Germany, but is largely consumed in Eastern Europe and in some regions of the United States and Canada. To produce sauerkraut, the fresh raw Brassica material is first submerged in sodium chloride, usually from 1.5% to 3%. Then, fermentation could be conducted spontaneously by the microorganisms present naturally on the vegetable (natural fermentation) or by using starter cultures. During this process, GLS content is affected, to the extent that no GLS are detected in fermented cabbage and stored sauerkraut (Martinez-Villaluenga et al., 2009). However, different works reported the formation of several GLS breakdown products, including indole-3-carbinol, indole-3-acetonitrile, thiocyanate ion, and ascorbigen from glucobrassicin, 2-phenylethyl ITC from gluconasturtiin, and 1-cyano-3-methyl sulfinylpropane from glucoiberin, among many others (Ciska and Pathak, 2004; Daxenbichler et al., 1980; Tolonen et al., 2002). With regard to pickling method, raw vegetables, such as nozawana (B. rapa L.), are submerged in hot acetic acid solution and stored at room temperature for 48 h. As occurs after a fermentation process, most of GLS present in pickled Brassica are degraded to their breakdown products (Sosinska and Obiedzinski, 2011). By using these processing methods, myrosinase and its activity remain intact, which explains the high presence of GLS breakdown products in comparison with thermal-processed vegetables. Thus, the type and the level of GLS degradation products are strongly dependent on the content of native GLS of the raw materials, as well as on

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the fermentation and pickling conditions, such as salt concentration or maturation period (Nugrahedi et al., 2015; Suzuki et al., 2006).

6.6 Processed food ingredients enriched in GLS The journey of food from farm to plate is subjected to various losses. The first loss occurs at postharvest and processing levels, improper agricultural practices, and insufficient transportation and storage facilities. The losses at the consumer and retail levels due to stringent market and consumer requirements are at the same level in terms of millions of tons and according to the United Nation’s Food and Agricultural Organization (FAO), one-third of the food that is produced for human consumption is lost or wasted globally, accounting for around 186 kg of food per person lost annually (FAO, http://www.fao.org/docrep/014/mb060e/mb060e00.htm). Many by-products of the agrifood industry may be useful as sources of nutrients and potentially functional ingredients, giving the opportunity to obtain added value products. The marketable edible parts usually represent a minor part of the total crop biomass (e.g., inflorescences of broccoli, turnip greens and turnip tips, cabbage leaves, etc.) generating a vast amount of crop remains representing a useful resource rich in GLS, ITC, phenolic compounds (flavonoids, phenolic acids), carotenoids including b-carotene (provitamin A), vitamins (C, E, K, etc.), and minerals (Fe, Ca, Mn, Se, etc.) for the evaluation of by-product utilization in human diet, as well as feedstocks enriched in bioactive compounds for industry (DominguezPerles et al., 2010; Liu et al., 2018). The use of by-products is still limited at the industrial level, but the interest and applications are growing rapidly in present times and some of the latest findings in these opportunities for agrowaste recovery by sourcing GLS- and ITC-enriched products are presented in this section. To increase the Brassica vegetable consumption, several attempts have been made developing new ingredients and formulas, but unfortunately, due to their sensory characteristics, these vegetables tend to be disliked, prompting the research and food industry to develop new food products rich in cruciferous bioactive molecules. Broccoli sprouts are considered functional food as they are naturally enriched in GLS and therefore the broccoli sprout juice is becoming popular (Bello et al., 2018). During the juice preparation, the GLS (e.g., glucoraphanin) hydrolysis to bioactive SFN, and other products (e.g., SFN-nitrile), was studied. The ITC production during the juice preparation involves conversions to

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other forms (sulforaphane-amine or conjugation to glutathione (GSH), and with proteins) in reaction with other elements present in the food matrix. Therefore, all the new developed beverages, foods, snacks, ingredients, etc., enriched in GLS/ITC need protocols of research including the different phases of the demonstration of functionality from bioaccessibility and bioavailability to innocuousness and proven modes of action in biological activities of interest as health promoters, without missing the consumer acceptance (Deng et al., 2015; Dominguez-Perles et al., 2018). The development of a new apple beverage enriched in ITC from cauliflower by-products showed significant differences in smell and taste when adding 20% and 40% of extracts, and, therefore, the addition of 10% was selected as optimum, for a new and acceptable apple beverage rich in ITC (AmofaDiatuo et al., 2017), but research on bioaccessibility and bioavailability of the GLS/ITC is needed. Smoothies represent an excellent and convenient alternative to promote the daily consumption of fruit and vegetables to obtain their healthpromoting benefits. A new smoothie with cucumber (77%), broccoli (12%), and spinach (6%) was elaborated and treated thermally to prevent spoilage (T1, 3 min, 80 C; T2, 45 s, 90 C). The samples were stored in darkness at 5 and 15 C, and the vitamin C, phenolic compounds, and GLS studied during these stages. The glucobrassicin accounted for the 81% of the initial total GLS content and no losses of GLS were observed after T2, showing good quality and bioactive compound retention in a green fresh vegetable smoothie under cold storage (Castillejo et al., 2016). Organic green tea, one of the most-consumed beverages worldwide, is rich in bioactive compounds (flavonols and flavanols) and using this organic green tea as food matrix, novel beverages enriched in GLS from broccoli by-products (leaves and stalks) were tested for antioxidant capacity that would depend on the proportion of broccoli extracts added to the green tea (Dominguez-Perles et al., 2011). The distinct compounds present in the prepared beverages were identified by HPLC-PDA-ESI-MSn and Caco-2 and CCD-18Co cell lines were exposed to growing percentages (0.2%e5%) of infusions of distinct combinations of green tea and GLS from broccoli by-products. The broccoli GLS added to the green tea resulted in a combination of phytochemicals with in vitro antitumoral activity increased, for further developments in mechanistic models and the design of novel foods (Domínguez-Perles et al., 2012). The antioxidant-rich beverages (e.g., lemon-mustard seed extract) could be a novel designer nutraceutical

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foods, besides, the methodology of formulation of the beverages based on synergistic activities of multiple antioxidants could be successfully adopted industrially in development of innovative antioxidant-rich food products (Chakraborty and Bhattacharjee, 2018). The ITC play an important role in health promotion and cancer prevention due to their antibacterial, antiinflammatory, and anticancerogenic properties. When elaborating new beverages using GLs/ITC-enriched ingredients, the high reactivity of the ITC with other food components is very likely, and certain examples of these reactions has been documented, for example, in milk and curd after adding ITC-containing garden cress (Lepidium sativum L.) conjugates of ITC with amino acids were detected in the samples, as well as dithiocarbamates and thioureas (Kuhn et al., 2018). With regard to metabolism, the ITC react with GSH in the human body after consumption of ITC-containing foods, forming ITC-GSH conjugates, which are further metabolized via the mercapturic acid pathway, but the fate of the ITC in new food matrices, before consumption, merits further research and attention. The bioconversion of GLS to ITC is affected by many factors including heat and therefore cooking of Brassica products may result in significant loss of SFN production (see Sections 6.3 and 6.4). When developing a suitable food system as a vehicle for the delivery of ITC in the human diet in adequate quantities, these aspects need to be taken into consideration. For example, incorporating broccoli floret and stalk (by-products) ingredients in a dry-mix ready soup, when preparing the soups by microwave heating, the delivery of the ITC from GLS is possible (Alvarez-Jubete et al., 2014a), and therefore, the bioaccessibility and bioavailability of the final product must be evaluated, before designing any nutritional intervention. Incorporating vegetables containing phytochemicals (e.g., broccoli florets rich in GLS) into potato-based snacks and assessing their bioaccessibility and bioavailability in vitro and in vivo (intervention in human study) in comparison with equivalent steamed vegetables showed that significant quantities of freeze-dried vegetables can be incorporated into snacks with good retention of phytochemicals and similar bioavailability (Perez-Moral et al., 2018). The incidence of food intolerances and allergies including glutensensitivity disorders caused by allergic and immune reactions is rising worldwide. The gluten-free diet is the only approved method of treating gluten intolerance, and bearing this in mind, broccoli leaf powder rich in biologically active compounds (GLS/ITC) was incorporated in mini sponge

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cakes. The GLS content was higher than expected in the cakes, the incorporation of the broccoli ingredient increased the antioxidant capacity, and the overall sensory acceptance of the gluten-free mini sponge cakes with 2.5% broccoli leaf powder added as a starch substitute resulted in an optimal improvement in the nutraceutical potential of the new cakes without compromising their sensory quality (Drabi nska et al., 2018). Many authorities and public health services recommend adults and children to eat more vegetables. However, children tend to dislike and avoid eating vegetables. On the other hand, they do like pasta-like products and, therefore, Silva et al. (2013) incorporated GLS form broccoli in dried and cooked pasta and noodles. The GLS present in the pasta and noodles increase linearly with the volume fraction of broccoli powder up to 20%, a value much higher than that found in common commercial products (normally a few percent), and the combination resulted in acceptable and GLS-enriched pasta products (Silva et al., 2013). Hummus is a dip or spread made mainly with cooked mashed chickpeas blended with tahini, olive oil, lemon juice, and salt. The consumption of hummus is increasing worldwide and the recipe may be excellent for masking the organoleptic characteristics of bitterness of Brassica ingredients (GLS/ITC), which could potentially lead to consumer rejection. A formulation of hummus with broccoli allowed to obtain an acceptable product with up to 28 days shelf-life under refrigeration with also excellent bioactive quality (e.g., levels of glucoraphanin and sulforaphane) (Klug et al., 2018). Other possibility for the GLS/ITC when incorporated in hummus recipes as antimicrobials and, therefore, the use of 0.1%e1.5% AITC against five strains of each of Salmonella enterica and Listeria monocytogenes were tested in hummus resulted in reduced risk of salmonellosis or listeriosis and extended its shelf-life (Olaimat et al., 2018). The use of ITC in food safety was previously reported for the control of Salmonella on fresh chicken breasts. The AITC (50 mL/g) was combined with 15 mg/g EDTA in k-carrageenan/chitosan-based coatings and had the potential to reduce Salmonella on raw chicken meat (Olaimat and Holley, 2015). The agrifood industry produces tons of waste and substandard products that are discarded at great expense. The valorization of industrial residues curbs issues related to food security and environmental problems (Dominguez-Perles et al., 2018; Thomas et al., 2018). The vegetables and ingredients derived from Brassicaceae are associated with varied beneficial health effects and the agrowastes and by-products are rich in GLS, predominantly glucoraphanin, whereas the nutritional (minerals,

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carotenoids, vitamins) and the polyphenolic composition is less exploited. The valorization of agriculture and processed food wastes would facilitate the production of high value functional foods and novel ingredients with socioeconomic sustainability. Different members of Brassicaceae family are also used as condiments and relishes, among which we can highlight wasabi (Wasabia japonica, Cochlearia wasabi, or Eutrema japonica) and mustard (white or yellow mustard, Sinapis hirta; brown or Indian mustard, Brassica juncea; or black mustard, Brassica nigra).Wasabi, also known as Japanese horseradish, is extracted from rhizome and is usually accompanied by soy sauce and used as flavor stimulator. The main responsible of its hotness and pungent taste is the AITC (reported to be around 2.0 g/kg). This sinigrin derivative is formed by myrosinase action immediately on grating the root (Izawa et al., 2010). Mustard is produced from grounded seeds mixed with water and other ingredients such as flour. The GLS content depend on the Brassica species used; as in wasabi, the main GLS present on black mustard is sinigrin, whereas that of white mustard is sinalbin. These GLS are hydrolyzed into ITC by myrosinase action, AITC and p-hydroxybenzyl ITC, respectively, which confer the typical pungent taste of this spice. Other factors which directly affect GLS and ITC final content, and therefore modify mustard flavor, are the production methods, especially the maceration step (Cools and Terry, 2018). Other less well-known product related with Brassicaceae family is honey, the only animal-derived food containing intact GLS. For production of this GLS-enriched honey, producers use pollen from B. napus or D. tenuifolia, among others (Persano-Oddo L et al., 2004). However, the total amount of GLS is too low to use this honey as a dietary source of GLS (Ares et al., 2015).

6.7 Conclusions Optimizing postharvest conditions of storage and industrial treatments of Brassicaceae vegetables may retain the GLS content of its fresh material for several weeks or months before consumption, which could have a big impact on the health benefits for the population. Cold temperatures and high HR are the most important parameters to avoid bioactive compounds loses during storage. Nonthermal treatments, such as HPP (100e600 MPa), have been described as promising to maintain the action of the myrosinase

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enzyme for ITC formation during consumption. UV light could efficiently reduce microbial contamination in Brassica vegetables and enhance their bioactive compounds. Among thermal industrial treatments, blanchfreezing does not alter GLS concentration, but leads to extensive myrosinase enzyme inactivation. In this sense, domestic cooking using temperatures higher to 60 C has similar effects, affecting dramatically the GLS content at the time of consumption. Therefore, an external source of myrosinase enzymes to enhance ITC bioavailability and bioaccessibility could be used during consumption of thermally treated vegetables. Indeed, using optimized postharvest industrial treatments for ESP enzymes inactivation, such as HPP or blanch-freezing, may increase the formation of ITC over the formation of ITC-nitriles, which have shown lower bioactive activities for human health. Preventing GLS destruction during postharvest treatments and domestic handling is a goal to achieve the consumption of high nutrient quality cruciferous vegetables. In addition, using by-products rich in bioactive compounds, such as GLS, phenolic compounds, and vitamins, for the food and pharmacological industry may be an opportunity to recover agrowaste while obtaining added value products.

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