Effect of preliminary processing and method of preservation on the content of glucosinolates in kale (Brassica oleracea L. var. acephala) leaves

Low-Temperature Vacuum Drying on Broccoli: Enhanced Anti-Inflammatory and Anti-Proliferative Properties Regarding Other Drying Methods

Low-temperature vacuum drying (LTVD) has shown great potential for drying vegetables. It could avoid excessive degradations of active compounds with potential therapeutic agents. In this study, the effect on several relevant bioactive compounds, anti-inflammatory activity, and anti-proliferative activity of broccoli (Brassica oleracea var. italica) were evaluated. Effects of other drying methods, including vacuum drying (VD), convective drying (CD), infrared drying (IRD), and freeze drying (FD), were also comparatively evaluated. The results of all dried samples showed high polyunsaturated fatty acid contents (of up to 71.3%) and essential amino acid contents (of up to 8.63%). The LTVD method stands out above the other drying methods, since it obtained the highest content of total phenols, chlorogenic acid, and ferulic acid. Both the LTVD and CD samples demonstrated high anti-inflammatory and anti-proliferative activities. These CD and LTVD samples were also the most active against the breast carcinoma MDA-MB-23 cell line. Due to the good retention of bioactive compounds via LTVD, the obtained dried broccoli here can be used in a near time as an ingredient for the development of novel natural products with anti-inflammatory and anti-proliferative effects.

Air-Frying Is a Better Thermal Processing Choice for Improving Antioxidant Properties of Brassica Vegetables

Brassica vegetables have demonstrated many health benefits over the years due to their composition of phenolic, flavonoid, and glucosinolate contents. However, these bioactive molecules can be easily depleted during gastronomic operations. Therefore, a sustainable method that improves their phenolic content and antioxidant activity is required for both the processors and consumers. Thermal processing has been demonstrated as a method to improve the phenolic content and antioxidant status of Brassica vegetables. In the current study, four different thermal processing methods, including freeze-drying, sautéing, steaming, and air-frying, were employed for five different Brassica vegetables, including kale, broccoli sprouts, Brussels sprouts, red cabbage, and green cabbage. The total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities were assessed using radical scavenging activity (DPPH and ABTS^•+), reducing power (FRAP), and the chelating ability of metal ions. Among the methods tested, air-frying at 160 °C for 10 min showed the highest TPC, TFC, and antioxidant activity of the Brassica vegetables, while sautéing showed the lowest. The steam treatments were preferred over the freeze-drying treatments. Within the vegetables tested, both kale and broccoli sprouts contained higher antioxidant properties in most of the employed processing treatments. The results also indicated that there is a strong correlation between the TPC, TFC, and antioxidant activity (p < 0.05). This study indicates that air-frying could be used as a sustainable thermal processing method for improving biomolecules in Brassica vegetables.

Glucosinolates and Cytotoxic Activity of Collard Volatiles Obtained Using Microwave-Assisted Extraction

Glucosinolates (GSLs) in Brassica oleracea L. convar. acephala var. viridis (collard) flower, leaf, stem, and root were analyzed qualitatively and quantitatively via their desulfo-counterparts using UHPLC-DAD-MS/MS. Twelve GSLs were identified, including Met-derived GSLs (sinigrin, glucoibervirin, glucoerucin, glucoiberin, glucoraphanin, progoitrin), Trp-derived GSLs (4-hydroxyglucobrassicin, glucobrassicin, 4-methoxyglucobrassicin, and neoglucobrassicin), and Phe-derived GSLs (glucotropaeolin and gluconasturtiin). Total GSL content was highest in the root, having 63.40 μmol/g dried weight (DW), with gluconasturtiin (34.02 μmol/g DW) as the major GSL, followed by sinigrin and glucoibervirin (12.43 and 7.65 μmol/g DW, respectively). Total GSL contents in the flower, leaf, and stem were lower than in root, having 6.27, 2.64, and 1.84 μmol/g DW, respectively, with Trp and/or Met-derived GSLs as the predominant ones. GSL breakdown products were obtained via microwave hydrodiffusion and gravity (MHG) and volatile breakdown products were analyzed using GC-MS techniques. Volatile isolates were tested for their cytotoxic activity using MTT assay. MHG volatile extract from the root demonstrated the best cytotoxic activity against human bladder cancer cell line T24 and breast cancer cell line MDA-MB-231 during an incubation time of 72 h (IC₅₀ 21.58, and 11.62 μg/mL, respectively). The activity of the root extract can be attributed to its major volatile, 2-phenylethyl isothiocyanate (gluconasturtiin breakdown product).

Effect of pre-treatment and drying methods on the content of minerals, B-group vitamins and tocopherols in kale (Brassica oleracea L. var. acephala) leaves

Dried vegetables are widely used in food production. Kale leaves, due to their high health-promoting properties, can be a valuable raw material for drying. The aim of the study was to evaluate the effect of blanching, drying methods (air-drying, freeze-drying), the time and temperature of storage on the content of ash, minerals, vitamins B₁, B₂, and tocopherols in dried kale products. The dried products were evaluated directly after processing and after 12 months of storage at ambient temperature, 18–20 °C and cold temperature, 8–10 °C. In 100 g dry matter from fresh raw material the dominant minerals were potassium (2613 mg), calcium (1346 mg), phosphorus (432 mg), magnesium (129 mg). Kale leaves had 0.828 mg vitamin B₁, 1.533 mg vitamin B₂ and 16.55 mg total tocopherols per 100 g of dry matter. Blanching, applied prior to drying, significantly reduced the levels of minerals (3–38%) and vitamins (8–45%), except for calcium, zinc and manganese. This pre-treatment had, however, a beneficial effect, especially on vitamin retention during the storage of dried products. After 12 month storage, the losses of vitamin B₁, B₂ and total tocopherols in dried, previously blanched, raw materials ranged from 3 to 10%, 1 to 4%, and 1 to 16%, respectively, depending on the type of sample. In the dried products obtained from unblanched raw material, the losses were larger and amounted to 10–17%, 8–16% and 4–17%, respectively. Throughout drying and storage, the minerals examined were fairly stable. Dried kale is generally a good source of minerals and vitamins. However, blanching before drying is recommended. In addition, freeze-drying and storage in cold temperature allows for higher vitamin preservation in dried kale.

Controlled fermentation of curly kale juice with the use of autochthonous starter cultures

The aim of this paper was to evaluate the influence of different indigenous lactic acid bacteria isolates - as a single culture or bacterial consortium - on the functional and physicochemical properties of fermented curly kale juice. All tested variants exhibited good growth parameters, manifested by efficient pH lowering, increases in acidity, and fructose and glucose metabolism, as well as a significant inhibition of pathogens. A slight increase in total phenolic content was observed, while antioxidant activity remained unchanged. L. sakei and MIX A were associated with an increase in riboflavin and pyridoxine content, while L. plantarum only contributed to an increase in vitamin B₆ content. Bioconversion of individual phenolic compounds, carotenoids, and glucosinolates strongly depended on the strain-specific metabolism. In the process, the levels of ferulic acid and other hydroxycinnamic acids were maintained, while the content of 9-cis lutein increased. Considering presented results and our previous research regarding probiotic features of LAB strains, among tested starter cultures - L. plantarum seemed to possess the best characteristics as a potential starter culture for controlled fermentation of curly kale juice.

Chilling and Freezing Temperature Stress Differently Influence Glucosinolates Content in Brassica oleracea var. acephala

Brassica oleracea var. acephala is known to have a strong tolerance to low temperatures, but the protective mechanisms enabling this tolerance are unknown. Simultaneously, this species is rich in health-promoting compounds such as polyphenols, carotenoids, and glucosinolates. We hypothesize that these metabolites play an important role in the ability to adapt to low temperature stress. To test this hypothesis, we exposed plants to chilling (8 °C) and additional freezing (-8 °C) temperatures under controlled laboratory conditions and determined the levels of proline, chlorophylls, carotenoids, polyphenols, and glucosinolates. Compared with that of the control (21 °C), the chilling and freezing temperatures increased the contents of proline, phenolic acids, and flavonoids. Detailed analysis of individual glucosinolates showed that chilling increased the total amount of aliphatic glucosinolates, while freezing increased the total amount of indolic glucosinolates, including the most abundant indolic glucosinolate glucobrassicin. Our data suggest that glucosinolates are involved in protection against low temperature stress. Individual glucosinolate species are likely to be involved in different protective mechanisms because they show different accumulation trends at chilling and freezing temperatures.

Glucosinolates in Brassica Vegetables: Characterization and Factors That Influence Distribution, Content, and Intake

Glucosinolates (GSLs) are a class of sulfur-containing compounds found predominantly in the genus Brassica of the Brassicaceae family. Certain edible plants in Brassica, known as Brassica vegetables, are among the most commonly consumed vegetables in the world. Over the last three decades, mounting evidence has suggested an inverse association between consumption of Brassica vegetables and the risk of various types of cancer. The biological activities of Brassica vegetables have been largely attributed to the hydrolytic products of GSLs. GSLs can be hydrolyzed by enzymes; thermal or chemical degradation also breaks down GSLs. There is considerable variation of GSLs in Brassica spp., which are caused by genetic and environmental factors. Most Brassica vegetables are consumed after cooking; common cooking methods have a complex influence on the levels of GSLs. The variationof GSLs in Brassica vegetables and the influence of cooking and processing methods ultimately affect their intake and health-promoting properties.

Influence of Cooking Methods on Glucosinolates and Isothiocyanates Content in Novel Cruciferous Foods

Brassica vegetables are of great interest due to their antioxidant and anti-inflammatory activity, being responsible for the glucosinolates (GLS) and their hydroxylated derivatives, the isothiocyanates (ITC). Nevertheless, these compounds are quite unstable when these vegetables are cooked. In order to study this fact, the influence of several common domestic cooking practices on the degradation of GLS and ITC in two novel Brassica spp.: broccolini (Brassica oleracea var italica Group x alboglabra Group) and kale (Brassica oleracea var. sabellica L.) was determined. On one hand, results showed that both varieties were rich in health-promoter compounds, broccolini being a good source of glucoraphanin and sulforaphane (≈79 and 2.5 mg 100 g⁻¹ fresh weight (F.W.), respectively), and kale rich in glucoiberin and iberin (≈12 and 0.8 mg 100 g⁻¹ F.W., respectively). On the other hand, regarding cooking treatments, stir-frying and steaming were suitable techniques to preserve GLS and ITC (≥50% of the uncooked samples), while boiling was deleterious for the retention of these bioactive compounds (20–40% of the uncooked samples). Accordingly, the appropriate cooking method should be considered an important factor to preserve the health-promoting effects in these trending Brassica.

Effect of stevia supplementation of kale juice spheres on their quality changes during refrigerated shelf life

BACKGROUND

Kale is a vegetable that contains a high proportion of health-promoting compounds although its consumption as a beverage is very limited due to its bitter flavor. Nonetheless, the bitter flavor of Brassica may be masked by sweetening. The effects were studied of different stevia extracts (CTRL, S0.5 (g L^-1 ), S1.25 and S2.5) added to a kale beverage on the quality of kale juice spheres over a period of 7 days at 5 °C. Kale juice spheres were produced with a double-spherification technique, which allowed hydrogel spheres to be produced with high mechanical resistance.

RESULTS

The addition of the stevia extracts did not affect the physicochemical quality of spheres. In particular, S2.5 spheres showed the least color changes after 7 days. All spheres showed good microbiological quality throughout storage, with loads < 7 log CFU g^-1 , regardless of the stevia concentration. The sulforaphane content of kale spheres was not affected by the stevia supplementation over the 7-day period.

CONCLUSION

The addition of stevia to the kale juice spheres led to a better flavor without altering product quality during refrigerated storage. © 2018 Society of Chemical Industry.

Kale (Brassica oleracea var. acephala) as a superfood: Review of the scientific evidence behind the statement

Kale (Brassica oleracea var. acephala) is a cruciferous vegetable, characterized by leaves along the stem, which, in recent years, have gained a great popularity as a ´superfood´. Consequently, in a popular culture it is listed in many ´lists of the healthiest vegetables´. Without the doubt, a scientific evidences support the fact that cruciferous vegetables included in human diet can positively affect health and well-being, but remains unclear why kale is declared superior in comparison with other cruciferous. It is questionable if this statement about kale is triggered by scientific evidence or by some other factors. Our review aims to bring an overview of kale's botanical characteristics, agronomic requirements, contemporary and traditional use, macronutrient and phytochemical content and biological activity, in order to point out the reasons for tremendous kale popularity.

Characterization of phenolics, glucosinolates and antioxidant activity of beverages based on apple juice with addition of frozen and freeze-dried curly kale leaves (Brassica oleracea L. var. acephala L.)

The aim of this study was to determine the polyphenols, glucosinolates and ascorbic acid content as well as antioxidant activity of beverages on the base of apple juice with addition of frozen and freeze-dried curly kale leaves. Upon enrichment with frozen (13%) and freeze-dried curly kale (3%), the naturally cloudy apple juice was characterized by an increase in phenolic compounds by 2.7 and 3.3-times, accordingly. The antioxidant activity of beverages with the addition of curly kale ranged from 6.6 to 9.4μmol Trolox/mL. The obtained beverages were characterized glucosinolates content at 117.6-167.6mg/L and ascorbic acid content at 4,1-31,9mg/L. The results of sensory evaluation of colour, taste and consistency of apple juice and beverages with the addition of kale did not differ significantly prior to pasteurization (P≤0.05), whereas after the pasteurization the evaluated factors decreased significantly.