Valorization of waste cabbage leaves by postharvest photochemical treatments monitored with a non-destructive fluorescence-based sensor.

The biosynthesis of polyphenolic compounds in cabbage waste, outer green leaves of white head cabbage (Brassica oleracea L. var. capitata subvar. alba), was stimulated by postharvest irradiation with UVB lamps or sunlight. Both treatments boosted the content of kaempferol and quercetin glycosides, especially in the basal leaf zone, as determined by the HPLC analysis of leaf extracts and by a non-destructive optical sensor. The destructive analysis of samples irradiated by the sun for 6 days at the end of October 2015 in Skierniewice (Poland) showed an increase of leaf flavonols by 82% with respect to controls. The treatment by a broadband UVB fluorescent lamp, with irradiance of 0.38 W m-2 in the 290-315 nm range (and 0.59 W m-2 in the UVA region) for 12 h per day at 17 °C along with a white light of about 20 µmol m-2 s-1, produced a flavonols increase of 58% with respect to controls. The kinetics of flavonols accumulation in response to the photochemical treatments was monitored with the FLAV non-destructive index. The initial FLAV rate under the sun was proportional to the daily radiation doses with a better correlation for the sun global irradiance (R2 = 0.973), followed by the UVA (R2 = 0.965) and UVB (R2 = 0.899) irradiance. The sunlight turned out to be more efficient than the UVB lamp in increasing the flavonols level of waste leaves, because of a significant role played by UVA and visible solar radiation in the regulation of the flavonoid accumulation in cabbage. The FLAV index increase induced on the adaxial leaf side was accompanied by a lower but still significant FLAV increase on the unirradiated abaxial side, likely due to a systemic signaling by mean of the long-distance movement of macromolecules. Our present investigation provides useful data for the optimization of postharvest photochemical protocols of cabbage waste valorization. It can represent a novel and alternative tool of vegetable waste management for the recovery of beneficial phytochemicals.

Sugar matters: sugar moieties as reactivity-tuning factors in quercetin O-glycosides.

Quercetin, one of the most abundant flavonoids in plant-based foods, commonly occurs in nature in various glycosylated forms. There is still a less explored aspect regarding the cause of diversity of its glycosides, depending on the sugar moiety attached. This work focuses on four wide-spread quercetin glycosides-hyperoside, isoquercitrin, quercitrin and rutin-by testing the property-tuning capacity of different sugar moieties and thus explains and predicts some of their functions in plant-based foods. The electron paramagnetic spectra of the semiquinone anion radicals of these glycosides were interpreted in terms of hyperfine coupling constants and linewidths, highlighting a clear link between spin density trends, the identity of the bound sugar, and their reactivity corroborated with their modelled structures. Redox potential and lipophilicity were connected to a specific flavonoid-enzyme interaction and correlated with their prooxidant reactivity assessed by oxidation of ferrous hemoglobin. Hyperoside and isoquercitin-galactose and glucose glycosides-exhibit the highest prooxidant reactivity owing to their lowest redox potential and lipophilicity whereas rutin and quercitrin-rutinose and rhamnose glycosides-behave vice versa. The ability of the tested glycosides to undergo HAT or SET-type reactions has also been tested using five different analytical assays, including inhibition of cytochrome c-triggered liposome peroxidation. In most cases, rutin proved to be the most unreactive of the four tested glycosides considering either steric or redox reasons whereas the reactivity hierarchy of the other three glycosides were rather assay dependent.

Simultaneous determination of individual isothiocyanates in plant samples by HPLC-DAD-MS following SPE and derivatization with N-acetyl-l-cysteine.

The procedure for the isothiocyanates (ITCs) determination that involves derivatization with N-acetyl-l-cysteine (NAC) and separation by HPLC was developed. Prior to derivatization, plant ITCs were isolated and purified using solid-phase extraction (SPE). The optimum conditions of derivatization are: 500µL of isopropanolic eluate obtained by SPE combined with 500µL of derivatizing reagent (0.2M NAC and 0.2M NaHCO3 in water) and reaction time of 1h at 50°C. The formed dithiocarbamates are directly analyzed by HPLC coupled with diode array detector and mass spectrometer if required. The method was validated for nine common natural ITCs. Calibration curves were linear (R(2)⩾0.991) within a wide range of concentrations and limits of detection were below 4.9nmol/mL. The recoveries were in the range of 83.3-103.7%, with relative standard deviations <5.4%. The developed method has been successfully applied to determine ITCs in broccoli, white cabbage, garden cress, radish, horseradish and papaya.

Application of response surface methodology to optimize solid-phase microextraction procedure for chromatographic determination of aroma-active monoterpenes in berries.

Most of scientific papers concern the qualitative or semi-quantitative analysis of aroma-active terpenes in liquid food matrices. Therefore, the procedure based on solid-phase microextraction and two-dimensional gas chromatography-time-of-flight mass spectrometry for determination of monoterpenes in fresh berries was developed. The optimal extraction conditions using divinylbenzene-carboxen-polydimethylsiloxane fiber were: temperature of 50°C, extraction time of 26min, equilibrium time of 29min. The developed procedure provides a high recovery (70.8-99.2%), good repeatability (CV<10.4%), high linearity (r>0.9915) and offers practical advantages over currently used methods: reliability of compounds identification, simplicity of extraction and at least one order of magnitude lower detection limits (0.10-0.011µg/L). The method was successfully applied to determine monoterpenes in 27 berry samples of different varieties and 4 berry products. Tukey's test revealed that monoterpenes content is a reliable indicator of fruit maturity and origin. It suggests that the method may be of interest to researchers and food industry.

Nondestructive Optical Sensing of Flavonols and Chlorophyll in White Head Cabbage (Brassica oleracea L. var. capitata subvar. alba) Grown under Different Nitrogen Regimens.

A multiparametric optical sensor was used to nondestructively estimate phytochemical compounds in white cabbage leaves directly in the field. An experimental site of 1980 white cabbages (Brassica oleracea L. var. capitata subvar. alba), under different nitrogen (N) treatments, was mapped by measuring leaf transmittance and chlorophyll fluorescence screening in one leaf/cabbage head. The provided indices of flavonols (FLAV) and chlorophyll (CHL) displayed the opposite response to applied N rates, decreasing and increasing, respectively. The combined nitrogen balance index (NBI = CHL/FLAV) calculated was able to discriminate all of the plots under four N regimens (0, 100, 200, and 400 kg/ha) and was correlated with the leaf N content determined destructively. CHL and FLAV were properly calibrated against chlorophyll (R(2) = 0.945) and flavonol (R(2) = 0.932) leaf contents, respectively, by using a homographic fit function. The proposed optical sensing of cabbage crops can be used to estimate the N status of plants and perform precision fertilization to maintain acceptable crop yield levels and, additionally, to rapidly detect health-promoting flavonol antioxidants in Brassica plants.

Optimization of capillary isotachophoretic method for determination of major macroelements in blue honeysuckle berries (Lonicera caerulea L.) and related products.

A reliable and repeatable isotachophoretic method for the simultaneous determination of K(+), Na(+), Ca(2+), Mg(2+), and ammonium in berries of different blue honeysuckle cultivars was developed. The usefulness of the complex-forming equilibria in determining the cations mentioned above was studied. The addition of 7.5 mM 18-crown-6 and 2 mM α-hydroxyisobutyric acid to sulfuric acid enhanced the separation capacity of the leading electrolyte. The terminating electrolyte of 10 mM TRIS buffered to pH 4.30 was chosen as most appropriate for these studies. An ultrasound-assisted procedure for the extraction of macroelements from dried fruit of Lonicera caerulea L. was investigated using response surface methodology. The Box-Behnken experimental design showed the optimal extraction conditions as follows: temperature of 36 °C, extraction time of 42.3 min and solid-to-liquid ratio of 1:800 v/w. Detection limits for the method ranged from 0.030 to 0.097 mg/l with precision expressed by RSD ranging from 1.4 % for Mg to 4.4 % for Na. The results showed that blue honeysuckle berries are a good source of potassium, from 199 to 402 mg/100 g FW, especially 'Zielona' and 'Zojka' cultivars. The average content of other analytes in these berries was 5.2 mg Na, 24.8 mg Ca, 7.5 mg Mg and 52.0 mg ammonium per 100 g FW. The berry products contained lower amounts of minerals especially Mg and K. However, a glass of freshly squeezed juice can provide almost 20 % of the RDI of potassium. The results obtained using both the developed isotachophoretic method and ion chromatographic procedure did not differ significantly.

Comprehensive two-dimensional gas chromatography for determination of the terpenes profile of blue honeysuckle berries.

Terpenes are the main group of secondary metabolites, which play essential role in human. The establishment of the terpenes profile of berries of different blue honeysuckle cultivars was achieved by headspace solid-phase microextraction coupled with comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (HS-SPME/GC×GC-TOFMS). The berries were found to contain 44 terpenes identified by GC×GC-TOFMS. From these, 10 were previously reported in blueberries. According to their chemical structure, the compounds were organised in different groups: monoterpene hydrocarbons and monoterpene oxygen-containing compounds (oxides, alcohols, aldehydes, and ketones). Positive identification of some of the compounds was performed using authentic standards, while tentative identification of the compounds was based on deconvoluted mass spectra and comparison of linear retention indices (LRI) with literature values. The major components of volatile fraction were monoterpenes, such as eucalyptol, linalool and p-cymene. Furthermore, quantitative analysis showed that eucalyptol was the most abundant bioactive terpene in analysed berries (12.4-418.2 µg/L).