Effect of sulfur and nitrogen fertilization on the content of nutritionally relevant carotenoids in spinach ( Spinacia oleracea )

The Effects of Nitrogen Application and Varietal Variation on the Product Quality and In Vitro Bioaccessibility of Bioactive Compounds of Baby Spinach Varieties Grown in a Soilless Growth Medium

Baby spinach is becoming increasingly popular as a salad ingredient and needs high fertiliser rates to grow well and attain higher-quality leaves (dark green leaves). Chemical fertilisers, especially nitrogen (N), boost yields. There are many risks associated with nitrogen fertilisation. Additionally, spinach contains phenolic compounds and carotenoids. Nitrogen fertilisation affects growth, development, yield and metabolites. This study examined the impact of lower concentrations of N (0, 30, 60, 90, 120, 150 mg/L) on yield and colour properties [light intensity (L*) colour coordinates, unique for green colour (a*) and yellow colour (b*)], as well as the impact of varying N concentrations on the total phenolic content and p-coumaric acid, quercetin, ferulic acid, kaempferol, lutein, zeaxanthin, β-carotene and antioxidant activities in the baby spinach varieties 'Acadia', 'Crosstrek' and 'Traverse', and it was established that N fertilisation improves phytochemical bioaccessibility and antioxidant activity. In a split strip plot design, three baby spinach varieties were treated with different N concentrations, including 0, 30, 60, 90, 120 and 150 mg/L. For 40 days, three baby spinach varieties were grown on soilless Mikskaar Professional substrate 300. During both seasons, 'Crosstrek' had the highest fresh mass (921.4 g/m2, 856.3 g/m2) at 120 mg/L N, while 'Traverse' had the highest fresh mass at 554.8 g/m2 and at 564.3 g/m2 at 90 mg/L N and did not differ significantly from 90 to 150 mg/L N during either season. During both seasons, 'Acadia' at 90 mg/L N increased fresh mass to 599 g/m2 and 557.9 g/m2. The variety × N supply interaction significantly affected the leaf colour; chlorophyll content across seasons; the levels of bioactive compounds, p-coumaric acid, quercetin, ferulic acid, kaempferol, lutein, zeaxanthin and β-carotene in spinach varieties; the in vitro bioaccessibility; and the antioxidant activity. Varietal differences influenced the bioaccessibility of phenolic compounds and carotenoid components. The appropriate N levels can be used during plant cultivation to optimise the bioaccessibility of this spinach variety. Thus, fertilising 'Traverse' with 90 mg/N mL increased the in vitro bioaccessibility of β-carotene (35.2%), p-coumaric acid (7.13%), quercetin (8.29%) and ferulic acid (1.92%) without compromising the yield.

Results of the BfR MEAL Study: Highest levels of retinol found in animal livers and of β–carotene in yellow-orange and green leafy vegetables

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Data of retinol and β-carotene in 333 and 271 foods prepared as consumed in Germany.

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Highest levels of retinol were found in liver and liver-based food.

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High β-carotene levels occurred in orange/green leafy vegetables and fruit nectars.

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In some foods, levels varied significantly based on production type and seasonality.

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Margarine represents a food often fortified voluntarily with retinol and β-carotene.

This Total Diet Study (TDS) provides representative data on substance levels in foods, prepared as typically consumed by the population in Germany for future dietary exposure assessment. Vitamin A is essential and must be obtained from the diet, either as preformed vitamin A or as provitamin A carotenoids. Levels of retinol and β-carotene were analysed in 333 and 271 foods, respectively. Highest mean retinol levels were found in cod liver (25,000 µg∙100 g⁻¹), followed by other animal livers, liver-based products, butter, eel and fortified margarine. In contrast, highest mean β-carotene levels were found in carrots (4,650 µg∙100 g⁻¹), followed by other yellow-orange fruits and vegetables, green leafy vegetables and fortified fruit nectars. Sampling by production type and seasonality revealed differences in retinol and β-carotene levels in individual foods. This TDS expands the existing data for β-carotene and vitamin A extensively by providing representative data on most consumed foods.

Validation of a Method for Quantification of Lutein in Spinach Using High-Performance Liquid Chromatography: Interlaboratory Study

BACKGROUND

Lutein is gaining attention as a strong antioxidant contained in foods. It accumulates in the human blood and retina, and is considered to play an important role in the body, especially in the eyes.

OBJECTIVE

A method to determine the lutein content of raw spinach (Spinacia oleracea L.) was developed with the aim of its enactment as a Japanese agricultural standard (JAS) measurement method for components beneficial to human health.

METHODS

An interlaboratory study was conducted to evaluate an analytical method for the determination of lutein in spinach. The detection limit and quantification limit of lutein for this method were 0.2 and 0.7 mg/kg, respectively. Twelve participating laboratories independently analyzed test samples (five pairs of blind duplicates) using high-performance liquid chromatography (HPLC).

RESULTS

After removal of a few outliers, the repeatability relative standard deviation (RSDr), reproducibility (RSDR), and predicted RSDR of the evaluated method were 3.4-7.5, 4.6-13, and 7.5-8.5%, respectively, in a concentration range from 64.9-150 mg/kg.

CONCLUSIONS

The HorRat values (RSDR/predicted RSDR) of the lutein concentration were calculated to be 0.61-1.6.

HIGHLIGHTS

The study results indicate the acceptable precision of this method.

Growing and processing conditions lead to changes in the carotenoid profile of spinach

This study aimed to evaluate the influence of different light regimens during spinach cultivation on the isomeric composition of β-carotene. Irradiation with a halogen lamp, which has a wavelength spectrum close to that of daylight, was used to mimic field-grown conditions. The additional use of optical filters was established as a model system for greenhouse cultivation. Field-grown model systems led to a preferential increase of 9-cis-β-carotene, whereas 13-cis-β-carotene was just formed at the beginning of irradiation. Additionally 9,13-di-cis-β-carotene decreased significantly in the presence of energy-rich light. Isomerization of β-carotene was strongly suppressed during irradiation in greenhouse-grown model systems and led to significant differences. These results were verified in biological samples. Authentic field-grown spinach (Spinacia oleracea L.) showed among changes of other isomers a significantly higher level of 9-cis-isomers (7.52 ± 0.14%) and a significantly lower level of 9,13-di-cis-isomers (0.25 ± 0.03%) compared to authentic greenhouse-grown spinach (6.49 ± 0.11 and 0.76 ± 0.05%). Almost all analyzed commercial spinach samples (fresh and frozen) were identified as common field-grown cultivation. Further investigations resulted in a clear differentiation of frozen commercial samples from fresh spinach, caused by significantly higher levels of 13-cis- and 15-cis-β-carotene as a result of industrial blanching processes.

Response of carotenoids and tocols of durum wheat in relation to water stress and sulfur fertilization

Lipophilic antioxidants are essential components of plant defense against stressful conditions. The response of carotenoids and tocols to water deficit and sulfur fertilization was investigated in durum wheat cultivars. The amounts of tocols and carotenoids were evaluated in both whole meal and semolina samples. Differences among cultivars were observed. Simeto cultivar showed a significant effect of water regime on whole meal and semolina carotenoids, with about 20% and 15% increase, respectively. Also tocols and tocotrienols of Simeto were positively affected by water stress (about 10% increase and 15% increase in whole meals and semolinas). Sulfur fertilization positively impacted mainly Ofanto whole-grain and semolina carotenoids, semolina tocols, and tocotrienols. In conclusion, water deficit occurring under a Mediterranean environment was responsible for an improvement of lipophilic antioxidant content in durum wheat; in contrast sulfur supplementation did not improve the response of the antioxidant pool under water deficit.