Elsevier

Food Chemistry

Volume 295, 15 October 2019, Pages 412-422
Food Chemistry

Brassica-enriched wheat bread: Unraveling the impact of ontogeny and breadmaking on bioactive secondary plant metabolites of pak choi and kale

https://doi.org/10.1016/j.foodchem.2019.05.113Get rights and content

Highlights

Abstract

Consumption of Brassica vegetables is linked to health benefits, as they contain high concentrations of the following secondary plant metabolites (SPMs): glucosinolate breakdown products, carotenoids, chlorophylls, and phenolic compounds. Especially Brassica vegetables are consumed as microgreens (developed cotyledons). It was investigated how different ontogenetic stages (microgreens or leaves) of pak choi (Brassica rapa subsp. chinensis) and kale (Brassica oleracea var. sabellica) differ in their SPM concentration. The impact of breadmaking on SPMs in microgreens (7 days) and leaves (14 days) in pak choi and kale as a supplement in mixed wheat bread was assessed. In leaves, carotenoids, chlorophylls, and phenolic compounds were higher compared to those of microgreens. Breadmaking caused a decrease of SPMs. Chlorophyll degradation was observed, leading to pheophytin and pyropheophytin formation. In kale, sinapoylgentiobiose, a hydroxycinnamic acid derivative, concentration increased. Thus, leaves of Brassica species are suitable as natural ingredients for enhancing bioactive SPM concentrations in bread.

Introduction

While humans get older, they have to deal with an increasing variety of non-communicable, age-related diseases that are often induced by oxidative stress and inflammation (World Health Organisation, 2019). To counteract these unfavorable processes, a vegetable-rich diet is recommended (World Health Organisation, 2019). Vegetables contain a wide variety of secondary plant metabolites (SPMs), which are bioactive and can exert antioxidant and anti-inflammatory effects (Andersen and Markham, 2006, Manach et al., 2009). Unfortunately, the current overall vegetable consumption in a typical Western diet is comparatively low (World Health Organisation, 2019). Hence, a strategy to overcome this dietary problem might be to add supplementary bioactive, health-promoting SPMs to food products that are highly consumed in a Western diet such as bread (Krems, Walter, Heuer, & Hoffmann, 2013).

Brassica species, in particular, are a valuable source of health-promoting SPMs. For example, kale is known for its high lutein concentration, a carotenoid that can prevent age-related ophthalmologic disorders and that is positively associated with cancer prevention and cardiovascular health (Buscemi et al., 2018). In addition to high concentrations of carotenoids, chlorophylls, and phenolic compounds, Brassica species also contain glucosinolates (GLSs), typical to plants from the order Brassicales (Wittstock, Kurzbach, Herfurth, & Stauber, 2016). Upon cell disruption, GLSs are broken down by the enzyme myrosinase to secondary products (GLS breakdown products) such as isothiocyanates (ITCs), nitriles, and epithionitriles (EPTs) (Wittstock et al., 2016). Especially, ITCs are thought to exert antimicrobial, anti-inflammatory, and even anticancerogenic effects (Oliviero, Verkerk, & Dekker, 2018). Due to the variety of structurally different SPMs, the regular consumption of Brassica vegetables is linked to health-promoting effects, such as antioxidant, anti-inflammatory, and anticancer activities (Francisco et al., 2017). Previous studies on added ingredients to bread have involved the addition of purified substances, e.g., quercetin, or lyophilized plant powders of, e.g., quinoa leaves (Lin and Zhou, 2018, Świeca et al., 2014). Thus, adding fresh or gently processed vegetative plant tissues, for instance microgreens (developed cotyledons) or leaves of the Brassica vegetables, to bread could be a promising, innovative, health-promoting strategy to increase the consumption of bioactive SPMs in a typical Western diet. It is noteworthy that the composition and concentration of a plant’s SPMs profile, e.g., GLSs breakdown products, carotenoids, chlorophylls, and phenolic compounds, is species-specific and also highly dependent on the ontogenetic stage (Heinze et al., 2018). For example, while Brassica sprouts/microgreens form higher concentration of GLSs, young leaves contain higher levels of carotenoids, chlorophylls, and phenolic compounds (Heinze et al., 2018). We therefore hypothesized differences in the profiles of SPMs not only between pak choi and kale, but also between microgreens and leaves of both plant species. Thus, we first characterized the composition and concentration of GLS breakdown products, carotenoids, chlorophylls, and phenolic compounds in pak choi (Brassica rapa subsp. chinensis) and kale (Brassica oleracea var. sabellica) at two ontogenetic stages, namely 7 day old microgreens and 14 day old leaves, in order to reveal the optimal profile of SPMs in terms of health-promoting substances.

Besides pre-harvest factors (e.g., developmental stage), post-harvest factors (e.g., processing) also have an impact on composition and concentration of SPMs. For example, during the breadmaking process, plant tissue is exposed to both mechanical impacts and thermal processing that can affect the composition and concentration of the desired metabolites (Klopsch et al., 2018). The influence of food processing on SPMs is thus dependent on the specific kind of processing (e.g., cutting, cooking, steaming, frying, baking) as well as various other parameters such as plant genotype, ontogenetic stage, overall plant composition (‘matrix’), and the chemical structure of the specific SPM (Chaaban et al., 2017, Klopsch et al., 2018). We therefore hypothesized that fresh leafy plant material from Brassica is suitable to be used as an added ingredient for enhancing bioactive, health-promoting SPMs in a typical Western diet in food products that are regularly consumed such as bread. Thus, we also evaluated how stable the SPMs are during the breadmaking process.

Section snippets

Chemicals and reagents

Ammonium acetate, ferulic acid, kaempferol-3-O-glucoside, methanol, methylene chloride (for GLS breakdown product analysis), quercetin-3-O-glucoside, sinapic acid, and tert-butyl methyl ether were obtained from Carl Roth GmbH + Co. KG (Karlsruhe, Germany). Acetic acid, methylene chloride (for carotenoid and chlorophyll analysis) and 2-propanol were bought from Merck KGaA (Darmstadt, Germany). Acetonitrile and 3-indoleacetonitrile were obtained from J. T. Baker (Fisher Scientific GmbH,

Results and discussion

The impact of ontogeny on the composition and concentration of bioactive SPMs in two Brassica species (pak choi and kale) was investigated. For this purpose, pak choi and kale were grown under controlled conditions in a climate chamber and harvested after 7 days (microgreens) and 14 days (leaves). These plants were analyzed for their SPM composition and concentration: GLS breakdown products, carotenoids, chlorophylls, and phenolic compounds. To study how suitable pak choi and kale are for

Conclusion

Microgreens as well as leaves of both Brassica species (pak choi, kale) possess the potential to provide the consumer with a variety of health-promoting bioactive SPMs such as GLS breakdown products, carotenoids, chlorophyll metabolites, and phenolic compounds. The total concentration of lipophilic carotenoids and chlorophylls was higher in the Brassica leaves compared to their corresponding microgreens, whereas hydrophilic GLS breakdown products, hydroxycinnamic acid derivatives, and

Declaration of Competing Interest

None.

Acknowledgements

This research was developed by and embedded in the competence cluster NutriAct – Competence Cluster Nutrition Research Berlin‐Potsdam funded by the Federal Ministry of Education and Research (FKZ: 01EA1408A‐G). We would also like to thank Elke Büsch for her excellent technical support in carrying out the growth experiments.

References (41)

  • S. Park et al.

    Pheophytin a and chlorophyll a suppress neuroinflammatory responses in lipopolysaccharide and interferon-γ-stimulated BV2 microglia

    Life Sciences

    (2014)
  • A. Patras et al.

    Effect of thermal processing on anthocyanin stability in foods; mechanisms and kinetics of degradation

    Trends in Food Science & Technology

    (2010)
  • S. Rohn

    Possibilities and limitations in the analysis of covalent interactions between phenolic compounds and proteins

    Food Research International

    (2014)
  • R.L. Scalzo et al.

    Anthocyanin composition of cauliflower (Brassica oleracea L. var. botrytis) and cabbage (B. oleracea L. var. capitata) and its stability in relation to thermal treatments

    Food Chemistry

    (2008)
  • A. Schieber et al.

    Occurrence of carotenoid cis-isomers in food: technological, analytical, and nutritional implications

    Trends in Food Science & Technology

    (2005)
  • M. Świeca et al.

    Bread enriched with quinoa leaves–The influence of protein–phenolics interactions on the nutritional and antioxidant quality

    Food Chemistry

    (2014)
  • Wittstock et al.

    Glucosinolate breakdown

  • M. Ahmed et al.

    Flavonoids in fruits and vegetables after thermal and nonthermal processing: A review

    Critical Reviews in Food Science and Nutrition

    (2017)
  • O.M. Andersen et al.

    Flavonoids: Chemistry, biochemistry and applications

    (2006)
  • P. Baardseth et al.

    Vitamin C, total phenolics and antioxidative activity in tip-cut green beans (Phaseolus vulgaris) and swede rods (Brassica napus var. napobrassica) processed by methods used in catering

    Journal of the Science of Food and Agriculture

    (2010)
  • Cited by (0)

    View full text