The Multifaceted Health Benefits of Broccoli-A Review of Glucosinolates, Phenolics and Antimicrobial Peptides

Abstract

Broccoli, a highly valued Brassica vegetable, is renowned for its rich content of bioactive substances, including glucosinolates, phenolic compounds, vitamins, and essential minerals. Glucosinolates (GSLs), secondary plant metabolites, are particularly abundant in broccoli. The global consumption of broccoli has increased due to its high nutritional value. This review examines the essential bioactive compounds in broccoli and their biological properties. Numerous in vitro and in vivo studies have demonstrated that broccoli exhibits various biological activities, including antioxidant, anticancer, antimicrobial, anti-inflammatory, anti-obesity and antidiabetic effects. This review analyzes several aspects of the chemical and biological activity of GSLs and their hydrolysis products, isothiocyanates such as sulforaphane, as well as phenolic compounds. Particular emphasis is placed on sulforaphane's chemical structure, the reactivity of its isothiocyanate fraction (-NCS), and given the different behavior of SFN enantiomers, a wide and detailed review of the chemical synthesis methods described, by microbial oxidation, or using a chiral ruthenium catalyst and more widely using chiral auxiliaries for synthesizing sulforaphane enantiomers. In addition, the methods of chiral resolution of racemates by HPLC are reviewed, explaining the different chiral fillers used for this resolution and a third section on resolution using the formation of diastereomeric complexes and subsequent separation on achiral columns. Additionally, this review highlights the presence of antimicrobial peptides in broccoli, which have shown potential applications in food preservation and as natural alternatives to synthetic antibiotics. The antimicrobial peptides (AMPs) derived from broccoli target bacterial membranes, enzymes, oxidative stress pathways and inflammatory mediators, contributing to their effectiveness against a wide range of pathogens and with potential therapeutic applications.

Keywords: HPLC; bioactive compounds; broccoli; chemical synthesis; enantioseparation; sulforaphane; sulforaphane diastereomer.

Figure 1

Broccoli (Brassica oleracea L. var. italica) anatomy.

Figure 2

Summary of nutritional and health benefits of broccoli.

Figure 3

Glucosinolate structure.

Figure 4

Hydrolysis of glucosinolates by myrosinase (an enzyme found in plants and intestinal microflora) to form isothiocyanates and glucose.

Figure 5

Chemical structure of the different thiohydroxymate-O-sulphate decomposition compounds.

Figure 6

Structures of desulfoglucosinolates found in Broccoli.

Figure 7

Examples of isothiocyanates and their glucosinolate precursors.

Figure 8

Aliphatic glucosinolate chain elongation.

Figure 9

Glucosinolate core biosynthesis.

Figure 10

SFN activation of Nrf2 signaling.

Figure 11

Chemical structure of the functional groups of SFN.

Figure 12

Mesomeric structures proposed for –NCS group.

Figure 13

(A) β-elimination without, transforming SFN into a butenyl isothiocyanate and methylsulfenic acid. (B) Reaction with SFN and water.

Figure 14

Interaction of SFN with Keap1.

Figure 15

SFN is metabolized via the mercapturic acid pathway upon conjugation with glutathione and undergoes further biotransformation to produce different metabolites.

Figure 16

Progoitrin is biologically inactive, but upon hydrolysis by the enzyme myrosinase it is transformed into goitrin.

Figure 17

Chemical structures of glucoraphanin and enantiomers (R y S) of SFN. The stereogenic sulfur atom is indicated as S* and highlighted in red.

Figure 18

Methods for obtaining sulforaphane enantiomers.

Figure 19

Diasteromeric intermediate used for the synthesis of enantioenriched R-SFN.

Figure 20

General procedures for the synthesis of chiral sulfinate esters via chlorosulfinates. In red, sulfur configuration in chiral sulfonate esters.

Figure 21

Synthesis of both enantiomers of SFN using (+)-(1S,2R)-trans-2-phenylcyclohexanol as a chiral auxiliary.

Figure 22

Enantio-divergent synthesis of both enantiomers of SFN.

Figure 23

Amylose-based chiral stationary phases used in HPLC to discriminate SFN enantiomers.

Figure 24

Formation of SFN diastereoisomers by (S)-Leucine reaction.

Figure 25

Biosynthesis of I3C starting from glucobrassicin.

Figure 26

Formation of DIM in vivo by dimerization in acidic medium of indole-3-carbinol.

Figure 27

Most abundant flavanols in broccoli.

Figure 28

Some of the most common hydroxycinnamic acids in broccoli.

Figure 29

Chemical structure of carotenoids in broccoli.

Figure 30

Chemical structure of phytosterols in the head of broccoli.

Figure 31

Broccoli antimicrobial peptide ARFEELNMDLFR. Structure was modeled using Alphafold2. Image was generated using the software ChimeraX 1.9. The peptide is displayed in stick representation, with a transparent hydrophobic surface overlay colored using a gradient from blue (hydrophilic) to yellow (hydrophobic).

Figure 32

Broccoli anti-inflammatory peptide SIWYGPDRP. Structure was modeled using Alphafold2. Image was generated using the software ChimeraX 1.9. The peptide is displayed in stick representation, with a transparent hydrophobic surface overlay colored using a gradient from blue (hydrophilic) to yellow (hydrophobic).