Modifying the Processing and Handling of Frozen Broccoli for Increased Sulforaphane Formation

Abstract

Frozen broccoli can provide a cheaper product, with a longer shelf life and less preparation time than fresh broccoli. We previously showed that several commercially available frozen broccoli products do not retain the ability to generate the cancer-preventative agent sulforaphane. We hypothesized that this was because the necessary hydrolyzing enzyme myrosinase was destroyed during blanching, as part of the processing that frozen broccoli undergoes. This study was carried out to determine a way to overcome loss of hydrolyzing activity. Industrial blanching usually aims to inactivate peroxidase, although lipoxygenase plays a greater role in product degradation during frozen storage of broccoli. Blanching at 86 °C or higher inactivated peroxidase, lipoxygenase, and myrosinase. Blanching at 76 °C inactivated 92% of lipoxygenase activity, whereas there was only an 18% loss in myrosinase-dependent sulforaphane formation. We considered that thawing frozen broccoli might disrupt membrane integrity, allowing myrosinase and glucoraphanin to come into contact. Thawing frozen broccoli for 9 h did not support sulforaphane formation unless an exogenous source of myrosinase was added. Thermal stability studies showed that broccoli root, as a source of myrosinase, was not more heat stable than broccoli floret. Daikon radish root supported some sulforaphane formation even when heated at 125 °C for 10 min, a time and temperature comparable to or greater than microwave cooking. Daikon radish (0.25%) added to frozen broccoli that was then allowed to thaw supported sulforaphane formation without any visual alteration to that of untreated broccoli.

A Glance at… Broccoli, glucoraphanin, and sulforaphane

“…Others have observed 7-to 12-fold increases in sulforaphane absorption when broccoli products or glucoraphanin are ingested in the presence of myrosinase activity [18][19][20][21][22]. All of these data confirm the importance of myrosinase activity for human absorption of sulforaphane from broccoli and broccoli products [6,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

“…Myrosinase is activated by exposure to oxygen but is heat sensitive [10][11][12][13]. Blanching broccoli before freezing [6], or steaming [14] or cooking raw broccoli [15], reduces myrosinase activity and, in humans, decreases the net total bioavailability of sulforaphane from frozen broccoli by 90% [6,14,15].…”

Concentrations of thiocyanate and goitrin in human plasma, their precursor concentrations in brassica vegetables, and associated potential risk for hypothyroidism

“…The anticarcinogenic benefits of sulforaphane, phenethyl isothiocyanate, and myrosinase-induced degradation products of indole glucosinolates can be maximized by raw consumption of the vegetables mentioned above or by the addition of functional myrosinase to denatured myrosinase (which results from cooking or blanching of frozen vegetables). 53 Comparison between isothiocyanate plasma concentrations from brassica vegetable ingestion and endogenous thiocyanate plasma concentrations…”

Thermal and pressure stability of myrosinase enzymes from black mustard (Brassica nigra L. W.D.J. Koch. var. nigra), brown mustard (Brassica juncea L. Czern. var. juncea) and yellow mustard (Sinapsis alba L. subsp. maire) seeds

“…In recent studies, it was found that addition of an exogenous source of myrosinase (Daikon radish root and mustard seeds) to processed Brassica can reinitiate the hydrolysis of glucosinolates (Dosz & Jeffery, 2013;Ghawi, Methven, & Niranjan, 2013). Hence, evaluating other sources of myrosinase that are more stable under processing conditions is of importance.…”