Placing broccoli under pressure enhances its disease-fighting compounds

By Tim Cutcliffe

- Last updated on GMT


Related tags Broccoli sprouts Brussels sprout

A high-pressure processing method could rid broccoli of harmful bacteria while preserving the vegetable’s cancer-fighting glucosinolate compounds, according to German researchers.

The method subjects broccoli to pressures of 400 - 600 megapascals (MPa), a process that increases the amount of glucosinolates that turn into the anti-cancer and anti-inflammatory isothiocyanate compounds.

Trials carried out at the Friedrich Schiller University in Germany found that the highest degree of conversion (85%) was observed after treatment with 600 MPa

“High pressure pasteurization (HPP) treatments use pressures in the range of 600 MPa at chilled or ambient temperatures for specified duration,”​ explained the team, led by professor Volker Böhm, lecturer at the Friedrich Schiller University of Jena in Germany.

“Since 1997, HPP has been successfully applied to ready-to-eat (RTE) meats, seafood, marinated raw ​meats, juices, salads, and fruit and vegetable products.”

“Because more glucosinolates were turned over into isothiocyanates after HPP at 400–600 MPa, these treatments may be interpreted to have a positive effect on the health potential of broccoli sprouts.”

Broccoli's health credentials 

Broccoli sprouts are a rich source of glucosinolates, a group of phytochemicals that may play a role in tackling multiple types of cancer.

Broccoli sprouts have recently become popular as a result of their 10–100 times higher levels of glucoraphanin compared to that of mature broccoli.

Thus, consuming smaller amounts of broccoli sprouts may exert the same efficacy in reducing cancer risk as much higher quantities of mature broccoli.

The predominant glucosinolates in broccoli and broccoli sprouts are glucoraphanin and glucoerucin, which are hydrolysed into the isothiocyanates sulforaphane and erucin, respectively.

The plant enzyme myrosinase is released when the tissue of broccoli is attacked by insects, herbivores, or microorganisms.

As a result, glucosinolates are hydrolysed to various breakdown products, including isothiocyanates, thiocyanates, and nitriles.

Study details

Along with colleagues from Ohio State University in the US, the team took 6-day-old broccoli sprouts and placed 1.5–2 grams (g) into sterile filter bags that were vacuum-packed and heat-sealed.

The broccoli sprout samples were treated for 3 min at 100, 200, 300, 400, 500, and 600 MPa (±5 MPa) at 30 ± 2 °C.

After the pressurization, the pouches were flash-frozen in liquid nitrogen and stored at −80 °C until glucosinolate and isothiocyanate analysis.

Additional pouches with 1.5–2.0 g of fresh, raw broccoli sprouts were prepared by vacuum packaging the sprouts and heat-sealing the samples.

 A mild heat treatment at 60 °C and boiling at 100 °C were used as positive and negative controls, respectively.

These control sprouts were flash-frozen in liquid nitrogen and stored at −80 °C until analysis.

The team found that raw, untreated sprouts had a total isothiocyanate content of 0.57 micromols per gram (μmol/g).

The 60 °C mildly heated sprouts (positive control) had significantly increased levels, while the boiling at 100 °C (negative control) resulted in concentrations that were not quantifiable.

The isothiocyanate contents of the sprouts treated at 100–300 MPa were comparable to the raw, untreated sprouts.

However, a significant increase of the isothiocyanate content was recorded for the sprouts treated at 400, 500, and 600 MPa.

“From 400 MPa onward, the degree of conversion increased up to 85% for 600 MPa,”​ the study commented.

“With increasing pressure, more decompartmentalisation was achieved, myrosinase remained active, and possibly ESP was selectively inactivated, to effect the conversion to isothiocyanates.

“The formation of isothiocyanates was observed in all HP-treated broccoli sprouts, suggesting that myrosinase was active after HPP.”

The results are in keeping with a previous study​ that found after pressure treatment considerable amounts of glucosinolates were also hydrolysed into isothiocyanates.

After a 35 min treatment, the 300 MPa treatment exhibited the highest conversion. After the 500 MPa treatment, only a small amount of sulforaphane were formed, which was explained by myrosinase inactivation.

Source: Journal of Agriculture and Food Chemistry

Published online ahead of print: DOI: 10.1021/acs.jafc.7b01380

“High-Pressure Processing of Broccoli Sprouts: Influence on Bioactivation of Glucosinolates to Isothiocyanates.”

Authors: Volker Böhm et al.

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