Optimizing glucosinolate analysis

I’ll highlight microwave findings of this 2021 study:

“Glucosinolates (GSLs) are important precursor compounds with anticancer activities in Brassicaceae vegetables and are readily hydrolyzed by myrosinase. Given the diversity of these species, establishing an accurate and universal method to quantify intact GSLs in different plant tissues is necessary.

We compared and optimized three tissue disruption methods for sample preparation:

  • Recoveries of GSLs in a Chinese cabbage sample were significantly lower than 100% after microwave treatment for 60 s, due to insufficient inactivation of myrosinase.
  • After microwave treatment for 90 s, recoveries of 13 GSLs were in the range of 73–124%, indicating that this condition could inactivate myrosinase completely.
  • The increase in GSL recoveries with microwave treatment for 120 s might be due to increased extractability of GSLs.
  • A limitation of this method was that different tissues could not be processed under the same microwave conditions.

molecules-27-00231-g001

SIN, Sinigrin; NAP, Gluconapin; GBN, Glucobrassicanapin; PRO, Progoitrin; ERU, Glucoerucin; RAE, Glucoraphenin; RAA, Glucoraphanin; ALY, Glucoalyssin; GBC, Glucobrassicin; 4ME, 4-Methoxyglucobrassicin; NEO, Neoglucobrassicin; TRO, Glucotropaeolin; NAS, Gluconasturtiin.

Five GSLs without available standards were estimated using calibration curves of structurally similar compounds. Specifically, the pair glucoberteroin (GOB) and glucoerucin (ERU), glucoiberin (GIB) and glucoraphanin (RAA), gluconapoleiferin (GNL) and PRO, and 4OH and 4ME are homologs that differ in structure by one -CH2 group, with glucoraphasatin (GRH) containing an alkenyl group in its molecular structure, which is two hydrogen atoms less than ERU.

The verified method of intact GSLs by UHPLC-MS/MS established in this study was more accurate and time-saving than the commonly used ISO method for desulfo-GSLs.”

https://www.mdpi.com/1420-3049/27/1/231/htm “Determination of 18 Intact Glucosinolates in Brassicaceae Vegetables by UHPLC-MS/MS: Comparing Tissue Disruption Methods for Sample Preparation”


This study was in line with other studies that increased GLS amounts by microwaving. For example, most of the above graphic’s Chinese cabbage GLS measurements at 90 seconds were greater than raw samples, which kept going:

“The increase in GSL recoveries with microwave treatment for 120 s might be due to increased extractability of GSLs.”

Unlike this study, my goal is to optimize glucosinolate hydrolysis products such as sulforaphane. I increase myrosinase enzyme activity rather than decrease it, and want to have less GLS amounts than what I started with after processing.

I facilitate myrosinase activity by:

  • Adjusting immersion water to pH 5; and
  • Stopping at 60°C (140°F) to avoid a myrosinase deactivation cliff between 60°C and 65°C.

This study used a 900W microwave to process 30-gram broccoli floret samples at Figure S1 different times (20, 40, 60, 90, 120, 180 seconds). I use a 1000W microwave to process a 65-gram broccoli / red cabbage / mustard sprouts mix in 100 ml water for 40 seconds.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.