A thiourea-UV assay for total glucosinolate content in rapeseed meals

Determination of glucosinolates in rapeseed meal and their degradation by myrosinase from rapeseed sprouts

The utilization of rapeseed meal in food is limited due to its abundant glucosinolates (GLs). In this study, an LC-MS/MS method for GLs determination in rapeseed meal was developed. Then, the degradation of GLs using rapeseed sprouts derived myrosinase (MYR) was investigated. Results showed that 11 kinds of GLs were identified in rapeseed meal. The LC-MS/MS method had a high linearity (R² greater than 0.9999), repeatability (RSD < 5%) and recovery rate (92%-102%). The optimum condition for hydrolyzing GLs in rapeseed meal was reacting for 4 h with the addition of 2236.35 U/g MYR, 9.63 μg/g ascorbic acid and 26.68 μg/g EDTA. Under this condition, more than 80% of GLs were degraded and the yields of isothiocyanates and oxazolidinone-2-thione were 859.30 μg/g and 685.59 μg/g, respectively. To conclude, this study reported a reliable method for GLs determination and an effective way to degrade GLs in rapeseed meal.

A 96-Well Plates-based UV Spectrophotometric Assay for Determination of Total Glucosinolates in Isatis indigotica Roots

Background:

Glucosinolates (GLS) are important secondary metabolites in Cruciferae vegetables and herbs. Currently, the assays of total GLS determination are cumbersome (requiring acidic or enzymatic hydrolysis and addition of staining reagents), time-consuming, and indirect. High concentrations of inorganic salts are inevitably incorporated into the GLS products during separation. There is a need for a quantitative method for simple and rapid determination of total GLS after desalting process.

Methods:

A 96-well plates-based UV spectrophotometric method for determination of total GLS of Isatis indigotica roots was developed in the present study. The detection wavelength is set at 230 nm using quartz plates. This assay was validated using gluconapin and sinigrin as reference standards, and applied to determine the total GLS of I. indigotica roots prepared from five different desalting methods.

Results:

This assay is specific for total GLS prepared from I. indigotica roots, and it has acceptable accuracy (91.76–98.18% for quality control, and 95.59–102.52% for addition/recovery), precision (0.24–0.70% pooled RSD), reproducibility (0.31–1.84% RSD), and stability (0.24–1.45% RSD) over a 72-h period.

Conclusion:

The 96-well plates-based UV spectrophotometric assay is simple and accurate for high-throughput determination of total GLS.

Correlation between Flavour Compounds and Sensory Properties of Potherb Mustard (Brassica juncea, Coss.) Pickle

To characterise the flavour of the indigenous Chinese potherb mustard (Brassica juncea, Coss.) pickle, 28 samples representing two typical types with different brining storage time were sourced from 14 cities in the Yangtze River Delta Megalopolis area in China, either short time storage or long time storage pickles sampled from cities open markets. Pickle samples were assessed by descriptive sensory evaluation conducted using a trained panel and an established pickle flavour lexicon. Pickle samples were also analysed for flavour components, as expressed by physico-chemical parameters. The relationships between the flavour compounds and sensory properties of pickles were studied by the partial least squares (PLS) regression method. Results demonstrated that some latent variables both in the independent variables (physico-chemical parameters) and dependent variables (taste sensory attributes) can be extracted to build the PLS models for prediction. PLS1 regression of sensory data revealed that preference was predominantly related to umami taste, whereas umami taste was mainly related to free amino acid of glutamic acid and aspartic acid contents in the pickle juice. The biplot of PLS2 with all the samples and variables explained 100% of the X-variables (instrumental measurements) and 85% of the Y-variables (taste sensory attributes). The prediction abilities of the PLS models obtained yield good results for the prediction of taste sensory characteristics of potherb mustard pickle according to physico-chemical parameters analysis. However, the total instrumental analysing parameters collected for judgement of potherb mustard pickle quality was a rather large set of data, sensory values evaluated by trained panelists are relatively convenient to obtain. These results illustrated the application of multivariate analysis as an effective strategy for improving the quality of potherb mustard pickles.