Effects of Novel Processing Techniques on Glucosinolates and Membrane Associated Myrosinases in Broccoli

Abstract

longed shelf-life by inactivation of micro-organisms and enzymes. HP/HT can at temperatures above 50 o C lead to pasteurization using pressure levels from 250-500 MPa [Wilson et al., 2008], while sterilization can be obtained with HP at temperatures higher than 70 o C . Focus is thus on the application of HP in combination with high temperatures (HT), which may lead to tissue compression, cell wall breakage and cell membrane disruption, depending on the HP and HT levels as well as the type of vegetable or fruit that are treated [Michel & Autio, 2002]. In the present study, where broccoli has been processed, the food quality is particularly connected with the enzyme-substrate (myrosinase--glucosinolate) system, where the different types of non-enzymatic and enzymatic catalyzed hydrolysis products give rise to effects from being health promoting to affecting the taste and odor [Hansen et al., 1995[Hansen et al., , 1997 Jeffery & Aray, 2009].PEF is considered a non-thermal treatment, which can lead to pasteurization at ambient temperatures using electrical field strengths of 20-30 kV/cm, and short pulses of 1-10 µs [Mosqueda-Melgar et al., 2008]. Application of short electric pulses may result in pore formation in cell membranes, and depending on the treatment intensity, time, electric field and pulse energy the membrane permeabilisation High pressure/high temperature (HP/HT) and pulsed electric field (PEF) treatment of food are among the novel processing techniques considered as alternatives to conventional thermal food processing. Introduction of new processing techniques with fast and gentle processing steps may reveal new possibilities for preservation of healthy bioactive compounds in processed food. However, effects on various food components due to autolysis and fast reactions prior to the applied HP/HT or PEF need to be considered as the total contribution of processing steps affects the obtained food quality. The present experiments were performed on broccoli (Brassica oleracea var. Italica) florets, purée and juice. Specific focus was given to effects of HP/HT and PEF processing on the content of glucosinolates and activities of myrosinase isoenzymes (EC.3.2.1.147) in the broccoli preparations. Certain conditions applied in HP/HT processing of broccoli florets were able to maintain a high level of intact glucosinolates. Treatment at 700 MPa and 20°C for 10 min was found to inactivate myrosinase activity, but also pressure treatments at 300 MPa and 20°C were able to maintain a high level of intact glucosinolates present in the untreated broccoli florets. PEF processing of broccoli purée and juice showed that the myrosinase activities resulted in nearly total glucosinolate transformations as result of autolysis during puréeing and juice making prior to the PEF processing. These data demonstrated that insight into potential effects on myrosinase activities from application of PEF processing implies specific focus on the sample steps preceding the PEF processing. Processing of broccoli and autolysis reaction...

The impact of high pressure on glucosinolate profile and myrosinase activity in seedlings from Brussels sprouts

“…It is, anyway, more likely that the observed degradation of the glucosinolates is a result of a fast interaction with the active enzyme myrosinase, as shown in previous studies (Bellostas et al, 2008). The pattern observed in glucosinolate concentration related to pressure is similar to the results obtained when broccoli heads were HP-treated for 10 min at different pressure levels (Frandsen et al, 2014), where a decrease in glucosinolate content was observed at 300 MPa, followed by an increase at 700 MPa.…”

“…In these studies, HP parameters had an impact on the myrosinase activity and the extent of glucosinolate hydrolysis. The effects from the HP treatment may however be blurred by pre-processing effects on enzymes and bioactive compounds upon disruption of (Frandsen et al, 2014). This stresses the importance of investigating the myrosinase-glucosinolate interactions in a well-defined and homogenous plant matrix in order to provide basic knowledge of the HP impact on the health beneficial compounds from cruciferous vegetables.…”

“…by cutting, or juice preparation, the myrosinase will be able to degrade glucosinolates. The effect of pre-processing is very clear when the glucosinolate levels are examined in different pre-processed products (Frandsen et al, 2014).…”

Taste and Flavor Perceptions of Glucosinolates, Isothiocyanates, and Related Compounds

“…Compounds such as sinigrin, gluconapin, progoitrin, and indole GSLs (glucobrassicin, neoglucobrassicin) are cited as imparting bitterness in crops such as broccoli, and other varieties of B. oleracea ; however, this effect is not universal, as taste panelists do not uniformly detect or describe these as bitter in isolation (Table ) . This suggests that some individuals may be “non‐tasters” or “bitter blind” for these GSL compounds, as with PROP and PTC.…”

Effects of Pulsed Electric Fields Processing Strategies on Health-Related Compounds of Plant-Based Foods

“…In a recent study, Frandsen et al [21] evaluated the effect of PEF treatment conditions on broccoli glucosinolates and associated myrosinase isoenzymes. The study could not find differences in glucosinolate contents related to the type of waveform and treatment time.…”