A Mechanistic Perspective on Process-Induced Changes in Glucosinolate Content inBrassicaVegetables: A Review

Abstract

Brassica vegetables are consumed mostly after processing, which is expected to give beneficial effects on the vegetable properties, such as improved palatability and bioavailability of nutrients, or shelf life extension. But processing also results to various changes in the content of health promoting phytochemicals like glucosinolates. This paper reviews the effects of processing on the glucosinolates content by using a mechanism approach underlying processing method employed. Cultural differences between Eastern and Western preparation practices and their possible effect on glucosinolate retention are highlighted. Boiling and blanching considerably reduce the glucosinolate content mainly due to mechanisms of cell lysis, diffusion, and leaching, and partly due to thermal and enzymatic degradation. Steaming, microwave processing, and stir frying either retain or slightly reduce the glucosinolates content due to low degrees of leaching; moreover, these methods seem to enhance extractability of glucosinolates from the plant tissue. Fermentation reduces the glucosinolate content considerably, but the underlying mechanisms are not yet studied in detail. Studying the changes of glucosinolates during processing by a mechanistic approach is shown to be valuable to understand the impact of processing and to optimize processing conditions for health benefits of these compounds.

Glucosinolates in Food

“…Much lower, or no, losses have been observed when shorter time is applied to boiling of broccoli florets (3 to 8 min) and Brussels sprouts (10 min), whereas significant losses (38 %) have still been found after a relatively short boiling time (10 min) on cauliflowers [120,206]. Steaming, by preventing direct contact to boiling water, results as a much more effective method in preserving the original GLS content of the freshly harvested vegetable: tests carried out on cabbages, broccoli, cauliflowers, and Brussels sprouts, by varying cooking time up to 20 min, have shown either slight decreases or increases in total GLS content [199]. The increase of GLS content may be ascribed to an increased extractability of GLS from the food matrix in the analytical process due to the effect of the heat treatment.…”

“…It is generally agreed that the impact of postharvest handling and storage is in most cases less pronounced than the effects of processing and preparation, even though the extent of these changes critically depends on the type of vegetables, the processing method, and the specific processing conditions applied [199]. Transport and storage are key steps in postharvest life of vegetables before consumer purchase and environmental conditions in these steps are generally optimized with reference to visual quality.…”

“…There is a great variety of preparation methods worldwide, ranging from boiling to steaming, microwave cooking, stir-frying, and fermentation, the combination of procedures and ingredients changing across regions and cultures [199]. In addition, variability in home preparation is further widened by individual preferences about sensory properties of cooked vegetables, which dictate time-temperature settings of the applied domestic cooking processes.…”

“…Among cooking methods, boiling is probably the most common used for Brassica vegetables, at least in Western countries, and in some instances it may produce a substantial depletion of the GLS content present in the raw vegetable. Losses of GLS due to boiling are strongly influenced by the time of cooking, ratio of vegetable to water, and type of vegetable and mainly occur through leaching into cooking water [199]. Regarding the effect of the type of vegetable, it has been observed a progressive increase of GLS losses from 58 % to 65 %, 75 %, and 77 %, moving from Brussels sprouts to green cabbages, cauliflowers, and broccoli, respectively, after 30 min of boiling [204].…”

“…In the above sections, GLS content has been mainly discussed as determined in the freshly harvested vegetables, but it is important to keep in mind that this original content can be, even substantially, affected by the several steps of the food supply chain occurring before actual consumption: transport, storage, industrial processing, and home preparation [72,[197][198][199]. It is generally agreed that the impact of postharvest handling and storage is in most cases less pronounced than the effects of processing and preparation, even though the extent of these changes critically depends on the type of vegetables, the processing method, and the specific processing conditions applied [199].…”