Stir-Frying of Chinese Cabbage and Pakchoi Retains Health-Promoting Glucosinolates

Abstract

Stir-frying is a cooking method, originating from Asia, in which food is fried in small amount of very hot oil. Nowadays in many other parts of the world stir-frying is a very popular method to prepare vegetables, because it is fast and fried vegetables are tasty. However, the retention of phytochemicals like the health-beneficial glucosinolates in Brassica vegetables is less explored for stir-frying in comparison to other cooking methods. This study investigates the retention of glucosinolates in Chinese cabbage (Brassica rapa ssp. pekinensis) and pakchoi (Brassica rapa ssp. chinensis) as affected by stir-frying at various cooking durations and temperatures. Stir-frying experiments were performed at set pan temperatures ranging from 160 to 250 °C for a duration of 1 to 8 min. Results showed that aliphatic glucobrassicanapin is the most abundant glucosinolate identified in fresh Chinese cabbage and pakchoi, contributing for 48 and 63% of the total glucosinolate content, respectively, followed by glucoiberin and gluconapin. Stir-frying retains the glucosinolates even at the highest temperature applied. Such retention is explained by the quick inactivation of the glucosinolate-hydrolytic enzyme myrosinase during the first minutes of frying, and by the thermal stability of the glucosinolates at those temperature/time conditions. Moreover, due to the absence of a separate water phase, leaching losses did not occur, in contrast to what is observed when boiling Brassica vegetables. These results show that stir-frying may be a suitable health-beneficial cooking option that prevents the loss of glucosinolates.

Isothiocyanates from Brassica Vegetables—Effects of Processing, Cooking, Mastication, and Digestion

“…Thermal degradation is the primary process observed during stir‐frying, since no water is added to the pan and no leaching into the cooking water can occur. Several studies report full retention of GLs after stir‐frying, but in other studies losses are reported . Stir‐frying “nero di Toscana” ( Brassica oleracea L .…”

“…Air drying may retain GLs depending on the treatment conditions (water content, temperature, and time) . Various air drying temperatures (50–100 °C) led to varying extents of reduction (17–45%) of total indole‐containing GLs in broccoli, while the more heat labile MYR was completely inactivated . However, by optimizing the conditions, all of the glucoraphanin and 55% of the endogenous MYR could be retained upon air drying of broccoli …”

“…Studies show that a small portion of the intact GLs can be absorbed and excreted intact, although the absorption mechanism is unclear (passive diffusion or facilitated transport) ( Figure ) . The portion of GLs that arrive in the lower gut is bioaccessible for MYR‐like activity of the human microbiota, although the formation of ITCs is reported to be lower than the conversion that occurs under plant conditions (Figure ) …”

Effect of cooking methods on the health‐promoting compounds, antioxidant activity and nitrate of tatsoi (Brassica rapaL. ssp.narinosa)

“…Both total aliphatic and indole GSLs reduced by stir‐frying was observed in broccoli (Yuan et al, ). In contrast, Nugrahedi, Oliviero, Heising, Dekker, and Verkerk () found stir‐frying enhanced the total GSLs content in Chinese cabbage and pak‐choi by 30%–100%. Nugrahedi, Verkerk, Widianarko, and Dekker () proposed that well preserving or increase in the total GSLs content in stir‐fried Brassica vegetables were ascribed to a low degree of leaching into water, thermal degradation and enzymatic hydrolysis during stir‐frying cooking.…”

“…Nugrahedi, Verkerk, Widianarko, and Dekker () proposed that well preserving or increase in the total GSLs content in stir‐fried Brassica vegetables were ascribed to a low degree of leaching into water, thermal degradation and enzymatic hydrolysis during stir‐frying cooking. Moreover, quick inactivation of myrosinase at high temperature/time conditions and breakdown of plant tissue upon heat resulted in thermal stability of the GSLs when frying (Nugrahedi et al, ; Vallejo et al, ).…”