The flavonoid composition of immature leaves of pak choi [Brassica rapa L. ssp. chinensis L. (Hanelt.)] was investigated. Flavonol aglycone content was measured in 11 pak choi varieties, indicating significant differences (P < 0.05) in content between varieties and relatively high contents of kaempferol and isorhamnetin. Levels of quercetin ranged from 3.2 to 6.1 mg/100 g of dry weight (DW), whereas levels of isorhamnetin and kaempferol were significantly higher (8.1-35.1 and 36.0-102.6 mg/100 g of DW, respectively). A large number of glycoside and hydroxycinnamic acid derivatives of quercetin, kaempferol, and isorhamnetin were identified in cv. 'Shanghai' by LC/UV-DAD/ESI-MS/MS. The UV-DAD data allowed identification of hydroxycinnamic acid derivatives, but detailed MS/MS fragmentations were required for the structure elucidation. Pak choi could be a potentially important source of dietary flavonols, in particular, kaempferol and isorhamnetin.

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Carrots are one of the highest dietary sources of beta-carotene and are naturally high in the (all-E)-beta-carotene isomer, which has higher bioavailability, provitamin A activity, and antioxidant capacity compared to Z (cis) isomers. The objectives of the present study were to investigate the effects of storage temperature, time, and cooking (boiling for 15 min) on the levels of carotene isomers in 'Stefano' carrots. Storing carrots at either 4 degrees C to simulate long-term storage or 20 degrees C to simulate marketing practices resulted in increases in (all-E)-beta-carotene of 20.3% after 3 days at 4 degrees C and 34.4% after 14 days at 20 degrees C, respectively. The levels of Z isomers in raw carrots were low with (13Z)-beta-carotene and (9Z)-beta-carotene accounting for less that 1.8% of the total beta-carotene present. Levels of (9Z)-beta-carotene decreased during storage at either temperature, whereas storage at 4 degrees C resulted in a 109% increase in (13Z)-beta-carotene after 56 days. Cooking significantly increased the levels of (13Z)-beta-carotene and (9Z)-beta-carotene and resulted in the production of (15Z)-beta-carotene, which was absent in raw carrots. Storage at 4 degrees C for 15 days or more prior to cooking reduced the susceptibility of (all-E)-beta-carotene to thermal isomerization during cooking, resulting in lower levels of all three Z-beta-carotene isomers being generated, while storage at 20 degrees C for up to 21 days resulted in significantly higher levels of (all-E)-beta-carotene before and after cooking but had no effect on Z-isomer production during cooking. Consequently, we conclude that, for the greatest health benefit, fresh carrots can be stored for up to 21 days at 20 degrees C or at 4 degrees C for up to 56 days without significant reduction in (all-E)-beta-carotene and should be consumed raw or boiled for less than 15 min to limit Z-beta-carotene isomer formation.

Broccoli (Brassica oleracea var. italica) heads are commonly consumed in the Western diet and frequent consumption is thought to help protect against certain cancers and cardiovascular disease. Broccoli heads contain relatively high levels of glucosinolates and flavonols, thought to be the key phytochemicals that contribute to the health benefits gained upon consumption. In this study, we investigated the effect of applied nitrogen (N) at either 0, 15, 30 or 60 kg/ha, or 30, 60, 90 or 150 kg/ha with applied sulfur (S) at 50 or 100 kg/ha on the glucosinolates glucoraphanin, glucobrassicin and progoitrin, and the flavonols quercetin and kaempferol in broccoli cv. Marathon florets. Trials were conducted in two sites in either heavy clay or sandy loam to also assess the effect of soil type on phytochemical content. Application rates were based around recommended N and S applications for this crop in south-east Australia. N applications over 30 kg/ha caused a decrease in the content of glucoraphanin (18–34%) and both flavonols (20–38%). Progoitrin content was not affected while glucobrassicin increased by up to 44% with N applications >30 kg/ha. S applications of 50 or 100 kg/ha had no significant effect on either glucosinolates or flavonols. Crop yield (fresh weight), however, was significantly depressed (up to 40%) by N applications below 60 kg/ha. Fresh weight was also significantly depressed in plants grown in heavy clay compared with plants grown in a sandy loam, and phytochemical content increased, possibly due to a concentration effect. Therefore, low N applications to optimise phytochemicals may be only commercially useful if growers are producing mini-broccoli heads, as levels required to optimise phytochemical content (<30 kg/ha) also caused a significant decline in yield.

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