Investigation Of Glucosinolates And Their Effect Factors In Chinese Brassica Vegetables

Glucosinolates (GSs), a group of plant secondary metabolites, are mainly found in the family of Brassica. Over 120 different GSs have been identified in some of oil plants, vegetables, spices, medicament and other economically important varieties. Their enzymatical degradation products are responsible for the characteristic flavor, pathogen defense system and insect attractants of Brassica, and have been shown to possess anti-carcinogenic, cholesterol-reducing and other pharmacological effects. There is abundance of GSs in Cruciferous plants. Plenty of speices and cultivars of Chinese Brassica vegetables are largerly produced and consumed in China. However, there is little information about GSs in Chinese Brassica vegetables. The effects of species, cultivars, organs, leaf positions, harvest dates and nutrition levels (N and S) on the profiles and contents of GSs will be investigated in the thesis. The objectives are to know the effects of genotypes, havesting (organ, leaf positions and date) and fertilization (N, S) on the profiles and contents of GSs in Chinese Brassica vegetales, and therefore to optimize and regulate the GSs in vegetables. The main results obtained in our experiment are as follows:(1) The extraction, purification, isolation and identification of GSs in purple flowering Chinese cabbage were optimized. Nine individual GSs were isolated and identified by HPLC/ESI-MS, including four individual aliphatic GSs, four individual indolyl GSs and one individual aromatic GS. The method of quantitative determination of GSs by HPLC has been set up.(2) There were very significant differences of the compositions and contents of GSs among Chinese Brassica vegetables. Turnip (B. campestris ssp. rapifera) and purple flowering Chinese cabbage {B. campestris ssp. chinensis var. purpurea) had the highest content of GSs (8-13 mg/g DW), leaf mustard (B. juncea) and Chinese kale (B. alboglabra) the second (6.5-7.5 mg/g DW), Chinese cabbage (B. campestris ssp. pekinensis) and flowering Chinese cabbage (B. campestris ssp. chinensis var. utilis) the third (3-7 mg/g DW), and pakchoi (B. campestris ssp. chinensis var. communis) the lowest (2-3.5 mg/g DW). The main kind of GSs was inolyl GSs in Chinese cabbage and aliphatic GSs in other six Chinese Brassica vegetables. The mainindividual GS was gluconapin in pakchoi, turnip, Chinese kale and purple flowering Chinese cabbage, and glucoraphanin in flowering Chinese cabbage, and sinigrin in leaf mustard, and glucobrassicin and neoglucobrassicin in Chinese cabbage.(3) There were very significant differences of compositions and contents of GSs among 16 genotypes of pakchoi. The highest content of total GSs was about 4 mg/g DW, and the lowest about 1 mg/g DW. The relative percentage of aliphatic, indolyl and aromatic GSs to total GSs ranged from 30% to 80%, 10% to 50%, and 5% to 30%, respectively. The main individual GS was also observed very significant different among 16 genotypes. These results showed that the contents of GSs in pakchoi varied largely and could be improved through selecting genotype.(4) Very significant differences of compositions and contents of GSs were observed among 12 genotypes of Chinese kale. The total content of GSs ranged from 1-9 mg/g DW. The relative percentage of aliphatic and indoyl GSs to total GSs was 94%~65% and 35%~6%, respectively. The main GS was gluconapin.(5) Pakchoi can be havested in different growth periods in the production. The experiment with 3 harvest dates and 4 genotypes showed that the compositions and contents were significantly affected by both genotypes and harvest dates, and there was a significant interaction of harvest date and genotype. The total content of GSs and aliphatic, indolyl and aromatic GSs were decreased with the delay of harvest date. With the increase of growth period, there was an increase trend for relative percentage of aliphatic GSs and a decrease trend for relative percentage of indoyl GSs.(6) Both tender leaves and bolting stems are edible parts of Chinese kale. The very significant differences of compositions and contents between two organs were found in three cultivars of Chines kale. The contents of GSs in bolting stems were significantly higher than in leaves, for aliphatic GSs being 3-4.5 foldes, for indoyl GSs being 2-4 foldes, and for total GSs being 2.5-5.5 foldes. These results showed that there were significant differences of the distribution and accumulation of GSs in different organs, and these differences also were affected by genotype.(7) The analysis of GSs in different positions of pakchoi showed that the contents of individual GSs were considerably influenced by leaf position or leaf age, althoughthere was the same profile. The total content of GSs was firstly increased with leaf age and then decreased with leaf age, being the highest in the leaf before the largest (heaviest) leaf. The changes of the contents of aliphatic GSs and aromatic GSs were similar to the total GSs content. However, the content of indolyl GSs was decreased with leaf age. The relative percentage of aliphatic GSs was increased with leaf age, however, and those of indolyl GSs and aromatic GSs were decreased. It indicated that the leaf age could considerably affect the contents of GSs and have different effects on individual GS.(8) GSs are a kind of plant secondary metabolites which containing N and S. The effects of N and S on the contents of of GSs were investigated in three trials under different supply of N and S. The first was conducted in field experiment for pakchoi, the second in hydroponics for pakchoi, and the third in vermiculite for Chinese kale. There were significant influence of N, S and their interaction on the contents of aliphatic, indolyl, aromatic and total GSs. It suggests that N and S supply arc important effect factors in influencing the GSs contents and suitable supply level of N and S be favourable for the accumulation of GSs.