Effects of ethylene, cytokinin and physical treatments on BoPaO gene expression of harvested broccoli

BACKGROUND: Broccoli is a highly perishable vegetable that shows enhanced postharvest senescence and intense de‐greening caused by chlorophyll degradation. One of the key steps of chlorophyll catabolism is the opening of chlorophyll tretrapyrrole catalysed by pheophorbide a oxygenase (PaO). In this study the expression of a gene encoding a putative PaO was characterised under several chemical and physical treatments. RESULTS: A fragment of a gene encoding a PaO from broccoli (BoPaO) was cloned. The expression of BoPaO showed an important increment during postharvest senescence, in correlation with chlorophyll degradation. Furthermore, broccoli heads were treated with the hormones cytokinin and ethylene. Cytokinin delayed the increment in BoPaO expression, while ethylene accelerated the process. Also, several postharvest treatments were applied in order to evaluate their effect on BoPaO expression. Samples treated with modified atmosphere, hot air, UV‐C or white light showed a delay in chlorophyll degradation and de‐greening. In most cases the treatments also delayed the increment in BoPaO expression during senescence. CONCLUSION: A close correlation between chlorophyll degradation and BoPaO expression was found during broccoli senescence. This relationship was corroborated in samples treated with different hormonal and physical applications. Copyright © 2011 Society of Chemical Industry     

Effect of hot air treatments on senescence and quality parameters of harvested broccoli (Brassica oleracea L var Italica) heads

Treatments with hot air were applied to broccoli (Brassica oleracea L) florets to investigate the effect on several quality and senescence parameters. To select the optimum treatment, florets were treated with different combinations of time/temperature ranging from 1 to 3 h and 37 to 50 °C and then placed in darkness at 20 °C. Most treatments delayed yellowing and loss of chlorophylls, except those performed at 37 °C, which accelerated senescence. Treatment at 48 °C for 3 h caused the highest delay in chlorophyll loss and was chosen to analyse its effect on quality and senescence. Non‐treated florets showed yellowing and reduced their chlorophyll content during storage. Heat treatment delayed the onset of chlorophyll catabolism by 1 day and slowed down the rate of degradation. Treated florets also showed lower losses of total sugars and proteins and an inhibition of protein solubilisation. Control heads showed an increment in CO₂ production, which was not detected in heat‐treated florets. Total antioxidants decreased and thiobarbituric acid‐reactive substances (TBARS) increased during storage. The treatment delayed the decrease in antioxidant content and inhibited the increment in TBARS. In conclusion, treatment at 48 °C for 3 h delayed broccoli senescence at 20 °C and contributed to maintaining an overall better quality of the product. Copyright © 2005 Society of Chemical Industry     

Hot air treatment decreases chlorophyll catabolism during postharvest senescence of broccoli (Brassica oleracea L. var. italica) heads

A hot air treatment was applied to broccoli (Brassica oleracea L. var. italica) florets and its effect on chlorophyll catabolism during postharvest senescence was analyzed. Florets were treated at 48 °C for 3 h and then placed in darkness at 20 °C. During storage, the yellowing of florets occurred simultaneously with a decrease in chlorophylls and an increase in pheophytins. Heat treatment delayed the appearance of yellowing by 2–3 days and a similar extension of shelf‐life could be inferred. Also, the treatment delayed the onset of chlorophyll catabolism and slowed both the rate of chlorophyll a degradation and pheophytin accumulation. No effect on chlorophyll b degradation was found. Chlorophyllase and Mg‐dechelatase activities increased from the first day of storage in untreated florets, whereas peroxidase‐linked chlorophyll bleaching activity increased from day 3. In heat‐treated florets, chlorophyllase activity did not increase until day 2 and then increased at lower rate than in controls. Mg‐dechelatase and peroxidase‐linked chlorophyll bleaching activities were similar in treated and control florets during the first 2 days of storage, but thereafter the activity of both enzymes was lower in heat‐treated samples. In conclusion, a treatment at 48 °C for 3 h delayed chlorophyll a catabolism in broccoli during postharvest senescence and decreased the activities of chlorophyllase, Mg‐dechelatase and peroxidase, three of the enzymes probably involved in chlorophyll degradation in plants. Copyright © 2006 Society of Chemical Industry     

Influence of postharvest UV‐C treatment on refrigerated storage of minimally processed broccoli (Brassica oleracea var. Italica)

Minimally processed broccoli was treated with UV‐C light (8 kJ m^?2) and subsequently stored for 21 days at 4 °C. The UV‐C treatment delayed yellowing and chlorophyll degradation during storage. Treated broccoli florets displayed lower electrolyte leakage and respiratory activity, indicating higher tissue integrity. Treated samples showed higher phenolic and ascorbic acid contents as well as higher antioxidant activity than controls. Treated samples also had a higher content of soluble sugars, but no differences in the content of soluble proteins between control and treated samples were detected. The UV‐C treatment also affected bacterial and mould populations. After 21 days at 4 °C the number of colony‐forming units of both populations was lower in treated than in control broccoli florets. The results suggest that UV‐C treatment reduces tissue damage of minimally processed broccoli during storage at 4 °C, thus maintaining nutritional quality and reducing microbial growth. Copyright © 2007 Society of Chemical Industry     

Maintaining quality and bioactive compounds of broccoli by combined treatment with 1‐methylcyclopropene and 6‐benzylaminopurine

BACKGOUND: Broccoli deteriorates very quickly after harvest at ambient temperature due to the loss of green colour and the consequent yellowing of florets. To search for an effective method to control quality deterioration, the effect of 1‐methylcyclopropene (1‐MCP) combined with 6‐benzylaminopurine (6‐BA) treatment on visual quality, antioxidant enzymes and bioactive compounds in broccoli florets were investigated. RESULTS: A combined treatment of 2.5 µL L^?1 1‐MCP and 200 mg L^?1 6‐BA significantly reduced the increase of lightness (L*) value, and retained a high level for the hue value (H) and chlorophyll content. Superoxide dismutase, ascobate peroxidase and catalase activities increased while the activity of peroxidase decreased during storage in treated samples in comparison with the controls. The combined treatment enhanced the biosynthesis of glucosinolate and the formation of the anticarcinogen sulforaphane, which improved the health benefit of broccoli. CONCLUSION: These results indicate that a combined treatment of 1‐MCP and 6‐BA could be a good candidate for maintaining the visual quality and enhancing the nutritional value in broccoli during storage at 15 °C. © 2012 Society of Chemical Industry     

Advances in the use of white light on broccoli and kale postharvest shelf life

In this work, the effect of irradiation with three different intensities of white light-emitting diodes (LED) on the quality and senescence of refrigerated broccoli and green and red kale was studied. A high increase in weight loss was observed in samples exposed to high (80 μmol m⁻² s⁻¹) and low (10 μmol m⁻² s⁻¹) LED intensity. Samples stored under mid-intensity (30 μmol m⁻² s⁻¹) significantly reduced the change of total color (∆E), hue angle, and lightness (L*) values. Broccoli florets and green kale subjected to mid-intensity illumination retained higher chlorophyll levels than the other treatments (P < 0.05), and about 30% more compared to the dark stored samples. These differences were even more evident in red kale. Mid-intensity illumination also markedly reduced sugar losses and improved carotenoid contents. As a whole, results show that the selected intensity of white light used for postharvest illumination has a key influence on treatment efficacy.Industrial relevancePostharvest shelf life of green vegetables is very limited and there is a need to use environmentally friendly tools to extend it. The use of white light during storage has been proven to be a clean and non-chemical methodology to delay vegetable senescence, but the appropriate illumination conditions to maximize the quality of unprocessed vegetables are still unknown. In the present work, the effect of different lighting conditions on the visual and nutraceutical quality of refrigerated broccoli and green and purple kale was studied, and the best condition was defined. The selected light intensity may be considered for fresh market storage.     

采后青花菜花球抗氧化水平变化与衰老的关系

为研究采后青花菜花球抗氧化水平变化与衰老的关系,将采后青花菜花球贮藏于20℃条件下,连续4 d测定了花蕾衰老生理指标(叶绿素、蛋白质、丙二醛(MDA)含量)及抗氧化水平指标(抗坏血酸(AsA)和β-胡萝卜素(β-Car)含量、超氧化物岐化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化氢酶(APX)活性)。结果表明:贮藏过程中,叶绿素和蛋白质含量逐渐减少,MDA含量逐渐增多;AsA和β-Car含量逐渐减少,SOD、CAT和POD活性逐渐升高,APX活性逐渐降低;这些抗氧化水平指标与衰老生理指标的线性相关性均在1%水平显著。说明采后青花菜花球的抗氧化水平变化与衰老密切相关。     

微酸性电解水对采后西兰花贮藏品质的影响

为了探究微酸性电解水（Slightly acidic electrolyzed water,SAEW）对采后西兰花贮藏品质的影响,本研究首先进行了微酸性电解水浓度的筛选,将西兰花切成均等的小花球,随机分成五组,以自来水浸泡15 min后晾干作为对照,以25、50、75和85 mg/L的微酸性电解水浸泡15 min后晾干作为不同处理组,置于15±1 ℃贮藏4 d,依据不同浓度微酸性电解水对采后西兰花外观品质、总叶绿素及丙二醛（MDA）含量的影响筛选最适宜的浓度。结果表明,与对照和其它浓度的SAEW处理相比,50 mg/L SAEW可更好地维持采后西兰花的外观品质及总叶绿素含量,并抑制其MDA含量的积累。进一步研究显示,与对照组相比,50 mg/L SAEW可有效维持采后西兰花的感官品质,抑制其菌落总数的升高,延缓其维生素C、可溶性糖、可溶性蛋白、可滴定酸、总硫苷和萝卜硫素含量的下降,并可有效抑制组织中亚硝酸盐含量的升高。这些结果表明50 mg/L SAEW可作为一种维持采后西兰花贮藏品质、延缓其衰老进程的有效处理方法。     

Effect of controlled atmospheres with varying O2/CO2 levels on the postharvest senescence and quality of broccoli (Brassica oleracea L. var. italica) florets

Controlled atmosphere (CA) has been widely used to help extend the shelf life and maintain the quality of horticultural products. In the present study, broccoli (Brassica oleracea L. cv. Youxiu) florets were stored under CA with high levels of O₂/CO₂ at 15 °C, including 100 % O₂, 80 % O₂ + 20 % CO₂, 60 % O₂ + 40 % CO₂, 40 % O₂ + 60 % CO₂, and air (control), to determine the effects of CA on storage period and on some physiological properties during storage. The results showed that compared with the control, the treatments combining O₂ and CO₂ effectively extended the storage period and inhibited respiration rate, ethylene production, and reductions in weight loss, chlorophyll, and ascorbic acid levels. Moreover, the CA treatments inhibited the increases in both superoxide radicals (O ₂ ^?· ) production rate and hydrogen peroxide (H₂O₂) level and reduced malondialdehyde accumulation, which could be beneficial in delay of senescence by alleviation of oxidative damage. In addition, broccoli florets exposed to CA conditions maintained lower activities of superoxide dismutase and peroxidase that are responsible for scavenging of O ₂ ^?· and H₂O₂ and alleviating lipid peroxidation. Among the treatments, the maximum efficacy was observed with a CA of 40 % O₂ + 60 % CO₂, which prolonged the storage period of broccoli heads to 17 days (d) compared with 4 d under air treatment. Conversely, 100 % O₂ treatment accelerated senescence and deterioration in the quality of broccoli, resulting in a shorter storage period. These results suggest that the establishment of an appropriate CA condition with high levels of O₂/CO₂ may be an ideal strategy for maintaining the quality of broccoli florets during storage.     

Effect of industrial processing on amino acid content of broccoli

The levels of amino acids in broccoli stems and florets before and after various blanching times (in the case of freezing) and after bottling have been studied to elucidate to what extent nutrient quality is affected by industrial processing. The following amino acids (mg kg^?1 fresh weight) were identified by ion exchange chromatography in raw broccoli florets: glutamine (1338), proline (732), asparagine (578), valine (310), arginine (296), isoleucine (204), threonine (169), leucine (166), phenylalanine (159), aspartic acid (140), lysine (127), alanine (122), tyrosine (105), S‐methylcysteine (96), histidine (89), ornithine (59), glutamic acid (44), γ‐aminobutyric acid (31), glycine (11) and serine (0.2). Raw stems contained the same amino acids but at lower levels (p < 0.05). The levels of all these amino acids fell during both industrial processes studied (bottling and freezing after blanching for 60, 90, 120 and 150 s), particularly in the frozen samples (losses of 50–70% in the florets and 20–50% in the stems). In summary, losses of broccoli amino acids were lower if blanching times were kept short. The optimal blanching time at 94 °C for florets and stems intended for freezing was 90 s, and this did not result in any great loss of nutritional value related to amino acid content. Bottled florets had greater nutritional value than those frozen after being exposed to the longest blanching times (120 and 150 s). © 2001 Society of Chemical Industry     

Suppression of postharvest blue mould of apple fruit by Cryptococcus laurentii and N6‐benzyladenine

BACKGROUND: Cryptococcus laurentii is a well‐known postharvest yeast antagonist. N⁶‐benzyladenine (6‐BA), a cytokinin plant hormone, has a role in retarding ripening and senescence of harvested produce. This study was conducted to evaluate the efficacy of C. laurentii and 6‐BA in reducing the blue mould disease of apple fruit. RESULTS: The combination of C. laurentii with 6‐BA (20 µg mL^?1) was more effective in suppressing the Penicillium expansum infection in apple fruit wounds than C. laurentii alone, although 6‐BA (20 µg mL^?1) alone neither affected the growth of C. laurentii nor reduced the incidence of the blue mould disease in vivo. Moreover, treatment of apple fruit with C. laurentii and 6‐BA (20 µg mL^?1) resulted in stimulation of superoxide dismutase activity but in inhibition of the increase in peroxidase activity. CONCLUSION: 6‐BA (20 µg mL^?1) could enhance the efficacy of C. laurentii in reducing the postharvest blue mould disease of apple fruit, which offered great potential in minimizing the postharvest decay of apple fruit in an integrated pest management strategy. Copyright © 2008 Society of Chemical Industry     

Physiology and Quality Responses of Fresh-cut Broccoli Florets Pretreated with Ethanol Vapor

ABSTRACT:  The exposure of intact broccoli to 6 mL/kg ethanol for 5 h was effective in inhibiting the senescence of fresh-cut broccoli florets. During the 8 d of storage at 10 °C, the weight loss, protein, and chlorophyll degradation of the treated broccoli florets were significantly retarded. The ethanol content of the ethanol-treated broccoli rose sharply and then descended rapidly to a level close to that of the control broccoli stored at 10 °C after 8 d. The acetaldehyde level of the treated broccoli was higher than that of the control broccoli over the whole storage period. The alcohol dehydrogenase activity of the treated broccoli was significantly higher than that of the control after 6 d. There had been higher activities of peroxidase, superoxide dismutase, and catalase in ethanol-treated broccoli. Our study showed that the fresh-cut broccoli treated with ethanol maintained better quality during the storage. Ethanol vapor would be commercially a good candidate for extending the shelf-life of fresh-cut broccoli florets and reducing the loss in postharvest.     

Evolution of ascorbic acid and peroxidase during industrial processing of broccoli

The ascorbic acid content and peroxidase activity of raw, canned and frozen (after blanching times of 60, 90, 120 and 150 s) broccoli florets and stems were determined. The ascorbic acid content represented 1.12 and 0.78 g kg⁻¹ fresh weight in raw florets and stems respectively. After blanching (for different times) and freezing, the ascorbic acid content decreased to values of 0.55–0.56 g kg⁻¹ fresh weight in florets and 0.35–0.36 g kg⁻¹ fresh weight in stems. The industrial processing involved in canning decreased the ascorbic acid content to 0.18 g kg⁻¹ fresh weight in florets. The peroxidase activity observed in the florets and stems of raw broccoli was 308.8 and 278.6 µmol min⁻¹ per 100 g fresh weight respectively. The peroxidase activity remaining in frozen florets varied from 0.9 to 0.2%, while that in stems showed values of between 7.5 and 8.4%. These values for stems were within the range recommended for residual activity after blanching and freezing. The peroxidase activity of canned broccoli florets was practically undetectable. © 2000 Society of Chemical Industry     

Effect of drying conditions on bioactive compounds and antioxidant activity of broccoli (Brassica oleracea L.)

The effect of air‐drying parameters on antioxidant activity and changes in antioxidant compounds of broccoli (Brassica oleracea L.) were studied. Broccoli samples were dried to 70 g kg^?1 moisture content using temperatures ranging from 50 to 100 °C and air flow‐rates from 1.20 to 2.25 m s^?1, resulting in drying times from 25 to 90 min. Temperature, owing to its positive effect on the oxidation kinetics, was negatively correlated with ascorbic acid and free and total polyphenol contents but not with kaempferol, even though the sample dried at the highest temperature showed the lowest kaempferol content. The air flow‐rate was positively correlated with the total (TPP) and free (FPP) polyphenol contents because it led to a reduction in the drying time. No correlation was found between air flow‐rate and kaempferol content. Air flow‐rate and temperature positively affected the antioxidant activity by reducing the drying time. High‐temperature, short‐time processes maximised the antioxidant activity of broccoli owing to the negative effect of drying time on antioxidant activity. The antioxidant activity of broccoli was positively and significantly correlated with the FPP content but not with TPP and kaempferol. The evaluation of hydroxymethylfurfural content as an indicator of the occurrence of a Maillard reaction in dried broccoli did not support the hypothesis of a contribution of MRPs to the antioxidant activity of dried broccoli. Copyright © 2006 Society of Chemical Industry     

Influence of a combined hot air and UV‐C treatment on quality parameters of fresh‐cut broccoli florets at 0 °C

Broccoli is a horticultural product with a high nutritional value that can be consumed fresh but also minimally processed. However, broccoli is highly perishable since it develops a senescence quickly that deteriorates commercial and nutritional quality of the product. In this work we analysed the effect of a combination of UV‐C and heat treatment on quality and senescence of fresh‐cut broccoli florets stored at 0 °C. Combined treatment delayed yellowing as evidenced by higher Hue values and lower chlorophyll degradation. The treatment diminished respiratory activity indicating higher tissue integrity. Treated samples showed higher phenolic content and antioxidant capacity. On day 21 of storage, treated samples had higher levels of total sugars, and total proteins. The results suggest that a combined treatment with heat and UV‐C may reduce senescence, tissue damage and helps to maintain a better quality of the product during storage at 0 °C.     

Potential bioactive compounds in health promotion from broccoli cultivars grown in Spain

Glucosinolates, phenolic compounds and vitamin C were evaluated in two commercial and 12 experimental cultivars of broccoli (Brassica oleracea L var italica) grown under uniform cultural conditions. The predominant glucosinolates in all broccoli cultivars were 4‐methylsulphinylbutyl glucosinolate (glucoraphanin) and 3‐indolylmethyl glucosinolate (glucobrassicin). Other glucosinolates such as 4‐OH‐glucobrassicin and N‐methoxyglucobrassicin were detected in lower amounts. The total glucosinolate concentration ranged from 3.0 µmol g^?1 dw (dry weight) in Pentathlon (experimental cultivar) to 28.3 µmol g^?1 dw in I‐9905 (experimental cultivar). Flavonoids, caffeic acid derivatives and sinapic acid derivatives were quantified in methanol extracts. The largest content of flavonoids was found in the commercial cultivars Marathon and Lord, around 60 mg kg^?1 fw (fresh weight). The vitamin C content of broccoli ranged from 43.1 mg per 100 g fw in Lord (commercial cultivar) to 146.3 mg per 100 g fw in SG‐4515 (experimental cultivar). © 2002 Society of Chemical Industry     

Use of postharvest UV-B and UV-C radiation treatments to revalorize broccoli byproducts and edible florets

UV-B radiation (5, 10 and 15 kJ m^− 2) treatments, single or combined with UV-C (9 kJ m^− 2), were hereby firstly studied as bioprocessing tools to enhance bioactive compounds of broccoli byproducts (leaves and stalks) compared to edible florets during storage (72 h/15 °C). Leaves showed similar total phenolic content (TPC) and antioxidant capacity (TAC) than florets, and 2.5/14.5 higher glucoraphanin/glucobrassicin contents than florets. UV increased initial TPC and TAC of leaves/stalks up to 31–97/30–75 and 20–120/170–420%, respectively. UV-B10 + C induced the highest TPC increase (110%) in leaves while UV-B10 and UV-B10 + C led to the highest TPC of stalks after 48 h. UV-B10 + C increased (34%) glucobrassicin levels of leaves while UV-B15 and UV-B15 + C induced the highest glucoraphanin levels (131 and 117 mg kg^− 1) in florets after 72 h. Conclusively, single or combined postharvest UV-B and UV-C treatments can revalorize such agricultural byproducts and also add value to edible broccoli parts.Industrial relevanceThis work demonstrates the high potential of the use of postharvest treatments with UV-B and UV-C, optimized as single or combined treatments, to be used as bioprocessing tools to enhance the bioactive compounds of broccoli byproducts (leaves and stalks) being compared to edible florets. Thought this innovative application of this technology such agricultural wastes may be highly revalorized with a cheap technology leading to high production of health-promoting compounds with such eco-sustainable technology whose benefits can be even reach to the pharmaceutical industry.     

Effect of ethanol treatment on quality and antioxidant activity in postharvest broccoli florets

Broccoli deteriorates very quickly after harvest at ambient temperature due to the loss of green color and the consequent yellowing of florets. To search for an effective method to control quality deterioration, the effect of ethanol treatment on visual quality, antioxidant enzymes and health-promoting compounds in broccoli florets was investigated. Ethanol treatment (500?μL/L) markedly extended shelf-life, inhibited the increase of L ^* value and the decrease of H value. It also reduced the rate of chlorophyll degradation by inhibiting the activities of chlorophyllase, Mg-dechelatase and peroxidase. In addition, the 1, 1-diphenyl-2-picrylhydrazyl radical scavenging activity and the activities of superoxide dismutase, ascorbate peroxidase and catalase were enhanced in florets treated with ethanol. The contents of total phenolic compounds, glucosinolates and sulforaphane in broccoli were also profoundly increased after treating with ethanol. These results indicated that a postharvest application of ethanol can prolong shelf-life, maintain visual quality and enhance the nutritional value of broccoli florets.     

Effect of processing and storage of brined white (Nabulsi) cheese on fat and cholesterol oxidation

Brined white (Nabulsi) cheese was studied for cholesterol oxidation and for oxidative and hydrolytic rancidities during cheese processing, during storage in closed transparent and light‐protected glass jars at room temperature for 3, 6 and 9 months and during storage on an open tray exposed to atmospheric air and light for 1, 2 and 3 weeks. The peroxide value (PV), free fatty acid (FFA) content and 7‐ketocholesterol level were determined. The cheese processing steps (curd formation, salting and boiling in brine) had no significant effect on PV, FFAs and 7‐ketocholesterol. However, the storage conditions had a significant effect (p ≤ 0.5) on these parameters. Peroxides were not detected or were very low in the freshly boiled cheese, while the FFA content was 2.9 g kg^?1. The PV and FFA content increased to approximately 5 meq kg^?1 and 11 g kg^?1 respectively after 9 months of storage in transparent or light‐protected jars. The 7‐ketocholesterol level was 1.2 µg g^?1 in the freshly boiled cheese and reached maximum values of 2.3 and 5.2 µg g^?1 after 9 months of storage in light‐protected and transparent jars respectively. Cheese samples displayed on an open tray showed a higher increase in PV, FFAs and 7‐ketocholesterol than samples stored in closed jars, reaching values of 6.1 meq kg^?1, 6.8 g kg^?1 and 8.8 µg g^?1 respectively after 3 weeks of storage. © 2002 Society of Chemical Industry     

不同糖处理对离体青花菜抗氧化酶以及品质的影响

本文采用含有150 mmol/L葡萄糖、果糖、蔗糖的培养基对青花菜花蕾进行离体培养,研究了外源糖对青花菜抗氧化酶活性以及品质的影响。结果表明,葡萄糖、果糖、蔗糖处理均能有效延缓离体青花菜黄化和抑制叶绿素的降解,而空白组青花菜完全黄化,果糖组处理组叶绿素含量最高,是空白组的1.83倍;外源糖处理能有效提高青花菜中过氧化氢酶(catalase,CAT)、过氧化物酶(peroxidase,POD)、过氧化物歧化酶(superoxide dismutase,SOD)及抗坏血酸过氧化物酶(ascorbate peroxidase,APX)的活性,但三种糖的效果并不相同,三种糖中,果糖能维持最高水平CAT和APX活性,蔗糖则保持最高的POD、SOD活性;三种外源糖处理不能提高离体青花菜总酚含量,但均能维持离体青花菜较高水平的总糖含量、总黄酮含量,提高DPPH自由基清除率,保持了青花菜较好的品质。