Partial purification and characterization of polyphenoloxidase from durum wheat (Triticum durum L.)

A bright yellow color of pasta is an important qualitative trait for the durum wheat industry. Final color is the result of the balance between yellow and brown components in semolina. Polyphenoloxidase (PPO) is implicated as playing a significant role in darkening. This study aimed to characterize PPO activity of durum wheats. PPO was extracted and partially purified by ion-exchange chromatography on a column packed with diethyaminoethyl cellulose (DEAE). This procedure led to 26.33-fold purification with 24.7% recovery. The optimum temperature and pH of PPO were found to be 40 °C and 6.5, respectively. Heat stability of durum wheat PPO decreased as the temperatures increased from 30 to 80 °C. The z-value was calculated as 23.4 °C. It increased to 26.3 and 48.4 °C in the presence of 40% sucrose and 1 M NaCl, respectively. Durum wheat PPO was shown to use several phenolic compounds as substrate. Among the substrates used, the greatest substrate specificity was observed with catechol. Durum wheat PPO was sensitive to inhibitors such as ascorbic acid, cysteine, oxalic acid and citric acid. Ascorbic acid was the most effective inhibitor.     

Postharvest decay control and quality retention in litchi (cv. McLean's Red) by combined application of modified atmosphere packaging and antimicrobial agents

The effects of modified atmosphere packaging (MAP) [bioriented polypropylene (BOPP-1 or BOPP-2)] in combination with antimicrobial agents Bacillus subtilis, 10⁷ colony-forming units (cfu) ml⁻¹; ethylenediamine tetraacetic acid, calcium disodium salt hydrate (EDTA) (0.1%); or 4-hexylresorcinol (4-HR) (0.15%) on postharvest decay control and quality retention of litchi cv. McLean's Red were assessed as possible replacements for commercial SO₂ fumigation. Fruits dipped in B. subtilis, EDTA or 4-HR (5 min) separately, blow dried (25 °C, 3 min), packed in BOPP-1, held for 18 d at 2 °C, 95% RH, and 2 d at 14 °C, 75% RH were significantly less decayed. The antagonist–BOPP-1 combination also promoted the best bacterial survival during storage. B. subtilis was observed to survive effectively in BOPP-1 (16% O₂, 6% CO₂; 90% RH), but its survival was adversely affected in BOPP-2 (5% O₂, 8% CO₂; 93% RH). Alternaria alternata and Cladosporium spp. were the major decay-causing fungi in BOPP-1 treatments, and Candida, Cryptococcus and Zygosaccharomyces were the predominant yeasts in BOPP-2 treatments. Combination treatments EDTA, 4-HR or B. subtilis in BOPP-1 inhibited polyphenol oxidase (PPO) and significantly reduced pericarp browning and severity. Although the combination treatments EDTA, 4-HR or B. subtilis in BOPP were equally effective in controlling decay and browning, the EDTA and 4-HR affected the natural pinkish-red colour of the pericarp by showing higher h° values (orange–pink). Among the combination treatments, B. subtilis+BOPP-1 had the best potential to control decay, retain the colour and the overall litchi fruit quality during a marketing chain of 20 d.     

Ascorbic acid-ferrous iron (Fe++)complexes and after cooking darkening of potatoes

A complex of ascorbic acid plus ferrous iron (Fe^{+ +}) forms a purple pigment similar to the after cooking darkening pigment (ACD) in potatoes. The ascorbic acid-Fe^{+ +} complex is similar to the ACD pigment in the following ways:

1. Both require O₂ in an oxidation reaction to form the final pigment.
2. The color changes with pH are similar.
3. Strong chelating or complexing agents such as citric acid, EDTA and sodium acid pyrophosphate will cause loss of color.

The ascorbate-Fe^{+ +} complex is much less stable than the chlorogenic acid-Fe⁺⁺⁺ complex, which is the currently accepted cause of after cooking darkening.     

Exogenous ascorbic acid scarcely ameliorates inhibition of photosynthesis in rice leaves by O3

The role of ascorbic acid on acute O₃-induced inhibition of photosynthesis in solution-cultured paddy rice was evaluated. As pre-treatment, ascorbic acid (0, 5, and 10 mM) was added to the culture solution for 5 d before 5 h of O₃ exposure (0, .1, and .3 cm³ m^?3 O₃) during daytime. O₃ decreased photosynthesis-related parameters, total ascorbic acid content, and the redox state (RDS) of ascorbic acid. Ascorbic acid treatment enhanced the total ascorbic acid contents and its RDS level of rice leaves, but scarcely ameliorated O₃-induced inhibition of photosynthesis-related parameters. Inhibition of net photosynthetic rate (P_N) by O₃ was slightly ameliorated by exogenous ascorbic acid only at 1 d after O₃ exposure. These results indicate that ascorbic acid is a component of protection from O₃ injury but has a marginal role in the acute inhibition of P_N by O₃ in rice leaves.     

荔枝果实干制加工的热烫和无硫护色工艺

荔枝是我国南方一种重要的热带、亚热带水果,具有较高的营养价值和商业潜力.然而,在高温高湿季节,采后荔枝果实极易发生腐烂变质、果皮褐变、病原菌侵染等品质劣变现象.因此,荔枝果实除鲜食外,常被加工成不同的商业产品,特别是荔枝果干.干制荔枝由于干制加工时间较长,易发生果皮褐变,导致其外观色泽、产品质量和风味丧失,最终限制荔枝...     

外源硫诱导玉米镉胁迫耐性的生理机制研究

采用水培试验,研究根部施加外源SO_4~(2-)对Cd胁迫下玉米幼苗相关关键生理指标的影响,并分析Cd在玉米组织和亚细胞分布情况,探究外源硫S对玉米响应镉(Cd)胁迫的影响机制。结果表明,外源SO_4~(2-)处理,可显著降低Cd胁迫下玉米叶片与根中的丙二醛含量、相对电导率和抗氧化酶(SOD、CAT)活性。同时,根中抗坏血酸、非蛋白硫醇、植物螯合素含量在外源SO_4~(2-)处理后显著上升,在叶片中的变化不显著。外源SO_4~(2-)处理可降低玉米叶片中Cd含量,提升在根中的含量。根细胞壁和液泡中的Cd含量显著上升,从而减少Cd向地上部分的运输量。根细胞液泡膜中Cd运输专一性基因HMA3在外源SO_4~(2-)处理后,表达水平显著增强。因此,外源S可以通过提升Cd胁迫处理下玉米根细胞壁中Cd含量和抗坏血酸的保护作用,同时促进液泡的区室化作用,降低Cd向玉米地上部位的转运,以增强玉米对Cd胁迫的耐受性。     

Continuous Spectrophotometric Assay and Properties of Ascorbic Acid Oxidising Factors in Wheat

A continuous spectrophotometric assay was developed to measure ascorbic acid oxidation in crude Na₂SO₄ extracts of flour. The rate of ascorbic acid oxidation in flour extracts measured using this method was similar to the rate in flour-water suspensions and 2–4 fold less than the rate in dough measured using an indophenol-xylene extraction method. Flour extracts appeared to contain two ascorbic acid oxidising factors; one with optimal activity at pH 6·3 and 30 °C and the other with optimal activity at pH 10 and 40 °C. The pH 6·3 factor had properties similar to those of ascorbate oxidase (EC 1·10·3·3) in its pH and temperature stability, strong inhibition by NaN₃, KCN and diethyldithiocarbamate, inactivation by proteases, and greater stereospecificity towards -ascorbic acid than -isoascorbic acid. The pH 6·3 factor was most concentrated in the pollard milling fraction of wheat and was lowest in flour. The pH 10 factor had several properties indicating non-enzymic oxidation of ascorbic acid; it was not inactivated by proteases, it was inhibited poorly or not at all by the above ascorbate oxidase inhibitors, and it had low specificity for stereoisomers of ascorbic acid.     

Response of potato cell cultures to aluminium and selection of tolerant cell lines

Summary We developed a method for the selection of aluminium-tolerant cell lines by using a liquid medium which more closely simulates acid soil conditions than media used previously. This medium has a pH of 4.8 and contains Al₂(SO₄)₃ instead of Al-EDTA as the selective agent to avoid the toxic effects of EDTA. It is shown that Al₂(SO₄)₃ exhibits a similar toxic effect on the growth of intact plants and cultured cells. With this medium, potato cell lines tolerating 2 mmol/l aluminium have been selected.     

Role of oxidative cleavage and acid hydrolysis of oat beta-glucan in modelled beverage conditions

The effects of organic acids (ascorbic, citric and malic acids) associated with beverages were studied in an unpurified oat beta-glucan extract with the purpose of examining the stability of cereal beta-glucan in beverage conditions. Addition of ascorbic acid caused an immediate decrease in viscosity of the extract and the MW of beta-glucan. Citric and malic acid affected moderately and only after a heat treatement. This indicated a dominating role of ascorbic acid induced oxidative cleavage compared to the generally proposed acid hydrolysis of beta-glucan. The nature of ascorbic acid induced cleavage was studied with inhibitors (glucose, mannitol, catalase and phytic acid) and catalysts (Cu- and Fe-ions) of hydroxyl radical attacks. Glucose, mannitol and catalase inhibited and the metals effectively catalysed the viscosity decrease. These indicated that the degradation of beta-glucan in the ascorbic acid treated extract was induced by metal-catalysed hydroxyl radicals. Also, the beta-glucan extract used as a matrix lost its viscosity during storage (+6 °C) concurrently with MW decrease of beta-glucan. When added to the extract, mannitol, glucose and catalase each showed a slight stabilising trend and Fe²⁺-ions caused an immediate decrease in viscosity. The oxidative cleavage appeared to be an important factor to consider in developing novel aqueous beta-glucan enriched products.     

OsPHR2对小麦酸性磷酸化酶活性和根系土壤有机酸含量的影响

为了明确水稻低磷胁迫转录因子OsPHR2对小麦酸性磷酸化酶活性、根系土壤有机酸含量和根系活力的影响，以转OsPHR2小麦纯合株系和受体对照为试验材料，在不施磷（低磷）、施易溶性磷（0.200 g·kg^-1，KH₂PO₄为磷源）和施难溶性磷（0.200 g·kg^-1，以AlPO₄为磷源）3个处理下开展转OsPHR2小麦酸性磷酸化酶活性、根际土壤有机酸含量和根系活力的研究。结果表明，拔节期、抽穗期和灌浆期，在低磷和施AlPO₄处理下2个转OsPHR2小麦株系旗叶和根部酸性磷酸化酶活性均显著高于受体对照；施KH₂PO₄处理下，2个转基因株系旗叶酸性磷酸化酶活性在抽穗期和灌浆期均显著高于对照，根部在抽穗期显著高于对照，其他时期差异均不显著。随着小麦生育进程，小麦根际土壤草酰乙酸、草酸、乙酸、丙二酸和柠檬酸等有机酸含量逐渐增加。拔节期和抽穗期，在低磷、施AlPO₄和施KH₂PO₄处理下转基因系OsT5-28根际土壤五种有机酸含量均显著高于对照。转基因小麦根际土壤有机酸含量较对照的提高幅度在拔节期或抽穗期较大。三种处理下转基因系OsT5-28根系TTC还原力在三个时期均显著高于对照。这说明低磷胁迫下OsPHR2可提高小麦酸性磷酸化酶活性和根系活力，促进根系有机酸的分泌，增加分泌量，从而提高小麦磷素吸收效率。     

Oxidation of ortho‐diphenols in red clover with and without polyphenol oxidase (PPO) activity and their role in PPO activation and inactivation

Oxidation of phenol to quinone with its subsequent binding and complexing with protein in red clover (Trifolium pratense L.) when fed to ruminant livestock has been shown to improve nitrogen‐use efficiency and the deposition of polyunsaturated fats into animal products. This oxidation has, almost exclusively, been attributed to the activity of the enzyme group polyphenol oxidases (PPOs) and, specifically, catecholase during conservation. However, during conservation, temporal inactivation of PPO occurs and oxidation of phenolic substrate may occur through other mechanisms not associated with PPO. T₁ progeny of a cross between a red clover clone having normal levels of foliar PPO activity and a transgenic PPO‐silenced red clover plant with undetectable levels of PPO activity were divided into two populations based on the presence of the silencing transgene and lack of measurable PPO activity (PPO?) or the absence of the silencing transgene and normal levels of PPO activity (PPO+). This material was subsequently used to determine the relevant extent of phenolic oxidation in the presence and absence of PPO activity under two damage regimes (heavy and light). PPO+ and PPO? material was passed through a garden shredder as the light‐damaged regime, or frozen at ?20°C as the heavy damaged regime. Material was left at room temperature and sampled at regular intervals for the determination of PPO enzyme activity (active and total), PPO activation (conversion from latent to active forms) and formation of protein‐bound phenol (PBP) as a measure of oxidation. Experiments with red clover leaf extracts were carried out to determine the mechanism for the temporal activation and inactivation (loss of enzymatic activity) of PPO during wilting. PBP formation was evident in both PPO? and PPO+ treatments with the response further catalysed during the first 2 h by extent of damage that increased the activation of PPO, but which also resulted in a more rapid temporal inactivation of PPO. PBP formation, PPO activation and PPO inactivation were all shown to be mediated predominantly by quinone binding. A role of non‐PPO oxidation in PBP formation in wilted red clover is reported, showing the importance of o‐diphenolic substrate concentration and not just PPO activity to increase nitrogen use efficiency and the deposition of polyunsaturated fats into animal products.     

硅与青枯菌互作对茄子幼苗抗氧化酶活性的影响

以抗性不同的2个茄子品种为试材,通过水培试验,探讨青枯菌侵染下外源硅对茄子青枯病的抗性及抗氧化酶活性的影响,为茄子青枯病的预防提供参考依据。结果表明：Si+Rs可显著降低病情指数,同时,显著提高茄子根系活力;对于感病品种而言,接菌前,加硅与否对茄苗叶片中的PAL和PPO活性无显著影响,接菌后,Si+Rs的PAL和PPO活性显著高于Rs;而在抗病品种中,不论接菌与否,加硅处理的茄苗叶片中PAL和PPO活性均显著高于不加硅处理。说明施加外源硅能提高叶片中相关抗氧化酶活性并增强茄子对青枯病的抗性。     

Quality indices of Jew's mallow and spinach during frozen storage

In this study, Jew's mallow and spinach were heat treated and kept frozen, at –18°C, for 3 months. Analysis of some chemical components and enzymatic activities as well as a sensory evaluation were undertaken. At the end of the storage period, blanched spinach showed no PPO (polyphenyloxidase) activity at all, but still contained PO (peroxydase) and LO (lipoxygenase) activities. The untreated spinach stored under the same conditions showed high activities of PO, PPO and LO. The heat treated mallow still contained high enzyme activities which decreased slowly during frozen storage. Statistical analysis of the chemical composition and the sensory evaluation results indicated that heat treatments of mallow caused significant differences in total solids, pH, chlorophylla and total chlorophyll, while frozen storage, of samples of the same treatment for 3 months caused no significant differences in moisture, ash, oxalic acid, pH, chlorophylla and total chlorophyll. No significant differences could be noticed in the overall acceptability between mallow samples mixed with hot water and those mixed in the overall acceptability between mallow samples mixed with hot water and those mixed with a hot 0.1% MgCO₃ solution. Significant differences were found between the heat treated and the untreated mallow. Changes of the chemical composition and the overall acceptability of blanched spinach during frozen storage showed almost the same trend noticed for the Jew's mallow.     

Antioxidant activity and phenolic content of chestnut (Castanea sativa) shell and eucalyptus (Eucalyptus globulus) bark extracts

Chestnut (Castanea sativa) shell and eucalyptus (Eucalyptus globulus) bark, waste products of the food and wood industries, respectively, were analysed as potential sources of antioxidant compounds. The extraction yield, the antioxidant activity and total phenols content of the extracts were greater in chestnut shell than in eucalyptus bark for most of the extraction conditions essayed. Extraction of chestnut shell with a 2.5% Na₂SO₃ aqueous solution led to the highest extraction yield, 25.6%, total phenols, 13.4 g gallic acid equivalent/100 g oven-dried shell, and FRAP antioxidant activity, 80.7 mmol ascorbic acid equivalent/100 g oven-dried shell. Extraction with methanol:water (50:50, v/v) provided the best results for eucalyptus bark. The antioxidant activity and the total phenols content of the extracts had a positive linear correlation. FTIR spectroscopy confirmed the higher content of phenolic compounds in chestnut shell extracts compared to eucalyptus bark extracts. Chestnut shell extracts were characterized by the presence of high molecular weight species whereas lower molecular weight species were predominant in eucalyptus bark extracts.     

Radiation-induced changes in the chemical composition ofSolanum tuberosum cv.Kufri Sindhuri tubers after germination

Summary The chemical composition of⁶⁰Co γ-irradiated potato tubers (Solanum tuberosum cv.Kufri Sindhuri) after germination shows significant changes. The contents of ‘total’ solanine, a glycoalkaloid, citric and ascorbic acids and total solids increase. Malic acid decreases to some extent while pyroglutamic acid does not follow any regular pattern. Except glutamic acid all other free amino-acids increase. Under the influence of low doses titratable acids show an appreciable increase but a 4-krad dose retards their synthesis. No appreciable change has been noted for nitrogen percentage. The size of the starch granules increases with higher doses and the quantity of anthocyanin decreases.     

柠檬酸处理对鲜切粉葛褐化保鲜效果研究

研究柠檬酸处理对鲜切粉葛护色效果的影响,将鲜切粉葛分别放入0.5%、1.0%、1.5%柠檬酸溶液浸泡15 min后沥干,放置塑料托盘中,用聚乙烯保鲜膜包装后置于5℃恒温恒湿箱中贮藏,定期取样测定相关生理指标。结果表明,不同浓度柠檬酸处理能有效减轻鲜切粉葛的褐变程度,以0.5%柠檬酸处理效果较好,能显著降低PAL活性和总酚含量,抑制PPO和POD活性,减少丙二醛积累,保持较低的LOX活性,从而延缓鲜切粉葛的褐变,同时提高了总黄酮含量,减少淀粉、可溶性蛋白等营养物质的损失,有助于保持粉葛的良好品质。适宜浓度柠檬酸预处理可显著减轻鲜切粉葛褐变程度,维持较好的营养品质。研究结果为鲜切粉葛护色工艺提供参考。     

油菜皮壳中多酚氧化酶活性的组织化学检定及其与粒色的关系

以组织化学法及抑制剂处理研究了油菜种子成熟前皮壳中的多酚氧化酶活性有无、存在部位及其与粒色的关系。结果表明,甘蓝型和白菜型油菜种子成熟前,皮壳(包括种皮和糊粉层,下同)的栅栏层存在较强的多酚氧化酶活性;黄籽皮壳的活性略低于黑籽皮壳的,但当有足够的多酚化合物存在时,黄籽皮壳也能象黑籽皮壳一样变为黑色。黑籽油菜变色前的种子用抗坏血酸处理,多酚氧化酶活性受到抑制,呈色过程中断,种子呈纯黄状态。说明多酚氧化酶对籽粒的呈色极为重要。     

硫营养对绿茶产量和品质的影响

研究了硫营养对绿茶产量和品质的影响及其可能的机理。试验设2个硫处理(0,50 kg S.ha-1.a-1),每个处理重复4次,完全随机区组设计。结果表明:施硫能够提高产量、增加氨基酸和抗坏血酸(AsA和DAsA)含量,降低茶多酚和酚氨比(TP/AA)。施硫对茶叶品质的改善与降低多酚氧化酶(PPO)的活性、提高硝酸还原酶(NR)和苯丙氨酸解氨酶(PAL)活性有关。     

Silage fermentation characteristics of three common grassland species in response to advancing stage of maturity and additive application

This study investigated the effects of advancing stage of maturity and additive treatment on the fermentation characteristics of three common grassland species. Perennial ryegrass (PRG; Lolium perenne L., var. Gandalf), timothy (Phleum pratense L., var. Erecta) and red clover (Trifolium pratense L., var. Merviot) were harvested at three dates in the primary growth (11 May, 8 June and 6 July; Harvests 1–3) and ensiled with the following additive treatments: (1) control (i.e. no treatment), (2) formic acid‐based additive, (3) homofermentative lactic acid bacterial (LAB) inoculant and (4) heterofermentative LAB inoculant. Additive application to the PRG (irrespective of harvest date), the late‐harvest timothy (Harvest 3) and the red clover (Harvests 2 and 3) herbages had little impact on silage fermentation characteristics, where a lactic acid dominant fermentation already prevailed. However, the application of the formic acid‐based additive to the Harvest 1 and 2 timothy and Harvest 1 red clover herbages, where the silage fermentation characteristics were poorer, resulted in an increase in the proportion of lactic acid in total fermentation products and a decrease in pH. In contrast, the heterofermentative LAB inoculant had a negative impact on silage fermentation characteristics where a poor preservation prevailed in the corresponding control silage.     

Glandular trichomes: Enzymic browning assays for improved selection of resistance to the green peach aphid

Polyphenoloxidase (PPO) activity in the glandular trichomes of 32Solanum tuberosum ×S. berthaultii F₃ hybrid clones differentially resistant to the green peach aphid,Myzus persicae (Sulzer) was determined. Within this population of segregating clones, aphid infestation levels varied 8-fold, while a 5-fold difference in glandular trichome PPO activity was observed. PPO activity and aphid resistance at three sample dates were correlated as follows: r = 0.38 (P = 0.05), r = 0.31 (P = 0.10), and r = 0.55 (P = 0.01), respectively. The total browning potential test (TBP), a modification of the PPO assay, was developed for use in screening for aphid resistance. The TBP procedure is rapid, inexpensive, and highly effective in identifying aphid resistant clones.