Effect of blanching time and salt concentration on pectolytic enzymes,texture and acceptability of fermented green beans

Effect of blanching time, salt concentration and fermentation on texture of green beans (var. Tuf) was determined. Beans were blanched at 90 °C for 1, 10 or 20 minutes and fermented with brine containing 3.08 and 4.6% salt (corresponding to 1.2 and 1.8% salt in the finished product). The beans were assessed for texture mechanically using Universal Testing Machine (Model 1011, Instron). Sensory evaluation was carried out to assess the taste, texture and overall acceptability of the products. Pectolytic enzyme (pectinestarase and exopolygalacturonase) activities were determined in fresh and fermented beans. Increase in blanching time improved the texture significantly. Significant (p<0.05) decreases in shearing energy of the beans were observed in the first two days of fermentation and, thereafter, there were no significant (p>0.05) changes except for samples blanched for one minute. Salt concentration showed a small but significant effect on texture only in samples blanched for one minute and this was probably due to activation by salt of residual pectolytic enzymes in the beans. Most acceptable beans were those blanched for 20 minutes and fermented with 1.2% salt brine.     

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.     

水杨酸对花生种子及幼苗几种酶活性的影响

采用不同浓度的水杨酸 (SA)处理花生种子及幼苗后 ,苯丙氨酸解氨酶 (PAL)、过氧化物酶 (PO)和多酚氧化酶 (PPO)活性的变化不同。水杨酸 (SA)处理三叶期花生幼苗和叶片 ,其PAL、PO、PPO活性显著提高。这些反应过程都与抗病性反应相类似     

Nitrate-nitrite levels in commercially processed and home processed beets and spinach

Nitrate and nitrite content of commercially processed and home processed beets and spinach samples were analyzed using specific ion electrode and colorimetric methods. The home processed beets were found to be significantly higher in nitrate content than the commercially processed beets. This difference was attributed to differences in processing methods. Pickled and Harvard beets contained significantly lower amounts of nitrate/nitrite on a dry weight basis than the other types of processed beets, evidently due to the diluting effect of added sucrose. Home frozen spinach showed a trend toward lower nitrate content than commercially frozen spinach, although the difference was not significant. Length of storage of home processed beets and spinach did not appear to affect nitrate or nitrite content.Published as Nebraska Agricultural Research Division Journal Series 7495. Supported by funds from teh Nebraska Agricultural Research Division Project No. 91-031 and U.S.D.A. C.S.R.S. Project No. W-143.     

Effects of wilting,blanching and storage temperatures on ascorbic acid and total carotenoids content of some Nigerian fresh vegetables

Four fresh vegetables (fluted pumpkin leaf, okra, African spinach, and water leaf) were studied. Determinations were made of the amounts of ascorbic acid and total carotenoids in fresh, wilted and blanched begetables as well as in fresh and blanched vegetables stored at ?10°C and 5°C. Results showed that wilting accounted for the highest losses in both ascorbic acid and carotenoids in all vegetables investigated. The least losses in the two nutrients were observed in blanched vegetables. In general carotenoid was more stable to the different treatments than ascorbic acid.     

Polyphenol oxidase and peroxidase activities of apricots (Prunus armeniaca L.) as affected by cultivar,location, and year of harvest

A total of 22 samples of apricots belonging to ten cultivars from two locations and picked in the years 1975–78 were assayed for polyphenol oxidase (PPO) and partly for peroxidase (POD) activities, heat resistance of these enzymes,o-dihydroxy phenol (ODP) content, and initial rate of enzymatic browning (BA). Of these characteristics, ODP content showed the greatest and BA the least variation. PPO activity relative to fresh weight was found to depend on the year of harvest rather than on the cultivar, while POD activity relative to fresh weight was cultivar dependent. The values of BA and ODP content were markedly influenced by both cultivar and year. For a given cultivar, PPO and POD activities relative to fresh weight as well as BA were higher in the samples picked in 1976 at one location than in those picked in the other years at the other location.The initial rate of browning of apricots was primarily dependent on the ODP content as shown by linear regression analysis with two independent variables. The relative influence of ODP content as compared with that of PPO activity related to fresh weight was the stronger the higher the value of the ratio of PPO-ODP, i.e. the smaller the values of the endogenous substrate available to the enzyme in the tissues. This suggests substrate depletion to be the limiting factor in the enzymatic browning of apricots.Heat inactivation of PPO was found to be a simple exponential process, while that of POD a biphasic one. PPO was less heat resistant than POD: total inactivation occurred after 10-min heat treatment at 75°C and 85°C, respectively.     

Effect of Freezing Technology and Storage Conditions on Folate Content in Selected Vegetables

Folates (B vitamins) are essential for the proper function of many bodily processes. Although a rich natural source are vegetables, the literature lacks data on the effect of the pre-treatment and freezing technologies used in vegetable processing and frozen storage time on the folate content in these materials. Moreover, since folates are very unstable nutrients, the amount available in processed and stored foods can be significantly lower than in raw products. In tested vegetables (green beans, yellow beans, peas, cauliflower, broccoli and spinach), one folate form was identified, 5-methyltetrahydrofolate (5-CH₃-H₄folate). It was observed that pre-treatment and freezing technology significantly (p?<?0.05) decreased 5-CH₃-H₄folate content only in vegetables with the largest degree of fragmentation (cut and briquetted spinach) and the smallest size (peas). In all analyzed samples, the 5-CH₃-H₄folate content decreased with the time of frozen storage. In frozen cauliflower, the 5-CH₃-H₄folate loss exceeded 95 % compared to the fresh product just after the third month of frozen storage. Meanwhile, in green and yellow beans, significant 5-CH₃-H₄folate losses (at the level of 75 % and 95 %, respectively) were observed no earlier than after the 9th month of frozen storage.     

福建主要乌龙茶品种PPO酶活特性的研究

对四种乌龙茶茶树鲜叶的多酚氧化酶(PPO)进行粗提,测定并比较不同品种酶的特性。结果表明:在邻苯二酚与被测酶液的反应体系中,当底物邻苯二酚(C6H6O2)量为0.3~0.9ml时,毛蟹、铁观音、黄旦、肉桂酶活力随底物浓度的增加呈曲线增长,含量太高会产生抑制作用,当底物含量∶酶含量=1.5∶1时,酶活力表现最高;毛蟹、铁观音、黄旦、肉桂酶活力在45~65℃范围内均呈ω型变化趋势,依次在45℃、55℃、65℃时出现高峰。在50~90℃下水浴处理1h,毛蟹、铁观音、黄旦、肉桂酶活力分别丧失34.66%~55.91%,22.68%~50.89%,23.14%~53.57%,31.58%~57.89%;酶活力的适宜pH相对偏碱,在pH8.6时表现为一个活力高峰。相同浓度的五种抑制剂对酶均有一定的抑制效果,其中NaHSO3对酶活力的抑制作用最强,L-半胱氨酸其次,NaCl的抑制效果最差。     

红茶制造中多酚氧化酶同工酶谱与活性的变化

本文运用聚丙烯酰胺凝胶垂直板状电泳技术和酶活性测定相结合的方法,初步探明了红茶萎凋、揉捻、发酵和干燥工序中多酚氧化酶(PPO)活性及同工酶谱的变化动态,以及酶试液制备方法对PPO活性及同工酶的影响,发现造成萎凋期间PPO活性变化两种研究结果的原因,在于酶制液的制备方法不同。同时,在鲜叶和萎凋叶中发现了第7条小分子PPO组分。本试验还证明了红茶中残余酶活性的存在,并探讨了残余酶在贮藏中可能发生的作用。文中还探讨了PPO各组分在红茶制造中作用的大小,从酶学角度论证了萎凋工序的重要性。     

The control of polyphenol oxidase activity in fruits and vegetables

Objective of this research was to find alternative methods for the control of polyphenol oxidase (PPO) activity in fruits and vegetables with the purpose of reducing or eliminating the use of SO₂ for this purpose. Interactions between the use of ascorbic acid, citric acid, EDTA, sodium metabisulphite and heat treatment (70 °C for 2 min) in the control of PPO activity were studied in avocado (var. Fortuna), banana (var. Nanica), apple (var. Ana, Fuji, Gala & Golden), pear (var. D'Agua), peach (var. Real), potato (var. Bintje), eggplant (var. Super F100), mushroom (Agaricus bisporus) and hearts-of-palm (Euterpe edulis Mart.). The results demonstrated that PPO of avocado and eggplant was most resistant to inhibition by the methods used. The least efficient method tested for the control of PPO was the addition of ascorbic acid and EDTA, while the most efficient methods investigated included the use of ascorbic acid, citric acid, sodium metabisulphite and heat treatment. The results indicated that, with the exception of PPO from avocado, the most adequate alternative method to substitute for the use of SO₂ in the control of PPO was a combination of ascorbic acid, citric acid and heat treatment.     

Combined application of antagonist Bacillus amyloliquefaciens and essential oils for the control of peach postharvest diseases

Bacillus amyloliquefaciens PPCB004 was selected as a potential antagonist to control Botrytis cinerea, Penicillium expansum and Rhizopus stolonifer on peach fruit. The HPLC data of PPCB004 indicated the lipopeptides iturin A, fengycin and surfactin as secondary metabolites. The GC/MS analysis of PPCB004 showed 3-hydroxy-2-butanone as the dominant compound (97.52% of relative peak area). Thyme (TO) and lemongrass (LO) oils showed over 50% and 25% inhibition of radial mycelial growth respectively with 8 μl oil per plate for all pathogens. Combination treatment with both oils failed to increase the percentage inhibition of radial mycelial growth of the pathogens. Combined application of PPCB004 with TO or LO was tested to assess the effectiveness in the control of these pathogens during postharvest storage. The biofilm formation of PPCB004 was significantly higher in LO than TO. LO (6 μl plate⁻¹) and PPCB004 completely inhibited the mycelial growth of the pathogens. Fruit inoculation trials with PPCB004 + LO in NatureFlex™ modified atmosphere packaging (MAP), showed lower disease incidence and severity at 25 °C for 5 d than treatments with PPCB004 + MAP, PPCB004 + TO + MAP, LO + MAP, TO + MAP or stand-alone MAP. On naturally infected fruit, PPCB004 + LO + MAP and LO + MAP treatments retained the total soluble solids/titratable acidity ratio and flesh firmness but failed to stimulate the levels of total phenolic content, phenylalanine ammonia-lyase, β-1,3-glucanase and chitinase activities. Combination of PPCB004 (spray treatment) + LO (in pad delivery system) in NatureFlex™ MAP showed absence of disease and off-flavour development, retained the overall appearance and increased the overall acceptance at market shelf conditions (20 °C for 2 d) after cold storage at 4 °C for 14 d.     

小麦籽粒PPO同工酶及其活性分析

为探讨小麦籽粒PPO同工酶与其活性的关系,以PPO活性差异较大的小麦品种为材料,分别检测了不同发育时期的籽粒、成熟籽粒以及浸润籽粒的PPO同工酶谱带及其活性.结果表明:花后10～20d,小麦籽粒PPO同工酶在高、低PPO活性品种间差异不明显.而花后20～30 d,高PPO活性小麦品种的中、低分子量PPO同工酶谱带明显强于低PPO活性品种.总体来说,PPO同工酶谱带强度随着籽粒成熟而降低,而PPO活性在花后30 d达到最大值.在成熟籽粒中,PPO同工酶的强弱与其活性的高低有着较好的一致性.随着籽粒的萌动,其PPO同工酶谱带逐渐增强,尔后降低;PPO活性亦有类似变化.与低PPO活性小麦品种相比,高PPO活性品种在浸润期间有着较强的同工酶谱带和较高的PPO活性.     

Changes in some enzyme activities and browning rate of apricots during storage

Samples of two apricot cultivars grown in central Hungary were picked at canning maturity and stored for ten days at 5°C and 85% relative humidity in normal atmosphere. The initial rate of enzymatic browning (BA), polyphenol oxidase (PPO) and peroxidase (POD) activities as well as o-dihydroxy phenol (ODP) concentration of the fruit flesh were assayed at picking and after five and ten days of storage. During storage, BA decreased and POD activity increased. PPO activity and ODP concentration varied irregularly: the trends of the variations differed with cultivar but were similar for the two characteristics.(Cegled Research Station of the Research Institute of Fruits and Ornamental Plants, Budapest, Hungary), Cegled     

不同抗性大豆品种感染SMV后过氧化物酶、多酚氧化酶、超氧化物歧化酶的变化分析

本文采用两个高抗SMV3号株系种质哈91R3-184、哈91R3-301，两个感病品种合丰25、黑农16于真叶期分别接种SMV3号株系，在R1、R3、R5期分别测定过氧化物酶（POD），多酚氧化酶（PPO）、超氧化物歧化酶（SOD）同工酶活性，结果表明：1、抗感病品种未接种健株POD、PPO酶谱构型没有差异，只是活性高低有别，说明抗性与POD、PPO活性有关。2、接种SMV后感病品种POD、SOD酶活性明显高于未接种健株和抗病品种，其POD、PPO部分酶带加宽色深，部分酶带缺失，3、各生育阶段抗感品种PPO、POD、SOD酶活性动态的变化，可作为抗感病品种的生化鉴定指标。     

低温贮藏对琯溪蜜柚汁胞粒化与木质素代谢的影响

以琯溪蜜柚果实为材料,分别在1、4、7 ℃和室温下贮藏琯溪蜜柚果实,探讨贮藏温度对汁胞粒化、木质素含量以及汁胞木质素代谢相关酶活性的影响。结果表明：木质素合成相关酶的活性在整个贮藏过程中逐渐升高,汁胞粒化指数和木质素含量也均随着贮藏时间的延长而增高;在4、7 ℃下贮藏时,汁胞木质素含量、粒化指数以及木质素合成相关酶PAL、CAD、PPO和POD的活性均显著低于室温和1 ℃;在不同的贮藏温度下,琯溪蜜柚汁胞粒化程度与汁胞中木质素含量均呈正相关的关系。因此,1 ℃的低温不适宜琯溪蜜柚的贮藏,而4~7 ℃较适宜琯溪蜜柚的贮藏。     

热处理对椰子水过氧化物酶和多酚氧化酶活力及色泽变化的影响

研究热处理对新鲜椰子水过氧化物酶(Peroxidase,简称POD)和多酚氧化酶(Polyphenol oxidase,简称PPO)相对酶活力和色泽变化影响,探讨椰子水酶活力与其色泽的相关性。结果表明,随着热处理温度升高或时间的延长,椰子水的POD和PPO相对酶活力均随之降低,其中90℃和95℃热处理4 min后,可分别使POD和PPO的活力降低90%以上。随着热处理温度的升高,椰子水的色泽随之加深;椰子水的PPO和POD相对酶活力与色泽加深程度呈负相关关系,且具有一定的显著性。该结果可为后续研究椰子水色变控制技术提供一定的理论基础。     

Comparison of Polyphenol Oxidase Activities in Wheats and Flours from Australian and U.S. Cultivars

Polyphenol oxidase (PPO) activities of wheats from various classes and cultivars (grown both in the U.S.A. and in Australia), of some U.S. and Australian wheats, of wheat flours at various extraction rates and of kernels separated by size from various cultivars were measured by the oxygen electrode method. PPO activity of wheats was affected by both cultivar and growing location. Wheat flour contained on the average 3% of the PPO of the wheat grain. PPO activities of the flours increased as the flour extraction rates increased. Contrary to expectation, for a single cultivar, small kernels contained less PPO (on a weight basis and especially on a kernel basis) than did large kernels. Differences among kernels of various sizes for a single cultivar were smaller than differences in PPO among kernels of comparable sizes among various cultivars.     

Contents of minerals in green leafy vegetables cultivated in soil fortified with different chemical fertilizers

Content of selected minerals in spinach (Spinacea oleracea) andambat chuka (Rumex vesicarius) cultivated in soil fortified withdifferent chemical fertilizers was determined in a pot experiment.Addition of NPK (Nitrogen, Phosphorus and Potassium) fertilizer alongwith micronutrients, iron and zinc, enhanced the concentration of zinc,iron and magnesium in selected green leafy vegetables markedly (p<0.05),while the concentration of copper was not altered significantly(p>>0.05). Potassium content in the green leafy vegetables was notaffected (p>0.05) by the addition of chemical fertilizers to soil.Spinach and ambat chuka differed remarkably in their mineral contents.Contents of potassium, zinc and copper were significantly high in spinach,while the contents of magnesium and iron were markedly high in ambatchuka (p<0.05).     

特异性MAPK抑制剂U0126对玉米大斑病菌细胞膜透性及防御酶活性的影响

依据实验室前期研究发现,MAPK特异性抑制剂U0126对玉米大斑病菌分生孢子及附着胞发育、HT-毒素的产生和活性以及致病性都有着较显著的影响。以不同浓度的U0126处理玉米大斑病菌菌株,研究该抑制剂对病菌细胞膜透性及防御酶活性的影响。结果表明,U0126对病菌菌丝电导率和PAL活性均无显著影响,但对POD及PPO活性均有显著影响,且U0126对POD活性的影响具有浓度依赖性,即低浓度U0126可提高POD活性,高浓度U0126抑制POD活性;U0126对PPO活性的影响具有菌株特异性,且对菌株01-27的PPO活性的影响与对POD活性的影响相似,都具有浓度依赖性;随着U0126浓度增加菌株01-19的PPO活性反而显著下降。U0126对玉米大斑病菌细胞膜透性和苯丙氨酸代谢没有显著影响,但与过氧化物代谢和多酚代谢密切相关;U0126对过氧化物代谢和多酚代谢的影响具有一定的菌株特异性和浓度依赖性。     

温度、pH对马铃薯多酚氧化酶活性的影响

对加工型马铃薯试管苗、茎段愈伤组织、块茎及块茎芽在不同温度、不同 pH条件下PPO活性的检测结果表明 :pH对马铃薯PPO活性具有明显的影响 ,块茎芽以及愈伤组织PPO活性均在 pH 5～ 5 5之间最高 ,分别为 94 2 0及 2 0 4 0 (0 0 1ΔOD/min) ,而试管苗在培养基 pH为 8时PPO活性最高 (19 80 (0 0 1ΔOD/min) )。不同温度下不同品种PPO活性表现不同 ,甘农薯 1号、Atlantic试管苗PPO活性在 18～ 2 5℃之间达到高峰 ,分别为 16 80和 37 2 0 (0 0 1ΔOD/min) ;Shep ody、Snowden试管苗在 5℃下PPO活性较高 ;除此之外 ,不同品种贮藏块茎PPO活性均在 2 5℃表现最高。