Polyphenoloxidase (PPO) activity and osmotic dehydration in Granny Smith apple

Osmotic dehydration (OD) permits the preservation of foods via a decrease in water content and an increase in solute concentration. Osmotically dehydrated fruits such as apple are suitable for the manufacture of desserts, cakes, salads, yoghurts, etc. Different microstructural and engineering aspects of OD are already known, but its effects on enzymatic activity are still unknown. This study analyses the activity of polyphenoloxidase (PPO) in fresh Granny Smith apples and the effect that OD by immersion in sucrose‐saturated syrup has on this activity. The low PPO activity found in the edible parenchyma of osmotically dehydrated apples is attributed to penetration by the osmotic agent and flooding of the intercellular spaces, which produces a low moisture content and a limited O₂ concentration in the immediate environment of the enzyme. These results show that OD prevents enzyme–substrate interaction. Thus the low PPO activity would reduce browning of this type of product. Copyright © 2005 Society of Chemical Industry     

金帅苹果多酚氧化酶提取及部分酶学特性研究

实验确定了从金帅苹果中提取多酚氧化酶(PPO)的最佳条件,研究了该酶的某些特性。确定pH7.4磷酸氢二钠-柠檬酸缓冲液(含2%的PVPP和0.25%TritonX100)、料液比1.6mL/g为最优提取参数。金帅苹果PPO酶促反应产物在412nm下有最大吸收峰;以邻苯二酚为底物的酶促反应的米氏常数为Km=2.6667×10-2mol/L,PPO动力学方程为:V=3333.33犤S犦0.027 犤S犦;该PPO的最适pH为5.0,在pH5.0～6.8范围内有较高的稳定性;最适温度为40℃。     

浑浊苹果汁加工中苹果PPO热失活条件的研究

研究了热处理苹果汁(加或不加防褐变剂)、苹果浆使其中的PPO完全及部分失活所需要的温度和时间。结果为:在90℃处理苹果汁15s可使其中的PPO完全失活,而对于苹果浆则需要90℃处理20s以上。加了防褐变剂的苹果汁经90℃处理10s可使其中的PPO完全失活;此外,经80℃处理30s以上虽不能使其中的PPO完全失活,但添加的防褐变剂及果汁自身的pH值可抑制残余的PPO从而防止酶促褐变的发生。70℃处理苹果汁40s不能防止其中的酶促褐变。     

不同抑制剂对澳洲青苹中多酚氧化酶活性的影响

以澳洲青苹为试验材料,邻苯二酚为底物,在波长420nm下,采用分光光度法测定澳洲青苹中多酚氧化酶的活力。本文分别研究了亚硫酸氢钠、抗坏血酸、柠檬酸对澳洲青苹多酚氧化酶(PPO)活性的影响,并通过正交试验筛选出最佳复合抑制剂组合。试验结果表明:添加量为50mg/kg的亚硫酸氢钠、125mg/kg的抗坏血酸浓度为、600mg/kg的柠檬酸均能有效抑制PPO活性,三种抑制剂中亚硫酸氢钠对澳洲青苹中PPO活性抑制效果最好,最高抑制率为78.58%。复合抑制剂对澳洲青苹中PPO抑制效果明显,最佳复合抑制剂组合为亚硫酸氢钠25mg/kg、抗坏血酸125mg/kg、柠檬酸600mg/kg,抑制率能达90.09%。     

牛蒡多酚氧化酶的特性及酶促褐变的抑制

采用制作丙酮粉的方法提取了牛蒡中的多酚氧化酶(PPO),并对其酶学特性进行了研究。实验结果表明,牛蒡多酚氧化酶最适温度为40℃,最适pH为6.0,在40℃下热稳定性较好,而在70℃加热3min即可使其完全失活。牛蒡PPO的米氏常数为0.1337mol/L,最大反应速率Vmax为7.387U/min。通过响应面实验设计的方法对防止牛蒡酶促褐变的配方进行了优化,结果表明当复合护色液中EDTA、L-半胱氨酸和柠檬酸亚锡二钠的护色剂的浓度都为0.04%(w/v)时,牛蒡的褐变度最小。     

Extraction of Golden Delicious apple puree: Experimental comparison of three different methods

In this paper, three different processes for puree extraction from Golden Delicious apples and enzyme inactivation are analyzed and compared: (i) hot extraction technique, (ii) cold extraction technique and (iii) a newly developed vacuum puree extraction technology (Zenith Chrono®). The analysis was carried out by means of manual laboratory operations reproducing the three processes. The primary objective of this study was the evaluation of the minimum amount of ascorbic acid that must be added to the three fruit purees in order to contain oxidization and color change in the products. Afterwards, the residual enzymatic activity was checked and characteristics of the products were compared (i.e. fraction of dried solids and consistency of the puree). All of the processes achieved complete enzyme deactivation and an imperceptible color change, and the results of this paper support interest in vacuum puree extraction technology.     

Effects of argon enriched low-oxygen atmospheres and of high-oxygen atmospheres on the kinetics of polyphenoloxidase (PPO)

Abstract: The reported benefits of enrichment of air atmospheres with argon or oxygen for control of enzymatic browning were investigated by determining the effects of these atmospheres on PPO kinetics. Kinetics of purified apple PPO and a commercially available mushroom PPO were studied in an in vitro model system. Enrichment with argon produced greater inhibitory effects than the current industry practice of enrichment with nitrogen. Km^app values (mM) for apple PPO in 3%O₂/97%Ar, 3%O₂/97%N₂, and air, were 133, 87, and 48, respectively. The data indicate that inhibition by both gases is competitive, and also support the hypothesis that the greater inhibitory effect of argon was proportional to the size of the Van der Waals radius of argon against nitrogen (1.91Å against 1.54Å). Much smaller inhibitory effects were observed in the presence of 80% O₂ (Km^app 57mM), and the nature of this inhibition was less clear. The results suggest that the benefits of argon enrichment may be relatively small, and may require critical enzyme, substrate, and gas levels to be successful. However, these benefits may be exploitable commercially in some fresh‐cut products, and may allow less anoxic atmospheres to be used. Practical Application: Control of enzymatic browning without sulfites continues to be a challenge in some fresh‐cut products. While sporadic benefits of these atmospheres in control of enzymatic browning have been reported, results have been inconsistent in commercial practice. The results suggest that the benefits of argon enrichment may be relatively small, and may require critical enzyme, substrate, and gas levels to be successful. However, these benefits may be exploitable commercially in some fresh‐cut products, and allow less anoxic atmospheres to be used.     

Kinetics of colour development in aqueous fructose systems at high temperatures

Non‐enzymatic browning was studied in aqueous model systems containing fructose and aspartic acid, glutamic acid or asparagine at three different soluble solid concentrations (150, 300 and 450 g kg⁻¹), which were heat treated for different times at four temperatures (85, 90, 95 and 100 °C). Various indicators were used to evaluate the extent of the Maillard reaction: spectrophotometric measurements at 280 and 420 nm (A₂₈₀ and A₄₂₀) and CIE (Commission Internationale de l'Eclairage) parameters L* (lightness), a* (redness), b* (yellowness) and ΔE* (colour difference, which is expressed as [(Δa*)² + (Δb*)² + (ΔL*)²]^1/2). The pH and the formol index were also determined. The indicator for colourless intermediate formation, A₂₈₀, showed that the kinetic constant values increased with increasing heat treatment temperature, while the influence of soluble solid concentration was not clear. After a short induction period the data were well described by assuming zero‐order kinetics. Glutamic acid turned out to be the most reactive amino acid, while asparagine was the least reactive. With reference to brown pigment formation, A₄₂₀ and ΔE*, glutamic acid was the least reactive amino acid. In all the experiments assayed, except for glutamic solutions with fructose concentrations of 150 and 300 g kg⁻¹, the data were best correlated with combined kinetics. © 2000 Society of Chemical Industry     

Biological variation in the colour development of Golden Delicious apples in the orchard

BACKGROUND: In managing apple orchards, crop load and rate of nitrogen (N) fertilisation are two factors with a significant influence on fruit quantity and quality, because they affect all physiological processes in the tree. Both factors are strongly related to external and internal fruit quality, especially to skin colour, sugar and acid contents and mineral composition, and consequently to the keeping quality of fruits. The aim of this study was to assess the effects of both factors (three crop load levels and two N fertilisation levels) on the colour development of Golden Delicious apples during the last month on the tree in two consecutive seasons. Data on skin colour (L*, a*, b* values) were analysed using nonlinear mixed effects modelling to extract information on the variation in biological shift factor for colour and to link this variation to the different strategies used concerning N fertilisation and crop load. RESULTS: The major source of information is contained in the a* value. The behaviour of the a* value could be described by a logistic or an exponential model depending on the season and the experimental set‐up. Nonlinear mixed effects analysis estimating the biological shift factor (maturity) for each individual fruit (random effect) while estimating the rate constant of the decolouration process in common (fixed effect) resulted in explained parts well over 95%. CONCLUSION: The variation in maturity stage between individual fruits is large. Season has the most profound effect on the estimated values, far more important than that of crop load or fertilisation level. The magnitude of variation in colour due to crop load and N fertilisation is not too large. Its effect on the maturity stage of fruits is more profound: the higher the crop load, the higher the variation. The effect of fertilisation seems to be opposite: the higher the fertilisation level, the lower the variation. Copyright © 2009 Society of Chemical Industry     

The effects of Maillard reaction products on apple and potato polyphenoloxidase and their antioxidant activity

The effects of Maillard reaction products (MRPs) on apple and potato polyphenol oxidase (PPO) were estimated spectrophotometrically. Model systems of glucose and amino acids [lysine (lys), tyrosine (tyr), proline (pro), cysteine (cys), glumatic acid (glu), aspartic acid (asp), and histidine (his)] were heated at 90 °C for 3 h. The MRPs showed inhibitory effects on PPO extracted from apple and potato. These effects depend on the type of MRP and origin of PPO. The antioxidant activity of MRPs was evaluated. It was found that MRPs exhibit different free radical scavenging activity and these effects were significant. The colour intensity of MRPs was estimated. Browning was not directly related to the antioxidant activity.     

“黑美人”马铃薯多酚氧化酶的特性研究

以邻苯二酚为底物,在413nm处测定黑美人马铃薯多酚氧化酶(PPO)的活性,研究了温度、pH、底物浓度对其活性的影响,并建立了酶促褐变反应动力学方程,探讨了L-半胱氨酸、抗坏血酸、柠檬酸、EDTA及亚硫酸氢钠五种抑制剂对酶促褐变的抑制效果。结果表明:黑美人马铃薯多酚氧化酶最适反应pH为6.3;最适反应温度为35℃;酶促褐变反应动力学符合米氏方程描述的单底物酶促反应动力学,以邻苯二酚为底物,Km=0.0011mol/L,Vmax=142.23U/min.g;动力学方程为V=142.23[S]/(0.0011+[S]);五种抑制剂均对PPO酶促褐变具有抑制作用,其强弱依次为亚硫酸氢钠>L-半胱氨酸>抗坏血酸>EDTA>柠檬酸。     

Phenolic profiling reveals the metabolite basis of flesh colour and fresh-cut browning in apple fruit

Flesh colour, which is affected by cultivars and browning, can largely impact consumer acceptance in fresh-cut apples. The study profiled phenolic metabolites from apple flesh of twenty-three cultivars by widely targeted metabolomics. Comparison among white- and yellow-fleshed cultivars showed fifteen phenolics, mainly quercetin 3-O-glucoside, hyperoside, hesperetin 5-O-glucoside and cymaroside, in white-fleshed apples were significantly higher than those in yellow-fleshed apples. It may indicate a metabolite basis of yellow and white flesh colour, and better potential nutrition in white-fleshed apples. In addition, ten phenolic metabolites including five cyanidin glycosides showed significant differences between the highest and the lowest browning groups, indicating them may be crucial in browning of fresh-cut apple. This work elucidates the differences of phenolic profiles among apple cultivars with different flesh colour and provides useful data to evaluate the suitability of apple for fresh-cut processing.     

Purification,properties and heat inactivation of pectin methylesterase from apple (cv Golden Delicious)

Pectin methylesterase from apple (cv Golden Delicious) was extracted and purified by affinity chromatography on a CNBr‐Sepharose®‐PMEI column. A single pectin methylesterase peak was observed. Isoelectric points were higher than 9. Kinetic parameters of the enzyme were determined as K_m = 0.098 mg ml⁻¹ and V_max = 3.86 µmol min⁻¹ ml⁻¹ of enzyme. The optimum pH of the enzyme was above 7.5 and its optimum temperature was 63 °C. The purified PME required the presence of NaCl for optimum activity, and the sodium chloride optimum concentration increased with decreasing pH (from 0.13 M at pH 7 to 0.75 M at pH 4). The heat stability of purified PME was investigated without and with glycerol (50%), and thermal resistance parameters (D and Z values) were calculated showing that glycerol improved the heat resistance of apple PME. © 2000 Society of Chemical Industry     

烫漂方式对苹果脆片褐变和多酚及其抗氧化活性的影响

为阐明烫漂方式对热风干燥苹果片品质特性的影响,采用热水、蒸汽和微波对苹果片进行烫漂处理,测定苹果片在烫漂和干燥过程中的色泽、多酚及其抗氧化活性的变化情况。结果表明,热水烫漂苹果片的干燥时间最短,为270 min;不同烫漂方式对苹果片褐变有显著影响(P<0.05),其中热水烫漂的苹果片色泽变化最小,微波烫漂的苹果片色泽最差;与鲜样相比,烫漂方式对苹果片还原糖含量影响较小;干燥过程中微波烫漂的苹果片中产生的5-羟甲基糠醛含量最高,蒸汽烫漂次之,热水烫漂最低;苹果片经热水烫漂和干燥后维生素C损失率分别为34%和52%,而蒸汽烫漂和微波烫漂的苹果片中维生素C损失率较小;热水烫漂的苹果脆片总酚含量最高,达到11.82 mg GAE/g DW;苹果片经烫漂处理后游离多酚和结合多酚单体无显著性变化(P>0.05),但干燥后,所有样品中结合多酚单体含量均显著提高(P<0.05)而游离多酚单体的含量无显著性变化(P>0.05),表明3种烫漂方式都有利于多酚单体的保留;多酚抗氧化能力实验表明烫漂和干燥后苹果片中结合多酚抗氧化活性有显著性变化(P<0.05),其中热水烫漂的苹果...     

Effects of aqueous chlorine dioxide treatment on polyphenol oxidases from Golden Delicious apple

Effects of chlorine dioxide (ClO₂) treatment on the activity and characteristics of polyphenol oxidase (PPO) in Golden Delicious apples were studied. The treatment with 50 mg/l ClO₂ for 1 h did not affect some characteristics of the PPO, including its optimum pH value (5.0) and temperature (40 °C) as well as the maximum absorption wavelength (412 nm) of the final products. With increasing ClO₂ concentrations from 0 to 100 mg/l, the value reduced and value changed irregularly. When the concentration of ClO₂ increased from 0 to 60 mg/l, residual PPO activities significantly decreased, showing a negative linear-correlation with ClO₂ concentration. For 10 and 50 mg/l ClO₂ treatments, partial inhibition of PPO was achieved within 0.5 h and the PPO activities did not significantly decrease after 0.5 h. The inhibition and inactivation of PPO by ClO₂ treatment were observed at processing temperatures (30 and 70 °C) and storing temperatures (20, 0-4, and −18 °C).     

Influence of processing and storage on the antioxidant activity of apple derivatives

The antioxidant activity of seven apple varieties was determined on fresh fruits and processed products (dried fruits and purees) and during storage. The antioxidant activity of apples correlated with the total phenol concentration but not with ascorbic acid concentration. Apple derivatives showed a lower antioxidant activity than the counterparts of the fresh fruits and the occurrence of browning phenomena during processing resulted in lower antioxidant activity. Dried fruits showed higher antioxidant activity per gram of dried matter than fruit purees probably because of the lower total thermal effect of processing. The antioxidant activity of all products increased within the first month of storage, and then declined. The extent of early increase was related to the polyphenol content of the fruit. Packaging conditions further influenced the antioxidant activity increase during storage possibly by affecting the oxygen availability.     

苹果浓缩汁加工中热灭酶工艺研究

通过在不同温度和时间下热处理苹果汁,研究了使果汁中多酚氧化酶(PPO)部分或完全失活的条件,并考察了与果汁自然pH值相近的模拟体系对处理后的果汁酶活的抑制情况。表明:75℃、30s虽不能完全灭活PPO,但对其活性破坏较大,处理后的PPO酶活可以较好地被接近果汁自身pH值的低pH(3.8)所抑制,为最佳处理条件。     

Impact of appearance on degree of liking and eating quality expectations of selected apple cultivars

This study investigated the effect of taste expectations based on cultivar recognition on the preference for apple‐eating quality. Consumer preference for eating quality was assessed using three levels of product information, viz. (i) no visual information, (ii) a photograph depicting the typical appearance of the specific cultivar and (iii) an incorrect photograph, misleadingly depicting a different cultivar. Consumers scored the eating quality of ‘Pink Lady^?’ served with the correct photograph significantly higher compared with presentation without pictorial information, suggesting a positive image for this trademark cultivar. Conversely, consumers had lower eating quality expectations for ‘Starking’ and ‘Golden Delicious’ indicated by lower scores when supplied with matching photos. Cultivar developers and researchers should be mindful of the confounding effect of fruit appearance on the hedonic assessment of eating quality. The order of presentation (matching or wrong photograph first) affected the preference scores and should be considered in future studies.