Studies on enzymic browning of potatoes (Solanum tuberosum). II. The quantitative relationship between browning and its causative factors (author's transl)]

Ten potato varieties, with different rates of browning, were analyzed quantitatively for phenoloxidase, tyrosine, chlorogenic acid, caffeic acid, and for reducing substances (ascorbic acid). The rate of tyrosine turnover was calculated from the data. The fact that the further reactions of the primary oxidation products leading to browning only take place after complete oxidation of the reducing substances, was taken into account. This leads to the same classification of the varieties as does visual observation of the rate of discolouration. Thus a clear relationship between browning and potato constituents is demonstrated.     

Enzymatic browning and after-cooking darkening of Jerusalem artichoke tubers (Helianthus tuberosus L.)

Jerusalem artichoke tubers (Helianthus tuberosus L.) undergo enzymatic browning when peeled or cut, and turn grey after boiling, due to after-cooking darkening reactions between iron and phenolic acids. In an attempt to reveal the components responsible for these discolouration reactions, sensory evaluation and instrumental colour measurements were related to contents of total phenolics, phenolic acids, organic acids and iron in three varieties of raw and boiled Jerusalem artichoke tubers harvested in the autumn and the spring. No differences were found between varieties in sensory evaluated enzymatic browning, but Rema and Draga had higher scores than Mari in after-cooking darkening. Jerusalem artichoke tubers had higher contents of total phenolics, phenolic acids and citric acid in the autumn and low contents in the spring, while it was the opposite for malic acid. None of the chemical parameters investigated could explain the discolouration of the Jerusalem artichoke tubers.     

Time Course of PPO-Related Browning of Yams

The time course of polyphenol oxidase (PPO) activity and tissue browning was investigated in five Dioscorea species. In three of the yam species, 86% of the browning was associated with the peak of PPO activity. In D dumentorum and D rotundata, only 9 and 40%, respectively, of browning was PPO-related, while most of the tissue browning occurred after PPO activity had declined to the control value. The browning incidence was temperature-dependent such that the optimal temperature for PPO activity (30°C) also coincided with that of maximal browning in all the yam species expect in D dumentorum. Classical inhibitors of PPO prevented the browning in tissues where the enzymic mechanism predominated while failing to reduce browning in D dumentorum and D rotundata where most of tissue browning was not enzyme associated. The results put the incidence of yam discolouration in proper perspective in terms of the timescale of PPO and non-PPO-catalysed discolouration.     

Studies on enzymic browning of potatoes (Solanum tuberosum)

Summary Using analytical data from the literature the tyrosine turnover was calculated by a method published previously by us for 72 potato samples with different rates of browning. The samples included 9 varieties grown at three locations in 1969, which were analysed after harvest and after different times of storage at three temperatures. For 58 samples (81%) this calculation led to the same classification of the varieties as did visual observation of the rate of discolouration. It is concluded that enzymic browning of potatoes is correlated rather with tyrosine turnover, which depends on the concentrations of phenol oxidase, tyrosine, chlorogenic acid, and ascorbic acid, than with any single parameter.

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Untersuchungen zur enzymatischen Bräunung bei Kartoffeln (Solanum tuberosum)IV. Beziehung zwischen Tyrosinumsatz und Bräunung

Zusammenfassung Aus Analysendaten der Literatur wurde für 72 unterschiedlich bräunende Kartoffelproben der Tyrosinumsatz nach einer von uns kürzlich veröffentlichten Methode berechnet. Die Proben beinhalten 9 Sorten aus 3 Standorten im Jahr 1969, die nach der Ernte and nach verschiedenen Lagerzeiten bei 3 verschiedenen Temperaturen analysiert wurden. Die Berechnung des Tyrosinumsatzes führte bei 58 Proben (81%) zur gleichen Klassifizierung der Sorten wie die sensorische Beurteilung der Bräunung. Es wird gefolgert, daß die enzymatische Bräunung bei Kartoffeln eher mit dem Tyrosinumsatz, der von den Konzentrationen an Phenoloxydase, Tyrosin, Chlorogensäure und Ascorbinsäure abhängig ist, als mit einem einzelnen Parameter korreliert ist.

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Dedicated to Prof. Dr. L. Acker on his 65 ^th birthday     

板栗品种褐变度差异性及其多酚氧化酶活性的相关性研究

以37个板栗品种为试材,研究了板栗果实褐变差异性及其与多酚氧化酶（PPO）活性之间的关系,并根据褐变差异性对各品种进行聚类分析。结果表明:板栗不同品种间褐变差异显著（p<0.05）,根据褐变差异性聚类分析,可将37个品种可以分为5个等级;不同品种间PPO活性差异显著（p<0.05）;通过探讨不同品种间褐变度与PPO活性的关系,发现随着板栗品种间PPO活性的升高,褐变度也开始升高,当PPO活性达到90 U·min-1·g-1时,PPO活性对褐变影响开始降低;通过褐变聚类分析,将板栗PPO活性分为5类,在优选或改良品种时,可将品种的PPO活性在第一或第二类活性范围以下作为选择依据之一。      

Polyphenol oxidase activity and browning of three avocado varieties

A comparison between the in vitro total and specific activity of polyphenol oxidase of three avocado varieties, Fuerte, Horeshim and Lerman, showed clear differences that were correlated with the in vivo rate of browning of the corresponding freshly cut mature fruit; Fuerte had the highest values, followed by Horeshim and then Lerman. A good correlation existed between the PPO activity in the crude homogenate of the fresh fruit and the crude enzyme extracted from the acetone powder prepared from each variety. The possibility that the relatively low PPO activity in the crude enzyme of the Lerman avocado was due to the presence of an inhibitor and to factor(s) degrading the enzyme, or that the relatively high activity of the Fuerte enzyme was due to an activator, was tested in various ways and ruled out. It was therefore concluded that the differences in the rate of browning of the three avocado varieties studied were directly related to the PPO activities as expressed in the crude enzyme fraction.     

Enzymatic Browning in Five Olive Varieties

Enzymatic activities (polyphenoloxidase and peroxidase) and o-diphenols content were estimated in fruits of five olive varieties differing in browning rate. Significant differences were observed among the varieties. The browning rate correlated with o-diphenols content and polyphenol oxidase activity, but not with peroxidase activity.     

A new method to apply and quantify bruising sensitivity of button mushrooms

Mushrooms are prone to develop brown discolouration due to bruising caused by mechanical damage during harvest, which leads to reduced quality of the mushrooms. In order to study the mechanism behind discolouration and to breed for bruise-related browning resistant strains, a high throughput bruise application method and reliable quantification of browning sensitivity is essential. In this study a new bruising device was developed to bruise mushrooms in a fast and reproducible way. The bruising device can apply damage to the cap tissue of button mushrooms by a slip-shear sliding process. The severity of the bruise was quantified with a computer imaging system combined with a newly developed software programme. A protocol was developed to obtain the most reliable and reproducible method to compare browning sensitivity of different Agaricus bisporus strains. For this purpose, the extent of damage applied, time between harvest and bruising, developmental stage of the mushrooms and flushes were taken into account. The new method of bruising and image based quantification was subsequently applied to a collection of wild, commercial and hybrid A. bisporus strains and a distinction could be made between bruise-related browning sensitive mushrooms and tolerant mushrooms.     

大蕉后熟期的褐变相关性及褐变底物鉴定

以粉蕉和香牙蕉为对照,观察大蕉后熟过程中褐变度、多酚氧化酶和过氧化物酶的变化规律,同时考察大蕉总酚和游离酚含量分别在大蕉褐变过程中起的作用。结果表明：三种香蕉在后熟过程中,褐变度均呈逐渐增长趋势,在储藏13d后,粉蕉与香牙蕉的褐变速率明显高于大蕉,说明大蕉更适合于作为深加工的原料。在储藏13d后,大蕉的多酚氧化酶和过氧化物酶比活力均比较低,游离酚含量也比较低,但总酚含量较高,最终导致褐变速率较慢,说明大蕉的褐变度同多酚氧化酶和过氧化物酶有一定的相关性,大蕉的褐变速率与游离酚的含量呈负相关。对褐变度与多酚氧化酶和过氧化物酶进行相关性分析,大蕉后熟过程中的褐变度与多酚氧化酶和过氧化物酶的相关性(R2值)分别为0.8789和0.9240,说明大蕉后熟过程中的褐变潜力与多酚氧化酶和过氧化物酶密切相关;通过紫外-可见吸收光谱扫描和高效液相色谱分析等方法初步鉴定,大蕉的褐变底物主要为没食子酸和表儿茶素。     

The role of polyphenol oxidase and peroxidase in the browning of water caltrop pericarp during heat treatment

The mechanism of browning involving enzymatic browning was investigated in the pericarp of water caltrop, an Asian vegetable popular for its taste and medicinal properties. Polyphenol oxidase (PPO) and peroxidase (POD) activities were determined in pericarp at various times and temperatures. Water caltrop consisted of 44.22% moisture content, 37.23% crude fibre, and 2.63% crude protein. PPO and POD activities dropped from 62 and 38 units/g sample, respectively, as water temperature was increased from 30 to 80 °C. Optimum pH and temperature for PPO activity was at pH 5.0, 25–45 °C, and POD activity peaked at 60 °C. High PPO and POD activities at 40–50 °C resulted in degradation of phenolic compounds, which led to increased aggregation of browning pigments and discolouration (lower L-values) of the pericarp. Enzymatic browning was determined as the major factor in the browning discolouration of heat-treated water caltrop pericarp.     

鲜切甘薯不同部位褐变机理差异

以‘渝薯17’甘薯为实验材料,将鲜切甘薯分为皮部、周边以及中心3 个部位。通过对冷藏过程中鲜切甘 薯不同部位褐变情况、褐变底物酚类物质含量、褐变相关酶活力的比较研究,探讨鲜切‘渝薯17’不同部位的褐变 机理及差异。结果表明,绿原酸是甘薯褐变的主要底物,鲜切甘薯不同部位褐变存在差异,皮部褐变最严重,周边 次之,中心最弱。皮部总酚和游离酚含量均显著高于周边和中心组织（P＜0.05）,其中主要底物绿原酸含量为周 边和中心组织的3～4 倍。多酚氧化酶（polyphenoloxidase,PPO）是引起皮部组织褐变的主要酶,苯丙氨酸解氨酶 对酚类物质的积累起促进作用;周边组织褐变由PPO和过氧化物酶（peroxidase,POD）协同作用催化;中心组织 褐变则主要由POD引起。     

Reassessment of treatments to retard browning of fresh‐cut Russet potato with emphasis on controlled atmospheres and low concentrations of bisulphite

The cultivar Pacific Russet with high browning susceptibility was used for most testing. Controlled atmospheres (0.3%, 3% and 21% O₂ in combination with 0%, 6% or 12% CO₂) and anti‐browning chemicals were studied in relation to quality retention and wound‐induced phenolic metabolism of fresh‐cut slices for up to 16 days at 5 °C. The 3% O₂+ 12% CO₂ atmosphere was most effective among those tested, and retarded increases in phenolics and phenylalanine ammonia lyase activity, but had only slight benefit on visual quality. A 1.25% ascorbic acid +1.25% citric acid treatment was ineffective, but when combined with 3% O₂+ 12% CO₂, it was comparable with 0.025% sodium bisulphite. Bisulphite concentrations from 0.05% to 0.25% provided similar effective control of discolouration. Bisulphite as low as 0.025% with 3% O₂+ 12% CO₂ resulted in a visual quality score at the limit of marketability after 8 days at 5 °C. Chemical treatments did not retard increases in phenolic concentrations or phenolic enzyme activities.     

基于品质指标的苹果浊汁品种与产地差异性分析

以来自7?个不同主产区的21?个主栽品种,共41?份苹果鲜果为研究对象,对每个品种鲜榨浊汁的出汁率、浊度、果汁颜色、褐变度、透光率、可溶性固形物、可滴定酸、总酚、糖、有机酸、VC、矿物质、抗氧化性等品质指标进行测定。运用描述性分析、逐步线性判别分析进行数据处理。结果表明：不同品种或不同产地的苹果浊汁,品质差异较大。总体来看,a*值、原始浊度、褐变度、可滴定酸、葡萄糖、蔗糖、苹果酸等指标的变幅均较大,分别为94.07%、70.41%、42.86%、35.26%、42.02%、42.40%、37.69%。对于不同品种的苹果浊汁,由于褐变度、总酚、抗氧化性等色泽品质指标以及糖、酸等营养品质指标间具有较大差异,其分布呈现分散状态。其中新红星品种的褐变度、总酚含量、DPPH自由基清除率等品质指标普遍居高,色泽品质差异最显著。富士品种大部分样品的果糖、葡萄糖、蔗糖、苹果酸等指标含量较高,具有较好的营养品质。然而对于不同产地间的样品,其浊度、可滴定酸、可溶性固形物等加工品质指标具有较大差异,样品分布较为分散。河北省样品的出汁率、原始浊度、可滴定酸等指标普遍较低,加工品质较差。来自山东省不同品种苹果浊汁的样品以及来自不同产地富士苹果浊汁的样品间均具有较大差异,并且分别获得了77.8%和72.7%的判别准确率。以上结果表明,不同产地、不同品种苹果原料制得的苹果浊汁存在较大差异,通过对其品质指标进行差异性分析,可为上游育种与种植产业结构调整提供数据基础;通过判别模型的建立实现品种与产地的识别与预测,可以指导企业对苹果原料进行制汁专用化筛选。     

不同贮藏温度下鲜切紫甘薯褐变相关因素研究

为研究鲜切紫甘薯的褐变条件与机理,本文对不同贮藏温度下(4和12℃)的鲜切紫甘薯的褐变程度、褐变相关酶活力以及褐变底物酚类物质进行分析。结果表明,12℃贮藏组的鲜切紫甘薯褐变度始终显著高于4℃贮藏组(P<0.05)。贮藏期间,褐变重的鲜切紫甘薯多酚氧化酶(Polyphenol oxidase,PPO)和过氧化物酶(Peroxidase,POD)活性更高,丙二醛(Malondialdehyde,MDA)含量更多。2~8 d,不同贮藏温度下鲜切紫甘薯绿原酸和阿魏酸含量显著不同(P<0.05),因此推断褐变相关酶活性、膜脂过氧化程度以及酚类物质含量可能是引起鲜切紫甘薯褐变的关键因素。通过相关性分析,多酚氧化酶(PPO)和过氧化物酶(POD)是引起鲜切紫甘薯褐变的关键酶。绿原酸和阿魏酸是鲜切紫甘薯褐变的主要底物。     

川中丘陵区冬作不同品种马铃薯鲜切加工适宜性评价

以四川省川中丘陵区冬作马铃薯10个主栽品种为试验材料,考察了不同品种经鲜切加工后常温贮藏条件下总体感官质量、切片表面色差、褐变度和多酚氧化酶活性。结果表明,不同品种鲜切马铃薯在贮藏过程中各项指标均存在明显差异;中薯2号在贮藏过程中总体感官值相对较高,常温贮藏至第4 d时仍具有一定的商品性,而川芋802在贮藏至第2 d时外观商品性就接近5分(商品临界点);中薯2号和川芋10号的色差变化值相对较小,而川芋50和川芋802变化较大;川芋10号、费乌瑞它和青薯9号贮藏过程中褐变度相对较低;对PPO活性进行聚类分析将10个供试品种分为两个大类;综合多项测试指标表明,中薯2号和川芋10号鲜切加工后常温贮藏过程中产品品质较好,抗褐变能力较强,而川芋802和川芋50较易发生褐变,该研究结果可为马铃薯鲜切加工原料的选择提供参考依据。     

FACTORS AFFECTING THE PRODUCTION OF α-AMYLASE IN BARLEY GRAINS

The production of α-amylase by the endosperm of barley varieties, both commercial and non-commercial, in normal germination and after incubation with gibberellic acid, has been measured. The level of activities produced differed considerably between varieties. All varieties tested produced considerably more enzyme when supplied with a source of exogenous gibberellic acid than under normal germination. In general the differences between varieties were less in the de-embryonated treatment.     

Tyrosine metabolism in pigment-forming Yarrowia lipolytica strains isolated from English and European speciality mould-ripened cheese exhibiting a brown discolouration defect

Yarrowia lipolytica s4fd was isolated from a UK-manufactured speciality mould-ripened cheese as the causative micro-organism of a brown surface discolouration spoilage defect. Comparative studies utilizing Y. lipolytica isolates indicated that inter-strain variations in pigment accumulation were attributable to differences in tyrosine uptake and metabolism to homogentisic acid. The range and activity profiles of proteolytic enzymes involved in tyrosine release and turnover in isolates that differed in pigment formation were, however, similar. Homogentisic acid formation was affected by physiological parameters, and approaches that may be developed by the cheesemaker to prevent spoilage losses associated with the development of the brown discolouration defect are discussed.     

鸡腿蘑速冻预处理工艺及护色研究

研究了鸡腿蘑速冻保鲜工艺。在测定PPO活力的基础上通过对EDTA2Na、NaHSO3、抗坏血酸、柠檬酸4种护色剂对鸡腿蘑褐变度(BD)的影响及采用热处理法钝化酶活性的方法研究,确定了控制速冻鸡腿蘑酶促褐变的工艺条件。结果表明,4种护色剂对鸡腿蘑褐变均有一定的抑制作用,其中抗坏血酸的抑制效果最好,最弱的为EDTA2Na;沸水加热3min,能有效钝化酶的活性。     

Freeze-dried fresh onion powder prevents green discolouration (greening) in macerated garlic

Green discolouration (greening) of macerated garlic products is a major concern in the garlic-processing industry, and is caused by reactions between free amino acids and 2-propenyl 1-propenyl (2-Pe/1-Pe) thiosulphinates in the garlic. Efficacy of freeze-dried fresh onion powder that contains the active onion enzyme lachrymatory factor synthase (LFS) to prevent greening in processed garlic was evaluated. LFS converts 1-propenesulphenic acid to the volatile lachrymatory factor (LF). We hypothesised that this conversion would decrease the production of 2-Pe/1-Pe thiosulphinates, and thus, would reduce the subsequent discolouration of the garlic. Cooked onion powder added to fresh garlic, which was equivalent to adding crude 1-PeCSO, resulted in intensified green discolouration and increased 2-Pe/1-Pe thiosulphinate levels. On the other hand, fresh onion powder added to fresh garlic (0.5 g powder to 100 g fresh garlic) prevented greening and decreased the 2-Pe/1-Pe thiosulphinate levels. Similarly, a crude onion enzyme solution prevented greening in a garlic homogenate. The 2-propenyl 2-propenyl thiosulphinate (allicin) content was inconsistently altered by the addition of onion powder. However, the expected production of LF by the fresh onion powder or enzyme solution was not detected by gas chromatography, possibly due to changes in the sample matrix. This method using fresh onion powder is an effective technique for preventing greening of fresh garlic that does not use artificial food additives or cause safety concerns.     

POLYPHENOLOXIDASE ACTIVITY, BROWNING POTENTIAL AND PHENOLIC CONTENT OF PEACHES DURING POSTHARVEST RIPENING

Changes in the polyphenoloxidase (PPO) activity and the phenolic content of peaches (Prunus persica cv. Premier) during postharvest ripening were studied. The fruits were stored at 12 or 25C for up to 15 days. The quantity of extractable proteins was maximum at 6–10 days storage at 25 and 12C, coinciding with the onset of the yellowness in the fruits. The PPO activity increased up to the ripening stage, showing a maximum value at 8 days of storage. This was coincident with the maximum degree of browning as evaluated by the absorbance at 440 nm. The amount of total phenolics and chlorogenic acid in the fruits decreased during storage; however, the differences were not significant. The browning potential closely correlated with the enzyme activity, but not with the phenolic content.