首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Polyphenol oxidase and peroxidase were extracted from two different varieties of strawberry fruit (Fragaria x ananassa D, cv. 'Elsanta' and Fragaria vesca L, cv. 'Madame Moutot') and characterized using reliable spectrophotometric methods. In all cases, the enzymes followed Michaelis-Menten kinetics, showing different values of peroxidase kinetics parameters between the two cultivars: Km = 50.68 +/- 2.42 mM ('Elsanta') and 18.18 +/- 8.79 mM ('Madame Moutot') mM and Vmax = 0.14 +/- 0.03 U/g ('Elsanta') and 0.05 +/- 0.01 U/g ('Madame Moutot'). The physiological pH of fruit at the red ripe stage negatively affected the expression of both oxidases, except polyphenol oxidase from 'Madame Moutot' that showed the highest residual activity (68% of the maximum). Peroxidase from both cultivars was much more thermolable as compared with PPO, losing over 60% of relative activity already after 60 min of incubation at 40 degrees C. The POD activation energy was much lower than the PPO activation energy (DeltaE = 97.5 and 57.8 kJ mol-1 for 'Elsanta' and 'Madame Moutot', respectively). Results obtained from d-glucose and d-fructose inhibition tests evidenced a decreasing course of PPO and POD activities from both cultivars as the sugar concentration in the assay medium increased. Changes in CIE L*, a*, b*, chroma, and hue angle values were taken as a browning index of the samples during storage at 4 degrees C. A decrease in L* was evident in both cultivars but more marked in 'Elsanta'. PPO and POD activities from cv. 'Elsanta' were very well-correlated with the parameter L* (r2=0.86 and 0.89, respectively) and hue angle (r2=0.85 and 0.93, respectively). According to these results, the browning of the fruit seemed to be in relation to both oxidase activities.  相似文献   

2.
Destabilization of thermostable polyphenol oxidase (TS-PPO) during the ripening of peaches has been previously shown (Yemenicio?lu, A.; Cemero?lu, B. Tr. J. Agric. For. 1998, 22, 261-265). This work studied the effect of ripening on thermal stability of apricot PPO for three different cultivars. Kabaa?i cultivar contained thermolabile PPO, whereas TS-PPO appeared in Hacihalilo?lu and Catalo?lu cultivars. The TS-PPO showed biphasic inactivation curves, and its D and z values between 60 and 90 degrees C varied in the ranges of 357-1.12 min and 11.9-12.7 degrees C, respectively. In Hacihalilo?lu cultivar the TS-PPO was very consistent and existed at all stages of ripening, whereas in Catalo?lu cultivar it appeared only at the half-ripe stage. The loss of consistent TS-PPO in Hacihalilo?lu apricots after partial purification by acetone precipitation and DEAE-cellulose chromatography suggested the non-covalent nature of its stabilization. The main purified fractions (F1 and F2) showed monophasic inactivation curves with similar thermal inactivation parameters (z(F1) = 10.4 degrees C, z(F2) = 10.1 degrees C). However, their kinetic properties against catechol (K(mF1) = 61 mM, K(mF2) = 122.7 mM) and substrate specificities were considerably different. The results of this study showed the presence of TS-PPO forming and destabilizing mechanisms in apricots. Further studies are needed for the solution of these mechanisms and to develop some new strategies that may be utilized by molecular techniques for a planned production of apricot cultivars provided with heat labile but normal PPO activity.  相似文献   

3.
This study was undertaken to follow the kinetics of polyphenoloxidase (PPO), peroxidase (POD), and phenolic compounds during yam blanching at different temperatures and after drying and to identify by high-performance liquid chromatography (HPLC) the main phenolic compounds present in yam products. PPO activity was 50% higher in nonprocessed freeze-dried Florido (Dioscorea alata) than in nonprocessed freeze-dried Deba (Dioscorea rotundata). It decreased progressively during blanching. Forty-five percent of PPO activity remained after 50 min of blanching at 60 or 65 degrees C, whereas the POD activity dropped sharply to less than 20% of the initial activity after 10 min of blanching, whatever the blanching temperature. No anthocyanidins could be detected by HPLC at 520 nm in nonprocessed freeze-dried yam. Flavanols with a maximum absorption wavelength (lambda(max)) at 280 nm and cinnamic acid compounds with 320 nm lambda(max) were detected. Catechin was identified as the major flavanol with concentrations ranging from 0.26 to 0.41 microM g(-)(1) depending on cultivar. One cinnamic compound, ferulic acid, was identified and assessed in both cultivars (0.03-0.04 microM g(-)(1)). Total phenol, flavanol, and cinnamic contents decreased during blanching independently of temperature whereas some unresolved peaks were detected by HPLC in dried product. The latter was probably due to the consumption of coloring precursors and the appearance of polymerized or complex colored products.  相似文献   

4.
Cut tissues from distinct anatomical locations in iceberg lettuce (Lactuca sativa L.) were subjected to washing in cold (4 degrees C) and warm (47 degrees C) water with or without chlorine to assess their propensity to discoloration during storage. Total protein (Bradford method) and phenolic (TPH; Folin-Ciocalteu method) contents and polyphenol oxidase (PPO; spectrophotometric method using catechol as a substrate), peroxidase (POD; guaiacol substrate), and phenylalanine ammonia-lyase (PAL; phenylalanine substrate) activities were determined in photosynthetic and vascular tissue from outer and inner leaves. Unprocessed photosynthetic and inner leaf tissues had significantly higher (P < 0.05) levels of protein and TPH and PPO and POD activities than vascular and outer leaf tissues. PAL activities (on a fresh weight basis) were similar in all tissues. Changes in browning (light reflectance measurement) and phenolic metabolism in all four tissue types were observed during aerobic storage at 5 degrees C over 10 days. PAL activity increased in all tissues after 1-2 days of storage and then gradually decreased. POD activity also increased steadily for the storage duration. Protein content and PPO activity remained constant. Edge browning (measured with a Minolta Chroma Meter) and TPH increased in all tissues, especially in outer vascular tissue. Cut photosynthetic and vascular tissues washed at 4 and 47 degrees C with and without 100 microg mL(-1) chlorine for 3 min were analyzed during 7 days in storage at 5 degrees C. Enzyme activities and accumulation of phenolics in all tissues washed at 47 degrees C were significantly (P < 0.05) lower compared to controls or tissues washed at 4 degrees C. Chlorine had no additional effect at 47 degrees C but significantly (P < 0.05) reduced browning and accumulation of phenolics in lettuce washed at 4 degrees C. These results showed that inherent differences between tissues affect phenolic metabolism and browning in stored, fresh-cut lettuce.  相似文献   

5.
The effect of wounding on polyphenol oxidase (PPO), peroxidase (POD), and phenylalanine ammonia-lyase (PAL) was studied in six minimally processed lettuce (Lactuca sativa L.) cultivars upon storage for 7 days at 5 degrees C (Iceberg Mikonos (IM), I. Green Queen (IGQ), I. Asdrúbal (IA), Little Gem Sandra (LGS), Romaine Cazorla (RC), and R. Modelo (RM)). Wounding of lettuce tissue midribs (because of minimal processing) caused an exponential increase in PPO activity due to the activation process from latent to fully active PPO by following first order kinetics in the time range from 3.7 days (LGS) to 6.3 days (RC). However, total PPO activity (active plus latent) remained constant. Isoform pattern of PPO changed upon storage probably because of posttranslational processes. POD activity linearly increased with induction of new POD isoenzymes. PAL activity presented a typical bell-shaped induction pattern in four cultivars. Only IM and IGQ showed a second induction response which has not been previously described in the literature. IM was the cultivar most susceptible to browning and RC was the cultivar least susceptible. However, no clear correlation was observed between browning and any of the biochemical and physiological attributes investigated (PPO, PAL, and POD activities, total and individual phenols accumulation, and ascorbic acid content).  相似文献   

6.
Polyphenol oxidase (PPO) of cauliflower was purified to 282-fold with a recovery rate of 8.1%, using phloroglucinol as a substrate. The enzyme appeared as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The estimated molecular weight of the enzyme was 60 and 54 kDa by SDS-PAGE and gel filtration, respectively. The purified enzyme, called phloroglucinol oxidase (PhO), oxidized phloroglucinol (K(m) = 3.3 mM) and phloroglucinolcarboxylic acid. The enzyme also had peroxidase (POD) activity. At the final step, the activity of purified cauliflower POD was 110-fold with a recovery rate of 3.2%. The PhO and POD showed the highest activity at pH 8.0 and 4.0 and were stable in the pH range of 3.0-11.0 and 5.0-8.0 at 5 °C for 20 h, respectively. The optimum temperature was 55 °C for PhO and 20 °C for POD. The most effective inhibitor for PhO was sodium diethyldithiocarbamate at 10 mM (IC(50) = 0.64 and K(i) = 0.15 mM), and the most effective inhibitor for POD was potassium cyanide at 1.0 mM (IC(50) = 0.03 and K(i) = 29 μM).  相似文献   

7.
Polyphenol oxidase (EC 1.10.3.1, o-diphenol: oxygen oxidoreductase, PPO) of banana (Musa sapientum L.) peel was partially purified about 460-fold with a recovery of 2.2% using dopamine as substrate. The enzyme showed a single peak on Toyopearl HW55-S chromatography. However, two bands were detected by staining with Coomassie brilliant blue on PAGE: one was very clear, and the other was faint. Molecular weight for purified PPO was estimated to be about 41 000 by gel filtration. The enzyme quickly oxidized dopamine, and its Km value (Michaelis constant) for dopamine was 3.9 mM. Optimum pH was 6.5 and the PPO activity was quite stable in the range of pH 5-11 for 48 h. The enzyme had an optimum temperature at 30 degrees C and was stable up to 60 degrees C after heat treatment for 30 min. The enzyme activity was strongly inhibited by sodium diethyldithiocarbamate, potassium cyanide, L-ascorbic acid, and cysteine at 1 mM. Under a low buffer capacity, the enzyme was also strongly inhibited by citric acid and acetic acid at 10 mM.  相似文献   

8.
Abstract

Chlorophyll content of butterhead lettuce leaves was estimated by correlations between the Minolta SPAD‐502 and Minolta chroma meter CR 300. The SPAD‐502 readings and extractable chlorophyll (Chl a, Chl b, and total Chlorophyll) contents were related. High linear correlations were obtained for chlorophyll a (R2=0.90), chlorophyll b (R2=0.85), and total chlorophyll (R2=0.92). After that, during the growth cycle of butterhead lettuce grown in soilless culture, leaves were selected and SPAD‐502 and chroma meter readings were made. Finally, correlations between SPAD‐502 readings and leaf color (L*, a*, b*, C*, and hue angle) determined by the chroma meter were calculated. Hue angle (H°; R2=0.75) and lightness index (L*; R2=0.68) were the parameters that better relate with SPAD‐502 readings, so these parameters can also be used for rapid and nondestructive estimates of leaf chlorophyll in situ.  相似文献   

9.
Polyphenol oxidase (E.C. 1.14.18.1) (PPO) extracted from yacon roots (Smallanthus sonchifolius) was partially purified by ammonium sulfate fractionation and separation on Sephadex G-100. The enzyme had a molecular weight of 45 490+/-3500 Da and Km values of 0.23, 1.14, 1.34, and 5.0 mM for the substrates caffeic acid, chlorogenic acid, 4-methylcatechol, and catechol, respectively. When assayed with resorcinol, DL-DOPA, pyrogallol, protocatechuic, p-coumaric, ferulic, and cinnamic acids, catechin, and quercetin, the PPO showed no activity. The optimum pH varied from 5.0 to 6.6, depending on substrate. PPO activity was inhibited by various phenolic and nonphenolic compounds. p-Coumaric and cinnamic acids showed competitive inhibition, with Ki values of 0.017 and 0.011 mM, respectively, using chlorogenic acid as substrate. Heat inactivation from 60 to 90 degrees C showed the enzyme to be relatively stable at 60-70 degrees C, with progressive inactivation when incubated at 80 and 90 degrees C. The Ea (apparent activation energy) for inactivation was 93.69 kJ mol-1. Sucrose, maltose, glucose, fructose, and trehalose at high concentrations appeared to protect yacon PPO against thermal inactivation at 75 and 80 degrees C.  相似文献   

10.
Polyphenol oxidase (EC 1.10.3.1, PPO) in the pulp of banana (Musa sapientum L.) was purified to 636-fold with a recovery of 3.0%, using dopamine as substrate. The purified enzyme exhibited a clear single band on polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate (SDS)-PAGE. The molecular weight of the enzyme was estimated to be about 41000 and 42000 by gel filtration and SDS-PAGE, respectively. The enzyme quickly oxidized dopamine, and its K(m) value for dopamine was 2.8 mM. The optimum pH was at 6.5, and the enzyme activity was stable in the range of pH 5-11 at 5 degrees C for 48 h. The enzyme had an optimum temperature of 30 degrees C and was stable even after a heat treatment at 70 degrees C for 30 min. The enzyme activity was completely inhibited by L-ascorbic acid, cysteine, sodium diethyldithiocarbamate, and potassium cyanide. Under a low buffer capacity, the enzyme was also strongly inhibited by citric acid and acetic acid at 10 mM.  相似文献   

11.
The effect of storage time on pH, titratable acidity, degrees Brix, organic acids, sugars, amino acids, and color of minimally processed cantaloupe melon (Cucumis melo L. var. reticulatus Naud. cv. Mission) was determined at 4 degrees C and 20 degrees C. Changes in most of the biochemical parameters with storage time were relatively slow at the lower temperature. At 20 degrees C, a 17% loss in soluble solids and a 2-fold increase in acidity occurred after 2 days. Organic acid content also increased considerably with time at this temperature as a result of the production of lactic acid. Oxalic, citric, malic, and succinic acids were the organic acids, and glucose, fructose, and sucrose were the sugars present in the freshly cut cantaloupe. Malic acid concentration decreased concurrently with lactic acid production indicating the possible involvement of anaerobic malo-lactic fermentation along with sugar utilization by lactic acid bacteria. The effect of storage on microbial growth was determined at 4, 10, and 20 degrees C. Gram-negative stained rods grew at a slower rate at 4 degrees C and 10 degrees C than the Gram-positive mesophilic bacteria that dominated microorganism growth at 20 degrees C. Eighteen amino acids were identified in fresh cantaloupe: aspartic acid, glutamic acid, asparagine, serine, glutamine, glycine, histidine, arginine, threonine, alanine, proline, tyrosine, valine, methionine, isoleucine, leucine, phenyl alanine, and lysine. The dominant amino acids were aspartic acid, glutamic acid, arginine, and alanine. Total amino acid content decreased rapidly at 20 degrees C, but only a slight decrease occurred at 4 degrees C after prolonged storage. Changes in lightness (L), chroma, and hue at both temperatures indicate the absence of browning reactions. The results indicate the potential use of lactic acid and lactic acid bacteria as quality control markers in minimally processed fruits.  相似文献   

12.
A partial characterization of peroxidase (POD) and polyphenol oxidase (PPO) activities in blackberry fruits is described. Two cultivars of blackberry (Wild and Thornless) were analyzed for POD and PPO activities. Stable and highly active POD and PPO extracts were obtained using insoluble poly(vinylpyrrolidone) and Triton X-100 in 0.05 M sodium phosphate, pH 7.5, buffer. Blackberry POD and PPO activities have a pH optimum of 6.5, in a reaction mixture of 0.2 M sodium phosphate. Optimal POD activity was found with 3% o-dianisidine. Maximum PPO activity was found with catechol (catecholase activity) followed by 4-methylcatechol. Polyacrylamide gel electrophoresis of blackberry extracts under non-denaturing conditions resolved in various bands. In the POD extracts of Wild fruits, there was only one band with a mobility of 0.12. In the Thornless POD extracts there were three well-resolved bands, with R(f) values of 0.63, 0.36, and 0.09. Both the Wild and Thornless blackberry cultivars produced a single band of PPO, with R(f) values of 0.1 for Wild and 0.06 for Thornless.  相似文献   

13.
Polyphenol oxidase (PPO) of garland chrysanthemum (Chrysanthemum coronarium L.) was purified approximately 32-fold with a recovery rate of 16% by ammonium sulfate fractionation, ion exchange chromatography, hydrophobic chromatography, and gel filtration. The purified enzyme appeared as a single band on PAGE and SDS-PAGE. The molecular weight of the enzyme was estimated to be about 47000 and 45000 by gel filtration and SDS-PAGE, respectively. The purified enzyme quickly oxidized chlorogenic acid and (-)-epicatechin. The K(m) value (Michaelis constant) of the enzyme was 2.0 mM for chlorogenic acid (pH 4.0, 30 degrees C) and 10.0 mM for (-)-epicatechin (pH 8.0, 40 degrees C). The optimum pH was 4.0 for chlorogenic acid oxidase (ChO) and 8.0 for (-)-epicatechin oxidase (EpO). In the pH range from 5 to 11, their activities were quite stable at 5 degrees C for 22 h. The optimum temperatures of ChO and EpO activities were 30 and 40 degrees C, respectively. Both activities were stable at up to 50 degrees C after heat treatment for 30 min. The purified enzyme was strongly inhibited by l-ascorbic acid and l-cysteine at 1 mM.  相似文献   

14.
Polyphenol oxidase (PPO) was purified and characterized from Chinese cabbage by ammonium sulfate precipitation and DEAE-Toyopearl 650M column chromatography. Substrate staining of the crude protein extract showed the presence of three isozymic forms of this enzyme. The molecular weight of the purified enzyme was estimated to be approximately 65 kDa by gel filtration on Toyopearl HW-55F. On SDS-PAGE analysis, this enzyme was composed of a subunit molecular weight of 65 kDa. The optimum pH was 5.0, and this enzyme was stable at pH 6.0 but was unstable below pH 4.0 or above pH 7.0. The optimum temperature was 40 degrees C. Heat inactivation studies showed temperatures >40 degrees C resulted in loss of enzyme activity. PPO showed activity to catechol, pyrogallol, and dopamine (K(m) and V(max) values were 682.5 mM and 67.6 OD/min for catechol, 15.4 mM and 14.1 OD/min for pyrogallol, and 62.0 mM and 14.9 OD/min for dopamine, respectively). The most effective inhibitor was 2-mercaptoethanol, followed in decreasing order by ascorbic acid, glutathione, and L-cysteine. The enzyme activity of the preparation was maintained for 2 days at 4 degrees C but showed a sudden decreased after 3 days.  相似文献   

15.
Color is a key quality trait of wheat products, and polyphenol oxidase (PPO) is implicated as playing a significant role in darkening and discoloration. In this study, total and soluble PPO activities were characterized in whole kernel assays and bran extracts. In whole kernel assays similar to AACC Approved Method 22–85, four wheat cultivars were ranked the same for both total and soluble (leached) PPO activity with L‐DOPA (diphenol) as the substrate. Total kernel PPO activity was much greater than soluble PPO activity in three hexaploid wheat cultivars, indicating that insoluble PPO was the major contributor to kernel PPO measurements. Tyrosine (monophenol) was an excellent PPO substrate in kernel assays as expected but had no activity as a substrate for soluble PPO. However, soluble PPO activity with tyrosine was activated by the addition of the diphenols chlorogenic acid and caffeic acid. When PPO was assayed in homogenized bran, 89–95% of total PPO activity remained insoluble, associated with the bran particles. The kernel assay detected <2% of PPO measured in an equivalent amount of homogenized bran. However, total PPO activity was 2‐fold higher in Klasic than in ID377s, both when measured in the kernel assay and in homogenized bran, indicating that the kernel assay was an accurate predictor of relative total extracted PPO activity in these two cultivars. Adding detergents (0.1% SDS plus 0.2% NP‐40) to the bran extraction buffer increased both soluble and insoluble PPO activity. Results indicate that relative PPO activities among wheat cultivars are similar in whole kernel and kernel leachate assays, and that the predominant insoluble fraction of PPO, which is relatively uncharacterized, may be largely responsible for wheat product discoloration.  相似文献   

16.
Chlorogenic acid is the major diphenol of many fruits, where it is oxidized enzymatically by polyphenol oxidase (PPO) or peroxidase (POD) to its o-quinone. In spectrophotometric studies of chlorogenic acid oxidation with a periodate ratio of [CGA]0/[IO4-]0 < 1 and [CGA]0/[IO4-]0 > 1, the o-quinone was characterized as follows: lambda(max) at 400 nm and epsilon = 2000 and 2200 M-1 cm-1 at pH 4.5 and 7.0, respectively. In studies of o-quinone generated by the oxidation of chlorogenic acid using a periodate at ratio of [CGA]0/[IO4-]0 > 1, a reaction with the remaining substrate was detected, showing rate constants of k = 2.73 +/- 0.17 M-1 s-1 and k' = 0.05 +/- 0.01 M-1 s-1 at the above pH values. A chronometric spectrophotometric method is proposed to kinetically characterize the action of the PPO or POD on the basis of measuring the time it takes for a given amount of ascorbic acid to be consumed in the reaction with the o-quinone. The kinetic constants of mushroom PPO and horseradish POD are determined.  相似文献   

17.
Freshly squeezed orange juice samples were ozonated with control variables of gas flow rate (0-0.25 L min (-1)), ozone concentration (0.6-10.0%w/w), and treatment time (0-10 min). Effects of ozone processing variables on orange juice quality parameters of pH, degrees Brix, titratable acidity (TA), cloud value, nonenzymatic browning (NEB), color values ( L*, a*, and b*), and ascorbic acid content were determined. No significant changes in pH, degrees Brix, TA, cloud value, and NEB ( p < 0.05) were found. L*, a*, and b* color values were significantly affected by gas flow rate, ozone concentration, and treatment time. The changes in lightness ( L*) values and total color difference (TCD) values were fitted well to zero-order kinetics, whereas a*, b*, and ascorbic acid degradation followed first-order kinetics. The rate constants for a*, b*, and TCD were linearly correlated with ozone concentration ( R (2) = 0.88-0.99), whereas the rate constants for L* and ascorbic acid were exponentially correlated ( R (2) = 0.94-0.98).  相似文献   

18.
Cantaloupe cultivar variability from various U.S. regions and growing seasons within a given year was evaluated. As expected, there was often considerable quality and volatile variation among cultivars. Eight of 11 cultivars met the standard U.S. No. 1 requirement for degrees Brix (> or =9), and in most cultivars, degrees Brix declined during fresh-cut storage at 4 degrees C. Hunter L (loss of lightness color value) and a (decline of typical orange hue) colors also generally declined during storage in most cultivars. Volatile ester compounds generally decreased during fresh-cut storage or exhibited a transient increase before declining after 5-7 days of storage. The relative percentage of acetate esters declined during storage in all cultivars, and declines were accompanied by simultaneous non-acetate ester increases. Slight imbalances in compound concentrations may alter the overall perception of desirable, typical "cantaloupe" aroma/flavor during fresh-cut storage. Upsetting the unique aroma balance through storage may negatively affect flavor and the consumer's perception of desirable attributes, even though total volatile levels might not decrease substantially until after 5-7 days in storage. Subtle volatile and quality decreases are likely to be exacerbated with immature-harvested cantaloupe and are likely in out-of-season exports that have likewise been harvested at less mature stages. Altogether, this study indicates the difficulty in procuring cantaloupes of consistent quality from local producers, in a given year, for domestically grown fruit.  相似文献   

19.
Polyphenol oxidase (PPO) from eggplant was extracted and partially purified by a two-step fractionation-precipitation using ammonium sulfate and phenylsepharose hydrophobic interaction chromatography. The eggplant PPO extract was characterized concerning its kinetic properties. Optimal conditions to obtain Maillard reaction products (MRPs) with a maximal inhibitory potency (IP) toward PPO activity were determined using the surface response methodology and a four-factor and five-level experimental design. The MRPs were prepared from cysteine (0.25 M) and glucose (0-1 M), at several initial pH values (2-6) and at differing heating times (3-19 h) and temperatures (95-115 degrees C). The maximal IP was obtained after heating a model system of glucose/cysteine (1/0.25 M) at pH 2 for 3 h 20 min at 115 degrees C. The soluble part of this MRP, called MRP(IPmax), was a noncompetitive inhibitor toward eggplant PPO. The IP of MRP(IPmax) on PPO activity was very potent as compared to that displayed by benzoic, p-coumaric, and t-cinnamic acids, as well as sorbic acid and 4-hexylresorcinol. The activity of preincubated PPO at 0 degrees C with MRP(IPmax) was only slightly restored after dialysis or gel filtration.  相似文献   

20.
The effect of minimal processing on polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL), and phenolic compounds was studied in five potato cultivars (Agria, Cara, Liseta, Monalisa, and Spunta). Minimal processing caused an overall increase in PPO, POD, and PAL activities. The isoform pattern of PPO was the same for all of the cultivars before and after processing. No latent PPO was detected. The isoperoxidase pattern was approximately the same among cultivars. An increase in POD activity was related to the specific induction of an acidic isoperoxidase. PAL showed an induction pattern characterized by the presence of a maximum peak of activity after 4 days of processing for all of the cultivars. The sequence of browning susceptibility of potato cultivars was as follows: Monalisa > Spunta > Liseta > Cara > Agria. Browning development was only partially correlated to PAL activity (only during the first 4 days after wounding). However, this correlation could not explain the above sequence of browning susceptibility. Minimal processing caused an increase of chlorogenic acid, whereas tyrosine content remained unchanged. In summary, no significant correlation was found between either rate or degree of browning and any other biochemical and physiological attribute investigated (PPO, POD, hydrogen peroxide, ascorbic acid content, and initial phenolics content as well as total and individual phenolics accumulation).  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号