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1.
Hong Y Lin S Jiang Y Ashraf M 《Plant foods for human nutrition (Dordrecht, Netherlands)》2008,63(4):200-204
Eriobotrya plants are known to have significant amounts of phenolics and flavonoids, and exhibit a strong antioxidant activity. Experiments
were conducted to examine variation in the contents of total phenolics and flavonoids, and antioxidant activities in the leaves
of 11 Eriobotrya species (Tibet loquat, Daduhe loquat, Hengchun loquat, Taiwan loquat, Oak leaf loquat, Bengal loquat, Fragrant loquat, Guangxi
loquat, Obovate loquat, Big flower loquat, and common loquat, the last species include two materials, one is a cultivar ‘Zaozhong
6’, another is a wild tree). In these species, ‘Zaozhong 6′ loquat is a cultivar. The leaf extracts of ‘Tibet’, ‘Obovate’,
‘Taiwan’, ‘Bengal’ and ‘Hengchun’ loquats exhibited significantly higher contents of total flavonoids and total phenolics,
compared with those of other species. Of these 11 species, the highest contents of total phenolics and total flavonoids were
observed in ‘Tibet’ and ‘Obovatae’ loquats, respectively. The significantly stronger antioxidant abilities assessed by the
DPPH radical scavenging activity and reducing power were obtained in the leaf extracts of ‘Taiwan’, ‘Tibet’, ‘Bengal’, ‘Oak
leaf’, ‘Hengchun’ and ‘Obovate’ loquats, compared with the other species. In addition, significant correlations were found
between the contents of total phenolics or flavonoids and DPPH radical scavenging activity/reducing power. This work indicates
that the leaf extracts of the wild Eriobotrya species, ‘Tibet’, ‘Obovatae’, ‘Taiwan’, ‘Bengal’, ‘Oak leaf’ and ‘Hengchun’ loquats, exhibited significantly higher levels
of total phenolics and flavonoids, and significantly stronger antioxidant activities, compared with the cultivated species,
‘Zaozhong 6′ loquat, which suggests that these wild species have a better utilization value. 相似文献
2.
In this study, we evaluated tartary buckwheat during germination to provide an effective process that can lead to a rapid accumulation of both the total flavonoids and d-chiro-Inositol (DCI), as well as the elimination of trypsin inhibitor activity. At different concentrations of Al3+, Cu2+, and Zn2+, we found significant differences of the total flavonoids and DCI accumulation, and we observed changes in phenylalanine ammonia-lyase (PAL), chalcone isomerase (CHI), and α-Galactosidase (α-Gal) activities in germinated tartary buckwheat (p < 0.05). Correlation analysis between these enzymes (PAL, CHI and α-Gal) activities and the total flavonoids and DCI contents revealed a significant correlation in germinated tartary buckwheat. The maximum accumulation of the total flavonoids and DCI were 1315.52 mg/100 g DW and 60.46 mg/g DW with the addition of Al3+, 1315.41 and 63.59 with the addition of Cu2+, and 1189.42 and 53.10 with the addition of Zn2+. In these metal-treated samples, both total flavonoids and DCI were significantly higher than in the control (p < 0.05). Moreover, the metallic additives at the optimum concentration had no influence on total protein content, whereas a lower trypsin inhibitor activity was observed in correlation with higher protein digestibility. 相似文献
3.
为明确艾纳香抗菌药效物质基础,采用硅胶柱色谱, 凝胶色谱和反相色谱等技术从艾纳香乙酸乙酯部位中分离获得15个单体化合物,经波谱学鉴定分别为：3,3°,5-三羟基-4°,7-二甲氧基二氢黄酮 (1)、4°,5-二羟基-3,3°,7-三甲氧基黄酮 (2)、艾纳香素 (3)、3,5,3°,4°-四羟基-7-甲氧基黄酮 (4)、香叶木素 (5)、3°,4°,5-三羟基-3,7-二甲氧基黄酮 (6)、异鼠李素 (7)、chrysosplenol C (8)、金丝桃苷 (9)、异槲皮苷 (10)、3°,5,7-三羟基-4°-甲氧基二氢黄酮 (11)、sakuranetin (12)、pilloin (13)、5,7,3°,4°-四羟基-3-甲氧基黄酮 (14)、5-羟基-3,7,3°,4°-四甲氧基黄酮 (15),其中化合物7、11、12和13为首次从该植物中分得。抗菌活性评价结果显示：化合物1、3、6、8和12对3株细菌具有不同程度的抑制活性,其中化合物3对金黄色葡萄球菌抑制活性最强, 最低抑菌浓度MIC值为32 μg/mL。 相似文献
4.
Thermotropic polyurethanes were synthesized from 1,6-hexane diisocyanate (HDI) as a diisocyanate, 1,6-hexane diol (HD), and
rigid diols containing imide unit such as N,N′-bis(4-hydroxyphenyl)-3,4,3′,4′-biphenyl-dicarboxyimide (BPDI) or bis-N-(4-hydroxyphenyl)-4,4′-oxydiphthalimide
(ODPI). The effects of structure difference between BPDI and ODPI and composition of HD/BPDI (ODPI) on the thermal and liquid
crystalline behavior were studied. Thermotropic polyurethanes with an inherent viscosity of 0.59–0.70 were obtained. The melting
temperature of BPDI-based polyurethanes were in the range of 150–290°C, however, those of ODPI-based polyurethanes were in
the range of 150–190°C. All the polyurethanes based on ODPI (25–100 mole %) clearly exhibited a stable liquid crystalline
phase, and BPDI-based polyurethane having 5–25% of BPDI showed a mesophase. The melting and isotropization temperatures (T
m
, T
i
) andΔT(T
i
−T
m
) increased with increasing BPDI and ODPI content. The polyurethanes based on BPDI has higher melting points and thermal stability
compared to ODPI-based polyurethanes. 相似文献
5.
以先玉335为试验材料,研究4个密度水平(4.5×104、5.25×104、6.0×104、6.75×104株/hm2)对旱地春玉米形态指标、灌浆特征、干物质积累、产量及其构成因素的影响。结果表明,随密度增加,株高表现为先增大后减小的趋势,处理间无显著差异,地上部分干物质积累量和叶面积指数提高,营养物质向子粒转运的效率降低。不同处理下产量受有效穗数的影响较大,随着密度增大,群体有效穗比例由77.00%降低至69.00%;灌浆速率和灌浆时间共同影响百粒重,密度较低时,子粒最大灌浆速率出现所用天数提前,有助于子粒灌浆过程提前完成;随着密度增加,穗行数和行粒数均表现为增大趋势,百粒重先增大后减小。因此,本试验中种植密度为4.5×104株/hm2左右时,可以较好地协调玉米群体和个体生长关系之间的矛盾,实现子粒高产和水分高效利用的目标。 相似文献
6.
José A. Fernández-López Luís Almela José M. Obón Rosario Castellar 《Plant foods for human nutrition (Dordrecht, Netherlands)》2010,65(3):253-259
An analytical study was carried out on the presence of antioxidant constituents and the in vitro antioxidant capacity in the extracts of three species of Spanish red-skinned cactus pear fruits (Opuntia ficus-indica, Opuntia undulata and Opuntia stricta). The cactus pear fruit extracts were analyzed for determined constituents: ascorbic acid, flavonoids (quercetin, isorhamnetin,
myricetin, kaempferol and luteolin), betalains, taurine, total carotenoids and total phenolics. The antioxidant capacity was
assessed by means of two different methods: the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (Trolox equivalent antioxidant
capacity) method and the 2,2-diphenyl-1-picrylhydrazyl radical method. Opuntia ficus-indica fruit extract had the strongest antioxidant capacity and taurine content. O. stricta fruits were the richest in ascorbic acid and total phenolics, whereas O. undulata fruits showed the highest carotenoid content. Quercetin and isorhamnetin were the main flavonoids detected. This study provides
basic information on the presence of bioactive compounds and antioxidant capacity in extracts of cactus pear fruits, in order
to consider these extracts as ingredient for the production of health-promoting food. 相似文献
7.
8.
Hou Min Combet Emilie Edwards Christine Ann 《Plant foods for human nutrition (Dordrecht, Netherlands)》2019,74(3):383-390
Orange juice is an important source of flavanones in the Western diet. However, little is known of the variation in flavanone content of shop-bought orange juice with pulp (OJP) or without pulp (OJ), nor the impact of pulp on the fate of flavanones in the gut. Total phenols, total flavonoids, antioxidant capacity, hesperidin and narirutin, and dietary fibre were measured in six orange juice brands sold as OJP and OJ. The inclusion of pulp had little impact on fibre content. Apart from total phenols (OJ: 208.4?±?10.7 μg gallic acid equivalents (GAE) ml?1; OJP: 225.9?±?16.7 μg GAE ml?1, P?<?0.05), there were no differences between OJ and OJP. The fate of flavanones in OJ and OJP (Tropicana) were further compared using in vitro gastrointestinal (GI) models. After in vitro upper GI digestion, recovery of hesperidin was higher in OJ compared with OJP (89?±?6 vs. 68?±?3%, P?=?0.033). After 2 h colonic fermentation, hesperidin was 1.2 fold higher in OJP than OJ. However, after 24 h colonic fermentation there was no significant difference between juices in terms of hesperidin, hesperetin, narirutin, naringenin and catabolites. In conclusion, the amount of pulp included in these shop-bought orange juices had little impact on flavanone metabolism in models of the GI tract. The effects of greater amounts of orange pulp remain to be determined.
相似文献9.
Paśko P Zagrodzki P Bartoń H Chłopicka J Gorinstein S 《Plant foods for human nutrition (Dordrecht, Netherlands)》2010,65(4):333-338
The effect of Chenopodium quinoa seeds on lipid profile, glucose level, protein metabolism and selected essential elements (Na, K, Ca, Mg) level was determined
in high—fructose fed male Wistar rats. Fructose decreased significantly LDL [42%, p < 0.01] and activity of alkaline phosphatase [20%, p < 0.05], and increased triglycerides level [86%, p < 0.01]. The analysis of blood of rats fed quinoa indicated, that these seeds effectively reduced serum total cholesterol
[26%, p < 0.05], LDL [57%, p < 0.008] and triglycerides [11%, p < 0.05] when compared to the control group. Quinoa seeds also significantly reduced the level of glucose [10%, p < 0.01] and plasma total protein level [16%, p < 0.001]. Fructose significantly decreased HDL [15%, p < 0.05] level in control group but when the quinoa seeds were added into the diet the decrease of HDL level was inhibited.
Quinoa seeds did not prevent any adverse effect of increasing triglyceride level caused by fructose. It was shown in this
study that quinoa seeds can reduce most of the adverse effects exerted by fructose on lipid profile and glucose level. 相似文献
10.
以常规锰浓度为对照,设置锰缺乏和锰过量胁迫条件,研究游离态和络合态锰对不同基因型玉米早期氮代谢影响。结果表明,随着锰浓度的升高,根系硝态氮含量下降,品种东青1号下降幅度最小。品种垦粘1号和双玉201铵态氮含量随锰浓度增加呈先降低后升高趋势。吉农大516和东青1号随着锰胁迫增强,根部铵态氮含量下降。MnCl2·4H2O处理的玉米幼苗根系铵态氮积累程度大于EDTA-Mn处理,锰胁迫显著抑制根系可溶性蛋白合成。随着锰浓度增大,根系可溶性蛋白含量逐渐降低。MnCl2·4H2O处理根部可溶性蛋白下降程度大于EDTA-Mn处理。吉农大516根部可溶性蛋白含量最高。双玉201可溶性蛋白合成受抑制程度较大。锰胁迫影响根部氮素养分的有效分配,阻碍韧皮部运输而使得部分氮素于根部积累。锰胁迫条件下,东青1号为耐受品系,双玉201为敏感品系;游离态锰离子对玉米幼苗氮素转化抑制程度大于络合态锰离子。 相似文献
11.
Chutima Septhum Saowanee Rattanaphani John B. Bremner Vichitr Rattanaphani 《Fibers and Polymers》2009,10(4):481-487
Silk yarn was dyed with morin (2′,3,4′,5,7-pentahydroxyflavone) by using alum as mordant. In order to optimize the process,
three methods of dyeing involving: pre-mordanting, simultaneous mordanting, and post-mordanting were assessed and compared
with a mordant-free process. The adsorption of alum-morin dye onto silk fibers indicated that the adsorption capacities were
significantly affected by pH, the initial dye concentration, and temperature. The initial dye adsorption rates of alum-morin
dye on silk before equilibrium was reached increased with higher dyeing temperatures. The pseudo second-order kinetic model
was indicated for alum-morin dyeing (simultaneous mordanting) of silk at pH 4.0 with an activation energy (E
a
) of 45.26 kJ/mol. The value of the enthalpy of activation (ΔH
#) for alum-morin dyeing on silk at pH 4.0 was −31.29 kJ/mol. Also, the free energy (ΔG
o) and entropy changes (ΔS
o) for alum-morin dyeing on silk were −17.73 kJ/mol and −45.7 J/molK, respectively, consistent with a spontaneous and exothermic
adsorption process. 相似文献
12.
为评估CO2倍增对霍山石斛光合特性和生长的影响,本研究以霍山石斛幼苗为试材,比较了CO2浓度400 μmol/mol（大气浓度,对照组）和800 μmol/mol（处理组）栽培180 d对霍山石斛光合特性、生长和有效成分的影响。结果表明,CO2倍增处理显著提高了霍山石斛的净光合速率（Pn）、气孔导度（Gs）、蒸腾速率（Tr）和水分利用率（WUE）,但霍山石斛未出现“光合适应”现象。栽培30 d后,处理组的存活率、着根率和新芽数始终显著高于对照组,而60 d后,处理组的叶片可溶性蛋白含量显著低于对照组。栽培180 d后,CO2倍增处理组显著提高了霍山石斛的茎鲜重、茎干重、茎长、单株叶片数和叶片厚度,而对茎粗和单叶面积无显著影响。同时,处理组也显著提高了茎的多糖含量,比对照组提高94%,但生物碱含量则显著下降。茎的总氨基酸含量与总黄酮含量在两组间无显著差异。综上,CO2倍增处理能显著促进霍山石斛的生长,提高成活率及其主要药用部位茎的产量和多糖含量。 相似文献
13.
2019～2020年以陕单 650(中熟)和东单 60(晚熟)为材料,设置 4个种植密度 6.0×104、 7.5×104、 9.0×104和10.5×104株/hm2,研究密度对玉米产量及子粒含水率的影响。结果表明,增密可以提高不同熟期玉米品种的产量,陕单 650在密度为 9.0×104株/hm2时最优产量为 18 083.5 kg/hm2,东单 60在密度 7.5×104株/hm2时最优产量为17 472.9 kg/hm2。两个品种粒重及子粒含水率随密度的增大而减小,陕单 650达到最大灌浆速率的天数、平均灌浆速率较东单 60均早 4 d和高 0.06 g/d;陕单 650和东单 60子粒平均脱水速率为 0.98%/d和 0.93%/d,陕单 650在生理成熟 4 d后子粒含水率迅速降至 25%。当密度为 9.0×104株/hm2时,陕单 650的叶片干物质转运率明显高于东单 60。通过适度增密提高产量、缩短生育期降低子粒水分的技术途径,协同实现陕西春玉米密植高产机械子粒收获生产。 相似文献
14.
A series of new metallized direct dyes based on benzidine congeners, 2,2′-dimethyl-5,5′-dipropoxybenzidine and 5,5′-dipropoxybenzidine,
were evaluated for mutagenicity in Salmonella typhimurium strains TA98 and TA100. All of the dyes examined were judged to
be non-mutagenic with and without metabolic activation while toxicity was seen in some dyes at high doses. The study also
suggested that the standard Salmonella mutagenicity plate-incorporated assay was an excellent method for evaluation of dyes
for mutagenicity. 相似文献
15.
Tatjana Topalovic Vincent A. Nierstrasz Marijn M. C. G. Warmoeskerken 《Fibers and Polymers》2010,11(1):72-78
We have developed a homogeneous model system to study the mechanism of hydrogen peroxide bleaching using [Mn2O3(N,N′,N″-trimethyl-1,4,7-triazacyclononane)2](PF6)2 (MnTMTACN) as catalyst. The primary model pigment examined is morin (3,5,7,2′,4′-pentahydroxyflavone) owing to its presence
in native cotton fiber. Additionally, a series of model compounds with systematic structural differences are examined in order
to facilitate the development of a mechanistic understanding of the bleaching system. The pigment oxidative degradation reaction
is monitored by UV-Vis spectrophotometry. The influence of pH is examined in both homogeneous and heterogeneous model systems.
The use of MnTMTACN catalyst enables low-temperature hydrogen peroxide bleaching of cotton fabric at slightly lower pH values. 相似文献
16.
A series of new direct dyes based on benzidine congeners, 2,2′-dimethyl-5,5′-dipropoxybenzidine and 5,5′-dipropoxybenzidine,
were evaluated for mutagenicity in Salmonella typhimurium strains TA98 and TA100. All of the dyes examined were judged to
be non-mutagenic with and without metabolic activation while toxicity was seen in some dyes at high doses. The study also
suggested that the standard Salmonella mutagenicity plate-incorporated assay was an excellent method for evaluation of direct
dyes for mutagenicity. 相似文献
17.
In recent years, colored sorghum genotypes high in flavonoids have been developed. Flavonoid levels of eight black sorghum genotypes grown in four locations in Texas were evaluated to assess the relative genotype, environment and genotype × environment effects. Levels of total 3-deoxyanthocyanidins ranged from 292 μg/g to 499 μg/g and 251 μg/g to 804 μg/g across environments and genotypes, respectively. Total 3-deoxyanthocyanidins in sorghums from Halfway were low (178–694 μg/g) due to the reduction of their non-methoxylated forms. This reduction is likely due to significant grain weathering which was observed only at Halfway. In addition, flavanone and flavone levels were the lowest at Halfway with levels of 12 μg/g and 78 μg/g, respectively. For all flavonoids there was a genotype by environment interaction (p < 0.01) which suggests that environment had a different effect on flavonoid levels depending on the genotype. Color values L*, a* and b* did not correlate with flavonoid content. Due to genotype, environment and their interactions, sorghum breeders must evaluate these traits in multiple environments to identify genotypes with high and stable production of flavonoid compounds. 相似文献
18.
Dyeing properties of a series of 4-amino-4′-fluorosulfonylazobenzene disperse dyes on poly(ethylene terephthalate) (PET) were
investigated. Build-up properties and color properties on PET were examined. In particular, the 4-aminoazobenzene dyes containing
a nitro group instead of a fluorosulfonyl group at 4′-position were also synthesized in order to compare their dyeing properties
on PET with that of 4′-fluorosulfonyl analogues. 相似文献
19.
The influences of a series of new azo direct dyes including copper-complexes based on benzidine congeners, 2,2′-dimethyl-5,5′-dipropoxybenzidine
and 5,5′-dipropoxybenzidine, were examined using microorganism, Daphnia magna. The purpose of the research described in this
paper was to use bioassays with daphnids to determine the aquatic toxicity of new azo dyes in which copper was incorporated.
The results clearly show that copper has negative effects to aquatic ecosystem as expected. The study also suggested that
the assay with Daphnia magna was an excellent method to evaluate the influences of dyes to the aquatic environment. 相似文献
20.
Summary An optimum release of 5′-nucleotides in Bintje potato homogenates occurs at 52°C and pH 6.0. At higher temperatures there
is an accumulation of 3′-nucleotides and oligonucleotides; at lower temperatures and lower pH-values there is an accumulation
of nucleosides and further degradation products. Optimum activities in enzyme raw extract are reported for phosphodiesterase
I (50°C, pH 5.5), phosphodiesterase II (60°C, pH 5.5), ribonuclease (70°C, pH 5.0), phosphatase (45–50°C, pH 5.0), phosphatase
+5′-nucleotidase (45–50°C, pH 5.0). The relationship between the total enzymatic activities and the formation of 5′-nucleotides
during cooking of potatoes is discussed.
Zusammenfassung 5′-Nukleotide wirken in Lebensmitteln als geschmacksverst?rkende Verbindungen. Buri et al. (1970) hat bereits früher auf die Bedeutung dieser Verbindungen für den Geschmack von Kartoffeln hingewiesen und konnte zeigen, dass 5′-Nukleotide w?hrend des Kochprozesses aus Ribonukleins?ure (RNS) gebildet werden. Eine chemische Hydrolyse von RNS zu 5′-Nukleotiden kann ausgeschlossen werden; somit kommt nur eine enzymatische Freisetzung in Frage. Diese wird in der vorliegenden Arbeit untersucht. Es wurde aus Bintje-Kartoffeln ein vorgereinigter enzymatischer Extrakt hergestellt und dessen Enzymaktivit?ten wurden zun?chst mit spezifischen Substraten charakterisiert. Ribonuklease wurde mit zyklischem 2′, 3′-Cytidinmonophosphat gemessen und ergab optimale Aktivit?ten bei 70°C und pH 5.0 (Abb. 1 und 2). Phosphodiesterase I, untersucht mit dem Substrat α-Naphthyl-Thymidin-5′-Monophosphat, ergab optimale Aktivit?ten bei 50°C und pH 5.5 (Abb. 3 und 4). Phosphodiesterase II wurde mit Thymidin-5′-Monophosphat-p-Nitrophenylester geprüft und zeigte optimale Aktivit?ten bei 60°C und pH 5.5 (Abb. 5 und 6). Phosphatase wurde mit p-Nitrophenylphosphat gemessen und zeigte Optima der Aktivit?t bei 45–50°C und pH 5.0 (Abb. 7 und 8). Schliesslich konnte die gesamte Aktivit?t von Phosphatase und 5′-Nukleotidase gemeinsam mit dem Substrat 5′-Adenosinmonophosphat bestimmt werden, mit optimalen Aktivit?ten bei 45–50°C und pH 5.0 (Abb. 9 und 10). Sodann wurde mit RNS als Substrat die Anreicherung l?slicher Abbauprodukte im Bereich von 40–70°C und pH 4.0–7.0 untersucht. Dabei wurden 3′-Nukleotide, 5′-Nukleotide und Nukleoside getrennt erfasst. Die Resultate sind in Tabelle I zusammengestellt und zeigen das folgende. Die Freisetzung von Nukleotiden ist optimal bei 50°C und pH 6.0; es handelt sich vor allem um 5′-Nukleotide. Die Reaktion ist abh?ngig vom pH. 3′-Nukleotide werden erst bei Temperaturen von über 50°C freigesetzt, mit einem Optimum bei 70°C und pH 5.0. Nukleoside bilden sich bevorzugt bei 50°C und pH 5.0–5.5. Auf Grund dieser Ergebnisse wurde ein Kartoffelhomogenisat hergestellt und autoinkubiert; bei 52°C und pH 6.0 ergab sich eine maximale Freisetzung von 5′-Nukleotiden (Tab. 2). Aus diesen Ergebnissen kann geschlossen werden, dass ein spezifischer RNS-Abbau in der Kartoffel bis zu Temperaturen von 50°C bevorzugt durch das Enzym Phosphodiesterase I erfolgt, unter Bildung von 5′-Nukleotiden. Ribonuklease wird erst bei h?heren Temperaturen aktiv, sofern noch genügend Substrat vorhanden ist. Dabei ist auch der pH-Wert der Knollen von Bedeutung. Die freigesetzten 5′-Nukleotide sind stabil, weil die entsprechenden Nukleotidabbauenden Enzyme eine stark verschiedene pH-Abh?ngigkeit ihrer Aktivit?ten aufweisen. Die Knollenform und die damit verbundenen Kochzeiten sind sicherlich ein wichtiger Faktor, der diese enzymatischen Vorg?nge beeinflusst. Abschliessend kann festgestellt werden, dass nicht nur das Enzymsystem, sondern auch das pH der Knolle und die Temperaturverh?ltnisse w?hrend der Verarbeitung für die spezifische Freisetzung von 5′-Nukleotiden in zubereiteten Kartoffeln von Bedeutung sind.
Résumé Les 5′-nucléotides sont d'importants renforcateurs de go?t dans les denrées alimentaires. Buri et coll. (1970) ont déjà mis en évidence l'influence de ces composés sur le go?t des pommes de terre et ont montré que les 5′-nucléotides se forment pendant la cuisson à partir d'acide ribonucléique (ARN). Une hydrolyse chimique de l'ARN libérant les 5′-nucléotides a pu être exclue, de sorte que seul un processus enzymatique peut être envisagé, lequel fait l'objet du présent travail. Un extrait enzymatique purifié a été préparé à partir de pommes de terre Bintje et son activité caractérisée à l'aide de substrats spécifiques. La ribonucléase, en présence de 2′, 3′-cytidine-monophosphate cyclique, a donné des activités optimales à 70°C et pH 5.0 (fig. 1 et 2). La phosphodiestérase I examinée avec le substrat α-naphtylthymidine-5′-monophosphate a présenté des optimums d'activité à 50°C et pH 5.5 (fig. 3 et 4). Les activités optimales de la phosphodiestérase II ont été situées à 60°C et pH 5.5 en présence de thymidine-5′-monophosphate-p-nitrophénylester (fig. 5 et 6). La phosphatase en présence de p-nitrophénylphosphate a donné des optimums d'activité à 45–50°C et pH 5.0 (fig. 7 et 8). Enfin, l'activité globale de la phosphatase et de la 5′-nucléotidase réunies a été déterminée avec le substrat 5′-adénosine-monophosphate, les optimums se situant à 45–50°C et pH 5.0 (fig. 9 et 10). Puis, en prenant l'ARN comme substrat, l'enrichissement en produits de dégradation solubles a été étudié entre 40 et 70°C et pH 4.0 et 7.0. Ces produits de dégradation, 3′-nucléotides, 5′-nucléotides et nucléosides ont été déterminés séparément et les résultats présentés dans le tableau 1. Il ressort de ces résultats que la libération de nucléotides, principalement des 5′-nucléotides, est optimale à 50°C et pH. 6.0 et que la réaction est dépendante du pH. Les 3′-nucléotides ne sont libérés qu'à des températures supérieures à 50°C avec un optimum à 70°C et pH 5.0–5.5. Sur la base de ces résultats, un homogénéisat de pommes de terre a été préparé et autoincubé; à 52°C et pH 6.0, on observe une libération maximale de 5′-nucléotides (tableau 2). On peut en conclure qu'il se produit une dégradation spécifique de l'ARN dans la pomme de terre jusqu'à une température de 50°C, due principalement à la phosphodiestérase I avec formation de 5′-nucléotides. La ribonucléase ne devient active qu'à des températures supérieures et pour autant qu'il reste suffisamment de substrat. Le pH des tubercules joue également un r?le. Les 5′-nucléotides libérés sont stables, les enzymes dégradant les nucléotides ayant des activités qui varient de manière très diverses avec le pH. La forme des tubercules, ainsi que les temps de cuisson qui en découlent, sont certainement un facteur important pouvant influencer ces processus enzymatiques. Finalement, et on peut constater que non seulement le système enzymatique, mais également le pH du tubercule et les températures mises en oeuvre pendant la préparation des pommes de terre ont une incidence sur la libération des 5′-nucléotides dans celles-ci.相似文献