Inactivation of orange pectinesterase by combined high-pressure and -temperature treatments: a kinetic study

Pressure and/or temperature inactivation of orange pectinesterase (PE) was investigated. Thermal inactivation showed a biphasic behavior, indicating the presence of labile and stable fractions of the enzyme. In a first part, the inactivation of the labile fraction was studied in detail. The combined pressure-temperature inactivation of the labile fraction was studied in the pressure range 0.1-900 MPa combined with temperatures from 15 to 65 degrees C. Inactivation in the pressure-temperature domain specified could be accurately described by a first-order fractional conversion model, estimating the inactivation rate constant of the labile fraction and the remaining activity of the stable fraction. Pressure and temperature dependence of the inactivation rate constants of the labile fraction was quantified using the Eyring and Arrhenius relations, respectively. By replacing in the latter equation the pressure-dependent parameters (E(a), k(ref)(T)()) by mathematical expressions, a global model was formulated. This mathematical model could accurately predict the inactivation rate constant of the labile fraction of orange PE as a function of pressure and temperature. In a second part, the stable fraction was studied in more detail. The stable fraction inactivated at temperatures exceeding 75 degrees C. Acidification (pH 3.7) enhanced thermal inactivation of the stable fraction, whereas addition of Ca(2+) ions (1 M) suppressed inactivation. At elevated pressure (up to 900 MPa), an antagonistic effect of pressure and temperature on the inactivation of the stable fraction was observed. The antagonistic effect was more pronounced in the presence of a 1 M CaCl(2) solution as compared to the inactivation in water, whereas it was less pronounced for the inactivation in acid medium.     

Effect of temperature and/or pressure on tomato pectinesterase activity

The activity of tomato pectinesterase (PE) was studied as a function of pressure (0.1-900 MPa) and temperature (20-75 degrees C). Tomato PE was rather heat labile at atmospheric pressure (inactivation in the temperature domain 57-65 degrees C), but it was very pressure resistant. Even at 900 MPa and 60 degrees C the inactivation was slower as compared to the same treatment at atmospheric pressure. At atmospheric pressure, optimal catalytic activity of PE was found at neutral pH and a temperature of 55 degrees C. Increasing pressure up to 300 MPa increased the enzyme activity as compared to atmospheric pressure. A maximal enzyme activity was found at 100-200 MPa combined with a temperature of 60-65 degrees C. The presence of Ca(2+) ions (60 mM) decreased the enzyme activity at atmospheric pressure in the temperature range 45-60 degrees C but increased enzyme activity at elevated pressure (up to 300 MPa). Maximal enzyme activity in the presence of Ca(2+) ions was noted at 200-300 MPa in combination with a temperature of 65-70 degrees C.     

Inactivation of heat-resistant pectinmethylesterase from orange by manothermosonication

Pectinmethylesterase of navel oranges shows two fractions greatly differing in thermostability. The most thermostable fraction accounts for approximately 10% of total activity. The thermal inactivation of this fraction follows first-order kinetics both in 5 mM, pH 3.5, citrate buffer and in orange juice at the same pH, showing a z value of 5.1 degrees C and an activation energy (E(a)) of 435 kJ mol(-)(1) K(-)(1). The heat resistance of the enzyme is approximately 25-fold higher in the juice than in citrate buffer. When ascorbic acid, sucrose, glucose, and fructose are added to the citrate buffer at the concentrations found in orange juice, the heat resistance of the enzyme increases 3-fold. The addition of pectin at 0.01% concentration multiplies it by a factor of 50. Manothermosonication (MTS), the simultaneous application of heat and ultrasound under moderate pressure (200 kPa), at 72 degrees C, increases the inactivation rate 25 times in buffer and >400 times in orange juice. MTS inactivation shows a higher z value (35.7 degrees C) and lower E(a) (56.9 kJ mol(-)(1) K(-)(1)) than simple heating.     

Structural changes of microbial transglutaminase during thermal and high-pressure treatment

The activity of microbial transglutaminase (MTG) and the corresponding secondary structure, measured by circular dichroism (CD), was analyzed before and after treatment at different temperatures (40 and 80 degrees C) and pressures (0.1, 200, 400, 600 MPa). Irreversible enzyme inactivation was achieved after 2 min at 80 degrees C and 0.1 MPa. Enzyme inactivation at 0.1, 200, 400, and 600 MPa and 40 degrees C followed first-order kinetics. The enzyme showed residual activity of 50% after 12 min at 600 MPa and 40 degrees C. Mobility of aromatic side chains of the enzyme molecule was observed in all temperature- and/or pressure-treated samples; however, high-pressure treatment at 600 MPa induced a loss of tertiary structure and a significant decrease in the alpha-helix content. The relative content of beta-strand substructures was significantly increased after 30 min at 600 MPa and 40 degrees C or 2 min at 0.1 MPa and 80 degrees C. We conclude that the active center of MTG, which is located in an expanded beta-strand domain, is resistant to high hydrostatic pressure and pressure-induced inactivation is caused by destruction of alpha-helix elements with a corresponding influence on the enzyme stability in solution.     

Impact of preferential interactions on thermal stability and gelation of bovine serum albumin in aqueous sucrose solutions

The influence of sucrose (0--40 wt %) on the thermal denaturation and gelation of bovine serum albumin (BSA) in aqueous solution has been studied. The effect of sucrose on heat denaturation of 1 wt % BSA solutions (pH 6.9) was measured using ultrasensitive differential scanning calorimetry. The unfolding process was irreversible and could be characterized by a denaturation temperature (T(m)), activation energy (E(A)), and pre-exponential factor (A). As the sucrose concentration increased from 0 to 40 wt %, T(m) increased from 72.9 to 79.2 degrees C, E(A) decreased from 314 to 289 kJ mol(-1), and ln(A/s(-1)) decreased from 104 to 94. The rise in T(m) was attributed to the increased thermal stability of the globular state of BSA relative to its native state because of differences in their preferential interactions with sucrose. The change in preferential interaction coefficient (Delta Gamma(3,2)) associated with the native-to-denatured transition was estimated. The dynamic shear rheology of 2 wt % BSA solutions (pH 6.9, 100 mM NaCl) was monitored as they were heated from 30 to 90 degrees C, held at 90 degrees C for either 15 or 120 min, and then cooled to 30 degrees C. Sucrose increased the gelation temperature due to thermal stabilization of the native state of the protein. The complex shear modulus (G) of cooled gels decreased with sucrose concentration when they were held at 90 degrees C for 15 min because the fraction of irreversibly denatured protein decreased. On the other hand, G of cooled gels increased with sucrose concentration when they were held at 90 degrees C for 120 min because a greater fraction of irreversibly denatured protein was formed and the strength of the protein-protein interactions increased.     

Effects of thermal treatments and storage on pectin methylesterase and peroxidase activity in freshly squeezed orange juice

A specific indicator of freshness, allowing routine distinction between freshly squeezed orange juices (FSOJs) and FSOJ-like products, was to be identified. Using the Actijoule unit of a tubular heater at a flow rate of 60 L/h, FSOJs from Citrus sinensis (L.) Osbeck cv. Valencia Late were continuously heated on a pilot plant scale at six different temperatures (42-92 degrees C), followed by continuous cooling to ambient temperature and subsequent filling into sterilized glass jars. The cloud stability and residual activities of pectin methylesterase (PE) and peroxidase (POD) were monitored over the storage at 4 degrees C for up to 62 days, thus considering the storage conditions of FSOJs in retail markets. As shown by the viable microbial counts throughout storage, microbial activity was insignificant due to good sanitary practice, thus proving that the enzyme activities detected were of plant origin. The juices processed at temperatures > or =62 degrees C were characterized by minor residual activities. When exposed to temperatures <62 degrees C in the genuine acidic matrix of the juices, the heat stability of PE exceeded that of POD. Compared with the aforementioned samples, the juice processed at 52 degrees C with a residual PE activity of 33.8% was hardly inferior in terms of cloud stability within the first 14 days. After the juice was processed at 42 degrees C, rapid clarification occurred within the first 8 days, consistent with undetectable PE deactivation. Hence, only the range of approximately 50-60 degrees C is relevant in minimal heat-processing for the retention of cloud stability within the short turnover period of FSOJ-like products, with partial PE and POD deactivation being already sufficient to distinguish those juices from FSOJs. Irrespective of the previous thermal treatment, the total PE activity remained nearly constant during storage, whereas the POD activity rapidly declined to minor levels after 20 days. Consequently, as to the future analysis of samples with unknown processing history, PE was suggested as an indicator enzyme for the freshness of FSOJs, allowing their unambiguous distinction from minimally heat-processed juices.     

Isolation and thermal characterization of an acidic isoperoxidase from turnip roots

An acidic peroxidase (pI approximately 2.5) was purified from turnip roots (TAP), and its thermal properties were evaluated. TAP is a monomeric protein having a molecular weight (MW) of 49 kDa and a carbohydrate content accounting for 18% of the MW. The yield of pure TAP was relatively high ( approximately 2 mg/kg of fresh roots), with a specific activity of 1810 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) units/mg at pH 6. The activity increased 4-fold at the optimum pH (4.0) to 7250 ABTS units/mg, higher than that of most peroxidases. TAP was heat stable; heat treatment of 25 min at 60 degrees C resulted in 90% initial activity retention, whereas an activity of 20% was retained after 25 min of heating at 80 degrees C. TAP regained 85% of its original activity within 90 min of incubation at 25 degrees C, following heat treatment at 70 degrees C for 25 min. Thermal inactivation caused noticeable changes in the heme environment as evaluated by circular dichroism and visible spectrophotometry. TAP was rapidly denatured by heating in the presence of 1.0 mM ethylene glycol bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid, but the Soret band and activity were fully recovered by adding an excess of Ca(2+). This is further evidence that Ca(2+) plays an important role in the stability of TAP. The high specific activity of TAP, together with its relatively high thermal stability, has high potential for applications in which a thermally stable enzyme is required.     

Studies on kinetics and thermostability of a novel acid invertase from Fusarium solani

The present investigation deals with purification and thermal characterization of an acid invertase produced by Fusarium solani in submerged culture. The maximum enzyme activity (9.90 U mL(-1)) was achieved after 96 h of cultivation at pH 5.0 and 30 degrees C in a basal medium containing molasses (2%) as the carbon and energy source supplemented with 1% peptone. Invertase was purified by ammonium sulfate fractionation and column chromatography on DEAE-cellulose and Sephadex G-200. The purified enzyme was proven to be homogeneous by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The molecular mass of the enzyme was 65 kDa. The optimum pH and temperature for activity were 2.6 and 50 degrees C, respectively. The Km value for sucrose was 3.57 mM with an activation energy of 4.056 kJ mol(-1). Enthalpies of activation (DeltaH) were decreased while entropies (DeltaS) of activation increased at higher temperatures. The effects of alpha-chymotrypsin and 4 M urea were tetraphasic with periodic gain and loss of enzyme activity. A possible explanation for the thermal inactivation of invertase at higher temperatures is also discussed.     

Influence of industrial processing on orange juice flavanone solubility and transformation to chalcones under gastrointestinal conditions

Orange juice manufactured at industrial scale was subjected to digestion under in vitro gastrointestinal conditions (pH, temperature, and enzyme and chemical conditions) to evaluate the influence of individual industrial processing treatments on flavanone solubility, stability, and ability to permeate through a membrane under simulated physiological conditions. Four industrial processes including squeezing, standard pasteurization, concentration, and freezing were evaluated. Hand squeezing was compared with industrial squeezing. After in vitro gastrointestinal digestion of the orange juices, the flavanones able to permeate through a dialysis membrane, and those remaining in the retentate were evaluated by HPLC as were those present in the insoluble fraction. In all of the assayed orange juices, a high content of precipitated chalcones ( approximately 70% of the total flavanones) was formed under the physiological conditions of the gastrointestinal tract. Hand squeezing provided a higher concentration of flavanones in the permeated fraction and lower transformation to chalcones than industrial squeezing. Standard pasteurization did not influence the solubility and permeability of the orange juice flavanones and chalcones. Industrial concentration did not affect the amount of flavanones able to permeate but decreased the chalcones produced. Juices produced from frozen orange juice contained considerably smaller amounts of both soluble flavanones and insoluble chalcones.     

Optimization of Temperature,Time, and Lactic Acid Concentration to Inactivate Lipoxygenase and Lipase and Preserve Phytase Activity in Barley (cv. Blenheim) During Soaking

A barley-soaking process was studied to find conditions that inactivate the prooxidative enzyme lipoxygenase and the lipolytic enzyme lipase but preserve phytase activity to develop possible procedures for production of barley products with potentially high mineral bioavailability and good oxidative stability. Lactic acid concentration, temperature, and soaking time were studied. The study was done using a multivariate experimental design. Lactic acid concentration varied between 0 and 1%, temperature varied between 45 and 70°C, and soaking time varied between 30 and 120 min. Although conditions under which lipoxygenase was inactivated were found, total inactivation of lipase was not obtained. Total lipoxygenase inactivation with <20% remaining lipase activity and >60% remaining phytase activity was reached after soaking in 1% lactic acid at suitable time-temperature combinations of 70–110 min and 53–58°C.     

Kinetic study of the irreversible thermal and pressure inactivation of myrosinase from broccoli (Brassica oleracea L. Cv. italica).

Thermal and pressure inactivation of myrosinase from broccoli was kinetically investigated. Thermal inactivation proceeded in the temperature range 30-60 degrees C. These results indicate that myrosinase is rather thermolabile, as compared to other food quality related enzymes such as polyphenol oxidase, lipoxygenase, pectinmethylesterase, and peroxidase. In addition, a consecutive step model was shown to be efficient in modeling the inactivation curves. Two possible inactivation mechanisms corresponding to the consecutive step model were postulated. Pressure inactivation at 20 degrees C occurred at pressures between 200 and 450 MPa. In addition to its thermal sensitivity, the enzyme likewise is rather pressure sensitive as compared to the above-mentioned food quality related enzymes. By analogy with thermal inactivation, a consecutive step model could adequately describe pressure inactivation curves. At 35 degrees C, pressure inactivation was studied in the range between 0. 1 and 450 MPa. Application of low pressure (<350 MPa) resulted in retardation of thermal inactivation, indicating an antagonistic or protective effect of low pressure.     

Tomato (Lycopersicon esculentum) pectin methylesterase and polygalacturonase behaviors regarding heat- and pressure-induced inactivation.

The combined high pressure/thermal (HP/T) inactivation of tomato pectin methyl esterase (PME) and polygalacturonase (PG) was investigated as a possible alternative to thermal processing classically used for enzyme inactivation. The temperature and pressure ranges tested were from 60 degrees C to 105 degrees C, and from 0.1 to 800 MPa, respectively. PME, a heat-labile enzyme at ambient pressure, is dramatically stabilized against thermal denaturation at pressures above atmospheric and up to 500-600 MPa. PG, however, is very resistant to thermal denaturation at 0.1 MPa, but quickly and easily inactivated by combinations of moderate temperatures and pressures. Selective inactivation of either PME or PG was achieved by choosing proper combinations of P and T. The inactivation kinetics of these enzymes was measured and described mathematically over the investigated portion of the P/T plane. Whereas medium composition and salinity had little influence on the inactivation rates, PME was found less sensitive to both heat and pressure when pH was raised above its physiological value. PG, on the other hand, became more labile at higher pH values. The results are discussed in terms of isoenzymes and other physicochemical features of PME and PG.     

Immobilization of recombinant invertase (re-INVB) from Zymomonas mobilis on D-sorbitol cinnamic ester for production of invert sugar

The recombinant invertase (re-INVB) from Zymomonas mobilis was immobilized by adsorption onto the totally cinnamoylated derivative of D-sorbitol. The polymerization and cross-linking of the derivative initially obtained was achieved by irradiation in the ultraviolet region, where this prepolymer shows maximum sensitivity. Immobilization of re-INVB on this support involves a process of physical adsorption and intense hydrophobic interactions between the cinnamoyl groups of the support and related groups of the enzyme. Enzyme concentration, immobilization time, and irradiation time were important parameters affecting the immobilization efficiency. The optimum reaction pH of immobilized enzyme was 5, and the optimal reaction temperature was 40 degrees C. The apparent Michaelis constant and the apparent catalytic constant of re-INVB immobilized on the SOTCN derivative acting on sucrose was 78+/-5 mM and 5x10(4)+/-3x10(2) s(-1), respectively, while for the free enzyme, it was 98.0+/-4 mM and 1.2x10(4)+/-2.5x10(2) s(-1), respectively, suggesting a better apparent affinity of the enzyme for the substrate and a better hydrolysis rate when immobilized than when in solution. Immobilized re-INVB also showed good thermal stability and good operational stability (40% of the initial activity remaining after 45 cyles of 1 min duration and 90.6 mg of sucrose being hydrolyzed in 45 min per 2.5 mg of immobilized protein). The results showed that cinnamic carbohydrate esters of D-sorbitol are an appropriate support for re-INVB immobilization and the production of invert sugar.     

Changes in water-soluble vitamins and antioxidant capacity of fruit juice-milk beverages as affected by high-intensity pulsed electric fields (HIPEF) or heat during chilled storage

The effect of high-intensity pulsed electric fields (HIPEF) or thermal processes and refrigerated storage on water-soluble vitamins and antioxidant capacity of beverages containing fruit juices and whole (FJ-WM) or skim milk (FJ-SM) was assessed. Peroxidase (POD) and lipoxygenase (LOX) inactivation as well as color changes were also studied. High vitamin C retention was observed in HIPEF and thermally treated beverages, but a significant depletion of the vitamin during storage occurred, which was correlated with antioxidant capacity. HIPEF treatment did not affect the concentration of group B vitamins, which also remained constant over time, but thermally treated beverages showed lower riboflavin (vitamin B2) concentration. With regard to enzyme activity, thermal processing was more effective than HIPEF on POD and LOX inactivation. The color of the beverages was maintained after HIPEF processing and during storage. Consequently, HIPEF processing could be a feasible technology to attain beverages with fruit juices and milk with high vitamin content and antioxidant potential.     

Heat inactivation and reactivation of broccoli peroxidase

Heat inactivation characteristics differed for acidic (A), neutral (N), and basic (B) broccoli peroxidase. At 65 degrees C, A was the most heat stable followed by N and B. The activation energies for denaturation were 388, 189, and 269 kJ/mol for A, N, and B, respectively. Reactivation of N occurred rapidly, within 10 min after the heated enzyme was cooled and incubated at room temperature. The extent of reactivation varied from 0 to 50% depending on the isoenzyme and heating conditions (temperature and time). The denaturation temperature allowing the maximum reactivation was 90 degrees C for A and horseradish peroxidase (HRP) and 70 and 80 degrees C for B and N, respectively. In all cases, heat treatment at low temperatures for long times prevented reactivation of the heated enzymes. Calcium (5 mM) increased the thermal stability of N and B but had no effect on reactivation. The presence of 0.05% bovine serum albumin decreased thermal stability but increased the extent of reactivation of A..     

钙处理对葡萄柚果实细胞壁物质代谢及其相关基因表达的影响

【目的】研究采前、 采后钙处理对葡萄柚果实细胞壁组分、 细胞壁降解酶活性变化及其相关基因表达的影响,可为了解钙与果实细胞壁物质代谢之间的关系,揭示钙对果实软化的作用机理,为调控葡萄柚果实膳食纤维含量,提高果实质地品质提供理论依据。【方法】试验于2011年2月至11月在云南省玉溪市葡萄柚果园进行,供试品种为‘里约红’葡萄柚,该品种于2005年嫁接于当地砧木,株行距为3 m×3 m。试验由采前和采后钙处理两部分组成。采前钙处理在幼果初期、 幼果末期、 膨大初期、 膨大末期、 转色期,叶面喷施2% CaCl2; 采后钙处理在果实成熟采后浸于2% CaCl2溶液5 min, 室温贮藏。之后每15天取样一次,每次取10个果实,测定葡萄柚果肉细胞壁组分、 细胞壁降解酶活性及其基因表达量。【结果】随葡萄柚果实后熟软化,紧密结合型果胶(共价结合型果胶)解聚为松散结合型果胶(水溶性果胶、 离子结合型果胶),紧密结合型半纤维素(24% KOH可溶性半纤维素)解聚使其含量下降,而松散结合型半纤维素含量增加(4%KOH可溶性半纤维素)。果实PG、 PME、 Cx、 α-L-Af和β-Gal酶活性及其基因表达量均随果实软化呈不同程度增加。PME活性在果实采收后表现出较高含量,而PG活性在果实贮藏前期急剧增加,其酶基因的表达量与酶活性变化趋势基本一致。Cx、 α-L-Af和β-Gal活性在贮藏中、 后期上升较快,相关酶基因的表达量亦明显增加。钙处理显著地降低果实细胞壁降解酶活性和基因表达水平,其中采后钙处理对α-L-Af和β-Gal活性和基因表达在贮藏中、 后期的调控作用较显著,酶活性和基因表达均维持在较低水平。【结论】外源钙处理降低细胞壁降解酶活性及其基因表达,抑制了细胞壁物质的解聚,采后钙处理对细胞壁物质代谢的调控效果优于采前钙处理。外源钙处理抑制了细胞壁降解酶基因表达水平,降低了细胞壁降解酶活性,减缓了果胶、 半纤维素的解聚,从而达到调控果实膳食纤维含量、 维持果实质地品质、 延长果实货架期寿命的目的。     

Biogenic amine formation and nitrite reactions in meat batter as affected by high-pressure processing and chilled storage

Changes in biogenic amine formation and nitrite depletion in meat batters as affected by pressure-temperature combinations (300 MPa/30 min/7, 20, and 40 degrees C), cooking process (70 degrees C/30 min), and storage (54 days/2 degrees C) were studied. Changes in residual nitrite concentration in raw meat batters were conditioned by the temperature and not by the pressure applied. Cooking process decreased (P < 0.05) the residual nitrite concentration in all samples. High-pressure processing and cooking treatment increased (P < 0.05) the nitrate content. Whereas protein-bound nitrite concentration decreased with pressure processing, no effect was observed with the heating process of meat batters. High-pressure processing conditions had no effect on the rate of residual nitrite loss throughout the storage. The application of high pressure decreased (P < 0.05) the concentration of some biogenic amines (tyramine, agmatine, and spermine). Irrespective of the high processing conditions, generally, throughout storage biogenic amine levels did not change or increased, although quantitatively this effect was not very important.     

Thermal and high-pressure inactivation kinetics of polyphenol oxidase in Victoria grape must

The inactivation kinetics of polyphenol oxidase (PPO) in freshly prepared grape must under high hydrostatic pressure (100-800 MPa) combined with moderate temperature (20-70 degrees C) was investigated. Atmospheric pressure conditions in a temperature range of 55-70 degrees C were also tested. Isothermal inactivation of PPO in grape must could be described by a biphasic model. The values of activation energy and activation volume of stable fraction were estimated as 53.34 kJ mol(-1) and -18.15 cm3 mol(-1) at a reference pressure of 600 MPa and reference temperature of 50 degrees C, respectively. Pressure and temperature were found to act synergistically, except in the high-temperature-low-pressure region where an antagonistic effect was found. A third-degree polynomial model was successfully applied to describe the temperature/pressure dependence of the inactivation rate constants of the stable PPO fraction in grape must.     

Beta-glucosidase from Chalara paradoxa CH32: purification and properties

The hyphomycete Chalara paradoxa CH32 produced an extracellular beta-glucosidase during the trophophase. The enzyme was purified to homogeneity by ion-exchange and size-exclusion chromatography. The purified enzyme had an estimated molecular mass of 170 kDa by size-exclusion chromatography and 167 kDa by SDS-PAGE. The enzyme had maximum activity at pH 4.0-5.0 and 45 degrees C. The enzyme was inactivated at 60 degrees C. At room temperature, it was unstable at acidic pH, but it was stable to alkaline pH. The purified enzyme was inhibited markedly by Hg(2+) and Ag(2+) and also to some extent by the detergents SDS, Tween 80, and Triton X-100 at 0.1%. Enzyme activity increased by 3-fold in the presence of 20% ethanol and to a lesser extent by other organic solvents. Purified beta-glucosidase was active against cellobiose and p-nitrophenyl-beta-D-glucopyranoside but did not hydrolyze lactose, maltose, sucrose, cellulosic substrates, or galactopyranoside, mannopyranoside, or xyloside derivatives of p-nitrophenol. The V(max) of the enzyme for p-NPG (K(m) = 0.52 mM) and cellobiose (K(m) = 0.58 mM) were 294 and 288.7 units/mg, respectively. Hydrolysis of pNPG was inhibited competitively by glucose (K(i) = 11.02 mM). Release of reducing sugars from carboxymethylcellulose by a purified endoglucanase produced by the same organism increased markedly in the presence of beta-glucosidase.     

有机无机肥料及抽穗期气温升高对水稻籽粒淀粉合成相关酶活性及淀粉品质形成的影响

为探讨不同肥料处理下抽穗期高温胁迫对水稻籽粒淀粉酶活性及淀粉品质形成的影响,本试验以优质食味水稻南粳9108为材料,设置施用有机肥(OF)和常规化肥(CF)处理,于抽穗期进行常温(NT)、+2℃(较常温增加2℃,MT)和+5℃(较常温增加5℃,HT)处理,对籽粒淀粉合成特性进行研究。结果表明,抽穗期温度升高降低了蔗糖合成酶(SS)、淀粉合成酶(SSS)和淀粉分支酶(SBE)的活性,提高了蔗糖磷酸合成酶(SPS)和焦磷酸化酶(AGP)的活性。蔗糖含量、淀粉平均粒径、热焓值与峰值温度均表现为HT>MT>NT;淀粉含量、直链淀粉含量与黏度值则随着温度升高而下降。在肥料处理方面,各淀粉相关酶活性均表现为OF>CF,且在OF处理下有较好的淀粉品质。综上所述,温度升高通过抑制淀粉合成,加速了形成淀粉原料的积累,进而导致籽粒中蔗糖含量升高;有机肥处理能促进蔗糖合成并提高淀粉合成相关酶活性。从气候变暖应对措施方面,可选择有机肥替代化肥调控淀粉相关酶活性,进一步改善淀粉品质。本研究结果为减少高温对水稻的危害与提高淀粉品质提供了技术参考。