草莓浑浊汁维生素C降解动力学模型

为了弄清贮藏温度对草莓浑浊汁内维生素C降解的影响,建立其降解动力学模型,为选择草莓浑浊汁的贮藏温度提供依据。该文通过研究草莓浑浊汁贮藏过程中还原型维生素C和氧化型维生素C的降解与贮藏温度、贮藏时间的关系,建立了还原型维生素C和氧化型维生素C降解动力学模型。结果表明：草莓浑浊汁在贮藏过程中还原型维生素C和氧化型维生素C对热不稳定,还原型维生素C和氧化型维生素C降解符合一级反应动力学。经过验证表明该降解动力学模型有效,可用于草莓浑浊汁贮藏温度的选择和预测不同温度下的贮藏期。     

红枣汁中维生素C热降解的动力学研究(简报)

为了了解加热温度对红枣汁中维生素C含量变化的影响,降低红枣汁在加工过程中维生素C的损失,该文以红枣澄清汁为材料,采用可逆的一级反应模型研究了不同加热温度下还原型维生素C(AA)的降解规律并推导出氧化型维生素C(DHAA)含量变化的数学模型.在此基础上利用Arrhenius方程计算得到AA和DHAA的降解反应活化能.结果表明,在303,313,323,333,343 K温度条件下,可逆的一级反应模型适用于表达红枣汁中AA的降解规律,非线性回归决定系数γ2均大于0.98.DHAA的数学模型也能较好地预测DHAA在红枣汁中的含量变化规律.在不同的加热温度下,AA与DHAA均能发生降解反应,但DHAA的降解速率较AA低,DHAA的降解主要发生在AA的降解反应达到平衡之后.AA热降解反应活化能较低,表明红枣汁中的AA对热处理较敏感.该研究为优化红枣汁的加工工艺、提高红枣汁的品质提供理论依据.     

水稻田土壤甲烷氧化活性及其环境影响因子的研究

报道环境因子土壤含水量、温度和pH对发育于河流沉积物母质的水稻田土黄松泥田土氧化外源甲烷活性影响的研究结果。表明土壤中存在有氧和无氧两个甲烷氧化系统。有氧甲烷氧化系统 (AMOS)最适条件下的氧化甲烷最大活性比无氧甲烷氧化系统(AAMOS)最适条件下的氧化甲烷最大活性高 1至 2倍。在土壤通气良好的条件下 ,AMOS占主导地位 ,在无氧或极微氧的土壤中 ,AAMOS起主要作用。影响活性的主要因子是土壤的分子氧含量、甲烷含量、水含量、温度和pH值。分子氧对AAMOS氧化甲烷的活性具有一定抑制作用 ,土壤中甲烷量和含水量对AAMOS氧化甲烷活性的影响比对AMOS氧化甲烷活性的影响更为强烈。土壤氧化甲烷的活性对温度较为敏感 ,其最适氧化甲烷的温度范围在 2 5～ 35℃之间。当土壤在 5 0℃培养的时间超过 6h后 ,土壤氧化外源甲烷的活性全部丧失 ,且不能在2 8℃下得到恢复。pH是另一个影响土壤氧化甲烷的重要环境因子。其最适pH范围在 6～ 7之间 ,pH低于 3或pH高于 9时 ,几乎完全丧失氧化外源甲烷的活性。     

锥栗贮藏过程维生素C的降解速率以及保鲜条件研究

采用试验研究了锥栗贮藏过程中维生素C(维生素C)的降解速率及其保鲜条件。将3个不同品种的锥栗经不同浓度的抑霉唑浸泡，并在3个不同温度(-1～0℃、5℃、10℃)中进行贮藏，测定贮藏中锥栗维生素C的含量的变化。锥栗中维生素C的降解速率与维生素C的浓度成正比，求得降解速率系数k，对其进行非线性拟合，并用极差分析法和方差分析法进行分析研究。试验结果表明，最优的保鲜条件为：温度-1～0℃、品种为长芒、抑霉唑浓度2000 μL/L。     

热辅助超声波处理对猕猴桃浊汁的杀菌效果及品质影响研究

针对热杀菌猕猴桃浊汁中营养成分损失严重的问题,本试验对不同热辅助超声波处理工艺参数对猕猴桃浊汁理化特性的影响及杀菌效果进行研究,并优化最佳工艺参数。以猕猴桃浊汁为样品,选取猕猴桃浊汁的理化指标及杀菌率为响应值,以超声功率、超声时间、温度为因素,进行响应面试验,在筛选猕猴桃浊汁理化特征指标的基础上,建立杀菌率及猕猴桃浊汁理化特征指标模型并优化得出最佳工艺参数。结果表明,猕猴桃浊汁的理化特征指标为叶绿素保存率、PPO活性、△E值、糖酸比;最佳工艺参数为:超声功率420 W、超声时间30 min、温度60℃,在此条件下,猕猴桃浊汁的叶绿素保存率为30.99%、PPO活性为19.48 U·mL^-1、△E值为4.43、糖酸比为6.17、杀菌率为95.68%。本研究为热辅助超声波技术应用于猕猴桃浊汁的加工提供了理论依据和技术指导。     

酶解条件对红枣汁主要成分的影响

以延川团枣为材料,在前期单因素试验的基础上采用正交设计试验方案,对温度、 提取时间和酶用量等提取红枣汁的工艺参数进行优化。结果表明：影响红枣汁中可溶性固形物、维生素C和总糖含量的因素大小顺序为温度、提取时间、酶用量。温度的影响达到显著,而提取时间和酶用量未达到显著。在温度40℃、提取时间4 h和酶用量2400 mg/L时,红枣汁中可溶性固形物含量13.9%、维生素C含量0.32 mg/(100 mL)、总糖含量9.37%,具有较好的提取效果。     

两品种猕猴桃果实采后淀粉降解特性比较分析

为探究猕猴桃果实采后淀粉降解规律,本试验以红阳(HY)和翠玉(CY)猕猴桃果实为材料,比较分析了不同品种猕猴桃果实采后淀粉含量变化以及淀粉降解相关基因的表达模式。结果表明,猕猴桃采后25℃贮藏过程中,HY猕猴桃果实硬度迅速下降并伴随出现乙烯跃变,CY果实硬度缓慢下降但并未出现乙烯释放高峰。2个品种猕猴桃果实的淀粉含量随贮藏时间的延长显著下降。扫描电镜(SEM)结果显示,随着贮藏时间的延长,2个品种猕猴桃果实淀粉粒表面的光滑球面均出现不同程度的消化和破碎,说明淀粉存在酶促降解。同时,HY猕猴桃果实贮藏后期的乙烯释放速率极显著高于CY猕猴桃(P<0.001)。HY猕猴桃果实外果肉中淀粉含量在贮藏前期(0~2 d)极显著高于CY猕猴桃(P<0.01),但在贮藏后期(8~12 d)极显著低于CY猕猴桃(P<0.001);HY猕猴桃果实果心中淀粉含量在贮藏前期(2~4 d)与CY猕猴桃无显著差异,但在贮藏后期(6~12 d)极显著低于CY猕猴桃(P<0.001)。本研究结果为进一步揭示猕猴桃果实采后淀粉降解机理提供了一定的理论依据。     

都江堰地区发展猕猴桃产业对策探讨

猕猴桃是当今世界的主要水果之一。其维生素C含量在水果中名列前茅,一颗猕猴桃能提供一个人一日维生素C需求量的两倍多,被誉为“维C之王”。据分析,每100克新鲜猕猴桃果肉便含有100至400毫克维生素C,比苹果高出20至80倍,比柑桔则高5至10倍,因而深受消费者追捧,市场需求量大。但因其适生区很少,     

杨梅澄清汁及浓缩汁中花色苷热降解动力学的研究

杨梅花色苷易受温度、pH值等因素的影响而发生降解，是导致产品外观品质变劣的主要原因。本文研究了杨梅澄清汁及浓缩汁内花色苷在不同pH值和不同加热温度下的热稳定性。花色苷降解动力学数据的分析结果表明：杨梅花色苷热降解属动力学一级反应，随着pH值和温度的升高，杨梅花色苷降解的半衰期(t_1/2)和热降解活化能(Ea)显著下降，即花色苷的降解速度增大；同一处理条件下，浓缩果汁的t_1/2明显低于澄清汁。而反应速率常数k和Ea值大于澄清果汁，说明澄清汁花色苷的热稳定性优于浓缩汁。     

超滤对血橙果汁中抗氧化成分及总抗氧化能力的影响

采用管式聚偏氟乙烯(PVDF)超滤膜，探讨了超滤对血橙果汁中抗氧化成分及总抗氧化能力的影响。结果表明，其对维生素C和花青素类成分的保存率约为85%左右，对几种酚酸和类黄酮组分（除槲皮素外）的保存率均在90%以上。同未杀菌的血橙原汁相比，巴氏杀菌汁的总抗氧化能力(TAA)损失率为23%，而超滤澄清汁仅为10%左右，主要与维生素C和花青素含量损失有关。     

Browning in ethanolic solutions of ascorbic acid and catechin

Nonenzymatic browning occurs readily in alcoholic beverages and degrades their color quality. Ascorbic acid degradation in the presence of phenolic compounds is a major browning pathway in alcoholic beverages with fruit or fruit juice as the raw material or an ingredient. In the present study ethanolic solutions of ascorbic acid and catechin were prepared to simulate the alcoholic beverages. Ascorbic acid degradation and browning in these model solutions were investigated. Glycerol solutions with the same water activity (A(w)) values as those of the ethanolic model solutions were used as controls in the evaluation of browning rate. Results showed that the aerobic degradation of ascorbic acid dominates over the anaerobic one in ethanolic solutions, that the browning rate decreases as the ethanol concentration increases, that the compound 3-hydroxy-2-pyrone may not be a good indicator of browning in ethanolic ascorbic acid-catechin solutions, and that A(w) is a major factor responsible for the difference in the browning rate among ascorbic acid-catechin solutions with different ethanol concentrations.     

Comparative study on pressure and temperature stability of 5-methyltetrahydrofolic acid in model systems and in food products

A comparative study on the pressure and temperature stability of 5-methyltetrahydrofolic acid (5-CH(3)-H(4)folate) was performed in model/buffer systems and food products (i.e., orange juice, kiwi puree, carrot juice, and asparagus). Effects of pH and ascorbic acid (0.5 mg/g) on 5-CH(3)-H(4)folate stability in buffer systems were studied on a kinetic basis at different temperatures (from 65 to 160 degrees C) and different pressure/temperature combinations (from 100 to 700 MPa/from 20 to 65 degrees C). These studies showed that (i) the degradation of 5-CH(3)-H(4)folate in all model systems could be described by first-order reaction kinetics, (ii) the thermostability of 5-CH(3)-H(4)folate was enhanced by increasing pH up to 7, (iii) 5-CH(3)-H(4)folate was relatively pressure stable at temperatures lower than 40 degrees C, and (iv) ascorbic acid enhanced both the thermo- and barostabilities of 5-CH(3)-H(4)folate. In food products, temperature and pressure stabilities of 5-CH(3)-H(4)folate were studied at different temperatures (70-120 degrees C) and different pressure/temperature combinations (from 50 to 200 MPa/25 degrees C and 500 MPa/60 degrees C). 5-CH(3)-H(4)folate in orange juice and kiwi puree was relatively temperature (up to 120 degrees C) and pressure (up to 500 MPa/60 degrees C) stable in contrast to carrot juice and asparagus. Addition of ascorbic acid (0.5 mg/g) in carrot juice resulted in a remarkable protective effect on pressure (500 MPa/60 degrees C/40 min) and temperature degradation (120 degrees C/40 min) of 5-CH(3)-H(4)folate.     

Ultraviolet-induced oxidation of ascorbic acid in a model juice system: identification of degradation products

Degradation products of ultraviolet (UV-C, 254 nm) treated ascorbic acid (AA) are reported. Analysis by high-performance liquid chromatography-mass spectroscopy (HPLC-MS) conducted in a 0.5% malic acid model juice system (pH 3.3) demonstrated increased degradation of AA above untreated controls with concomitant increases in dehydroascorbic acid (DHA) and 2,3-diketogulonic acid (DKGA) levels. Electron spin resonance (ESR) spectroscopy studies, conducted in phosphate buffer (pH 7.0) to increase detection sensitivity, demonstrated that ascorbyl radical (AA?) formation occurs simultaneously with AA degradation. Consistent with a previous study in which UV treatments were shown to accelerate dark storage degradation, AA? radicals continued to form for up to 200 min after an initial UV treatment. Results from this study suggest that the mechanism for UV-induced degradation is the same as the general mechanism for metal-catalyzed oxidation of AA in juice.     

Tetrahydro-beta-carboline alkaloids occur in fruits and fruit juices. Activity as antioxidants and radical scavengers

Tetrahydro-beta-carbolines are biologically active alkaloids that occur and accumulate in mammalian tissues, fluids, and brain, but their ultimate origin or biological role is still uncertain. Four tetrahydro-beta-carboline alkaloids: 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, 1-methyl-1,2,3,4-tetrahydro-beta-carboline, and 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline, are found as naturally occurring substances in some fruit and fruit juices. These compounds occur in the microg/g level in those products, and a characteristic and distinct profile appears to exist depending on the type of fruit and juice involved. Thus, 1-methyl-1,2,3,4-tetrahydro-beta-carboline may appear in tomato, tomato juice, and kiwi; 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline in bananas, pineapple, tomato, and their corresponding juices; and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid in oranges and grapefruits, although it also occurred in most juices. Fruit-occurring tetrahydro-beta-carboline alkaloids acted as antioxidants and free radical scavengers in the ABTS assay when compared with ascorbic acid and Trolox. This suggests that tetrahydro-beta-carboline alkaloids might act as antioxidants when absorbed and accumulated in the body, contributing to the antioxidant effect of fruit products containing these compounds.     

Aromatic characterization of pot distilled kiwi spirits

This study contributes fundamental knowledge that will help to develop a distillate of kiwi wine, made from kiwis of the Hayward variety grown in the southwest of Galicia (Spain). Two yeast strains, L1 (Saccharomyces cerevisiae ALB-6 from the EVEGA yeast collection) and L2 (S. cerevisiae Uvaferm BDX from Lallemand) were assessed to obtain a highly aromatic distillate. The kiwi spirits obtained were compared with other fruit spirits, in terms of higher alcohols, minor alcohols, monoterpenols, and other minor compounds, which are relevant in determining the quality and taste of the kiwi spirits. It was found that the kiwi juice fermented with yeast L1 produced a more aromatic distillate. In addition, kiwi distillates produced with both yeasts had the same ratio of trans-3-hexen-1-ol and cis-3-hexen-1-ol, which is lower than that found in other fruit distillates.     

Thermal degradation of antioxidant micronutrients in citrus juice: kinetics and newly formed compounds

The thermal degradation kinetics of vitamin C, two carotenoids (beta-carotene and beta-cryptoxanthin), and hesperidin, as a function of temperature, were determined for Citrus juice [Citrus sinensis (L.) Osbeck and Citrus clementina Hort. ex Tan]. The influence of dissolved oxygen on the rate of ascorbic acid degradation was also assessed. Analysis of kinetic data suggested a first-order reaction for the degradation of vitamin C and carotenoids. The kinetics parameters Dtheta, z, and Ea have been calculated. Following the Arrhenius relationship, the activation energy of ascorbic acid was 35.9 kJ mol-1 and agreed with the range of literature reported value. The results on vitamin C and carotenoids from citrus juice made it possible to validate the predicting model. Thermal degradation of carotenoids revealed differences in stability among the main provitamin A carotenoids and between these and other carotenoids belonging to the xanthophyll family. The activation energies for the two provitamin A carotenoids were 110 and 156 kJ mol-1 for beta-carotene and beta-cryptoxanthin, respectively. On the other hand, no degradation of hesperidin was observed during thermal treatment. Finally, the vitamin C in citrus juice was not as heat sensitive as expected and the main provitamin A carotenoids present in citrus juice displayed a relative heat stability. The high-performance liquid chromatography-diode array detection-mass spectrometry analysis of degradation products showed that the isomerization of the epoxide function in position 5,6 into a furanoxide function in position 5,8 was a common reaction for several xanthophylls. These findings will help determine optimal processing conditions for minimizing the degradation of important quality factors such as vitamin C and carotenoid in citrus juice.     

Phytochemical stability and color retention of copigmented and processed muscadine grape juice

Muscadine (Vitis rotundifolia) grape juice was assessed for color and phytochemical stability as influenced by anthocyanin copigmentation with a water-soluble rosemary extract, fortification with ascorbic acid, and processing by heat or high hydrostatic pressure (HHP). The roles of polyphenolic cofactors in the presence and in the absence of ascorbic acid were assessed as a means to improve the overall processing stability of the juice. Addition of rosemary extract from 0 to 0.4% (v/v) readily formed copigment complexes with anthocyanins and resulted in concentration-dependent hyperchromic shifts from 10 to 27% that corresponded to increased antioxidant activity. The presence of ascorbic acid was generally detrimental to juice quality, especially in the presence of rosemary extract, and resulted in overall anthocyanin, ascorbic acid, and antioxidant activity losses. Although thermal and high-pressure processing methods were detrimental to juice quality, HHP resulted in greater losses after processing, likely due to action from residual oxidase enzymes. Although physicochemical attributes were enhanced by copigmentation with rosemary extract, methods to inactivate residual enzymes should be addressed prior to copigmentation to prevent degradation of anthocyanins in the presence of ascorbic acid.     

线性优化在山萸肉复合晶配料优选中的应用研究

该文以线性优化技术进行了山萸肉复合晶配料的优选研究,获取了科学的、合理的山萸肉复合晶配料、配比：山萸肉浓缩汁（６２．２Ｂｒｉｘ）７９％、沙棘浓缩汁（６１．０Ｂｒｉｘ）６％、猕猴桃浓缩汁（６９．８Ｂｒｉｘ）１５％。