猕猴桃汁维生素C降解动力学的研究

以猕猴桃原汁为试材,采用控制温度、调节pH值以促使维生素C氧化降解的方法,探讨猕猴桃汁中维生素C的降解动力学,为控制猕猴桃汁加工中维生素C损失提供理论依据。结果表明：猕猴桃汁中的维生素C降解十分复杂,存在多种降解途径,但主要是有氧降解;其还原型维生素C不经氧化型维生素C生成其他产物的不可逆途径可能存在,但不占主导地位。猕猴桃汁中维生素C无氧降解速度比有氧降解速度慢,温度升高,维生素C有氧降解速度加快,无氧降解速度变化不明显。     

外源抗坏血酸和谷胱甘肽对荔枝保鲜效果的影响

为了探讨外源抗坏血酸（AsA）和谷胱甘肽（GSH）对荔枝保鲜效果的影响。分别在多菌灵500 mg/L+施保克 3 mL/L+ 柠檬酸15.0 mmol/L溶液中分别加入抗坏血酸50.0 mmol/L（AsA处理）和谷胱甘肽50.0 mmol/L（GSH处理）浸果5 min,以多菌灵500 mg/L+施保克3 mL/L+柠檬酸15.0 mmol/L浸果5 min为对照处理,分别置于常温和6℃低温贮藏、相对湿度为80%。结果表明：AsA和GSH处理均能降低荔枝果皮多酚氧化酶（PPO）活性和相对电导率;提高果肉的超氧化物岐化酶（SOD）和过氧化氢酶（CAT）活性;降低果肉过氧化氢（H2O2）和丙二醛（MDA）的含量,维持果肉中较高的维生素C和GSH含量。低温下,AsA和GSH处理均能提高荔枝保鲜效果,降低果实的腐烂率,但AsA处理的保鲜效果要优于GSH处理的效果,而常温下GSH处理并不能提高荔枝的保鲜效果。     

棉种储存期不同温湿度对其发芽力的影响

通过对棉种不同温湿度储存条件下的发芽力试验，分析棉种适宜储存环境及其种子的复苏能力。     

Effect of drying conditions and storage period on polyphenolic content, antioxidant capacity, and ascorbic acid of prunes

In this study the main chemical parameters, ascorbic acid and polyphenol content, and antioxidant activity of two varieties of prunes, dried by high-temperature (85 + 70 degrees C) and low-temperature (60 degrees C) procedures, were monitored during storage. Ascorbic acid content was higher in the prunes dried at 60 degrees C but significantly decreased in both varieties during storage. The different classes of polyphenols analyzed (cinnamates, anthocyanins, flavonols) showed different stabilities during storage. Neochlorogenic acid decreased only in the President variety, whereas chlorogenic acid increased in both varieties; anthocyanins, present only in the President prunes, disappeared in the first months of storage, and the flavonol content fell significantly in both cultivars during the year of the study. Drying temperature significantly affected the polyphenol content, with different effects according to the class of polyphenols. Antioxidant activity showed a significant increase at the end of the storage period and in the President variety was higher in the sample dried at the higher temperature.     

Adenosine triphosphate (ATP) and microbial biomass in soil: Effects of storage at different temperatures and at different moisture levels

Abstract

On air‐drying, the ATP contents of two moist soils fell to about one quarter of their original values. When a freshly‐sampled soil (field temperature 5.5°C) was stored moist (43% water holding capacity) for 7 days at 25°C the ATP content increased from 4.54 to 7.84 μg ATP g^‐1 soil. Storage at 10°C caused a smaller increase; to 5.39 μg g^‐1 soil. Microbial biomass C also increased on storage but the relative increase was less than that of ATP. Thus the biomass C/ATP ratio fell from 234 in the freshly sampled soil to 168 in the soil stored moist for 7 days at 25°C. The ATP content declined to less than half its starting value if storage was under waterlogged conditions.

The ATP method for determining microbial biomass in soil depends on the use of a constant factor (5.85 mg ATP g^‐1 biomass C) for converting ATP content to biomass C. This factor came from work on soils that had been stored moist at 25°C for several days before biomass C and ATP measurements were made: it is only applicable to soils that have been stored in this way.     

Changes in the free amino acid contents of honeys during storage at ambient temperature

This study was carried out to establish the changes in the free amino acid contents of floral honeys, honeydew honeys, and blend honeys during storage at room temperature and to test the capacity of the amino acids to distinguish the origin of the honeys after storage. For this purpose, 54 artisanal honeys (39 floral, 5 honeydew, and 10 blend) were studied. Samples were taken from recently collected honeys and at 3, 6, 9, 12, 16, 20, and 24 months after harvesting. The contents of most of the free amino acids were found to decrease with storage time, with the greatest reduction observed in the first 9 months. The contents of the amino acids aspartic acid, beta-alanine, and proline increased in the first few months after storage, reaching maximum values at 6 months, suggesting the possible existence of enzymatic activities. The application of stepwise discriminant analysis to the free amino acid content data demonstrated that the contents of the amino acids valine, beta-alanine, gamma-aminobutyric acid, serine, isoleucine, alpha-alanine, ornithine, and glutamine correctly assigned 87% of honeys to their group of origin: floral, honeydew, or blend.     

Physicochemical and sensory characteristic changes in fortified peanut spreads after 3 months of storage at different temperatures

Three amino acid-balanced, vitamin- and mineral-fortified peanut spreads were stored at 4, 23, and 40 degrees C for 3 months. These were 69.6% peanut/19% soybean-40.5% fat, 61.9% peanut/19% soybean-44.5% fat, and 74.1% peanut/14% nonfat dry milk (NFDM)-40% fat. The peanut spreads were fortified with vitamin A, thiamin, riboflavin, vitamin B(6), vitamin C, calcium, and iron to provide 33.3% of the Recommended Dietary Allowances for children. Water-soluble vitamins were quite stable in deaerated peanut spreads. The antioxidant activity of phytochemicals in soybean prevented vitamin A degradation in soy-containing spreads, whereas the NFDM spread lost 70% of the initial content. Instron analysis detected major changes in texture when peanut spreads were stored at 40 degrees C, suggesting that the polymorphic form of lipid transformed and the proper crystallization of stabilizer was destroyed. Panelists did not detect the texture changes in peanut spreads stored at different temperatures. At 40 degrees C, the primary deteriorative changes in sensory quality were increased browning and the development of "soybean" and "oxidized" flavors as well as decreased "roasted peanutty" flavor.     

Effect of cultivar and processing method on the contents of polyphenols in table olives

Polyphenols were determined by HPLC in the juice and oil of packed table olives. The phenolic compositions of the two phases were very different, hydroxytyrosol and tyrosol being the main polyphenols in olive juice and tyrosol acetate, hydroxtyrosol acetate, hydroxytyrosol, tyrosol, and lignans (1-acetoxypinoresinol and pinoresinol) in oil. The type of processing had a marked influence on the concentration of polyphenols in olive juice and little on the content in oil. The analyses carried out on 48 samples showed that turning color olives in brine had the highest concentration in polyphenols ( approximately 1200 mg/kg), whereas oxidized olives had the lowest ( approximately 200 mg/kg). Among olive cultivars, Manzanilla had a higher concentration than Hojiblanca and Gordal. The type of olive presentation also influenced the concentration of polyphenols in olives, decreasing in the order plain > pitted > stuffed. The results obtained in this work indicate that table olives can be considered a good source of phenolic antioxidants, although their concentration depends on olive cultivar and processing method.     

Adenylates in the soil microbial biomass at different temperatures

Five soils from temperate sites (Germany; 2 arable and 3 grassland) were incubated aerobically at 5, 10, 15, 20, 25, 35, and 40 °C for 8 days. Soils were analysed for soil microbial biomass C, biomass N, AMP, ADP, and ATP to determine whether the increase in the ATP-to-microbial biomass C ratio with increasing temperature was either due to an increase in the adenylate energy charge (AEC) or de novo synthesis of ATP, or both. Around 80% of the variance in microbial biomass C and biomass N was explained by differences in soil properties, only 7% by the temperature treatments. Averaging the data of all 5 soils for each incubation temperature, the microbial biomass C content decreased with increasing temperature from 15 to 40 °C continuously by 2.5 μg g⁻¹ soil °C⁻¹ after 8-days' incubation. However, this decrease was not accompanied by a similar decrease in microbial biomass N. The average microbial biomass C/N ratio was 6.8. Between 54 and 76% of the variance in AMP, ADP, ATP and the sum of adenylates was explained by differences in soil properties and between 14 (ADP) and 27% (ATP) by the temperature treatments. However, temperature effects on AMP and ADP were variable and inconsistent. In contrast, ATP and consequently also the sum of adenylates increased continuously from 5 to 30 °C followed by a decline to 40 °C. The AEC showed similarly a small, but significant increase with increasing temperature from 0.73 to 0.85 at 30 °C. Consequently, the majority of the variance, i.e. roughly 60% in AEC values, but also in ATP-to-microbial biomass C ratios was explained by the incubation temperature. The mean ATP-to-microbial biomass C ratio increased from 4.7 μmol g⁻¹ at 5 °C to a 2.5 fold maximum of 12.0 μmol g⁻¹ at 35 °C. This increase was linear with a rate of 0.26 μmol ATP g⁻¹ microbial biomass C °C⁻¹. The energy for the extra ATP produced during temperature increase is probably derived from an accelerated turnover of endocellular C reserves in the microbial biomass.     

Thermal stability of ascorbic acid and ascorbic acid oxidase in african cowpea leaves ( Vigna unguiculata ) of different maturities

Cowpea, an African leafy vegetable ( Vigna unguiculata ), contains a high level of vitamin C. The leaves harvested at 4-9 weeks are highly prone to vitamin C losses during handling and processing. Therefore, the purpose of this research was to study the effect of thermal treatment on the stability of ascorbic acid oxidase (AAO), total vitamin C content (l-ascorbic acid, l-AA), and dehydroascorbic acid (DHAA) and l-AA/DHAA ratio in cowpea leaves harvested at different maturities (4, 6, and 8 weeks old). The results showed that AAO activity, total vitamin C content, and l-AA/DHAA ratio in cowpea leaves increased with increasing maturity (up to 8 weeks). Eight-week-old leaves were the best source of total vitamin C and showed a high ratio of l-AA/DHAA (4:1). Thermal inactivation of AAO followed first-order reaction kinetics. Heating at temperatures above 90 °C for short times resulted in a complete AAO inactivation, resulting in a protective effect of l-AA toward enzyme-catalyzed oxidation. Total vitamin C in young leaves (harvested at 4 and 6 weeks) was predominantly in the form of DHAA, and therefore temperature treatment at 30-90 °C for 10 min decreased the total vitamin C content, whereas total vitamin C in 8-week-old cowpea leaves was more than 80% in the form of l-AA, so that a high retention of the total vitamin C can be obtained even after heating and/or reheating (30-90 °C for 10 min) before consumption. The results indicated that the stability of total vitamin C in situ was strongly dependent on the plant maturity stage and the processing conditions applied.     

Combined effect of ascorbic acid and gamma irradiation on microbial and sensorial characteristics of beef patties during refrigerated storage

The present study was undertaken to evaluate the effect of ascorbic acid concentrations (0.03 to 0.5%) and irradiation doses (0.5 to 4 kGy) on microbial growth, color coordinates (L, a, and b), and sensory characteristics (taste and odor) of beef patties during storage at 4 +/- 1 degrees C. Ascorbic acid was also compared to citric acid at a similar pH value in order to differentiate the effects of ascorbic acid from those of pH reduction. Results showed significant reduction (p< or = 0.05) of aerobic plate counts (APCs) and total coliforms, and a significant interaction (p< or = 0.05) between ascorbic acid and irradiation dose was observed. The irradiation treatment had detrimental effects on redness, yellowness, and hue angle values of meat. However, incorporation of ascorbic acid into the meat before irradiation resulted in significant (p< or = 0.05) stabilization of color parameters. The color improvement obtained with ascorbic acid was not related to the pH reduction. Also, no significant detrimental effect on taste or odor was found in irradiated samples containing ascorbic acid.     

青花菜贮藏期间颜色变化动力学模型的建立

该试验利用CIE-L^*a^*b^*(Commission International de I'Eclairage,国际照明委员会制定的色彩空间坐标表色系统)中的a^*、b^*、H°、TCD(Total Color Difference,总色差)以及叶绿素含量和黄化级数来衡量青花菜色泽的变化情况, 旨在建立贮藏期间多种颜色指标的动力学模型。试验组分为0℃、5℃、10℃条件下分别在HDPE(high-density polyethylene高密度聚乙烯)薄膜单球包装与不包装两种情况下进行。试验结果显示，包装提升了青花菜贮藏期间的活化能，延迟了呼吸跃变的启动。非线性回归分析的结果表明，色泽参数b^*和TCD的速率常数符合Arrhenius模型，模型符合一级动力学反应；而a^*和H°的变化则可用多项式表示。贮藏青花菜的黄化级数与色泽参数b^*之间具有良好的相关性，为利用计算机视觉系统进行颜色分级提供了理论依据。     

Interaction between ascorbic acid and chlorogenic acid during the formation of nitric oxide in acidified saliva

When saliva and gastric juice are mixed, salivary nitrite is transformed to nitrous acid to produce nitric oxide (NO). The NO formation in acidified saliva was enhanced by ascorbic acid and chlorogenic acid. Thiocyanate ion (SCN(-)) also enhanced the transformation of nitrous acid to NO. During the NO formation in the presence of both ascorbic acid and chlorogenic acid, ascorbic acid was preferentially oxidized. Chlorogenic acid was oxidized after ascorbic acid had been oxidized. Ascorbyl radical was detected during the oxidation of ascorbic acid, and the radical intensity was decreased by chlorogenic acid. The decrease is discussed to be due to the reduction of the oxidation intermediate or product of chlorogenic acid by ascorbyl radical. The result obtained in this study suggests that ascorbic acid was preferentially oxidized and that not only ascorbic acid but also ascorbyl radical could interact with the oxidation intermediate or product of chlorogenic acid when chlorogenic acid was added to the mixture of saliva and gastric juice that contained ascorbic acid.     

Influence of cultivar, harvest time, storage conditions, and peeling on the antioxidant capacity and phenolic and ascorbic acid contents of apples and pears

Apple and pear fruits are important sources of secondary plant metabolites and one of the major sources of dietary phenolics consumed all year round. The aim of this work was to identify the main variables influencing phenolic content and antioxidant capacity in apples. Higher phenolic and antioxidant contents were observed in some varieties (such as the Delbar Estival apple and Durondeau pear). Storage conditions were important. Our results also showed that fruits should be consumed rapidly after purchase and with their peel. After one week of domestic storage, the ascorbic acid content was found to decrease by 75%. Peeling led to a more than 25% decrease in total phenolics and ascorbic acid. The harvest time (at normal ripeness) had only a limited impact, but significant year-to-year variations were observed. In conclusion, well-chosen and well-stored apples and pears may contribute to an antioxidant-rich diet if consumed rapidly and with their peel.     

Adsorption of deoxyribonucleic acid (DNA) by willow wood biochars produced at different pyrolysis temperatures

Adsorption of DNA by biochars was investigated in the present study. Biochars were produced from air-dried willow wood chips at 300, 400, 500, and 600 °C under limited oxygen supply. The resulting products, referred to as BC300, BC400, BC500, and BC600, respectively, were characterized for their elemental composition, cation exchange capacity (CEC), specific surface areas (SSA), and microporosity. According to a Langmuir isotherm, maximum DNA adsorption capacity of biochars was ranked as BC500?>?BC600?>?BC400?>?BC300. Increasing solution pH (from 4.0 to 9.0) faintly decreased DNA adsorption onto biochars. The addition of Na⁺, Mg²⁺, and Ca²⁺ slightly increased the adsorption of DNA, and the effect decreased by increasing the pyrolysis temperature of biochars, indicating that electrostatic interaction was not the main driving force for DNA adsorption onto those biochars. Correlation analysis showed that SSA and micropore surface area were the main factors influencing DNA adsorption on biochars.     

Quenching mechanisms and kinetics of Trolox and ascorbic acid on the riboflavin-photosensitized oxidation of tryptophan and tyrosine

The effects of 0, 0.3, 0.6, and 0.9 mM Trolox and ascorbic acid on the singlet oxygen oxidation of tryptophan and tyrosine containing 25 ppm of riboflavin were determined by measuring tryptophan and tyrosine concentration by high-performance liquid chromatography analysis. The samples were stored in the a 1000 lx light storage box for 4 h at 30 degrees C. As the concentration of Trolox and ascorbic acid increased, the degradation of tryptophan and tyrosine decreased significantly at p < 0.05. Trolox reduced tryptophan and tyrosine degradation by quenching both singlet oxygen and excited triplet riboflavin, whereas ascorbic acid quenched singlet oxygen only. The total singlet oxygen quenchings of Trolox in the presence of tryptophan and tyrosine were 1.55 x 10(7) and 1.32 x 10(7) M(-1) s(-1), respectively. The total singlet oxygen quenchings of ascorbic acid in the presence of tryptophan and tyrosine were 1.16 x 10(7) and 1.10 x 10(7) M(-1) s(-1), respectively. Trolox was more effective than ascorbic acid in preventing the degradation of tryptophan and tyrosine.     

Pectins as possible source of the copper involved in the green staining alteration of cv. Gordal table olives

The pectic and pigment compositions and Ca and Cu contents of the alcohol-insoluble solid (AIS) residues were determined in cv. Gordal olives treated with NaOH solution and kept at different constant pH values (3.5-6.5). The same controls were made in table olives presenting green staining alteration. The ratio between the various pectin fractions of the more acid pH experiment samples remained similar in fruits not showing green staining. In altered fruits, the protopectin fraction was lower, and the calcium pectate or EDTA soluble pectins were higher. Regarding the presence of Ca and Cu in the AIS, it was observed that, whereas Ca levels fell at the most acid pH values, those of Cu increased. The concentration of Ca was higher in the AIS of altered olives than in nonaltered ones. The same trend was seen for the zone with or without green staining of an altered fruit. In the case of Cu, the relationship was the opposite: a decrease in the levels of AIS Cu in fruits and zones of fruits with green staining. This result was correlated with the highest concentration of Cu-chlorophyll complexes found in such samples and suggested that pectins might act as a reservoir of Cu involved in the alteration.     

Adsorption of Copper by Soils in aqueous media at different temperatures

Soils of Azamgarh, U.P. have been found to fix copper fairly in good amounts. The fixation is found to be endothermic and is accompanied by a decrease in the resultant pH. The fixation is more with loam soils and generally increases with the depth of soil. pH, sesquioxide, magnesium oxide, exchangeable magnesium and C/N ratio have been found to affect the fixation. Copper is fixed as Cu(OH)⁺ in the acid systems.     

Volatile fatty acid production with alfalfa (Medicago sativa) and glucose in denitrifying soil at different temperatures

Summary A laboratory study was done to determine how, if at all, temperatures affect the production of volatile fatty acids and the rate of denitrification in soil. Glucose and alfalfa were compared as C substrates at temperatures of -2, 10, and 25°C under anaerobic conditions. At -2°C (soil not frozen), the denitrification rate was slow but was as rapid with alfalfa as glucose. This indicated that the production of volatile fatty acids by fermenters or other C substrates from alfalfa were adequate to sustain denitrifiers. No volatile fatty acids were apparently produced with glucose at -2°C whereas acetate and propionate were produced with alfalfa during the 26-day incubation period. During the 8-day incubation period at 10°C, there were also greater accumulations of acetate and propionate with alfalfa than with glucose. At 25°C, there was no major difference in the denitrification rate between glucose and alfalfa over a 4-day period. In a contrast to the other temperatures, more butyrate than propionate was produced at 25°C, especially with alfalfa. Acetate was the dominant volatile fatty acid produced and generally increased with temperature, especially after NO₃ exhaustion at 10 and 25°C. This indicated that acetate was a source of C for denitrifiers.     

Validation of a method for the analysis of iron and manganese in table olives by flame atomic absorption spectrometry

There is no generally accepted method for determination of the amounts of iron and manganese in table olives. Application of flame atomic absorption spectrometry to the analysis of both elements has been examined to validate a method that may be used by the industry's quality control laboratory as well as by the laboratories of regulatory agencies. The method has detection limits of 0.106 and 0.022 mg/L and quantification limits of 0.271 and 0.057 mg/L, for Fe and Mn, respectively, referred to the solution to be measured. There was no significant effect due to the matrix, but a slight bias due to the presence of Ca has been detected. Recoveries were excellent, and the method was robust. Influence of operator, HCl and Mg salt compounds, calcination equipment, or dates on results was not found. Relative errors were, in general, below 4% for both cations, and repeatability was below 3.43 and 0.38 mg/kg of olive paste for Fe and Mn, respectively. The method is proposed for the analysis of Fe and Mn in ripe olives and table olives in general.