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The applicability of the crocin bleaching assay (CBA) to structure-activity relationship (SAR) studies of a great number (n = 39) of selected phenolic compounds was thoroughly investigated. The focus was on the activity of hydroxybenzoic, hydroxyphenylacetic, hydroxyphenylpropanoic, and hydroxycinnamic acids. Other assays [oxygen radical absorbance capacity (ORAC), lipid oxidation] were applied when necessary. Hydroxybenzoic acids were less active than the respective simple phenols. The position of the -COOH group relative to hydroxyl substituents was critical. The number and position of the -OH groups governed the order and size of activity within the subgroup of these acids. Gallic acid was the most active, being 1.6- and 3.4-fold superior to protocatechuic and syringic acids, respectively. The effect of proximity of the -COOH group to the phenyl ring was more distinct for 3,4-guaiacol acids (ferulic > dihydroferulic congruent with homovanillic > vanillic) than for 3,4-catechol ones (caffeic > protocatechuic > or = dihydrocaffeic congruent with homoprotocatechuic). Compounds such as vanillin, tyrosol, ferulic acid derivatives, rosmarinic acid, and quercetin were examined to reinforce discussion on the basis of physical organic chemistry principles. Taking into account the acidity of most compounds, the CBA-derived order of activity was meaningful. 相似文献
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The role of squalene in olive oil stability was studied for various concentrations and experimental conditions. No effect was found in induction periods of olive oil at elevated temperatures using the Rancimat apparatus. Samples were then stored at 40 and 62 degrees C in the dark, and the extent of oxidation was followed by periodic measurements of peroxide value and conjugated dienes. A concentration dependent moderate antioxidant activity was evidenced which was stronger in the case of olive oil compared to that found for sunflower oil and lard. In the presence of alpha-tocopherol (100 mg/kg) and caffeic acid (10 mg/kg) the contribution of squalene (7000 mg/kg) was not significant. No radical scavenging activity was observed using DPPH(*) in 2-propanol. The weak antioxidant activity of squalene in olive oil may be explained by competitive oxidation of the different lipids present which leads to a reduction of the oxidation rate. Squalene plays a rather confined role in olive oil stability even at low temperatures. 相似文献
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辽宁省主要耕地土壤速效钾含量及其区域分布状况 总被引：5，自引：0，他引：5
为了对辽宁省耕地土壤钾素水平进行正确的评价 ,于 1 993～ 1 997年在全省 1 3个市的 32个县(市、区 )采集了有代表性的主要耕地土壤样本846份。利用ＡＳＩ法分析了土壤速效钾含量 ,并绘制出辽宁省土壤速效钾含量分布图。这是我省第 2次土壤普查以来 ,辽宁省农业科学院土肥所第 1次进行土壤速效钾分析化验工作 ,将为辽宁省钾肥的合理施用提供科学依据。1 土样的采集根据全省第 2次土壤普查各地区不同土壤类型 ,按每 3333ｈｍ2 取一个土壤样本 ,不足 3333ｈｍ2 的土类不取样的原则 ,共采集了 846份抽查土样。旱田取 0～ 2 0ｃｍ、水田取 0～… 相似文献
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Virgin olive oil samples with similar oxidative stabilities and fatty acid compositions were stored for 24 months. Changes in the lipid substrate were followed by peroxide value and K(232) measurements. HPLC was used to evaluate changes in the alpha-tocopherol, pigment, and squalene contents. Total polar phenol content was measured colorimetrically. The loss of alpha-tocopherol and carotenoids was comparable with that of polar phenol content, suggesting an active participation in autoxidation. The limited role of squalene in autoxidation was further confirmed using an olive oil model and in the presence of alpha-tocopherol. Pheophytin a degradation was high, although spectrometric estimation of chlorophyll content did not indicate so. Evaluation of pheophytin a activity at three different levels of addition on the oil model indicated a concentration-dependent antioxidant role more pronounced at elevated temperatures, which could be partially due to the activity of certain degradation products. 相似文献
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Virgin olive oil samples with similar oxidative stabilities and fatty acid compositions were exposed to 12100 lx (25 +/- 1 degrees C) in closed bottles until bleached. The observed low changes in the substrate and polar phenols were related to oxygen availability. HPLC monitoring showed that pheophytin agradual degradation (> 90%) was accompanied by a considerable alpha-tocopherol loss (22-35%) due to the reaction of the latter with singlet oxygen. No changes were recorded for carotenoids, which acted as physical quenchers and light filters. Squalene loss was confined (4-12%). Complementary experiments on the activity of pheophytin a, using olive oil models, indicated a concentration dependence, enhanced by oxygen availability. In closed bottles, the degradation rate constant was higher at low amounts of pheophytin a. Squalene was preferentially consumed to protect alpha-tocopherol. An urgent change in the practice of packaging is needed to preserve the precious characteristics of the product during commercialization. 相似文献
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Zalacain A Ordoudi SA Díaz-Plaza EM Carmona M Blázquez I Tsimidou MZ Alonso GL 《Journal of agricultural and food chemistry》2005,53(24):9337-9341
Near-infrared reflectance spectroscopy has been applied for the first time to saffron spice to determine the chemical composition and geographical origin of 111 samples from the there main producers' countries: Iran, Greece, and Spain. The validation procedures with the results obtained by UV-vis and HPLC-DAD measurements demonstrated that this technique is appropriate to determine the following parameters: moisture and volatile content, coloring strength, (250 nm), and (330 nm), established on the ISO 3632 Technical Specification Normative and used to certify saffron quality in the international market. Also, it can be used to estimate the content of the five main crocetin glycosides, the compounds responsible for saffron color, the best correlations being for trans-crocetin di-(beta-D-gentibiosyl) ester (R2= 0.93), trans-crocetin (beta-D-glucosyl)-(beta-D-gentibiosyl) (R2= 0.94), and picrocrocin (R2= 0.92), the compound accepted as responsible for saffron bitterness. Finally, a discriminant analysis among the three geographical origins reveals that Iranian samples are the most different, whereas Greek and Spanish samples are more similar. All of these results reveal that NIRS spectroscopy has an enormous potential for its application to saffron quality control as the results are obtained in 2 min and without any sample manipulation. 相似文献
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E Naziri F Mantzouridou MZ Tsimidou 《Journal of agricultural and food chemistry》2012,60(36):9195-9201
The present work is a systematic approach for valorization of wine lees regarding the recovery of squalene, a bioactive lipid. Such a study is presented for the first time in literature. Separate examination of squalene content in "light" and "heavy" lees from different vinification processes by RP-HPLC demonstrated that these waste streams can be used as a source for this lipid, despite variations due to technological or genetic effects. Next, ultrasound assisted extraction of squalene from the "industrial waste" (the mixture of wine lees generated from different wines) using n-hexane was optimized with the aid of response surface methodology (independent variables: sonication duration and duty cycles). Autolysis was monitored through optical microscopy. Squalene yield (0.6 ± 0.08 g SQ/kg dry lees) was comparable to that of recently examined potential sources (0.2-0.35 g SQ/kg dry olive pomace and 0.06 g SQ/kg olive leaves). 相似文献
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Pegklidou K Mantzouridou F Tsimidou MZ 《Journal of agricultural and food chemistry》2008,56(12):4482-4490
The potential role of 2-methyl imidazole in improving lycopene production by Blakeslea trispora with regards to yield, selectivity, and safety aspects was investigated in batch culture. Optimization of the bioprocess conditions in terms of (a) (+) and (-) strain ratio in the inoculum, (b) initial crude soybean oil (CSO) addition level, and (c) the amount of 2-methyl imidazole was based on response surface methodology to achieve maximum lycopene production. The dependence of growth kinetics, lycopene yield, and selectivity of the bioprocess on the above factors was clear. 2-Methyl imidazole at 50 mg/L was found equally active in terms of lycopene cyclase inhibition with that at 200 or 100 mg/L; in all cases, lycopene accounted for 94% of the total carotenoids. The highest yield was observed at a 50 mg/L level of addition (24 mg/g of biomass dry weight,) in a substrate supplemented with CSO (48 g/L of culture medium) and inoculated with 1(+)/7(-) strain ratio. 相似文献
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Examination of the crocin bleaching assay performance and in-house validation were focused on probe and test compound characteristics, conditions for peroxyl radical generation, reaction monitoring, and expression of results. HPLC and spectrometric examination showed that any authentic commercial saffron (origin, grade) can be used for probe preparation given that (a) interferences, such as tocopherols, are removed, (b) working solution concentration is adequately adjusted, and (c) stock probe solution changes during storage are not neglected. As suggested by log P values, calculated for a great number of radical scavengers (AHs), any AH more polar than Trolox (common reference compound) can be tested in the aqueous environment of the assay. AH activities order obeyed principles of structure-activity relationships. The assay was robust toward preheating of the azo-initiator (2,2'-azobis(2-aminopropane) dihydrochloride). Reaction monitoring through periodic UV-vis spectra recording was very informative. An alternative expression of results as "percent inhibition of crocin bleaching value", % Inh = [(DeltaA(0) - DeltaA)/DeltaA(0))] x 100, is proposed for [AH]/[crocin] = 1, instead of the so far used k(rel) values. The above findings also lead to analysis cost and time reduction. 相似文献