苯甲酸的酯化及其抑菌活性研究

对苯甲酸甲酯化的合成工艺条件及抑菌效果进行了研究。合成实验结果表明苯甲酸甲醇酯化混合液（ｌｍｏｌ：５ ｍｏｌ）在８５℃时酯化反应速度最快；不同类型酯化催化剂间适当组合对苯甲酸甲酯的合成可产生显著的增效作用。抑菌实验结果表明苯甲酸经酯化修饰后，可显著抑制微生物的生长，缩短对数生长期和减少微生物的生长量。     

苯甲酸的酯化及其抑菌活性研究

对苯酸甲酯化的合成工艺条件及抑菌效果进行了研究,合成实验结果表明苯甲酸甲醇酯化混合液（1mol:5mol）在85℃时酯化反应速度最快;不同类型脂化催化剂间适当组合对苯甲酸甲酯的合成可产生显著的增效作用,抑菌实验结果表明苯甲酸经酯化修饰后,可显著抑制微生物的生长,缩短对数生长期和减少微生物的生长量。     

甾醇酯化反应中催化剂的研究

研究了以硅胶为催化剂,用甾醇与脂肪酸直接酯化合成甾醇酯的合成工艺,探索了不同反应配比、催化剂用量、温度及反应时间对酯化率的影响。结果表明：硅胶催化酯化反应中当酸醇摩尔比1.5：1,温度190℃,反应10h后酯化率最高,可高达94.3%,并通过分子蒸馏提纯,温度为200℃时甾醇酯含量可达到98.4%。     

活性炭固载磷钨酸催化合成顺丁烯二酸二异辛酯

利用颗粒状活性炭固载磷钨酸和聚乙二醇(400)为混合催化剂，以顺丁烯二酸酐和异辛醇为原料，合成渗透剂T的中间体顺丁烯二酸二异辛酯．研究了反应中的催化剂用量、醇酐量比及反应时间对酯化率的影响．确定了合成该酯的最佳工艺条件为n(醇)：n(酐)：3：1，反应温度为120℃，反应时间为2h．在此条件下酯化率超过95％．此法催化剂用量少，酯化率高，反应时间短，工艺简单．副反应少，无废酸排放，有利于环保。     

植物甾醇脂肪酸酯的胶束催化合成研究

植物甾醇脂肪酸酯可以通过脂肪酸和植甾醇在酸和碱的催化下直接酯化合成.为提高酯化率,采用胶束催化剂合成脂肪酸植物甾醇酯,研究了反应条件对反应的影响.研究表明,胶束催化剂十二烷基硫酸铜为合成植物甾醇脂肪酸酯的良好高效催化剂,并可回收利用.在酸醇摩尔比1.2∶1,十二烷基硫酸铜用量为植物甾醇摩尔百分比为1％,反应温度110℃,无溶剂反应4h的最佳条件下,植物甾醇的酯化率为80.7％～86.4％.     

FeCl_3改性蒙脱土催化合成油酸甲酯的研究

用氯化铁改性蒙脱土制备了改性催化剂FeCl_3–蒙脱土,并以此为催化剂催化油酸与甲醇酯化合成油酸甲酯。通过XRD、FT–IR等方法对催化剂进行了表征。考察了催化剂用量、油醇摩尔比、反应温度、反应时间等因素对转化率的影响。研究结果表明:在催化剂用量5 wt%、油醇摩尔比1∶10、反应温度70℃的条件下反应3 h,油酸转化率为71.5%,且该催化剂适用于各种游离脂肪酸酯化反应及高酸值油脂酯化降酸反应。     

活性炭基固体酸催化合成酒用脂肪酸乙酯的研究

以白酒酒糟为原料,通过浓硫酸磺化制备了活性炭基固体酸催化剂,并催化合成乙酸乙酯、乳酸乙酯、己酸乙酯和丁酸乙酯4种酒用脂肪酸乙酯。结果表明,乙酸乙酯最佳反应条件为活性炭基固体酸催化剂添加量3%,酸醇物质的量比1∶5,酯化时间4 h,酯化温度80 ℃,酯化率达86%;乳酸乙酯最佳反应条件为催化剂添加量4%,酸醇物质的量比1∶8,酯化时间10 h,酯化温度95 ℃,酯化率达76%;己酸乙酯最佳反应条件为催化剂添加量4%,酸醇物质的量比1∶10,酯化时间12 h,酯化温度98 ℃,酯化率达68%;丁酸乙酯最佳反应条件为催化剂添加量4%,酸醇物质的量比1∶9,酯化时间8 h,酯化温度90 ℃,酯化率达73%。活性炭基固体酸催化剂可以重复使用6次。     

AlCl3／D72催化合成渗透剂T

改进老产品的合成工艺，解决使用浓硫酸催化剂合成渗透剂存在的诸多问题。以顺丁烯二酸酐与仲辛醇为原料，AlCl3/D72替代浓硫酸催化剂合成渗透剂T。探讨了催化剂用量、酯化磺化反应时间、酸醇量比对反应的影响。AlCl3/D72催化效果较好，酯化率、磺化率与原催化剂基本相同，而且副反应少，没有废酸排放，环保价值高。     

无溶剂直接酯化法合成亚油酸甾烷醇酯的研究

为了得到甾烷醇与亚油酸在无溶剂条件下,直接酯化法合成亚油酸甾烷醇酯的最佳工艺条件,以酯化率和体系氧化程度为考察指标,单因素考察筛选利于合成的底物酸醇摩尔比、催化剂添加量、反应温度和反应时间,并采用L9(34)正交实验进一步优化得出最佳合成工艺:亚油酸与甾烷醇的摩尔比3∶1,催化剂用量3%,反应时间5h,反应温度150℃,在此条件下,亚油酸甾烷醇酯的酯化率达到81.23%。采用薄层色谱,高效液相色谱和近红外光谱对亚油酸甾烷醇酯进行了鉴定,并研究了亚油酸甾烷醇酯的热力学特性。     

活性炭基固体酸催化合成己酸乙酯的研究

以白酒酒糟制备的活性炭作为载体,通过磺化反应制备具有高酸值的活性炭基固体酸催化剂,确定最佳制备条件为:活性炭目数120目,固液比1∶5,磺化时间24h。用制备的固体酸催化剂催化合成己酸乙酯,分别考察了固体酸催化剂的添加量、酸醇比、酯化时间和酯化温度对酯化反应的影响,得出反应的最佳条件是:固体酸添加量是己酸质量的4%,酸醇比为1∶10,酯化时间为12h,酯化温度为98℃。此时己酸乙酯酯化率达71%。     

Resistance of Listeria monocytogenes F2365 cells to synthetic gastric fluid is greater following growth on ready-to-eat deli turkey meat than in brain heart infusion broth

Ready-to-eat (RTE) deli meats have been categorized as high-risk foods for contraction of foodborne listeriosis. Several recent listeriosis outbreaks have been associated with the consumption of RTE deli turkey meat. In this study, we examined whether the growth of Listeria monocytogenes F2365 on commercially prepared RTE deli turkey meat causes listerial cells to become more resistant to inactivation by synthetic gastric fluid (SGF). Listerial cells grown on turkey meat to late logarithmic-early stationary phase were significantly more resistant to SGF at pH 7.0, 5.0, or 3.5 than listerial cells grown in brain heart infusion (BHI) broth. The pH was lower in the fluid in packages of turkey meat than in BHI broth (6.5 versus 7.5). However, listerial cells grown in BHI broth adjusted to a lower pH (6.0) did not exhibit enhanced resistance to SGF. The lesser resistance to SGF of listerial cells grown in BHI broth may be due, in part, to the presence of glucose (0.2%). This study indicates the environment presented by the growth of L. monocytogenes on deli turkey meat affects its ability to survive conditions it encounters in the gastrointestinal tract.     

Influence of lactate and acetate salt adaptation on Salmonella Typhimurium acid and heat resistance

The aim of the present study was to determine the survival of Salmonella Typhimurium adapted with sodium lactate (NaL), potassium lactate/sodium acetate mixture (KL/NaA) or sodium acetate (NaA) in simulated gastric fluid (SGF) and during heat treatment. NaL-, KL/NaA- and NaA-adapted cells were prepared by incubating in tryptic soy broth (TSB) containing these salts at 5, 5 and 3% (w/v) concentration levels, respectively, for 24 h at 37 °C. The Baranyi model was used to compare the growth kinetic parameters of adapted cells. The acid and heat resistance of adapted cells were determined by incubating in SGF (pH 2.04) at 37 °C and in TSB at 55.8, 57.8 and 59.8 °C, respectively. Adapted cells had significantly (P < 0.05) longer lag phase duration (LPD) and slower maximum growth rate (MGR) than non-adapted cells. The acid resistance of KL/NaA-adapted cells was not significantly (P > 0.05) different from that of non-adapted cells. NaL-adapted cells were more susceptible to the low pH environment, whereas NaA-adapted cells showed enhanced acid resistance compared to non-adapted and other adapted cells. Unlike acid resistance, both NaL- and NaA-adapted cells showed enhanced heat resistance with increased D-values, regardless of treatment temperatures. Thus, this study indicates that adaptation of S. Typhimurium to 5% NaL or 3% NaA could enhance their ability to survive thermal processes or in the human stomach, possibly increasing the risk of Salmonella outbreaks.     

Survival of Listeria monocytogenes strain H7762 and resistance to simulated gastric fluid following exposure to frankfurter exudate

Listeria monocytogenes strain H7762, a frankfurter isolate, was tested to determine whether it was able to survive at 4 degrees C in frankfurter pack fluid (exudate) and to determine whether food exposure affects its acid sensitivity. Cultures were sampled and tested for acid sensitivity by challenge with simulated gastric fluid (SGF). SGF challenges performed immediately after inoculation revealed that between 20 and 26% of the cells survived the full 30 min of SGF challenge regardless of whether the cells were inoculated into brain heart infusion broth (BHI) or exudate. After 2 days of incubation, cells exposed to both exudate and BHI had significantly decreased SGF resistance; however, the cells exposed to exudate were significantly more SGF resistant than cells exposed to BHI (after 15 min of SGF treatment, 33% of the exudate-exposed cells survived and 12% of the BHI-exposed cells survived). L. monocytogenes exposed to exudate had greater SGF resistance at all challenge times compared with BHI-exposed cells from day 2 through day 4. From days 8 to 15, exudate-exposed cells continued to have greater SGF resistance than BHI-exposed cells up to 10 min of SGF challenge but were as sensitive as the BHI-exposed cells at 20 to 30 min of challenge. By day 25, cells exposed to exudate were significantly more sensitive to SGF challenge than BHI-exposed cells. The survivor data generated from SGF challenges were modeled by a nonlinear regression analysis to calculate the underlying distribution of SGF resistance found in the challenged populations. These analyses indicated that L. monocytogenes exposed to exudate at 4 degrees C had a broader distribution of resistance to SGF compared with cells exposed to BHI at 4 degrees C. In addition, the mean time of death during SGF treatment was greater after exposure to exudate, indicating that cells exposed to exudate were more resistant to killing by SGF These data suggest that exposure to frankfurter exudate might render L. monocytogenes more able to survive the stomach environment during the initial stages of infection.     

Effects of in vitro digestion on the composition of flavonoids and antioxidant activities of the lotus leaf at different growth stages

The lotus leaf is rich in phenolic compounds and has good antioxidant activity. The effects of simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) digestions on the active substances and antioxidant activity of the lotus leaf in different growth stages (D25, D45 and D65) were investigated. The total phenolic content of D25 and D45 significantly increased by SGF digestion but not D65 compared to the DW treatment. However, SIF treatment saw markedly increased total phenolic content across all growth stages (D25, D45 and D65). Moreover, the total flavonoid content at all growth stages was increased by SIF digestion compared to SGF treatment. The pepsin and trypsin had different effects on the FRAP and ABTS (2, 2'‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonic acid)) antioxidant activities of the lotus leaf. The SGF digestion increased the FRAP antioxidant capacity of the lotus leaf, and SIF digestion increased the ABTS antioxidant capacity of the lotus leaf. The HPLC results showed that the main flavonoid compound in the lotus leaf was isoquercetin. This study provides a theoretical basis for the development and utilisation of the lotus leaf as an inexpensive natural and functional food ingredient.     

转高赖氨酸融合蛋白基因水稻蛋白消化稳定性

以我国自主培育的转高赖氨酸融合蛋白基因水稻(简称转GL基因水稻)为材料,参考中华人民共和国国家标准,通过体外模拟胃/肠液消化实验,研究转GL基因水稻蛋白的消化稳定性。结果表明：质量浓度为5g/L的总蛋白在胃液中2min内完全消化,质量浓度为2g/L的总蛋白在肠液中15s～2min内完全消化;而以5倍于国标规定的质量浓度进行消化时,总蛋白在模拟胃液中60min仍可观察到未降解片段,在模拟肠液中2min内则全部消化;两步法体外模拟消化结果,胃液中极难降解的蛋白片段在经肠液作用5min后,完全被降解。本研究表明,转GL基因水稻蛋白在模拟胃肠液中不具有消化稳定性。     

Enhanced alginate microspheres as means of oral delivery of bacteriophage for reducing Staphylococcus aureus intestinal carriage

Bacteriophage therapy could provide additional treatment for control of intestinal colonization of microbial pathogens. But, efficacy of its oral application may be reduced by sensitivity of certain phages to the low pH in the stomach. The aim of this study was to develop an improved encapsulation formulation with enhanced acid protection for oral delivery of Staphylococcus aureus phage K. Calcium carbonate microparticles were co-encapsulated with phage K into alginate microspheres and tested their efficacy for improved phage viability under in vitro acidic conditions. Free phage was completely destroyed when exposed to simulated gastric fluid (SGF) of pH 2.5. In contrast, alginate encapsulated phage K had a decrease of only 2.4 log units in viability when incubated for 1 h in SGF at pH 2.5. By adding calcium carbonate as an antacid excipient to the alginate microspheres, the survival of encapsulated phage K in SGF was significantly improved, with only a 0.17 log units reduction after 2 h exposure to SGF at pH 2.5. A number of protective agents including trehalose, sucrose, skim milk, and maltodextrin were also tested and were found to increase the viability of encapsulated phage K when subjected to drying. The protective effects varied with the type and concentration of each incorporated additives. The improved encapsulation formulation increased efficacy of phage K survival when exposed to the simulated gastric condition. Here we tested S. aureus phage K as a model but further improvement of the encapsulation formulation could provide a potential technology for reducing intestinal colonization of other pathogens.     

燕麦β-葡聚糖-表没食子儿茶素没食子酸酯复合物的体外稳定性

为研究燕麦β-葡聚糖-表没食子儿茶素没食子酸酯复合物在模拟胃肠液中的稳定性,采用真空冷冻干燥法制备燕麦β-葡聚糖-表没食子儿茶素没食子酸酯复合物。在模拟胃肠液中通过不同pH值和复合物质量浓度,探讨在胃肠液中pH值和复合物质量浓度对于复合物稳定性的影响。结果表明：在胃液和肠液中,pH值越低,复合物越稳定。由于进食会使得胃肠液的pH值增大,表明在禁食状态下复合物状态更稳定。复合物质量浓度越大,其在胃肠液中的稳定性越高,且达到在0.8 mg/L时,180 min孵育后复合物稳定性均达到80%以上。由此表明可以通过适当增大复合物的质量浓度来提高胃肠液的稳定性。     

Effects of modified atmosphere packaging with different sizes of silicon gum film windows on Salicornia bigelovii Torr. storage

BACKGROUND: Salicornia bigelovii Torr. is a promising seasonal plant using seawater production but perishable with short shelf‐life under ambient conditions. To develop a modified atmosphere packaging (MAP) for extension of S. bigelovii shelf‐life, a nonselective polyethylene/polyamide (PE/PA) bag combining different sizes (0.6, 1.0 and 1.4 cm²) of silicon gum film (SGF) windows was tested, and low‐density polyethylene (LDPE) and perforated (1.0 cm²) PE/PA bags were used as controls. RESULTS: During 36 days of storage at 2 °C, the equilibrium compositions of O₂/CO₂ in LDPE, SGF1 (0.6 cm²), SGF2 (1.0 cm²) and SGF3 (1.4 cm²) were 3.0–5.0/4.5–6.5 kPa, 0.5–1.5/8.5–19.0 kPa, 2.5–5.0/5.5–10.0 kPa, and 6.0–13.0/4.0–6.5 kPa, respectively. Passive MAP treatments improved the quality attributes of S. bigelovii during initial storage; however, the 0.6 cm² SGF package markedly accelerated deterioration over the latter storage. The 1.0 cm² SGF package was observed to provide the optimal condition for S. bigelovii storage. CONCLUSION: The results show that passive MAP with optimized sizes of SGF windows could be an effective technique for prolonging shelf‐life of S. bigelovii. Copyright © 2009 Society of Chemical Industry     

Changes in the phenolic contents and antioxidant activities of citrus peels from different cultivars after in vitro digestion

The aim of this study was to investigate the effects of in vitro digestion on the phenolic contents and antioxidant activities of citrus peels. Three different varieties of citrus peels (mandarin, ponkan and red tangerine) were treated with simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). The results showed that the SGF or SIF treatments of the citrus peels did not significantly increase the total phenolic content (TPC) or total flavonoid content (TFC), except for that of the TFC of ponkan peel treated with SGF. However, simulated in vitro digestion did improve the antioxidant activities measured with FRAP and ABTS methods. The effect of SGF was more positive than those of SIF for the FRAP assay, but the opposite was true for ABTS. Notably, both simulated digestion techniques decreased the DPPH free radical scavenging abilities. Simulated digestion in vitro changed the antioxidant activities of the citrus peels.     

Risk ranking of bioaccessible metals from fly ash dissolved in simulated lung and gut fluids

Power plant fly ash from two fuels, coal and a mixture of coal and shredded tires, were evaluated for trace metal solubility in simulated human lung and gut fluids (SLF and SGF, respectively) to estimate bioaccessibility. The proportion of bioaccessible to total metal ranged from zero (V) to 80% (Zn) for coal-derived ash in SLF and from 2 (Th) to 100% (Cu) for tire-derived fly ash in SGF. The tire-derived ash contained much more Zn. However, Zn ranked only 5th of the various toxic metals in SGF compared with international regulations for ingestion. On the basis of total concentrations, the metals closestto exceeding limits based on international regulations for inhalation were Cr, Pb, and Al. On dissolution in SLF, the most limiting metals were Pb, Cu, and Zn. For metals exposed to SGF there was no relative change in the top metal, Al, before and after dissolution but the second-ranked metal shifted from Pb to Ni. In most cases only a proportion of the total metal concentrations in either fly ash was soluble, and hence bioaccessible, in either biofluid. When considering the regulatory limits for inhalation of particulates, none of the metal concentrations measured were as hazardous as the fly ash particulates themselves. However, on the basis of the international ingestion regulations for Al, the maximum mass of fly ash that could be ingested is only 1 mg per day (10 mg based on bioaccessibility). It is possible that such a small mass could be consumed by exposed individuals or groups.