香芹酮/羟丙基-β-环糊精包合物的制备、表征及对硫色镰刀菌的抑制作用

为开发新型马铃薯抑菌保鲜材料,本研究通过共蒸发-冷冻干燥法制备出香芹酮/羟丙基-β-环糊精包合物,采用相溶解度法测定其稳定常数,并采用紫外光谱、¹H NMR光谱、热重分析、扫描电镜及X-射线衍射分析的方法进行表征,探究香芹酮/羟丙基-β-环糊精包合物对硫色镰刀菌的抑制效果。结果表明,香芹酮与羟丙基-β-环糊精成功生成了主客体比为1∶1的包合物,产率达到93.6%,表观稳定常数为409.39 L·mol^-1。生成包合物后,香芹酮的水溶性和热稳定性都明显增强,且对硫色镰刀菌具有明显的抑制作用,EC50值为3.11 mmol·L^-1。因此,将挥发性液体香芹酮制备成羟丙基-β-环糊精固体包合物可行,且对马铃薯贮藏病害干腐病病原菌硫色镰刀菌具有较强的抗菌活性。本研究结果为开发新型马铃薯抑菌保鲜材料提供了理论依据。     

反式-2-己烯醛对猕猴桃贮藏过程扩展青霉生长的抑制作用

为研究反式-2-己烯醛对扩展青霉生长及展青霉素产生的抑制作用。选取反式-2-己烯醛和研究报道的8种具有抑菌效果的物质对5株扩展青霉进行体外抑菌试验,研究反式-2-己烯醛的抑菌效果并测定其最小抑菌浓度,然后进行猕猴桃活体试验,通过测定硬度、可溶性固形物、可滴定酸、维生素C、pH值等指标研究反式-2-己烯醛对猕猴桃品质的影响,并采用高效液相检测抑菌试验前后猕猴桃活体中展青霉素含量,最终通过扫面电子显微镜观察反式-2-己烯醛对5株扩展青霉形态的影响。结果反式-2-己烯醛与8种抑菌物质相比,反式-2-己烯醛抑菌效果最好,能够完全抑制5株扩展青霉生长且得到对5株试验菌的最小抑菌浓度(MIC,minimuminhibitoryconcentration);反式-2-己烯醛能够极显著降低扩展青霉对猕猴桃果实硬度、可滴定酸、维生素C的的影响(P0.01),并且对猕猴桃硬度、可溶性固形物、pH值和还原糖及维生素C含量等没有极显著影响(P0.01),极显著降低了染菌猕猴桃果实的腐烂率(P0.01),较好的保持了猕猴桃品质,经反式-2-己烯醛处理的染菌猕猴桃均没有展青霉素检出;扫面电子显微镜显示5株试验菌出现菌丝皱缩、折叠、干瘪,孢子生成减少现象。研究反式-2-己烯醛对扩展青霉生长及展青霉素产生均具有很好的抑制作用,可为开发具有抑菌作用可替代农药的天然产物提供理论基础。     

桔梅奇酵母液体制剂的制备及其在柑橘果实上的应用

桔梅奇酵母是分离自柑橘果园叶面的新种酵母,可有效控制柑橘果实采后青霉病、绿霉病和酸腐病,前景广阔且可替代化学杀菌剂。但生物防治剂效果不稳定、生防作用机制不明确等因素导致拮抗酵母商业化应用的成功率较低。因此开发货架期较长且防治效果稳定的拮抗酵母生物制剂是实现桔梅奇酵母商业化的关键。该研究以桔梅奇酵母为研究对象,制备以桔梅奇酵母为主要活性成分的液体制剂,并探究制剂对柑橘果实采后主要病害的控制效果。结果表明：经单因素试验和响应面优化试验得到的保护剂配方：海藻糖19.74%、谷氨酸钠1.05%、吐温80 4.24%、脯氨酸1.11%对酵母的保护效果最好,酵母存活率可从5.02%提高到54.96%。贮藏稳定性试验表明,当温度低于10 ℃时,在贮藏30 d后酵母存活率仍大于60%,适当降低温度有利于延长制剂的货架期。离体试验发现,与新鲜酵母相比,液体制剂对柑橘采后病原菌的抑制作用无显著变化（P>0.05）,抑菌圈可达到12 mm以上。在柑橘果实上能够有效控制柑橘果实采后青霉病、绿霉病、酸腐病和炭疽病,可将发病率降低25.00%～48.33%。综上,对桔梅奇酵母进行制剂化处理后能够有效保留其细胞活力和生防效力,以桔梅奇酵母为主要活性成分制备的液体制剂对柑橘采后病害具有良好的控制效果。     

基于桔梅奇酵母冻干粉制备可湿性粉剂及其在柑橘上的应用

确保生防制剂的贮藏稳定性是保证微生物种群数量和生物防治效果不受影响的关键因素。为开发货架期较长且防治效果稳定的拮抗酵母生物制剂,该研究通过助剂的单因素筛选试验和混料试验研制出一种基于桔梅奇酵母冻干粉制备得到可湿性粉剂,经过升温加速贮藏试验预测制剂的贮藏稳定性,同时评价了制剂在离体和活体条件下对柑橘采后主要病害的控制效果。试验结果表明：试验筛选得到制剂优化配方的质量分数分别为皂角粉5.69%、亚甲基二萘磺酸钠8.74%、母粉85.57%。冻干制剂中酵母活菌数可达到4.72×108 CFU/g,贮藏稳定性试验表明,冻干制剂的贮藏稳定性较好,预测在4℃贮藏后制剂中酵母活菌数约为4.6×108 CFU/g。适当降低贮藏温度可延长冻干制剂贮藏期。离体试验发现,与新鲜酵母相比,液体制剂对柑橘采后病原菌的抑制作用无显著变化,抑菌圈可达到9 mm以上。在柑橘果实上能够有效控制柑橘果实采后青霉病、绿霉病、酸腐病和炭疽病,可将发病率降低约40%～70%。综上,对桔梅奇酵母进行制剂化能够延长其货架期并维持其对柑橘果实采后病害防治效果。     

热水处理对草莓采后病害的抑制作用及对贮藏品质的影响

研究热水处理对草莓采后病害的抑制作用及对贮藏品质的影响。在预试验的基础上,分别采用38℃、15 min,44℃、10 min,48℃、5 min对新鲜草莓进行热处理,处理后的草莓置于常温下((20±1)℃),每隔12 h观察草莓的腐烂情况,并对草莓品质指标进行检测。结果表明：热水处理能够有效地起到抑制草莓采后病害的作用,热水处理对草莓的失重率、硬度、可滴定酸度等水果品质没有显著的不利影响,热水处理后草莓的细胞膜透性与对照相比没有升高。     

裸脚菇0612-9提取物对柑橘青、绿霉的抑菌活性及作用机制

为探索裸脚菇0612-9提取物(GSFE)对意大利青霉(Penicillium italicum)和指状青霉(P. digitatum)的抑菌活性和作用机理,本试验采用菌丝生长速率法测定GSFE对意大利青霉和指状青霉的抑菌活性,分析GSFE处理后意大利青霉和指状青霉的菌丝形态、细胞膜通透性和麦角固醇含量变化情况,并通过靶位竞争剂试验探究GSFE的抑菌机理。结果表明,GSFE对意大利青霉和指状青霉的半有效浓度(EC₅₀)值分别为116.76和147.74 μg·mL^-1,最小抑菌浓度(MIC)均为200 μg·mL^-1;经质量浓度为EC₅₀和MIC的GSFE处理后意大利青霉和指状青霉菌丝体均发生严重的皱缩、干瘪,并且胞内呈空泡状结构,细胞质大量减少,胞外相对电导率显著上升,菌体内核酸、可溶性蛋白等胞内物质含量显著降低。这表明意大利青霉和指状青霉细胞膜通透性增加,胞内物质外泄,细胞膜完整性遭到破坏。经浓度为EC₅₀的GSFE处理的意大利青霉和指状青霉菌丝体,其麦角固醇含量均显著降低,分别仅为对照组的17.92%和20.13%。由此可见,GSFE主要通过抑制意大利青霉和指状青霉菌丝体的麦角固醇合成而损伤病原真菌细胞膜的结构和功能。本研究结果为后续开发新型微生物源柑橘采后保鲜剂提供了设计思路。     

Stability of natamycin and its cyclodextrin inclusion complexes in aqueous solution

Aqueous solutions of natamycin and its beta-cyclodextrin (beta-CD), hydroxypropyl beta-cyclodextrin, and gamma-cyclodextrin (gamma-CD) inclusion complexes were completely degraded after 24 h of exposure to 1000 lx fluorescent lighting at 4 degrees C. After 14 days of storage in darkness at 4 degrees C, 92.2% of natamycin remained in active form. The natamycin:beta-CD complex and natamycin:gamma-CD complex were significantly more stable (p < 0.05) than natamycin in its free state in aqueous solutions stored in darkness at 4 degrees C. Clear poly(ethylene terephthalate) packaging with a UV light absorber allowed 85.0% of natamycin to remain after 14 days of storage under 1000 lx fluorescent lighting at 4 degrees C. Natamycin:cyclodextrin complexes can be dissociated for analysis in methanol/water/acetic acid, 60:40:5, v/v/v. Natamycin and its complexes in dissociated form were quantified by reverse phase HPLC with detection by photodiode array at 304 nm.     

Inhibitory effects of citrus essential oils and their components on the formation of N-nitrosodimethylamine

Twenty-eight kinds of citrus essential oils and their components were studied for inhibitory effects on the formation of N-nitrosodimethylamine (NDMA). The reaction mixture consisted of dimethylamine and sodium nitrite adjusted at pH 3.6, in addition to essential oils and an emulsifying agent. The quantification was determined by high-performance liquid chromatography monitored at 220 nm. All of the essential oils inhibited the formation of NDMA in the range of 20-85%. The oils of ujukitsu (Citrus ujukitsu Hort. ex Shirai), yuzu (C. junos Tanaka), mochiyu (C. inflata Hort. ex Tanaka), and ponkan (C. reticulata Blanco cv. F-2426) inhibited the formation of NDMA much more effectively than other citrus oils. The inhibitory proportions of components of citrus essential oils such as myrcene, alpha-terpinene, and terpinolene were as high as 80%.     

Tyrosinase inhibitory activity of citrus essential oils

Thirteen kinds of citrus essential oils and their volatile flavor constituents were investigated for tyrosinase inhibitory activity. Eureka lemon, Lisbon lemon, Keraji, and Kiyookadaidai significantly inhibited the oxidation of L-dihydroxy phenylalanine (L-DOPA) by mushroom tyrosinase. Citral and myrcene among volatile flavor constituents of citrus essential oils exhibited tyrosinase inhibitory activities with Ki values of 0.318 and 2.38 mM, respectively. The inhibition kinetics analyzed by a Lineweaver-Burk plot indicated that citral is a noncompetitive inhibitor and myrcene is a competitive inhibitor. These results indicated that citral and myrcene are responsible for the tyrosinase inhibitory activity of citrus essential oils.     

Formation of natamycin:cyclodextrin inclusion complexes and their characterization

Natamycin is a broad spectrum antimycotic with very low water solubility, which is used to extend the shelf life of shredded cheese products. beta-Cyclodextrin (beta-CD), hydroxypropyl beta-cyclodextrin (HP beta-CD), and gamma-cyclodextrin (gamma-CD) were found to form inclusion complexes with natamycin in aqueous solution. The increase in solubility of natamycin with added beta-CD was observed to be linear (type A(L) phase solubility diagram). The 1:1 stability constant of natamycin:beta-CD complex was estimated from its phase solubility diagram to be 1010 M(-1). The phase solubility diagrams of both gamma-CD and HP beta-CD exhibited negative deviation from linearity (type A(N) diagram) and, therefore, did not allow the estimation of binding constants. The water solubility of natamycin was increased 16-fold, 73-fold, and 152-fold with beta-CD, gamma-CD, and HP beta-CD, respectively. The natamycin:CD inclusion complexes resulted in in vitro antifungal activity nearly equivalent to that of natamycin in its free state.     

Contamination of Italian citrus essential oils: presence of chloroparaffin

In this study, the contamination by chloroparaffin of Sicilian and Calabrian citrus essential oils, produced in the crop years 1994-1996, was investigated. The analyses were carried out on 102 lemon oils, 98 orange oils, and 96 mandarin oils, using a dual-channel GC-ECD. It was found that 53% of lemon oil, 33% of orange oil, and 38% of mandarin oil samples were contaminated. The mean contamination levels were 7.1 ppm (lemon), 2.5 ppm (orange), and 5.3 ppm (mandarin). The highest concentration of chloroparaffin found was 60 ppm in a lemon oil sample.     

Comparison of fast and conventional GC analysis for citrus essential oils

This investigation concerns the application of fast GC in the analysis of essential oils. These are complex matrixes that usually undergo GC separation with conventional methods involving long columns, slow programmed temperature rates, and consequently, a high cost in terms of time. Fast GC techniques are based on the use of narrow bore capillary columns that allow the achievement of high-speed separations on complex samples while maintaining excellent resolution. This work saw the application of two methods on five different citrus essential oils and the comparison of all the results obtained.     

Production process contamination of citrus essential oils by plastic materials

Twelve samples of plastic materials employed in the industrial extraction of citrus essential oils were analyzed for the presence of phosphorated plasticizers, chloroparaffins, and phthalate esters. The samples tested were found to release these contaminants into the essential oils during the production process. Contamination tests were carried out using dichloromethane and uncontaminated samples of citrus essential oils as extractants. The extracts were analyzed by HRGC/FPD, ECD, and MS. Only one sample of plastic material was found to release triaryl phosphates, 5 samples released chloroparaffins, 6 released diisobutyl phthalate, and 8 released bis(2-ethylhexyl) phthalate. Significantly larger quantities of contaminants were released by new plastic parts than by used plastic parts.     

Lipolytic effects of citrus peel oils and their components

This study was conducted to determine the lipolytic effects of eight kinds of citrus peel oils and their components. All of the citrus peel oils revealed lipolytic effects on olive oil model solution ranging from 10.9 to 73.8%. Hakyul (Citrus natsudaidai Hayata) showed the highest lipolytic effect (73.8%), followed by yuza (Citrus junos Sieb. ex Tanaka, 68.1%) and lemon (Citrus limonium, 63.4%), and their effects were comparable with or stronger than that of 5 mM raspberry ketone (p < 0.05). Among 17 authentic compounds relating to citrus peel oils, octanal (78.6%) showed the highest lipolytic effect, followed by gamma-terpinene (76.3%), limonene (75%), terpinen-4-ol (70.7%), nerol (69.9%), p-cymene (67.7%), and geranyl acetate (67.2%), and their effects were stronger than that of 5 mM raspberry ketone (p < 0.05). Ethyl acetate, alpha-pinene, myrcene, citronellal, linallyl acetate, and citronellol exhibited poor lipolytic effect in the model solution. Lipolytic effect was found to be high when the oils included a higher content of gamma-terpinene and p-cymene. Limonene showed potential lipolytic effect, and its effect is likely to be enhanced by the presence of gamma-terpinene and p-cymene. It is considered that monoterpene hydrocarbons consisting of one or two double bonds would have stronger lipolytic effect than those having three double bonds.     

Contamination of Italian citrus essential oils: presence of phthalate esters.

Contamination by phthalate esters of Sicilian and Calabrian citrus essential oils, produced in the crop years 1994-1996, was investigated using a GC-MS system with direct injection of the samples. A total of 35 lemon oils, 31 orange oils, and 21 mandarin oils were analyzed. Diisobutyl phthalate and/or bis(2-ethylhexyl) phthalate were found in almost all samples, while di-n-butyl phthalate was present in 8. Concentrations up to a maximum of 62 ppm were found for diisobutyl phthalate and up to a maximum of 29.9 ppm for bis(2-ethylhexyl) phthalate.     

Enhancement of plant essential oils' aqueous solubility and stability using alpha and beta cyclodextrin

Sodium benzoate has been shown to produce benzene in combination with ascorbic acid. This has led to research for safe alternatives from plant essential oils and parabens that have shown some antimicrobial activity, but many of these compounds exhibit poor solubility in aqueous solutions. Cyclodextrins can increase the solubility of many compounds. This work aimed to investigate the solubility of 23 plant essential oils and 4 parabens in water and an apple juice medium. Four of these compounds were chosen for their low aqueous solubility to determine if complexing the compound with α- and β-cyclodextrin would increase solubility. Three of the complexes were dissolved in an acidified aqueous solution and then studied in glass and polyethylene terephthalate (PET) to determine if storage material would affect the stability. Solubility of the 27 compounds in distilled water ranged from 1.6 mg/L to 2460.6 mg/L and the solubility of 18 of the compounds decreased from 2.5 to 84.7% in apple juice medium (pH = 3.4, 12-13 °Brix). Complexation with cyclodextrin dramatically increased the solubility of the compounds, up to 10-fold. Packaging material had no effect on concentration of compounds present over 7 days. Cyclodextrins were able to increase solubility of these compounds to more suitable concentrations, and may lead to viable natural alternatives to sodium benzoate.