利用紫外光降解花生油中黄曲霉毒素B1

目的评价紫外光照射对花生油中黄曲霉毒素B_1(AFB_1)的降解效果以及油品质的安全性的影响。方法采用波长为365 nm,功率100 W的紫外灯设备对花生油中的AFB_1进行照射处理后,分别利用高效液相色谱(HPLC)对花生油中的AFB_1的含量,滴定法对过氧化值,Ranciment法对氧化稳定性以及气相色谱法(GC)对不饱和脂肪酸的含量进行跟踪测定。结果结果表明,随着紫外照射时间的延长,花生油中黄曲霉毒素的含量逐渐降低,在25 min内降解率可达90%,过氧化值、不饱和脂肪酸的含量以及氧化稳定性这些品质指标数值均无明显变化。结论紫外光照射脱毒技术不仅对花生油中的AFB_1有很好的降解效果,并且对油品质无显著影响。     

Degradation of aflatoxin B1 by fungal laccase enzymes

The enzymatic degradation of aflatoxin B₁ (AFB₁) by white rot fungi through laccase production was investigated in different liquid media. A significant (P < 0.0001) correlation was observed between laccase activity and AFB₁ degradation exhibited by representatives of Peniophora and Pleurotus ostreatus cultivated in minimal salts (MSM) (r = 0.93) and mineral salts — malt extract (MSB–MEB) (r = 0.77) liquid media. Peniophora sp. SCC0152 cultured in MSB–MEB liquid medium supplemented with veratryl alcohol and sugarcane bagasse showed high laccase activity (496 U/L), as well as 40.45% AFB₁ degradation as monitored using high performance liquid chromatography. P. ostreatus St2-3 cultivated in MSM liquid medium supplemented with veratryl alcohol resulted in laccase activity of 416.39 U/L and 35.90% degradation of AFB₁. Aflatoxin B₁ was significantly (P < 0.0001) degraded when treated with pure laccase enzyme from Trametes versicolor (1 U/ml, 87.34%) and recombinant laccase produced by Aspergillus niger D15-Lcc2#3 (118 U/L, 55%). Aflatoxin B₁ degradation by laccase enzyme from T. versicolor and recombinant laccase enzyme produced by A. niger D15-Lcc2#3 coincided with significant (P < 0.001) loss of mutagenicity of AFB₁, as evaluated in the Salmonella typhimurium mutagenicity assay. The degradation of AFB₁ by white rot fungi could be an important bio-control measure to reduce the level of this mycotoxin in food commodities.     

Degradation of aflatoxin B1 in peanut meal by electron beam irradiation

The effects and safety of electron beam irradiation (EBI) treatment on the detoxification of aflatoxin B₁ (AFB₁) in the peanut meal were evaluated in this article. The AFB₁ degradation was predominantly affected by both initial AFB₁ and water concentrations. The degradation of AFB₁ in the selected concentrations (0.5–5 ppm) was proven to follow pseudo first-order reaction kinetics (R² > 0.95). The AFB₁ degradation was faster when the initial concentration was 5 ppm and the moisture content was 21.47%, in comparison with the initial concentration of 1 ppm and 0.5 ppm and the moisture content of 14.32% and 8.74%, respectively. The Ames and cytotoxicity tests were employed to evaluate the residual toxicity of EBI-treated peanut meal. The mutagenic activity of EB-treated samples was completely lost compared with that of untreated samples and the degradation products in peanut meal has almost no cell toxicity.     

低温射频等离子体降解农产品中黄曲霉毒素B1效果的研究

研究采用低温射频等离子体技术处理农产品中的黄曲霉毒素B_1(AFB_1),并通过HPLC分析其中黄曲霉毒素的降解率。结果表明,等离子体降解农产品中AFB_1效果显著,150 W等离子处理500 s,花生中AFB_1的降解率达到88.3%,玉米中AFB_1的降解率达到92.2%。等离子体功率越大,处理时间越长,AFB_1的降解率越大。在相同降解条件下,不同细度样品中AFB_1降解率有显著差异。花生、玉米粗粉试样中AFB_1的降解率低于花生、玉米细粉试样。     

常压等离子体降解黄曲霉毒素B1的效果研究

采用常压等离子体对乙腈中黄曲霉毒素B_1(AFB_1)进行降解。利用单因素实验,考察了放电间距、处理电压、放电时间以及AFB_1初始浓度对AFB_1降解率的影响,在此基础上进行了BoxBehnken的实验设计,选取AFB_1降解率作为响应值,优化了AFB_1的降解条件。结果表明:各因素对AFB_1降解率的影响大小依次为处理电压放电时间AFB_1初始浓度。常压等离子降解AFB_1的最佳工艺条件为处理电压170 V、放电时间236 s、AFB_1初始浓度5 mg/L、放电间距2 cm。AFB_1的降解率高达92.45%,与预测值93.94%相接近,偏差为1.49%。     

乳过氧化物酶的抑菌试验

分别采用分光光度法、菌体量法以及孔扩散法研究了乳过氧化物酶(LP)的抑菌作用。结果表明,LP对常见的几种食品污染菌均有一定的抑制作用,其中,LP对黄曲霉的抑制作用最显著,4μg/mL就能完全抑制其生长;在中性偏酸性环境中的抑菌活性比碱性环境的抑菌活性强;一定温度内处理不影响LP的抑菌活性;在中性条件下抑制供试革兰阴性菌、霉菌和酵母菌的能力强于Nisin,且LP和Nisin具有协同抗菌作用。     

Factors affecting lactoperoxidase activity

The extent to which lactoperoxidase (LP) activity was affected while varying the concentration of various compounds normally present in the reaction medium was investigated. LP activity increased with increasing concentrations of 2,2'-azino-bis-3-ethylbenz-thiazoline-6-sulphonic acid (ABTS) but decreased with increasing thiocyanate concentrations. Maximum activity was at 0.1 mm for peroxide. Activity increased in the presence of lactose, whey protein concentrate, sodium, magnesium and calcium chlorides, but decreased in the presence of casein. Activity was similar in either acetate or phosphate buffers but higher in either citrate or succinate buffers. These compounds influence LP activity and should be considered when optimum activity conditions are being established.     

One-step purification of lactoperoxidase from bovine milk by affinity chromatography

Sulphanilamide was determined to be a new inhibitor of lactoperoxidase (LPO) with an IC₅₀ of 0.848.10⁻⁵ M. The K_i for sulphanilamide was determined to be 3.57.10⁻⁵ M and sulphanilamide showed competitive inhibition, which makes it a suitable ligand for constructing a Sepharose 4B-l-tyrosine affinity matrix. The affinity matrix was synthesised by coupling sulphanilamide as the ligand and l-tyrosine as the spacer arm to a cyanogen bromide (CNBr)-activated-Sepharose 4B matrix. Lactoperoxidase was purified 409-fold from the synthesized affinity matrix in a single step, with a yield of 62.3% and a specific activity of 40.9 EU/mg protein. The enzyme activity was measured using ABTS as a chromogenic substrate (pH 6.0). The degree of LPO purification was monitored by SDS–PAGE and its R_z (A₄₁₂/A₂₈₀) value. The R_z value for the purified LPO was found to be 0.7. Maximum binding was achieved and K_m and V_max values were determined.     

低温放电等离子体处理对黄曲霉毒素B1的降解效果及对巴旦木仁品质的影响研究

目的 研究低温放电等离子体对黄曲霉毒素B1 (aflatoxin B1,AFB1)的降解效果及对巴旦木仁品质的影响。方法 以黄曲霉毒素B1为目标毒素,首先研究了低温放电等离子体在不同处理时间、不同电压和不同初始浓度下对目标毒素的降解效果,其次评估了低温放电等离子体处理对巴旦木仁中的理化指标及色差和香气成分的影响。结果 低温放电等离子体不同处理条件对AFB1的降解效果明显,以75 kV低温放电等离子体处理5 min,50 μg/mL的AFB1的降解率为95.03%。低温放电等离子体处理对巴旦木仁的理化性质、蛋白浓度、色差均未出现显著性差异(P>0.05),巴旦木仁的香气成分也得到了良好的保持。结论 低温放电等离子体对AFB1具有较明显的降解效果,且对巴旦木仁的品质无影响。这一研究有望为干果中真菌毒素的降解提供新思路,为保证干果的食品安全提供新途径。     

Inhibition of aflatoxin formation by some spices

The effects of black pepper, cinnamon, peppermint, cumin, ginger and clove on growth and aflatoxin formation of Aspergillus flavus were studied in rice powdercorn steep (RC) medium. The effects of the first five spices were judged to be inhibition of aflatoxin formation rather than of mycelial growth. Clove completely inhibited both mycelial growth and aflatoxin formation at a concentration above 0.1%. No aflatoxin was produced when cumin and mint levels of 5% and 10% were used. Black pepper and ginger levels of 10% decreased aflatoxin formation by 100%. Higher concentrations of cinnamon, mint, cumin and ginger stimulated mycelial growth.     

Antimicrobial effect of the lactoperoxidase system in milk activated by immobilized enzymes

Immobilized lactase and glucose oxidase were used to produce H₂O₂ to activate the lactoperoxidase system in milk. The enzymes were immobilized on nylon pellets. With a ratio of 35 g of catalyst/L of milk, a concentration of 0.75 mM was produced in 3 min. Raw milk treatment with the catalyst reduced coliforms by 79%; Staphylococcus aureus reduction was 68%, psychrotrophs 91%, and fungi 100%. Results were similar when milk was treated by addition of H₂O₂. Thiocyanate was not limiting because addition of NaSCN did not increase the effectiveness of the lactoperoxidase system.

The stability of the catalyst was poor when successive treatments were applied to milk, having lost one half of the activity every eight determinations. Activation of the lactoperoxidase system by immobilized enzymes could be of interest if stability could be ensured.     

Antimicrobial and physical properties of edible chitosan films enhanced by lactoperoxidase system

Effects of lactoperoxidase system (LPOS) incorporated directly into chitosan films at different concentrations (0.5, 1 and 1.5%) were studied. Films obtained were tested on the inhibition of phytopathogenic strains such as Xanthomonas campestris pv. Mangifera indica, Colletotrichum gloeosporioides (C. 64, C. 4612 and C. 62) and Lasiodiplodia theobromae ngr 05A. Water vapor permeability and mechanical properties of films with LPOS and/or not iodine were also studied. Antibacterial effect obtained by disc diameter technique indicated that chitosan concentration at 1 and 1.5% (w/w) incorporated with LPOS and/or not iodine inhibited higher X. campestris pv. M. indica than chitosan film alone or at low concentrated of 0.5% incorporated by LPOS. The antimicrobial technique using puncture gave very good information on the antifungal effect and on the variability in susceptibility of strains of fungi. C. gloeosporioides C64 and L. theobromae were inhibited completely by 1 and 1.5% chitosan incorporated by LPOS contained or not iodine, while C. gloeosporioides C4612 was sensitive to the presence of iodine and C62 were resistant strains. The properties of chitosan films were not significantly changed by the incorporation of the enzyme system.     

牦牛乳过氧化物酶体系及其酶热动力学研究

以麦洼牦牛乳为原料,分析了其乳过氧化物酶体系相关成分的浓度,并研究了不同温度下牦牛乳过氧化物酶(LPO)的热稳定性,利用一级反应动力学模型和阿仑尼乌斯方程,分析了牦牛乳中LPO在63～67℃热变性过程中的动力学参数。结果表明,牦牛乳LPO在63℃时具有较高的热稳定性。热动力学分析表明,牦牛乳LPO在63、65和67℃的D值分别为207.43、33.41、13.42min,在63～67℃范围内的Z值和表观活化能(Ea)分别为3.36℃和557.20kJ/mol。     

Binding of aflatoxin B1 by probiotic bacteria

The ability of six probiotic bacteria to bind a common food carcinogen, aflatoxin B₁, was assessed. The studied strains included Lactobacillus strains and one Bifidobacterium strain. The strains were incubated in vitro with alfatoxin B₁ and the toxin residue in the supernatant was measured using high‐performance liquid chromatography. The aflatoxin‐binding capacity of the strains was found to range from 5.8 to 31.3%. The results further support the observation that a number of probiotic bacteria are able to bind specific dietary contaminants. Although the extent of binding varies depending on the bacterial strain used, the data may explain some of the antimutagenic and anticarcinogenic effects of probiotic micro‐organisms. © 2000 Society of Chemical Industry     

Inhibition of foodborne bacteria by the lactoperoxidase system in a beef cube system

Biopreservatives are being developed to inhibit the growth of foodborne pathogens and thus improve food safety. The lactoperoxidase system (LPS) is a naturally occurring system that has potential for use as an antimicrobial agent in foods. Growth of single strains of the pathogens Staphylococcus aureus, Listeria monocytogenes, Escherichia coli O157:H7, Salmonella enterica subsp. enterica serovar Typhimurium, Yersinia enterocolitica, Pseudomonas aeruginosa and beef microflora were assessed on LPS-treated meat surfaces in an experimental system. Beef cubes inoculated with approximately 10(4) cfu cm(-2) of bacteria were treated with the LPS and incubated at 37 degrees C for 24 h, 12 degrees C for 7 days or in a chilling regime: 12 to -1 degrees C over 1 week and held at -1 degrees C for 4 weeks. Treatment with LPS was more effective at storage temperatures non-permissive for rapid bacterial growth with strong inhibition of growth achieved on LPS-treated cubes at 12 degrees C and reduction in pathogen viable counts at chilling temperatures. At chilling temperatures, the LPS inhibited the growth of native pseudomonads but did not prevent the development of native lactic acid bacteria.     

Inhibition of bacterial foodborne pathogens by the lactoperoxidase system in combination with monolaurin

The lactoperoxidase system (LPS) and monolaurin (ML) are potential natural antimicrobial agents for use in foods. The LPS is considered to have greatest activity against Gram-negative bacteria while ML is usually considered to have greatest activity against Gram-positive bacteria. An LPS-ML combination system (utilizing lactoperoxidase (LPX) in the range 5-200 mg kg(-1) and ML in the range 50-1,000 ppm) inhibited growth of Escherichia coli O157:H7 and Staphylococcus aureus. Growth of S. aureus was inhibited more strongly in broth than in milk, in milk than in ground beef A similar pattern was observed for E. coli O157:H7, though enhanced inhibition by LPS-ML systems over that obtained in comparable LPS only systems was not observed in ground beef The inhibitory action of the LPS in combination with other lipids was also examined, with progressively weaker inhibition observed in combinations including palmitoleic acid, monopalmitolein, lauric acid, caprylic acid, and sodium lauryl sulphate.