真菌发酵法产油脂的研究

本文以深黄被孢霉(Mortierellaisabellina)为试验菌株,采用发酵法生产油脂。采用单因素试验设计,研究了产脂培养基中碳源、氮源种类及其浓度对菌体生长和油脂积累的影响。试验确定酶法水解的玉米淀粉水解糖为最佳碳源,其最适添加浓度为100g/L;酵母膏为最适氮源,其最适添加浓度为3g/L。优化培养基条件下获得菌体生物量为12.350g/L,油脂含量为52.19%,油脂产量为6.4376g/L。但还有待于进一步优化培养基中的其它成分,以有效提高菌体油脂产量。     

响应面法优化皮状丝孢酵母产油脂发酵培养基

以皮状丝孢酵母（Trichosporon cutaneum）为出发菌株,对其产油脂的发酵培养基进行研究。以油脂产量为评价指标,通过单因素试验研究发酵培养基中的碳源、氮源、外源因子对油脂产量的影响,然后利用响应面试验对培养基进行优化。结果表明,最佳培养基配方为葡萄糖97.6 g/L、玉米浆干粉4.4 g/L、乙酸钠0.09 g/L。在该优化条件下,皮状丝孢酵母的油脂产量达到了14.4 g/L。     

啤酒生产废水培养斯达油脂酵母发酵油脂培养基的优化

以啤酒生产废水及添加一定的营养因子为发酵基质,采用单因素和正交试验设计对斯达油脂酵母(Lipomyces starkeyi 1809)发酵产油脂和COD降解的培养基进行了优化,并利用气相色谱分析比较了菌体油脂的脂肪酸组成.结果表明:最佳培养基组成为在啤酒生产废水中添加碳源和氮源的C/N为55∶1(即木糖28.88 g/L和硫酸铵1.0 g/L),FeCl3·6H2O3 mg/L,色醇150 μmol/L(在发酵36 h时添加),初始pH 5.5;用此培养基在摇床转速120 r/min、温度28℃下培养斯达油脂酵母120 h,菌体生物量、油脂产量、油脂含量和废水的COD降解率分别达到12.28 g/L、4.40 g/L、35.80%和50.32%,生物量和油脂产量比优化前分别提高了137.98%和117.82%,所产菌体油脂的不饱和脂肪酸指数( IUFA)达到63.95%,其中油酸的相对含量高达56.29%,比优化前提高了5.45%,优化效果显著.     

黏红酵母产油脂培养基的响应面优化

利用单因素试验和响应面设计相结合,对黏红酵母产油脂培养基进行了优化。单因素试验得到初步发酵培养基成分为葡萄糖、蛋白胨、KH2PO4。经响应面优化发现,当发酵培养基中葡萄糖含量为73.40g/L,蛋白胨含量为1.06 g/L,KH2PO4含量为3.56 g/L时,油脂产量的理论预测值可达到3.49 g/L,比优化前提高了13%。气相分析其油脂组成,多不饱和脂肪酸质量分数为26.97%。然后又对高产菌株的发酵特性进行研究,在10 d时,生物量和油脂产量达到最高,此时达到发酵终点,生物量为47.98 g/L(菌体湿重),油脂产量达到7.81 g/L。     

基于BPNN和GA的油脂酵母ZW-25发酵木薯水解液产油脂培养基优化研究

在均匀设计试验的基础上,将BP神经网络和遗传算法结合对油脂酵母ZW-25发酵木薯水解液产油脂的培养基进行了优化,得到的最优培养基配方为:木薯水解液稀释倍数1.0倍,蛋白胨0.6129g/L,NaNO_3 1.8687g/L,KH_2PO_4 1.1406g/L,MgSO_4·7H_2O 0.6379g/L。利用此培养基,在pH 7.0、接种量10%、培养温度25℃、摇床转速100 r/min的条件下将油脂酵母ZW-25振荡培养120h,生物量可达16.18g/L,油脂产量可达3.91g/L,菌株平均油脂含量可达24.17%。试验结果表明,将BP神经网络和遗传算法结合应用于培养基配方的优化是可行的。     

白灵菇产胞外多糖液体培养条件优化

以菌丝体生物量及发酵液中胞外多糖(exopolysaccharides,EPS)含量为指标对白灵菇产胞外多糖的液体培养基组成和发酵条件进行了优化。结果表明,最适碳源是麦芽糖,最适氮源是酵母膏。正交实验确定最佳培养基组成为麸皮200g/L,麦芽糖25g/L,酵母膏3g/L,KH2PO41g/L,MgSO·47H2O1g/L。最佳发酵条件为起始pH8.0,培养温度25℃,摇床转速160r/min,装液量100mL/250mL,接种量0.50cm2菌种块,发酵时间4d。在此条件下,白灵菇菌丝体生物量(0.413g/100mL)及胞外多糖含量(2403.2mg/L)分别是对照(0.177g/100mL和664.533mg/L)的2.3倍和3.6倍。     

菊芋提取液的皮状丝孢酵母发酵产油脂试验研究

以皮状丝孢酵母为产油脂菌种,研究其发酵菊糖提取液产油脂情况。首先研究了从菊芋中提取菊糖的条件,获得最适提取条件为:温度85℃,时间80 min,菊芋粉质量浓度70 g/L,在此最优提取条件下,菊糖提取率达95%;然后考察了pH值、接种量、培养温度和氮源对皮状丝孢酵母发酵菊糖提取液产油脂的影响,获得最优条件为:初始pH值5.5、培养温度30℃、接种量10%。在此优化条件下,5 L发酵罐分批扩大培养,其生物量、出油率和油脂得率分别达到13.93 g/L、34.73%和4.89 g/L。补充添加氮源对生物量、出油率和油脂得率的提高不显著。气相色谱法测定脂肪酸成分主要是C16和C18系列,其中80.2%以上是C16:0、C18:1和C18:2,尤其是C18:1(43%),其油酸、棕榈酸和亚油酸占总脂肪酸的比例和植物油脂非常接近。     

纤维质水解液发酵生产生物油脂

为提高发酵性丝孢酵母对纤维质水解液的适应性,对该菌株进行了驯化。利用驯化后的菌株发酵纤维质水解液生产生物油脂,并对纤维质水解液发酵体系进行优化。通过摇瓶培养试验,得到了优化体系。结果表明:驯化后的菌株发酵纤维质水解液的糖利用率比原来提高了37.2%,生物量提高了24.3%,油脂含量提高了18.3%,油脂浓度提高了45.6%。优化后的发酵条件为:初始糖浓度60~80 g/L,初始pH 6.0,质量比3∶1的酵母粉+(NH4)2SO4复合氮源。在该条件下,可得菌体生物量、油脂含量和油脂浓度分别为22.6 g/L、46.3%和10.5 g/L。同时对其生物油脂的成分进行了分析。     

油脂酵母CHB5产油脂发酵条件优化

以油脂酵母CHB5为实验材料,通过设计单因素试验,对各项与菌体产油脂有关的条件进行优化,确定摇瓶发酵最优产油脂条件:碳源,葡萄糖;氮源,硫酸铵;培养温度为25℃,接种量为10%,初始pH为7.0,发酵时间为96h。最后可得油脂产量为1.22g/L,油脂含量达30.5%;菌体生物量为5.93g/L。     

产谷胱甘肽重组巴斯德毕赤氏酵母发酵条件的研究

考察了培养基组成及培养条件对重组巴斯德毕赤氏酵母(Pichia pastoris)x-33(pGAPZA-gsh 1)合成谷胱甘肽(GSH)的影响。优化后的培养基组成为:甘油30g/L、蛋白胨40g/L、酵母膏9g/L、半胱氨酸0.36 g/L、KH_2PO_4 3g/L;培养条件为:自然pH、摇床转速200r/min、装液量为30mL/250mL、接种量为10%。在此优化条件下重组酵母的GSH产量是98.5mg/L,为优化前的2.33倍,生物量最大值达到19.6g/L。在5L发酵罐上进行放大实验,发酵结束后GSH产量、重组菌的生物量分别为97.9mg/L,18.7g/L与摇瓶发酵结果基本吻合。     

Arsenic content of some edible mushroom species

The arsenic contents of 162 fruit body samples of 37 common edible mushroom taxa were analyzed. The samples were gathered from different habitats of Hungary (mainly from mountains) between 1984 and 1999. The arsenic content of the samples was measured by the inductively coupled plasma spectrometry method. Very low [lower than 0.05 mg/kg dry matter (DM)] concentrations were found in the samples of 13 taxa, while higher (or very high) contents were quantified in other common taxa (the highest arsenic content was recorded in the fruit body of Laccaria amethysthea at 146.9 mg/kg DM). The species of eight genera (Agaricus, Calvatia, Collybia, Laccaria, Langermannia, Lepista, Lycoperdon, Macrolepiota) belong to the so-called accumulating taxa, and this tendency is evident on all habitats. This arsenic accumulation capability is found in two orders of Basidiomycetes (Agaricales and Gasteromycetales), which is to say this phenomenon occurs in the families Agaricaceae, Tricholomataceae and Gasteromycetaceae. The accumulating taxa found all have a saprotrophic type of nutrition; arsenic accumulation is not detectable in xilophagous or in mycorrhizal species. The consumption of the accumulating species found has only a low toxicological risk for three reasons: the consumed fresh fruit bodies contain about a tenfold lower arsenic level than the dried ones, the majority of arsenic occurs not in poisonous inorganic, but in less dangerous (or not poisonous) organic forms, and the frequency of consumption is low.     

Organization and localization of the dnaA and dnaK gene regions on the multichromosomal genome of Burkholderia multivorans ATCC 17616

The Burkholderia multivorans strain ATCC 17616 carries three circular chromosomes with sizes of 3.4, 2.5, and 0.9 Mb. To reveal the distribution and organization of the genes for fundamental cell functions on the genome of this bacterium, the dnaA and dnaK gene regions of ATCC 17616 were cloned and characterized. The gene organization of the dnaA region was rnpA-rmpH-dnaA-dnaN-gyrB with a single consensus DnaA-binding box (TTATCCACA) between the rmpH and dnaA genes. This intergenic region, however, did not work as an autonomously replicating sequence in ATCC 17616. On the other hand, the gene organization of the dnaK region was grpE-orf1 (gene for thioredoxin homologue)-dnaK-dnaJ-pabB (gene for p-aminobenzoate synthetase component homologue). A putative heat-shock promoter that showed good homology to the sigma32-dependent promoter consensus sequence in Escherichia coli was found upstream of the grpE gene, suggesting that these five genes constitute an operon. In M9 succinate minimal medium the dnaJ mutant grew more slowly than the wild-type strain, indicating that this operon is functional. Pulsed-field gel electrophoresis and Southern blot analyses indicated that both the dnaA and dnaK gene regions exist as single copies on the 3.4 Mb chromosome.     

Microbial profiles of frozen trimmings and silver sides prepared at Indian buffalo meat packing plants

To assess microbiological quality of buffalo meat trimmings (TT = 114) and silver sides (SS = 41), samples were collected from four different Indian meat packing plants. The aim of this study was: (i) to evaluate standard plate count (SPC), psychrotrophic count (PTC), Enterococcus feacalis count (EFC), Staphylococcus aureus count (SAC) and Escherichia coli count (ECC) and the presence of Salmonella spp. and Listeria monocytogenes; and (ii) also to determine vero toxic E. coli (VTEC) by polymerase chain reaction (PCR). TT samples had significantly higher (P < 0.001) SPC, PTC, EFC, and SAC than SS, while across the meat types there was no difference (P > 0.05) in ECC. E. coli was recovered from 32.4% TT and 19.5% SS samples. The prevalence rate of Salmonella spp. and L. monocytogenes in TT was 1.75% and 0.87%, respectively. But no SS sample was found to be positive for any of these two pathogens. VTEC was found in 2.58% of all the tested samples. This finding suggests that TT contain higher microbes but only small numbers of pathogens of latent zoonotic importance. The present study confirmed the importance of maintaining good process hygiene at meat plants for microbiological status of buffalo meat.     

Susceptibility of stored product insects to high concentrations of ozone at different exposure intervals

Ozone is a highly reactive gas with insecticidal activity. Past studies have indicated that ozone technology has potential as a management tool to control insect pests in bulk grain storage facilities. The objective of this study was to determine the efficacy of short periods of exposure to high ozone concentrations to kill all life stages of red flour beetle (Tribolium castaneum (Herbst)) (Coleoptera: Tenebrionidae), and Indianmeal moth (Plodia interpunctella (Hübner)) (Lepidoptera: Pyralidae), adult maize weevil (Sitophilus zeamais (Motsch.)) (Coleoptera: Curculionidae) and adult rice weevil (S. oryzae (L)) (Coleoptera: Curculionidae). Insects were treated with six ozone concentrations between 50 and 1800 ppm. The specific objective was to determine minimal time needed to attain 100% mortality. The most ozone-tolerant stages of T. castaneum were pupae and eggs, which required a treatment of 180 min at 1800 ppm ozone to reach 100% mortality. Eggs of P. interpunctella also required 180 min at 1800 ppm ozone to reach 100% mortality. Ozone treatments of 1800 ppm for 120 min and 1800 ppm for 60 min were required to kill all adult S. zeamais and adult S. oryzae, respectively. The results indicate that high ozone concentrations reduce the treatment times significantly over previously described results. Our results also provide new baseline information about insect tolerance to ozone treatment.     

Contamination with storage fungi of human food from Cameroon

In a mycological study, a total of 95 human food samples were investigated to evaluate the incidence of fungal contamination in Cameroon by conventional identification method and partly confirmed by DNA sequencing. The isolated fungal spp. were further studied to determine their toxigenic potentials. The investigation revealed the predominance of Aspergillus and Penicillium with 96% of samples contaminated with at least one species of these fungi, whereas the incidence of co-contamination of samples was 85%. Aspergillus flavus and Aspergillus parasiticus (Flavi section) were the most predominant species contaminating mainly maize and peanuts. In addition, P. crustosum and P. polonicum were the most common contaminants belonging to the genus Penicillium. On the other hand, A. ochraceus (Circumdati section) registered a low incidence rate of 5%, including other members of the Aspergillus group. Other members of the genera Rhizopus and Alternaria spp. were also registered in the study. A majority of fungal strains of A. ochraceus, A. parasiticus, P. crustosum and P. polonicum isolated were toxigenic, producing the mycotoxins tested for, while none was detected in cultures of A. fumigatus. The high incidence rate of fungi contamination coupled with their potentials in producing mycotoxins gives a strong indication that the samples tested may likely be contaminated with various mycotoxins. There is need for further study to assess the incidence of mycotoxins contamination in similar food samples.     

Effect of Zataria multiflora Boiss. essential oil and nisin on Salmonella typhimurium and Staphylococcus aureus in a food model system and on the bacterial cell membranes

The effects of different concentrations of Zataria multiflora Boiss. essential oil (EO: 0, 5, 15 and 30 μl 100 ml⁻¹) and nisin (N: 0, 0.25 and 0.5 μg ml⁻¹), temperatures (T: 25 and 8 °C), and storage times (up to 21 days) on growth of Salmonella typhimurium and Staphylococcus aureus in a commercial barley soup were evaluated in a factorial design study. The growth of S. typhimurium was significantly (P < 0.05) decreased by EO concentrations and their combinations with N concentrations at 8 °C. For S. aureus, the viable count was significantly (P < 0.05) inhibited by EO and N concentrations and their combinations, incubated at both storage temperatures. The mechanism of the antimicrobial action of EO, N, and their combinations against cell membranes of the tested organisms were also studied by measurement of the release of cell constituents and by the electronic microscopy observations of the cells. The significant increase of the cell constituents’ release of both organisms was observed as a result of treatments with EO and EO in combination with N. Electronic microscopy observations revealed that the cell membranes of S. typhimurium treated by EO and EO in combination with N were significantly damaged, while cells treated with only N looked similar to untreated cells. The electron micrographs of treated cells of S. aureus with EO, N, and their combination also showed important morphological damages and disrupted membranes.     

Formation of cereulide and enterotoxins by Bacillus cereus in fermented African locust beans

Afitin, iru and sonru are three spontaneously fermented African locust bean Benin condiments. The fermentation processes are exothermic, with temperatures mostly being above 40 °C. A total of 19 predominant Bacillus cereus isolates from afitin, iru and sonru, were investigated. The enterotoxin genes nhe (A, B, C) were present in all 19 isolates, the hbl (A, C, D) in one (afitin), and the cytK gene in three isolates (afitin). Levels of cytotoxicity to Vero cells and NheA production in BHI-broth was within the range of known diarrheal outbreak strains. Autoclaved cooked African locust beans inoculated with emetic (cereulide producing) B. cereus Ba18H2/RIF supported growth at 25, 30 and 40 °C with highly different maximum cereulide productions of 6 ± 5, 97 ± 3 and 0.04 ± 0.02 μg/g beans, respectively (48 h). For non-autoclaved cooked beans inoculated with 2, 4 and 6 log₁₀B. cereus Ba18H2/RIF spores/g beans, cereulide production was 5 ± 4, 64 ± 8 and 69 ± 34 μg/g beans, respectively at 24 h, while it was 70 ± 43, 92 ± 53 and 99 ± 31 μg/g at 48 h of fermentation at 30 °C. Even though high toxin levels were observed, to date there are no known reports on diarrhea or vomiting due to the consumption or afitin, iru and sonru in Benin, which also according to the present study is likely to be expected from the low levels of cereulide produced at 40 °C.     

Cloning and expression analysis of two catalase genes from Aspergillus oryzae

Fungi contain distinct genes encoding the same class of enzyme that are differentially regulated according to conditions. We cloned two catalase genes, catA and catB, from Aspergillus oryzae. The catA gene predicts a 747-amino-acid polypeptide sharing 81% identity with Aspergillus fumigatus catalase (catA) and 77% with Aspergillus nidulans catalase (catA). The catB gene predicts a 725-amino-acid polypeptide sharing 82% identity with A. fumigatus catalase (catB) and 75% with A. nidulans catalase (catB). However, the catA and catB genes share little homology (41%) with one another, suggesting that each gene belongs to a distinct gene family. Overexpression studies demonstrated that both genes encode a functional catalase. Promoter assays indicated that the catA gene is developmentally regulated as it was preferentially expressed in solid-state cultures undergoing sporulation. However, its expression was not affected by hydrogen peroxide treatment. Conversely, the catB gene was highly expressed under all culture conditions tested, and it was induced by hydrogen peroxide treatment. These results suggest that the catB gene may be mainly used for detoxification of oxidative stress while the catA gene may have another role such as chaperoning proteins in the spore.