Effect ofβ-lonone onaspergillus flavus andaspergillus parasiticus growth,sporulation, morphology and aflatoxin production

The ketoneβ-ionone is reported to be one of the naturally occurring volatile metabolites of developing corn ears. In testing the effects of volatile compounds onAspergillus flavus andA. parasiticus, we found thatβ-ionone applied to the surface of PDA plates had a striking inhibition of growth and sporulation of these fungi. The colonies were restricted, remained buff-colored and had little or no sporulation. There were major effects on the morphology of the asexual reproductive structures. The conidiophore development was arrested and normal sporulation did not occur. Mycelial transfers from these atypical cultures to potato dextrose agar had normal growth and conidia. Incorporation ofβ-ionone at levels of 10-1000μL/L, in liquid media seeded with spore suspensions ofA. parasiticus (NRRL 2999) severely depressed aflatoxin accumulation in shake culture.     

Effects of oilseed storage proteins on aflatoxin production by aspergillus flavus

Potential involvement of seed storage proteins in susceptibility to aflatoxin contamination was assessed with in vitro tests. Initially, two oilseed storage proteins [cottonseed storage protein (CSP) and zein] were compared with bovine serum albumin (BSA) and collagen. Supplementation of a complete defined medium with either oilseed storage protein resulted in significantly more aflatoxin production by Aspergillus flavus than supplementation with either BSA or collagen. Little or no aflatoxin was produced when either BSA, CSP, or zein was employed (at 0.5%) as both the sole carbon and the sole nitrogen source. Media with collagen (0.5%) as the sole nitrogen and carbon source supported aflatoxin production similar to the complete defined medium. Although lower than levels observed with defined medium, aflatoxin production increased with both increasing CSP concentration (0 to 2.0%) and increasing zein concentration (0 to 6.0%) when these proteins served as both the sole carbon and sole nitrogen source. Denaturing polyacrylamide gel electrophoresis and protease activity assays indicated that fungal acquisition of protein carbon was probably via hydrolysis mediated by the 35 kD metalloprotease of A. flavus. Media lacking nitrogen but containing sucrose (5.0%) and supplemented with either zein (1.7%) or CSP (2.0%) supported three- to eightfold more aflatoxin production than the complete defined medium. The results suggest seed storage proteins, when present with an accessible carbon source, may predispose oilseed crops to support production of high levels of aflatoxins by A. flavus during seed infection.     

Effects of oilseed storage proteins on aflatoxin production by Aspergillus flavus

Potential involvement of seed storage proteins in susceptibility to aflatoxin contamination was assessed with in vitro tests. Initially, two oilseed storage proteins [cottonseed storage protein (CSP) and zein] were compared with bovine serum albumin (BSA) and collagen. Supplementation of a complete defined medium with either oilseed storage protein resulted in significantly more aflatoxin production by Aspergillus flavus than supplementation with either BSA or collagen. Little or no aflatoxin was produced when either BSA, CSP, or zein was employed (at 0.5%) as both the sole carbon and the sole nitrogen source. Media with collagen (0.5%) as the sole nitrogen and carbon source supported aflatoxin production similar to the complete defined medium. Although lower than levels observed with defined medium, aflatoxin production increased with both increasing CSP concentration (0 to 2.0%) and increasing zein concentration (0 to 6.0%) when these proteins served as both the sole carbon and sole nitrogen source. Denaturing polyacrylamide gel electrophoresis and protease activity assays indicated that fungal acquisition of protein carbon was probably via hydrolysis mediated by the 35 kD metalloprotease of A. flavus. Media lacking nitrogen but containing sucrose (5.0%) and supplemented with either zein (1.7%) or CSP (2.0%) supported three- to eightfold more aflatoxin production than the complete defined medium. The results suggest seed storage proteins, when present with an accessible carbon source, may predispose oilseed crops to support production of high levels of aflatoxins by A. flavus during seed infection.     

The inhibitory effect of neem (Azadirachta indica) leaf extracts on aflatoxin synthesis inAspergillus parasiticus

The effect of neem (Azadirachta indica) leaf extracts onAspergillus parasiticus growth and aflatoxin biosynthesis was investigated. The extracts were prepared by blending 50 g (wet weight) of fresh leaves in one 1 of 10 mM potassium phosphate (pH 7.0) or by boiling the leaves in the buffer. Extracts were added to fungal growth media at 1, 5, 10, 20 and 50% (vol/vol) concentrations prior to inoculation. The formulations did not affect fungal growth (i.e., mycelial dry weight) but essentially blocked (>98%) aflatoxin biosynthesis at concentrations greater than 10% (vol/vol). The inhibitory effect was somewhat diminished (60–70%) inhibition) in heated leaf extracts. Volatile components of the extracts were analyzed using capillary gas chromatography/mass spectrometry; the major volatile component was 3-methyl 2-buten-1-ol. However, volatiles from blended leaf extracts did not affect either aflatoxin synthesis or fungal growth. The neem-mediated inhibition appears to involve regulation of secondary metabolism, because once secondary biosynthesis was initiated the inhibitory effect of the neem leaf constituents was lost. Presented at the AOCS meeting in New Orleans in May 1987.     

The correlation of aflatoxin and norsolorinic acid production

Production of aflatoxins and norsolorinic acid by a mutant strain ofAspergillus parasiticus follows a similar course. Both substances are completely or partially inhibited when the mutant is grown in a chemically defined medium while illuminated continuously, at 37 C, in medium lacking zinc, and in the presence of para-aminobenzoic acid. Higher yields of both compounds are obtained when the mold is grown in an enriched medium. So. Utiliz. Res. Dev. Div., ARS, USDA.     

Inhibition of aflatoxin production inAspergillus flavus by cotton ovule extracts

The effect of cotton ovule extracts onAspergillus flavus growth and aflatoxin biosynthesis was investigated. Extracts derived from either noninoculated cotton ovule tissue or cotton ovule tissue challenged withA. flavus inhibited aflatoxin (B₁) synthesis by fungal cultures ofA. flavus. When added to fungal cultures in concentrations of 50 μg per mL of medium, extracts derived from fungus-challenged ovule tissue inhibited aflatoxin synthesis by as much as 93%. The ED₅₀ for this type of extract was 18 μg per mL of medium (P < 0.01; r²=0.46). Similar experiments with a noninoculated ovule extract (50 μg/mL medium) produced aflatoxin inhibition levels of up to 77%. The ED₅₀ for noninoculated extracts was 35 μg per mL of medium (P < 0.01; r²=0.66). These extracts did not inhibit the growth ofA. flavus in culture. Cultures ofA. flavus that contained pure gossypol (10–50 μg/mL medium) also showed significantly reduced levels of aflatoxin production. Gossypol may account for the aflatoxin-inhibitory activity observed in the extracts derived from noninoculated cotton ovule tissue.     

Fumaric acid production from hydrolysates of starch-based substrates

Fumaric acid production by Rhizopus arrhizus from commercial hydrolysates of corn starch (i.e. glucose molasses) was studied at different initial concentrations of glucose (S) and C:N ratios (R) by performing a 3² factorial experiment. By using the response surface methodology and statistical analysis, fumaric acid (Y_F) and mycelial biomass (Y_x) yields, as referred to the initial concentration of glucose and fumaric acid productivity (P_F), were fitted to the only significant first-order effects of S and R with mean percentage errors ranging from 11 to 15%. The resulting empiric models were used to determine the optimal values of S (100–130 g dm^?3) and R (150–210 g-atom C per g-atom N) associated with Y_F and P_F varying in the ranges 40–49% and 7–8.5 g dm^?3 day^?1, respectively. After establishing the validity of these data at the 95% confidence level, an optimal operating condition (S = 120 g dm^?3 and R = 150) was further tested using other substrates (i.e. glucose and acid or enzymatic hydrolysates of cassava, corn and potato flours). Statistically significant improvements in the fumaric acid yield and productivity were determined with respect to the predicted values. Since the highest values of Y_F and P_F were obtained from the acid hydrolysates of the starch-based materials and such values were also found to be insensitive to the substrate used (at a probability level of 0.05), the above operating condition might be further employed to minimise fumaric acid production costs as a function of the feedstock used.     

Effect of carbon dioxide,temperature, and relative humidity on production of aflatoxin in peanuts

Effects of carbon dioxide (CO₂) in combination with reduced relative humidities (RH) and temperatures on growth and aflatoxin production byAspergillus flavus in peanuts were investigated. Sound mature kernels of Early Runner peanuts were surface disinfested, inoculated withA. flavus, and incubated at various temperatures, RH, and CO₂ concentrations. Visible growth, aflatoxin production, and free fatty acid (FFA) formation byA. flavus was inhibited at approximately 86% RH by 20% CO₂ at 17C and by 60 and 40% CO₂ at 25C. Aflatoxin and FFA levels decreased as RH decreased from approximately 99% to 92% to 86%. At a constant temperature, an increase in CO₂ concentration caused a decrease in aflatoxin and percentage FFA; and, at a given CO₂ concentration, lowering the temperature resulted in a decrease in aflatoxin and percentage FFA.     

Effects of gradient density on thermal protection performance of AVCOAT composites under varied heat flux

Effective heat capacity is a key index to estimate the performance of the thermal protection system of reentry vehicles subjected to aerodynamic heating. To explore the effect of gradient density on the effective heat capacity in this paper, considering variable density we develop the one‐dimensional pyrolysis interface model with surface ablation, and design two kinds of the gradient density of AVCOAT composites. The computer codes are written to simulate the thermal behavior of a homogeneous AVCOAT composites and that of two types of gradient AVCOAT composites under aerodynamic heat flux during Apollo capsule reentry. Numerical results indicate that gradient density can improve the thermal protection performance of homogeneous AVCOAT composites, e.g. the piecewise linear and the parabola designs have larger effective heat capacity than homogeneous AVCOAT composites, which owe to exceptional thermal response of gradient density. This study will be helpful for the design of the thermal protection system in re‐entry vehicles. POLYM. COMPOS. 37:1034–1041, 2016. © 2014 Society of Plastics Engineers     

氧化剂对钢铁表面氟铁酸盐转化膜的影响

通过中性盐雾试验,研究了过氧化氢、钼酸钠、澳酸钾、碘酸钾和过硫酸铵等氧化剂对Q195冷轧钢表面所形成的氟铁酸盐转化膜耐蚀性的影响.结果表明,氧化剂为过硫酸按时,形成的转化膜效果最好,其质量浓度为7 g/L时,转化膜的耐盐雾时间可达到8h.过硫酸按的加入使氟铁酸盐转化膜的形成加快,形成的无定形结构亦使得膜层耐蚀性能更好.     

Effects of current density on adhesion of copper electrodeposits to polyimide substrates

To provide protection, electrical conductivity, or a decorative finish, plastic components are often metallized by a three-step process: deposition of a catalytic palladium layer followed by electroless and electrolytic plating. In this paper we focused on determining the relationship between applied current density used to electrodeposit copper and adhesion of the metal to a polyimide substrate. To test a range of current densities on a single sample, we deposited a series of copper strips on a planar sheet of the polyimide material and electrodeposited copper in a modified Hull cell. From peel tests we found that strips subjected to higher current density adhered more strongly to the substrate. This experimental procedure should be generally applicable to other metal-polymer systems.     

挤出机螺杆对PVC型材生产的影响

介绍了平行双螺杆和锥形双螺杆的安装,分析了PVC型材生产过程中与螺杆有关的质量问题,并提出了相应的解决措施。     

Effects of supplement additives on anaerobic biogas production

Anaerobic digestion (AD) converts biomass to biogas. However, its performance is often affected by the nutrient condition of AD substrate. In this study, a few substrate supplements were selected to promote the biogas production; MgO, FeCl₃, and cellulase were selected based on the result from elemental analyses of the biomass. The potential impact of the additives on AD process was evaluated by performing a series of biochemical methane potential (BMP) tests. BMP reactors with the substrate with one of the selected additives (i.e., MgO of 380 mg Mg L^?1, FeCl₃ of 88 mg Fe L^?1 or cellulase of 25 mg L^?1) exhibited higher microbial activity; 5–15% more biogas production was observed, compared to the blank. Microbial community analysis showed that different additives resulted in proliferation of different microbial species. Therefore, it was decided to add the mixture of the three additives to the biomass. Addition of the mixed additive resulted in 22% more gas production.     

底物对亚铁硫杆菌生物氧化过程的影响

实验表明T .ferrooxidans对FeSO4和硫等单或双底物利用的难易程度次序为 :单底物培养基中FeSO4最易利用 ,Na2 S2 O3 其次 ,单质硫最难利用 ;双底物培养基中 ,T .Ferrooxidans首先利用Fe2 + ,然后利用硫 ,此外培养液中还伴随发生化学氧化反应、中和沉淀、生物氧化等反应 ,以上反应使培养液中亚铁的浓度在培养中期上下波动直至铁氧化酶抑制被解除。