Aflatoxin B1 production by Aspergillus parasiticus and strains of Aspergillus section Nigri in currants of Greek origin

Aflatoxin B₁ (AFB₁) mostly produced by Aspergillus flavus and Aspergillus parasiticus, is an extremely toxic and carcinogenic metabolite. Currants are used in the Mediterranean diet as a food with antioxidant properties. Four strains of Aspergillus section Nigri have been isolated from currants originated from Crete and Corinth. In this study AFB₁ production by A. parasiticus and the four strains of Aspergillus section Nigri in Cretan and Corinthian currants (Vitis vinifera L.) is investigated. AFB₁ determination was performed by HPLC–FID. Results revealed that the four strains Aspergillus section Nigri, as well as the aflatoxigenic strain A. parasiticus produced AFB₁ (0.0052–1.31 μg AFB₁ 15 g⁻¹, corresponding to 0.0003–0.087 μg AFB₁ g⁻¹) in both type of currants (Cretan and Corinthian) on the 12th day of observation. Moreover, AFB₁ production, by A. parasiticus in the synthetic Yeast Extract Sucrose (YES) medium was also studied. The ability of AFB₁ production has been affected by the special characteristics of each isolate and the currants substrate.     

防腐剂对复合型生物絮凝剂防腐保质性能的影响

分别探讨了山梨酸钾、月桂酸单甘油酯两种防腐剂对复合型生物絮凝剂防腐保质方面的影响,同时考察了复合型生物絮凝剂的絮凝率以及细菌总数等指标.试验结果表明:添加两种防腐剂能够有效延长复合型生物絮凝剂絮凝率的高效稳定性,同时有效抑制细菌等微生物的生长繁殖.综合防腐剂价格、絮凝率稳定性以及抑制细菌总数效果等因素,确定单独添加0.50 g/L山梨酸钾或单独添加0.15 g/L月桂酸单甘油酯为最佳处理,保质期从原来的3个月延长到9个月.     

烟叶蔗糖酯研究进展

综述了近些年来国内外有关烟草蔗糖酯的提取、分离与鉴定、生物学活性以及在烟株内的合成路径研究,并提出了未来烟草蔗糖酯研究的重点和方向。     

新型高效食品防腐剂-甘油单月桂酸酯

简单叙述了高效食品防腐剂应具备的分子结构特征,同时介绍了一处新的防腐剂—甘油单月桂酸酯的性质及合成方法。     

固定化酶法合成蔗果低聚糖的研究

本文对以壳聚糖为载体制备蔗果低聚糖的固定化酶进行了研究。选择了制备固定化酶最佳的戊二醛浓度、交联温度和交联ｐＨ值。与液体酶相比，固定化酶具有很好的活性和操作稳定性，显示了其在蔗果低聚糖生产中极有希望的应用前景。     

蔗糖转化生产纯结晶果糖的工艺研究

本文研制出了一条以蔗糖为原料，生产纯结晶果糖技术路线。其工艺流程包括：①蔗糖的水解，②果糖、葡萄糖的分离，③果糖液精制，④果糖结晶。采用化学法分离果、葡糖浆，并得到了可进行果糖结晶的高质量的果糖液，克服了色谱分离技术要求高、在我国难以实现工业化的缺点。在进行果糖结晶前，对果糖液进行脱盐和脱色等精制处理。可根据不同的要求采取两种不同的结晶工艺，生产出两种结晶果糖产品。一种产品为小颗粒结晶果糖，另一种产品为大颗粒结晶果糖，其晶体颗粒大小达到０．２～０．３ｍｍ。两种结晶果糖产品果糖的结晶率可达到６０％。其纯度均超过试剂果糖纯度。采用本工艺流程，１００吨蔗糖可产２４．７吨结晶果糖，３２．５吨结晶葡萄糖，５３．８吨果葡糖浆。     

功能性共结晶糖品性质的研究

蔗糖共结晶技术为食品，医药配料的夹带提供了新的方向。本文简要地介绍了共结晶工艺过程的原理、工艺过程和用途，重点研究了共结晶糖品的微细外观结构及糖品的有关性质，研究结果表明，共结晶糖品是一种由蔗糖微小晶体组成的聚集体，糖品具有添加配料在产品中分布的均匀性和产品溶解速度加快的特性，并且夹带乳化剂的共结晶糖品增强了乳化剂的乳化作用，作者从工艺过程，产品结构等方面解释了糖品具有这些功能特性的原因。     

Baroprotective effect of increased solute concentrations on yeast and moulds during high pressure processing

The baroprotective effect of increasing solute concentrations on yeast cells and fungal conidia subjected to high pressure processing (HPP) was studied. Suspensions of yeast cells (Saccharomyces cerevisiae, Pichia anomala and Hanseniaspora uvarum) or fungal spores (Penicillium expansum, Fusarium oxysporum and Rhizopus stolonifer) in citrate phosphate buffer formulated with sucrose at 40, 50 and 60 °Brix, or with glycerol and NaCl at equivalent water activity (a_w) values (0.925, 0.903 and 0.866 a_w) were subjected to 600 MPa pressure for varying times, and then were enumerated by spread plate technique to assess survival. There was an increasing resistance to inactivation by high pressure with an increase in solute concentration. The two moulds with easily wetted spores, R. stolonifer and F. oxysporum, showed strongest resistance to HPP at 0.866 a_w. Differing responses to the three solutes were observed among the fungal species tested, indicating that the chemical nature of the solute may also be important in protecting yeasts and moulds during and after pressure treatment. Sucrose had a stronger baroprotective effect for S. cerevisiae than the other solutes, at two of the three investigated a_ws. For P. expansum at 0.903 a_w, NaCl gave the best protective effect. Scanning electron microscopy of HPP treated cells showed the protective effects of increased sucrose concentration. The results reported here have practical implications for the food industry in the application of HPP for production of fruit preparations or syrups, and should be taken in account in establishing efficient process design.

Industrial relevance

As high concentrations of sugar, salt and glycerol provide protection for yeasts and moulds during high pressure processing, foods containing high levels of solutes may need longer processing times or higher pressures to achieve inactivation of these fungi.     

C NMR and electrospray ionization mass spectrometric study of sucrose aqueous solutions at high pH: NMR measurement of sucrose dissociation constant

The ¹³C NMR technique is used for the measurement of the first dissociation constant of sucrose (HL) in highly alkaline solutions. In 1.0 M NaCl/NaOH medium and for 25 °C, the concentration dissociation constant (pK₁) was 13.1 ± 0.3; and, for 60 °C, pK₁ = 12.30 ± 0.05. The β-d-fructofuranosyl ring was found to be responsible for dissociation. The NMR data reveal no clear evidence of the second dissociation step below pH 14, either at 25 °C or at 60 °C. In the solutions with 4–10 mol dm⁻³ NaOH content the ¹³C NMR technique indicated the chemical shift changes, treated as the second dissociation step of sucrose and a sodium complex formation. A very rough estimation, for variable ionic strength, gives the value: pK₂ ∼ 15.8 ± 0.8. The anionic species L⁻ and NaH₋₁L⁻ have been registered by electrospray ionization time-of-flight mass spectrometry (ESI-ToF MS) for 0.01 M sucrose solutions with initial pH 13.     

无溶剂一步合成蔗糖酯工艺的研究

本法以油脂和蔗糖为原料，一步反应合成脂肪酸蔗糖酯，反应产物可按所需的HLB值进行精制和分离，同时尚可副产单脂肪酸甘油酯。