利用重组酵母菌株发酵混合碳源分泌表达角质酶

克隆来自Thermobifida fusca(嗜热放线菌)的编码角质酶基因tfu,并在N端人为添加了α-factor信号肽,以引导重组角质酶的分泌表达。在成功构建了重组菌株后,深入分析了半乳糖浓度对重组菌株表达角质酶的影响,并对诱导方式进行了优化分析。此外,还分析了混合碳源对重组菌株产角质酶的影响。依靠α-factor信号肽的引导,成功实现了重组酵母菌株角质酶的活性分泌表达。混合碳源实验表明,棉子糖和半乳糖的组合能够更好地促进角质酶的分泌表达,这为角质酶发酵生产及应用于食品医药及保健品行业提供了参考和借鉴。     

Raffinose family oligosaccharides in seed of Glycine max cv. Chiang Mai60 and potential source of prebiotic substances

Raffinose family oligosaccharides (RFOs) content in Glycine max seed of cultivar Chiang Mai60, a local soybean of Thailand, was investigated. RFOs and other low molecular weight sugars were extracted by 50% (v/v) ethanol and quantified by high‐performance liquid chromatography (HPLC). The prebiotic property of this extract was subsequently studied by in vitro method. The results showed that the concentrations of raffinose, stachyose and verbascose were 6.74 ± 1.62, 145.32 ± 18.74 and 1.60 ± 0.52 mg g^?1 dry seed, respectively, while glucose and sucrose were detected at 10.73 ± 1.35 and 13.28 ± 2.16 mg g^?1 dry seed, respectively. The growth of four Lactobacilli probiotics were increased significantly in a basal liquid medium supplemented with this ethanolic extract as carbon source compared to glucose supplementation. Subsequently, defined mixed culture was studied and it was found that growth stimulation of total Lactobacilli by extracted sugars resulted in the suppression of Escherichia coli and Salmonella enterica serovar Typhimurium growth. It could be concluded that this cultivar showed the RFOs‐rich content and a potential to be a source of an effective prebiotic substance for food application.     

High-performance liquid chromatographic determination of oligosaccharides in leguminous seeds

A simple and reliable high-performance liquid chromatographic (h.p.l.c.) method has been developed for the determination of sucrose, raffinose and stachyose in leguminous seeds. A LiChrosorb NH₂ column (Merck) and an acetonitrile+water solvent (65:35, by vol) at a flow rate of 1 ml min^?1 were used for the separation. An interference type refractive index detector (Tecator) was used for the detection. With this detector the smallest amount of oligosaccharide detectable was 10 ng. With a traditional deflection type refractive index detector the smallest amount of oligosaccharide detectable was 240 μg. The oligosaccharides were extracted by placing the whole, dry seeds in boiling water for 30 min, blending the seeds and water, placing the whole suspension in a shaking bath at 60°C for 60 min, and removing the solid material by centrifuging. The extract was deproteinated by adding 65 parts of acetonitrile to 35 parts of extract (by vol), placing the mixture at 5°C for 60 min, and filtering off the resulting proteinaceous precipitate before injection into the chromatograph. The entire procedure has been successfully applied to soya beans, chick peas, garden peas and red kidney beans with recoveries of added raffinose in the range 97–102%.     

Lipid‐based fat substitutes

Fats and oils account for 38% of the total calories in the diet of Western populations, especially in the U.S. They provide the most concentrated source of energy, 9 kcal/g of a triacylglycerol molecule compared with 4 kcal/g provided by carbohydrate and protein. In response to consumer demands for low‐calorie or calorie‐free fats and their reluctance to give up the taste of fat, current research efforts have been directed toward the development of lipid‐like fat substitutes. These fat substitutes contain the fatty acids found in conventional fats and oils, with all the physical and organoleptic properties of fats, but provide few or no calories in the diet. Some of the fat substitutes are modified triacylglycerols (glycerol backbone) with reduced digestion and absorption; others are digestible and nondigestible carbohydrate fatty acid esters and polyesters, respectively. Sucrose polyester (Olestra^®), a sucrose molecule esterified with six to eight fatty acids, is the most studied of the lipid‐based fat substitutes containing a carbohydrate backbone. If approved by the FDA, sucrose polyester will find application in almost all fat‐containing foods. Specialty fats or fat substitutes targeted to certain individuals with special needs are being developed. Among these are the medium‐chain triacylglycerols and structured lipids (glycerol backbone), or “nutraceuticals” with reduced absorption and medical applications. Enzyme biotechnology is another tool available to lipid chemists to selectively modify, esterify, transform, transesterify, and interesterify fats and oils or synthesize new lipids such as structured lipids of food, nutritional, and medical importance. These designer fats may be the trend in the future to produce medical lipids that do not occur normally in nature. The different types of lipid‐based fat substitutes are reviewed with respect to their synthesis, analysis, metabolism, potential applications/uses, and the future of fat substitutes.     

用乙醇-水从双液相棉粕中提取棉子糖的研究

用双液相萃取工艺处理后的棉籽粕为原料,乙醇-水溶液为溶剂进行了棉子糖的提取试验,并考察了影响浸出率的因素。在单因素实验的基础上,通过正交实验得出优化后的提取工艺条件为:乙醇体积分数为70%,提取温度60℃,提取时间150 m in,物料溶剂比1∶14(即每克物料需14 mL溶剂)。在此工艺条件下,棉子糖的浸出率为92.5%。     

Highly automated and fast determination of raffinose family oligosaccharides in Lupinus seeds using pressurized liquid extraction and high‐performance anion‐exchange chromatography with pulsed amperometric detection

BACKGROUND: Taking into account several requirements for the determination of raffinose family oligosaccharides (RFOs) from Lupinus seeds—e.g., conducting plant breeding projects or food product development—a reasonable combination of efficient automated sample preparation and reliable analysis need to be developed and validated. RESULTS: In this regard pressurized liquid extraction was applied to extract the RFOs from ground and defatted lupin flour. Compared to many other publications, no further pretreatment, such as protein precipitation, was necessary to obtain satisfactory results applying ion chromatography with pulsed amperometric detection. The oligosaccharide content for the examined Lupinus albus samples were in the range 5.19–9.25 g kg⁻¹ and for Lupinus angustifolius RFOs 3.49–4.75 g kg⁻¹. Stachyose has always been the main component followed by raffinose and verbascose. CONCLUSION: The developed sample preparation and analytical method is suited to quantify raffinose, stachyose, verbascose and the disaccharide sucrose and, owing to a high degree of automation for sample preparation and relatively short analysis times by pretty peak separation, particularly high sample numbers can be accomplished. Copyright © 2008 Society of Chemical Industry     

Nutritional potential and functional properties of tempe produced from mixture of different legumes. 1: Chemical composition and nitrogenous constituent

Fermented foods such as Tempe represent a technological alternative for a great variety of legumes and combination of them to improve their nutritional quality and to obtain edible products with palatable sensorial characteristics. The chemical composition, carbohydrate fraction and nitrogenous constituents were investigated for individual different legumes, i.e. faba bean; lupine, chickpea; peas and their mixture before and after fermentation by Rhizopus oligosporus. Tempe had a higher (P < 0.05) protein and fibre content compared with legume mixtures before fermentation, while it had a lower fat, ash and carbohydrate contents. Also, reducing and non‐reducing sugars, stachyose as well as raffinose were reduced after fermentation of legume mixtures. A significant reduction was observed in non‐protein nitrogen and protein nitrogen, while total nitrogen and true protein were increased.     

双液相萃取棉仁粉工艺中甲醇相棉子糖的精制

以双液相溶剂（石油醚+甲醇混合）浸取棉仁粉工艺中甲醇相为原料，在预处理的基础上，依次采用硅藻土与活性炭混合物脱色，超滤膜脱蛋白，溶剂丙酮-乙醇-水（体积比2:1:0.5） 重结晶的方法精制棉子糖，并以棉子糖收率和脱色率（或纯度）为指标，优化纯化工艺。结果表明最佳工艺条件为：1) 脱色：在50 ℃下，采用3%（混合物与棉子糖溶液质量比）的硅藻土与活性炭混合物对棉子糖粗品进行2 h脱色；2) 超滤：棉子糖溶液pH值为8，温度40 ℃，操作压力0.016 MPa；3) 重结晶：在料液比1:14下，冷冻重结晶24 h。最终得到棉子糖的纯度为94.5%，回收率为63.1%。     

Effect of raffinose on sucrose recrystallization and textural changes in soft cookies

ABSTRACT:  Sucrose recrystallization and the release of moisture that occurs as molecules of sugar are incorporated into a growing crystal lattice have been hypothesized as the cause of firming in soft cookies over time. Raffinose, a trisaccharide and known sucrose crystallization inhibitor, was tested as a means to inhibit or slow this process. Texture changes in the cookies were quantified using peak force measurements obtained by employing a puncture test. Sucrose recrystallization was successfully suppressed by the addition of 5% raffinose (w/w), as demonstrated by quantitative results obtained using powder x-ray diffraction and the degree of crystallization correlated with texture. Cookies with added raffinose were found to be significantly softer in texture, as well as having significantly decreased quantities of recrystallized sucrose. The hypothesis that sucrose recrystallization is responsible in part for the firming of cookies was shown to be logical.