谷氨酸钠及5′-肌苷酸钠+5′-鸟核酸钠(I+G)添加到食品中的稳定性研究

谷氨酸钠和5′-肌苷酸钠+5′-鸟苷酸钠(I+G)常被添加到食品中来提高鲜味。为了有效利用谷氨酸钠和I+G,将其添加到新鲜萝卜、腌制蔬菜、面粉中,并做热处理实验。谷氨酸钠和I+G含量采用HPLC法测定。结果表明,将谷氨酸钠和I+G添加到新鲜萝卜中,经过85℃和100℃热处理,放置3d,谷氨酸钠保存率分别为76.0%和76.3%,I+G保存率分别为95.6%和95.8%。而先放置3d,再分别85℃和100℃热处理,谷氨酸钠保存率分别为49.0%和41.8%,I+G保存率分别为8.7%和6.9%。将谷氨酸钠和I+G添加到腌制榨菜和腌制雪菜中,经过85℃热处理5min并放置7d,榨菜和雪菜中谷氨酸钠保存率分别为62.5%和67.5%,I+G保存率分别为86.2%和87.2%。而先放置7d,再85℃热处理5min,榨菜和雪菜中谷氨酸钠保存率分别为7.5%和7.5%,I+G保存率分别为38.7%和38.4%。将谷氨酸钠和I+G加到面粉中,180℃高温油炸处理3min,谷氨酸钠保存率为18.8%,I+G保存率为7.9%。在新鲜切割蔬菜和腌制蔬菜中添加谷氨酸钠和I+G,需进行85℃以上热处理,油炸食品的油炸温度不宜过高。     

双波长比值光谱法测定5＇-鸟苷酸钠、5＇-肌苷酸钠、5＇-尿苷酸钠含量

依据5＇-鸟苷酸钠、5＇-肌苷酸钠和5＇-尿苷酸钠三组分的比值光谱特征,以尿苷酸钠为干扰组分时,选择258、285、244、280nm作为测定鸟苷酸钠和肌苷酸钠的波长;以肌苷酸钠为干扰组分时,选择211、241nm作为测定尿苷酸钠的波长。结果显示鸟苷酸钠在0.15～5mg/100ml,肌苷酸钠在0.2～6mg/100ml,尿苷酸钠在0.25～4mg/100ml范围具有良好的线性关系,平均回收率分别为100.2%、100.2%和99.5%。本法具有测定波长少、计算简单、光谱＂分离＂能力强以及能在低档分光光度计上实现、易于推广等特点。     

Decomposition of the Flavor Enhancers, Monosodium Glutamate, lnosine-5'-Monophosphate and Guanosine-5'-Monophosphate during Canning

Monosodium glutamate (MSG) was found to be very stable to canning conditions. Both flavor nucleotides inosine-5'-monophosphate (IMP) and guanosine-5'-monophosphate (GMP) were lost through hydrolysis, up to 50% or more, depending on the canning conditions. IMP was more stable than GMP with increased hydrolysis for both compounds occurring at lower pH and longer canning time. The loss of IMP and GMP was shown to go via phosphate hydrolysis to the corresponding nucleosides, inosine and guanosine, followed by base hydrolysis of the nucleosides to hypoxanthine and guanine.     

Hydrolytic Stability of l-(+)-Ascorbic Acid in Low Methoxyl Pectin Films with Potential Antioxidant Activity at Food Interfaces

l-(+)-Ascorbic acid (AA) was compartmentalized into a low methoxyl pectin (LMP) film in view of localized antioxidant activity at food interfaces. The AA hydrolysis was specifically studied in the present work in order to determine the ability of the formulated LMP film to stabilize AA. Hence, films were stored at controlled relative humidity (RH) in the absence of air. A commercial LMP characterized by a 40% degree of methylesterification (DM) was used. Since sucrose is normally added for its standardization, films were also made with the dialyzed LMP in order to determine the sucrose effect. Glycerol was used for plasticization. Kinetics of AA loss and subsequent browning development were determined, which are dependent on the RH. Considerable AA retention (t _1/2?=?744, 727, and 185 days) was achieved at 33.3%, 57.7%, or 75.2% RH, respectively, at 25 °C. Browning rate constants decreased in one order of magnitude with respect to kinetic constants determined from films previously developed with high methoxyl pectin (HMP; DM of 73%). Absence of sucrose in the LMP network only affected the browning kinetics at 75.2% RH. The glass transition temperature (T _g) decreased with the increment of moisture content of the films and in a similar degree (T _g?≈??90 °C) to that observed for the HMP films, indicating the contribution of water to the network plasticization. However, water was more confined in the LMP network as inferred from the water availability determined by the ¹H-NMR and DSC. This was attributed to the water interaction at the Ca²⁺ junction zones. Sucrose seemed to hinder the retention of water molecules by the polymeric network at 75.2% RH.     

Thermal Degradation of Flavor Enhancers, Inosine 5'-monophosphate, and Guanosine 5'-monophosphate in Aqueous Solution

The mechanism of thermal degradation of inosine 5′-monophosphate (IMP) and guanosine (GMP) was investigated kinetically in aqueous solution as a function of pH and temperature. The degradation of IMP and GMP followed first order kinetics. The rate constants were considerably affected by pH and temperature. The half-life times at 100°C were: IMP, 8.7 hr (pH 4.0), 13.1 hr (pH 7.0), 46.2 hr (pH 9.0); GMP, 6.4 hr (pH 4.0), 8.2 hr (pH 7.0), 38.5 hr (pH 9.0). These times were shortened to about one-third by raising the temperature 10°C. The predominant degradation products were nucleosides and phosphoric acid, indicating that the main reaction of the thermal degradation was the hydrolysis of the phosphoric ester bond in the nucleotides.     

食品中嘌呤的降低方法及低嘌呤产品研究进展

嘌呤代谢紊乱是引起人体内诸如痛风、肾衰竭等一系列病理表征的重要因素之一。人体从食物中摄取的嘌呤虽少但却几乎都转变成为了诱发痛风、肾衰竭等病症发作的有害物质,因此研发低嘌呤产品具有重要的营养健康价值。以降低高嘌呤食物中的嘌呤为出发点,论述国内外低嘌呤产品的研究进展,并对常见的降嘌呤方法进行分析论述。为低嘌呤产品以后的进一步研究提出了建议。     

常见食物过敏原结构稳定因素与致敏性的关系研究进展

食物过敏原所引发的食品安全问题是目前亟待解决的卫生学问题,而分析过敏原蛋白结构稳定性与致敏性的关系,对于了解食品过敏的机理以及探索消减过敏原致敏性的方法具有十分重要的意义。本文选取几种主要食物过敏原蛋白,探讨维持过敏原蛋白结构稳定性的因素（二硫键、糖基、疏水作用以及氢键）,以及结构稳定与致敏性的关系,为如何消减过敏原致敏性提供一定的理论指导。     

常见干豆类及豆制品中嘌呤含量研究

目的:检测常见干豆类及豆制品中的嘌呤含量,为高尿酸血症与痛风患者健康膳食提供指导。方法:采用高效液相色谱法测定嘌呤含量,色谱柱选用Waters Atlantis T3柱(4.6mm×250mm×5μm),流动相为10.0mmol/L甲酸铵(pH3.6)和甲醇(99%∶1%),流速1.0mL/min,柱温30℃,检测波长254nm。结果:不同种类干豆及豆制品中嘌呤含量具有显著差异,干豆类中嘌呤含量显著高于豆制品;干豆类中,蚕豆最高。豆制品中,豆粉最高。结论:不同种类干豆及豆制品中嘌呤含量有差别;干豆类普遍高于豆类制品。     

Thermal Stability of Folic Acid and 5-Methyltetrahydrofolic Acid in Liquid Model Food Systems

The effects of temperature, iron and ascorbate fortification, and oxygen concentration on the stabilities of folic acid (FA) and 5- methyltetrahydrofolic acid (5-CH₃-THF) were examined in liquid model food systems. Small retort pouches were used as reaction vessels and the model systems were processed at 100°C, 120°C, and 140°C. A cation-exchange procedure was devised to provide sample extract purification before quantitation using high-performance liquid chromatography (HPLC). FA and S-CH₃-THF were found to be very stable under these conditions. Lactose, protein, iron and ascorbate were all found to be capable of reducing the oxygen partial pressure within the model systems, thereby enhancing the stability of FA and 5-CH₃-THF. FA and 5-CH₃-THF degradation was not zero or first order but possibly second order as a result of limiting oxygen concentrations.     

聚合硅酸硫酸铝的铝形态及其水解稳定性

利用２７Ａｌ核磁共振技术分析了聚合硅酸硫酸铝的铝形态,发现铝单双核组分随碱化度的提高和硅铝比的降低而增加,表明硅的引入相对降低了聚合硅酸硫酸铝的聚合程度。但未发现Ａｌ１３的存在。聚合硅酸硫酸铝的水解稳定性随其聚合程度的提高及水解ｐＨ值的增加而下降。     

Activity of two histidine decarboxylases from Photobacterium phosphoreum at different temperatures, pHs, and NaCl concentrations

The major causative agent of scombroid poisoning is histamine formed by bacterial decarboxylation of histidine. The authors reported previously that histamine was exclusively formed by the psychrotrophic halophilic bacteria Photobacterium phosphoreum in scombroid fish during storage at or below 10 degrees C. Moreover, histamine-forming ability was affected by two histidine decarboxylases: constitutive and inducible enzymes. This article reports the effect of various growth and reaction conditions, such as temperature, pH, and NaCl concentration, on the activity of two histidine decarboxylases that were isolated and separated by gel chromatography from cell-free extracts of P. phosphoreum. The histidine decarboxylase activity of the cell-free extracts was highest in 7 degrees C culture; in 5% NaCl, culture growth was inhibited, and growth was best in the culture grown at pH 6.0. Moreover, percent activity of the constitutive and inducible enzymes was highest for the inducible enzyme in cultures grown at 7 degrees C and pH 7.5 and in 5% NaCl. The temperature and pH dependences of histidine decarboxylase differed between the constitutive and inducible enzymes; that is, the activity of histidine decarboxylases was optimum at 30 degrees C and pH 6.5 for the inducible enzyme and 40 degrees C and pH 6.0 for the constitutive enzyme. The differences in the temperature and pH dependences between the two enzymes extended the activity range of histidine decarboxylase under reaction conditions. On the other hand, histidine decarboxylase activity was optimum in 0% NaCl for the two enzymes. Additionally, the effects of reaction temperature, pH, and NaCl concentration on the constitutive enzyme activity of the cell-free extracts were almost the same as those on the whole histidine decarboxylase activity of the cell-free extracts, suggesting that the constitutive enzyme activity reflected the whole histidine decarboxylase activity.     

黄原胶与其它食品胶协同增效作用及其耐盐稳定性的研究

以黄原胶、羟丙基淀粉、ＣＭＣ－Ｎａ、瓜尔豆胶、刺槐豆胶、魔芋精粉等为主要研究对象,系统地研究了黄原胶与其它食品胶２种或３种之间的协同增效作用及其耐盐稳定性。研究结果表明：黄原胶与羟丙基淀粉、ＣＭＣ－Ｎａ复配无协同增效作用,黄原胶与刺槐豆胶、魔芋精粉、瓜尔豆胶有良好的协同增效作用,两者或三者按适当比例配合后,耐盐稳定性显著提高,用量比任一单一胶少,而且使用成本大幅度降低,因此复配食品胶在高盐食品中使用具有明显的优越性和广阔的应用前景。     

黄原胶与其它食品胶协同增效作用 及其耐盐稳定性的研究

以黄原胶、羟丙基淀粉、ＣＭＣ－Ｎａ、瓜尔豆胶、刺槐豆胶、魔芋精粉等为主要研究对象,系统地研究了黄原胶与其它食品胶２种或３种之间的协同增效作用及其耐盐稳定性。研究结果表明：黄原胶与羟丙基淀粉、ＣＭＣ－Ｎａ复配无协同增效作用,黄原胶与刺槐豆胶、魔芋精粉、瓜尔豆胶有良好的协同增效作用,两者或三者按适当比例配合后,耐盐稳定性显著提高,用量比任一单一胶少,而且使用成本大幅度降低,因此复配食品胶在高盐食品中使用具有明显的优越性和广阔的应用前景。     

高压液相色谱法测定金丝小枣环磷酸腺苷的含量

建立了用高压液相色谱法测定枣汁中环磷酸腺苷的方法.用Shim-Pack VP-ODS色谱柱,流动相为甲醇-0.1mol/L磷酸二氢钾缓冲液（30：70,V/V）,检测波长260nm,流速0.6ml/min,回收率101.5%.该法简便,灵敏,重现性好,可以快速测定含环磷酸腺苷的溶液及其制剂的含量.     

水解氨基酸微量元素络合物食品添加剂的合成工艺研究

利用豆粕的１３９８中性蛋白酶水解液作为复合氨基酸来源，对食品添加剂复合氨基酸锌络合物的合成工艺条件进行了初步研究。重点研究了配体摩尔比和ｐＨ值对络合反应的影响，确定合适的配比反应条件为配位摩尔比２：１，ｐＨ＝８．０，产品络合率达到９８％以上，用化学分析法及红外光谱法鉴定了产品，初步试验得出复合氨基酸锌具有抗氧化性，这为其以后的应用拓展了思路。     

PG、TBHQ、BHA和BHT4种常见抗氧化剂部分稳定性的研究

研究PG、TBHQ、BHA和BHT 4种常见抗氧化剂在不同溶荆、酸碱中稳定性为检测工作者及科研工作者在试验过程中储存或者提取时提供参考依据。采用高效液相色谱法(HPLc),以4种抗氧化剂的保留率为指标,考察4种抗氧化剂的稳定性。从试验结果来看:PG、TBHQ、BHA和BHT在甲醇以及酸性条件下具有较好的稳定性。     

Hydrolytic Stability and Changes in E Vitamers and Oryzanol of Extruded Rice Bran During Storage

Rice bran was extruded at 110, 120, 130, and 140°C with post extrusion holding times of 0, 3, and 6 min and stored at ambient temperatures for 1 yr. Holding time had no effect (p>0.05) on hydrolytic stability whereas 110°C was slightly less effective in maintaining hydrolytic stability. Increased holding times reduced (p<0.05) total vitamin E content. Oryzanol concentration was lower (p<0.05) only after 6 min holding time. Oryzanol was relatively more stable to extrusion temperatures than vitamin E. The highest retentions of total vitamin E and oryzanol were found in raw rice bran during storage. Increased extrusion temperatures reduced the retention of vitamin E and oryzanol during storage.     

有效应对五大挑战确保我国食品安全

一、中国食品安全将长期面临五大挑战 (一)中国的食品供应基数大,食品安全事故的发生概率大.中国食品工业用30年的高速发展,以年均15%以上的高速,铸就了6.3万亿产值的自身的强大.为了满足"13亿人口全球第一大食品市场"的需求,我们每天平均加工和生产10亿公斤以上的食品,日均创造着172.6亿元的工业产值.这个全球最大的基数必然使中国发生食品安全事故的几率、概率与显示度增高,食品安全的风险加大.     

常见食品机械故障分析及其对策

本文阐述常见食品机械故障分析及其对策 ,这对拥有同类型食品机械的用户来说 ,它具有重要现实意义。     

保健食品中红景天甙含量测定及其稳定性研究

采用十八烷基硅烷键合硅胶柱,以乙腈-水(1∶9)为流动相,流速为1.0ml·min-1,检测波长为280nm测定保健食品中红景天甙的含量以控制产品质量。结果表明,红景天甙在0.4～4.0μg范围内呈线性关系,平均回收率(n=6)为98.96%(RSD=1.16%)。该方法简便、准确、重现性好,可用于保健食品中红景天甙的质量控制。