Hydrolytic Stability at Intermediate pHs of the Common Purine Nucleotides in Food, Inosine-5'-monophosphate, Guanosine-5'-monophosphate and Adenosine-5'-monophosphate

When the purine nucleotides, inosine-5′-monophosphate (IMP), guanosine-5′-monophosphate (GMP) and adenosine-5′-monophosphate (AMP) were subjected to canning temperatures (121°C) at pHs between 3 and 8, extensive phosphate bond hydrolysis to the corresponding nucleoside occurred. The half life for hydrolysis at pH 5 was 63, 41, and 51 min for IMP, GMP, and AMP, respectively. Rates of hydrolysis were even greater at pH 3 because both hydrolysis of the phosphate bond and the glycosidic bond occurred simultaneously. An Arrhenius plot of data collected at different temperatures illustrated that the nucleotides were very stable at room temperature. Half lives for IMP, GMP, and AMP were estimated to be 36, 19, and 40 yr, respectively, at 23°C and a pH of 5.     

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.     

谷氨酸钠及I+G的热杀菌稳定性

谷氨酸钠(MSG,谷氨酸一钠)、5'-肌苷酸二钠(IMP)和5'-鸟苷酸二钠(GMP),是主要增味成分。I+G是IMP和GMP按照1∶1混合的物质。研究谷氨酸钠及I+G的热处理稳定性,在食品烹调和食品加工过程中具有重要意义。实验主要采用高效液相色谱法测定杀菌温度、杀菌时间、pH对谷氨酸钠和I+G含量的影响。实验发现:杀菌时间为30 min时,经85℃,100℃,121℃杀菌,谷氨酸钠浓度分别损失3.16%,13.21%和30.10%;I+G浓度分别损失8.18%,12.91%和22.97%。在100℃下,经5,15,30 min杀菌,谷氨酸钠浓度分别损失1.43%,7.25%和8.63%;I+G浓度分别损失6.08%,8.78%和10.12%。在100℃下加热15 min,pH分别为7,6,5,4,3时,谷氨酸钠浓度分别损失2.2%,10.30%,22.4%,39.09%,52.50%;I+G浓度分别损失7.59%,9.30%,10.60%,12.89%,26.33%。     

呈味核苷酸及其在食品调味中的应用

以5′-肌苷酸和5′-鸟苷酸为代表的5′-核苷酸及其一些衍生物,已逐渐应用于食品的调味中.本文综述了5′-核苷酸及其一些衍生物呈鲜味特点、呈味性质与化学结构的关系以及在食物调味中的运用情况.以便为进一步开发和利用5′-核苷酸类鲜味调味剂提供资料.     

双波长分光光度法测定呈味核苷酸二钠混合物含量

在 2 0 0～ 3 0 0nm波长范围内扫描 5’ 肌苷酸二钠 (IMP)和 5’ 鸟苷酸二钠 (GMP)溶液 ,根据双波长分光光度法波长选择原理 ,确定 2个波长分别为λ1=2 5 0nm与λ2 =2 80nm。分别配制一定浓度的IMP、GMP溶液 ,并在 2波长处测定其吸光值 ,由比耳定律推算出常数εΙΜΡλ2 50 ,εGΜΡλ2 50 ,εΙΜΡλ2 80 ,εGΜΡλ2 80 的数值 ,根据加和性原理推导出IMP、GMP和呈味核苷酸二钠 (I+G)的测定公式。结果表明 ,此测定方法稳定性好 ,重复性高 ,专属性高 ,可代替液相色谱法 (HPLC)测定I+G的含量。     

Sensory Changes in Umami Taste of Inosine 5'-Monophosphate Solution after Heating

Discrimination in umami taste of inosine 5′-monophosphate (IMP) solution caused by thermal degradation was investigated by sensory evaluation. The difference threshold of umami taste of 0.005% IMP solution in the presence of 0.05% monosodium glutamate (MSG) was 0.002%. The difference threshold of a 0.005% IMP solution decreased by about one half when heated at 95°C for 15 h. Inosine, one of the main products of the thermal degradation of IMP, had a bitter taste. The detection threshold of inosine varied widely among panelists. Heating a 0.005% IMP solution at 95°C for 15 h formed inosine at about one tenth of its lowest detection threshold.     

高效毛细管电泳法测定酱油中5'-单磷酸核苷酸

建立高效毛细管电泳同时分离测定酱油中两种核苷酸鸟嘌呤-5O`-单磷酸(GMP)和次黄嘌呤-5O`-单磷酸(IMP)的方法。电泳条件：以50μm×60.2cm(有效长度50cm)未涂敷石英毛细管为分离柱,30mmol/L硼砂＋30mmol/L碳酸钠＋60mmol/L羟丙基-β-环糊精为分离缓冲溶液,50mmol/L醋酸溶液为样品介质,检测波长为254nm。GMP及IMP的校正峰面积与质量浓度在5～100mg/L范围内具有良好线性关系,线性相关系数分别为0.9998和0.9997,检出限均为2mg/L,定量限均为5mg/L。用该法测定了9种酱油,并与文献报道的高效液相色谱法的结果进行比较,结果满意。     

超声辅助低共熔溶剂提取新疆红枣中环磷酸腺苷的工艺优化

针对新疆红枣,采用绿色、高效的低共熔溶剂（Deep Eutectic Solvent,DES）为提取剂,通过超声波辅助技术提取其中的功能性成分——环磷酸腺苷（cyclic adenosine 3',5'-monophosphate,cAMP）。研究低共熔溶剂的摩尔比、含水量以及料液比、超声时间、超声温度与cAMP提取量的关系,通过单因素实验和响应面优化试验,得出新疆红枣中cAMP提取的最佳条件为:氯化胆碱与丙三醇摩尔比为1:3,DES体系含水量为44%,红枣粉末与DES的料液比为1:35 g/mL,超声时间为45 min,超声温度为45 ℃,此时与同等超声条件下的水提法和醇提法相比,低共熔溶剂法提取cAMP的含量最高为（284.15±0.06） μg/g。因此,选用超声波辅助低共熔溶剂提取新疆红枣中的cAMP是获得较高提取量的一种新型、高效和安全的方法。     

Early Postmortem Detection of Exudative Pork Meat Based on Nucleotide Content

The content of nucleotide metabolites in the muscle L. dorsi was analyzed for the detection of pale, soft and exudative (PSE) pork meats at just 2 h postmortem. PSE meat was characterized by significantly lower (p < 0.05) amounts of adenosine 5'-triphosphate (ATP) and higher adenosine 5'-monophosphate (AMP), inosine 5'-monophosphate (IMP), inosine (ino) and hypoxanthine (hyp) than normal meat. IMP and ino classified all the samples from both groups with statistical significance (p < 0.05). The K₀ value, R' value and IMP/ATP ratios were also useful indicators for full distinction of PSE meats. Thus, the assay of any of these nucleotide metabolites may allow a good detection of PSE meats at very short, only 2 h, postmortem time.     

Determination of Inosine-5-Monophosphate in Fish Tissue with an Enzyme Sensor

An enzyme sensor for IMP consisted of immobilized enzymes and an oxygen electrode. A nucleotidase (E.C. 3.1.3.5.), nucleoside phosphorylase (E.C. 2.4.2.1.) and xanthine oxidase (E.C. 1.2.3.2.) were immobilized on a membrane prepared from cellulose triacetate, 1,8-diamino-4-aminomethyloctane and glutaraldehyde. Optimum conditions for IMP determination were pH 7.8, 30°C, a flow rate of 1 ml min⁻¹ and sample volume of 20 μl. A calibration curve for IMP was linear up to 15 mM. This sensor could be applied to the determination of IMP in meats of sea bass, mackerel, yellowfish and saurel. Good correlative results were observed between the values obtained by the sensor and the conventional method. The sensor was stable for more than 15 days at 5°C and 100 assays.     

Simultaneous determination of flavor enhancers in stock cube samples by using spectrophotometric data and multivariate calibration

Spectrophotometric data followed by a suitable treatment of chemometric analysis were used for the simultaneous determination of monosodium glutamate (MSG), guanosine 5′-monophosphate (GMP) and inosine 5′-monophosphate (IMP) in stock cube samples, without any previous extraction step. By this way, the overlapping of the absorption spectra was resolved using a PLS-1 model. The concentration for experimental calibration matrix were varied between 5.03–34.2 μg mL⁻¹ for IMP and GMP, and 448–1399 μg mL⁻¹ for MSG. The relative errors of prediction (REPCV %) were 1.8, 2.8 and 3.1 for IMP, GMP and MSG, respectively.     

Pacific Cod Muscle 5'-Nucleotidase

SUMMARY: A 5'-nucleotidase, widely distributed in teleost fish muscles, was purified about 20-fold from Pacific cod (Gadus macrocephalus) by chromatography of a dialyzed aqueous extract of the muscle on DEAE-cellulose. The enzyme was unstable and lost 85% of its activity in 1 hr at 37°C 53% in 10 min at 42°C and 40% in 1 hr at 30°C. It was stable for 6 days at 0°C, could be dialyzed for up to 3 days at 0°C against 1 mM tris buffer pH 7.5 and quickly frozen and thawed without loss of activity. However, it was inactivated rapidly when held at −30°C. Brief exposure to pH 4.0 or 5.0 effected marked destruction. Attempts at further purification by means of chromatography on hydroxylapatite, adsorption using alumina Cγ and starch gel electrophoresis failed due to instability.
The enzyme was strongly inhibited by EDTA, pyrophosphate, KF and ZnCl₂ (1-10 mM); less markedly inhibited by GSH, 2-mercaptoethanol, carbonate and CaCl₂ (10 to 100 mM). It was strongly activated by Mn⁺⁺ and weakly activated by Mg⁺⁺. The optimum pH was 7.6, and the Km was 5 × 10⁻⁴M with UMP and 8 ⁻⁴M with IMP. It hydrolyzed, in order of effectiveness, LJMP, IMP, CMP, d-AMP, GMP, d-IMP, d-GMP, d-UMP and AMP, but not p-nitro phenylphosphate, sugar phosphates or a number of other compounds including 2',3'-nucleotides.     

EFFECT OF HIGH PRESSURE TREATMENT ON CYTOPLASMIC 5'-NUCLEOTIDASE FROM RABBIT SKELETAL MUSCLE

We investigated the effect of high‐pressure treatment on the properties of cytoplasmic 5′‐nucleotidase (NT), which converts inosine monophosphate (IMP) into inosine. After pressure treatment at 400 MPa, the activity of purified IMP‐NT remained at almost 100%, but the activity of partially purified adenosine monophosphate (AMP)‐NT decreased to about 40%. These data suggest that there is a difference in the pressure stability between the enzymes. In situ fluorescence spectroscopy of IMP‐NT under pressure showed that its pressure‐induced denaturation was reversible. When the pressure was reduced from the highest pressure to ambient pressure, hysteresis was observed. This suggests that high pressure treatment may lead to a partial change in the affinity of the subunits for each other once they have dissociated. The activities of IMP‐NT and AMP‐NT extracted from pressure‐treated muscles decreased remarkably between 250 and 450 MPa, but IMP‐NT was more stable than AMP‐NT.     

多功能鲜味汁的调配研究

本文采用正交实验法对多功能鲜味汁的配方设计进行了研究。结果表明：鲜味汁的最佳配方是：食盐18%、味精1.4%、I G0.055%、辛香液20%、酵母精0.1%、米酒1.5%、焦糖色素2%、蔗糖10%、酱油香精1%、干贝素和植物蛋白水解物适量。所得产品味道鲜美,碱甜适口,诸味调和,具有增鲜、调味、调香、除腥等作用。     

紫外分光光度法与荧光光谱法探究呈味核苷酸与EGCG及其蛋白络合物的相互作用

为了探究IMP、GMP是否与EGCG及其蛋白络合物发生相互作用从而影响呈味特性，利用紫外分光光度法和荧光光谱法测定光谱的变化，结果表明: IMP、GMP与EGCG会发生相互作用，改变EGCG的光谱特性，且只存在一种结合方式，GMP与EGCG相互作用的效应强于IMP与EGCG的相互作用，两种呈味核苷酸1:1混合时对EGCG影响最大；IMP、GMP均不单独与BSA发生相互作用，但两者同时存在时会对BSA产生静态荧光淬灭，结合常数为0.6634，结合位点数为0.88；与EGCG蛋白络合物相互作用中，GMP单独存在时只与EGCG反应，IMP、GMP同时存在时以与蛋白的相互作用为主，结合常数为1.1054，结合位点数为1.49。此研究可更清晰地了解茶汤的呈味机制，为茶叶品质提高及茶饮料风味改善提供理论基础。     

海鲜酱制备工艺技术的研究

利用罗非鱼下脚料自溶及南美白对虾虾头酶解制取水解液,并以这两种水解液为主要原料,研制营养丰富的海鲜酱.其配方为:水解液 50%、白糖5%、食盐 15%、味精0.5%、淀粉4%、黄原胶0.25%、白酒2%、I G:0.25%、酱油6%、姜汁甘草汁6%.该加工工艺简单易行,为水产品加工下脚料的综合利用提供了新思路.     

呈味核苷酸的新应用介绍

文章主要介绍5’-肌苷酸二钠(IMP)和5’-鸟苷酸二钠(GMP)在食品领域中的新应用.IMP能增强产品的成感、酸感及入口香辛料风味;GMP能增强产品奶油感、脂肪感并能增强产品的回味,同时起到改善产品质构的效果.IMP能增强成感因此可降低产品中的盐分含量,具有减盐功效;GMP能增强乳制品奶油和脂肪的风味与口感,因此可降低乳制品中的脂肪含量同时具有良好的口感.     

酶解河蟹边角料制备调味汁的加工工艺研究

该研究以河蟹冷冻边角料为原料,通过蛋白酶解及美拉德反应增香技术,制备调味汁。以水解度和感官评分为评价指标,通过单因素试验和正交试验对河蟹边角料的酶解工艺条件和产品的调配工艺进行优化。结果表明,最佳酶解工艺为：河蟹边角料反应液料液比1∶4（g∶mL）,碱性蛋白酶650 U/g,酶解pH 10.5,酶解时间4 h,酶解温度45 ℃。在此条件下得到的氨基酸态氮含量为0.53 g/100 mL的河蟹边角料美拉德反应液。以此为基液配制调味汁,获得河蟹调味汁最优配方为：味精7%、白砂糖7%、盐6%、淀粉2.5%、料酒2%、卡拉胶0.2%、焦糖色0.1%、5'肌苷酸二钠＋5'鸟苷酸二钠（I+G）0.05%（以美拉德反应液为基准）。该产品各项理化和微生物指标均符合国家标准。按此工艺制备的河蟹调味汁呈红褐色,具有独特的蟹的鲜香味。     

挤压喷雾生产香菇粉工艺优化及产品理化性质

利用挤压喷雾技术生产香菇粉调味料。在单因素试验基础上进行正交试验优化挤压条件,通过对比挤压前后香菇粉的理化性质变化,研究香菇粉的使用条件、范围以及营养成分的变化规律。结果表明:最佳工艺为香菇原料初始水分含量50%、挤压温度150℃、模孔直径3 mm,此条件下制得的香菇粉香味物质I+G(I表示肌苷酸,G表示鸟苷酸)含量最高。挤压喷雾处理后的香菇粉脂肪含量下降,热性质稳定,表面更加致密光滑,粉状性质变佳且活性基团没有明显变化。挤压喷雾处理的香菇粉,在食品生产中可作为调味料和功能性添加剂使用。     

挂糊鳙鱼块油炸工艺优化及不同工艺对非挥发性呈味物质的影响

基于模糊数学综合感官评价法对油炸鳙鱼块制作工艺参数（腌制时间、油炸温度、油炸时间）进行优化,同时测定不同工艺油炸鱼块的理化指标并与感官指标进行相关性分析;利用高效液相色谱法（HPLC）对油炸鱼块中非挥发性呈味物质进行分离鉴定。结果表明:最佳制作工艺条件为腌制时间20 min,油炸温度180℃,油炸时间5 min,在此条件下,游离氨基酸总量为408.53 mg/100 g,呈味核苷酸总含量为73.06 mg/100 g。结合理化指标分析进一步得到含水量、a*和b*是影响感官评价的主要品质因素。不同工艺对游离氨基酸和呈味核苷酸含量影响显著（p<0.05）,游离氨基酸中谷氨酸、甘氨酸、组氨酸和丙氨酸含量较高,其中谷氨酸和组氨酸均超过其阈值,对鱼块有较强呈味作用;呈味核苷酸以5’-IMP为主,而5’-AMP在所有样品中均未检测到,5’-IMP和5’-GMP均超过阈值,对鱼块的味道具有贡献作用。因此,在腌制时间20 min,油炸温度180℃,油炸时间5 min条件下,油炸挂糊鳙鱼块的品质最佳。