Stability of Glutamic Acid and Monosodium Glutamate Under Model System Conditions: Influence of Physical and Technological Factors

The stability of glutamic acid and monosodium glutamate as regards pH, temperature and oxygen was studied during storage and two thermal processings, the residual products and those which appeared being determined. The initial molecules only change into pyrrolidonecarboxylic acid, never into glutamine nor γ-aminobutyric acid. Preservation is good in all cases at pH 0 and pH 14, but glutamic acid is converted to pyrrolidonecarboxylic acid at intermediate pH values. The change is favored by pH values ranging from 2 - 3, by temperature increase and by oxygen.     

外界环境和食品体系对菊苣酸稳定性的影响

本实验研究pH值、温度、金属离子、紫外线以及不同食品体系（果汁饮料、奶粉和果冻）对菊苣酸稳定性的影响。菊苣酸的含量由高效液相色谱法（high performance liquid chromatography,HPLC）测定。结果表明：随着pH值（3、5、7、9）和温度（60、70、80 ℃）的升高,菊苣酸的稳定性逐渐降低;相同浓度的Na+和K+对菊苣酸的稳定性无显著影响,但Ca2+溶液遇菊苣酸会瞬间发生变色反应;菊苣酸对紫外线敏感度较高,且在甲醇中的异构化率明显高于在水中的异构化率;菊苣酸在果汁饮料中,室温（25 ℃）贮藏3 个月后保存率约为85%,4 ℃贮藏3 个月后含量无明显变化;室温下避光贮藏3 个月,菊苣酸在奶粉和果冻体系中能够保持相对稳定。不同食品体系对菊苣酸稳定性的影响有差异,总体上食品体系能在一定程度上维持菊苣酸的稳定性,保护其免受降解。     

Influence of Spray-Drying Conditions on Physical and Morphological Characteristics of Microencapsulated Benzoic Acid

Benzoic acid is widely used as a preservative in the food and feed industry, and microencapsulation is important in the application of this ingredient in various food products. The objective of this work was to evaluate the effect of benzoic acid concentration and drying air temperature on the physical characteristics of powders produced by spray drying, using maltodextrin and modified starch as the wall materials. A rotatable central composite design was used; the independent variables were inlet air temperature (145–180 °C) and benzoic acid concentration (2–10 %, m/m). Maximum yield was obtained when higher concentrations of benzoic acid and higher inlet air temperatures were applied. The highest microencapsulation efficiency was reached at intermediate temperatures (160 °C) and low concentration of benzoic acid. The particles size (D _[4,3]) ranged from 24.99 to 29.52 μm and, in general, presented amorphous structure, spherical shape with rough surfaces and had no cracks The optimum condition, considering all the response variables together, was drying air temperature 169 °C and benzoic acid concentration 6 % (m/m). Under these conditions, the particles presented solubility of 75.96 g/100 g and wettability of 56.8 s/g. Moreover, the process showed microencapsulation efficiency of 76.77 g/100 g and yield of 40.1 %. Spray drying was considered a potential process to provide microencapsulated benzoic acid.     

高压均质对二十二碳六烯酸功能因子输送体系稳定性影响

以酪蛋白酸钠-葡萄糖美拉德反应产物（Millard reaction products,MRPs）作为乳化剂,在不同的均质条件下制备O/W型二十二碳六烯酸（docosahexaenoic acid,DHA）藻油乳状液,以相同条件下单独的酪蛋白酸钠作为对比,利用稳定性分析仪分析、贮藏期间的氧化程度分析和激光共聚焦显微镜观察对DHA藻油乳状液的物理稳定性、氧化稳定性和微观结构进行评价。结果显示：利用酪蛋白酸钠-葡萄糖MRPs制备的DHA藻油乳状液的物理稳定性和氧化稳定性远优于同等条件下单独的酪蛋白酸钠,说明酪蛋白酸钠经美拉德反应改性后具有优良的乳化性和抗氧化活性;同时,均质压力和次数对乳状液的稳定性和微观结构具有明显的影响。较优的工艺条件为均质压力95 MPa、均质3 次,此时酪蛋白酸钠-葡萄糖MRPs制备的DHA藻油乳状液的状态较好,Turbiscan稳定性分析仪对其扫描结果显示,乳状液只有轻微的顶部脂肪上浮和底部澄清,稳定性系数为1.55,小于其他各组;室温（25 ℃）贮藏28 d期间的总氧化值处于同期的最低水平;激光共聚焦显微镜下乳状液中油滴的粒径较小,主要分布在0.47～0.59 μm之间,且形态完整、较为均一。     

褐色益生菌乳饮料稳定性研究及工艺条件优化

基于近红外发射光谱的背反射光随时间的ΔBS 得到的SI 为评价指标,采用Box-Behnken 设计研究了果胶用量、均质压力、均质温度对褐色乳饮料稳定性的影响,回归分析得到优化参数为：果胶用量2.8g/L,均质压力21MPa,均质温度42℃。     

天然番茄红素在不同环境条件下的稳定性研究

研究了番茄中的色素--番茄红素在不同环境下的稳定性。实验结果表明:天然番茄红素对光敏感;酸性条件下(pH<6)不稳定;Fe3+、Cu2+引起番茄红素的损失较大;氧化剂、还原剂、防腐剂、糖对番茄红素的稳定性影响不显著。     

还原型谷胱甘肽的稳定性研究

本文研究了pH、温度、光照以及外加抗氧化剂等因素对还原型谷胱甘肽(GSH)纯品溶液稳定性的影响.结果表明,GSH水溶液在pH=2.0～4.0范围内最为稳定;在30℃以下,24h内自身氧化较少;应避光处理或保存;外加抗氧化剂在pH=6.0时,保护作用明显.     

牛骨咸味肽氨基酸分析及在模拟加工条件下功能稳定性分析

以牛骨为原料酶解制备咸味肽,牛骨咸味肽中重金属含量均处于国家标准的安全范围之内,其氨基酸含量为56.25 mg/100 mg,其中甘氨酸含量最高。以咸味质量浓度值为指标,考察不同处理条件对咸味肽稳定性的影响,结果表明:咸味肽加热温度在50℃以下、加热时间在20 min以内稳定性较好,添加可食用糖对咸味肽稳定性影响不明显,添加有机酸则会降低咸味肽的稳定性。     

果胶对果胶-麦醇溶蛋白-儿茶素模拟体系稳定性的影响

改善浑浊苹果汁中果胶-蛋白-酚类物质三元复合物的混浊稳定性。在从苹果中提取的果胶中加入儿茶素和麦醇溶蛋白,组成模拟体系,以浊度保留率为指标,分别采用单因素和正交试验研究果胶相对分子质量、果胶酯化度(degree of esterification,DE)、体系pH值对三元复合物稳定性的影响。结果表明：在实验范围内,随果胶相对分子质量的增大、果胶DE值的增加和体系pH值的升高,体系的稳定性均呈先增加后降低的趋势;通过正交试验可知,果胶相对分子质量84700、果胶DE值62.85%、体系pH3.7时,三元复合物的稳定性达到最好,浊度保留率达到最大68.80%。     

Influence of Low Concentrations of an Acid Preservative on Sponge Cakes under Different Storage Conditions

ABSTRACT:  In a previous study, we demonstrated the efficiency of an acid test preservative at concentrations higher than 10 g/kg of product. The aim of the current study has been to assay, in a pilot plant, a preservative at lower and different doses than tested in the aforementioned study, in contrast with different storage temperature and relative humidity (RH) conditions and to check the possibilities of the growth of molds with a toxigenic capacity. The effect of the test preservative is not demonstrable at very low concentrations, as occurs in batch 2. In this case, the influence of the other storage parameters, temperature and RH, has a mixed effect, which makes it difficult to draw conclusions about the convenience of the preservative. In our opinion, the minimal concentration of the test preservative to reach readable results is 4 g/kg, but it is not enough to guarantee a longer shelf life. Regarding the mycotoxigenic study, the majority of molds obtained in the isolations from the cakes after their macroscopic identification corresponded to the genera Aspergillus and Penicillium. Only 5 turned out to be mycotoxigenic, with citrinin and viridicatumtoxin being detected.     

The Influence of Drying Process Conditions on the Physical Properties,Bioactive Compounds and Stability of Encapsulated Pumpkin Seed Oil

In this study, the influence of encapsulation process conditions on the physical properties and chemical composition of encapsulated pumpkin seed oil was investigated. Four variants of encapsulated oil were prepared: spray-dried non-homogenized emulsions at the inlet temperatures of 180 and 130 °C, spray-dried homogenized emulsion at the inlet temperature of 130 °C, and freeze-dried homogenized emulsion. The emulsion was prepared by mixing 10.6% oil with 19.8% wall materials (15.9% maltodextrin + 0.5% guar gum + 3.9% whey protein concentrate) and 69.6% distilled water. The quality of encapsulated pumpkin seed oil was evaluated by encapsulation efficiency, surface oil, total oil and moisture contents, flowing properties, color, and size. Additionally, fatty acid composition, pigment characteristics, and the content of bioactive compounds (tocopherols, squalene, and sterols) were determined. Changes of these components after the encapsulation process in comparison to the control pumpkin seed oil were considered as stability parameters. The highest encapsulation efficiency was obtained by spray-drying at the inlet temperature of 130 °C. Generally, the spray-drying process had a positive effect upon the physical parameters of encapsulated pumpkin seed oil but results were dependent on process conditions. The higher inlet temperature generated more surface oil, but capsules obtained at the lower temperature were greater in size and more deformed. Although freeze-drying proceeded at a very low temperature, the powder obtained with this technique was characterized by the highest bioactive compound losses (with the exception of sterols) and the lowest stability. The homogenization process applied before spray-drying affected greater polyunsaturated fatty acid, squalene, and pigment degradation. In conclusion, results of the study showed that the spray-drying non-homogenized emulsion was a more recommendable technique for the encapsulation of pumpkin seed oil because of smaller changes of native compounds and better oxidative stability.     

Starch Phosphates Produced by Extrusion: Physical Properties and Influence on Yogurt Stability

Starch phosphorylation with sodium tripolyphosphate (STP) was performed using a single‐screw extrusion process. The extrusion variables studied were temperature (from 99.5°C to 200.4°C), water content (16.3% to 19.7%, w/w), and STP content (0.82% to 4.18%, w/w). The resulting phosphorylated starch was evaluated with respect to expansion, water solubility index (WSI), water absorption index (WAI), degree of substitution (DS), and viscosity. The phosphorylated starch was tested as a stabilizing additive in yogurt formulations, with respect to the syneresis index (SI) and the syneresis susceptibility coefficient (SSC). The results show that the expansion increases with increasing STP content, and decreases with increasing temperature and water content employed in the process. Increasing extrusion temperatures and decreasing water content resulted in increasing WSI and decreasing WAI. The DS was dependent on STP content, increasing as STP content increased, but appeared to be insensitive to changes in water content (between 16% and 20%, w/w). The highest level of yogurt stability, as measured by the syneresis index (SI) and the syneresis susceptibility coefficient (SSC), were obtained when the yogurt was formulated with the starch of the highest DS (0.018), which had been obtained at 150°C, 18% water content, and 4.12% (w/w) of STP.     

超声局部效应对咖啡酸稳定性及抗氧化性的影响

将超声区域定位划分成高低两个超声辐射面和5 个不同超声位置（P1、P2、P3、P4、P5）,对比研究低超声辐射面与高超声辐射面、超声位置、提取溶剂对咖啡酸稳定性及其抗氧化性的影响。结果表明,低超声辐射面能造成咖啡酸显著降解（P＜0.05）;高超声辐射面、超声能量对咖啡酸稳定性的影响不显著。溶剂类型是影响咖啡酸稳定性的主要因素之一,其中体积分数80%乙醇是咖啡酸理想的提取溶剂。超声槽不同位置上,超声能量的分布是不均一和动态变化的,咖啡酸在P4或P5位置时降解较为显著（P＜0.05）。此外,超声处理同样能显著影响咖啡酸的抗氧化性,1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl,DPPH）法、铁离子还原力（ferricreducing antioxidant potential assay,FRAP）法及2,2’-联氮-二（3-乙基-苯并噻唑-6-磺酸）二铵盐（2,2’-amino-di)3-ethyl-benzothiazoline 6-sulphonic acid) ammonium salt,ABTS）法3 种方法测定的咖啡酸抗氧化性的变化规律存在一定差异性。DPPH法与FRAP法同时得到P5位置是影响咖啡酸抗氧化性最显著的位置,该位置咖啡酸降解产物的抗氧化性高于咖啡酸自身的。不同超声辐射面上,ABTS法测定咖啡酸的抗氧化性与其含量成正相关,而DPPH自由基清除能力与其含量成负相关。以上表明低超声辐射面,有效的超声能量能显著影响咖啡酸的稳定性和增加其抗氧化性。     

Stability of Mackerel Surimi Prepared under Lipid-Stabilizing Processing Conditions

Surimi from mackerel whole and light muscle was prepared under conditions designed to minimize oxidation and development of rancidity. The lipid-stabilizing procedure included early addition of both lipid-and water-soluble antioxidants, avoidance of added sodium chloride, and exclusion of oxygen. Surimi prepared from light muscle was stable to rancid odor development in both the raw and cooked form; gel strength was reasonably stable during frozen storage, although the color was somewhat dark. Surimi prepared from mackerel whole muscle was darker, its odor quality lower and less consistent, and its gel strength lessened more rapidly during frozen storage than surimi prepared from light muscle.     

乳酸链球菌素脂质体在不同pH值条件下的稳定性及其抑菌效果

为了提高乳酸链球菌素（Nisin）的利用率,实现其长效、缓释型抑菌性能,采用薄膜-超声法制备Nisin脂质体,以大豆卵磷脂为壁材,利用傅里叶变换红外光谱分析Nisin脂质体的内部结构及不同pH值条件对Nisin脂质体稳定性及其包埋率和缓释效果的影响,比较不同pH值条件下热处理对Nisin脂质体抑菌效果的影响。结果表明：Nisin被结合在卵磷脂内部,两者通过相互作用形成的氢键结合在一起。随着体系pH值的降低,Nisin脂质体的粒径逐渐增大,颗粒规整度变差,同时包埋率降低、缓释性变差,稳定性逐渐降低。当pH值为7.0时,Nisin脂质体的包埋率（82.26%）达到最大。此外,pH 6.0时体系缓释能力最强,6 d后总释放率达到96.49%。最小抑菌浓度和最小杀菌浓度分析结果表明,Nisin脂质体的抑菌效果受pH值的影响较小,且与Nisin相比抑菌效果较弱。然而,Nisin脂质体在121 ℃、15 min灭菌处理后仍具有良好的抑菌效果,表明该体系具有热稳定性。动态杀菌曲线结果表明Nisin脂质体具有一定的持续抑菌性能。     

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.     

影响硼酸结晶形状的因素

从硼酸的结晶机理入手,探讨了影响硼酸结晶形状及大小的因素,在合理地控制操作条件的同时,加入合适的晶习改性剂,可以加大硼酸结晶体的粒状比例。     

Physical Stability of Spray-Dried Milk Fat Emulsion as Affected by Emulsifiers and Processing Conditions

ABSTRACT: The effects of emulsifiers, wall, carbohydrate, and processing conditions on the physical properties of encapsulated powders were studied. Unstable emulsion causes an increase in the surface fat of spray-dried powder. Surface fat decreased with increasing DE and was unaffected by drying outlet temperature. A seven-fold decrease in surface fat was observed when the oil droplet size increased from 0.5 to 1.2 μm. At best, about 98% of the milk fat was encapsulated. Powder average particle size changed with outlet air temperature, oil droplet size, and DE. Particles contained air cells with some large voids and more spherical shape for 36 DE but dented and irregular shape for 10 DE.     

Survival of Lactic Acid Bacteria and Their Lactases under Acidic Conditions

Effects of sonication, survival, and β-galactosidase activity of four lactic cultures were investigated in pH 1.5-3.5 range. Lactobacillus delbruekii subsp. bulgaricus and Streptococcus thermophilus exhibited the highest β-galactosidase activity in skim milk and broth systems, respectively. The β-galactosidases from L. delbruekii subsp. bulgaricus, S. thermophilus, and L. acidophilus showed optimum activity in the neutral pH range and 55°C. Viable count of all four cultures decreased most rapidly at pH 1.5, but L. acidophilus and L. delbruekii subsp. bulgaricus survived better than the other organisms. The decrease of enzyme activity of unsonicated cultures with pH was slight, especially at pH 3.5. However, acidification of sonicated cultures to pH 3.5 or lower resulted in rapid and permanent loss of enzyme activity.