添加赖氨酸的猪肉脯在不同干燥温度下的质构稳定性

为改善猪肉脯在不同热风干燥温度下的质构稳定性,研究在干燥温度55～75℃条件下添加0.25%～0.75%赖氨酸对猪肉脯质构稳定性的影响。结果表明：添加0.50%赖氨酸可显著降低高温（70～75℃）干燥下猪肉脯的硬度和内聚性（P<0.05）,显著提高其弹性（P<0.05）,减小猪肉脯硬度、弹性、内聚性和咀嚼性在干燥温度55～75℃条件下的极差值,并可在（60±5）℃和（65±5）℃变化范围内将猪肉脯咀嚼性的极差值控制在1.4%以内;赖氨酸可能通过提高并稳定猪肉脯体系pH值、改善微观结构、提高肉蛋白及其二级结构的热稳定性、增强内部氢键作用力和水分流动性、阻滞肌球蛋白热降解等作用,提升猪肉脯在不同干燥温度下的质构稳定性。     

Determination of neohesperidin dihydrochalcone in foods

An HPLC method was developed for the determination of neohesperidin dihydrochalcone (NHDC) in foods. A solid sample was extracted with methanol. The extract was evaporated and the residue was dissolved in methanol-water (2:8) mixture. In the case of fluid sample, the sample solution was prepared by dilution with methanol-water (2:8) mixture. The sample solution was cleaned up on a C18 cartridge. The cartridge was washed with water and methanol-water (3:7) mixture, and NHDC was eluted with methanol-water (7:3) mixture. NHDC in the eluate was separated on an ODS column and determined with a UV detector (282 nm). The identity of NHDC in foods was confirmed by means of HPLC with a photodiode-array detector. The recoveries of NHDC added to various kinds of foods were 75.2-134%. The determination limit of NHDC was 1 microgram/g.     

Sweeteners interacting with the transmembrane domain of the human sweet-taste receptor induce sweet-taste synergisms in binary mixtures

Sweet enhancing effect of neohesperidin dihydrochalcone (NHDC) or cyclamate has been reported to be synergistic in human sensory tests. However, little is known about whether these synergisms are caused by the mechanism mediated by the human sweet-taste receptor. Here, we examined the sweetness intensity of sweet tastant mixtures by measuring the responses of cultured cells stably expressing the human sweet-taste receptor. The results showed that the cell response to sucrose was synergistically potentiated by the addition of NHDC or cyclamate. Moreover, a point mutation in the transmembrane domain of hT1R3 almost completely eliminated the enhancing effects of NHDC and cyclamate. These results suggest that ligand–receptor interactions in the transmembrane domain of hT1R3 are necessary for NHDC and cyclamate to elicit the synergistic potentiation of the receptor activation. Our results may provide the foundation of a molecular basis for receptor-based synergisms of sweet tastes in mixtures of diverse sweet substances.     

Stability Modeling of Red Pigments Produced by Monascus purpureus in Submerged Cultivations with Sugarcane Bagasse

Monascus purpureus red pigments were produced in submerged cultivations employing sugarcane bagasse (SB) as carbon source in combination with various nitrogen sources. Peptone and soy protein isolate (SPI) as nitrogen sources generated the best pigment yields. NH₄Cl has not supported high pigment production. Red pigments produced using SB and SPI as growth substrates were submitted to temperature and pH stability analysis. Data from thermal pigment degradation were fitted to five mathematical models, and a first-order equation was accepted as the best one to describe color decay. Red pigments showed high stability at low temperatures (30–60 °C) and at near-neutrality pH values (6.0–8.0) when compared to that at high temperatures (above 60 °C) and at acidic pH values (4.0–5.0). Monascus pigments produced using a low-cost agroindustrial waste (SB) as carbon source could be utilized as colorants in foods and foodstuffs manufactured under mild process conditions.     

Gelation of mixed systems whey protein concentrate–gluten in acidic conditions

Gels of whey protein concentrate (WPC)–gluten were prepared by heating WPC–gluten dispersions (10% whey protein/0–5–10% gluten protein, w/w; pH 3.75 or 4.2). Gels were characterized through solubility assays in different extraction solutions, measures of water-holding capacity (WHC), firmness, elasticity and relaxation time, and light microscopy. Differential scanning calorimetry (DSC) of WPC–gluten dispersions was also performed. Gluten increases the firmness and elasticity of gels, mainly at pH 4.2. The WHC also increases with gluten content, being higher at pH 3.75 than at pH 4.2. Solubility assays indicate that electrostatic forces, hydrophobic and H bindings would be involved in maintaining the gel structure of WPC gels at pH 3.75 and 4.2, whereas in mixed gels of WPC–gluten, the principal forces responsible for the maintenance of the gel structure at these pHs would be hydrophobic and H bindings, and in gels prepared at pH 4.2 also disulfide bonds, but in a minor extent. The presence of gluten shifts the apparent transition temperature for whey protein denaturation towards lower temperatures. Gels with gluten present a smooth network with gaps and a more elastic appearance, as observed by light microscopy.     

新甲基橙皮苷二氢查耳酮及合成前体药理作用研究进展

新甲基橙皮苷二氢查耳酮（Neohesperidin dihydrochalcone,NHDC）是一种无毒、高甜度、低热量的甜味剂,具有增甜、增香、掩盖苦味、修饰风味的功能与抗氧化、抗炎、降血脂等药理活性,在食品及医药领域具有一定的开发潜力。当前NHDC的合成前体主要包括橙皮苷（Hesperidin,HSD）、新橙皮苷（Neohesperidin,NHP）和柚皮苷（Naringin,NRG）,具有抗氧化、保护肝肾、抑菌和改善胃肠道等多种生物学活性。NHDC的药理研究相对具有发展进程缓慢、研究系统欠缺、机制深度缺乏等特点。本文以NHDC及其合成前体为关键词在SciFinder、Web of Science、CNKI等科学数据库中进行检索,综述了NHDC的药理作用和机制,并对其合成前体的药理研究进展进行总结,以期为NHDC的进一步综合利用和开发高附加值产品提供参考。     

钯碳对合成新橙皮苷二氢查尔酮的影响

在碱性条件下,以新橙皮苷为原料、钯碳(Pd/C)为催化剂合成新橙皮苷二氢查尔酮(NHDC),研究新橙皮苷与催化剂的投放比例、催化剂的循环次对产率的影响。结果表明,新橙皮苷与催化剂比例为4∶1时,该条件下NHDC的产率最大,产率接近99%;循环次数与产率成反比,循环1~5次时,产率始终在80%以上,循环次数为1时产率最高。     

Correlation between antiradical activity and stability of betanine from Beta vulgaris L roots under different pH,temperature and light conditions

When the antiradical activity and stability of betanine were studied at pH values of 3.5 and 8.5 and temperatures of 25, 50 and 75 °C, the results showed that the antiradical activity was greater at acidic pH and lower at higher temperatures. At basic pH the activity of betanine correlated well with its stability at the three temperatures assayed, suggesting that the degradation products, betalamic acid (BA) and cyclo DOPA 5‐O‐β‐D ‐glucoside (CDG), did not contribute to this activity under the experimental conditions used. However, at acidic pH the degradation product, CDG, did seem to contribute to the antiradical activity. Furthermore, at pH 3.5, betanine stability was so great that light conditions had no effect on the antiradical activity. At basic pH, too, light had no effect on betanine activity owing to the high instability of the pigment. © 2001 Society of Chemical Industry     

Accelerated Kinetic Study of Aspartame Degradation in the Neutral pH Range

The degradation of aspartame in solution as a function of temperature (70–100°C), buffer concentration (0.01–0.1M phosphate), and pH (6–7) was studied in order to estimate losses during thermal processing and storage of aseptic milk-based drinks. Prior data have been mostly on acid carbonated beverages. First order rate constants were obtained in all the conditions with activation energies in the range 14–20 kcal/ mole. An increase in both pH and buffer concentration caused an increase in rate of loss. These data were used to predict losses that would occur during pasteurization and sterilization conditions. Experiments at 4 and 30°C showed significant losses would occur during 4 and 30°C temperature storage and extrapolation from high temperatures predicted faster degradation rates than those found.     

The protective effect of sodium dodecylsulphate on the thermal precipitation of conalbumin. A study on thermal aggregation and denaturation

The thermal precipitation and denaturation of conalbumin was studied separately at different pH values, low concentrations of an anionic detergent and salt concentrations relevant to food products. Sodium dodecylsulphate (SDS) was used as a model detergent and was found to lower the limit for thermal precipitation from pH 10–11 to pH 6–8 leaving a neutral pH region open for heat processing without any decrease in solubility. This protection against precipitation took place at the expense of a reduced thermal stability of conalbumin. Analysis at linearly increasing temperatures was shown to be a productive method to study the coupling between the thermal precipitation and denaturation processes. This coupling was examined at two heating rates, 10 and 1.25°C/min, respectively. Two types of precipitation behaviour were identified, a rapidly and a slowly sedimenting one. At the lower heating rate and under conditions where rapidly sedimenting precipitates were formed there was a close correlation between precipitation and denaturation. The precipitation was, however, always completed prior to denaturation. When approaching conditions where no precipitation took place, which also implied a successive transition towards slowly sedimenting precipitates, the precipitation process became delayed compared to denaturation. Precipitation could thus be registered at temperatures far above those of complete denaturation. The precipitates formed showed a considerable variation in particle size and water holding capacity.     

Effect of pH and temperature on the thermostability of prickly pear (Opuntia ficus‐indica) yellow‐orange pigments

The colour stability of the yellow‐orange pigment (λ_max = 476 nm) of prickly pear (Opuntia ficus‐indica) fruit was determined as a function of temperature and pH. The experiments were carried out at three different temperatures (50, 70 and 90°C) with pigment solutions at pH values ranging from 2–7. The degree of pigment retention decreased with increasing temperature as a function of increasing thermal exposure time with least pigment degradation at pH 5. The reaction rate constants were determined as 0.0062, 0.0383 and 0.1102 min^–1 for a thermal degradation reaction rate of pseudo‐first order. The activation energy was calculated as 65.1 kJ·mol^–1.     

Stability of casein micelles cross-linked with genipin: A physicochemical study as a function of pH

Chemical or enzymatic cross-linking of casein micelles (CMs) increases their stability against dissociating agents. In this paper, a comparative study of stability between native CMs and CMs cross-linked with genipin (CMs-GP) as a function of pH is described. Stability to temperature and ethanol were investigated in the pH range 2.0–7.0. The size and the charge (ζ-potential) of the particles were determined by dynamic light scattering. Native CMs precipitated below pH 5.5; CMs-GP precipitated from pH 3.5 to 4.5, whereas no precipitation was observed at pH 2.0–3.0 or pH 4.5–7.0. The isoelectric point of CMs-GP was determined to be pH 3.7. Highest stability against heat and ethanol was observed for CMs-GP at pH 2, where visible coagulation was determined only after 800 s at 140 °C or 87.5% (v/v) of ethanol. These results confirmed the hypothesis that cross-linking by GP increased the stability of CMs.     

The stability properties of golden beet and red beet pigments: influence of pH, temperature, and some stabilizers.

Golden beet (Beta vulgaris var. lutea) color was found to contain 8 components, of which the most important seemed to be vulgaxanthin-I and -II. Purified vulgazanthin -I solutions are easily degraded at high temperatures. The stability is, however, strongly dependent on pH: the stability is best at pH values between 5 and 6, the poorest at low pH values, but at pH 7 the stability is better than that of betanin. Vulgaxanthin-I is more stable in the raw extract than in a purified solution. EDTA, even in ppm amounts, was found to improve the stability of betanin. The effect was dependent on pH value, being most efficient at pH 2.0 and 5.0. Stability of vulgaxanthin-I was not improved by EDTA. Tannin did not show stabilizing influence. Ascorbic acid was found to have an unfavorable influence on stability, especially in the case of betanin.     

Stability and Antioxidant Activity of Food-Grade Phycocyanin Isolated from Spirulina platensis

Food-grade phycocyanin was obtained from Spirulina platensis cultured in seawater-based medium and purified by ammonium sulfate precipitation. The stability of phycocyanin under different conditions, including different pH, temperature, light, and edible stabilizing agents, was systematically investigated by spectroscopy methods. The optimum pH range for phycocyanin was found to be 5.0–6.0. Phycocyanin was kept stable at temperatures up to 45ºC over short time periods (i.e., no significant changes were observed in the relative concentration of phycocyanin, C_R). In contrast, incubation at a relatively high temperature resulted in a decrease in the C_R and half-life in a temperature-dependent manner. Constant exposure to light at 100 μmol m^–2 s^–1 for 36 h, decreased the C_R value of phycocyanin (pH5.0) to 78.4%. Sodium chloride was an effective stabilizing agent for phycocyanin, and its efficacy increased in a concentration-dependent manner for all concentration ranges assessed in this study. Moreover, phycocyanin exhibited concentration-dependent antioxidant activities in 2,2′-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) and α,α-Diphenyl-β-pricrylhydrazyl assays. Taken together, our results suggest that the optimal conditions for preserving the stability of food-grade phycocyanin isolated from S. platensis are a pH of 5.0–6.0, low temperature, darkness, and the addition of edible stabilizing agents.     

Stability of α-L-aspartyl-L-phenylalanine methyl ester hydrochloride in aqueous solutions

The stability of USAL (α-L-aspartyl-L-phenylalanine methyl ester hydrochloride) was studied in solutions in relation to the pH value (1.10–6.95 at 20 °C), the temperature (20–80 °C at pH 2.2) and the ionic strength (0.16–2.0 at 20 °C and pH 4.0). The effects of pH and temperature of the medium were very significant. From the point of view of the stability the optimum pH value lies in the pH range 2.5–4.5 and at lower temperature. The ionic strength did not affect the stability in the tested range. The effects of citric acid (0–10%) and sucrose (0–75%) were also investigated. An addition of citric acid exhibited an effect on USAL stability corresponding to the shift of pH value that it caused. The occurrence of sucrose in the solution had a favorable effect at higher concentrations.     

疏水淀粉皮克林乳液凝胶的稳定机理及影响因素

研究不同因素（温度、pH值和离子强度）对淀粉-脂质复合物（starch-fatty acid complex,SFAC）稳定的皮克林乳液凝胶的影响规律并揭示其稳定机理。激光共聚焦扫描显微镜和扫描电子显微镜结果显示,SFAC颗粒通过吸附于油水界面,形成一层紧密的屏障包裹油滴,形成呈圆状的乳滴,乳滴之间紧密堆积形成稳定的乳液凝胶网络结构。光学显微镜、粒径分布及Zeta电位等结果显示该疏水淀粉皮克林乳液凝胶在pH 3～9范围内以及离子浓度0.1～0.9 mol/L条件下都能维持乳液凝胶结构并具有良好的贮藏稳定性。此外,该皮克林乳液凝胶具有热可逆性,在高温下粒径增大、黏度下降,出现流动性,冷却后可重新呈现凝胶状。研究结果表明疏水淀粉皮克林乳液凝胶在较宽的温度、pH值和离子强度范围内均有较高稳定性,适用于多种植物油的稳定。     

Influence of temperature and pH on the degradation of deoxynivalenol (DON) in aqueous medium: comparative cytotoxicity of DON and degraded product

Deoxynivalenol (DON), a toxic fungal metabolite, is stable under different processing conditions; however, its stability in aqueous medium at different temperatures and low pH (1–2) (present in the gastrointestinal tract) has not been investigated. In the present study, DON standard was used to study the influence of temperature and pH on DON stability in aqueous medium, the characterisation of the degraded product, and the comparative toxicity profile of the degraded and the parent compound. The results suggest that standard DON was unstable at 125–250°C showing 16–100% degradation whereas DON at pH 1–3 had 30–66% degradation, with a concomitant increase in the formation of a degraded product. Further ESI-MS characterisation of the dominant precursor ion of the HPLC eluate of the DON-degraded product was found to be m/z 279, resembling the known metabolite DOM-1. The degraded product of DON was reconfirmed as DOM-1 by comparison with standard DOM-1 and both gave a similar λ_max at 208 nm. Comparative studies of both standard DOM-1 and the degraded product of DON showed no cytotoxicity up to 6400 ng ml^–1 while significant cytotoxicity was observed for DON (400 ng ml^–1). The results suggest that a highly acidic environment (pH 1–2) could be responsible for the de-epoxydation of DON leading to the formation of DOM-1.     

Microbial dynamics during aerobic deterioration of silages

Factors affecting microbial dynamics during aerobic deterioration of silages were evaluated in laboratory, pilot-scale and full-scale experiments. Yeasts usually caused the initial deterioration but in some samples with fairly good storage stability (>10 days) the activity was associated with the growth of moulds and bacteria. At a later stage, and especially at higher temperatures (>40°C), the activity was caused by bacilli. The increase in pH as a result of lactate metabolism permitted the growth of Enterobacteria. Evaluation of storage stability in samples from different levels in a bunker silo indicated low stability in surface samples and fairly good stability in samples from 160cm depth. The surface samples contained higher numbers (100–1000 times) of yeasts but the pH levels were similar. The establishment of yeasts during storage is probably due to diffusion of oxygen by leakage through the plastic cover. Compared with a plastic cover (0.1mm polythene), a rubber seal improved storage stability in laboratory silage (pH4.0) inoculated with lactic acid bacteria and infected with Candida albicans. An increase in acid content and a reduction in pH (3.7) by means of an efficient inoculant did not seem to increase the storage potential under the conditions described above. The content of adenosine triphosphate has been used as a measure of microbial activity during aerobic deterioration of silages. The main activity was concentrated at the surface (0–5cm). At 20°C, the activity was about ten times higher at the surface than at a depth of 30cm; above 30°C it was about 100 times higher.     

Application of Carbohydrases in Extracting Protein from Rice Bran

Enzymatic pretreatments of rice bran, using commercial carbohydrases to improve nitrogen extractability, were investigated. The pretreatment used a response surface method which included the variations in concentration of Viscozyme L (0–120 FBG unit) and Celluclast 1.5L (0–360 NC unit), time of incubation (1–5 h) and pH (3·8–5·4). The experiments were conducted at two different temperatures, 40 and 50°C. At 40°C, the maximum nitrogen extraction predicted by the model was obtained when the Viscozyme–Celluclast mixture at pH 3·8 with incubation time of 5 h was applied, giving an extracted N of 51%. At the process temperature of 50°C, the model predicted that the use of Viscozyme alone, under similar conditions, would have a most significant effect in increasing the efficacy of the nitrogen extraction, producing a 57% extracted N. This enzymatic pretreatment method improved the nitrogen extractability of rice bran at the neutral pH. © 1997 SCI.     

THE ROLE OF BACILLUS spp. IN N-NITROSAMINE FORMATION DURING WORT PRODUCTION

The relative importance of bacterial and acid catalysed formation of Apparent Total N-Nitrosocompounds (ATNC) and N-nitrosodimethylamine (NDMA) following reduction of nitrate by a strain of Bacillus coagulans was investigated. The bacterium was isolated from the brewhouse and could grow and reduce nitrate at temperatures up to 70°C. Although evidence of thermophilic denitrification was observed, the predominant end products of nitrate reduction were ammonia and nitrous oxide. Bacterial catalysis of ATNC formation in sweet wort at pH 5.3 coincided with high nitrate and nitrite reductase activities and was, at 741 μg h^?1 (mg cell protein)^?1, three times faster than would be expected due to acid catalysis alone. The formation of NDMA at pH 7.8 was 300–500 times faster in the presence of nitrite than in the presence of nitrate possibly implicating the involvement of nitrite reductase .