天然抗氧化剂及其协同作用

抗氧化剂是指能够减缓或者消除氧化反应的一类物质,根据来源不同,分为天然和合成两大类,常见的天然抗氧化剂有茶多酚、维生素E、槲皮素、虾青素等。研究发现,合成抗氧化剂存在一定的安全问题,而且单一的天然抗氧化剂活性比较低,因此具有高活性以及低细胞毒性的复配抗氧化剂是最近研究的热点。本文对天然抗氧化剂之间复配的机制及研究进展进行了阐述,以期能够对其发展提供一定的参考价值。     

Solidification behaviour of binary sitosteryl esters mixtures

Phytosterol esters are known for their blood cholesterol lowering effect and have consequently been incorporated into vegetable oil table-spread products. In furtherance to gaining knowledge about these materials in a fat-blend environment, the current work describes the phase-diagram based thermal characteristics of a series of β-sitosterol alkyl-ester homologues prepared as binary mixtures and observed using differential scanning calorimetry. A scanning speed of 10 K min⁻¹ was chosen and, whilst not representing true equilibrium conditions, was more indicative of the likely dynamic melting or cooling conditions found in a fat-blend product during processing. The thermal behaviours presented reflect therefore this concept. Long-chain saturated esters showed ideal solubility behaviour of immiscible solids. In contrast, the shorter-chain homologues produced complex and dynamic phase behaviours, including some mesophase development. In all cases, supercooling was observed on cooling due to retarded crystallisation, which could equally result in two crystal conformations, depending on the actual composition.     

Rheological behavior of binary and ternary mixtures of polysaccharides in aqueous medium

The rheological behavior of mixtures of xanthan with different galactomannans is examined to evaluate the influence of the structure of galactomannan and that of the mixture composition on the physical properties; the larger synergy is observed for locust bean gum in the presence of xanthan. It is also shown that pH has only a slight influence on the rheology down to pH = 3.59; at lower pH, the G′ modulus decreases significantly.Then, the behavior of xanthan–methylcellulose mixtures is studied, paying particular attention to the storage modulus (G′) of the system, often equated to “gel strength”. The modulus values for direct dissolution of the two polysaccharides in 0.1 M NaCl show that xanthan and methylcellulose are incompatible. The rheological behavior observed is in agreement with DSC results which indicate that no specific interaction between the two polymers exists. However, upon increasing temperature, the modulus of methylcellulose increases substantially between 65 and 70 °C because of physical gelation and dominates the rheology of the mixtures. When temperature is decreased to 37 °C, the clear methylcellulose gel formed remains stable, still giving the main contribution to the overall rheology of the system. Finally, ternary systems are studied when xanthan is mixed with galactomannan and methylcellulose. In this case H-bonds involved in galactomannan–xanthan interaction break when temperature increases causing a decrease in rheological moduli which is then compensated by the gelation of methylcellulose giving an original large increase in moduli for the ternary systems. This can be interpreted as the presence of two independent but interpenetrating networks. The role of pH for these ternary systems is interesting: it is still dominated by methylcellulose and nearly independent of acidic pH (down to pH = 1.8).     

Rheological characterization and activation energy values of binary mixtures of gellan

The present study determined the flow behavior and activation energy of high (HA) and low (LA) acyl gellan dispersions (0.2%) and their mixtures as a function of preparation temperature (25 and 90 °C) and of the presence or absence of Ca²⁺ (30 mM). Heated gellan mixtures containing calcium were acidified with δ-gluconolactone to obtain gels and determine linear viscoelasticity using the Kelvin–Voigt model. The studied dispersions showed non-Newtonian shear-thinning behavior. HA dispersions (with and without Ca²⁺) showed the highest activation energy values, 88.60 and 51.18 kJ/mol. Whereas, LA dispersions showed the lowest activation energy values, 3.73 and 9.19 kJ/mol. With respect to the rheological studies, it was observed that the relationships between HA and LA gellan did not affect the recovery percentages because similar values were obtained (86.90–90.00%), and this behavior along with the mean viscosity values obtained in the gel mixtures could indicate that the hydrogen bond formation between both gellan helix (HA, LA) is possible. These results can contribute to possible industrial applications of gellans in the development of new alimentary products.     

Photoacoustic study of heated binary mixtures containing whey and skimmed-milk powders

 A novel methodology is proposed to determine the amount of whey powder in a binary mixture containing whey and skimmed-milk powders. This new approach is based on measurement of the amplitude of the photoacoustic (PA) signal obtained when the mixture is exposed to a controlled thermal treatment; the latter was shown to affect the colour of the powder. The limit of detection for the whey powder adulterant was 2% by weight. The PA and reflectance spectra (in the visible region) of the mixtures were also compared. Received: 27 February 1998 / Revised version: 8 June 1998     

黄酮混合物体外抗氧化活性的相互作用

测定槲皮素、异槲皮素、杨梅素、山萘酚、儿茶素、表儿茶素、芹菜素、飞燕草素-3-O-葡萄糖苷、矢车菊素-3-O-葡萄糖苷等9种黄酮类化合物及其两两混合物的体外抗氧化活性,以研究黄酮混合物的协同、拮抗与加合作用。以DPPH清除能力、羟基自由基清除能力、总抗氧化性、还原能力为评价指标。结果表明,含有较多B环羟基的黄酮类化合物更易发生拮抗作用,可通过调节黄酮单品的比例减小混合物的拮抗作用或是增强其协同作用,不同反应机理的评价指标所得结果不同。     

Physicochemical and psychophysical characteristics of binary mixtures of bulk and intense sweeteners

Correlating psychophysical characteristics with physicochemical properties of sweeteners is of relevance to the understanding of the origin of sweetener synergy, an essential parameter for the food manufacturer. Psychophysical evaluation was carried out on bulk sweeteners (sucrose and maltitol) and intense sweeteners (aspartame, sodium cyclamate, acesulfam-K, alitame) in mixtures. The concentrations of mixtures were calculated to be equisweet to 10% sucrose and sweetness intensity was evaluated by reference to sucrose solutions using a “sip and spit” method. While a positive synergistic phenomenon is observed for sugar/sodium cyclamate and maltitol/acesulfamK mixtures, a significant suppression effect is obtained when aspartame is added to sugars. Additivity is observed for sucrose/alitame and sucrose/acesulfamK mixtures. The origin of these differences lies in the influence of the two molecules on water structure and in the nature of their hydration. From physicochemical properties (intrinsic viscosity, Huggins coefficient, apparent specific volume, hydration number, surface tension and contact angle), alitame and aspartame seem characterised by hydrophobic hydration; sodium cyclamate, as well as the bulk sweeteners, appear more compatible with water structure and possess hydrophilic hydration. ACK is differentiated from other sweeteners by a negative hydration. Synergy occurs when components with identical types of hydration are mixed. This phenomenon is accompanied by an increase in the mobility of water molecules in the proximity of bulk sweeteners (maltitol and sucrose) and a reduction of volume of the hydrated solute molecule. Inversely, suppression and additivity occur when constituents of the mixture possess different natures of hydration, as in sucrose/aspartame mixtures, and when physicochemical properties show a reduction of the mobility of water around the sweeteners. For suppression effects, an increase in volume of the hydration sphere is also observed. Interpretation of the sweetness of mixtures of sugars and artificial sweeteners, in terms of their compatibility with water structure, is of relevance at an economic level in food formulations.     

Enhanced bacterial inactivation in apple juice by synergistic interactions between phenolic acids and mild food processing technologies

This study demonstrated an innovative processing approach based on synergistic antimicrobial activity of two phenolic acids with mild thermal and non-thermal processing technologies. The two selected model phenolic acids were gallic acid (GA; 10 mM) and ferulic acid (FA; 1 mM). The processing technologies evaluated for processing of a model clarified apple juice were UV-A light, mild heat (55 °C) and moderate pressure (250 MPa), with processing times ranging from 1 to 30 min. The results demonstrated that combinations of selected phenolic acids and a mild physical processing were able to lower E. coli O157:H7 and Listeria innocua counts from 6-log CFU mL⁻¹ to below the detection limit of 1-log CFU mL⁻¹. Bacterial inactivation was significantly enhanced by the combination of UV-A light processing and FA, where 10 min of treatment enhanced bacterial inactivation by 5-log as compared to light processing alone, which presented no bacterial inactivation. In contrast, the combination of GA and mild-temperature thermal processing (55 °C) or mild-levels of high-pressure processing (250 MPa), enhanced bacterial inactivation by 4-log as compared to the physical treatments alone, which presented only 1-log of inactivation. The influence of these synergistic combinations on bacterial membrane damage was assessed by selective plating technique under osmotic pressure. Furthermore, the total intracellular thiol content was also measured to assess for thiol oxidation. Overall, the results demonstrated enhanced bacterial inactivation based on synergistic interactions of selected phenolic acids with both mild-thermal and non-thermal technologies in a model food system and illustrate potential to create diversity of novel antimicrobial strategies for food processing.Industrial relevanceThis study showed that the presence of naturally-based compounds can significantly reduce intensity levels of physical processing required to inactivate model gram-positive and gram-negative bacteria in apple juice. In this study two phenolic acids, ferulic acid and gallic acids were selected as these compounds are naturally present in many fruits and other food products including grains. Furthermore, the levels of these natural phenolic acids used in this study are comparable to the levels naturally present in some of the food materials.     

天然抗氧化剂复配研究进展

天然抗氧化剂是从天然动、植物体或其代谢物中提取出来的具有抗氧化活性的物质,如多酚类、多糖类、黄酮类、维生素类、植酸、含氮化合物等。它们能够有效阻止或推迟物质的氧化。在单独使用某种抗氧化剂时,结构的单一性可能使其抗氧化性受到局限。因而复配可以达到提高抗氧化性能、降低使用成本的目的。在天然抗氧化剂的研究基础之上,对抗氧化剂复配研究进展进行综述,旨在为相关研究提供参考。     

Antimicrobial activity of binary combinations of natural and synthetic phenolic antioxidants against Enterococcus faecalis

This study investigated the antimicrobial activity of 3 natural (thymol, carvacrol, and gallic acid) and 2 synthetic [butylated hydroxyanisole (BHA) and octyl gallate] phenolic compounds, individually and in binary combinations, on 4 dairy isolates of Enterococcus faecalis with different virulence factors (β-hemolytic, gelatinase, or trypsin activities; acquired resistance to erythromycin or tetracycline; and natural resistance to gentamicin). A checkerboard technique and a microdilution standardized method were used. All compounds individually tested exhibited antimicrobial activity against E. faecalis, with minimal inhibitory concentrations (MIC) ranging from 30 μg/mL (octyl gallate) to 3,150 μg/mL (gallic acid), although no significant differences were detected among strains to each phenolic compound. Carvacrol in combination with thymol or gallic acid, and gallic acid combined with octyl gallate showed partial synergistic inhibition of all E. faecalis strains. The most effective combinations were thymol + carvacrol and gallic acid + octyl gallate, as the MIC for each of these compounds was reduced by 67 to 75% compared with their respective individual MIC. These results highlight the possibility of using combinations of these phenolic compounds to inhibit the growth of potential virulent or spoilage E. faecalis strains by reducing the total amount of additives used in dairy foods.     

Light exposure and wounding: synergistic effects on steroidal glycoalkaloid accumulation in potato tubers during storage

Potato tubers contain undesirable steroidal glycoalkaloids (SGAs), which have evoked global concern in terms of feed and food safety due to their toxic effects in humans. The cultivar Unica was exposed to a combination of light and wounding. SGA content among different tissues was analysed. Our results showed that SGA contents of tubers subjected to light was higher than that of intact tubers stored in darkness, and SGA content in the skin varied with time; however, SGA content in the flesh remained stable at a relatively low level. SGA content in the wound was higher than that of intact tubers. Importantly, light and wounding were shown to have synergistic effects on SGA content in the tuber, which only influenced SGA content within approximately 3 mm of the wound surface. Our study provides a theoretical basis for the reasonable and safe consumption of potatoes.     

酚类化合物的吸收特性及对肠道菌群的作用

作为常见的植物次生代谢产物,酚类化合物在果蔬、谷物、茶、咖啡等植物性农产品、食品和饮料中广泛存在。酚类已被证明具有多种生物活性,包括调节血糖血脂、抗肿瘤、抗菌、抗病毒、调节肠道微生态等。酚类复杂混合物的生物利用度与其吸收特性密切相关。本文综述了酚类在消化道小肠和结肠段的吸收规律,总结了肠道菌群在消化过程中的作用,并介绍了近年来酚类对肠道菌群调节研究的进展。膳食酚类复杂多样,与肠道菌群相互作用并相互影响,且这一过程存在个体差异,因此酚类的吸收和作用机制研究仍处于起步阶段,未来可借助宏基因组、转录组、蛋白质组以及高通量代谢组学的发展来不断推进本领域的理论研究。