Influence of light exposure, ethanol and copper(II) on the formation of a precursor for xanthylium cations from tartaric acid

The production of xanthylium cation pigments was greatly increased when an aged, tartaric acid buffered, 12% (v/v) aqueous ethanol solution was used in a model white wine system. This suggested the formation of a precursor to the pigments during the ageing of the tartaric acid solution. On examining factors responsible for the generation of tartaric acid oxidation products in wine-like solutions it was observed that on exposure of samples to sunlight, glyoxylic acid, a known precursor to xanthylium cations, was produced. The production of glyoxylic acid was achieved in both the absence and presence of ethanol and copper(II). Hydrogen peroxide was also detected in these solutions. The results were consistent with the presence of glyoxylic acid in the aged tartaric acid buffered, 12% (v/v) aqueous ethanol solution that had frequent aeration and periodic exposure to sunlight throughout its storage. Studies on the role of hydrogen peroxide in the production of glyoxylic acid were also investigated. On the addition of hydrogen peroxide to tartaric acid solutions, with heating at 45°C in darkness, glyoxylic acid was only determined in solutions without ethanol.     

Effect of Sweet Humectants on Stability and Antimicrobial Action of Sorbates

ABSTRACT: The effect of glucose or polyols on sorbate stability and on its antimicrobial action were studied in aqueous systems (pH 3.0). All humectants promoted preservative degradation, but polyols decreased browning development. Depression of water activity did not inhibit the growth of Zygosaccharomyces bailii , but xylitol increased the lag phase and decreased the growth rate and the stationary phase level. Sorbate minimum inhibitory concentration (MIC) concerning Z. bailii growth acquired slightly lower values (0.020% w/w) when sorbitol or xylitol were present for systems with water activity of 0.971. The residual level of the preservative after 3 wk of storage at 35 °C was smaller than the MIC for all studied systems with the exception of the humectant-free system.     

Enzymatic browning in avocado (Persea americana) revisited: History,advances, and future perspectives

Considering nearly 80 years of research regarding one of the enzymes responsible for catalyzing the formation of pigments in higher animals, plants, fungi and bacteria, this review will focus on collecting and categorizing the existing information about polyphenol oxidase (PPO) in fruits, with particular emphasis on the information in relation to avocado, which is one of the hardiest species in terms of inactivation, has documented dual activity (EC 1.14.18.1/EC 1.10.3.1), and represents one of the oldest challenges for food science research and fruit processors.

It is expected that this review will contribute to the further development of the field by highlighting the questions that have arisen during the characterization of PPO, the progress that has been made and the questions that remain today, in addition to new methodologies that are being applied to study this system. Holistic methodologies offer unexplored potential for advancing our understanding of the complex phenomena that govern PPO activity in fruits, because these methodologies will enable the characterization of this family of enzymes in all of its complexity. Subsequently, it will be possible to develop better techniques for controlling enzymatic browning in this valuable fruit.     

Inhibitory effect of onion extract on polyphenol oxidase and enzymatic browning of taro (Colocasia antiquorum var. esculenta)

The inhibitory effect of onion extract on polyphenol oxidase and enzymatic browning of taro was investigated. The polyphenol oxidase from taro was strongly inhibited by various reducing agents, such as l-ascorbic acid, l-cysteine, dithiothreitol, glutathione and sodium pyrosulfite. The enzyme was also inhibited by addition of onion extract. Regardless of substrates used, the addition of heated onion extract at 100 °C for 10 min, gave a stronger inhibitory effect on taro polyphenol oxidase activity than did fresh unheated extrtact. The inhibitory effect of onion extract was dependent on heating temperature and time. The addition of glucose, glycine, or both to the onion extract, during heating, stimulated the inhibitory effect of the onion extract, suggesting that non-enzymatic browning products, produced during heating, might be responsible for the stronger inhibitory action of the heated onion extract.     

Nonenzymatic browning of selected fruit juices affected by D-galacturonic acid

This work studies the effect of d ‐galacturonic acid (AGA) on the non‐enzymatic browning of three types of clarified concentrated fruit juices (apple, pear and peach). It was observed that the presence of AGA increases the browning of juices. This was evaluated by the evolution of the absorbance at 420 nm (A₄₂₀) with the treatment time that these juices show. The evolution at A₄₂₀ over time was fitted to first‐order kinetics and it was observed that the kinetic constant values increased with both the increase in the AGA content and the rise in the treatment. The effect of the temperature treatment on the non‐enzymatic browning of these juices was quantified by fitting the variation of the kinetic constants with the Arrehnius equation, thus obtaining the corresponding activation energies. In the case of apple juice, it was observed that for the increase in AGA content the activation energy increases considerably, while for the pear and peach juices, a slight increase of the activation energy was observed with the increase in AGA.     

豆类发酵液抑制马铃薯浆液褐变的研究

为了找到抑制褐变的替代方法,采用豌豆自然发酵液来进行抗褐变和抑制马铃薯多酚氧化酶(PPO)活性的研究,并对其抗褐变机理和发酵条件进行了初步的探索。结果表明,豌豆自然发酵液可以有效的抑制马铃薯浆液褐变;有机酸并不是影响发酵液抗褐变的主要因素,它能够抗褐变是因为它可以抑制PPO的活性。通过单因素以及正交试验,确定了豌豆自然发酵液的最佳发酵条件:发酵时间为2 d,发酵温度为30℃,料水比为1∶5。经过验证,按最佳发酵条件得到的发酵上清液对PPO的抑制率可高达95.21%。     

香菇采后贮藏期间褐变的因素研究

褐变是影响香菇的食用品质的主要原因,为深入了解香菇在贮藏期间褐变发生的规律和成分的变化,本实验以新鲜香菇为原材料,研究了贮藏期间,香菇的多酚氧化酶(PPO)、过氧化物酶(POD)活性,总酚、还原糖含量,褐变度(BD值)及Vc含量的变化,分析了上述指标对褐变的影响。结果表明,总酚和PPO活性与褐变度显著相关;还原糖和Vc的含量与香菇的非酶促褐变也有一定的关系。     

秘鲁鱿鱼丝褐变抑制剂的筛选

建立了糖-赖氨酸与鱿鱼丝浸提液-硅藻土体系两种秘鲁鱿鱼丝褐变的模拟体系,对亚硫酸钠、谷胱甘肽、肉桂酸、柠檬酸、乳酸钙、阿魏酸和多聚磷酸钠这7种褐变抑制剂,以及阿魏酸、肉桂酸与柠檬酸的协同抗褐变作用进行探讨,并将选出的褐变抑制剂应用于秘鲁鱿鱼丝中进行验证。结果表明:在模拟体系中,柠檬酸和阿魏酸的混合物抗褐变作用较为突出。在阿魏酸与柠檬酸的混合褐变抑制剂中,50mmol/L的柠檬酸的添加量在60℃时有效抑制秘鲁鱿鱼丝中的褐变反应,其抗褐变率随反应时间的延长而增大,在反应的第4d可达到23%。此混合物中柠檬酸在抗褐变过程中起主导作用,且在本实验范围内,随着其添加量的增加抗褐变效果增强,而阿魏酸的添加量对总抗褐变效果无明显影响。     

涂膜处理对鲜切山药褐变及抗氧化性的影响

为保持鲜切山药的色泽及抗氧化性,延长其货架期,研究壳聚糖、卡拉胶、海藻酸钠及复合涂膜剂对鲜切山药涂膜处理后,在5℃贮藏期间褐变及抗氧化性的影响。结果表明:壳聚糖1.57%+卡拉胶0.9%+海藻酸钠1.55%涂膜后,鲜切山药储存期间,可明显降低山药的褐变程度及抑制PPO的比活力,防止贮藏后期酚类物质的氧化,提高鲜切山药的整体抗氧化能力。