The influence of water activity on thermal stability of horseradish peroxidase

The thermal stability of horseradish peroxidase in the solid state was studied as a function of water activity, from 0.11 to 0.88. At all activities the enzyme was found to be much more stable in the solid state than in solution. Inactivation temperatures were in the range of 140–160°C. Inactivation curves show a biphasic behaviour which can be described by a model assuming two fractions (heat labile and heat stable) with independent first order inactivation kinetics. The labile fraction represents approximately 30% of the total activity. The z-value for both stable and labile fractions depends on water activity (moisture content) and has a maximum at a_w= 0.76 (44.4°C and 43.8°C, respectively).     

Influence of water activity on the stability of betanine

Summary The influence of water activity on the stability of betanine isolated using Sephadex G-25 and crystallized with 0.1% HCl was investigated. The influence of water activity was studied in water/glycerol model systems with water activities ranging from 0.37 to 1.00 at 75° C. From the results obtained, the rate constants for betanine degradation and the half-lives of betanine were calculated. The non-linar dependence obtained was verified using mathematical methods.

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Einfluß der Wasseraktivität auf die Stabilität von Betanin

Zusammenfassung Es wurde der Einfluß der Wasseraktivität auf die Stabilität von Betanin, das mit Sephadex G-25 isoliert und aus 0.1% HCl kristallisiert wurde, verfolgt. Der Einfluß der Wasseraktivität wurde in Modellsystemen Wasser-Glycerol mit Werten der Wasseraktivität von 0,37 bis 1,00 (bei 75°C) untersucht. Aus den experimental gewonnenen Daten wurden die Geschwindigkeitskonstante und die Halbwertszeit des Zerfalls von Betanin errechnet. Die erhaltene nichtlineare Abhängigkeit wurde mathematisch getestet.

     

The stability of pelargonidin-based anthocyanins at varying water activity

The stability of pelargonidin 3-glucoside, pelargonidin 3-sophoroside and pelargonidin 3-sophoroside 5-glucoside acylated with malonic and cinnamic acids was determined at varying water activities. Model systems, containing purified anthocyanin in pH 3.4 citrate buffer and glycerol, were stored at 25°C in the dark for 242 days. Changes in pigment, degradation index, and anthocyanin profile, as monitored by high-performance liquid chromatography (HPLC), were studied. In general, anthocyanin degradation followed first order kinetics and the degree of anthocyanin degradation increased with water activity. Half lives of the anthocyanins ranged from 56 to 934 days. Changes in the chromatographic profile showed hydrolysis of pelargonidin 3-sophoroside to pelargonidin 3-glucoside and production of malonic acid from the acylated anthocyanin.     

非离子分散剂的结构对C.I.分散黄64稳定性的影响

分散剂在分散染料加工和应用过程中的作用至关重要.研究了不同种类非离子分散剂对C.I.分散黄64分散稳定性的影响,并探讨了分散剂结构与性能之间的关系,结果表明:分散体系的稳定性与非离子分散剂的亲水亲油性、分散剂与染料颗粒的结合状况有很大关系.合适的亲水亲油性、分散剂疏水部分和染料颗粒结合较牢,有利于提高分散体系的稳定性.因分散剂用量较低,所制备分散体系的高温稳定性主要与非离子分散剂的浊点和其与染料颗粒的结合状况有关.同时,分散体系中加入过量的非离子分散剂将会导致其高温稳定性降低.     

Sorbic acid stability in meat products of reduced water activity

This study investigated the behavior of sorbic acid in shelf-stable meats with 0.91 water activity during processing (70 °, 80 °, 90 °C) and accelerated storage (33 °, 45 °, 57 °C). In meat systems stored at 70 °, 80 ° and 90 °C, after approximately 0·5-3 days, the destruction rate of sorbic acid diminished. This change in behavior (break) was probably caused by the limited availability of oxygen and/or the inhibitory action of nonenzymatic browning products on sorbate destruction. Before the break, the rate constants were found to be related to temperature, pH, the acid used to adjust it and the humectants added to depress water activity (NaCl, glycerol, the mixture NaCl 3·5% and glycerol). After the break, none of the above mentioned effects were observed. In meat systems stored at 33 °, 45 ° and 57 °C the rate of destruction was constant with time. The rate constants of meat systems were higher than the ones obtained for aqueous systems of similar composition, revealing that meat components played an important role in the destruction of sorbates.     

水分活度对全脂羊奶粉贮藏期间脂肪稳定性的影响

采用加速氧化的方法研究水分活度对全脂羊奶粉贮藏期间脂肪稳定性的影响。通过测定全脂羊奶粉的酸值、过氧化值、硫代巴比妥酸值(TBA)、颜色等指标评价全脂羊奶粉贮藏期间的氧化状况。结果表明,水分活度为0.32的全脂羊奶粉贮藏期间酸值、TBA值显著高于水分活度为0.11和0.23的全脂羊奶粉(p<0.05),且水分活度为0.32的全脂羊奶粉过氧化值变化速率较快(p<0.05),且褐变严重。因此,降低全脂羊奶粉的水分活度可以提高其贮藏稳定性。      

水分活度对全脂羊奶粉贮藏期间脂肪稳定性的影响

采用加速氧化的方法研究水分活度对全脂羊奶粉贮藏期间脂肪稳定性的影响.通过测定全脂羊奶粉的酸值、过氧化值、硫代巴比妥酸值(TBA)、颜色等指标评价全脂羊奶粉贮藏期间的氧化状况.结果表明,水分活度为0.32的全脂羊奶粉贮藏期间酸值、TBA值显著高于水分活度为0.11和0.23的全脂羊奶粉(p＜0.05),且水分活度为0.32的全脂羊奶粉过氧化值变化速率较快(p＜0.05),且褐变严重.因此,降低全脂羊奶粉的水分活度可以提高其贮藏稳定性.     

The influence of unmalted barley on the oxidative stability of wort and beer

The aim of this study was to investigate the influences of unmalted barley on the brewing process and the quality of the resulting beer‐like beverages, with the main focus on the oxidative stability, using traditional beer analyses, GC‐MS for the determination of aging compounds and electron paramagnetic resonance spectroscopy to determine free radical activity. For the investigation, brews with different barley proportions and 75% barley brews with a colour malt addition, to compensate for a lower colour using barley, were produced. In general, it can be said that beers with a proportion of up to 50% barley achieved a comparable or higher extract yield and final attenuation owing to the combined effectiveness of the malt and microbial enzymes. Although all analytical values were within the normal range according to Methodensammlung der Mitteleuropäischen Brautechnischen Analysenkommission (MEBAK), a slight decrease in total polyphenols and free amino nitrogen content was observed. Also in response to higher barley portions, an increase of higher molecular weight proteins and β‐glucan was detected. Barley is not exposed to heat and oxidative stress in the malting plant, which explains the lower values of the thiobarbituric acid index and colour as an indicator of Maillard reaction products in the resulting wort and beer. Additionally, the results demonstrate a slower increase of aging compounds during beer storage with increasing barley proportions. Furthermore, it was observed that higher barley proportions led to a better oxidative stability indicated by a lower radical generation (T₄₅₀‐value) in wort and an increasing beverage antioxidant index/endogenous antioxidative potential (BAX/EAP value) in the final beverage. The case of ‘barley beers’ showed that the positive effect of barley on the oxidative beer stability was greater than the negative effect of the addition of colour malt, to adjust the colour of a 100% malt beer. In sensory comparison with beer produced with 100% malt, the beers brewed with a barley proportion up to 50% showed a slight flavour preference and up to a 75% equivalent evaluation. Copyright © 2012 The Institute of Brewing & Distilling     

甲醛处理对壳聚糖固定化酪氨酸酶稳定性的影响

壳聚糖被戊二醛活化后,会被多巴醌攻击,造成酶催化活性降低,而经甲醛处理了的壳聚糖则可降低多巴醌的攻击。经过甲醛处理后制得的固定化酶显示出很高的使用稳定性,在25、45℃分别使用50次后,固定化酶的活力只下降了2.13%与1.85%,而未经甲醛处理制得的固定化酶在25℃下使用50次后,酶的活力则下降了40.39%。显然,经甲醛遮蔽剩余氨基能提高固定化酶的稳定性。     

核桃油微量组分对其氧化稳定性的影响

测定核桃油对DPPH·、ABTS+·的清除能力,结合β-胡萝卜素脱色法,评价核桃油体外抗氧化能力。通过相关性分析、回归分析评价核桃油中共轭烯烃、羰基化合物、多酚、生育酚、黄酮、β-胡萝卜素及磷脂对核桃油氧化稳定性的影响。结果表明:核桃油具有一定的体外抗氧化活性,对DPPH·和ABTS+·的半抑制浓度(IC50)分别为0.161 g/m L和0.841 g/m L,通过β-胡萝卜素脱色法测得的核桃油抗氧化半抑制浓度(IC50)为1.292 g/m L,且核桃油体外抗氧化活性与其OSI显著相关(P<0.05)。同时发现,核桃油中7种微量组分含量与其OSI有显著相关性(P<0.05),其相关程度依次为:生育酚>总酚>黄酮>共轭烯烃>羰基化合物>β-胡萝卜素>磷脂,且抑制初级氧化的能力为:生育酚>β-胡萝卜素>黄酮>总酚>磷脂,而抑制次级氧化的能力:总酚>生育酚>黄酮>磷脂>β-胡萝卜素。     

The influence of the cationic of quaternized chitosan on antifungal activity

Quaternized chitosan: N-(2-hydroxyl-phenyl)-N,N-dimethyl chitosan (NHPDCS), N-(5-chloro-2-hydroxyl-phenyl)-N,N-dimethyl chitosan (NCHPDCS), N-(2-hydroxyl-5-nitro-phenyl)-N,N-dimethyl chitosan (NHNPDCS) and N-(5-bromic-2-hydroxyl-phenyl)-N,N-dimethyl chitosan (NBHPDCS) were synthesized and their antifungal activities against Botrytis cinerea Pers. (B. cinerea Pers.) and Colletotrichum lagenarium (Pass) Ell.et halst (C. lagenarium (Pass) Ell.et halst) were investigated. The results indicated that the quaternized chitosan derivatives had better inhibitory effects than chitosan, and the antifungal activities should be affected by the cation in these compounds.     

The influence of selenium on the antioxidant activity of green tea

This study was aimed at determining the effects of selenium on the contents of vitamin C, amino acid, total water‐soluble solids and tea polyphenol, and whether the antioxidant activity of selenium‐enriched green tea is enhanced compared with regular green tea by linoleic acid oxidation and the lard oxidation method. The contents of selenium, vitamin C and tea polyphenol in green teas were greatly increased by foliar application of selenium‐enriched fertilizer. No significant differences of the contents of vitamin C, amino acid and tea polyphenol were observed between green tea treated with sodium selenite and that without selenium. The selenium‐enriched green tea exhibited significantly higher antioxidant activity than regular green tea, both in linoleic acid oxidation and in the lard oxidation system. These results suggest that the antioxidant activity of green tea is significantly enhanced by the combination of selenium and green tea constituents compared with that of regular green tea. Copyright © 2003 Society of Chemical Industry     

水分含量对小麦淀粉颗粒结晶度的影响

应用X射线衍射方法对不同水分含量的小麦淀粉颗粒的结晶度进行了研究.结果表明:随着水分含量的增加,样品的结晶度逐渐增加,并达到一个平衡值(约45%).室温下,当w(水)＜11.27%时,小麦淀粉颗粒中的无定型区域处于玻璃态,衍射图形显示的是微晶区域和无定型区域两部分的衍射图形的综合;由于塑化作用的影响,增大含水量会导致更多的微晶结构的形成.当w(水)＞19.4%时,淀粉颗粒中的无定型区域处于橡胶态,其X射线衍射图形仅由微晶区域形成;再增大水分含量,会导致微晶片层和剩余的无定型片层的同时分解.     

含湿量对织物热舒适性的影响

通过对不同纤维原料和组织的织物在不同含水率下的热舒适性指标及导热系数的测试,探讨了含水率大小对不同织物接触热舒适性的影响规律.     

The stability of dichlofluanid and vinclozolin and their influence on the quality of strawberries

Summary The content of dichlofluanid and vinclozolin found on strawberries treated with Euparen and/or Ronilan, respectively, did not exceed the residue tolerance. Further decrease of the amount of these fungicides occured during heatsterilisation of the fruit and storage of the products. The rate of decomposition of dichlofluanid and/or vinclozolin in model solutions (pH 3.0–6.0) followed pseudo-first-order kinetics.The taste and flavour of untreated fruit was preferred to those of strawberries treated with fungicides. There were differences in the content of reducing sugars, volatile fatty acids and titrable acidity in individual samples. Gas-chromatographic profiles of volatile substances isolated from treated and untreated berries also differed.

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Die Stabilität des Dichlofluanid und des Vinclozolins und ihr Einfluß auf die Qualität von Erdbeeren

Zusammenfassung Der auf Erdbeeren nach Behandlung mit Euparen bzw. Ronilan festgestellte Gehalt an Dichlofluanid bzw. Vinclozolin überschritt nicht die Rückstands-Toleranzgrenze. Bei der Naßkonservierung und Lagerung der Produkte nahm der Gehalt dieser Fungicide weiter ab. Der Zerfall des Dichlofluanides und Vinclozolins in den Modellösungen bei pH 3,6–6,0 folgte einer Pseudo-1.Ordnung-Kinetik (pseudomonomolekulare Reaktion).Geschmack und Duft unbehandelter Erdbeeren waren besser als in den mit Fungiciden behandelten Früchten. Auch waren Unterschiede bei den reduzierenden Zuckern, den flüchtigen Fettsäuren, der Titrationsacidität und den gaschromatographisch untersuchten flüchtigen Stoffen festzustellen.

     

The influence of slaughter weight on the stability of pork sides in frozen storage

Eight groups of six pigs were obtained, two sources of supply × meal-fed and swill-fed × “light” (37 to 35 kg) and “heavy” (66 to 88 kg). The pigs were slaughtered, weighed, graded, chilled, split and the sides wrapped in stockinet and polyethylene, frozen in a room at below ?30 °C and stored commercially at below ?20 °C. Corresponding sides were withdrawn after four and nine months, weight losses were measured and samples cooked and submitted to a panel for appraisal of any differences in flavour. Samples of the fat of each side were also investigated chemically for extent of oxidation of the fat. There were no significant differences in flavour attributable to weight range, with either meal- or swill-feeding nor any chemical indication of oxidative rancidity.