比较研究纤维素、果胶和淀粉的燃烧行为和机理

本文利用微燃烧量热仪（MCC）比较研究了烟草中主要碳水化合物（纤维素、果胶和淀粉）的燃烧行为,并考察了燃烧气氛和升温速率对燃烧行为的影响。此外,利用热重-红外联用仪（TG-FTIR）比较研究了其在惰性气氛和10%氧气浓度下的热解过程,特别是主要热解气相产物（H2O、CO2、CO和羰基化何物）的形成规律,探讨了其燃烧机理。MCC测试结果发现,在相同的燃烧条件下,纤维素的燃烧性较优于淀粉,而果胶的燃烧性最差。升温速率较燃烧气氛对纤维素、果胶和淀粉燃烧行为的影响更大。TG-FTIR测试结果发现,果胶在燃烧过程中较淀粉和纤维素具有更好的焦炭化能力,且释放出更多的不可燃气相产物H2O和CO2,从而使其燃烧能力较纤维素和淀粉相对较弱。      

A comparative radiorespirometric study of glucose metabolism in yeasts

A comparative radiorespirometric study of glucose metabolism in glucose-limited chemostat cultures of Saccharomyces cerevisiae, Candida utilis and Rhodosporidium toruloides was performed in an attempt to estimate the contribution of the hexose monophosphate (HMP) pathway to glucose metabolism. Radioactively labelled glucose was administered directly to the cultures in a constant substrate feed, without disturbance of the steady state. The 14CO2 yields from [1-14C]- and [6-14C]-glucose demonstrated that the HMP pathway activities for the three yeasts were very similar. Furthermore, a quantitative analysis of results indicated that the HMP pathway activities were close to the theoretical minimum needed to cover the NADPH requirement for biomass formation.     

A comparative study of the purification of betanin

Betanin is a natural pigment with antioxidant properties used as a food colourant. This work describes the spectrophotometric and chromatographic quantification of betanin (2S/15S) and its epimer isobetanin (2S/15R) in fresh beetroot juice, food-grade beetroot powder and betanin standard diluted in dextrin. Absorption spectra of all three samples were deconvoluted using a mixed three-function model. Food-grade beetroot powder has the largest amount of violet-red impurities, probably formed during processing. The purification of betanin from these complex matrices was carried out by seven different methods. Ion exchange chromatography was the most efficient method for the purification of betanin from all samples; however, fractions contain high amounts of salt. Reversed-phase HPLC as well as reversed-phase column chromatography also produced good results at a much faster rate. The longer retention time of isobetanin when compared to betanin in reversed-phase conditions has been investigated by means of quantum-mechanical methods.     

A comparative study on properties of dual-core yarns

Core-spun yarns containing Spandex have been widely used for the production of elastic textile materials. However, it has been encountered various problems not only during the usage but also during textile processes due to its high recovery property. In order to solve these problems, multicomponent core-spun yarns called as dual-core (DC) yarns, have been developed. DC yarns can be produced on the modified ring spinning machine in two different ways. In the first method, previously combined two core yarns are fed simultaneously, whereas in the second method, two core yarns are given separately into the centre of sheath fibre bundle. In present study, it was aimed to research the effect of these production methods on yarn features. Polyester and Spandex core components and cotton wrapping fibres were brought together in both two ways and the properties of multicomponent core-spun yarns were compared with cotton ring counterparts for three different yarn counts.     

双元助留剂的比较

国内习惯上将使用两种助留剂并分别添加的助留剂系统大自然为双元助留剂系统,目前商业上获得广泛应用的双元助留剂有双聚合物助留剂和微粒助留剂两种类型,最近,某纸板公司在同一台纸机上先后使用了双聚合物助留剂和微粒助留剂,本文借此机会对这两种类型的助留剂进行了比较。     

酶脱墨与化学脱墨的效果比较

木聚糖酶或纤维素脱墨与化学脱墨相比,当木聚糖酶或纤维酶用量在1IU/g时,就能达到相同的脱墨效果,酶脱墨还能改善浆料的滤水性和强度,降低返黄程度。研究表明,纤维素酶脱墨效果稍优于木聚糖酶,但当用超过1IU/g后,对浆料强度损伤加剧。     

A comparative study of boar taint in cooked and dry-cured meat

A comparative study of boar taint in cooked and dry-cured pig meat products was performed. Forty-eight cooked loins and 48 dry-cured hams from entire males and castrates were studied. The samples were classified according to the androstenone (AN) and skatole (SK) fat content determined using HPLC. A trained sensory panel evaluated taste, aroma, boar odour, boar flavour, juiciness, tenderness and fatness in cooked and dry-cured samples. Threshold levels of AN and SK to separate (P<0.05) entire and castrate samples according to their boar odour and flavour were determined. The effects of castration and processing on the eating quality were studied. Finally, the relationships among boar taint and other sensory attributes in cooked and dry-cured meat were compared. Results from these studies show that the eating quality of processed meat was affected negatively by boar taint. Threshold values were higher in dry-cured ham (2 μg g(-1) AN and 0.12 SK) than cooked loin (0.5 AN and 0.1 SK). AN and SK had a synergistic effect on boar odour and flavour in both products. AN had a greater influence than SK on the aroma and taste, especially in cooked meat. Boar odour was perceived more intensely than boar flavour in both of the products studied. Castration favoured fatness and improved the aroma and taste of cooked and dry-cured meat. The loss of aroma and taste due to boar taint was more noticeable in cooking than drying and curing. In dry-cured meat boar taint was associated with less aroma, taste, juiciness and tenderness. However, in cooked meat, boar taint affected the aroma and taste more strongly, but was not related with juiciness and tenderness, probably because these attributes are influenced by cooking.     

The diastase number of honey: A comparative study

Summary In this article a review is given of the various methods which have been developed in order to determine, visually as well as photometrically the diastase number of honey. Particularly the various modifications of the photometric method are given, notably the influence of begin-and endabsorbance and the influence of the wavelength. It is demonstrated that the various photometric methods can give rise to diastase numbers which can vary a factor 2 for the same honey. As, according to the various honey regulations, the diastase number must have a minimum value of 8, independant of the method used in question, it is evident that in some cases false conclusions can be drawn where a possible excessive heating of the honey is concerned. It is recommended to follow the Codex alimentarius (FAO/WHO) procedure. A screening procedure based on this method is given.

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Zusammenfassung Eine Übersicht der verschiedenen Methoden zur visuellen and photo-metrischen Bestimmung der Diastasezahl von Honig wird gegeben. Insbesondere werden die verschiedene Modifikationen der photometrischen Methoden gegeben, und zwar wird auf den Einfluß der Anfaugs- und Endextinktion näher eingegangen. Es wird gezeigt, daß die verschiedenen photometrischen Methoden Diastasezahlen ergeben können, die für einen and denselben Honig um den Faktor 2 differieren. Da der Grenzwert für die Diastasezahl 8 beträgt, unabhängig von der Methode, sollte man darauf achten, keine falsehen Folgerungen zu ziehen, so weit es sich darum handelt, eine eventuelle zu starke Erhitzung des Honigs nachzuweisen. Es wird empfohlen die Codex alimentarius Methode (FAO/WHO) anzuwenden. Ein auf these Methode gegründetes Schnellverfahren wird beschrieben.

     

A comparative study of the anti-listerial activity of smear bacteria

Cell-free supernatants from Staphylococcus epidermidis, Staphylococcus warneri and Brevibacterium linens were found to possess anti-listerial activities. Anti-listerial activities were increased during exponential growth phase and reached a maximum during stationary growth phase. S. epidermidis (SE1) and S. warneri (SW1) were found to have particularly high activities against both Listeria monocytogenes and Listeria innocua as inhibition zones for 48 h cell-free supernatants of these strains were found on average to be approximately 10 times larger than those of B. linens (9174, M18 and BL1). Incubation of 48 h cell-free supernatants from S. epidermidis (SE1) and S. warneri (SW1) with proteolytic enzymes (trypsin and pronase E) resulted in a total loss of anti-listerial activity, which revealed its proteinaceous nature, and thus suggested that the observed anti-listerial activities were due to bacteriocin production. The bacteriocins were found to be relatively heat stable and had a molecular mass higher than 30 kDa.     

试样整经机纱线卷绕方式的比较研究

介绍了试样整经机纱线卷绕方式的分类、原理,并比较了3种不同卷绕方式即定幅卷绕法、规整卷绕法和定幅规整卷绕法的优缺点.通过比较分析得出,定幅规整卷绕法既可以按照整经密度整经,又可以加大整经长度.     

A comparative study of reproductive performance in organic and conventional dairy husbandry

A comparative cohort study of reproductive performance in organic and conventional dairy husbandry was conducted using longitudinal data from the Norwegian National Board of Animal Production Recording from January 1, 1994 to December 31, 1996. The present study is the first study comparing reproductive efficiency in organic and conventional husbandry in which characteristics such as herd size, breeding season, milk yield, parity, breed, use of artificial insemination (AI), and geographical distribution were taken into account. The organically managed cohort comprised 998 lactation periods, and the conventionally managed cohort comprised 3016 lactation periods. Both groups were similar in herd size and geographical distribution. The following reproduction variables were studied: days open, calving interval, calving to first AI interval, calving to last AI interval, and AI per cow. No consistent difference in reproductive performance was found between the cohorts before adjustments were made for milk yield, breeding season, service, and parity. After inclusion of these independent variables in the repeated measures, mixed-model analyses, reproductive efficiency of organically managed dairy cows was impaired compared with those under conventional management. In organic dairy farming, breeding efficiency was difficult to maintain in cows bred during winter. Organic husbandry proved more efficient than did conventional husbandry in converting roughage into milk. Furthermore, the average multiparity percentage was higher in organically managed cows.     

Antioxidant properties of several tropical fruits: A comparative study

Nine tropical fruits were analyzed for total phenol contents, ascorbic acid contents and antioxidant activities. The antioxidant activities were evaluated based on the ability of the fruit extracts to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH), reduce iron(III) to iron(II) and to bind to iron(II) ions. The results were compared to those of orange. It was found that guava, papaya and star fruit have higher primary antioxidant potential, as measured by scavenging DPPH and iron(III) reducing assays. Banana, star fruit, water apple, langsat and papaya have higher secondary antioxidant potential as measured by the iron(II) chelating experiment.     

Drying kinetics of semi-finished cassava crackers: A comparative study

Drying kinetics of semi-finished cassava crackers was investigated in this paper using a hot air dryer at seven levels of drying air temperatures in the rage of 50-80 °C, a fixed air flow velocity using a fan speed of 0.18 kW, and a fixed level of thickness at 1.5 mm. A comparative study was performed among mechanistic and empirical models: the diffusion model, Newton model, Page model, Modified Page model, Henderson and Pabis model, MFNN (Multilayer Feedforward Neural Network), and ANFIS (Adaptive-Network-based Fuzzy Inference System), to estimate dynamic drying behaviors of semi-finished cassava crackers. Among these models, MFNN was found to be the most suitable for predicting moisture ratio of the product based on r² (regression coefficient), and MSE (mean squared errors between the experimental data and predicted values).     

A comparative study and phage typing of silage-making Lactobacillus bacteriophages

To investigate basic characteristics of 10 virulent phages active on silage-making lactobacilli, morphological properties, host ranges, protein composition and genome characterization were separated into five groups based on host ranges and basic properties. The seven phages of groups I, II and V were active on Lactobacillus plantarum and Lactobacillus pentosus. Phage phiPY4 (group III) infected both L. casei and Lactobacillus rhamnosus. Phage phiPY5 (group IV) specifically infected Lactobacillus casei. Morphologically, three phages of groups I belonged to the Myoviridae family, while seven other phages of groups II, III and V belonged to the Siphoviridae family. SDS-PAGE profiles, restriction analysis, G + C contents of DNA and Dot blot hybridization revealed a high degree of homology in each group. Clustering derived from host range analysis was closely related to results of DNA and protein analyses. These phages may be applicable to phage typing for silage-making lactobacilli.     

A comparative study of sampling techniques for monitoring carcass contamination

Four bacteriological sampling techniques i.e. the excision, double swab, agar contract and modified agar contact techniques were compared by sampling pig carcasses before and after chilling. As well as assessing the advantages and disadvantages of the techniques particular attention was paid to variation due to the effects of chilling. The agar contact technique cannot be used for determining the contamination of carcasses because too many plates became overcrowded with micro-organisms. Results obtained by the double swab and modified agar technique gave standard deviations which were significantly higher than those of the excision technique. This may indicate a superior repeatability of the excision technique. Statistical analysis of the results showed that chilling influenced the differences between sampling techniques. The excision technique is to be regarded as the most suitable in view of its high accuracy and precision. When the technique is used properly, carcass damage is only small or negligible.     

内燃机用空气过滤纸的阻燃性研究

为了提高内燃机用空气过滤纸的阻燃性能,实验探讨了聚磷酸铵阻燃剂、溴-锑协同阻燃剂以及二者的复配阻燃剂分别在不同留着率条件下对空气过滤纸的阻燃效果、力学性能以及透气性的影响。结果显示：复配阻燃剂在留着率为20%,且聚磷酸铵阻燃剂与溴-锑协同阻燃剂留着率之比为1∶1时,滤纸的阻燃性能满足GB/T14656-93的要求且无烟,此时挺度基本不变,耐破度下降约12%,透气率下降约13%。     

A comparative study of in vitro gastrointestinal digestion of three strategic edible oils

Three strategic edible oils, that is, olive oil, microalgae oil, and shea butter, with a significantly different composition of fatty acids (FA), have been studied in a static in vitro digestion model to evaluate the rate of hydrolysis, bioaccessibility, and micellar phases formed in the process. Lipid composition of each phase and how the lipids are distributed in the different phases have been obtained using this in vitro digestion model. We demonstrate that the composition in FA and the physical properties of the oil are the key factors determining the distribution of lipids in the different phases. The fastest rate of hydrolysis was observed for olive oil and the highest triacylglycerol conversion was attained for shea butter. In contrast, the most abundant precipitate phase was obtained for shea butter, which also produces the highest co-crystallization of cholesterol among the three edible oils studied. This study reveals that digestibility of edible oils is directly related with the initial rate of hydrolysis.     

干红葡萄酒中二氧化硫测定方法的比较研究

以干红葡萄酒为原料,对其中残留二氧化硫的3种测定方法——直接碘量法、盐酸副玫瑰苯胺法、碘量蒸馏法进行比较研究。结果表明:直接碘量法测定过程快速简易,但误差较大;盐酸副玫瑰苯胺法试验操作繁琐,显色体系不稳定、重现性差,测定结果值较低;碘量蒸馏法操作方法较简易,测定结果值亦比较理想,重现性好,不存在颜色干扰现象,是目前测定干红葡萄酒中残留二氧化硫的较理想方法,也是以上3种方法中最好的。