1,720,960 research outputs found
Characterization of different hop (Humulus lupulus L.) cultivars: response to drought stress, chemical composition and sensory profile
Full text linkHop cones, the immature inflorescences of the female plant of Humulus lupulus L., have an important role in defining flavour, bitter stability and shelf life of beer. Hop cones are characterised by a wide range of molecules, such as α- and β-acids that contribute to the bitter taste of beer, and essential oils, which are responsible for the aroma. Nowadays hop is mainly cultivated in other countries and imported in Italy as raw material. Despite hop’s cultivation is not widespread in Italy, the number of Italian microbreweries is increasing and most of them are located in Northern-Italy. Taking into accounts this geographical distribution, it is therefore interesting to determine the achievable quality of hops cultivated in the Northern-Italy area. Among factors that limit the crop production, water availability is one of the major constraint since, in Mediterranean areas, the phenological cycle of hops coincides with a climate characterized by high air temperature and drought. For this reason, the selection of hop drought-tolerant varieties is crucial for the introduction of this crop in Italy. Hop physiological, molecular and metabolic responses activated in response to drought are poorly understood. For this reason eleven hop cultivars were subjected to drought and physiological and ionomic parameters were measured throughout water stress development. A total of 8 plants for each cultivar (4 controls and 4 water stressed-plants) were used. 3-L pots were sealed to avoid water evaporation, then control plants were watered every day while stressed plants were left without irrigation till the achievement of permanent wilting (after about 30 days). Physiological and growth parameters (pots weight, leaves axes, shoots length and SPAD chlorophyll meter) were measured. Results highlight that, compared to well-watered plants, most of stressed hop varieties did not reduce their transpiration until the Fraction of Transpirable Soil Water (FTSW) ≈0.7, showing, in general, an anisohydric behaviour. The experiment allowed us to pinpoint the more drought-tolerant/susceptible hop cultivars. Besides the selection of drought-tolerant cultivars, it is important to verify the achievable quality of hops cultivated in Northern-Italy and its variability among different cultivation years. Although the effect of climatological conditions on α and β-acids formation is well-known, no information are available on the variability of hops’ volatile profiles among different growing seasons. For this reason, hop acids and volatile compounds profiles of sixteen hop varieties cultivated in the same field in Parma (Emilia-Romagna, Italy) in two different years were analysed via High Performance Liquid Chromatography (HPLC) and comprehensive two-dimensional gas chromatography (GCXGC) respectively. In general, a strong variability in the dependence of the amount of hop acids and volatile compounds on the climate was found, nevertheless, hop acids and the key compounds of aroma showed a pattern specific for each variety. Moreover, cones of ten hop varieties cultivated in 2013 were subjected to ultrasonic extraction and the extracts were used to flavour a Blond Ale beer. Each beer was then sensory analysed by a trained panel. Finally, the sensory properties of flavoured beers were evaluated in relation to hops’ volatiles profiles and correlations were pinpointed. High and significant (p< 0.05) correlation coefficients were find between specific volatile compounds and aromatic descriptors as ‘hoppy’, ‘grassy’ and ‘spicy’, while few volatiles correlated with the descriptors ‘citrusy’, ‘fruity’ and ‘floral’. A chemical and sensory characterization of volatile compounds in different hop varieties was also performed to identify the odour-active molecules of particularly citrusy hops. Indeed, although different odour impressions such as grassy, floral/fruity or spicy notes have already been described, few attempts were made to clearly correlate the citrus aroma with the chemical profile of hop oil. The essential oil of three hop varieties with a well-known ‘citrus’ character and of three ‘spicy’/’hoppy’ varieties were chemically and sensory analysed. Each essential oil was fractionated by Solid Phase Extraction (SPE) and, according to a descriptive sensory analysis of the different fractions, the 70/30 ethanol/water (v/v) SPE fraction turned out to be the most citrusy one. This fraction was then analysed via Headspace Solid Phase Microextraction (HS-SPME) and Gas Chromatography−Mass Spectrometry/Olfactometry (GC-MS/O). A total of 59 volatiles were identified, 35 of which resulted to be odour-active. In this study the character-impact odorants in the citrusy fraction of hop essential oil were outlined; hierarchical cluster analysis and Principal Component Analysis (PCA) highlighted that hops that expressed a typical citrus aroma are characterized by high levels of specific esters as methyl (E)-4-decenoate, methyl nonanoate and methyl caprate, high levels of esters of geraniol and nerol and low levels of ‘grassy/spicy’ sesquiterpenes as α-humulene and β-caryophyllene.
Summarizing, in this work different responses to drought stress were highlighted in different hop cultivars, allowing us to determine the most tolerant and drought-sensitive hop cultivars. The quality of hops cultivated in Northern-Italy (expressed as hop acids content and volatile profile) and its variability were outlined for two cultivation years and some important odour impressions in hops (especially ‘citrusy’ notes) were characterized by a molecular point of view. This project has therefore increased our understanding of hop response to drought stress and of hop aroma, providing initial practical benefits for hop growers and for the hop industry
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Analisi del progetto di sviluppo di un'azienda agricola per la produzione di alimenti
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