Dynamic processes in the liquid state can be examined from different points of view; the rapid development of highly sophisticated time-resolved experiments and very complex computer simulation techniques have certainly improved the accuracy of some labratory results, but they are often not followed by an adequate attempt at interpretation. In any case, the extent of the subject and the enormous spread of experimental data do not help systematic analysis.This review attempts to contribute to a critical examination of a particular aspect of the dynamics of the liquid phase. Through a study of vibrational relaxation in isotropic molecular liquids it is possible to gain information about the molecular environment and the main intermolecular forces operative in this state of matter. It is therefore possible to formulate hypotheses about the force potentials and to describe the dynamic regime of the liquid system under consideration.(1) diatomic and/or highly symmetric molecules (e.g. HCl, 0, , CH,);(2) derivatives of hydrocarbons, especially methane (e.g. CH,NO, , CHCl, , CH,CI,);(3) aromatic and cyclic aliphatic molecules (e.g. benzene and its derivatives, cyclohexane, pyridine); (4) hydrogen bonded (with OH and/or HCO groups).This paper concerns the comparison between vibrational motions that have similar normal coordinate descrip tions; for this reason, we shall limit our considerations to the second and third groups in the above list. Hydrogenbonded and highly symmetrical systems are excluded because they need specific considerations.The currently used basic nomenclature of this field will be illustrated, in addition to the physical meaning of the dynamic parameters usually obtained by steady-state (continuous Raman and infrared), time-resolved spectroscopy and computer simulation techniques; these different experimental data will be compared, when available. We shall also outline and discuss current theoretical models, and attempt to emphasize their potential and limitations.At present, we may single out four groups of molecules that have been investigated by these methods: VIBRATIONAL RELAXATION IN LIQUIDS: THE PROBLEMSince the early 1960s, the study of vibrational relaxation in condensed phases has been considered a way of investigating dynamic processes,' but only with the advent of lasers as spectroscopic sources have frequency-and time-resolved experiments been performed; lineshape and coherent picosecond excitation studies allowed accurate information to be obtained on the dynamics in the solid and liquid states. Since that time, many papers2-14 have proved useful in the development of theoretical models and experimental results; for a detailed analysis of the whole question, one may refer to the above publications and references therein. For the purpose of this paper, the basic definitions of the main physical entities and variables involved in the subject must be clarified, avoiding the conflicts and ambiguities often present in the literature. DEPHASING: DEFINITIONSDephasing is important as probe of the...
The present experiment addressed the effects of two harvest stages, namely breaker (S1) and turning (S2), on compositional and sensory profile of grafted, greenhouse elongated tomatoes cv. “Sir Elyan”. The rootstocks “He-Man”, “Interpro”, and “Armstrong” were used. The S1 fruits showed a higher dry matter content, firmness and titratable acidity when compared to the S2 ones (by 6%, 3%, and 15%, respectively). They showed, also, the highest L-ascorbic acid concentration and antioxidant activity. Differently, soluble solid content, lycopene and β-carotene increased in the S2 fruits (by 4%, 92%, and 26%, respectively). Excepting methyl salicylate, all the volatiles detected peaked in the S2 fruits, which were scored by panelists as sweeter and more flavorful than the S1 ones. Among the rootstock genotypes, “He-Man” promoted fruits firmness, carotenoids concentration and antioxidant activity, irrespective of the harvest stage. “Interpro” enhanced the sensory attributes of the S1 fruits in terms of bitterness, sourness, sweetness and flavor. Differently, sweetness, sourness, and tomato flavor of the S2 fruits were promoted by “Armstrong”. The results highlight the influence of rootstock genotype on the nutraceutical and sensorial profile of “Sir Elyan” fruits harvested at early ripening stages.
Over the last few decades, the improvement of tomato aroma and flavour has gained growing attention among breeders, agronomists and food technologists, as it is reputed as a key tool to further consolidate tomato consumption in the global market. However, this represents a difficult task, since more than 400 volatile organic compounds (VOCs) differently contribute to tomato aroma and its flavour perception. The recent development of molecular tools has allowed us to identify some of the major alleles influencing the volatile composition of tomatoes. Nonetheless, such composition involves an intricate weave of polygenic systems, highly influenced by external, pre and postharvest factors. With few exceptions, our knowledge about the effects of these determinants is still scarce, making it difficult to draw sound conclusions to best manage the future genetic potential. The present review examines the existing knowledge on major VOCs influencing tomato organoleptic quality, including their classification, metabolic pathways, genetics, and technical features that affect their concentrations in fruits. Particular emphasis is placed on preharvest and postharvest factors influencing their quantitative and qualitative expression, whose integrated study with omic tools will be increasingly necessary for the perspective of disseminating reliable operational indications throughout the production/distribution chain.
A greenhouse experiment was conducted to study the effects of the O2 root zone level and grafting on chlorophyll fluorescence, photosynthesis and growth of cherry tomato grown in a hydroponic system. Two O2 concentrations in the root zone, namely Ox (saturation level) and Ox- (2–3 mg L−1), were applied for 30 days on self-grafted cherry tomato Dreamer or grafted onto the hybrids Arnold, Beaufort, Maxifort and Top Pittam. Root hypoxia increased minimum fluorescence (by 10%) while it decreased variable fluorescence and the maximum quantum yield of PSII (up to 16 and 8%, respectively). Moreover, it reduced leaf photosynthesis, transpiration and stomatal conductance (by 12, 17 and 13%, respectively), whereas it increased leaf electrolyte leakage (by 2.1%). The graft combinations showed a different ability in buffering the effects of root hypoxia on plant growth and related components, and these differences were related to their root biomass. The minimum fluorescence was negatively correlated to plant growth, so it may be a useful indicator to select tolerant rootstocks to root hypoxia. Our results suggest the occurrence of both diffusive and metabolic constraints to tomato photosynthesis under root hypoxia, a condition that can be mitigated by selecting rootstocks with a more developed root system.
The experiment addressed the effects of two storage temperatures, namely 10 (T10) and 20 °C (T20), on main quality and functional traits of three cherry tomato cultivars (‘Eletta’, ‘Sugarland’ and ‘Ottymo’), after 0 (S0), 7 (S7) and 14 (S14) days of storage. At T10 both fruit weight and firmness were better retained during storage. At S14, T10 promoted fruit Chroma and overall fruit color deviation (ΔE*ab). Total polyphenols content (TPC) of fruits peaked at S7 (4660 mg GAE kg−1 DW) then declined at S14 (by 16%), with the highest values recorded at T10. Lycopene showed a similar trend, but with a higher average concentration recorded at T20 (488 mg kg−1 DW). β-carotene content peaked at S14, irrespective of the storage temperature. At S14, the concentrations of phytoene and phytofluene were higher at T20 (48.3 and 40.9 mg kg−1 DW, respectively), but the opposite was found at S7. ‘Sugarland’ and ‘Ottymo’ showed the highest ΔE*ab along storage, with the former cultivar proving the highest TPC and lycopene content, whereas ‘Eletta’ did so for phytoene and phytofluene. Our results suggest that unravelling the possible functional interactions among these three carotenoids would allow for a better orientation of breeding programs, targeting the phytochemical evolution of tomatoes during refrigerated storage.
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