Raman imaging of changes in the polysaccharides distribution in the cell wall during apple fruit development and senescence

Main conclusion Du ring on-tree ripening, the pectin distribution changed from polydispersed in cell wall to cumulated in cell wall corners. During apple storage, the pectin distribution returned to evenly dispersed along the cell wall. The plant cell wall influences the texture properties of fruit tissue for example apples become softer during ripening and postharvest storage. This softening process is believed to be mainly connected with changes in the cell wall composition due to polysaccharides undergoing an enzymatic degradation. These changes in polysaccharides are currently mainly investigated via chemical analysis or monoclonal labeling. Here, we propose the application of Raman microscopy for evaluating the changes in the polysaccharide distribution in the cell wall of apples during both ripening and postharvest storage. The apples were harvested 1 month and 2 weeks before optimal harvest date as well as at the optimal harvest date. The apples harvested at optimal harvest date were stored for 3 months. The Raman maps, as well as the chemical analysis were obtained for each harvest date and after 1, 2 and 3 months of storage, respectively. The analysis of the Raman maps showed that the pectins in the middle lamella and primary cell wall undergo a degradation. The changes in cellulose and hemicellulose were less pronounced. These findings were confirmed by the chemical analysis results. During development changes of pectins from a polydispersed form in the cell walls to a cumulated form in cell wall corners could be observed. In contrast after 3 months of apple storage we could observe an substantial pectin decrease. The obtained results demonstrate that Raman chemical imaging might be a very useful tool for a first identification of compositional changes in plant tissue during their development. The great advantage Raman microspectroscopy offers is the simultaneous localization and identification of polysaccharides within the cell wall and plant tissue

A nanostructural view of the cell wall disassembly process during fruit ripening and postharvest storage by atomic force microscopy

Background: The mechanical properties of parenchyma cell walls and the strength and extension of adhesion areas between adjacent cells, jointly with cell turgor, are main determinants of firmness of fleshy fruits. These traits are modified during ripening leading to fruit softening. Cell wall modifications involve the depolymerisation of matrix glycans and pectins, the solubilisation of pectins and the loss of neutral sugars from pectin side chains. These changes weaken the cell walls and increase cell separation, which in combination with a reduction in cell turgor, bring about textural changes. Atomic force microscopy (AFM) has been used to characterize the nanostructure of cell wall polysaccharides during the ripening and postharvest storage of several fruits. This technique allows the imaging of individual polymers at high magnification with minimal sample preparation. Scope and approach: This paper reviews the main features of the cell wall disassembly process associated to fruit softening from a nanostructural point of view, as has been provided by AFM studies. Key findings and conclusions: AFM studies show that pectin size, ramification and complexity is reduced during fruit ripening and storage, and in most cases these changes correlate with softening. Postharvest treatments that improve fruit quality have been proven to preserve pectin structure, suggesting a clear link between softening and pectin metabolism. Nanostructural characterization of cellulose and hemicellulose during ripening has been poorly explored by AFM and the scarce results available are not conclusive. Globally, AFM could be a powerful tool to gain insights about the bases of textural fruit quality in fresh and stored fruits

Postharvest Monitoring of Tomato Ripening Using the Dynamic Laser Speckle

The dynamic laser speckle (biospeckle) method was tested as a potential tool for the assessment and monitoring of the maturity stage of tomatoes. Two tomato cultivars—Admiro and Starbuck—were tested. The process of climacteric maturation of tomatoes was monitored during a shelf life storage experiment. The biospeckle phenomena were captured using 640 nm and 830 nm laser light wavelength, and analysed using two activity descriptors based on biospeckle pattern decorrelation—C4 and ε. The well-established optical parameters of tomatoes skin were used as a reference method (luminosity, a*/b*, chroma). Both methods were tested with respect to their prediction capabilities of the maturity and destructive indicators of tomatoes—firmness, chlorophyll and carotenoids content. The statistical significance of the tested relationships were investigated by means of linear regression models. The climacteric maturation of tomato fruit was associated with an increase in biospckle activity. Compared to the 830 nm laser wavelength the biospeckle activity measured at 640 nm enabled more accurate predictions of firmness, chlorophyll and carotenoids content. At 640 nm laser wavelength both activity descriptors (C4 and ε) provided similar results, while at 830 nm the ε showed slightly better performance. The linear regression models showed that biospeckle activity descriptors had a higher correlation with chlorophyll and carotenoids content than the a*/b* ratio and luminosity. The results for chroma were comparable with the results for both biospeckle activity indicators. The biospeckle method showed very good results in terms of maturation monitoring and the prediction of the maturity indices of tomatoes, proving the possibility of practical implementation of this method for the determination of the maturity stage of tomatoes

A Comparative Study of the Application of Fluorescence Excitation-Emission Matrices Combined with Parallel Factor Analysis and Nonnegative Matrix Factorization in the Analysis of Zn Complexation by Humic Acids

The main aim of this study was the application of excitation-emission fluorescence matrices (EEMs) combined with two decomposition methods: parallel factor analysis (PARAFAC) and nonnegative matrix factorization (NMF) to study the interaction mechanisms between humic acids (HAs) and Zn(II) over a wide concentration range (0–50 mg·dm−3). The influence of HA properties on Zn(II) complexation was also investigated. Stability constants, quenching degree and complexation capacity were estimated for binding sites found in raw EEM, EEM-PARAFAC and EEM-NMF data using mathematical models. A combination of EEM fluorescence analysis with one of the proposed decomposition methods enabled separation of overlapping binding sites and yielded more accurate calculations of the binding parameters. PARAFAC and NMF processing allowed finding binding sites invisible in a few raw EEM datasets as well as finding totally new maxima attributed to structures of the lowest humification. Decomposed data showed an increase in Zn complexation with an increase in humification, aromaticity and molecular weight of HAs. EEM-PARAFAC analysis also revealed that the most stable compounds were formed by structures containing the highest amounts of nitrogen. The content of oxygen-functional groups did not influence the binding parameters, mainly due to fact of higher competition of metal cation with protons. EEM spectra coupled with NMF and especially PARAFAC processing gave more adequate assessments of interactions as compared to raw EEM data and should be especially recommended for modeling of complexation processes where the fluorescence intensities (FI) changes are weak or where the processes are interfered with by the presence of other fluorophores

Effect of divalent metal ions on rheological properties of polysaccharide matrix from apple pomace

Wytłoki powstające podczas produkcji soku jabłkowego składają się głównie z polisacharydów ścian komórkowych, które stanowią błonnik pokarmowy. Związki te powodują znaczny wzrost lepkości roztworów wodnych dzięki zdolności do sieciowania jonami metali dwuwartościowych według modelu egg-box. Wytłoki jabłkowe poddawano fizycznym i chemicznym przekształceniom, uzyskując matrycę polisacharydową MPSN. Celem badań było określenie zdolności do sieciowania matrycy polisacharydowej MPSN za pomocą dwuwartościowych kationów metali Ca²+, Mg²+ i Fe²+. Na podstawie wzrostu lepkości pozornej badanych roztworów stwierdzono, że każdy zastosowany kation miał zdolności sieciujące, ale w największym stopniu sieciowanie zachodziło pod wpływem Ca²+ i Fe²+. Krzywe płynięcia matrycy MPSN opisano modelem Ostwalda de Waele’a. Roztwory MPSN z dodatkiem jonów wapnia w stężeniu 12 i 15 mM cechowały się najniższymi wartościami wskaźnika płynięcia i tym samym największym stopniem pseudoplastyczności. We wszystkich analizowanych materiałach wystąpiło zjawisko tiksotropii, które w przypadku dodatku Ca²+ i Fe² było zależne od ich stężenia, co świadczy o zdolności do odtwarzania struktury podczas relaksacji.Pomace produced during the apple juice production is composed mainly of cell wall polysaccharides, which constitute a dietary fibre. Since those compounds can be cross-linked with some divalent metal ions according to an egg-box model, they cause the viscosity of aqueous solutions to significantly increase. The apple pomace analyzed was physically and chemically transformed in order to obtain an MPSN polysaccharide matrix. The objective of the research study was to determine the ability of MPSN polysaccharide matrix to cross-link by means of the divalent metal cations of Ca²+, Mg²+, and Fe²+. On the basis of the increase in the apparent viscosity of the solutions analyzed, it was found that each ion applied had the cross-linking ability; however, the greatest degree of cross-linking was obtained by the Ca²+ and Fe²+ ions. The flow curves of MPSN matrix were described by an Ostwald de Waele’s model. The MPSN solutions with calcium ions added at 12 and 15 mM concentration rates were characterized by the lowest flow behaviour indices and, thus, by the highest pseudoplasticity degree. In all the analyzed samples, a thixotropy phenomenon occurred: in the case of Ca²+ and Fe, this phenomenon depended on their concentration rate. This fact proves their ability to regenerate structure during relaxation

The Most Important Virulence Markers of Yersinia enterocolitica and Their Role during Infection

Yersinia enterocolitica is the causative agent of yersiniosis, a zoonotic disease of growing epidemiological importance with significant consequences for public health. This pathogenic species has been intensively studied for many years. Six biotypes (1A, 1B, 2, 3, 4, 5) and more than 70 serotypes of Y. enterocolitica have been identified to date. The biotypes of Y. enterocolitica are divided according to their pathogenic properties: the non-pathogenic biotype 1A, weakly pathogenic biotypes 2–5, and the highly pathogenic biotype 1B. Due to the complex pathogenesis of yersiniosis, further research is needed to expand our knowledge of the molecular mechanisms involved in the infection process and the clinical course of the disease. Many factors, both plasmid and chromosomal, significantly influence these processes. The aim of this study was to present the most important virulence markers of Y. enterocolitica and their role during infection

Assessment of changes in structure of dried tissue of sour cherry pretreated using ultrasound-assisted osmotic dehydration

Celem pracy było określenie wpływu oddziaływania ultradźwięków na strukturę wewnętrzną owoców wiśni poddawanych obróbce osmotycznej i suszeniu. Owoce wiśni odmiany ‘Nefris’ odwadniano w 60-procentowym roztworze sacharozy przez 120 min (40 ºC), w łaźni wodnej wyposażonej w przetwornik ultradźwiękowy (25 kHz, 0,4 W/cm²) i platformę wytrząsającą (30 rpm). Całkowity czas obróbki osmotycznej wynosił 120 min, w trakcie którego zastosowano różne warianty czasu traktowania ultradźwiękami (ang. ultrasound – US) i wytrząsania (ang. shaking – S). W pierwszej kolejności próbki traktowano US przez 0, 30, 60, 90 lub 120 min, po czym wytrząsano (S) przez odpowiednio: 120, 90, 60, 30 lub 0 min. Odwodnione owoce poddawano suszeniu konwekcyjnemu. Strukturę suszu osmo-konwekcyjnego owoców odwadnianych oraz surowca analizowano mikroskopowo. Potwierdzono, że zastosowanie ultradźwięków powoduje zmiany struktury tkanek. Dłuższy okres ekspozycji tkanki wiśni na działanie US sprzyjał zmniejszaniu się zwartości komórek bezpośrednio sąsiadujących z epidermą. Jednocześnie obserwowano zwiększanie deformacji komórek miękiszu dośrodkowego i zanikanie przestrzeni międzykomórkowych. Najbardziej ujednoliconą strukturą (komórki najmniej wydłużone i komórki okrągłe) charakteryzowały się wysuszone owoce poddane obróbce osmotycznej i równocześnie poddane przez 60 min: oddziaływaniu US i wytrząsaniu (60US+60S), co wskazuje na istnienie optymalnego stanu sprzyjającego redukcji naprężenia wewnętrznego. Suszenie konwekcyjne powoduje znaczny skurcz tkanki. W owocach suszonych, które nie były poddane działaniu ultradźwięków, ale były wytrząsane przez 120 min (0US+120S), zaobserwowano występowanie wolnych przestrzeni międzykomórkowych na przemian z dużymi zagęszczeniami. Zastosowanie US do 60 min sprzyjało zwiększeniu jednorodności struktury suszonego materiału (wariant optymalny – 60US+60S). Oddziaływanie ultradźwięków powyżej 60 min wyraźnie potęgowało efekt zagęszczania struktury, w związku z czym próbki traktowane US przez 120 min (120US+0S) charakteryzowały się największym skurczem tkanki.The objective of the research study was to determine the effect of ultrasounds on the microstructure of osmo-treated and dried sour cherry fruits. The ‘Nefris’ sour cherry fruit variety was osmotically dehydrated using a 60 % sucrose solution for 120 min. (40 ºC) in an ultrasonic bath equipped with a transducer (25 kHz, 0.4 W/cm²) and a shaking platform (30 rpm). The total time of osmotic dehydration was 120 min; during that time period, diverse time variants of ultrasound (US) treatment and shaking (S) were applied. First, the samples were treated by ultrasounds (US) for 0, 30, 60, 90, and 120 min.; next, they were shaken for 120, 90, 60, 30, or 0 min., respectively. The dehydrated fruits were convectively dried. The structure of osmo-convectively dried samples of dehydrated fruits and raw material was microscopically analyzed. It was confirmed that the application of ultrasounds caused changes in the structure of tissues. A longer time of exposing sour cherry tissue to ultrasounds resulted in a decrease in the density of cells directly adjacent to the epidermis. Concurrently, it was found that the deformation of parenchyma cells increased and the intercellular spaces faded away. By the most homogenous structure (the most elongated and circular cells) were characterized the dried fruits that were osmo-treated and, simultaneously, ultrasound-treated and shaken for 60 min. (60US+60S); thus the presence of optimal state was proved that supported the reduction in internal tension. The convective drying causes the tissue to considerably contract. In the dried fruits, which were not treated by ultrasounds, but only shaken for 120 min. (0US+120S), alternating free intercellular and highly compact spaces were found. The application of ultrasounds for max 60 min. caused the homogeneity of structure of the material being dried to increase (optimal variant: 6US+60S)