Roles of drying, size reduction, and blanching in sustainable extraction of phenolics from olive leaves

It is now known that olive leaves contain a sizable portion of polyphenols and there is much research highlighting that these natural ingredients favorably exhibit bio-functional activities. In this regard, many studies have focused on the exploration of optimum conditions involved directly in the extraction process. These investigations, while being highly valuable, may somewhat cast a shadow over other contributing factors such as those involved in the preprocessing of leaves, including size reduction, drying, and blanching. The use of these unit operations under appropriate conditions, together with other benefits, potentially exert improved surface area, homogeneity, and diffusion/mass transfer which may help develop the liberation of target bio-compounds. The research work in this area, particularly size reduction, is relatively limited. Although in various experiments they are incorporated, not many studies have focused on them as the main predictor variables. The performance of further research may help ascertain the magnitude of their effects. Consideration of the operational parameters in preprocessing step is equally important as those in the processing/extraction step that may comparably influence on the extraction efficiency. This review provides an overview of the potential roles of drying, size reduction, and blanching in the extraction efficiency of phenolics from olive leaves.(undefined)info:eu-repo/semantics/publishedVersio

Plasmonic biosensors: dark-field optical microscopy as a tool to detect cytokines

Plasmonic biosensors are amongst the promising types of biosensors for ultralow detection of biomolecules. One of the tools in plasmonic biosensors is dark-field optical microscopy. By exploiting an optical properties of noble metal nanoparticles, namely localized surface plasmon resonance (LSPR), dark-field microscopy is able to visualize small nanoparticles. LSPR response of metal nanoparticles changes as a result of the change in local environment of the nanoparticles. This phenomenon is used in plasmonic biosensor to detect biomolecules. In this project, performance of a colorimetric method on detection of Interleukin 6, a pro-inflammatory cytokine, was studied. Detection of ultra-small changes in concentration of IL6 has been attributed to early diagnosis of many inflammatory diseases and different types of cancers. Plasmonic biosensors are able to reach to single molecule detection level, yet normal employed procedures such as single particle spectroscopy, are time consuming. Consequently, it is not practical to analyse many single molecule events using these procedures. So, a fast colorimetric method, based on a code already developed in Smart Material and Surface (SMS) group, was employed for analysis of single plasmonic particles in a massive parallel way. First an ensemble method was proposed to check the viability of the analysis method for detection of IL6. Here 67 nm Au nanoparticles modified with Anti-IL6 antibodies interact with 20 nm Au nanoparticles modified by different Anti-IL6 antibodies which was used to capture IL6. As a result, a core-satellite assembly is formed which was immobilized on a surface and studies under darkfield microscopy. Since single 67 nm cores show different colour values than core-satellite assemblies, the colorimetric code was able to detect the antigen. In the next chapter a surface-based biosensor was proposed to improve sensitivity and change the concept from ensemble to single event measurement. Here darkfield images of immobilized 67 nm cores were analysed before and after addition of reporter nanoparticles. In the final chapter with the help of mapping between SEM and dark-field images the ability of colour analysis method to reach to single molecule counting was tested. Also, with the help of Comsol simulation best core-satellite design was proposed

Effect of ohmic heating on the extraction yield, polyphenol content and antioxidant activity of olive mill leaves

This study examined the influence of ohmic heating (OH), compared to the conventional heating (Conven) and Control (solvent) methods, on the extraction of olive mill leaves. The main extraction parameters were: (i) solvent ratio (aqueous ethanol; 40%, 60%, and 80%, v/v), and (ii) extraction temperature; 45 °C, 55 °C, and 75 °C (for OH and Conven), and room temperature (for Control). The selected response variables were extraction yield (%), total phenolic content (TPC), and antioxidant activity (ABTS and DPPH). The ohmic system, compared to Conven and Control, exhibited the greatest effects (p < 0.001) on increasing (i) extraction yield (34.53%) at 75 °C with 80% ethanol, (ii) TPC at 55 °C (42.53, 34.35, 31.63 mg GAE/g extract, with 60%, 40%, and 80% ethanol, respectively), and (iii) antioxidant potency at 75 °C detected by DPPH and ABTS, in the range of 1.21–1.04 mM TE/g, and 0.62–0.48 mM TE/g extract, respectively. Further, there were relatively similar trends in TPC and antioxidant activity (both methods), regardless of solvent ratios, p < 0.001. These findings demonstrate the potential of ohmic heating, as a green processing tool, for efficient extraction (15 min) of olive leaves. To date, no literature has described ohmic application for olive leave extraction.This work was supported by the Portuguese Foundation for Science and Technology (FCT), under the scope of the strategic funding of UID/BIO/04469/2020 unit.info:eu-repo/semantics/publishedVersio

Olive tree leaves - a source of valuable active compounds

The agricultural and processing activities of olive crops generate a substantial amount of food by-products, particularly olive leaves, which are mostly underexploited, representing a significant threat to the environment. Olive leaves are endowed with endogenous bioactive compounds. Their beneficial/health-promoting potential, together with environmental protection and circular economy, merit their exploitation to recover and reuse natural components that are potentially safer alternatives to synthetic counterparts. These biomass residues have great potential for extended industrial applications in food/dietary systems but have had limited commercial uses so far. In this regard, many researchers have endeavoured to determine a green/sustainable means to replace the conventional/inefficient methods currently used. This is not an easy task as a sustainable bio-processing approach entails careful designing to maximise the liberation of compounds with minimum use of (i) processing time, (ii) toxic solvent (iii) fossil fuel energy, and (iv) overall cost. Thus, it is necessary to device viable strategies to (i) optimise the extraction of valuable biomolecules from olive leaves and enable their conversion into high added-value products, and (ii) minimise generation of agro-industrial waste streams. This review provides an insight to the principal bioactive components naturally present in olive leaves, and an overview of the existing/proposed methods associated with their analysis, extraction, applications, and stability.FCT -Fundação para a Ciência e a Tecnologia(UID/BIO/04469/2020)info:eu-repo/semantics/publishedVersio

Single particle detection of protein molecules using dark-field microscopy to avoid signals from nonspecific adsorption

A massively parallel single particle sensing method based on core-satellite formation of Au nanoparticles was introduced for the detection of interleukin 6 (IL-6). This method exploits the fact that the localized plasmon resonance (LSPR) of the plasmonic nanoparticles will change as a result of core-satellite formation, resulting in a change in the observed color. In this method, the hue (color) value of thousands of 67 nm Au nanoparticles immobilized on a glass coverslip surface is analyzed by a Matlab code before and after the addition of reporter nanoparticles containing IL-6 as target protein. The average hue shift as the result of core-satellite formation is used as the basis to detect small amount of proteins. This method enjoys two major advantages. First it is able to analyze the hue values of thousands of nanoparticles in parallel in less than a minute. Secondly the method is able to circumvent the effect of non-specific adsorption, a major issue in the field of biosensing

A critical review of electrochemical noise measurement as a tool for evaluation of organic coatings

The simplicity of measuring equipment and versatility of data analysis makes electrochemical noise measurement an ideal technique for acquiring electrochemical information about the corrosion behavior of a painted metal relatively quickly. Hence the method has great potential for use in the laboratory as well as in field situations. However, special care must be taken in choosing data acquisition parameters, reference electrodes and symmetry of electrodes in order to achieve reproducible measurements. These areas have been discussed in this review along with methods of data analysis, alternative electrode configurations for on-site measurements and novel applications of the technique

Comparative study of different particle sizes of added olive leaves for the content of target polyphenols in virgin olive oil

The addition of olive leaves during processing of olive oil has been studied and reviewed from different perspectives but there is a paucity of information on the roles of particle sizes of the added leaves in phenolic content of the oil. Dry ground olive leaves with a range of particle size fractions (0.07–3.0 mm) were added to crushed olives prior to the malaxation to compare their effects on: (i) the content of total and selected polyphenols (particularly oleuropein and verbascoside), (ii) antioxidant capacity (in vitro), and (iii) physicochemical quality and the yield of the extracted olive oil. Besides particle size, that was the main factor of study, olive pitting and malaxation time (30 and 60 min) were also considered as independent variables. Olive leaves with 0.3 mm followed by 0.15 mm favorably exhibited significant effects (p < 0.001) in all assays. Indeed, the oil samples with 0.3 mm leaves produced from the pitted olives showed maximum values when the malaxation time was (i) 30 min – for oleuropein (5.85 mg per kg oil), verbascoside (4.02 mg per kg oil), luteolin (15.44 and mg per kg oil), and total phenolic content (TPC) (368.01 mg per kg oil), and (ii) 60 min – for hydroxytyrosol (19.14 mg per kg oil) and tyrosol (16.89 mg per kg oil). These findings indicate that the particle size of added olive leaves can play a significant role in the content of principal polyphenols of the resulting olive oil; a topic that has not been approached in the literature.This study was supported by the Portuguese Foundation for Science and Technology (FCT), under the scope of the strategic funding of UID/BIO/04469/2020 unit.info:eu-repo/semantics/publishedVersio

A graphene-based sensor for real time monitoring of sun exposure

The photoreduction of graphene oxide (GO) with titanium dioxide (TiO2) was exploited to fabricate a UV sensor for real time monitoring of sun exposure. The sensor was fabricated by simultaneous deposition of GO sheets and TiO2 nanoparticles onto interdigitated electrodes using an AC electrophoresis deposition method. Changes in the resistance of the GO sheets decorated with TiO2 nanoparticles during repeated cycles of exposure to UV were measured to understand the sensitivity of this sensor to UV radiation. Current-time traces revealed that the fabricated UV sensor retains a memory of each cycle of UV exposure; regardless of whether the sensor is exposed to UV for one long cycle or several short cycles. This memory of the extent of UV exposure is a biomimetic approach, analogous to the response of the skin to sun, and means the sensor requires no power except when the data is read from the sensor