Quantitative determination of the iodine values of unsaturated plant oils using infrared and Raman spectroscopy methods

Assessment of Changes in the Fat Profile of House Cricket Flour during 12 Months of Storage in Various Conditions

Considering Acheta domecticus flour's growing importance and utilization as an ingredient in many food products, research on its storage is essential. The objective of this study was to determine the chemical and nutritional fat profile of house cricket (Acheta domesticus) flour during storage for 12 months under different storage temperatures (-18 °C, +4 °C, and +20 °C in two variants, with and without access to light). Insect flour was studied using Fourier-transform infrared spectroscopy (FTIR). The fatty acids content was determined, and dietary indicators were calculated. The acid value, peroxide value, and anisidine value were also determined, and differential scanning calorimetry was performed. The results obtained from spectroscopic analysis of Acheta domesticus flour were consistent with the biochemical data. During the 12-month period of flour storage, the storage temperature significantly influenced the percentage composition of identified groups of fatty acids and the values of all presented ratios and dietary indices. During storage at refrigerated temperatures (-18 °C and +4 °C), no changes were observed in the fatty acid content and dietary indices, indicating that refrigerated temperatures provide oxidative stability to flour during 12 months of storage. Samples stored at 20 °C had higher acid values (AV), peroxide values (PV), and anisidine values (p-AV) compared to samples stored at lower temperatures (4 °C and -18 °C). Simultaneously, an increase in SFA and MUFA, as well as a decrease in PUFA and UFA, was noted in samples stored at room temperature. Storing cricket flour at lower temperatures when the storage period will be more than 12 months is essential to restrict the occurrence of fat oxidation. Elevated temperatures and exposure to light have a notable effect in hastening oxidation mechanisms, reducing thermal resilience, and inducing more pronounced alterations in the quality of fats.

Fabrication of paper-based analytical devices using stencil-printed glass varnish barriers for colorimetric detection of salivary α-amylase

BACKGROUND

Developing disposable paper-based devices has positively impacted analytical science, particularly in developing countries. Some benefits of those devices include their versatility, affordability, environmentally friendly, and the possibility of being integrated with portable electrochemical or colorimetric detectors. Paper-based analytical devices (PADs) comprising circular zones and microfluidic networks have been successfully employed in the analytical chemistry reign. However, the combination of the stencil-printing method and alternative binder has not been satisfactorily explored for fabricating colorimetric paper devices.

RESULTS

We developed PADs exploring the stencil printing approach and glass varnish as the hydrophobic chemical agent. As a proof-of-concept, the colorimetric assay of salivary α-amylase (sAA) was performed in saliva samples. Through the scanning electron microscopy measurements, it was possible to indicate satisfactory definitions between native fibers and barrier, and that the measured values for the channel width revealed suitable fidelity (R2 = 0.99) with the nominal widths (ranging from 400 to 5000 μm). The proposed hydrophobic barrier exhibited excellent chemical resistance. The analytical applicability for detecting sAA revealed linear behavior in the range from 2 to 12 U mL-1 (R2 = 0.99), limit of detection of 0.75 U mL-1, reproducibility (RSD ≤2.4%), recovery experiments ranged from 89 to 108% and AGREE response (0.86). In addition, the colorimetric analysis of sAA in four different saliva samples demonstrated levels ranging from 202 to 2080 U mL-1, which enabled monitoring the absence and presence of periodontitis.

SIGNIFICANCE

This report has presented the first use of a self-adhesive mask and glass varnish for creating circular zones and microfluidic architectures on paper without using thermic or UV curing treatments. Also, the proposed analytical methodology for detecting sAA exhibited suitable ecological impact considering the AGREE tool. We believe the proposed fabrication of paper devices emerges as a novel, simple, high-fidelity microfluidic channel and portable analytical approach for colorimetric sensing.

Chemical and Nutritional Fat Profile of Acheta domesticus, Gryllus bimaculatus, Tenebrio molitor and Rhynchophorus ferrugineus

The use of edible insects in the human diet is gaining importance because they are characterized by high nutritional value, and their cultivation is much more environmentally friendly than traditional livestock farming. The objective of this study was to determine the chemical and nutritional fat profile of selected edible insects as follows: house cricket (Acheta domesticus adult), field cricket (Gryllus bimaculatus adult), mealworm (Tenebrio molitor larvae), and palm weevil (Rhynchophorus ferrugineus larvae) which are now commercially available worldwide. Additionally, the degree of implementation of nutrition standards for selected nutrients by these insects was assessed. Freeze-dried insects were studied using infrared-attenuated total reflectance mid-infrared spectroscopy for basic differentiation. The content of fat and fatty acids was determined, and dietary indicators were calculated. The spectroscopic findings align with biochemical data, revealing that Rhynchophorus ferrugineus larvae contain the highest fat content and the least protein. Unsaturated fatty acids (UFAs) predominated in the fat of the assessed insects. The highest content of saturated fatty acids (SFAs), along with the lowest content of polyunsaturated fatty acids (PUFAs), was observed in the larvae of the Rhynchophorus ferrugineus species. From a nutritional standpoint, Tenebrio molitor larvae exhibit the most favorable indicators, characterized by minimal athero- and thrombogenic effects, along with an optimal balance of hypo- and hypercholesterolemic acids. Knowledge of the composition and quantities of fats in different insect species is valuable for planning and preparing meals with accurate nutritional profiles, among other applications.

The Use of Raman Spectroscopy to Monitor Changes in the Intensity of Ratio of Integral Unsaturated Bands in Bio-Greases

Bio-greases were developed on the basis of vegetable oil obtained from Crambe Abyssinic seeds. An important aspect of this research is to monitor changes in their quality taking place under the influence of external factors. Raman spectroscopy was used to identify changes taking place in the bio-lubricant under the influence of mechanical and thermal forces. The performed tests reflected the operating temperature and friction load that may occur during actual operating conditions for the lubricated friction systems. The Raman spectra provided information on qualitative changes in the structure of the tested bio-lubricants at the molecular level. The integral intensity of the bands used to assess the degree of lipid unsaturation was adopted as the evaluation criterion. The influence of the oxidation process under the PetroOxy and wear test conditions on changes in the structure of the bio-lubricants was assessed. Variation in the integral intensity of the bands (I1655/I1440) proves that the structure of vegetable lubricants changes under the influence of the tests performed. Thermal and mechanical forces influence, the bands originating in unsaturated and result in a decrease in the oxidation resistance of vegetable lubricants.

Sanches S, Da Silva D, Silva Júnior J, Da Silva L, Da C. Rodrigues A. Fatty acid profile and rheological behavior of annatto seed oil (Bixa orellana), cupuassu seed fat (Theobroma grandiflorum), and their blends

Annatto seed oil (ASO) and cupuassu seed fat (CSF) were combined at the ratios: 30:70, 50:50, and 70:30 (% w/w). Their fatty acid profile, nutritional quality, FTIR (Fourier Transform Infrared) spectra, and rheological behavior were evaluated. ASO increased the content of polyunsaturated fatty acids in the blends; whereas CSF conferred higher contents of monounsaturated fatty acids. The blends exhibited low atherogenicity and thrombogenicity indices, suggesting nutritional advantages. The Newtonian fluid behavior and FTIR results suggested that mixing ASO and CSF at different proportions did not affect the functional groups. ASO showed an activation energy value which indicated that this fat viscosity was more sensitive to temperature changes. The Newtonian model proved to be suitable to describe the behavior of samples, according to statistical fit parameters R2, χ2, and RSS. The resulting blends presented improved physicochemical properties and nutritional attributes, indicating their feasibility for the development of new products.

The effect of roasting, storage temperature, and ethanoic basil (Ocimum basilicum L.) extract on the oxidative stability of crude sesame (Sesamum indicum L.) oil

Sesame (Sesamum indicum L.) is an annual oilseed crop that is widely used for crude sesame oil (CSO) extraction. CSO is unrefined, thus, may impact the storage stability due to the uncontrolled processing and handling conditions, and absence of preservatives. The purpose of this study intends to analyze the fatty acid profile and oxidative stability of CSO. In a complete randomized (2*2*2) factorial design, clean sesame seeds (3.92% moisture content) were used for oil extraction with/without roasting treatment (200°C). The fatty acid profile and oxidative value of the CSO were analyzed. The roasted sesame seed oil extraction yield was higher (50.9%) and composed of 83.15% unsaturated fatty acids with an omega-6 to omega-3 ratio of 95.3. The ratio of polyunsaturated fatty acids (PUFAs) to saturated fatty acids (SFAs) was 2.9, while the moisture content of the CSO was 0.37%, exceeding the tolerable limit. The predominant fatty acids of CSO include palmitic, stearic, oleic, and linoleic acids. Elevated thermal condition during processing and handling speeding up oxidation exceeded the tolerable limit after 25 days of storage, while the ethanoic basil extract was found to inhibit oxidation in the range of 16.38%-90% (p-value < .05). The peroxide value (PV), para-anisidine value (p-AV), and total oxidation (TOTOX) value of CSO with 50 ppm (parts per million) basil extract were detected within the range of 0.29-3.92, 0.75-2.59, and 1.57-8.6 milliequivalents (meq) O2/kg oil, respectively, below the tolerable limit. Nevertheless, basil extract's antioxidant property was declined during prolonged storage, in particular, at elevated temperature. The use of organic extracts of locally available sweet basil herb is capable of mitigating oxidation and substituting inorganic antioxidant for a healthier diet.

Spectroscopic Evidence of Thermal Changes in Plant Oils during Deep-Frying—Chemical and Infrared Studies

For this study, the thermal degradation of palm, coconut, rice bran, and rapeseed (canola) oils was studied. Products formed during deep-frying were identified using chemical methods and these results were verified with those derived from FT-IR (Fourier-transform infrared spectroscopy) studies. Mathematically processed spectral data were analyzed in terms of the breaking of double bonds, the decomposition of the carotenoids, and the reduction of the C=O carbonyl group. Clearly visible changes in the position and intensity of some bands were used for explaining the structural changes in the studied oils. These changes prove that during the heating of the oils, decomposition of the plant fat into fatty acids appears, together with the reduction of the number of certain bonds (e.g., C=C, =C-H, and C=O) and cracking of the acylglycerol chains. The iodine values of the heated oils, determined from the FT-IR spectra measurements, show a significant decrease in their degree of unsaturation level. These effects, visible in the FT-IR spectra, confirm the chemical and structural changes derived from the chemical and physicochemical studies of the plant oils. The influence of heating time on the band intensity of proteins was also studied.

Statistical FT-IR Spectroscopy for the Characterization of 17 Vegetable Oils

Vegetable oils have been utilized for centuries in the food, cosmetic, and pharmaceutical industries, and they contribute beneficially to overall human health, to active skincare, and to effective treatments. Monitoring of the vegetable oils is carried out by the methods described in the European Pharmacopeia, which is time-consuming, has poor repeatability, and involves the use of toxic organic chemicals and expensive laboratory equipment. Many successful studies using IR spectroscopy have been carried out for the detection of geographical origin and adulteration as well as quantification of oxidation parameters. The aim of our research was to explore FT-IR spectroscopy for assessing the quality parameters and fatty acid composition of cranberry, elderberry, borage, blackcurrant, raspberry, black mustard, walnut, sea buckthorn, evening primrose, rosehip, chia, perilla, black cumin, sacha inchi, kiwi, hemp, and linseed oil. Very good models were obtained for the α-linolenic acid and linoleic acid contents, with R2 = 1.00; Rv2 values of 0.98, 0.92, 0.89, and 0.84 were obtained for iodine value prediction, stearic acid content, palmitic acid content, and unsaponifiable matter content, respectively. However, we were not able to obtain good models for all parameters, and the use of the same process for variable selection was found to be not suitable for all cases.

Rapid Iodine Value Estimation Using a Handheld Raman Spectrometer for On-Site, Reagent-Free Authentication of Edible Oils

Edible oil adulteration is a common and serious issue faced by human societies across the world. Iodine value (IV), the total unsaturation measure, is an authentication tool used by food safety officers and industries for edible oils. Current wet titrimetric methods (e.g., Wijs method) employed for IV estimation use dangerous chemicals and elaborate procedures for analysis. Alternate approaches for oil analysis require sophisticated and costly equipment such as gas chromatography (GC), liquid chromatography, high-performance liquid chromatography, mass spectrometry (MS), UV-Visible, and nuclear magnetic resonance spectroscopies. Mass screening of the samples from the market and industrial environment requires a greener, fast, and more robust technique and is an unmet need. Herein, we present a handheld Raman spectrometer-based methodology for fast IV estimation. We conducted a detailed Raman spectroscopic investigation of coconut oil, sunflower oil, and intentionally adulterated mixtures with a handheld device having a 785 nm excitation source. The obtained data were analyzed in conjunction with the GC-MS results and the conventional wet Wijs titrimetric estimated IVs. Based on these studies, a specific equation for IV estimation is derived from the intensity of identified Raman spectral bands. Further, an algorithm is designed to automate the signal processing and IV estimation, and a stand-alone graphical user interface is created in user-friendly LabVIEW software. The data acquisition and analysis require < 2 minutes, and the estimated statistical parameters such as the R ² value (0.9), root-mean-square error of calibration (1.3), and root-mean-square error of prediction (0.9) indicate that the demonstrated method has a high precision level. Also, the limit of detection and the limit of quantification for IV estimation through the current approach is ∼1 and ∼3 gI₂/100 g oil, respectively. The IVs of different oils, including hydrogenated vegetable oils, were evaluated, and the results show an excellent correlation between the estimated and reported ones.

Mechanism, indexes, methods, challenges, and perspectives of edible oil oxidation analysis

Edible oils are indispensable food components, because they are used for cooking or frying. However, during processing, transport, storage, and consumption, edible oils are susceptible to oxidation, during which various primary and secondary oxidative products are generated. These products may reduce the nutritional value and safety of edible oils and even harm human health. Therefore, analyzing the oxidation of edible oil is essential to ensure the quality and safety of oil. Oxidation is a complex process with various oxidative products, and the content of these products can be evaluated by corresponding indexes. According to the structure and properties of the oxidative products, analytical methods have been employed to quantify these products to analyze the oxidation of oil. Combined with proper chemometric analytical methods, qualitative identification has been performed to discriminate oxidized and nonoxidized oils. Oxidative products are complex and diverse. Thus, proper indexes and analytical methods should be selected depending on specific research objectives. Expanding the mechanism of the correspondence between oxidative products and analytical methods is crucial. The underlying mechanism, conventional indexes, and applications of analytical methods are summarized in this review. The challenges and perspectives for future applications of several methods in determining oxidation are also discussed. This review may serve as a reference in the selection, establishment, and improvement of methods for analyzing the oxidation of edible oil. HighlightsThe mechanism of edible oil oxidation analysis was elaborated.Conventional oxidation indexes and their limited values were discussed.Analytical methods for the determination of oxidative products and qualitative identification of oxidized and non-oxidized oils were reviewed.

GC-MS, FTIR and Raman spectroscopic analysis of fatty acids of Pistacia vera (Greek variety "Aegina") oils from two consecutive harvest periods and chemometric differentiation of oils quality

Pistacia vera oil is a rich source of unsaturated fatty acids, whose presence is associated with high quality and nutritional value. According to the literature, fatty acid oil composition is not constant every harvest year, but varies mainly depending on climate conditions. Therefore, the knowledge of oil composition in fatty acids is necessary to assess both its quality and its nutritional value. Twenty-two samples (11 samples from the harvest year 2017 and 11 samples from 2018) of the Greek variety "Aegina" were collected from four different Greek regions, from producers following the same cultivation and post-harvest cares. Extraction oil yields were found to be similar (61.7% w/w, 2017; 60.8% w/w, 2018). A reduction of the saturated fatty acids content was determined in 2018 (mean values 12.2% w/w against 13.8% w/w in 2017) by Gas Chromatography-Mass Spectrometry, accompanied by an increase of the unsaturated ones (mean values 87.9% w/w against 86.2% w/w in 2017). These results indicate that the harvest year 2018 may be considered superior to 2017 in terms of quality and nutritional value and may be correlated with an increased mean rain rate in 2018 and a slight decrease of the mean temperature. Fourier transform infrared (FTIR) and Raman spectroscopic studies of the oils were also performed. Three chemometric models were developed for the two consecutive harvest years of pistachio oil and the discrimination was based on GC-MS analysis, FTIR and Raman spectroscopic data combined with cross-validation techniques and comparison among them. The most successful chemometric model was that based on FTIR spectroscopy, which has the advantage of speed, simplicity and economy. Such a chemometric model may help in estimating the quality of Pistacia vera oils.

Dual-wavelength excitation combined Raman spectroscopy for detection of highly fluorescent samples

As fluorescence is the major limitation in Raman scattering, near-infrared excitation wavelength (>780nm) is preferred for fluorescence suppression in Raman spectroscopy. To reduce the risk of fluorescence interference, we developed a dual-wavelength excitation combined Raman spectroscopy (DWECRS) system at 785 and 830 nm. By a common optical path, each laser beam was focused on the same region of the sample by a single objective lens, and the dual-wavelength excitation Raman spectra were detected by a single CCD detector; in addition, 785 and 830 nm excitation Raman spectra can be directly constructed as combined Raman spectrum in the DWECRS system. The results of pure peanut oil and glycerol indicate that the combined Raman spectrum cannot only reduce fluorescence interference but also keep a high signal-to-noise ratio in the high-wavenumber region. The results of dye-ethanol solutions with different concentrations show that the handheld DWECRS system can be used as a smart method to dodge strong fluorescence. Furthermore, we developed a peak intensity ratio method with the DWECRS system to distinguish different types of edible oils. The peak intensity ratio distribution chart of edible oils showed each oil normalized center was relatively independent and nonoverlapped, which can be used as the basis of edible oil classification analysis. In the future, the DWECRS system has potential to be used as a tool for more complex applications.

Detection of Aflatoxin B1 Based on a Porous Anodized Aluminum Membrane Combined with Surface-Enhanced Raman Scattering Spectroscopy

An Aflatoxin B₁ (AFB₁) biosensor was fabricated via an Ag nanoparticles assembly on the surface of a porous anodized aluminum (PAA) membrane. First, the Raman reporter 4-Aminothiophenol (4-ATP) and DNA (partially complementary to AFB₁ aptamer) were attached to the surface of Ag nanoparticles (AgNPs) by chemical bonding to form a 4-ATP-AgNPs-DNA complex. Similarly, the surface of a PAA membrane was functionalized with an AFB₁ aptamer. Then, the PAA surface was functionalized with 4-ATP-AgNPs-DNA through base complementary pairing to form AgNPs-PAA sensor with a strong Raman signal. When AFB₁ was added, AgNPs would be detached from the PAA surface because of the specific binding between AFB₁ and the aptamer, resulting in a reduction in Raman signals. The detection limit of the proposed biosensor is 0.009 ng/mL in actual walnut and the linear range is 0.01-10 ng/mL. The sensor has good selectivity and repeatability; it can be applied to the rapid qualitative and quantitative detection of AFB₁.

Study of the Quality Parameters and the Antioxidant Capacity for the FTIR-Chemometric Differentiation of Pistacia Vera Oils

The aim of this work was to characterize the pistachio oil of the Greek variety, "Aegina", evaluate its various quality indices, and investigate the potential use of FTIR as a tool to discriminate different oil qualities. For this purpose, the antioxidant capacity, the tocopherol content and the oxidation and degradation of fatty acids, as described by k, Δk, R-values, and free acidity were evaluated using 45 samples from eight different areas of production and two subsequent years of harvesting. The antioxidant capacity was estimated using 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid diammonium salt (ABTS) and 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazine (DPPH) assays, and the tocopherol content was quantified through HPLC analysis. FTIR spectra were recorded for all samples and multivariate analysis was applied. The results showed significant differences between the oil samples of different harvesting years, which were successfully discriminated by a representative FTIR spectral region based on R-value, total antioxidant capacity, and scavenging capacity, through ABTS. A similar approach could not be confirmed for the other quality parameters, such as the free acidity and the tocopherol content. This research highlighted the possibility of developing a simple, rapid, economic, and environment friendly method for the discrimination of pistachio oils according to their quality profile, through FTIR spectroscopy and multivariate analysis.

Calibrated Optical Markers to Study Thermal Degradation in Edible Oils Using Raman and Optical Transmission Spectroscopy

An "all optical" methodology, including Raman and optical transmission spectroscopy, is presented to study the thermal degradation in edible oils. Oils rich in monounsaturated (MU), polyunsaturated (PU), and saturated (S) fatty acids (FA) were heated above and below their smoke point (∼230 ℃). While the intensity (I) of the identified saturated (C-C, 1440 cm^-1) FA Raman marker did not change appreciably, the identified unsaturated (C=C, 1265 cm^-1) FA marker decreased in these oils when heated above the smoke point. A Raman parameter, I₁₂₆₅/I₁₄₄₀, designating thermal degradation, is proposed that was found to decrease consistently for the PUFA-rich and MUFA-rich oils when heated above the smoke point, while the SFA-rich oil did not degrade at all over the whole temperature range. An optical transmission marker at 2140 nm was identified that decreased consistently with increased thermal stressing. These markers can be calibrated with the variations in the quantitative iodine value, an industrial benchmark for the degree of unsaturation, for thermally stressed oils.

Raman Spectroscopy and 2DCOS Analysis of Unsaturated Fatty Acid in Edible Vegetable Oils

Raman spectroscopy has been applied to study unsaturated fatty acid in edible vegetable oils. The relative intensity ratio of characteristic vibrational bands has been investigated as a function of the content of totally unsaturated fatty acid, polyunsaturated fatty acid, and monounsaturated fatty acid. The results suggest the intensity ratio of 1655 cm−1 to 1440 cm−1 or 1265 cm−1 to 1300 cm−1, i.e., a characteristic vibrational band correlated with carbon-carbon double bond in acid chain to a vibrational band not correlated with double bond, could be applied for preliminary analysis of the content of polyunsaturated fatty acid or monounsaturated fatty acid, but cannot be used to analyze the content of total unsaturated fatty acid. Additionally, two-dimensional correlation spectroscopy (2DCOS) has been performed on the content dependent Raman spectra. The 2DCOS result is consistent with that by Raman spectroscopy.