Secondary Lipid Oxidation Products Research Articles

Insect-based products commercialized online: a snapshot of lipid oxidation and mineral content

This research aims to monitor the conservation status of the lipid and mineral contents of four shelf-stable insect-based products (yellow mealworm, house cricket, mole cricket, and silkworm) marketed online. A total of 32 single-species packs were purchased from various online commercial suppliers. Moisture, lipids, fatty acids, titratable acidity, mineral elements, and primary and secondary lipid oxidation products were determined. Statistical multivariate approaches were applied to investigate the contribution of each chemical variable to the characterization of edible insects. Titratable acidity (up to 37.3 g oleic acid per 100 g of crickets), as well as primary and secondary lipid oxidation products, showed great variability within and between species. The study revealed a significant occurrence of rancidity (45.5% of the samples exceeded the peroxide limit of 10 mEqO2/kg; 100% of the samples exceeded the indication of 1 mg/kg malondialdehyde), whereas the heavy metal content indicated a relatively safe condition, suggesting the absence of potential risks to human health. Both the chemical and the elemental properties could be regarded as potential characteristics suitable for authenticating this food matrix. This study contributes to the description of several chemical features in commercialized processed insect-based products, aiming to highlight possible safety concerns and identify those unfit for human consumption.

Elevated Lipid Metabolites in Stored Clinical OCA Media Correlate With Chondrocyte Death

Background: A major limitation of osteochondral allografts (OCA) is the deterioration of cartilage health associated with cell death during prolonged storage. However, little is known about the mechanisms that contribute to chondrocyte death during storage. Purpose/Hypothesis: This study aimed to determine whether bioactive lipid metabolites accumulate in the storage media of OCA and whether they are associated with a loss of chondrocyte viability during prolonged storage. It was hypothesized that free fatty acids (FFAs) would accumulate over time in the storage media of OCA and adversely affect cartilage health during storage. Study Design: Controlled laboratory study. Methods: A group of 21 (n = 6-8 OCA/treatment group) fresh human hemicondylar OCA tissues and media were analyzed after 7, 28, and 68 days of prolonged cold (4°C) storage. Targeted mass spectrometry analysis was used to quantify bioactive FFAs, as well as primary (lipid hydroperoxide [ROOH]) and secondary (malondialdehyde) lipid oxidation products. Chondrocyte viability was measured using a fluorescence-based live/dead assay and confocal microscopy. Results: The concentration of all targeted fatty acid metabolites in storage media was significantly increased with increased cold storage time (P < .05). ROOH was significantly higher on day 28 of cold storage. No difference in secondary ROOH products in storage media was observed. Chondrocyte viability significantly declined in both the en face and the vertical cross-sectional analysis with increased cold storage time and inversely correlated with fatty acid metabolites (P < .05). Conclusion: It is well established that elevated levels of certain FFAs and lipid oxidation products can alter cell function and cause cell death via lipotoxicity and other mechanisms. This work is the first to identify elevated levels of FFA metabolites and primary oxidation lipid products in the storage media from clinical OCA. The concentrations of FFA metabolites were measured at levels (>100 µM) known to induce cell death and were directly correlated with chondrocyte viability. Clinical Relevance: These findings provide important targets for understanding why cartilage health declines during cold storage, which can be used to optimize media formulations and improve graft health.

Secondary Lipid Oxidation Products as Modulators of Calpain-2 Functionality In Vitro.

The objective was to understand the impacts of secondary lipid oxidation products on calpain-2 activity and autolysis and, subsequently, to determine the quantity and localization of modification sites. 2-Hexenal and 4-hydroxynonenal incubation significantly decreased calpain-2 activity and slowed the progression of autolysis, while malondialdehyde had minimal impact on calpain-2 activity and autolysis. Specific modification sites were determined with LC-MS/MS, including distinct malondialdehyde modification sites on the calpain-2 catalytic and regulatory subunits. 2-Hexenal modification sites were observed on the calpain-2 catalytic subunit. Intact protein mass analysis with MALDI-MS revealed that a significant number of modifications on the calpain-2 catalytic and regulatory subunits are likely to exist. These observations confirm that specific lipid oxidation products modify calpain-2 and may affect the calpain-2 functionality. The results of these novel experiments have implications for healthy tissue metabolism, skeletal muscle growth, and post-mortem meat tenderness development.

Effectiveness of different antioxidants in suppressing the evolution of thermally induced peroxidation products in hemp seed oil

Several scientific studies have warned that the ingestion of dietary lipid oxidation products (LOPs) may initiate or exacerbate the development of several chronic non-communicable diseases in humans. Indeed, the constantly increasing consumption of culinary oils by larger global populations indicates the need for scientific techniques to suppress the evolution of LOPs in thermo-oxidised oils. This study employed a 600.13 MHz frequency NMR spectrometer in evaluating the effect of 10, 50, and 100 ppm concentrations of chemical compounds reported to have antioxidant properties in continuously-stirred and thermally stressed polyunsaturated fatty acid (PUFA)-rich hemp seed oil at a frying temperature of 180℃ for 180 min. Research data acquired showed that the antioxidants α- and γ-tocopherol, γ-oryzanol, β-carotene, eugenol, resveratrol, ascorbyl palmitate, gentisic acid, and L-ascorbic acid all played a vital role in suppressing the evolution of secondary aldehydic lipid oxidation products in hemp seed oil. However, the most ineffective LOP-suppressing agent was L-lysine, an observation which may be accountable by its poor oil solubility. Nonetheless, trends deduced for compounds acting as antioxidants were mainly unique for each class of agent tested. Conversely, the antioxidant capacity of resveratrol was consistently higher, and this effect was found to be independent of its added amounts. This report provides a direct approach in developing scientific methods for the suppression of LOPs in thermo-oxidatively susceptible PUFA-rich cooking oils.

Effects of three polyphenols with different numbers of phenolic hydroxyls on the structural and interfacial properties and lipid-protein co-oxidation of oil body emulsions

Oil bodies (OBs) are organelles for storing lipids, and they are composed of lipid cores and monolayer phospholipid protein membranes. During storage, membrane proteins anchored in the lipid core are often damaged by lipid oxidation products, leading to oxidative damage and a decreased quality of emulsified foods. Here, three natural antioxidants (gallic acid (GA), epigallocatechin gallate (EGCG), and tannic acid (TA)) were added to OB emulsions to study the effects of polyphenols on protein interfacial properties during oxidation and the lipid-protein co-oxidation behavior. Compared to GA, EGCG and TA with higher molecular weights and hydroxyl substitution showed better antioxidant activity, metal chelating activity, iron reduction ability, and affinity for OB. The polyphenols significantly reduced the contents of free amino and sulfhydryl groups in OB. Infrared spectroscopy analysis indicate that hydrogen bonding and hydrophobic interactions may exist between the polyphenols and OB. During storage, polyphenols inhibited >23% of the primary and secondary lipid oxidation products in the emulsions, whereas the formation of carbonyl groups and disappearance of sulfhydryl groups were only inhibited by 10.7% and 7.4%, respectively, indicating that polyphenols preferentially inhibited lipid oxidation over protein oxidation. Electrophoresis results showed that moderate oxidation (3 days of storage) disrupted the disulfide bonds of proteins. Note that moderate oxidation enhanced the interfacial properties of OB proteins, whereas excessive oxidation led to protein aggregation. This study offers new perspectives on using polyphenols to regulate the lipid-protein co-oxidation in OB, as well as the different properties of OB proteins after oxidation.

Comparison of the Effect of Drying Treatments on the Physicochemical Parameters, Oxidative Stability, and Microbiological Status of Yellow Mealworm (Tenebrio molitor L.) Flours as an Alternative Protein Source

The increasing production of edible insects on an industrial scale makes it crucial to implement appropriate technologies after harvesting to process safe and high quality insect products. The aim of this work was to compare the impact of different drying treatments used in the production of flour from Tenebrio molitor larvae. The larvae were subjected to freeze-drying (FD), conventional drying (CD), microwave drying (MWD), microwave drying without freezing prior blanching (MWDL), and microwave drying with addition of 0.1% butylated hydroxytoluene (BHT) during the blanching of the larvae (MWDA). The studied parameters included water activity (aw), instrumental colour, chemical composition, lipid oxidative processes, antioxidant activity, as well as microbiological status. The freeze-drying and conventional drying of the larvae reduced the aw of the derived flours (p &lt; 0.0001); however, their nutritional profile revealed lower protein (p &lt; 0.0001) and considerably higher fat content (p &lt; 0.0001) compared to the flours after microwave treatments. The conventional drying and microwave treatment with BHT induced significantly darker colour (p &lt; 0.0001) in comparison to the other methods. Despite the advantages of the microwave drying as a fast and energy efficient method, it displayed some negative effects associated with low lipid stability such as higher acid value (AV) and secondary products of lipid oxidation (TBARS) (p &lt; 0.0001). This was also observed in the MWDA flour, indicating a certain pro-oxidative effect of the BHT. Regardless of the drying method, all the flours had a low microbial load.

Performance, Carcass Composition, and Meat Quality during Frozen Storage in Male Layer-Type Chickens

An experiment was carried out in the Institute of Animal Science—Kostinbrod, Bulgaria, to investigate the growth performance of male layer-type chickens (Lohmann Brown Classic), raised to 6 and 9 weeks of age, to evaluate the economic aspects of this rearing, as well as to present changes in the quality characteristics of the meat during frozen storage. The chickens were reared in a controlled microclimate with an initial stocking density of 9 birds/m2. After 6 weeks of age, fragmentation of the stocking density was applied, and then it diminished to 3 birds/m2. The chickens were slaughtered at 6 and 9 weeks of age. Ten 9-week-old chickens were subjected to carcass analysis. Meat quality parameters (pH, color), degree of proteolysis (free amino groups), and lipid oxidation (content of peroxides and TBARS) were assessed in fresh breast and thigh meat (0 d) and in samples stored for 60 and 120 days at −18 °C in chickens slaughtered at 6 and 9 weeks old. The mean live weight of the male layer-type chickens at 6 weeks was 608.81 g, while the 9-week-old chickens reached 1115.93 g. The feed conversion ratio (FCR) for the whole period of rearing was 2.75. There were no considerable deviations in the meat traits, indicating quality deterioration over the course of the frozen storage. There was a significant increase in the pH of the breast and thighs, reaching maximum values for 60 days of storage in the 6-week-old chicks, while in the 9-week-old birds, pH peaked in the samples stored for 120 days. The changes in the dynamics of pH corresponded to those of proteolysis. There was an increase in lightness (L*), allowing for higher values in the samples stored for 60 days to be reached regardless of the type of meat and age of the chickens. The content of the peroxides increased considerably for 60 days of frozen storage and decreased afterwards. During storage, there was a constant increase in the secondary products of lipid oxidation. Our results indicated that the application of practices such as the fragmentation of stocking density and finding the suitable age for slaughter have significant importance for the profitability of producing meat product from male layer-type chickens. We found that rearing this type of bird until 9 weeks of age resulted in lower costs and higher economic efficiency.

Cellular excitability and ns-pulsed electric fields: Potential involvement of lipid oxidation in the action potential activation

Recent studies showed that nanosecond pulsed electric fields (nsPEFs) can activate voltage-gated ion channels (VGICs) and trigger action potentials (APs) in excitable cells. Under physiological conditions, VGICs’ activation takes place on time scales of the order 10–100 µs. These time scales are considerably longer than the applied pulse duration, thus activation of VGICs by nsPEFs remains puzzling and there is no clear consensus on the mechanisms involved. Here we propose that changes in local electrical properties of the cell membrane due to lipid oxidation might be implicated in AP activation. We first use MD simulations of model lipid bilayers with increasing concentration of primary and secondary lipid oxidation products and demonstrate that oxidation not only increases the bilayer conductance, but also the bilayer capacitance. Equipped with MD-based characterization of electrical properties of oxidized bilayers, we then resort to AP modelling at the cell level with Hodgkin-Huxley-type models. We confirm that a local change in membrane properties, particularly the increase in membrane conductance, due to formation of oxidized membrane lesions can be high enough to trigger an AP, even when no external stimulus is applied. However, excessive accumulation of oxidized lesions (or other conductive defects) can lead to altered cell excitability.

Validation of thiobarbituric acid reactive substances (TBARS) method for measuring secondary lipid oxidation products in fresh Indian mackerel (Rastrelliger kanagurta)

The measurement of thiobarbituric acid reactive substances (TBARS), such as malondialdehyde (MDA), has been used as an indicator of lipid peroxidation. The TBARS method developed in this study was validated according to the guidelines set by the International Conference on Harmonisation (ICH), International Union of Pure and Applied Chemistry (IUPAC) and EURACHEM. The validation criteria included assessing linearity, limit of detection (LOD), limit of quantification (LOQ), recovery, repeatability, and uncertainty. To evaluate the quality changes in Indian mackerel (Rastrelliger kanagurta), the fish was placed in a refrigerator (4 °C) for six days. The sensory evaluation, TBARS and Total Volatile Base Nitrogen (TVBN) method were used to assess the quality changes at 48 h interval. The TBARS method validation results showed that the linearity range was 0.3–6.5 µmol/L. The calibration curve demonstrated a linear relationship between absorbance and concentration, with a coefficient of correlation 0.9999. The regression equation for the curve was Y = 0.1337X + 0.0905. The LOD and LOQ were determined to be 0.1 μmol/L and 1.5 μmol/L, respectively. The repeatability (% RSDr) was found to be 1.6. The percentage recoveries for MDA were calculated at three concentration levels and results was observed from 85.95% to 86.98%. The expanded uncertainty was within ± 5.18% (k = 2; 95% confidence interval). The TBARS method showed a high correlation coefficient 0.983 with storage time, indicating a strong relationship between TBARS value and freshness. Similarly, the sensory evaluation showed a correlation coefficient of 0.996 with storage time, indicating a high agreement between sensory evaluation and freshness. The TVBN method exhibited a correlation coefficient of 0.957 for chilled Indian mackerel. In conclusion, the developed TBARS method is suitable for measuring malondialdehyde as a quality parameter in assessing the freshness of tropical water fish.

Ultrasound-aided pH-shift processing for resource-smart valorization of salmon and herring side streams

The possibility of reducing the amount of fresh water used during alkaline the pH-shift processing of salmon head (SH) and herring frame (HF) was evaluated with ultrasound (US) as a tool to mitigate its negative effects on protein yield. The role of water ratio and US for homogenate viscosity, mass yield, crude composition, functional properties and lipid oxidation of the SH and HF protein isolates were also investigated. Applying US during the solubilization step of the pH-shift process completely compensated for the reduced protein yield coming from using 3 rather than 6 volumes of water for HF, but not for SH. Using US had no negative effect on the composition and protein functionality of the HF protein isolate. However, it slightly increased its level of secondary lipid oxidation products. Altogether, applying US during the pH-shift processing at low water ratios can be a promising solution for more resource-smart valorization of herring side streams.

Poster 124: Elevated Lipid Metabolites in Stored Clinical OCA Media are Associated with Chondrocyte Death

Objectives: A major limitation of osteochondral allografts (OCA) is the deterioration of cartilage health associated with cell death during prolonged storage. It is well established that chondrocyte viability in OCA is a critical factor for repair and clinical outcomes, but little is known about the mechanisms that contribute to chondrocyte death during storage. Elevated bioactive lipid metabolites and free fatty acids (FFAs) have been associated with cell death and tissue damage for various pathologies through lipotoxicity. However, the levels and effect of FFA accumulation in OCA media during prolonged storage are unknown. The purpose of this study was to determine if bioactive lipid metabolites accumulate in the storage media of OCA and are associated with a loss of chondrocyte viability during prolonged storage. We hypothesized that FFAs will accumulate over time in the storage media of OCA and adversely impact cartilage health during storage. Methods: To elucidate potential mechanisms of cartilage health decline during storage, 21 fresh human hemi-condyle osteochondral allograft tissues and media provided by a US tissue bank were analyzed after 7, 28, and 68 days of prolonged cold storage. Targeted metabolomics analysis measured bioactive FFAs, and primary (lipid hydroperoxide, ROOH) and secondary (malondialdehyde, MDA) lipid oxidation products. Chondrocyte viability was measured using standard LIVE/DEAD assay and confocal microscopy. Results: All fatty acid metabolites in storage media significantly increased with increased storage time (Figure 1; p&lt;0.05). ROOH was significantly higher at Day 28 of storage. No difference in secondary lipid hydroperoxide products in storage media were observed. Chondrocyte viability significantly declined in both the en face and vertical cross-section analysis with increased storage time (Figure 2) and inversely correlated with fatty acid metabolites (Figure 3; p&lt;0.05). Conclusions: It is well established that elevated levels of certain free fatty acids and lipid oxidation products can alter cell function and cause cell death through lipotoxicity and other mechanisms. This work is the first to identify elevated levels of FFA metabolites and primary oxidation lipid product in the storage media from clinical OCA. The concentrations of FFA metabolites were measured at levels (&gt;100µM) known to induce cell death and were directly correlated with chondrocyte viability. These findings provide important targets for understanding why cartilage health declines during storage to better optimize media formulations and improve graft health.

Conjugation of aminated sugar beet pectin–tannic acid nanoparticles with cinnamaldehyde at the oil–water interface to stabilize a 3D printable high-internal phase emulsion

In this work, we demonstrated the use of aminated sugar beet pectin (SBP–NH2)–tannic acid (TA) nanoparticles (NPs) conjugated with cinnamaldehyde (CA) to form 3D printable high-internal phase emulsions (HIPEs). Unlike the absorption of common stabilizers, the interfacial conjugation of SBP-NH2/TA NPs with CA formed ultra-absorbed NPs at the oil–water interface through electrostatic bonding, hydrogen bonding, hydrophobic interactions, and Schiff base reaction. The addition of CA (2.5 wt%) to the oil phase significantly reduced the mean droplet size of SBP-NH2/TA NPs stabilized HIPE (75 vol% oil; SBP-NH2/TA mass ratios of 1:0.5) from 23.03 to 18.33 μm and greatly improved the stability of HIPEs during a 90-day storage period at 25 °C. Concomitantly, rheological studies indicate that HIPEs with CA had high viscoelasticity up to 3 orders of magnitude, providing HIPE-based inks with exceptional support performance and smooth extrusion features. In particular, TA and CA act as the components of a stabilizer and adsorb onto the oil–water interface, imparting combined antioxidant and antimicrobial dual capabilities to HIPEs. In the SBP-NH2/TA NPs stabilized HIPEs, the addition of CA resulted in 0.34-fold lower amounts of primary and secondary lipid oxidation products and 0.4–0.5-fold higher antimicrobial properties against either E. coli or S. aureus. This work established that the interfacial conjugation of the SBP-NH2/TA NPs with CA advanced the antioxidant and antimicrobial properties, stability, water-holding capacity, and viscoelastic properties of HIPEs. Furthermore, the three-dimensional (3D) printed structure with notable mechanical strength was achieved.

A comparison of Echium, fish, palm, soya, and linseed oil supplementation on pork quality.

Long chain n-3 polyunsaturated fatty acids (PUFA) exert positive effects on human health. The long chain n-3 PUFA of pork can be increased by adding fish oil to the diet. Due to the cost and availability of fish oil an alternative source must be found. This study evaluated the effect of five dietary oils on meat quality, fatty acid composition and lipid stability. The five diets contained 1% palm oil (Control), 1% soya oil, 1% linseed oil, 1% fish oil, and 1% Echium oil, respectively. The trial consisted of 60 gilts, randomly allocated to five groups. All color parameters, extractable fat content, fat free dry matter, and moisture content of the m. longissimus muscle were unaffected by dietary treatment. Consumers and a trained sensory panel could not detect a difference between the control samples and the Echium oil sample during sensory analysis. Samples containing higher levels of PUFA (soya, linseed, fish, and Echium oil) had higher levels of primary and secondary lipid oxidation products after refrigerated and frozen storage. However, these values were still well below the threshold value where off flavors can be detected. The Echium oil treatment had significantly higher levels of long chain PUFA than the linseed oil treatment, but it was still significantly lower than that of the fish oil treatment. Echium oil supplementation did not increase the levels of n-3 to the same extent as fish oil did. The result did however suggest that Echium oil can be used in pig diets to improve muscle long chain n-3 fatty acid content without any adverse effects on meat quality when compared to linseed, soya, and palm oil.

Stabilization of Sunflower Oil with Biologically Active Compounds from Berries.

Sunflower oil (Helianthus annuus) contains a rich concentration of polyunsaturated fatty acids, which are susceptible to rapid oxidative processes. The aim of this study was to evaluate the stabilizing effect of lipophilic extracts from two types of berries, sea buckthorn and rose hips, on sunflower oil. This research included the analysis of sunflower oil oxidation products and mechanisms, including the determination of chemical changes occurring in the lipid oxidation process via LC-MS/MS using electrospray ionization in negative and positive mode. Pentanal, hexanal, heptanal, octanal, and nonanal were identified as key compounds formed during oxidation. The individual profiles of the carotenoids from sea buckthorn berries were determined using RP-HPLC. The influence of the carotenoid extraction parameters ascertained from the berries on the oxidative stability of sunflower oil was analyzed. The dynamics of the accumulation of the primary and secondary products of lipid oxidation and the variation of the carotenoid pigment content in the lipophilic extracts of sea buckthorn and rose hips during storage demonstrated good stability at 4 °C in the absence of light for 12 months. The experimental results were applied to mathematical modeling using fuzzy sets and mutual information analysis, which allowed for the prediction of the oxidation of sunflower oil.

Effects of Two Amphiphilic Diesters of L-Ascorbic Acid on the Oxidative Stability of Rabbit Meatballs

Lipid oxidation involves a cascade of phenomena leading to serious impairments of meat quality during storage. Novel strategies for lipid protection are therefore highly desirable. Herein, two amphiphilic diesters of L-ascorbic acid with myristic (DA) and stearic (DB) acids were synthesised and added at a 0.1% (w/w) to minced rabbit meat before preparing meatballs. Then, pH, colour indexes, weight loss, fatty acid profile and primary and secondary lipid oxidation products were analysed for meatballs treated with DA (n = 16), DB (n = 16), or not treated (C, n = 16), and stored for 80 days at −10 °C. Results showed that DA and DB did not specifically prevent weight loss and lipid oxidation. Nevertheless, the addition of DA on stored rabbit meatballs seemed to prevent colour modification and reduced (p = 0.0613) TBARS levels in the treated stored meat. For these reasons, further investigations on the properties of L-ascorbyl diesters on the oxidative stability of meat will likely be performed.

High Pressure Processing under Mild Conditions for Bacterial Mitigation and Shelf Life Extension of European Sea Bass Fillets

High pressure is an industrially established food preservation process applied for the minimal processing or cold pasteurization of chilled, fresh, or ready-to-eat products. This study aimed to quantify the effectiveness of high pressure on the inactivation of spoilage microflora and the shelf life extension of European sea bass (Dicentrarchus labrax) fillets. Fish fillets were subjected to mild, high pressure conditions (100–400 MPa; 3–25 °C; 5–10 min) and then stored at 0.0 ± 0.2 °C. Their shelf life was evaluated in terms of their microbiological, physicochemical, and sensorial quality. The results indicated that a shelf life extension of 1–5 d at 0 °C was achieved when pressures of 100 MPa were applied, whereas higher pressures resulted in an up to 5-fold increase in the shelf life of the fillets, depending on the applied pressure and temperature. A high pressure treatment combined with vacuum packaging showed an additional effect on the shelf life extension of the fillets, increasing the shelf life by 4–12 d when compared to aerobically stored products. Moreover, the high pressure treatment prevented lipid oxidation throughout the storage period, indicating no formation of secondary lipid oxidation products. The estimated shelf life of the fish fillets based on their sensorial quality was in accordance with the estimation based on the microbiological data.

Changes in fatty acids during storage of artisanal-processed freshwater sardines (Rastrineobola argentea).

For ages, indigenous small fish species have been important in food and nutritional security of poor communities in low income countries. Freshwater fish, in particular fatty fish species are attracting a great attention because they are good sources of health promoting long chain omega-3 fatty acids. Docosahexaenoic acid (DHA, C22:6n-3), Docosapentaenoic acid (DPA, C22:5n-3) and eicosapentaenoic acid (EPA, C20:5n-3) are the main omega-3 PUFAs known to confer health benefits in humans if consumed in required amounts. While nutritionally valued, omega-3 PUFAs in fish are susceptible to oxidative damage during processing, transportation and subsequent storage. Lake Victoria sardines (Rastrineobola argentea), are rich source of chemically unstable omega-3 fatty acids DHA, DPA and EPA. Traditionally, sardines are preserved by sun drying, deep frying and smoking. Sardine products are transported, stored and marketed at ambient temperatures. Generally, uncontrolled and higher temperatures are known to increase vulnerability of polyunsaturated fatty acids to oxidation which in turn results into loss of nutritional and sensory qualities. This study investigated changes of fat acids in sun dried, deep fried and smoked sardines during storage. Lipolysis and the progressive hydroperoxides formation were monitored by free fatty acids (FFAs) and peroxide value (PV) respectively. None volatile secondary products of lipid oxidation were measured by thiobabituric acid reactive substances (TBARS). Fatty acids were analyzed by gas chromatography with a flameionization detector (GC-FID). Deep fried sardines maintained the lowest and apparently stable PV, TBARS and FFAs. Proportions of saturated fatty acids and polyunsaturated fatty acids decreased with time while that of monounsaturated fatty acids increased. Omega-3 fatty acids EPA, DPA and DHA decreased with increase in storage time. In 21 days of storage, DHA was oxidized beyond detectable levels in all sardine products. Gradual increase in FFAs in sun dried sardines was suggestive of lipid hydrolysis induced by enzymes.

Migration of gallic acid from the aqueous phase to the oil–water interface using pea protein to improve the physicochemical stability of water–in–oil emulsions

The objective of this work was to effectively migrate gallic acid (GA) to the oil–water interface and inhibit the lipid oxidation in water–in–oil (W/O) emulsions by combining GA with a natural emulsifier (pea protein isolate, PPI). The results showed that the conjugate induced by ultrasound–assisted alkali treatment exhibited superior binding efficiency (17.27 mg/g) and stability (9.01 mg/g retained after 30 days). Such conjugate showed a decrease in particle size, ζ–potential and sulfhydryl content. The secondary and tertiary structure of the PPI were altered. The cross–linking sites for PPI and GA binding included Glu, Asp, His, Lys, Arg and Trp. The functional properties of the conjugates were enhanced with their structural changes, including antioxidant and interfacial properties. The improvement of interfacial properties (2.13 mN/m for interfacial tension and 95.51% for interfacial protein adsorption) was attributed to the increase in surface hydrophobicity and the decrease in particle size. When added to the W/O emulsion, the conjugate provided the emulsion with the highest physical stability (droplet size of 198.10 nm and ζ–potential of −110.97 mV). In terms of oxidative stability, conjugate significantly reduced the production of primary and secondary oxidation products of lipid oxidation (64.62 and 92.34% respectively). Compared with the antioxidant (octyl gallate, C8) with high interfacial activity, the combination of PPI and GA provided emulsions with equivalent or higher oxidative stability. This is instructive for improving the oxidative stability of W/O emulsion through interface engineering.

Development of a Novel Steam Distillation TBA Test for the Determination of Lipid Oxidation in Meat Products.

The 2-thiobarbituric acid (TBA) method has been used for the spectrophotometric determination of secondary lipid oxidation products, such as malonaldehyde (MA), due to its good correlation with sensorial perception of lipid oxidation. Other approaches have been proposed over time. Direct distillation can result in artificially increased MA concentrations due to intense heating. Extraction is a milder and faster method, but it suffers from false color development in the presence of sugars or other compounds. A novel approach using steam distillation for the recovery of MA was developed. Validation and optimization studies were conducted, aiming to maximize MA recovery from various meat product samples by adjusting the steam distillation parameters. For the optimal MA recovery, 10 g of the sample, 25 mL of H2O, and 5 mL of 2 N HCl were used. The sample was distilled using a stream of water vapor until 50 mL of the distillate was collected in less than 3 min. Subsequently, 5 mL of the distillate was reacted with 5 mL of 0.02 M TBA, and the absorbance was measured at 532 nm. MA recovery was 61.8%. Experimentation with varying nitrite levels suggested that the addition of sulfanilamide is necessary when NaNO2 is more than 50 mg MA/kg. The proposed method is fast, milder than direct distillation, and eliminates the issue of TBA interacting with sugars and other compounds.

Malondialdehyde treatment reduced immunoreactivity of amandin and delayed its digestion

AbstractObjectivesThe secondary products of lipid oxidation are one of the main factors inducing protein oxidation. The effects of oxidation treatment with malondialdehyde (MDA) on the immunoreactivity of amandin and its digestion were studied.Materials and MethodsThe rabbit IgG binding ability of amandin was analyzed by western blotting, and the changes in amandin oxidation and immunoreactivity during digestion of amandin with different degrees of oxidation were investigated in combination with an almond allergen enzyme-linked immunosorbent assay kit. Alteration of linear epitopes of amandin by oxidation was investigated by liquid chromatography–tandem mass spectrometry (LC-MS/MS).ResultsThe results showed that the immunoreactivity of amandin was significantly reduced after 1 mmol/L MDA and 100 mmol/L MDA treatment. However, the 1 mmol/L MDA treatment was owing to cleavage of linear epitope peptide in amandin and oxidation of the active amino acid. The 100 mmol/L MDA treatment was due to aggregation of amandin and significant decrease in its solubility. Oxidation also reduced digestibility of amandin and significantly affected immunoreactivity during digestion. LC-MS/MS also identified four oxidation-prone methionine sites (aa 264–274, 298–308, 220–240, and 275–297) in gamma conglutinin 1.ConclusionsMDA treatment reduced the immunoreactivity of amandin. MDA treatment also led to protein aggregation, which slowed down the digestion of amandin and altered the immunoreactivity of amandin during digestion.