Terms Of Oxidative Stability Research Articles

The effect of stabilization heat treatment on rice bran quality parameters, including total phenolic content, gamma oryzanol content, antioxidant potential, oxidative stability and extraction yield during storage

The impact of rice bran stabilization thermal treatments on oxidative stability, extractability, and antioxidant potential was investigated. Freshly milled rice bran samples of the variety “Ld 368 –red” were subjected to four heat treatments: steaming, hot air drying, microwave treatment, and a combination of microwave and steaming. Solvent extraction was used to obtain rice bran oil (RBO). The Phenolic, γ-oryzanol contents and antioxidant potential of RBO were analyzed. Oil yield, free fatty acid content (FFA), and peroxide value (PV) were measured during 50-days storage at room temperature, with data collected at an interval of 10 days. The highest extraction yield was in coupled treatment (22.26 %). The coupled treatment and microwave were the most effective for the stabilization of rice bran in terms of oxidative stability, which provided the lowest FFA value (2.950 % & 2.993 %) and PV (0.518 & 0.620 mEqv/kg oil) (p ≤ 0.05). The lowest increment of FFA (2.945 %) and PV (4.23 mEqv/kg) was detected in RB stabilized by coupled treatment in 50 days of storage time. The microwaved sample exhibited the highest total phenolic content (4.147±0.190 mg GAE/g of extract), γ-oryzanol content (1.536±0.0173 %), and the highest antioxidant activity/ lowest IC50 value among the stabilized sample.

Microemulsions: An Encapsulation Strategy to Increase the Thermal Stability of D-limonene.

D-limonene, derived from citrus essential oils, holds significant therapeutic potential but faces challenges due to its high volatility, especially in pharmaceutical formulations. This study investigates microemulsions as a promising delivery system for volatile compounds, emphasizing their thermal protection for D-limonene. The formulation development was guided by a pseudo-ternary phase diagram and involved assays with different surfactants. Microemulsions were achieved solely with Labrasol® (Gattefossé Brasil, São Paulo, Brazil), encompassing concentrations of 7.1% to 30.8% D-limonene, 28.6% to 57.1% Labrasol®, and 20.0% to 64.3% water. All formulations were homogeneous, transparent, and presented low viscosity, with adequate D-limonene content, indicating that the production is feasible at room temperature. While the formulations demonstrated robust physical stability under mechanical stress, they exhibited destabilization at temperatures exceeding 50 °C. In terms of oxidative stability, pure D-limonene exhibited an induction period of 4.88 min, whereas microemulsions extended this period by four to eight times. Notably, the induction period of the microemulsions remained practically unchanged pre and post-heating (70 °C), suggesting the formulation's ability to enhance the D-limonene thermal stability. This highlights the value of oxidative stability analysis as a quicker tool than conventional oxidative tests, while affirming microemulsions as a viable encapsulation strategy for D-limonene protection against elevated temperatures.

Comparative evaluation of different enzyme pretreatment on the oxidative stability and volatile compounds of sunflower oil

In order to determine the influence of enzyme pretreatment to modify the aromas of sunflower seed oil (SSO). In this study, different enzyme combinations prepared SSO as raw material, using reducing sugar, amino acids, oxidation stability, and basic aroma characteristics to compare the whole. The results show that reducing sugar increased approximately 1.5-fold after enzymatic hydrolysis. Arginine, lysine, and histidine decreased most after roasting. The combination of cellulase and protease showed the greatest increase in heterocyclic substances (from 1681.81 to 13865.84 μg/kg), resulting in a strong caramel and nutty flavor. Interestingly, it was identified by aroma extract dilution analysis (AEDA) combined with relative odor activity value (ROAV) that 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) was a common key aroma compound in enzyme-treated SSO, and phenylacetaldehyde, furfuryl alcohol and acetic acid were considered to be important contributors to the aroma after cellulase, hemicellulose and pectinase treatment, respectively. All of these were newly identified as odorants in enzyme-treated sunflower oil. The enzyme-treated oil also had advantages in terms of oxidative stability, including the reduction of acid value and peroxide value. This work provides a feasible method to enhance the aroma flavor and extend the shelf-life of sunflower oil in future production.

Extension of Biodiesel Aging Mechanism-the Role and Influence of Methyl Oleate and the Contribution of Alcohols Through the Use of Solketal.

The energy crisis and dependence on fossil fuels forces societies to develop alternative pathways to secure energy supplies. Therefore, non-fossil fuels such as biofuels and e-fuels can help counteract the resulting demand for existing combustion engines. However, biofuels, like biodiesel, have disadvantages in terms of oxidation stability. In general, aging of biodiesel is a complex mechanism due to interaction of various components. In order to develop an ideal fuel, the mechanism must be understood in full detail. In this work, an attempt is made to simplify the system by using methyl oleate as a biodiesel model component. In addition, other fuel components of interest such as alcohols and their respective acids help to clarify the aging mechanism. This work used isopropylidene glycerol (solketal) as the main alcohol, 1-octanol and octanoic acid. A holistic biodiesel aging scheme was developed by using generated data and evaluating the role of acids. They epoxidize unsaturated fatty acid via Prileschajev reactions. In addition, the role of epoxides in oligomerization reactions is confirmed. Moreover, the alcohols show that the suppression of oligomerization can be achieved by the reaction with methyl oleate. The alcohol-dependent aging products were determined by quadrupole time-of-flight (Q-TOF) mass spectrometry.

Enhanced castor seed oil extraction assisted by the synergistic effect of ultrasound and microwave: Impact on extraction effectiveness and oil quality

The present study first time utilizes synergistic effect of ultrasound and microwave for oil extraction from castor seeds, with methanol as solvent. Taguchi's orthogonal array is selected as a tool for design of experiment for castor oil extraction through mechanical stirring, ultrasound, and hybrid (ultrasound + microwave) intensification techniques. The maximum extraction yield effectiveness of 98.37% is achieved based on optimized process conditions: 45 s grinding time, 12:1 solvent-to-seed ratio (v/w), 30 min extraction time, and 50 °C temperature. Along with the yield, significant enhancement in extracted oil quality in terms of oxidation stability and chemical composition is observed. The chemical composition of oil extracted through a hybrid technique shows a lower unsaturation level than ultrasonication. Ultrasound and hybrid technique both significantly increased proportion of ω-6 and ω-9 fatty acids, which has industrial as well as medicinal values. The viscosity of the oil extracted through hybrid solvent extraction is 199 ± 6 cp, which is significantly lower than that of a crushing-based technique (279 ± 6 cp). The energy consumption for the hybrid reactor is reduced by up to 40 % and 28 % than conventional mechanical stirring and ultrasound techniques, respectively. The developed process is industrially viable and environmentally sustainable.

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.

Walnut Paste: A Healthy Alternative for Nutella Consumers

Nutella is the best-selling chocolate and hazelnut spread in the world. It is known that the main ingredients of Nutella are sugar (55%) palm oil (23%), hazelnuts (14%), cocoa solids and skimmed milk (8%). Currently, worldwide, there is a tendency to make healthier food choices, and the sugar and palm oil from Nutella’s formulation are ingredients blamed for causing certain health disorders (obesity, cardiovascular diseases and diabetes). In this order, the purpose of the research was to develop the technology for obtaining walnut paste, since walnuts have proven prophylactic properties, with a low sugar content and without palm oil. The quality of the elaborated walnut paste was determined and monitored during the shelf life in terms of oxidative stability (Acidity index (FFA) and Peroxide value (PV)), total phenols content, antioxidant activity and rheology. The obtained results demonstrated that during 4 months of storage the acidity index of the walnut paste did not register significant changes, reaching maximum values of 0.17±0,01 (Oleic g/100 g), while the peroxide values evolved up to 2.22±0,03 meq/kg oil. The slow evolution of the oxidative parameters can be due to the phenolic compounds in walnut paste that recorded a value of 47.2±0,36 mg GAE/g with an antioxidant activity (DPPH free radical scavenging) of 70±1,02 %. Concerning sensory characteristics, the walnut paste samples were positively appreciated in comparison with Nutella and no significant quality difference was observed after storage for 4 months.

Correlation between Microbial Population and Oxidative Stability of the Yogurt-Based Tzatziki Salad

Tzatziki is a deli salad widely consumed in the Eastern Mediterranean and Balkan countries, and it is acknowledged for its health benefits. So far, it is proved to exhibit extreme resistance to microbial spoilage by (pathogenic) microorganisms and microbial self-stabilization, but no research was carried out regarding its oxidative stability despite the fact that it contains a large amount of lipids. In this study, the factor that affects the oxidative stability of tzatziki was exploited. Different samples of tzatziki salad were prepared and stored for 16 or 27 days, depending on the conducted experiment. They varied in the type of yogurt (set yogurt or traditional Greek-style yogurt), the type of oil (olive oil or soybean oil), and the addition or not of preservatives, garlic, and cucumber. Samples were analyzed in terms of oxidative stability (by the Rancimat method), colony-forming units, and tocopherol content throughout the storage period. Among the examined parameters, no correlation between the tocopherol content and oxidative stability was recorded. However, a strong correlation between the microbial population and the oxidative stability was recorded. Therefore, this correlation can be used to prepare tzatziki salads with increased shelf life and decreased flavor deterioration (due to oxidation). Moreover, such correlations should be further exploited for other foods so as to promote their stability.

Effect of ultrasound on the structural characteristics and oxidative stability of walnut oil oleogel coated with soy protein isolate-phosphatidylserine

In this study, the three-dimensional network system formed by rice bran wax (RBW) was used as the internal structure, and the external structure formed by soybean protein isolate (SPI) and phosphatidylserine (PS) was added on the basis of the internal structure to prepare walnut oil oleogel (SPI-PS-WOG). Ultrasonic treatment was applied to the mixed solution to make SPI-PS-WOG, on the basis, the effects of ultrasonic treatment on SPI-PS-WOG were investigated. The results showed that both β and β’ crystalline forms were present in all SPI-PS-WOG samples. When the ultrasonic power was 450 W, the first weight loss peak in the thermogravimetric (TGA) curve appeared at 326 °C, which was shifted to the right compared to the peak that occurred when the ultrasonic power was 0 W, indicating that the thermal stability of the SPI-PS-WOG was improved by the ultrasonic treatment. Moreover, when the ultrasonic power was 450 W, the oil holding capacity (OHC) reached 95.3 %, which was the best compared with other groups. Both confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) showed that the ultrasonic treatment of appropriate power succeeded in making the SPI-PS-WOG samples more evenly dispersed in the internal structure and denser in the external structure. In terms of oxidative stability, it was found that the peroxide value of SPI-PS-WOG remained at 9.8 mmol/kg oil for 50 days under 450 W ultrasonic power treatment, which was significantly improved compared with liquid walnut oil (WO). These results provide a new idea for the preparation of oleogels, and also lay a theoretical foundation for the application of ultrasonic treatment in oleogels.

Quality assessment of cold-pressed strawberry, raspberry and blackberry seed oils intended for cosmetic purposes. [pdf

BACKGROUND Cold-pressed berry seed oils are used for consumption and other applications including skin and hair care. They are natural products which gain the attention of customers. In this study, strawberry, raspberry and blackberry seed oils used for cosmetic purposes, purchased from three different European producers, were analyzed. The aim of the study was to assess the quality and oxidative stability of the berry fruit oils, thus they were analyzed after purchase and after 4 and 8 weeks of storage at room temperature. METHODS Acid and peroxide values were determined in the tested oils, as was oxidative stability, which was measured using pressure differential scanning calorimetry (PDSC). Additionally, fatty acid profiles and thei. RESULTS nd. Cold-pressed berry seed oils are used for consumption and other applications including skin and hair care. They are natural products which gain the attention of customers. In this study, strawberry, raspberry and blackberry seed oils used for cosmetic purposes, purchased from three different European producers, were analyzed. The aim of the study was to assess the quality and oxidative stability of the berry fruit oils, thus they were analyzed after purchase and after 4 and 8 weeks of storage at room temperature. Materials and methods. Acid and peroxide values were determined in the tested oils, as was oxidative stability, which was measured using pressure differential scanning calorimetry (PDSC). Additionally, fatty acid profiles and their distribution at sn-1,3 and sn-2 positions of triacylglycerols were characterized. Results, principal. Most of the fatty acids of the tested berry seed oils are polyunsaturated fatty acids (67.04-74.95%). The results show the low quality of the tested oils in terms of oxidative stability (high peroxide values: 21.9-249.6 mEq O2/kg oil). CONCLUSIONS Based on this study, it is necessary to evaluate the effects of these products on the body. Moreover, standards clarifying the oxidation of cosmetic oils should be set internationally.

Aqueous Extraction of Seed Oil from Mamey Sapote (Pouteria sapota) after Viscozyme L Treatment

In this study, aqueous enzymatic extraction (AEE) was evaluated during the process of obtaining oil from mamey sapote seed (OMSS). Viscozyme L enzyme complex was used at pH 4 and 50 °C during the optimization of the extraction process by central composite design and response surface methodology. Optimal conditions were: 3.5% (w/w) of enzyme (regarding the seed weight), 5.5 h of incubation time, 235 rpm of agitation rate, and 1:3.5 of solid-to-liquid ratio. These conditions enabled us to obtain an OMSS yield of 66%. No statistically significant differences were found in the fatty acid profile and physicochemical properties, such as the acid and iodine values and the percentage of free fatty acids, between the oil obtained by AEE or by the conventional solvent extraction (SE). However, the oxidative stability of the oil obtained by AEE (11 h) was higher than that obtained by SE (9.33 h), therefore, AEE, in addition to being an environmentally friendly method, produces a superior quality oil in terms of oxidative stability. Finally, the high oil content in mamey sapote seed, and the high percentage of oleic acid (around 50% of the total fatty acid) found in this oil, make it a useful edible vegetable oil.

Effect of sea buckthorn biomass on oxidation stability and sensory attractiveness of cereal biscuits

The purpose of this work was to investigate the effect of 5%, 10%, 15%, and 20% additions of sea buckthorn biomass to cereal biscuits and analyze the oxidation stability and sensory attractiveness. The oxidation stability of the biscuits was evaluated with an Oxitest reactor under 6.0 bar oxygen pressure at 110 °C, and the increase in the induction period with increasing addition of sea buckthorn biomass up to 15% level was found. An increase in the induction period was observed with increasing addition of sea buckthorn biomass up to 15% level. In contrast, 20% addition of biomass caused a decrease in the induction period by 30 h compared to the induction period with 15% biomass addition. Sensory analysis revealed that brittleness and hardness of the biscuits decreased with increasing addition of sea buckthorn biomass. Overall, the most sensory acceptable from the point of view of assessors were biscuits with 15% addition. It was concluded that 15% addition of sea buckthorn biomass to cereal biscuits was the most optimal content in terms of oxidation stability and sensory attractiveness. The results of this study pointed out the excellent possibilities of fortification of cereal products with sea buckthorn biomass.

Oil yield, physicochemical characteristics, oxidative stability and microbial safety of perilla seeds stored at different relative humidity

This work investigated the effect of different relative humidity (RH) on the oil yields, physicochemical characteristics, oxidative stability, and microbial safety of perilla seed (PS) stored for 12 weeks. The PSs stored at 11 % RH gave the highest oil yield (34.24 g/100 g PSs), about 7.5-times higher compared with the yield from PSs stored at 93 % RH. During storage at 69–93 % RHs, the lightness (L*) decreased and the redness (a*) and yellowness (b*) increased, indicated a dark-brownish color. The PSs stored at 33–43 % RHs had higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (85.74 %) and iodine value (190 g/100 g sample) and lower acid value (1.40 mg KOH/g sample) and peroxide value (4.35 meq/kg sample) as compared with other PSs samples. During storage, the aerobic bacterial contents (3.08 log10 cfu/g) in PSs were plateaued at 11–69 % RHs, and significantly increased at 81–93 % RHs. Yeasts and molds were found only for those of the PSs stored at 69–93 % RHs. At higher RH (81–93 %), the microbial contents were uncountable due to too much growth after two weeks. This study could be useful for an appropriate storage condition to maintain quality in terms of oxidative stability and retarding microbial growth of PS.

Current Status of High Oleic Seed Oils in Food Processing

AbstractDietarytransfatty acids (TFA) from industrial partial hydrogenation continue to occupy the attention of health and regulatory authorities, prompting renewed recommendations and regulations around the world. Partial hydrogenation of liquid oils was widely used because it increases the oxidative stability and plasticity of vegetable oils. The development of high oleic (HO) oils appeared as an efficient and healthy strategy to replace partially hydrogenated vegetable oils. At present, the main sources of HO oils are the HO varieties of sunflower, canola, and soybean, covering almost the entire market. Although all these HO crops show oleic acid contents higher than 70%, they can be differentiated by their fatty acid profiles. Recent clinical evidence suggests that polyunsaturated content should also be considered since its intake has been associated with coronary heart disease. Comparison of the fatty acid compositions, places HO sunflower as the best option in terms of oxidative stability and beneficial effects on the health of consumers.

Effect of Using Moringa oleifera and Spirulina platensis as Feed Additives on Performance, Meat Composition and Oxidative Stability and Fatty Acid Profiles in Broiler Chicken

A study was conducted to determine mainly the n 3 fatty acids enrichment and decreased oxidation of broiler meat using the plant Moringa oleifera and a blue green algae Spirulina platensis. The effects of the dietary treatments were evaluated in terms of growth performance, carcass and meat yields, oxidative stability and fatty acids modulation. Two hundred and forty (240) one day old Cobb 500 broiler chicks were assigned to 5 dietary treatments for 5 weeks, with 4 replications having 12 chicks per replication. The diets of the treatments were formulated from the basal feed as follows: control (T1), including 2 different levels of M. oleifera leaf meal 1% (T2) and M. oleifera leaf meal 1.5%, (T3) and 2 different levels of S. platensis 1% (T4) and S. platensis 1.5% (T5). The birds were randomly distributed in each pen, and the data were analyzed using the SPSS statistical package. The final body weight (BW) gain was significantly higher in the T2 and T5 groups, and the feed conversion ratio improved in the T2 group (1.68). The lowest (p ≤ 0.05) thiobarbituric acid-reactive substances values (TBARS) of breast and thigh were obtained in T2 groups compared to T3-T5 group after the second week of preservation. Regarding fatty acid profile of breast and thigh meat, the omega-3 fatty acid levels, such as those of linolenic and docosahexaenoic acid (DHA), were increased in the additives groups. The results of the present study elucidated that dietary inclusion of the 2 medicinal plants in the T2 and T5 groups could be promising functional ingredients to produce value-added broiler meat in terms of oxidative stability and omega-3 fatty acids enhancement.

The effect of spray-drying and freeze-drying on encapsulation efficiency, in vitro bioaccessibility and oxidative stability of krill oil nanoemulsion system

A nanoemulsion system was employed to encapsulate the krill oil with different concentration. The combination of whey protein concentrate, maltodextrin and gum arabic with the ratio of 8:2:0.5 was used in nanoemulsion formulation to enhance nanoemulsion stability, as well as to construct the wall part of the encapsulates. Two different drying methods; freeze-drying and spray-drying were applied on krill oil nanoemulsion systems to obtained powder encapsulates. The physical characterization of nanoemulsions and chemical stability of krill oil in terms of oxidative stability and in vitro bioaccessibility (%) were evaluated before and after drying processes to understand the effect of different drying techniques on encapsulation ability of nanoemulsion systems. Dehydration of nanoemulsions with spray-drying caused approximately 7 folds increments on particle size. The sample with 8% (w/v) of krill oil concentration had an optimum encapsulation efficiency that was calculated 72% in spray-dried nanoemulsion and 67% in freeze-dried nanoemulsion. Both spray-dried and freeze-dried krill oil nanoemulsions showed similar oxidative stability in 8% (w/v) concentration during the 15 days storage period. In vitro bioaccessibility of encapsulated krill oil was changed between 32.7 to 72.4% and 20.0–83.0% in freeze-dried and spray-dried nanoemulsions, respectively. Still, the spray-drying process is recommended for the dehydration of krill oil nanoemulsion with 8% (w/v) concentration because a better encapsulation efficiency and the higher in vitro bioaccessibility was obtained compared to freeze-dried nanoemulsion systems at the same concentration of krill oil.

Improvement of encapsulation and stability of EPA and DHA from monolayered and multilayered emulsions by high‐pressure homogenization

This study aims to improve encapsulation and stability of eicosapentaenoic acid and docosahexaenoic acid by optimizing high‐pressure homogenization conditions of monolayered (lecithin + maltodextrine) and multilayered (lecithin + chitosan‐maltodextrine) fish oil emulsions. First, a positive influence of high‐pressure homogenization on quality characteristics of emulsion and microcapsules was observed. Trials were conducted to get optimum combination conditions of pressure and number of passes of homogenization of both types of emulsions for improving microencapsulation yield and efficiency and lipid oxidation of the corresponded microcapsules. These studied variables showed a notable effect on monolayered microcapsules, being less influencing on multilayered ones. Finally, 1,200 Ba—3 passes and 1,100 Ba—2 passes were selected as optimum combination for monolayered and multilayered emulsions, respectively. This led to microcapsules with improved quality characteristics in terms of microencapsulation yield, microencapsulation efficiency, and oxidation stability, especially in the case of monolayered microcapsules. PRACTICAL APPLICATIONS: The results of this study suppose an advance in the investigations about microencapsulation of bioactive compounds, being specifically useful to develop high stable vehicles of omega‐3 fatty acids to enrich food products. To the best of our knowledge, this kind of homogenization procedure has been used to elaborate fish oil microcapsules from monolayered (lecithin + maltodextrine) and multilayered (lecithin + chitosan‐maltodextrine) emulsions. The knowledge of the optimal homogenization conditions is important to achieve high quality microcapsules in terms of oxidative stability and efficiency of encapsulation.

Production and characterization of crude oils from seafood processing by-products

The potential use of fish by-products from different species (farmed bluefin tuna, farmed seabass and seabream, and wild sardines) for oil production was investigated. The yield, physicochemical quality, fatty acid profile and nutritive value of tuna by-product and liver oil, wild sardine and sardine by-product oil, and a combined farmed seabass and seabream by-product oil were determined and compared to commercial cod liver oil. In terms of oxidative stability, tuna, seabass and seabream by-product oils had the lowest free fatty acid content, peroxide, Totox, and anisidine value. The oxidative stability of the oils was good and the highest α-tocopherol content in the range of 70.9–79.4 μg/g was found in seabass and seabream by-products oils. The sum of eicosapentaenoic and docosahexaenoic fatty acids ranged from 11.6 in seabass and seabream oil to 32.8% in sardine oil. The n-3/n-6 ratio of the oils showed value ranging from 0.66 in seabass and seabream by-product oil to 11.0 in sardine oil showing a potential use of fish by-products in high quality oil production, adding economic value to the by-products and changing by-product disposal strategies.

Accelerated weathering and soil burial effects on colour, biodegradability and thermal properties of bamboo/kenaf/epoxy hybrid composites

This study aims to gain insight into the influence of environmental effects on the colour, biodegradability, oxidation stability, thermal stability and complex modulus of bamboo/kenaf fiber reinforced epoxy hybrid composites. The composites were prepared by the hand lay-up technique, with a fixed loading of 40% fibers for all the composites. Three types of hybrid composites were prepared with different mixing ratios of bamboo fibers (B) to kenaf fibers (K): (i) 30:70, (ii) 50:50, and (iii) 70:30. Kenaf/epoxy and bamboo/epoxy composites, as well as pure epoxy, were also prepared for comparison purposes. The kenaf, bamboo and hybrid composites were exposed to UV radiation at elevated temperature and humidity, for a total exposure period of 156 h. The colour changes occurring during the weathering process were assessed by colorimetric analysis. The effects of soil burial on the developed composites were also studied for different time periods of 3, 6 and 12 months. Thermal properties, in terms of oxidation stability, thermal stability and dynamic mechanical properties, were determined by differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical analysis, respectively. The results obtained from colorimetric analysis indicated that increasing the bamboo fiber loading in the formulation of hybrid composites induced higher total colour changes. The biodegradability of hybrid composites at higher kenaf loading increased as the soil burial period was longer. Overall, soil burial has led to more pronounced degradation, as compared to accelerated weathering, in terms of oxidation stability, thermal stability and dynamic mechanical properties. The findings of this work reveal that the hybrid composite formulation B:K:50:50 presents a balance of resistance to environmental effects, while maintaining the biodegradability characteristic, which makes it suitable for its use as a potential biocomposite material for structural applications.

Comparison of hydrogenated vegetable oil and biodiesel effects on combustion, unregulated and regulated gaseous pollutants and DPF regeneration procedure in a Euro6 car

The effects of traditional biodiesel (fatty acid methyl-esters, FAME) and a hydrotreated vegetable oil (HVO) were comprehensively investigated on a production Euro 6 diesel car, including fuel injection rate and timing, combustion analysis, emissions of regulated and unregulated pollutants, and regeneration of the diesel particle filter. The use of both biofuels is a part of the efforts to reduce emissions of greenhouse gases and health-relevant pollutants and to improve energy security and sustainability. HVO, albeit more expensive, offers benefits relative to FAME in terms of oxidation stability, injector fouling, energy content and cetane number. The car was fitted with an on-board instrumentation and subjected to a range of driving cycles on a chassis dynamometer. The fuel consumption calculated from instantaneous emissions data based on exhaust gas composition measured by an on-board FTIR and calculated exhaust flow matched directly measured fuel consumption within several percent on all fuels; differences in the consumption among the fuels correspond to different heating values. The combustion onset and maximum heat release rate were comparable for diesel and FAME but were advanced on HVO due to its higher cetane number, causing, at times, multiple distinct heat release peaks, suggesting that optimization of fuel injection timing for HVO might be beneficial. Emissions of methane and ammonia were negligible, of N2O were measurable and slightly lower for HVO than for other fuels, of formaldehyde were limited to cold engine accelerations and highest for FAME and negligible for HVO, of NO and NO2 were high on all fuels during all operating conditions except for the type approval test. The results confirm several relative advantages of HVO over RME, with penetration into engine lubricating oil during particle filter regeneration to be further investigated. The effects of HVO lubricity and other long-term effects were not evaluated here.