Changes in Total Polar Compounds,Peroxide Value,Total Phenols and Antioxidant Activity of Various Oils Used in Deep Fat Frying

In this study, the effect of deep fat frying on oil degradation, total phenols (TP) and total antioxidant activity (TAA) of hazelnut, corn, soybean and olive oils were investigated. Oil degradation and oxidation were monitored by measuring the total polar compounds (TPC) and the peroxide value (PV). The amount of TPC in corn, soybean and olive oils increased significantly with the time increment (p < 0.05). The PV of the oils did not exceed the maximum acceptable limit of 10 mequiv O₂/kg after 125 min frying except for hazelnut oil (10.64 mequiv O₂/kg). Deep-fat frying did not cause any significant change in the TP of corn oil, soybean oil and olive oil (p < 0.05). A significant decrease in the antioxidant activity was observed after 50 min frying using hazelnut oil and corn oil (p < 0.05). However, the antioxidant activity of soybean oil and olive oil significantly decreased after 75 and 25 min frying, respectively.     

Distribution and Antioxidant Activities of Free,Conjugated, and Insoluble-Bound Phenolics from Seven Species of the Genus Camellia

Free phenolic (FP), conjugated phenolic (CP), and insoluble-bound phenolic (IBP) acids were extracted from the seeds of seven species of oil-tea camellia and their antioxidant activities were evaluated. The results indicated that Camellia vietnamensis has the highest total phenolic content (TPC) (31.84 ± 0.11 g of gallic acid equivalent [GAE] kg⁻¹) and that Camellia polyodontia has the lowest TPC (12.34 ± 0.22 g GAE kg⁻¹) in the kernel. The average TPC among the species is similar in both the kernels and in the shells, and the content order of the three forms of phenolic compounds is FP > IBP > CP. HPLC-MS analysis showed the presence of 9–11 phenolic compounds in the FP, CP, or IBP extracts of the seven species of oil-tea camellia seed. Among the phenolics identified, ferulic acid, catechin, and epicatechin were the major contributors of antioxidant activity. Hierarchical cluster analysis conducted based on the phenolic properties showed that C. vietnamensis and Camellia semiserrata belong to the group characterized by high antioxidant capacities (FRAP, ferric-ion-reducing antioxidant power; ABTS assay), and Camellia chekiangoleosa and Camellia oleifera are arranged in a group with moderate phenolic properties. The other species constitute the third cluster with low phenolic content and antioxidant activity. The study demonstrated that oil-tea camellia seed contains significant amounts of phenolic acids. In addition, extracts from various parts of the seed could be interesting novel sources of natural antioxidants.     

Optimization of Ultrasound-Assisted Alkali Neutralization in the Refining of Safflower Oil to Minimize the Loss of Bioactive Compounds

In this study, ultrasound-assisted (UA) neutralization parameters are optimized using the response surface methodology to develop a novel alkali neutralization method based on the minimal refining concept. Sodium hydroxide (NaOH), magnesium oxide (MgO), and calcium hydroxide (Ca(OH)₂) are used in both the traditional (TR) and UA neutralizations. Optimum probe depth, duration, and intensity levels are calculated as 3.7 cm, 25 s, and 54.3%, respectively, for UA neutralization with NaOH, which is more successful at free fatty acid (FFA) reduction and total phenolic content (TPC) retention than MgO and Ca(OH)₂. Validation results of optimum conditions show that lowest average FFA content (0.29%) and highest average TPC (211.2 mg kg⁻¹) are determined for the UA-neutralized safflower oil samples. The comparison of all the neutralization experiments reveal that the UA neutralization under optimum conditions using NaOH reduced 82.8% of the FFA content, whereas the TR alkali neutralization reduced the FFA content at a maximum of only 47.8%. Practical Applications: From the results, it can be inferred that the UA neutralization exhibits good performance in FFA content reduction and bioactive compound retention while offering a good solution within the concept of minimal refining.     

Effect of Hydrothermal Treatment of Rapeseed on Antioxidant Capacity of the Pressed Rapeseed Oil

Response surface methodology (RSM) was used to evaluate the quantitative effects of two independent variables, rapeseed moisture content and conditioning temperature, on the antioxidant capacity (AC) and total phenolic (TPC), tocopherol (TTC), and phosphorus contents (PC) in the pressed rapeseed oils. The mean AC results for the crude rapeseed oils ranged from 199.8 to 947.2 μmolTE/100 g. TPC and PC in the crude rapeseed oils correlated significantly (P < 0.01) and positively with AC of oils (R ² = 0.9498 and 0.4396, respectively). The experimental results of AC, TPC, and PC were close to the predicted values calculated from the polynomial response surface model equations (R ² = 0.9801, 0.9747 and 0.9165, respectively). The effect of oil processing temperature on AC and TPC was about 1.5 times greater than the effect of moisture level in rapeseed.     

Quality Assessment of Heated Cooking Oil,Agab, Using a Simple Newly-Developed Spectrophotometric Method

Deep fat frying is one of the most widely used cooking practices but heat treatment produces many degradation products, some of which may cause health hazards. A simple, rapid, and inexpensive method for assessment of the quality of cooking oil used for frying was developed using a spectrophotometer. Potato slices were heated in Agab oil (soybean/sunflower:1/l volume) at 180 ± 5 °C for 8 h per day for 6 consecutive days. Heated samples were collected at 15-min intervals and UV absorbance at λ = 370–400 nm was measured; samples were also analyzed for anisidine value (AV), conjugated diene formation (CD), and total polar compounds (TPC). A systematic increase of absorbance in heated oil over frying time was observed. TPC was highest (R ² = 0.99) for the correlation with heating time followed by CD (0.93) and AV (0.89). The spectrophotometric method developed in the present study to assess the quality of heated oils is simple, quick, and reliable because its results were strongly correlated with the results from the TPC.     

Phenolic composition and antioxidant activity of Southern Italian monovarietal virgin olive oils

The phenolic composition and antioxidant activity of several monovarietal extra virgin olive oils used as blenders for the production of Collina di Brindisi protected designation of origin (PDO) oil, produced between December 2008 and January 2009 using two‐phases or three‐phases extraction system, were evaluated and compared with other manufacturer products designated as PDO. Oils were taken from the most representative ones industrial oil mills in the PDO geographical area. The parameters assessed were free acidity, peroxide value, K₂₃₂ and K₂₇₀ indices, organoleptic characteristics, total phenolic content (TPC), phenolic profile, and antioxidant activity coefficient (AAC). The phenolic contents and profiles of the monovarietal oils showed remarkable differences with respect to PDO oils. The variables that exerted a major influence on phenols concentration were the maturity degree of olives (December>January), followed by the extraction system (two‐phase>three‐phase), and place of growing. The Pearson r correlation index showed that AAC was positively correlated with TPC, p‐coumarate, and 3,4‐DHPEA‐EA, and negatively correlated with peroxide value. Practical applications: The results provide detailed information about: (i) the phenolic composition and the AAC of several monovarietal extra virgin olive oils used as blenders for the production of a PDO oil; (ii) the impact of genetic variability, place of growing, olive maturity degree, and extraction technology on oil phenol compounds; and (iii) the relationships among each phenolic compound and AAC, and their potential utilization as analytical index of antioxidant activity. It is important to study the phenolic compounds and antioxidant activity of monovarietal extra virgin olive oils used to produce PDO oil and to compare with the relative PDO samples in order to define a possible analytical tool able to verify what is stated in the label for consumer information and protection.     

Identification of bioactive compounds with GC–Q-TOF–MS in the extracts from Clinacanthus nutans using subcritical carbon dioxide extraction

Subcritical carbon dioxide Soxhlet extraction of biologically active compounds from Clincanthus nutans was investigated by full factorial design to identify and optimize the factors (particle size and co-solvent) affecting extract yield, antioxidant activity, total phenolic content, total flavonoid content, and α-glucosidase inhibitory activity. An average of 3.103% yield, 98.90% antioxidant activity, 49.40 mg/g (GAE) TPC, 43.76 mg/g (RE), and 88.58% AGI activity can be achieved using the optimum levels of independent variables. The GC-Q-TOF MS identification of optimized extract shown that different classes of phytoconstituents were successfully separated by CO₂-Soxhlet to produce potential antioxidant and α-glucosidase inhibitory activity.     

Comparison of the effects of oven- and microwave-roasting on the physicochemical properties and bioactive compounds of tomato seeds and oils

The tomato processing industry generates a significant amount of a by-product (pomace), which is a mixture of peels and seeds. The purpose of this study was to compare the effects of conventional oven-roasting (at 120°C, 150°C, and 180°C for 25 min) and innovative microwave-roasting (at 240, 388, and 536 W for 3 min) pretreatments on the physicochemical properties, fatty acid profiles, bioactive contents, and aroma profiles of tomato seeds and their hexane-extracted oils. The total flavonoids contents (TFCs) of the seeds decreased from 258.40 to 141.20 mg quercetin equivalent (QE) per kg after roasting. All roasting treatments improved the extractability of both α- and γ-tocopherols. The amounts of total tocopherols in the seeds increased from 917.61 to 1256.25 mg kg^–1 after pretreatment. Luteolin was found to be the most abundant phenolic in seed oils, increasing from 10.68 to 91.72 mg kg^–1, followed by quercetin, ferulic acid, and catechin. Within each roasting technique, the ones treated at 150°C and 338 W yielded the oils with the highest concentrations of aroma compounds, 418 and 92 mg kg^–1, respectively. The detrimental effect of microwave-roasting on these compounds was more pronounced. In conclusion, microwave-roasting at shorter times than conventional roasting produced tomato seed oils with well-preserved bioactive components and few unfavorable changes. Industrial relevance: Conventional oven-roasting has been widely applied to oilseeds to improve oil yield as well as to obtain desirable sensory characteristics of extracted oils for years. However, longer roasting times may also cause detrimental changes in the properties of oils. On the other side, microwave-assisted applications as an emerging technology provide homogenous and well-controlled heat distribution, shorter treatment times, and considerable energy savings for the processing of various foods. Microwave technology has been easily scaled up and is currently employed for sterilization, drying, pasteurization, precooking, and extraction by the food and chemistry industries. Therefore, the present research suggests the use of microwaves for comparatively short roasting times to produce edible oils with enhanced physicochemical attributes and bioactives contents, and well-maintained sensory properties. This promising innovative technology has the potential to be industrialized for a cost-effective seed roasting process.     

Effect of Operating Parameters on Oil and Phenolic Extraction Using Supercritical CO<Subscript>2</Subscript>

Supercritical fluid extraction (SFE) with carbon dioxide was used to extract oil from canola press cake. Different operating conditions, e.g. pressure, temperature, and co-solvent % were investigated to optimize extraction parameters to yield canola meal with <4% oil. The residual oil content in the extracted canola meal reduced to 2.1–2.9% in our experimental trials. Residues of the optimum conditions based on oil yield were compared for the total phenolic content and the main phenolic compounds. Sinapine (the choline ester of sinapic acid) was the major phenolic constituent in both the SFE and n-hexane extracted canola meals and press cakes. n-Hexane extracted residues showed the retention of the highest sinapic acid, sinapine, sinapoyl glucose and total phenolic contents (mg/g) while the SF-extracted residues showed the lowest values for these compounds.     

Obtaining phenolic compounds from jatoba (Hymenaea courbaril L.) bark by supercritical fluid extraction

The extraction of polyphenol compounds from jatoba (Hymenaea courbaril L. var stilbocarpa) bark using supercritical fluid extraction (SFE) with CO₂ and cosolvents has been investigated. Among the solvent systems studied, SFE using CO₂ and water (9:1, v/v), at 323 K and 35 MPa, presented the best results, with extract yield of 24%, and with high antioxidant activity (IC₅₀ of 0.2 mg/cm³). This solvent system was used to determine global yield isotherms, which were built at 323 and 333 K, and 15, 25, and 35 MPa, using a second lot of jatoba. The highest yield was 11.5% at 15 MPa and 323 K, with maximum total phenolic compounds (TPC) of 335.00 mg TAE/g extract (d.b.) and total tannins content of 1.8 g/100 g raw material. A kinetic experiment was performed using optimized conditions, yielding 18% extract, and the kinetic parameters were used to scale-up the process from laboratory to pilot scale. Chemical analyses showed high content of phenolic compounds in the extracts of jatoba bark mostly due to the presence of procyanidins.     

Antioxidant Activity and Total Polyphenols Content of Camellia Oil Extracted by Optimized Supercritical Carbon Dioxide

In this study, Camellia oil is co-extracted from Camellia oleifera seeds and green tea scraps by supercritical carbon dioxide (SC-CO₂), which is optimized on the extraction yield, ABTS-scavenging activity, and total polyphenols content (TPC) of oil by single-factor experiments combined with response surface methodology (RSM). The extraction temperature, pressure, dynamic time, carbon dioxide (CO₂) flow rate, and seed mass ratio were investigated with single-factor experiments. The results indicated the optimum CO₂ flow rate and dynamic extraction time were 15 L hour⁻¹ and 60 min (i.e., 2.382 kg CO₂/100 g sample). Furthermore, the complicated effects of extraction temperature (40–50 °C), pressure (20–30 MPa), and seed mass ratio (0.25–0.75) were optimized by RSM based on the Box–Behnken design (BBD). The models with high R-squared values were obtained and used to predict the optimum operating conditions of the process. Under the optimum operating conditions (i.e., temperature of 46 °C, pressure of 30 MPa, and seed mass ratio of 0.35), the extraction yield, ABTS-scavenging activity, and TPC of oil were 14.43 ± 0.17 g/100 g sample, 73.70 ± 0.34%, and 2.18 ± 0.05 mg GAE/g oil, which were in good agreement with the predicted values. In addition, the experiments indicated that the Camellia oil obtained was rich in polyphenols, resulting in better oxidation stability and antioxidant activity than the original oil.     

A Comparative Study on Response Surface Optimization of Supercritical Fluid Extraction Parameters to Obtain Portulaca Oleracea Seed Oil with Higher Bioactive Content and Antioxidant Activity Than Solvent Extraction

Portulaca oleracea (purslane) seed oil is a rich source of omega-6 and omega-3 fatty acids. Extraction of the purslane seed oil while preserving its high nutritive quality has been a challenge since conventional solvent extraction has many adverse effects on bioactive content. This study aims the optimization of purslane seed oil supercritical fluid extraction (SFE) conditions and to compare purslane seed oils obtained with SFE and conventional solvent extraction in terms of oil yield, along with the purslane seed oil quality and bioactive content. For this purpose, the SFE process parameters (pressure, temperature, static time, and dynamic time) are optimized for oil yield, omega-6, omega-3, and antioxidant activity using response surface methodology (RSM). Optimum SFE pressure, temperature, static time, and dynamic time levels are determined as 350 bar, 50 °C, 20 min, and 90 min, respectively. Oil yield and physicochemical quality properties of conventional solvent extract and SFE samples are determined and compared. Consequently, samples obtained via SFE and solvent extraction have similar quality properties. Distinctly, SFE allows an extraction with 5.6% higher total phenolic compound (TPC) and 33% higher antioxidant activity than solvent extraction. Practical Applications: In the study, the extraction of purslane oil using supercritical fluid extraction is optimized with different approaches. At optimum conditions, purslane oil is extracted and all physicochemical properties and the process efficiency (yield) are compared with the solvent-extracted samples. The results of this study make supercritical fluid extraction of purslane seed oil possible since all optimum operating conditions of a pilot-sized extractor are reported in the study. It is believed that the results provide a good starting point for industrial operations. Moreover, researchers also believe that research studies unveiling the new potential oil-bearing seeds are important to overcome the vegetable oil shortage that emerged this year.     

Effects of processing on oxidative stability of sesame oil extracted from intact and dehulled seeds

Oxidative stability of oils extracted from intact and dehulled sesame seeds was determined by monitoring changes in fatty acid composition, iodine value (IV), peroxide value (PV), conjugated diene (CD), para-anisidine value (p-AV), and 2-thiobarbituric acid (TBA) value and by nuclear magnetic resonance spectroscopy after storage under Schaal oven conditions at 65°C for up to 35 d. The oils from coated seeds were more stable, as reflected in PV, CD, p-AV and TBA values, than those extracted from dehulled seeds after roasting at 200°C, steaming at 100°C, roasting at 200°C plus steaming, or microwaving at 2450 MHz, except for TBA values of oil from microwaved seeds. After 35 d of storage at 65°C, the CD, p-AV, and TBA values of extracted oil from dehulled microwaved seeds were 17.72, 10.20, and 1.22, respectively, while those of their coated counterparts were significantly (P<0.05) different at 14.20, 16.47, and 1.26, respectively. Few significant changes were evident in the fatty acid composition of oil obtained from either coated and dehulled seeds subjected to different treatments. Nuclear magnetic resonance analyses found that R_ao (aliphatic to olefinic protons) and R_ad (aliphatic to diallylmethylene protons) ratios increased steadily over the entire storage period, which indicated progressive oxidation of unsaturated fatty acids.     

Comparison of two kinds of pumpkin seed oils obtained by supercritical CO2 extraction

The oils from two kinds of pumpkin seeds, black and white ones, were extracted by supercritical CO₂ (SC‐CO₂). The technological variables for SC‐CO₂ extraction were optimized and the resulting oils were analyzed by GC‐MS. As a result, the optimal conditions for SC‐CO₂ extraction were as follows: 25～30 MPa, 45 °C, SC‐CO₂ flow rate of 30～40 kg/h. The main compounds in the resulting oils were 9,12‐octadecadienoic acid, 9‐octadecenoic acid, stearic acid, palmitic acid for both types of pumpkin seeds, however, the black seed oil contains more unsaturated fatty acids (UFA) than the white seed oil. On the other hand, some compounds including heptadecanoic acid (0.27%), tetracosanic acid (0.1%), 9‐dodecaenoic acid (0.45%) and pentadecenoic acid (0.05%) were found in white seed oil but not in black seed oil; while eicosanic acid (0.05%), 11,14‐eicosadienoic acid (0.2%), 11‐octadecenoic acid (0.06%), 7‐hexadecenoic acid (0.02%) and 1,12‐tridecadiene (0.02%) were only found in black seed oil.     

Associations between Oil Yield and Profile of Fatty Acids,Sterols, Squalene,Carotenoids, and Tocopherols in Seed Oil of Selected Japanese Quince Genotypes during Fruit Development

Tocopherols, phytosterols, carotenoids, and squalene are present in mature seeds of Japanese quince. Yet, little is known about the relationship between these compounds and oil yield during fruit and seed development. The profile change of lipophilic compounds during fruit and seed development in Japanese quince cultivars “Darius,” “Rondo,” and “Rasa” is investigated. It is shown here that during fruit and seed development, there is a significant reduction, three‐ to over tenfold, in the concentration of minor bioactive compounds in seed oil. It is recorded that delay between synthesis of tocopherols and oil in Japanese quince seeds during the fruit development results in a logarithmic relationship between the oil content and tocopherols concentration in the seed oil (R² = 0.980). Similar trends are observed between oil yield and phytosterols, and carotenoids (R² = 0.927 and R² = 0.959, respectively). The profile of fatty acids during the development of the seeds significantly is changed. The reduction of linoleic, palmitic, and gondoic acids levels and increment of oleic acid is noted. The oil content, profile of fatty acids, and concentration of bioactive compounds in all three genotypes of Japanese quince do not change significantly statistically during the last month of fruit development. Practical Applications: Some fruits are harvested at different degrees of maturity mainly due to a logistic issue and uneven ripening of fruits, which affects the chemical composition of whole fruit including seeds. Therefore, it would be good to know how the chemical composition is changing in plant material during development especially in the last month before harvest. Production of Japanese quince continues to rise year to year and with it the volume of generated by‐products such as seeds. This study demonstrates how it changes the oil content, profile of fatty acid, and concentration of tocopherols, squalene, phytosterols, and carotenoids in the seeds and seed oil of three Japanese quince cultivars “Rondo,” “Darius,” and “Rasa” during plant development. The provided information can be very useful for the manufactories oriented on the processing of by‐products, mainly seeds, generated by other branches of industry, for instance, fruit‐processing.     

Bleaching of Olive Oil by Membrane Filtration

In this study the application of membrane processes for olive oil bleaching is investigated. Olive oil is treated by adding 0.7 wt% of bleaching earth, 0.3 wt% of activated charcoal, and 5% wt% of sodium dodecyl sulfate solution (0.05 m ) and then charged into the membrane cell. Operating conditions including pressure ((2?4) × 10⁵ Pa), temperature (25–45 °C), and stirring rate (100–300 rpm) are optimized. Physico‐chemical properties of membrane bleached oil are evaluated and compared with crude and industrially bleached olive oil. Results show that the filtration conditions for the optimized point are as follows: pressure = 3.7 bar (3.7×10⁵ Pa), temperature = 36.5 °C, and stirring rate = 300 rpm. Under optimum conditions, the amounts of carotenoid and chlorophyll contents are decreased (71.3% and 40.42%, respectively). Acidic and thiobarbituric acid values reduction in membrane‐processed oil (12.42% and 14.46%, respectively) are more than the industrial one. Also, some bioactive compounds such as sterols and phenolic compounds are increased in the membrane‐filtered sample (23.13% and 57.12%, respectively). Practical Applications: Olive oil bleaching is an important step along the refining process. Pigments and minor impurities that reduce olive oil stability are removed in this step. Given the disadvantages of conventional bleaching, alternative methods are introduced. In this study, the effect of membrane filtration on olive oil color is studied. Because of the mild operating conditions, the reduction of clay percentage, as well as the increase of bioactive compounds in optimum conditions, this method has the potential to be a good alternative to conventional bleaching processes.     

Optimization of the Extraction of <Emphasis Type="Italic">Alpinia oxyphylla</Emphasis> Essence Oil in Supercritical Carbon Dioxide

The essence oil of the Alpinia oxyphylla seed has been used as a vasodilatatory and analgesic agent in pharmacology. The extraction of the essence oil in supercritical carbon dioxide (SC-CO₂) from Alpinia oxyphylla seeds was investigated. Small particles were obtained after breaking open, sieving, and drying from the Alpinia oxyphylla seeds. The small particles were placed in a 5-L extraction tank in a temperature-controlled system. The CO₂ flow rate of the system was set at 1 L/min in this study. Response surface methodology with a three-factor and three-level Box-Behnken experimental design was used to evaluate the effects of the reaction parameters such as extraction time (1, 2, 3 h), temperature (45, 55, 65 °C), and pressure (20, 30, 40 MPa), on the extraction yield of the essence oil from Alpinia oxyphylla seeds. The results indicate that the extraction pressure was the most important parameter affecting the yield of the essence oil. A model for the estimation of the yield was developed. Based on the analysis of ridge max, the optimal extraction conditions were established as an extraction time of 2.8 h, a temperature of 67.5 °C, and a pressure of 28.5 MPa, with an expected yield of 2.78%. Extraction of Alpinia oxyphylla essence oil in SC-CO₂ under these optimal conditions was conducted, and a yield of 2.77 ± 0.19% was obtained.     

Effects of Seed Coat on Oxidative Stability and Antioxidant Activity of Apricot (Prunus armeniaca L.) Kernel Oil at Different Roasting Temperatures

Apricot kernels were roasted at various temperatures (120–180 °C) for 10 min and changes in the fatty‐acid profiles, oxidative stability, and antioxidant activity, as well as the total phenolic contents (TPC) of the oils and skin (seed coat), were monitored. Roasting has no obvious influence on profiles and contents of fatty acid, induction period (IP), browning index, TPC, and antioxidant activity (2,2‐diphenyl‐1‐picrylhydrazyl (DPPH), 2,2‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid), (ABTS) and Oxygen Radical Absorbance Capacity (ORAC) of oils obtained from apricot naked‐kernel, but increases IP, TPC, and oxidative stability in oils obtained from apricot kernel with skin. All results in the present work demonstrated that thermal treatment accelerated the production and transference of alcohol‐soluble phenolics into the oil, and improved the oil oxidative stability. It is not Maillard reaction products but alcohol‐soluble phenolic compounds in skins that play a role in improving the oxidative stability and antioxidant activity of oils, and inhibition for primary peroxide production was more effective than secondary peroxide production at a low roasting temperature and a short roasting time. The present findings can advance knowledge on the conditions used for utilization of coproducts (skin) of apricot kernel and facilitate large‐scale production of stable oil against oxidation.     

High Performance Liquid Chromatography–Size Exclusion Chromatography for Rapid Analysis of Total Polar Compounds in Used Frying Oils

Analysis of used frying oil samples by high performance liquid chromatography–size exclusion chromatography (HPLC–SEC or HPSEC) was compared to AOCS Official Method Cd 20-91 (silica gel column chromatography) for the purpose of developing a rapid analysis of total polar compounds (TPC). In a direct comparison of the two analytical methods using four different sets of used frying oils (21 total oil samples) ranging from fresh to discard quality (4.3 to 35.4% TPC by column chromatography), the weight percent total polar compounds (%TPC) determined by HPLC–SEC averaged 0.71% higher than the values by silica gel column chromatography. Reproducibility of the HPLC–SEC method of s _r = 0.30 and RSD_r% = 1.22 compares to the variability of s _r = 0.29 and RSD_r = 1.3 for samples of approximately the same %TPC, reported in AOCS Method Cd 20-91. Because the rapid method does not separate pure (non-polar) triacylglycerol (TAG) and polar, oxidized TAG (OX-TAG), a high concentration of OX-TAG will quantitatively affect the results. This places practical limits on the types of studies to which the method may be applied if a separate analysis for the OX-TAG is not performed. Advantages of the HPLC–SEC method include the following. It uses about 75% less solvent than standard column chromatography methods for determination of %TPC. This HPLC–SEC method is very similar to AOCS Official Method Cd 22-91, and thus, also separates and quantifies polymerized triacylglycerols. The HPLC–SEC method determines both TAG polymer concentration and %TPC of used frying oils in about 1 h.     

Antioxidant Activity of the Phenolic Leaf Extracts from <Emphasis Type="Italic">Monechma ciliatum</Emphasis> in Stabilization of Corn Oil

The total phenolic content and the antioxidant potential of methanolic extract (ME), ethyl acetate extract (EAE), and hexane extract (HE) from Monechma ciliatum leaves (MCL) were evaluated. The Folin-Ciocalteu, β-carotene bleaching, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and the accelerated oxidation methods were used for evaluation. Both the extraction yield and the antioxidant activity (AOA) were strongly dependent on the solvent. Among the extracts, ME exhibited highest total phenolic compounds (TPC) and IC₅₀ values for DPPH, followed by EAE and HE, respectively. Peroxide value (PV), anisidine value (AV) conjugated dienes (CD), and thiobarbituric acid reactive substances (TBARS) were taken as the parameters for evaluation of stabilization efficacy of MCL extracts and results revealed MCL to be a potent antioxidant for the stabilization of corn oil. As a general trend, increased AOA was observed for increased extract concentration. The predominant phenolic compounds identified by HPLC-DAD in MCL extracts were p-coumaric acid, vanillin and ferulic acid.