Acidolysis reactions lead to esterification of endogenous tocopherols and compromised oxidative stability of modified oils

Oxidative Stability in Lipid Formulations: a Review of the Mechanisms, Drivers, and Inhibitors of Oxidation

The importance of lipid-based formulations in addressing solubility and ultimately the bioavailability issues of the emerging drug entities is undeniable. Yet, there is scarcity of literature on lipid excipient chemistry and performance, notably in relation to oxidative stability. While not all lipid excipients are prone to oxidation, those with sensitive moieties offer drug delivery solutions that outweigh the manageable oxidative challenges they may present. For example, caprylocaproyl polyoxylglycerides help solubilize and deliver cancer drug to patients, lauroyl polyoxylglycerides enhance the delivery of cholesterol lowering drug, and sesame/soybean oils are critical part of parenteral nutrition. Ironically, excipients with far greater oxidative propensity are omnipresent in pharmaceutical products, a testament to the manageability of oxidative challenges in drug development. Successful formulation development requires awareness of what, where, and how formulation stability may be impacted, and accordingly taking appropriate steps to circumvent or meet the challenges ahead. Aiming to fill the information gap from a drug delivery scientist perspective, this review discusses oxidation pathways, prooxidants, antioxidants, and their complex interplay, which can paradoxically take opposite directions depending on the drug delivery system.

Occurrence of tocopheryl fatty acid esters in vegetables and their non-digestibility by artificial digestion juices

Tocopheryl fatty acid esters (TFAE) consist of tocopherols esterified to fatty acids, but only little is known about this substance class. In this study, twelve vegetable groups were screened on TFAE and contents of (free) tocopherols and TFAE were determined in red bell pepper, red chili pepper, cucumber and walnut (n = 5, respectively). Intact TFAE were separated by solid phase extraction from free tocopherols and analyzed by GC/MS. Highest TFAE values were determined in chili pepper (4.0–16 mg/100 g fresh weight, FW) and walnut (4.1–12 mg/100 g FW), followed by bell pepper (1.3–1.5 mg/100 g FW) and cucumber (0.06–0.2 mg/100 g FW). Contribution of TFAE to the total tocopherol content ranged from 7–84%. Neither the treatment with artificial digestion juices nor exposure to sunlight showed degradation of TFAE. This substance class might represent a hitherto overlooked storage form for free tocopherols in plants as they occur to be more stable. But as the ester bond in medium chain TFAE seems not to be fissile in the human body, they might not contribute in the same way as free tocopherols to the vitamin E activity of vegetables and might have to be determined separately.

Enzymatic synthesis of extra virgin olive oil based infant formula fat analogues containing ARA and DHA: one-stage and two-stage syntheses

Structured lipids (SLs) with high palmitic acid content at the sn-2 position enriched with arachidonic acid (ARA) and docosahexaenoic acid (DHA) were produced using extra virgin olive oil, tripalmitin, ARA and DHA single cell oil free fatty acids. Four types of SLs were synthesized using immobilized lipases, Novozym 435 and Lipozyme TL IM, based on one-stage (one-pot) and two-stage (sequential) syntheses. The SLs were characterized for fatty acid profile, triacylglycerol (TAG) molecular species, melting and crystallization profiles, tocopherols, and phenolic compounds. All the SLs had >50 mol % palmitic acid at the sn-2 position. The predominant TAGs in all SLs were PPO and OPO. The total tocopherol content of SL1-1, SL1-2, SL2-1, and SL2-2 were 70.46, 68.79, 79.64, and 79.31 μg/g, respectively. SL1-2 had the highest melting completion (42.0 °C) and crystallization onset (27.6 °C) temperatures. All the SLs produced in this study may be suitable as infant formula fat analogues.

Effect of ascorbyl palmitate on oxidative stability of chemically interesterified cottonseed and olive oils

The effects of 400 ppm ascorbyl palmitate (AP) on fatty acids composition, tocopherol, peroxide value (PV) and malonaldehyde (MAD) contents of refined cottonseed oil (CO) and virgin olive oil (OO) during chemical interesterification (CI), and storage at 60 °C for 28 days were investigated. CI significantly decreased (p < 0.05) the tocopherol contents of CO and OO. PVs and MAD contents of oil samples considerably increased up to 20 min of CI, followed by a reduction at 30 min. The unsaturated fatty acids/saturated fatty acids (UFA/SFA) ratios of the samples showed slight but significant (p < 0.05) reduction during accelerated oxidation process. Oils with added 400 ppm AP had higher tocopherol, and lower PVs and MAD contents than their counterparts without AP during CI, and storage at 60 °C. AP increased the oxidative stability of interesterified and non-interesterified CO and OO.

Identification of tocopherols, tocotrienols, and their fatty acid esters in residues and distillates of structured lipids purified by short-path distillation

The fate of endogenous vitamin E isomers during production and purification of structured lipids (SLs) was investigated. Two SLs involving tripalmitin, stearidonic acid soybean oil, and docosahexaenoic acid were synthesized by transesterification catalyzed by Novozym 435 (NSL) and acidolysis by Lipozyme TL IM (LDHA) and purified by short-path distillation (SPD). The electron impact and chemical ionization mass spectra of tocopheryl and tocotrienyl fatty acid esters in the distillates measured by GC-MS in synchronous scan/SIM mode demonstrated that these esters were formed during acidolysis as well as transesterification. The predominant esters were tocopheryl palmitate, tocopheryl oleate, and tocopheryl linoleate homologues, and no tocopheryl or tocotrienyl linolenate, stearidonate, or docosahexaenoate was found. Meanwhile, none of these esters were detected in the residues for either NSL or LDHA. Less than 50% of vitamin E isomers were present in residues after SPD. This loss played a major role in the rapid oxidative deterioration of SLs from previous studies with less contribution from the formation of tocopheryl and tocotrienyl esters. The lost tocopherols and tocotrienols present at high concentration in the distillates may be recovered and used to improve the oxidative stability of SLs.

Production of trans-free margarine with stearidonic acid soybean and high-stearate soybean oils-based structured lipid

Omega-3 fatty acids (n-3 FAs) have been positively associated with prevention and treatment of chronic diseases. Intake of high amounts of trans fatty acids (TFAs) is correlated with increased risk of coronary heart disease, inflammation, and cancer. Structured lipid (SL) was synthesized using stearidonic acid (SDA) soybean oil and high-stearate soybean oil catalyzed by Lipozyme(®) TLIM lipase. The SL was compared to extracted fat (EF) from a commercial brand for FA profile, sn-2 positional FAs, triacylglycerol (TAG) profile, polymorphism, thermal behavior, oxidative stability, and solid fat content (SFC). Both SL and EF had similar saturated FA (about 31 mol%) and unsaturated FA (about 68 mol%), but SL had a much lower n-6/n-3 ratio (1.1) than EF (5.8). SL had 10.5 mol% SDA. After short-path distillation, a loss of 53.9% was observed in the total tocopherol content of SL. The tocopherols were lost as free tocopherols. SL and EF had similar melting profile, β' polymorph, and oxidative stability. Margarine was formulated using SL (SLM) and EF (RCM, reformulated commercial margarine). No sensory difference was observed between the 2 margarines. The SL synthesized in this study contained no TFA and possessed desirable polymorphism, thermal properties, and SFC for formulation of soft margarine. The margarine produced with this SL was trans-free and SDA-enriched.

PRACTICAL APPLICATION

The current research increases the food applications of stearidonic acid (SDA) soybean oil. trans-Free SDA containing SL was synthesized with desirable polymorph, thermal properties, and SFC for formulation of soft margarine. The margarine produced with this SL had no trans fat and had a low n-6/n-3 ratio. This may help in reducing trans fat intake in our diet while increasing n-3 FA intake.

Effect of enzymatic randomization on positional distribution and stability of seal blubber and menhaden oils

In an effort to investigate the effect of positional distribution on oxidative stability of menhaden and seal blubber oils, Novozyme 435 was used as a random biocatalyst. Positional distribution of fatty acids was determined using gas chromatography. As some of the α-tocopherol was lost during randomization, its content was adjusted to the level prior to the process to eliminate this effect on oxidative stability of oils tested. Conjugated dienes (CD) and thiobarbituric acid reactive substances (TBARS) were used as indicators of oxidative stability. The results showed that the polyunsaturated fatty acids were distributed predominantly at terminal positions in randomized menhaden oil, whereas they were distributed more evenly among all positions in enzymatically randomized seal blubber oil, compared to their unrandomized counterparts. Results of CD and TBARS values indicated that randomized menhaden oil was more stable than the original oil, whereas randomized seal blubber oil was more vulnerable to oxidation compared to its counterpart. Changes of oxidative stability after randomization were mainly due to positional redistribution of fatty acids, especially those of the polyunsaturated types.

Effect of chemical randomization on positional distribution and stability of omega-3 oil triacylglycerols

Randomization has been commonly used to modify the chemical and physical properties of natural fats and oils. In this study, seal blubber oil (SBO) and menhaden oil (MHO) were modified through chemical randomization using sodium methoxide, and the effect on positional distribution of fatty acids was investigated using gas chromatography (GC) and (13)C nuclear magnetic resonance (NMR) spectroscopy. The effect of randomization on the stability of the original oils and their randomized counterparts was analyzed by comparing conjugated dienes and thiobarbituric acid reactive substances (TBARS) values after accelerated oxidation at 60 degrees C for 4 days. The omega-3 polyunsaturated fatty acids (PUFA) were distributed more evenly among the terminal sn-1,3 positions and the middle sn-2 position in chemically randomized oils when compared to the starting oils. The effect was more pronounced for SBO with omega-3 PUFA attached preferentially to sn-1,3 positions of triacylglycerols before randomization, and it was less pronounced for MHO, which contained omega-3 PUFA more evenly distributed before randomization. However, different levels of commonly known omega-3 fatty acids, namely, docosahexaenoic acid (DHA), docosapentaenoic acid (DPA), eicosapentaenoic acid (EPA), and stearidonic acid (STA), were obtained in both original and randomized oils from GC and (13)C NMR spectroscopy. The stability of the randomized oils was also affected to different degrees, depending on the storage time.

Physicochemical and volatiles characterization of trans-free solid fats produced by lipase-catalyzed interesterification

Trans-free solid fats were synthesized from fully hydrogenated soybean oil (FHSBO), olive oil (OO), and palm stearin (PS) at different substrate weight ratios (10:20:70, 10:40:50 and 10:50:40) via lipase-catalyzed interesterification. The interesterified products contained mostly TAG (98.8% to 99.0%), and small amounts of MAG and DAG as by-products. The major fatty acids were oleic acid, palmitic acid, and stearic acid in the interesterified products, and the melting points ranged from 39 to 45 degrees C. The amount of alpha-tocopherol was reduced by 75% to 92%. Volatile analysis by solid-phase microextraction indicated that OO and PS had distinct volatile profiles, in which 18 volatiles were retained in interesterified products. Furthermore, some volatiles disappeared or formed during processing. Electronic nose showed that the odors of substrates (OO and PS) were different from each other, and the odors of interesterified products were distinguishable from that of OO or PS. Among the interesterified products, the odor of blend FHSBO:OO:PS of 10:40:50 or 10:50:40 was different from that of blend FHSBO:OO:PS (10:20:70). However, no odor difference was observed between products blend FHSBO:OO:PS 10:40:50 and 10:50:40.