Atikorn Panya

What makes good antioxidants in lipid-based systems? The next theories beyond the polar paradox.

The polar paradox states that polar antioxidants are more active in bulk lipids than their nonpolar counterparts, whereas nonpolar antioxidants are more effective in oil-in-water emulsion than their polar homologs. However, recent results, showing that not all antioxidants behave in a manner proposed by this hypothesis in oil and emulsion, lead us to revisit the polar paradox and to put forward new concepts, hypotheses, and theories. In bulk oil, new evidences have been brought to demonstrate that the crucial site of oxidation is not the air-oil interface, as postulated by the polar paradox, but association colloids formed with traces of water and surface active molecules such as phospholipids. The role of these association colloids on lipid oxidation and its inhibition by antioxidant is also addressed as well as the complex influence of the hydrophobicity on the ability of antioxidants to protect lipids from oxidation. In oil-in water emulsion, we have covered the recently discovered non linear (or cut-off) influence of the hydrophobicity on antioxidant capacity. For the first time, different mechanisms of action are formulated in details to try to account for this nonlinear effect. As suggested by the great amount of biological studies showing a cut-off effect, this phenomenon could be widespread in dispersed lipid systems including emulsions and liposomes as well as in living systems such as cultured cells. Works on the cut-off effect paves the way for the determination of the critical chain length which corresponds to the threshold beyond which antioxidant capacity suddenly collapses. The systematic search for this new physico-chemical parameter will allow designing novel phenolipids and other amphiphilic antioxidants in a rational fashion. Finally, in both bulk oils and emulsions, we feel that it is now time for a paradigm shift from the polar paradox to the next theories.

Effects of chitosan and rosmarinate esters on the physical and oxidative stability of liposomes.

Liposomes have substantial potential to deliver bioactive compounds in foods. However, the oxidative degradation and physical instability of liposomes limit their utilization. This research evaluated the ability of chitosan and rosmarinic acid and its esters to increase the physical and oxidative stability of liposomes. Particle size analysis studies showed that the physical stability of liposomes was enhanced by depositing a layer of cationic chitosan onto the negatively charged liposomes. The combination of octadecyl rosmarinate (40 microM) and chitosan coating resulted in significantly greater inhibition of lipid oxidation in the liposomes compared to chitoson or octadecyl rosmarinate alone. Increasing the concentrations of octadecyl rosmarinate to a concentration of 40 microM in the chitosan-coated liposomes decreased lipid oxidation. Only butyl rosmarinate exhibited stronger antioxidant activity than free rosmarinic acid. Eicosyl rosmarinate (20 carbons) had lower antioxidant activity than all other rosmarinic acid derivatives. These results suggest that by combining the inclusion of appropriate antioxidants such as rosmarinic acid and the deposition of a chitosan coating onto the surface of liposomes may significantly increase the oxidative and physical stability of liposomes.

An investigation of the versatile antioxidant mechanisms of action of rosmarinate alkyl esters in oil-in-water emulsions.

The antioxidant polar paradox postulates that nonpolar antioxidants are more effective in oil-in-water emulsions than polar antioxidants. However, this trend is often not observed with antioxidants esterified with acyl chains to vary their polarity. In this study, the nonpolar eicosyl rosmarinate (20 carbons, R20) was less effective at inhibiting lipid oxidation in oil-in-water emulsions than esters with shorter fatty acyl chains such as butyl (R4), octyl (R8), and dodecyl (R12) esters. Interestingly, in the presence of surfactant micelles, the antioxidant activity of R20 was significantly increased while the antioxidant activity of R4 and R12 was slightly decreased. The presence of surfactant micelles increased the concentration of R20 at the interface of the surfactant micelles and/or emulsion droplets as determined by partitioning studies, front-face fluorescence properties, and the ability of R20 to interact with the interfacial probe, 4-hexadecylbenzenediazonium. A possible explanation for why the antioxidant activity of R20 was so dramatically increased by surfactant micelles is that a portion of the nonpolar R20 localizes in the emulsion droplet core and the surfactant micelles are able to increase the interfacial concentrations of R20 and thus its ability to scavenge free radicals produced from the decomposition of interfacial lipid hydroperoxides.

New Insights into the Role of Iron in the Promotion of Lipid Oxidation in Bulk Oils Containing Reverse Micelles

Formation of physical structures, known as association colloids, in bulk oils can promote lipid oxidation. However, the cause of this accelerated lipid oxidation is unknown. Therefore, the aim of this study was to investigate whether transition metals were important prooxidants in bulk oils containing reverse micelles produced from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and water. The Fe(III) chelator deferoxamine (DFO) increased the oxidative stability of stripped soybean oil (SSO) containing reverse micelles from 2 to 7 days. Because phosphatidylcholine (1,2-dibutyl-sn-glycero-3-phosphocholine) that does not form reverse micelles is not prooxidative, these results suggest that the prooxidant activity of DOPC reverse micelles could be due to their ability to concentrate both endogenous iron and lipid hydroperoxides at the water-lipid interface, thereby increasing the ability of iron to decompose lipid hydroperoxides. DFO was also able to improve the activity of α-tocopherol and Trolox in SSO containing DOPC reverse micelles increasing the lag phase from 2 to 11 and 13 days, respectively. DOPC reverse micelles decreased iron-promoted α-tocopherol and Trolox decomposition and decreased the ability of α-tocopherol and Trolox to decrease Fe(III) concentrations. Overall, these results suggest that iron is an important prooxidant in bulk oils containing reverse micelles; therefore, finding ways to control iron reactivity in association colloids could provide new technologies to increase the oxidative stability of oils.

Influence of whey protein–beet pectin conjugate on the properties and digestibility of β-carotene emulsion during in vitro digestion

The impact of a whey protein isolate (WPI)-beet pectin (BP) conjugate (formed by dry-heating) on the physical properties and digestibilities of β-carotene and carrier oil in oil-in-water emulsions was studied when they passed through a model gastrointestinal system. β-Carotene emulsions were stabilized by WPI, unconjugated and conjugated WPI-BP, separately. The emulsions were then passed through an in vitro digestion model and the mean droplet size, droplet distribution, zeta-potential, free fatty acids and β-carotene released were measured. The stability to droplet flocculation and coalescence during digestion was increased for the WPI-BP conjugate stabilized emulsion. Addition of BP onto the WPI stabilized emulsions could inhibit the releases of carrier oil (MCT) and β-carotene. The releases of free fatty acids and β-carotene did not differ greatly between the unconjugated and conjugated WPI-BP stabilized emulsions. These results have important implications for protein-polysaccharide stabilized emulsions and conjugates used for the protection and delivery of bioactive compounds.

Biogenic amine formation in Nham, a Thai fermented sausage, and the reduction by commercial starter culture, Lactobacillus plantarum BCC 9546.

Biogenic amines are of concern for sausage due to their toxicological effects on nervous, blood pressure, gastric and intestinal systems. In this study, the influence of raw pork meat quality and starter culture inoculation on biogenic amines accumulation in Nham, a Thai traditional fermented pork, were studied. Before Nham processing, pork meat was stored at 30°C for 6h, and at 4 and -20°C for 2days. Formation of biogenic amines (cadaverine, putrescine, histamine and tyramine) was significantly higher in Nham processed from stored meat. Accumulation of these biogenic amines in Nham reduced significantly by the addition of Lactobacillus plantarum BCC 9546, a commercial Nham starter culture. The results highlight the importance of using fresh meat products and the inclusion of an appropriate starter culture to minimise the formation of biogenic amines during the process of Nham fermentation.

Interactions between α-Tocopherol and Rosmarinic Acid and Its Alkyl Esters in Emulsions: Synergistic, Additive, or Antagonistic Effect?

Many antioxidants can interact to produce synergistic interactions that can more effectively inhibit lipid oxidation in foods. Esterification of rosmarinic acid produces a variety of compounds with different antioxidant activity due to differences in polarity and thus differences in partitioning in oil, water, and interfacial regions of oil-in-water emulsions (O/W). Therefore, rosmarinic acid and rosmarinate esters provide an interesting tool to study the ability of antioxidant to interact in O/W emulsions. In O/W emulsions, rosmarinic acid (R0) exhibited the strongest synergistic interaction with α-tocopherol while butyl (R4) and dodecyl (R12) rosmarinate esters exhibited small synergistic interaction and eicosyl rosmarinate esters (R20) exhibited slightly antagonistic interaction. Fluorescence quenching and electron paramagnetic resonance (EPR) studies showed that water-soluble rosmarinic acid (R0) exhibited more interactions with α-tocopherol than any of the tested esters (R4, R12, R20). This was also confirmed in O/W emulsions where R0 altered the formation of α-tocopherol quinone and α-tocopherol increased the formation of caffeic acid from R0. This formation of caffeic acid was proposed to be responsible for the synergistic activity of R0 and α-tocopherol since the formation of an additional antioxidant could further increase the oxidative stability of the emulsion.

Influence of minced pork and rind ratios on physico-chemical and sensory quality of Nham - a Thai fermented pork sausage.

The effects of incorporating varying levels of minced pork and rind on physico-chemical and sensory quality of Nham were studied. An increase in cooked pork rind resulted in higher moisture, lipid, and initial pH values of Nham (P<0.05). However, no significant effects were observed on fermentation characteristics of Nham (P>0.05). At the end of fermentation, Nham with a higher meat component exhibited higher texture profile analysis force, hardness, and cohesiveness (P<0.05). The results suggested the importance of meat on the restructuring effect, which contributes to the texture formation of Nham. Incorporation of a higher amount of cooked pork rind improved water-binding properties, leading to decreased weight loss and released water. Based on the results of sensory evaluation, up to 43% pork rind can be used in the formulation with no adverse effect on texture and overall liking of Nham. However, the ratio of 5:5 was the most appropriate for minimising the cost of production.

Antioxidant activity of protocatechuates evaluated by DPPH, ORAC, and CAT methods

Hibiscus sabdariffa L. is a worldwide consumed plant, principally after infusion of its dried sepals and calyces, which are usually discarded. Nevertheless, they represent a potential source of natural bioactive compounds, e.g. polyphenols, which could add value to this under-exploited plant. Protocatechuic acid (PA) was chosen as a model of the phenolic acids that can be extracted from H. sabdariffa. In order to modify PA hydrophilic character, which limits its use in lipid-rich food products, PA was esterified to C1-C18 alcohols, and the impact of lipophilization on its antioxidant activity was evaluated in both, an homogeneous (DPPH and ORAC methods) and an heterogeneous (CAT method) system. Results herein obtained showed that, depending on the grafted alkyl chain length, lipophilization could positively affect the antioxidant activity of PA in heterogeneous media; therefore, support its use as an innovative way to synthesize molecules with an improved antioxidant capacity and potential to be used as multifunctional preservatives in food.

Understanding antioxidant mechanisms in preventing oxidation in foods.

Abstract: Many foods are becoming more susceptible to oxidative rancidity due to attempts to make foods healthier by increasing polyunsaturated fatty acids, and more sustainable by introducing light weight oxygen-permeable and light-penetrating packaging. Unfortunately, very few new food antioxidants have been made available over the past several decades and the use of synthetic antioxidants is disfavored by many consumers. Thus, in order to make natural, more sustainable and healthier foods, the food technologist must find ways to use existing antioxidants more effectively. This requires a strong understanding of antioxidant chemistry. This chapter reviews the chemistry of free radical scavengers, metal chelators, singlet oxygen quenchers and antioxidant enzymes. Interactions between antioxidants to enhance activity are also discussed.