Influence of human gastric juice on oxidation of marine lipids – in vitro study

Food Polyphenols as Preventive Medicine

Reactive oxygen species (ROS) are the initiators in foods and in the stomach of oxidized dietary lipids, proteins, and lipid-oxidation end-products (ALEs), inducing in humans the development of several chronic diseases and cancer. Epidemiological, human clinical and animal studies supported the role of dietary polyphenols and derivatives in prevention of development of such chronic diseases. There is much evidence that polyphenols/derivatives at the right timing and concentration, which is critical, acts mostly in the aerobic stomach and generally in the gastrointestinal tract as reducing agents, scavengers of free radicals, trappers of reactive carbonyls, modulators of enzyme activity, generators of beneficial gut microbiota and effectors of cellular signaling. In the blood system, at low concentration, they act as generators of electrophiles and low concentration of H2O2, acting mostly as cellular signaling, activating the PI3K/Akt-mediated Nrf2/eNOS pathways and inhibiting the inflammatory transcription factor NF-κB, inducing the cells, organs and organism for eustress, adaptation and surviving.

Lipid oxidation and aldehyde formation during in vitro gastrointestinal digestion of roasted scallop (Patinopecten yessoensis) - the role of added antioxidant of bamboo leaves

This study investigated lipid oxidation and aldehyde formation in roasted scallop during in vitro gastrointestinal digestion, and the effects of co-digestion of antioxidant of bamboo leaves (AOB) on this process. The results showed that the contents of lipid hydroperoxides (LOOH), conjugated dienes (CD), and Schiff bases (SB) were increased during gastrointestinal digestion. Besides, malondialdehyde (MDA) levels and total aldehyde formation decreased initially at the gastric stage but increased at the intestinal stage. The results of HPLC-ESI-MS/MS analysis showed that the contents of hexanal (HEX), trans, trans-2,4-octadienal (ODE), trans, trans-2,4-decadienal (DDE), 4-hydroxyhexenal (HHE) and 4-hydroxynonenal (HNE) in the digestive juices were all initially decreased and then increased during gastrointestinal digestion. Meanwhile, the content of acrolein, propanal, and trans-2-pentenal at the end of intestinal digestion was lower than that in the initial stage of gastric digestion. Additionally, the digestion of roasted scallop caused significant oxidation of polyunsaturated fatty acids (PUFAs) and release of free fatty acids (FFA) in the intestinal phase, which were positively related to aldehyde production. However, co-digestion of AOB significantly reduced lipid oxidation and formation of lipid oxidation products (LOOH, CD, SB, and aldehyde) during gastrointestinal digestion, indicating that the addition of AOB was effective in reducing gastrointestinal lipid oxidation.

DHA rich algae oil delivered by O/W or gelled emulsions: strategies to increase its bioaccessibility

BACKGROUND

The bioaccessibility of bioactive compounds for functional food deserves evaluation. An in vitro gastrointestinal digestion model was applied to provide information about the extent of lipid hydrolysis, oxidative stability and bioaccessibility of algae oil (42% of docosahexaenoic acid; DHA), comparing three lipid delivery systems: bulk oil, soy protein stabilized O/W emulsion and carrageenan gelled emulsion.

RESULTS

Lipid digestion kinetics was slightly influenced by the delivery systems. Nevertheless, at the end of intestinal digestion, lipolysis in the three samples ranged between 49% and 52%, showing a partial oil digestion. Lipid oxidation, measured by malondialdehyde, was significantly lower (P < 0.01) in both emulsified oils after intestinal digestion compared to the bulk oil. Bioaccessibility of DHA was 58%, 71% and 84% for bulk oil, O/W emulsion and gelled emulsion, respectively.

CONCLUSION

These results suggest that both emulsified delivery systems used in the present study enhanced the solubilization of free fatty acids, in particular omega-3 fatty acids, and therefore their potential intestinal absorption. © 2018 Society of Chemical Industry.

Impact of Interfacial Composition on Emulsion Digestion Using In Vitro and In Vivo Models

This study explored the influence of different emulsification layers as mono- and bilayers on lipid digestion by using in vitro and in vivo digestion methods. The monolayer emulsion of rapeseed oil contained whey proteins and the bilayer emulsion, whey proteins and carboxymethyl cellulose. The in vitro digestion using human gastrointestinal enzymes showed that the lipid digestion as free fatty acids was slowed down in the bilayer emulsion compared with the monolayer. Droplet size was still low in the gastric phase and pseudoplasticity was well preserved (even though viscosity decreased) during in vitro gastrointestinal digestion. The in vivo studies confirmed a lower fat bioavailability from bilayer emulsions by a reduction in the triglyceride level in the blood of rats, fed by the bilayer emulsion. The results clearly showed that lipid digestion was slower in the bilayer emulsion than in the monolayer. These results provide bio-relevant information about the behavior of emulsions upon digestion. PRACTICAL APPLICATION: The layer-by-layer production approach that was presented here allows the preparation of emulsions with slower fat bioavailability. Such behavior of the bilayer emulsion made it interesting for the formulation of food products with low fat bioavailability.

Oxidation of marine oils during in vitro gastrointestinal digestion with human digestive fluids - Role of oil origin, added tocopherols and lipolytic activity

The formation of malondialdehyde (MDA), 4-hydroxy-2-hexenal (HHE), 4-hydroxy-2-nonenal (HNE), and 4-oxo-2-nonenal (ONE) in cod liver-, anchovy-, krill-, and algae oil during in vitro digestion with human gastrointestinal fluids was investigated. Adding rabbit gastric lipase, lipase inhibitor (orlistat) and tocopherols to cod liver oil, lipolysis and oxidation was also studied. Among the marine oils, the highest aldehyde levels (18 µM MDA, 3 µM HHE and 0.2 µM HNE) were detected after digestion of cod liver oil, while the lowest levels were detected in krill and algae oils. Addition of rabbit gastric lipase significantly increased the release of HNE during the digestion. Orlistat significantly reduced lipolysis and MDA formation. Formation of MDA and HHE was delayed by tocopherols, the tocopherol mix Covi-ox® T 70 EU being more effective than pure α-tocopherol.

Effects of Marine Oils, Digested with Human Fluids, on Cellular Viability and Stress Protein Expression in Human Intestinal Caco-2 Cells

In vitro digestion of marine oils has been reported to promote lipid oxidation, including the formation of reactive aldehydes (e.g., malondialdehyde (MDA) and 4-hydroxy-2-hexenal (HHE)). We aimed to investigate if human in vitro digestion of supplemental levels of oils from algae, cod liver, and krill, in addition to pure MDA and HHE, affect intestinal Caco-2 cell survival and oxidative stress. Cell viability was not significantly affected by the digests of marine oils or by pure MDA and HHE (0-90 μM). Cellular levels of HSP-70, a chaperone involved in the prevention of stress-induced protein unfolding was significantly decreased (14%, 28%, and 14% of control for algae, cod and krill oil, respectively; p ≤ 0.05). The oxidoreductase thioredoxin-1 (Trx-1) involved in reducing oxidative stress was also lower after incubation with the digested oils (26%, 53%, and 22% of control for algae, cod, and krill oil, respectively; p ≤ 0.001). The aldehydes MDA and HHE did not affect HSP-70 or Trx-1 at low levels (8.3 and 1.4 μM, respectively), whilst a mixture of MDA and HHE lowered Trx-1 at high levels (45 μM), indicating less exposure to oxidative stress. We conclude that human digests of the investigated marine oils and their content of MDA and HHE did not cause a stress response in human intestinal Caco-2 cells.

Polyunsaturated lipids and vitamin A oxidation during cod liver oil in vitro gastrointestinal digestion. Antioxidant effect of added BHT

The extent of cod liver oil hydrolysis and oxidation during in vitro gastrointestinal digestion was investigated by Proton Nuclear Magnetic Resonance (¹H NMR) and Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS). These techniques evidenced the degradation of polyunsaturated ω-3 and ω-6 lipids and, for the first time, that of vitamin A, naturally present in cod liver oil. Cis,trans-conjugated dienes associated with hydroperoxides, as well as monoepoxides, cis,trans-2,4-alkadienals, 4-hydroperoxy- and 4-hydroxy-2-alkenals, and several vitamin A derived metabolites were generated. Moreover, the effect of the addition of the synthetic antioxidant 2,6-di-tert-butyl-hydroxytoluene (BHT) at 20 and 800ppm was tackled. Both techniques showed BHT to be efficient in limiting oxidation reactions during digestion, almost inhibiting them at 800ppm. Therefore, the simultaneous intake of antioxidants with cod liver oil should be considered, in order to increase polyunsaturated lipid and vitamin A bioaccessibility and avoid formation of toxic oxidation compounds like oxygenated alpha,beta-unsaturated aldehydes.

Fish in Vitro Digestion: Influence of Fish Salting on the Extent of Lipolysis, Oxidation, and Other Reactions

A study of the various chemical reactions which take place during fish in vitro digestion and the potential effect of fish salting on their extent is addressed for the first time. Farmed European sea bass fillets, raw, brine-salted or dry-salted, were digested using a gastrointestinal in vitro model. Fish lipid extracts before and after digestion were analyzed by ¹H NMR, and the headspace composition of the digestates was investigated by SPME-GC/MS. During digestion, not only lipolysis, but also fish lipid oxidation took place. This latter was evidenced by the generation of conjugated dienes supported on chains having also hydroperoxy- and hydroxy-groups (primary oxidation compounds), by the increase of volatile secondary oxidation products, and by the decrease of the antioxidant 2,6-di-tert-butyl-hydroxytoluene (BHT). Likewise, esterification and Maillard-type reactions also occurred. Salting, and especially dry-salting, enhanced all these reactions, except for lipolysis, during digestion.

Formation of reactive aldehydes (MDA, HHE, HNE) during the digestion of cod liver oil: comparison of human and porcine in vitro digestion models

In this work, we investigated lipid oxidation of cod liver oil during gastrointestinal (GI) digestion using two types of in vitro digestion models. In the first type of model, we used human GI juices, while we used digestive enzymes and bile from porcine origin in the second type of model. Human and porcine models were matched with respect to factors important for lipolysis, using a standardized digestion protocol. The digests were analysed for reactive oxidation products: malondialdehyde (MDA), 4-hydroxy-trans-2-nonenal (HNE), and 4-hydroxy-trans-2-hexenal (HHE) by liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (LC/APCI-MS), and for free fatty acids (FFA) obtained during the digestion by gas chromatography-mass spectrometry (GC-MS). The formation of the oxidation products MDA, HHE, and HNE was low during the gastric digestion, however, it increased during the duodenal digestion. The formation of the oxidation products reached higher levels when digestive juices of human origin were used (60 μM of MDA, 9.8 μM of HHE, and 0.36 μM of HNE) [corrected] compared to when using enzymes and bile of porcine origin (0.96, and 1.6 μM of MDA; 0.16, and 0.23 μM of HHE; 0.026, [corrected] and 0.005 μM of HNE, respectively, in porcine models I and II). In all models, FFA release was only detected during the intestinal step, and reached up to 31% of total fatty acids (FA). The findings in this work may be of importance when designing oxidation oriented lipid digestion studies.

Malondialdehyde and 4-hydroxy-2-hexenal are formed during dynamic gastrointestinal in vitro digestion of cod liver oils

Marine long-chain polyunsaturated fatty acids (LC n-3 PUFA) are associated with reduced risk for inflammatory diseases, such as cardiovascular diseases and rheumatoid arthritis. These fatty acids, however, are rapidly oxidized, generating highly reactive malondialdehyde (MDA), 4-hydroxy-2-hexenal (HHE) and 4-hydroxy-2-nonenal (HNE). These oxidation products may interact with DNA and proteins, thus possibly leading to impaired cell functions. Little is known about the formation of MDA, HHE and HNE in fish oil in the gastrointestinal (GI) tract. In this study, the effect of dynamic in vitro digestion of cod liver oil on the generation of MDA, HHE and HNE was evaluated using the TNO Gastro-Intestinal Model (tiny-TIM). Effects of pre-formed oxidation products, pre-emulsification of the oil, and addition of oxidants (EDTA and hemoglobin, Hb) on GI oxidation were evaluated. Formation of aldehydes occurred during GI digestion. However, only emulsified oil fortified with 11.5 μM Hb oxidized to a degree that overcame the dilution induced by gastric secretion, which caused increased aldehyde concentrations in gastric lumen up to 90 min. The maximum levels of aldehydes generated in this study were 24.5 μM MDA, 1.6 μM HHE and 0.07 μM HNE. Oils containing different amounts of pre-formed lipid oxidation products maintained the same oxidation ranking order during digestion, even though the relative changes were not directly proportional. Emulsification of the oil had an unclear effect in the gastric phase, but a pro-oxidative effect in the intestinal phase. In general, higher aldehyde levels were reached in the intestinal lumen than in the initial meal, demonstrating that GI digestion promotes oxidation. Hence, epithelial cells may be exposed to elevated amounts of reactive aldehydes for several hours after a meal containing fish oil.

Formation of Malondialdehyde, 4-Hydroxynonenal, and 4-Hydroxyhexenal during in Vitro Digestion of Cooked Beef, Pork, Chicken, and Salmon

Red meat high in heme iron may promote the formation of potentially genotoxic aldehydes during lipid peroxidation in the gastrointestinal tract. In this study, the formation of malondialdehyde (MDA) equivalents measured by the thiobarbituric acid reactive substances (TBARS) method was determined during in vitro digestion of cooked red meat (beef and pork), as well as white meat (chicken) and fish (salmon), whereas analysis of 4-hydroxyhexenal (HHE) and 4-hydroxynonenal (HNE) was performed during in vitro digestion of cooked beef and salmon. Comparing products with similar fat contents indicated that the amount of unsaturated fat and not total iron content was the dominating factor influencing the formation of aldehydes. It was also shown that increasing fat content in beef products caused increasing concentrations of MDA equivalents. The highest levels, however, were found in minced beef with added fish oil high in unsaturated fat. This study indicates that when ingested alone, red meat products low in unsaturated fat and low in total fat content contribute to relatively low levels of potentially genotoxic aldehydes in the gastrointestinal tract.

Formation of malondialdehyde (MDA), 4-hydroxy-2-hexenal (HHE) and 4-hydroxy-2-nonenal (HNE) in fish and fish oil during dynamic gastrointestinal in vitro digestion

Reactive lipid peroxidation products (MDA, HHE and HNE) are formed during dynamic gastrointestinalin vitrodigestion of fish and fish oil.

Stability and bioaccessibility of anthocyanins in bakery products enriched with anthocyanins

Anthocyanins, water soluble polyphenols, have been associated with several beneficial health effects.

Lipid Peroxidation in a Stomach Medium Is Affected by Dietary Oils (Olive/Fish) and Antioxidants: The Mediterranean versus Western Diet

Red meat is an integral part of the Western diet, and high consumption is associated with an increased risk of chronic diseases. Using a system that simulated the human stomach, red meat was interacted with different oils (olive/fish) and lipid peroxidation was determined by measuring accumulation of malondialdehyde (MDA) and lipid peroxides (LOOH). Olive oil decreased meat lipid peroxidation from 121.7 ± 3.1 to 48.2 ± 1.3 μM and from 327.1 ± 9.5 to 77.3 ± 6.0 μM as assessed by MDA and ROOH, respectively. The inhibitory effect of olive oil was attributed to oleic acid rather than its polyphenol content. In contrast, fish oils from tuna or an ω-3 supplement dramatically increased meat lipid peroxidation from 96.2 ± 3.6 to 514.2 ± 6.7 μM MDA. Vitamin E inhibited meat lipid peroxidation in the presence of olive oil but paradoxically increased peroxidation in the presence of fish oil. The inhibitory properties of oleic acid may play a key role in the health benefits of the Mediterranean diet.