Sustainable extraction methods of carotenoids from mango (Mangifera indica L. 'Kent') pulp: Ultrasound assisted extraction and green solvents.

Mango is a good source of carotenoids for use in food, cosmetic, and pharmaceutical products because of their organoleptic and health-promoting properties. Safe and sustainable methods for their extraction is required. The present investigation was aimed to study concentration and carotenoid profile of 'Kent' mango pulp through a conventional extraction (CE) and ultrasound-assisted extraction (UAE) using traditional solvents (tetrahydrofuran-THF and diethyl ether: petroleum ether-DE:PE) and green solvents (GS) (2-metiltetrahydrofuran, 2 m-THF; cyclopentyl methyl ether, CPME). Mango showed (µg/g d.w.) ß-carotene (29.4), zeaxanthin (1.28), ß-cryptoxanthin (2.8), phytoene (18.68) and phytofluene (7.45) in a CE using DE:PE. Similar results were obtained applying DE:PE in UAE and GS in a CE, so CPME and 2-mTHF seem suitable solvents to replace DE:PE in CE. The yield of total carotenes, xanthophylls and carotenoids using GS combined with UAE was lower than with CE, but important enough to be used as a sustainable procedure for obtaining carotenoids from mango pulp.

Enhanced extraction of phenolic compounds from mango by-products using deep eutectic solvents.

Deep eutectic solvents (DESs) potential for the extraction of polyphenolic compounds (PC) from mango by-products (peel and seed) was evaluated. Ultrasound (US) and agitation were applied to evaluate the effects of solvent and extraction methodology. The extracts were characterized with antioxidant capacity and HPLC-DAD profile. A theoretical study was performed using density functional theory and the QTAIM approach. ß-alanine and choline chloride based DESs were effective to extract PC from peel and seed. Some DES increased PC extraction up to three times for peel (23.05 ± 1.22 mg/g DW) and up to five time for seeds (60.01 ± 1.40 mg/g DW). The PC profile varied with the solvent (DES vs EtOH/MeOH), procedure (US vs agitation) and material (peel or seed). Mangiferin extraction from peels was significantly increased with ß-alanine based DES (676.08 ± 20.34 µg/gDW). The strength of H-bonds had a determining effect on the viscosity of DESs. The solute-solvent solvation energy was suitable to estimate the strength of H-bond interactions between DES and target compounds. This study demonstrates the remarkable capacity of DESs to extract PC from mango by-products and provides insights into the factors controlling extraction properties.

Bile Acids and Short-Chain Fatty Acids Are Modulated after Onion and Apple Consumption in Obese Zucker Rats.

Gut microorganisms are involved in the development and severity of different cardiovascular diseases, and increasing evidence has indicated that dietary fibre and polyphenols can interact with the intestinal microbiota. The study objective was to investigate the effect of onion and apple intake on the major types of microbial-derived molecules, such as short-chain fatty acids (SCFAs) and bile acids (BAs). Obese Zucker rats were randomly assigned (n = eight rats/group) to a standard diet (OC), a standard diet/10% onion (OO), or a standard diet/10% apple (OA). Lean Zucker rats fed a standard diet served as a lean control (LC) group. Faecal samples were collected at baseline, and 8 weeks later, the composition of the microbial community was measured, and BA and SCFA levels were determined using high-performance liquid chromatography-mass spectrometry (HPLC-MS) and gas chromatography-mass spectrometry (GC-MS), respectively. Rats fed onion- and apple-enriched diets had increased abundance of beneficial bacteria, such as Bifidobacterium spp. and Lactobacillus spp., enhanced SCFAs (acetic, propionic, isobutyric, and valeric acids), decreased excretion of some BAs, mainly of the primary (CA, α-MCA, and ß-MCA) and secondary type (ω-MCA, HDCA, NCA, DCA, and LCA), and increased amount of taurine- and glycine-conjugated BAs compared to the OC group. The contribution of specific bioactive compounds and their metabolites in the regulation of the microbiome and the pathways linked to SCFA and BA formation and their relationship with some diseases needs further research.

Mango 'criollo' by-products as a source of polyphenols with antioxidant capacity. Ultrasound assisted extraction evaluated by response surface methodology and HPLC-ESI-QTOF-MS/MS characterization.

Ultrasound assisted extraction (UAE) was evaluated as a green procedure for the recovery of phenolic compounds with antioxidant capacity from underutilized mango 'criollo' (peel, pulp and seed). Magnetic stirred was performed as conventional extraction. Response surface methodology using a three-factor (% ethanol, amplitude and time) central composite design was used to maximize the extraction for total phenolic compounds (TPC), total flavonoids and antioxidant capacity. The operational conditions to maximize extraction were: peel, 46% ethanol/amplitude 60% (36 µm)/6.5 min; pulp, 25% ethanol/amplitude 75% (45 µm)/30 min; seed 49% ethanol/100% (60 µm) amplitude/20 min. The phenolic composition of the optimized extracts was characterized by HPLC-QTOF-MS/MS and 45 compounds were tentatively identified as xanthones (mangiferin), flavonoids (quercetin), ellagic acid, benzophenones (maclurin), gallate derivatives and gallotannins. UAE increased TPC extraction (33%); interestingly mangiferin extraction increased 53% in peel, similarly, ellagic acid increased up to 2.5 and 4.4 times in peel and seed extracts.

Greater bioavailability of xanthophylls compared to carotenes from orange juice (high-pressure processed, pulsed electric field treated, low-temperature pasteurised, and freshly squeezed) in a crossover study in healthy individuals.

This study examined the effect of the intake of orange juice provided freshly squeezed (FS) or processed using low-temperature pasteurisation (LP), high-pressure processing (HPP), or pulsed electric field (PEF) treatment on the serum carotenoid concentrations of 12 healthy individuals, aged 20-32 years, enrolled in a crossover study. Participants were instructed to consume 500 ml of orange juice/day for 14 days. Carotenoid concentrations in the orange juice as well as serum samples retrieved on days 7 and 14 were analysed via HPLC. A significant increase in serum xanthophyll concentrations, but not serum carotenes, was observed, with the highest increase in α- and ß-cryptoxanthin. The processing technologies applied appeared to affect serum carotenoid concentrations, with concentrations being similar in the HPP and FS orange juice types. As high variability in serum carotenoid concentrations was observed, the effect of different technologies on serum carotenoid concentration warrants further studies with larger sample sizes.

Impact of High-Pressure Processed Onion on Colonic Metabolism Using a Dynamic Gastrointestinal Digestion Simulator.

Onions are the main dietary source of flavonols that have been associated with important health-promoting properties. Onion treated by high-pressure processing (HPP-treated onion) was subjected to a dynamic gastrointestinal digestion and colon fermentation simulator (DGID-CF) to study the effect on the gut microbiota metabolism in the three colon regions (ascending-AC, transverse-TC, and descending-DC) by means of chronic feeding with 27 g/day for 14 days. HPP-treated onion presented a high content of the flavonols quercetin-3,4'-diglucoside and quercetin-4'-glucoside, and a large percentage of them reached the AC without change. TC and DC progressively increased the total phenolic metabolites 2.5 times respective to day 2, mainly 3-hydroxyphenylacetic, 4-hydroxyphenylacetic, 3-(4-hydroxyphenyl)-propionic, and 3,4-dihydroxyphenylpropionic acids. In addition, the chronic feeding increased the beneficial colon bacteria Bifidobacterium spp. and Lactobacillus spp. and the production of total SCFAs (acetic, propionic, and butyric acids) 9 times (AC), 2.2 times (TC), and 4.4 times (DC) respective to day 1. A multivariate analysis (principal component analysis, PCA) showed a clear separation between the three colon regions based on their phenolic composition (precursors and metabolites). These results showed that HPP-treated onion modulated the human gut microbiota's metabolism and the DGID-CF is a good system to study these changes.

Effects of combined application of high-pressure processing and active coatings on phenolic compounds and microbiological and physicochemical quality of apple cubes.

BACKGROUND: In recent years the use of high-pressure processing (HPP) of fruit products has steadily increased due to its antimicrobial effectiveness and the retention of nutritional and quality attributes compared to conventional thermal technologies. Edible coatings are already being used to enhance the quality of minimally processed fruits. Thus, apple cubes (AC) and alginate-vanillin-coated apple cubes (AVAC) were subjected to HPP (400 MPa/5 min/35 °C). The microbiological and physicochemical parameters were evaluated and the bioactive compounds were monitored before and after HPP of apple cubes. Also, an in vitro gastrointestinal digestion (GID) was conducted. RESULTS: HPP left L. monocytogenes counts below the detection limit (2 log UFC g-1 ), regardless of the presence of coating. For E. coli, HPP + active coating showed a synergism affording the greatest reduction (>5 log) for AVAC-HPP. Firmness was maintained in AVAC-HPP samples, while AC-HPP samples suffered reductions of 35%. Colour attributes were also better retained in AVAC-HPP samples. In general, HPP led to a decrease in phenolic compounds. Regarding the effects of GID, vanillin-based active coating exerted a protective effect on some phenolics. Thus, p-coumaroylquinic acid concentration was maintained for AVAC and AVAC-HPP during GID. Epigallocatechin, the compound with the highest concentration in apple cubes, increased for AVAC (106%) and AVAC-HPP (57%). Also, phloridzin concentration increased for AVAC-HPP (17%). At the end of GID, procyanidin B1 and epigallocatechin were the main phenolic compounds for all samples, AVAC showing the highest concentration. CONCLUSIONS: This work demonstrates that the combined application of HPP and active coatings on apple cubes could be used to obtain a safe and good-quality product. © 2021 Society of Chemical Industry.

Impact of high-pressure processing on the stability and bioaccessibility of bioactive compounds in Clementine mandarin juice and its cytoprotective effect on Caco-2 cells.

Mandarin juice is a rich source of antioxidant bioactive compounds. While the content and profile of bioactives are known, the impact of high-pressure processing (HPP) on their stability and bioaccessibility (BA) is unknown, but may allow obtaining safe, nutritious, and fresh-tasting juices with highly extractable bioactive compounds. The stability and BA of bioactive antioxidant compounds in untreated and HPP-treated (400 MPa/40 °C/1 min) Clementine mandarin juices, and the cytoprotective effect of its bioaccessible fractions (BF) obtained after simulated gastrointestinal digestion against H2O2-induced oxidative stress in differentiated Caco-2 cells were investigated. The BF of HPP-treated juices showed a better retention of carotenoids, flavonoids, ascorbic acid, total polyphenols and FRAP value, and slightly higher cytoprotection (mitochondrial membrane potential and ROS) than untreated juices. Therefore, HPP can be recommended as a suitable technology to retain or indeed increase antioxidant bioactives and their cytoprotective activity in mandarin juices after gastrointestinal digestion.

Effect of high-pressure processing applied as pretreatment on carotenoids, flavonoids and vitamin C in juice of the sweet oranges 'Navel' and the red-fleshed 'Cara Cara'.

This work examines the effect of HPP at 200 MPa/25 °C/1 min (HPP-200) as pretreatment on whole-peeled orange fruits from ordinary 'Navel' and red-fleshed 'Cara Cara' sweet oranges before juicing with the aim to improve the extractability of carotenoids, flavonoids, vitamin C and hydrophilic antioxidant activity in the juices. Untreated and HPP-200 juices were subsequently processed at 400 MPa/40 °C/1 min (HPP-400 and HPP-200-400). HPP-200 and HPP-200-400 increased the concentration of hesperidin (25% and 16%), narirutin (27% and 9%), phytoene (40% and 97%) and phytofluene (9- and 12-fold) in Navel-juice and maintained the vitamin C content and the antioxidant activity compared to untreated freshly-prepared juice. However, these two HPP treatments in Cara Cara-juices preserved flavonoids and vitamin C concentration but decreased 16% total carotenoid content mainly lycopene due to its more exposed position in the food matrix. However, a single HPP-400 treatment applied on freshly-prepared orange juices reduced bioactive compounds, mainly in Navel-juices, perhaps due to the mechanical juicing procedure (jar-blender) used or/and with the pressure-induced activation of detrimental food enzymes. All the HP-treated Cara Cara-juices presented higher carotenoid content than the corresponding Navel-juices, and can be considered an excellent dietary source of these compounds. Therefore, HPP applied to whole peeled orange did not modified the profiling of bioactive compounds of Navel- and Cara Cara-juices and increased the concentration of total and individual carotenoids, flavonoids, vitamin C and antioxidant activity depending on the type of bioactive compounds, the orange fruit cultivar and the HPP conditions.

Protective effect of bioaccessible fractions of citrus fruit pulps against H2O2-induced oxidative stress in Caco-2 cells.

Fruit pulps from Navel (N) and Cara Cara (CC) oranges, and Clementine mandarin freshly harvested (M) and refrigerated stored (M12) were used to evaluate the cytoprotective effect of their bioaccessible fractions (BF) against H2O2-induced oxidative stress in Caco-2 cells. BF of samples preserved viability vs. H2O2 treated cells, reaching values similar to controls. Lipid peroxidation was reduced to levels of control cells, but M did not reach control values. ROS and mitochondrial membrane potential changes (Δψm) values were reduced compared with H2O2 treated cells, but without achieving control levels. A significant reduction in cell proportions in G1 phase and a significant increase in sub-G1 phase (apoptosis) of cell cycle was shown in H2O2 treated cells, and BF allowed a recovery close to control levels. Thus, BF of samples protect the cells from oxidative stress by preserving cell viability, mitochondrial membrane potential and correct cell cycle progression, and diminishing lipid peroxidation and ROS.

Role of dietary onion in modifying the faecal bile acid content in rats fed a high-cholesterol diet.

The determination of faecal bile patterns offers new opportunities in the search for non-invasive biomarkers of disease status. The objective of this study was to describe the shifts in faecal bile acid (BA) composition induced by feeding a high-cholesterol/cholic acid diet (HC) over 7 weeks of experimental feeding in Wistar rats, and to evaluate the effect of onion included as a functional ingredient (HCO). A HPLC-MS/MS method allowed the detection of 29 bile acids, 10 of which were tentatively identified and 12 confirmed and quantified by means of standards and calibration curves. The excretion of bile acids revealed a discriminating bile acid profile between the HC and HCO groups compared with the C group. HCO feeding indicated significant changes in specific primary and secondary BA in both the unconjugated and conjugated forms caused by the addition of the onion ingredient to the diet. The results suggest that the induction of microbiome modifications by the HC and HCO diets acts as a critical modifier of the faecal bile acid composition. These modifications might reflect and be linked to changes in the reabsorption of BA at an intestinal level and the process of BA deconjugation in the course of hypercholesterolemia.

Influence of orange cultivar and mandarin postharvest storage on polyphenols, ascorbic acid and antioxidant activity during gastrointestinal digestion.

Polyphenols, ascorbic acid content and antioxidant activity of two sweet oranges (Navel-N and Cara Cara-CC) and mandarin (Clementine-M) as well as their bioaccessibilities were evaluated in pulps and compared to those in fresh juice. Thus, pulps of oranges and mandarins displayed higher hesperidin (HES), narirutin (NAR), total flavonoids (TF), total phenols (TP) and antioxidant activity (AAC) than their corresponding juices. Also, CC products presented higher bioactive compounds content than N ones. Bioaccessibility of bioactive compounds and AAC were higher in pulps of both oranges and mandarin than in their corresponding juices. Oranges (N and CC) pulps and juices presented higher bioaccessibilities than mandarin ones. The postharvest storage of mandarin at 12°C during 5weeks not only produced a significant increase of the bioactive compounds but also an increase of their bioaccessibility. The bioaccessibility of Citrus bioactive compounds is necessary for calculating more accurately their daily intake amount.

New insights into the effects of onion consumption on lipid mediators using a diet-induced model of hypercholesterolemia.

The levels and roles of lipid mediators can be modified in response to nutritional stimuli. The aim of this study was to investigate shifts in oxylipin and sphingolipid profiles stimulated by a hypercholesterolemic (HC) diet along with the modulating effects of onion introduced as an antioxidant functional ingredient characterized in the diet (HCO). Oxylipin and sphingolipid profiles were determined in plasma and tissues from Wistar rats using LC-MS/MS. Plasma ω-3 and ω-6 PUFA-derived oxylipins decreased in rats after 7 weeks of HC feeding, but did not evidence a further shift with HCO diet. Onion ingredient supplementation modulated the hepatic concentrations of prostaglandins and enhanced ω-3 oxylipins in the liver of HCO-fed rats relative to the HC group. The HC diet induced shifts in plasma sphingolipids, increasing sphingoid bases, dihydroceramides and ceramides, whilst the sphingomyelin, hexosylceramide and lactosylceramide families decreased. The HCO diet modified some HC diet-induced changes in sphingolipids in liver and spleen tissue. Onion supplementation effected changes in lipid mediator levels in diet-induced hypercholesterolemic Wistar rats. The potential of onion as regulator of pro-inflammatory mediators, and possible enhancer of pro-resolution pathways, warrants further study of the interaction of functional ingredients with bioactive lipid mediators and their potential impact on inflammation, oxidative stress and organ dysfunction.

Food matrix and processing influence on carotenoid bioaccessibility and lipophilic antioxidant activity of fruit juice-based beverages.

The biological activity of carotenoids depends on their bioaccessibility and solubilization in the gastrointestinal tract. These compounds are poorly dispersed in the aqueous media of the digestive tract due to their lipophilic nature. Thus, it is important to analyze the extent to which some factors, such as the food matrix and food processing, may improve their bioaccessibility. Beverages formulated with a blend of fruit juices and water (WB), milk (MB) or soymilk (SB) were treated by high-intensity pulsed electric fields (HIPEF) (35 kV cm(-1) with 4 µs bipolar pulses at 200 Hz for 1800 µs), high-pressure processing (HPP) (400 MPa at 40 °C for 5 min) or thermal treatment (TT) (90 °C for 1 min) in order to evaluate the influence of food matrix and processing on the bioaccessibility of carotenoids and on the lipophilic antioxidant activity (LAA). The bioaccessibility of these compounds diminished after applying any treatment (HIPEF, HPP and TT), with the exception of cis-violaxanthin + neoxanthin, which increased by 79% in HIPEF and HPP beverages. The lowest carotenoid bioaccessibility was always obtained in TT beverages (losses up to 63%). MB was the best food matrix for improving the bioaccessibility of carotenoids, as well as the LAA. The results demonstrate that treatment and food matrix modulated the bioaccessibility of carotenoids as well as the lipophilic antioxidant potential of beverages. Additionally, HIPEF and HPP could be considered as promising technologies to obtain highly nutritional and functional beverages.

Multiplatform metabolomic fingerprinting as a tool for understanding hypercholesterolemia in Wistar rats.

PURPOSE: The aim was to investigate the impact of hypercholesterolemic diet on the metabolome of male Wistar rats by a multiplatform metabolomic fingerprinting. METHODS: Male Wistar rats were fed with two different diets [control (C) and high-cholesterol diet (HC)-containing 2 % cholesterol and 0.5 % cholic acid]. After 7 weeks of experimental feeding, the rats were euthanized for blood collection and plasma recovery. The metabolite fingerprint was then achieved by applying a multiplatform comprising LC-MS, GC-MS and CE-MS. RESULTS: Multivariate statistical analysis showed a clear separation between the C and HC groups. Individual differences in metabolites were evaluated using univariate statistical analysis, and multiple metabolites were identified and confirmed in the plasma. A global profiling integrates for the first time pathways affected by high-cholesterol diet intake and allowed us to elucidate some of the associated alterations underlying the hypercholesterolemia event in Wistar rats. CONCLUSIONS: HC feeding stimulated the alteration of multiple pathways in Wistar rats, warning of the risk of developing important diseases, which can be modulated by the diet. Further studies are required to investigate the possibilities to revert or ameliorate the negative effects triggered by HC intake.

High-cholesterol diet enriched with onion affects endothelium-dependent relaxation and NADPH oxidase activity in mesenteric microvessels from Wistar rats.

BACKGROUND: The aim of the present study was to examine the effects of onion as functional ingredient on the oxidative status, lipoprotein levels (total cholesterol-TC, HDL-C, LDL-C), triacylglycerides (TAG) and vascular reactivity of mesenteric arteries in hypercholesterolemic Wistar rats. METHODS: Twenty-four animals were fed with three different diets [control, high-cholesterol diet (HC) and high-cholesterol enriched with onion diet (HCO)]. After seven weeks of experimental feeding the rats were euthanized for blood and tissues collection. TC, HDL-C, LDL-C and TAG were measured, and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS(•+)) scavenging capacity and ferric reducing antioxidant power (FRAP) were determined in plasma. Superoxide dismutase (SOD) and glutathione peroxidase (GPx) enzyme activities were assayed in erythrocyte lysates. Endothelium-dependent vasodilation to acetylcholine was evaluated in mesenteric arterial segments. NADPH oxidase (NOX) was also measured by lucigenin-derived chemiluminiscence. RESULTS: The dietary cholesterol content significantly affected plasma lipoprotein levels, increased superoxide generation from NOX, and caused impaired endothelium-dependent vasodilation in the rat mesenteric arteries. Onion ingredient improved antioxidant status in HCO group, as it was evidenced by ABTS(•+) and FRAP values and SOD and GPx enzyme activities compared to the HC-fed group, reduced the increment in NOX activity and reversed endothelial dysfunction promoted by the HC diet. Scavenging of superoxide with TEMPOL or inhibition of NOX with apocynin improved endothelium-dependent vasodilation only in HC-fed rats. CONCLUSIONS: Enrichment of diet with onion as functional ingredient could be proposed as a complementary approach to prevent or partially modulate vascular dysfunction, reducing some of the risk indexes linked to initial development of atherosclerosis.

Effects of hypercholesterolemic diet enriched with onion as functional ingredient on fatty acid metabolism in Wistar rats.

The complex biochemical composition of onions has been studied as a source of biological components with health-related properties. The evolution of hypercholesterolemia is associated with a large range of alterations considered as strong risk factors for many cardiovascular events. The objective of this study was to investigate the effects of onion as functional ingredient on plasma, erythrocyte, liver and adipose tissue fatty acid composition in hypercholesterolemic male Wistar rats. Rats (n=24) were randomly divided into three groups: control (C), high-cholesterol (HC), and high-cholesterol enriched with onion (HCO) groups. At the end of 7weeks, animals were anesthetized and euthanized by extracting blood by cardiac puncture. Plasma, erythrocytes, liver and adipose tissue were collected and immediately stored at -80°C. Fatty acid methyl esters were identified and quantified by GC/MS. Total fatty acid concentration decreased in liver and adipose tissue both in HC and HCO groups. SFA content was significantly higher in plasma, erythrocytes and liver in the C group compared to HC and HCO groups. In contrast, SFAs increased in adipose tissue both in HC and HCO groups compared to the C group. A significant increase in MUFA content in plasma was found in HC and HCO groups compared to the C group; in erythrocytes and liver the increase was lower. In plasma, PUFA content was significantly lower in HC and HCO groups compared to the C group. Interestingly, in liver and adipose tissue, PUFAs increased in HC and HCO groups compared to the C group. Results showed noticeable effects on individual fatty acid composition when assaying high-cholesterol diets in rats, in some cases enhanced by onion enrichment. Further research is needed to deeper understand the involved mechanisms and pathways.

Hyaluronidase inhibiting activity and radical scavenging potential of flavonols in processed onion.

The flavonol content and anti-inflammatory and antioxidant activities of onion treated by high-pressure processing (HPP) and HPP combined with freeze-drying and pulverization (HPP-FD-P) were evaluated. Allium cepa L. var. cepa, 'Recas' was treated at T1 (200 MPa/25 °C/5 min), T2 (400 MPa/25 °C/5 min), and T3 (600 MPa/25 °C/5 min). After treatment, HP-treated and untreated samples were frozen (diced onion, HP-treated). Subsequently, part of the diced samples was freeze-dried and pulverized (pulverized onion, HP-treated and freeze-dried). Flavonol content and anti-inflammatory and antioxidant activities (hyaluronidase inhibiting activity, NO(•), ABTS(•+), and DPPH(•) scavenging capacity, ferric reducing antioxidant power, and antioxidative capacity by photochemiluminescence) were measured in nonhydrolyzed and hydrolyzed extracts. Hydrolysis was carried out in order to evaluate the effect of HPP and HPP-FD-P on both anti-inflammatory and antioxidant activities of extracts mainly containing aglycone forms. HPP-FD-P increased quercetin 3,4'-diglucoside, quercetin 4'-glucoside, quercetin 3-glucoside, and isorhamnetin 3,4'-diglucoside extractability. The present study suggests that HPP (especially treatment at 400 MPa) and HPP-FD-P may be of benefit for obtaining functional ingredients from onion, as suggested by increased NO(•) scavenging capacity and maintenance of the antioxidant activity mainly in hydrolyzed extracts.

Changes in the structure and antioxidant properties of onions by high pressure treatment.

Onions have antioxidant properties and they are an important source of bioactive compounds such as phenols. The aim of this work was to study the effect of high hydrostatic pressure (HHP) (100-600 MPa/1-3 min/25 °C) on the microstructure and antioxidant properties of onions (cv. Doux) and its relationship with changes in the extractability of potential health-related compounds. Cryo scanning electron microscopy was used to study the microstructure. Vitamin C, total phenolic content and antioxidant activity (DPPH˙, ABTS˙(+), FRAP) were also analyzed. Tonoplast, plasmalemma and cell walls were affected by the HHP treatment and it favored the diffusion of the cellular content to the intercellular spaces. Vitamin C did not show significant changes, whereas the extracted phenolic content and antioxidant activity increased at pressures of 300 or 600 MPa. Therefore, it could be concluded that HHP produced changes in membrane permeability and disruption of cell walls favoring the release of phenolic compounds from tissue and, in consequence, improving their extractability.

Novel approach for the determination of volatile compounds in processed onion by headspace gas chromatography-mass spectrometry (HS GC-MS).

A novel headspace gas chromatography-mass spectrometry (HS GC-MS) method was developed for analysis of volatile compounds in onion (Allium cepa L. var. cepa, 'Recas'). MS was operated using full scan mode and selective ion monitoring (SIM) mode in order to quantify some specific compounds with increased sensitivity relative to full scan mode. The limits of detection and quantitation ranged from 0.01 to 0.10 µg/g and from 0.02 to 3.83 µg/g fresh weight, respectively, for studied compounds. The procedure allowed the identification of eighteen compounds and quantitation of nine compounds in the volatile fraction of onion, belonging mainly to di-, and trisulfides and aldehydes. These methods were applied to evaluate how high-pressure (HP) as a processing technology affects onion volatile compounds, responsible in part of the onion biological activity. Onion samples were treated at T1: 200 MPa/25°C/5 min, T2: 400 MPa/25°C/5 min and T3: 600 MPa/25°C/5 min (treatments). In addition, the difference among diced, freeze-dried and pulverized onions (groups) was studied, in order to select the process more adequate for better preserving volatile compounds. The results obtained in full scan mode showed that both main factors (group and treatment) had a significant effect (P<0.001). There were also significant differences between groups and treatments for all compounds, being the main effect of group more marked by HS GC-MS using selective ion monitoring (SIM) mode. For 2-methyl 2-pentenal, dimethyl trisulfide, and methyl propyl trisulfide it has been observed an increase in freeze-dried and pulverized onion samples compared with diced samples regardless the HP treatment. However, freeze-drying and pulverization processes affected the stability of propionaldehyde, 1-propanethiol, hexanal, dipropyl disulfide, and dipropyl trisulfide, diminishing their content regardless the HP treatment. HP at 200 and 400 MPa/25°C/5 min were the least detrimental treatments to the total fraction of volatile compounds, not affecting or even increasing the levels of some volatile compounds.