While use of synthetic antioxidants (such as butylated hydroxytoluene and butylated hydroxyanisole) to maintain the quality of ready-to-eat food products has become commonplace, consumer concern regarding their safety has motivated the food industry to seek natural alternatives. Phenolic antioxidants can inhibit free radical formation and/or interrupt propagation of autoxidation. Fat-soluble vitamin E (α-tocopherol) and water-soluble vitamin C (L-ascorbic acid) are both effective in the appropriate matrix. Plant extracts, generally used for their flavoring characteristics, often have strong H-donating activity thus making them extremely effective antioxidants. This antioxidant activity is most often due to phenolic acids (gallic, protocatechuic, caffeic, and rosmarinic acids), phenolic diterpenes (carnosol, carnosic acid, rosmanol, and rosmadial), flavonoids (quercetin, catechin, naringenin, and kaempferol), and volatile oils (eugenol, carvacrol, thymol, and menthol). Some plant pigments (anthocyanin and anthocyanidin) can chelate metals and donate H to oxygen radicals thus slowing oxidation via 2 mechanisms. Tea and extracts of grape seeds and skins contain catechins, epicatechins, phenolic acids, proanthocyanidins, and resveratrol, all of which contribute to their antioxidative activity. The objective of this article is to provide an overview of natural antioxidants, their mechanisms of action, and potential applications.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1541-4337.2011.00156.x

Natural antioxidants: sources, compounds, mechanisms of action, and potential applications

Polyphenol oxidases in plants and fungi: going places? A review.

Simulated gastro-intestinal digestion is widely employed in many fields of food and nutritional sciences, as conducting human trials are often costly, resource intensive, and ethically disputable. As a consequence, in vitro alternatives that determine endpoints such as the bioaccessibility of nutrients and non-nutrients or the digestibility of macronutrients (e.g. lipids, proteins and carbohydrates) are used for screening and building new hypotheses. Various digestion models have been proposed, often impeding the possibility to compare results across research teams. For example, a large variety of enzymes from different sources such as of porcine, rabbit or human origin have been used, differing in their activity and characterization. Differences in pH, mineral type, ionic strength and digestion time, which alter enzyme activity and other phenomena, may also considerably alter results. Other parameters such as the presence of phospholipids, individual enzymes such as gastric lipase and digestive emulsifiers vs. their mixtures (e.g. pancreatin and bile salts), and the ratio of food bolus to digestive fluids, have also been discussed at length. In the present consensus paper, within the COST Infogest network, we propose a general standardised and practical static digestion method based on physiologically relevant conditions that can be applied for various endpoints, which may be amended to accommodate further specific requirements. A frameset of parameters including the oral, gastric and small intestinal digestion are outlined and their relevance discussed in relation to available in vivo data and enzymes. This consensus paper will give a detailed protocol and a line-by-line, guidance, recommendations and justifications but also limitation of the proposed model. This harmonised static, in vitro digestion method for food should aid the production of more comparable data in the future.

https://hal.archives-ouvertes.fr/hal-01209876/document

A standardised static in vitro digestion method suitable for food – an international consensus

This paper reviews the phenolic-compound-extraction systems used to analyse fruit and vegetable samples over the last 10 years. Phenolic compounds are naturally occurring antioxidants, usually found in fruits and vegetables. Sample preparation for analytical studies is necessary to determine the polyphenolic composition in these matrices. The most widely used extraction system is liquid-liquid extraction (LLE), which is an inexpensive method since it involves the use of organic solvents, but it requires long extraction times, giving rise to possible extract degradation. Likewise, solid-phase extraction (SPE) can be used in liquid samples. Modern techniques, which have been replacing conventional ones, include: supercritical fluid extraction (SFE), pressurized liquid extraction (PLE), microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE). These alternative techniques reduce considerably the use of solvents and accelerate the extraction process.

https://www.mdpi.com/1420-3049/15/12/8813/pdf

Phenolic-Compound-Extraction Systems for Fruit and Vegetable Samples

Six species of edible Irish seaweeds; Laminaria digitata, Laminaria saccharina, Himanthalia elongata, Palmaria palmata, Chondrus crispus and Enteromorpha spirulina were screened for potential bioactivity. Extraction of secondary metabolites was carried out using different solvents to determine antioxidant and antimicrobial properties of the dried extracts. The total phenolic contents of dried methanolic extracts were significantly different (p < 0.05). H. elongata exhibited highest phenolic content at 151.3 mg GAE/g of seaweed extract and also had the highest DPPH scavenging activity (p < 0.05) with a 50% inhibition (EC50) level at 0.125μg/ml of extract. H. elongata also had the highest total tannin and total flavonoid contents (p < 0.05) of 38.34 mg CE/g and 42.5 mg QE/g, respectively. Antimicrobial activity was determined using a microtitre method which allowed detection of bacterial growth inhibition at low levels. All methanolic seaweed extracts inhibited the food spoilage and food pathogenic bacteria tested; Listeria monocytogenes, Salmonella abony, Enterococcus faecalis and Pseudomonas aeruginosa, except C. crispus extracts. It was found that dried methanolic extracts of red and green seaweeds had significantly lower antimicrobial activity than the brown species; H. elongata had the highest antimicrobial activity with up to 100% inhibition. In the studied work, the antimicrobial activity of red and green seaweed extracts significantly increased when ethanol and acetone were used as extraction solvents (p < 0.05). Inhibition of E. faecalis with C. crispus extracts increased from 39.28 to 100% when ethanol and acetone were applied as solvents.

/pdf/an-assessment-of-the-antioxidant-and-antimicrobial-activity-17ovpvdza5.pdf

An Assessment of the Antioxidant and Antimicrobial Activity of Six Species of Edible Irish Seaweeds

Phenolic Composition and Antioxidant Properties of Some Spices

Phenolic composition of Flacourtia indica, Opuntia megacantha and Sclerocarya birrea

The objective of the study was to determine and compare the effect of several solvents namely hot water, 50 % methanol, ethanol, 50 % ethanol, acetone, 50 % acetone and ethyl acetate on phenolic composition and free radical scavenging activity in black tea and selected herbal infusions from Zimbabwe and Brazil. For the black tea, made from Camellia sinensis, Quickbrew™ was used. Zimbabwean herbal infusions used were Lippia javanica and Ficus sycamore while those from Brazil were Syzygium jambolanum, Cuphea carthagenensis and Ilex paraguariensis. Total phenolic content and free radical scavenging activity were determined using Folin-Ciocalteu and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, respectively. IC50 values for each solvent were calculated and used to interpret radical scavenging activity. Aqueous organic solvents extracted higher quantities of phenolic compounds than in their absolute organic nature. Acetone (50 %) extracted a higher total phenolic content (TPC) in C. sinensis, L. javanica and I. paraguariensis. Hot water extracted the highest TPC in F. sycamore and S. jambolanum while 50 % ethanol was highest in C. carthagenensis. Free radical scavenging activity (FRSA) was not necessarily in the same order as TPC, indicating that high TPC does not always mean high FRSA and vice versa. The highest FRSA for S. jambolanum and C. carthagenensis extracts was in 50 % ethanol, F. sycamore in 50 % methanol, and I. paraguariensis, C. sinensis and L. javanica extracts in 50 % acetone. Ethyl acetate recorded the lowest TPC and FRSA in all plant samples analysed. Generally, solvent used affected TPC and free radical scavenging activity. Organic solvents may need to be separated from phenolics after extraction, as some of them namely acetone, methanol and ethyl acetate can be toxic to humans. Water and ethanol are the least toxic solvents which may need no further separation from extracts.

Effect of Solvent Type on Total Phenolic Content and Free Radical Scavenging Activity of Black Tea and Herbal Infusions

This study was conducted to identify soluble sugars, non-volatile acids and phenolic compounds in Ziziphus mauritiana fruit. Soluble sugars in Ziziphus mauritiana fruit were qualitatively determined by TLC. The sugars identified to be present in Ziziphus mauritiana were galactose, fructose and glucose. TLC was also used for qualitative analysis of phenolic compounds; five spots of phenolic compounds were observed. Only two of the observed spots were identified using the R
 f values of the standards that were available. The two phenolic compounds identified by TLC were caffeic acid and p-coumaric acid. Phenolic compounds were also quantified using HPLC. Twelve peaks of phenolic compounds were detected. Among these, p-hydroxybenzoic acid, caffeic, ferulic acid and p-coumaric acid were the most abundant with concentrations of 365.94, 30.76, 19.64 and 19.28 mg/kg dry mass respectively, whereas vanillic acid was the least abundant with a concentration of 2.52 mg/kg. The organic acids were qualitatively analysed by PC and citric acid, malonic acid and malic acid were identified in the Ziziphus mauritiana fruit.

Maud Muchuweti

Papers

Phenolic Composition and Antioxidant Properties of Some Spices

Phenolic composition of Flacourtia indica, Opuntia megacantha and Sclerocarya birrea

Effect of Solvent Type on Total Phenolic Content and Free Radical Scavenging Activity of Black Tea and Herbal Infusions

Sugars, organic acid and phenolic compounds of Ziziphus mauritiana Fruit

Effects of Thermal Treatment on the Phenolic Content and Antioxidant Activity of Some Vegetables