Summary Some of the most exciting research in the last decade has been the discovery of a group of nutrients, which have protective eAects against cell oxidation. These naturally occurring compounds impart bright colour to fruits and vegetables and act as antioxidants in the body by scavenging harmful free radicals, which are implicated in most degenerative diseases. Epidemiological studies have established a positive correlation between the intake of fruits and vegetables and prevention of diseases like atheroscelerosis, cancer, diabetes, arthritis and also ageing. So pronounced has been their eAect on ageing that they have been called ‘fountains of youth’. Fruits and vegetables have thus had conferred on them the status of ‘functional foods’, capable of promoting good health and preventing or alleviating diseases. Phenolic flavonoids, lycopene, carotenoids and glucosinolates are among the most thoroughly studied antioxidants. The present review highlights the potential of fruits and vegetables rich in antioxidants, their health benefits and the eAect of processing on the bioavailability of these nutrients. The paper also reviews some of the important methods used to determine the antioxidant activity.

Antioxidants in fruits and vegetables – the millennium’s health

Nutritional factors are widely considered to be critical for human health. Overwhelming evidence from epidemiological studies indicate that diets rich in fruit and vegetables are associated with a lower risk of several degenerative diseases. These results have created a new perspective concerning the potential of diet in preventing serious diseases in the future. However, the health-promoting capacity of fruit and vegetables strictly depends on their processing history. This aspect has been generally neglected or scarcely considered in present nutritional and epidemiological studies. Processing is expected to affect content, activity and bioavailability of bioactive compounds. The aim of this article, therefore, is to review the effects of processing on the antioxidant properties of foods by means of a multidisciplinary approach. It is believed that the implications of this challenging and rapidly advancing area may contribute to enhanced industrial competitiveness as well as consumer health and well-being.

Influence of processing on the antioxidant properties of fruit and vegetables

Browning reactions represent an interesting research area for the implications in food technology, nutrition and health. The development of some non-enzymatic browning reactions, such as Maillard reaction, has been recently associated to the formation of compounds with strong antioxidant capacity. In this paper, the relation between colour changes due to non-enzymatic browning and the formation of compounds with antioxidant activity is discussed. Simple positive or complex correlation between colour and antioxidant properties can be found depending on composition and technological history of the product. Complex relations between these variables are generally obtained in multi-component and in formulated foods, where the simultaneous development of a number of reactions, interacting or prevailing Maillard reaction itself, can affect in opposite ways the overall antioxidant properties and colour of the product.

Review of non-enzymatic browning and antioxidant capacity in processed foods ☆

Influence of heating on antioxidant activity and the chemical composition of some spice essential oils

CHAPTER 2 – Free Radical Mechanisms of Lipid Damage and Consequences for Cellular Membranes

To approximate in a model system the autoxidation of monomolecular layers of lipids on the cell surfaces of freeze-dried foods, the autoxidation of presumed monolayers of linoleic acid adsorbed from solution onto silica gel has been studied as a function of time and α-tocopherol and acid synergist content The method of Honn, Bezman and Daubert was used, modified by the substitution of linoleic acid for soybean oil and the use of gas chromatography to follow oxygen disappearance at 80 C It was found that adsorption of linoleic acid onto silica gel from petroleum ether solution conforms to a Langmuir isotherm, consistent with the formation of a monolayer Confirming the finding of Honn et al with soybean oil, it was found that the most rapid uptake of oxygen occurred at a linoleic acid-silica ratio close to that for the monolayer Without included antioxidant, oxidation commences at a nearly linear rate without observable induction period Time for consumption of one-half mole of oxygen per mole of linoleic acid is ca 60 min on acid-washed silica If very small amounts of α-tocopherol are included in the layer, virtually no oxygen uptake measurable in this system occurs during an induction period, the length of which is approximately proportional to tocopherol content The inflection point at the commencement of rapid oxidation is very sharp; the ensuing oxidation rate approximates that of the unprotected acid The induction period of linoleic acid with the same tocopherol content is as much as 100% longer when exposed in monolayer than in a bulk form However the rate after commencement of rapid oxidation is 8–10 times greater in the monolayer Acid washing of the silica reduced its iron content by 75% Acid washing also reduced by 60% the rate of autoxidation without α-tocopherol and increased the length of the induction period four-fold when α-tocopherol was present The effect of pretreatment of the silica by adsorption of the acid synergists, ascorbic, phosphoric, citric and ethylenediamine tetraacetic acid was qualitatively similar to the effect of acid washing The synergists extended the induction period in increasing order as listed, EDTA producing a 100-fold extension For ascorbic acid the rate reduction and increase of induction period were not found on unwashed silica and were dependent on the extent of washing These findings are consistent with synergist sequestration of metals in a complex that is ineffective in new chain generation by perioxide decomposition

Effects of surface concentration, metals and acid synergists on autoxidation of linoleic acid monolayers on silica

There is evidence that an addition compound of oxidizeddl-alpha-tocopherol and linoleic acid is formed when the components are absorbed in mixed monolayer on silica gel at a molecular ratio of 1∶20, and subjected to heating in air at 80C. A relatively nonpolar tocopheryl quinone is also formed in smaller amounts. These are the major tocopherol oxidation products isolated in this system and do not correspond to any known to the authors. The addition compound has about the same mobility as linoleic acid in most thin layer chromatography (TLC) and chromatographic systems, but can be isolated by successive chromatography on silica and gel filtration on Sephadex LH-20. It yields a single spot in TLC in several systems. The elemental analysis is reproducible and consistent with a simple addition compound of linoleic acid and bivalently oxidized tocopherol. The compound has a carboxyl group which can be esterified. The ester has about the same TLC mobility as methyl linoleate. The molecular weight of the ester is 722.6. The UV spectrum shows a single peak, 2
 max
 ETOH
 =3000 A, E=4.74. The IR spectrum shows a very strong chroman ether band at 9.12 μ, a strong methyl band at 7.24 μ and carboxyl but no hydroxyl absorption. The NMR spectrum shows, in contrast to that of tocopherol, a reduction in aromatic methyl protons, a carboxyl proteon exchangeable with deuterium oxide, but no hydroxy proton. The compound does not reduce Emmerie-Engel reagent prior to treatment with concentrated hydriodic acid, nor do the ether-extractable products after such treatment. The present data are consistent with an addition product whose bridging group is a new chroman ring.

An addition compound of oxidized tocopherol and linoleic acid

Some naturally occurring and synthetic phenolic antioxidants have been evaluated in a dry model system simulating the exposure of lipids in freeze-dried membranes of whole tissue foods. The system is a linoleic acid monolayer on activated silica gel autoxidized at 80°C in dry air. The system is dry and porous and the demonstrated monolayer adsorption and restricted translational mobility of the lipid present a plausible model of freeze-dried membrane characteristics. Although relative effectiveness of the common antioxidants in this system has some similarities to the reported order in other dry systems, there are notable exceptions. For example, butylated hydroxyanisole is by far the most effective antioxidant in the silica system whereas it is reported to be much less effective than propyl gallate in bulk oils and some other dry systems. Thus, special conditions appear to modify antioxidant effectiveness in the lipid monolayer on silica.

Evaluation of some natural and synthetic phenolic antioxidants in linoleic acid monolayers on silica

Flavor deterioration of salad dressings was investigated to determine the effect of hydrogenation of the oil. additives and storage conditions. Flavor quality tests were developed and correlated with gas chromat­ ographic analyses of volatile compounds in oils separated from the dressings. Hydrogenation of soybean oil with copper and nickel ca­ talysts effectively increased the storage stability of salad dressings at 21°C but not at 32°C. The use of BHA as an antioxidant in the oil or EDTA as a metal inactivator in the starch base as well as nitrogen packaging were effective in prolonging the storage stability of salad dressings made with unhydrogenated soybean oil. Therefore, these additives or nitrogen packaging may provide economic substitutes for hydrogenation of soybean oil used in salad dressings.

Storage Stability of Soybean Oil-Based Salad Dressings: Effects of Antioxidants and Hydrogenation

Autoxidation reactions of linoleic acid and tocopherol and of mixtures of the two have been monitored in the dry monolayer state while adsorbed on silica gel, by means of silica slurry spectrophotometry and oxygen uptake measurements. The UV absorbance of the products of linoleic acid alone is similar to that of previously characterized compounds, but that from tocopherol is not referable to any oxidation products known to the authors, regardless of whether the determination is made while adsorbed on silica or on the extracted products. Two compounds, designated A and B, having absorbance in ethanol at 2610–2670 and 3000 A, respectively, are the major products of tocopherol oxidation detectable by UV above 2200 A. They are a tocopheryl quinone without a hydroxyl group and an adduct of linoleic acid and oxidized tocopherol. The product distribution suggests that tocopherol may have a restricted migration in this system.

W. L. Porter

Papers

Effects of surface concentration, metals and acid synergists on autoxidation of linoleic acid monolayers on silica

An addition compound of oxidized tocopherol and linoleic acid

Evaluation of some natural and synthetic phenolic antioxidants in linoleic acid monolayers on silica

Storage Stability of Soybean Oil-Based Salad Dressings: Effects of Antioxidants and Hydrogenation

UV Spectrophotometry of autoxidized lipid monolayers while on silica gel