Free Radicals


There is much interest in antioxidants from the perspective of protecting foodstuffs from flavour decay, but increasingly for their potential value in countering afflictions such as cancer, rheumatoid arthritis and inflammatory bowel diseases. Figure 1.25 presents a range of these antioxidants. Many are phenolics and act either by scavenging or by neutralising (reduction) the radicals that effect deterioration or by chelating the metal ions that cause the production of these radicals.

Requirement for oxygen

Reduced glutathione reacts with superoxide and hydrogen peroxide and may represent another protective mechanism, as may sequestration of radicals by transition metals such as copper and iron. Finally, in humans it has been reported that squalene may serve as a scavenger of free radicals and prevent lipid peroxidation in the skin (Kohno et al., 1995). Since yeast cells accumulate squalene in the absence of oxygen a similar mechanism would be plausible. The effects of free radicals are far-reaching and are associated with degenerative processes such as mutagenesis, transformation of cell lines to malignancy and ageing (see Sections, and for implications in yeast). In respect of these effects, no eukaryotic cells are immune, regardless of the presence of the multiplicity of protective mechanisms. Brewing yeast is no exception. It was demonstrated that during an abrupt transition from anaerobiosis to aerobiosis there was a rapid increase in the specific activity of...

Nonenzymatic browning

These are chemical reactions that lead to a brown colour when food is heated. The relevant chemistry is known as the Maillard reaction, which actually comprises a sequence of reactions that occurs when reducing sugars are heated with compounds that contain a free amino group, for example, amino acids, proteins and amines (Fig. 1.22, Table 1.7). In reflection of the complexity of the chemistry, there are many reaction intermediates and products. As well as colour, Maillard reaction products have an impact on flavour and may act as antioxidants. These antioxidants are mostly produced at higher pHs and when the ratio of amino acid to sugar is high. It must also be stressed that some of the Maillard reaction products can promote oxidative reactions. Other Maillard-type reactions occur between amino compounds and substances other than sugars that have a free carbonyl group. These include ascorbic acid and molecules produced during the oxidation of lipids.

Manufacture of fermented olives

The main biological activities associated with oleuropein, hydroxytyrosol, tryosal, verbasco-side, and other phenolic compounds found in olives and olive oil are related to their antioxidant properties (Soler-Rivas et al., 2000). They have been found to inhibit low-density lipoprotein (LDL) oxidation and accumulation of oxidized end products. Oxidation of lipoprotein and other lipids is considered to be an important step in initiating coronary heart disease. Other cardioac-tive effects associated with these phenols include anti-arrhythmic and cardioprotective activities. Olive phenols also protect human cells against oxidative stress and injury. In addition, oxidative damage to DNA may be prevented by the free radical scavenging activity of olive phenols. Food Chem. 50 3688-3692. D'Angelo, S., C. Manna,V. Migliardi, O. Mazzoni, P. Morrica, G. Capasso, G. Pontoni, I Galletti, and V. Zappia. 2001. Pharmacokinetics and metabolism of hydroxytyrosol, a natural antioxidant from olive oil....

Packaging Materials

Packaging is the main preservation technology in the commercialization of food products. Through the correct selection of both materials and packaging technology, food freshness can be maintained to obtain the required shelf life. Traditionally, a package is considered a passive barrier that retards the adverse effect of the environment on the packaged product. The most visual example of such a package is a glass jar. However, packaging science and technology is in constant evolution, and current trends include the development of packaging materials that positively interact with the environment and the food, or even play an active role in the preservation of foods. The use of permeable or perm-selective plastic packages is an example of the former. Finally, active packaging is understood as a packaging system that acts to preserve and improve food quality. This technology makes use of materials that smoothly release antioxidants or fungicides (emitters) into foods or packages or...

Presence Absence of Receptor Ligand Interactions

Free-radical-mediated cellular damage has become an important area of study. In recent years there have been numerous reports that cell death following oxidative stress occur by apoptosis. Moreover, generation of free radicals has been postulated as being a universal triggering event in the induction of apop-tosis (33-38). Indeed, for a period in the early 1990s, it was suggested that the widely studied antiapoptosis gene bcl-2 functioned as an antioxidant (39). However, this theory has been challenged by the demonstration that anoxia-induced apoptosis can also be suppressed by Bcl-2 in the absence of measurable levels of free radicals (8,40,41).

Effect Of Packaging On Quality Changes In Cheeses

Photooxidation may take place by photolytic autoxidation or photosensitized oxidation. Photolytic autoxidation is a direct formation of free radicals initiated by high-energy light such as sunlight (10,000-100,000 1x) (5). However, visible light may also trigger oxidative changes due to the presence of photosensitizers (e.g., riboflavin in cheeses) and oxygen (photosensitized oxidation) (6). Riboflavin is an efficient photosensitizer it readily absorbs visible light energy, thereby exciting the sensitizer to a higher energy level, which makes for reactions with (for example) unsaturated free fatty acids or produces the very reactive singlet oxygen (1O2). Subsequently, the 1O2 reacts with the unsaturated free fatty acids, producing free radicals, lipid hydroperoxides, and finally volatile carbonyl compounds. Many of these photochemical reactions result in autocatalytical oxidative processes, implying that even short light exposure time may have detrimental effects on the stored product...


Kimchi can certainly be ascribed to the combination of these desirable sensory characteristics, there are also nutritional reasons that contribute to the its widespread consumption. For example, kimchi contains appreciable amounts of ascorbic acid (vitamin C), B vitamins, calcium, iron, potassium, dietary fiber, and naturally occurring antioxidants. It is also important to note that kimchi is most often eaten in its uncooked or raw state, and that a live microflora is ordinarily present.

Soy Sauce

New studies show that many soy sauce components also contribute an antioxidant effect when applied to food (23,24). They also contribute an umami taste. Umami is the fifth flavor, coined by the Japanese, added to four basic flavors sweet, salty, sour, and bitter. Often translated as ''savory'' or ''brothy,'' umami can be described as the tongue-coating, meaty flavor of sauteed mushrooms, a juicy steak, or a rich stock (25). Furthermore, soy sauce is found to show antiplatelet activity and its alkaloidal components are responsible. Therefore, it can be considered a functional seasoning (26).

Sulfur Compounds

The other major group of sulfur compounds found in wine are sulfur dioxide (SO2) and related aqueous forms that exist as sulfite ions. These substances are produced naturally by yeast, and are invariably present in wine, albeit at concentrations usually less than 50 mg L. However, sulfur dioxide and bisulfite salts are now commonly added to must due to their strong antimicrobial, antioxidant, and antibrowning properties. It is important to recognize that these activities occur only when the SO2 is in its free, un-bound form.When bound or fixed with other wine compounds, such as acetaldehyde, reducing sugars, and sugar acids, SO2 activity is diminished. How SO2 specifically functions in wine and its important role in wine making will be further discussed later.

Active Packaging

One type of AP is also termed interactive packaging because it actively interacts with the food by removing or adding substances to the internal gas atmosphere in the package or to the food itself. Best known are the oxygen absorbers, which within a short time after the product is packed will have reduced the oxygen content in the package down to a level at which most aerobic microorganisms will stop growing and product oxidation ceases or in some cases even reverts (81). Other absorbers remove carbon dioxide, moisture, off-flavors, or ethylene that otherwise would speed up maturation of fruits and cut flowers. The substances that can be added are antimicrobials, antioxidants, or flavors and, in some cases, color.


Oxidation of fatty acids can be chemical (peroxidation) or enzymatic (h-oxidation) (122). Peroxidation of mainly unsaturated fatty acids is a radical process that leads to the synthesis of hydroperoxides, which are oxidation products but also substrates for the formation of other radicals (RO, ROO, etc.) that propagate the chain reactions. The condensation of two free radicals halts the process and generates secondary oxidation products (aldehydes, alkanes, etc.) (61,123). Oxidation reactions are affected by many factors, such as oxygen content (diameter of sausages), the presence of pro-oxidative compounds (NaCl, metals) or anti-oxidative compounds (nitrite, spices), and the amount of unsaturated lipids