Volume 3 Number 1 2009
Antioxidant Properties of Crops I

Guest Editor

Robert D. Hancock

The Scottish Crop Research Institute, UK


www.scri.ac.uk/

CONTENTS AND ABSTRACTS

David E. Stevenson, Timothy Lowe (New Zealand) Plant-Derived Compounds as Antioxidants for Health - Are They all Really Antioxidants? (pp 1-12)

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ABSTRACT

Invited Review: Numerous epidemiological studies have demonstrated that high consumption of fruits and vegetables correlates with good health and lower incidence of diseases like cancer and cardiovascular disease. It has been widely believed for over 20 years that this can be explained by “antioxidants”. These phytochemicals were thought to “mop up” potentially harmful free radicals when they were produced in excess in the body, as a result of disease or environmental stress. The implication generally drawn from this "antioxidant hypothesis" is that the higher the antioxidant content of the plant foods we eat, the more antioxidants will be in our bloodstream and the healthier and longer lived we will be. Unfortunately, numerous studies carried out to test this hypothesis have produced contradictory evidence and it remains unproven. It appears, however, that both free radicals and phytochemicals can act as signalling molecules and that they can interact with our cellular systems at the molecular level and regulate genes and various biological pathways.  Other health benefits attributed to antioxidants may result from regulation of processes that lead to cancer, cardiovascular and other diseases. Thus there is increasing evidence that the numerous potential health benefits of phytochemicals, many of which are currently labelled as “antioxidants”, arise from mechanisms other than antioxidant capacity. We are only now starting to understand their mechanisms of action, which are much more complex than previously realised. We investigate the latest developments in this increasingly controversial area of research, to find out if science is any closer to understanding this area.

Tony K. McGhie (New Zealand) Fruit Antioxidants: Are they Beneficial for Human Health? (pp 13-21)

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ABSTRACT

Invited Review: There is substantial evidence that links increased consumption of fruits with increased protection from various degenerative diseases, such as cardiovascular disease, some cancers, and the onset of dementia. Fruits contain numerous components that could contribute to this health enhancing effect; many fruit components have the capacity to function as antioxidants, at least in vitro, and the antioxidant properties of fruit foods are often viewed as contributing substantially to the health effect. This review will attempt to describe and summarise the current knowledge about the antioxidant capacity of the major fruit types and the components that are consumed when these fruits are eaten. Although fruit components have substantial antioxidant capacity, as measured by in vitro assays, the significance in vivo of the consumption of fruit antioxidants is far from clear. The review will consider and summarise the research on the effect of fruit antioxidants on human health, with the aim of presenting an overall picture of the current state of knowledge in this area.

Rex Brennan, Julie Graham (UK) Improving Fruit Quality in Rubus and Ribes through Breeding (pp 22-29)

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ABSTRACT

Invited Review: The breeding of new berry fruit cultivars in the UK has in recent years focused more on fruit quality traits than agronomic characters, for both fresh and processing markets. This trend is aligned with increasing consumer awareness of cultivar differentiation in key traits and the perceived health benefits of berry fruit consumption, mainly linked to antioxidant activity of the fruit. The development of markers linked to QTLs for fruit quality traits and the identification of the genes involved has been progressed in berry fruits such as Rubus and Ribes for a number of nutritionally-relevant components and also for sensory characters. Using the phenotypic diversity across the range of germplasm available to breeders, combined with the increasing knowledge of the underlying genetics and regulation of these traits, new breeding strategies are now under development to enable a more rapid production of improved cultivars.

C. B. Rajashekar, Edward E. Carey, Xin Zhao, Myung-Min Oh (USA) Health-Promoting Phytochemicals in Fruits and Vegetables: Impact of Abiotic Stresses and Crop Production Practices (pp 30-38)

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ABSTRACT

Invited Review: Phytochemicals are the primary source of antioxidants in the human diet and play an important role in combating the damaging effects of oxidative stress and other adverse cell responses that can lead to a wide variety of chronic and degenerative illnesses. These phytochemicals typically consist of a wide array of phenolic compounds, ascorbic acid, alpha-tocopherol and carotenoids, and have been shown to promote health and provide protection against a growing list of diseases including various cancers and cardiovascular and neurodegenerative diseases. A significant part of the antioxidants found in plants is the products of plant secondary metabolism, and these antioxidants appear to have similar protective function in plants against oxidative damage caused by various stresses, as they do in animals, including humans. In response to stresses and, more importantly, as an adaptive mechanism, plants tend to shift toward secondary metabolism resulting in the accumulation of protective antioxidants. Accumulation of phytochemicals in response to various abiotic stresses such as high and low temperatures, water stress and high light has been studied in a wide range of plants. Thus, the use of mild and controlled environmental stresses may provide an opportunity to improve the health-promoting qualities of many commonly consumed fruits and vegetables. In addition, a number of factors such as plant nutrition, growing conditions (e.g., open fields, protective environments and organic culture) and crop production and postharvest management practices have also been known to have a significant impact on the phytochemical composition of many fruits and vegetables. The purpose of this review is to characterize the nature of the relationship between these factors and the phytochemical accumulation in fruits and vegetables, which is important in developing potential strategies to improve their quality through enhanced health-promoting and nutritive value.

Eulalia Julitta Borowska^, Agnieszka Narwojsz (Poland) Antioxidant Properties of Berry Fruit Juices as Dependent on Raw Material Quality and Technological Processing: A Review (pp 39-45)

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Invited Mini-Review: Berry fruit juices are characterized by a broad spectrum of bioactive properties, among which particular attention should be paid to antioxidant capacity. The highest antioxidant activity is exhibited by secondary metabolites in plants, primarily by polyphenols (phenolic acids, tannins, a large group of flavonoids and anthocyanins), carotenoids, vitamin C, organic acids, calcium, selenium and other. The antioxidant capacity of fruit juices is influenced by a variety of factors, including raw material quality and the conditions of the technological process. This review focuses on the antioxidant properties of berry fruit juices and on the compounds responsible for those properties, contained in various berry fruit species. The significance of environmental factors, such as climate and agricultural conditions, as well as storage conditions prior to processing, are also discussed. The effect of the technological process of juice production on antioxidant properties was determined, with special emphasis on the conditions of fruit crushing, mash maceration, heat treatment and storage. The advantages and disadvantages of the applied procedures and unit operations are presented. Particular attention was paid to fruit mash maceration with the use of enzymatic preparations obtained from genetically modified microorganisms. It was demonstrated that the antioxidant properties of berry fruit juices may be improved by proper selection of raw materials and by control over the parameters of the technological process.

Dietmar R. Kammerer, Reinhold Carle (Germany) Evolution of Polyphenols during Vinification and Wine Storage (pp 46-59)

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Invited Review: Beginning with the ‘French Paradox’ observations in the 1990’s much interest has been devoted to the profile and contents of plant secondary metabolites, not only of grapes and wines, but also of numerous other plant foods, due to their assumed health-beneficial properties. Grapes belong to the most important fruit crops, and some 80% of this crop is processed into red and white wines. Anthocyanins are the most important phenolic compounds of grapes imparting color to red wines. Together with non-colored phenolic co-pigments they are further characterized by their diverse bioactive attributes, which still need unequivocal proof in most cases. For these reasons, comprehensive efforts have been undertaken to optimize vinification technology in order to maximize extraction rates of polyphenols from the grapes. The present review provides a survey of process strategies applied to achieve this aim, also taking into consideration innovative technologies for the production of both red and white wines. Furthermore, novel findings with regard to the evolution of phenolic compounds in the course of wine aging and storage and to the potential of winemaking by-products as a source for the recovery of phenolic compounds are considered.

Junjie (George) Hao, Laura Li, Maxim Wolf, MengMeng Xu, Becky Brinsko, Mary Yanik, Serena Chen, Lena Binzer, Sarah Green, Christina Hitz, Liangli (Lucy) Yu (USA) Antioxidant Properties and Phenolic Components of Grape Seeds (pp 60-68)

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ABSTRACT

Invited Mini-Review: Grape seeds are primary by-products from grape processing industries. Evaluation of beneficial effects of grape seed components is critical for developing their value-added utilization for improving human health. This review focuses on the antioxidant components and antioxidant properties of grape seeds, as well as the effects of genotype, growing conditions, and post-harvest treatments on antioxidant availability in grape seeds. Also included is a brief summary of factors influencing antioxidant property estimation, along with other health beneficial activities and functionality of grape seed antioxidants. The information may be useful for developing grape seed-derived nutraceuticals and functional food ingredients such as natural antioxidants.

Lorenzo Cerretani, Tullia Gallina Toschi, Alessandra Bendini (Italy) Phenolic Fraction of Virgin Olive Oil: An Overview on Identified Compounds and Analytical Methods for their Determination (pp 69-80)

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ABSTRACT

Invited Review: Among edible oils, virgin olive oil (VOO) has nutritional, technological and sensory characteristics that make it a unique and basic ingredient of the Mediterranean diet. These properties of VOO are attributed not only to the fatty acid composition (high level of oleic acid), which is not significantly different from refined olive oil (ROO), but especially to the high content of phenolic compounds, which are reduced by refining (bleaching and deodorization phases). Phenolic compounds, acting as natural antioxidants, increase the resistance of the oil to storage and heating. Moreover, phenols are the main contributors to the typical tastes of VOO (bitter and pungent attributes), and may also contribute to the prevention of several human diseases. Polar phenolic compounds belong to different chemical classes: phenolic acids, phenyl ethyl alcohols, flavonoids, lignans and secoiridoids. Approximately 50 compounds present in the phenolic fraction have been separated and identified to date, although researchers have not reached a consensus for the correct identification/denomination for many of these compounds. Due to variety of analytical approaches carried out on the complex phenolic pattern of VOO by high performance techniques, some disagreements have been emphasized. The aim of this review paper is to summarize and critically analyze the available information about phenolic compounds in VOO.

Megan Kendall, Marijka Batterham, Paul D. Prenzler, Danielle Ryan, Kevin Robards (Australia) Absorption, Metabolism and Excretion of Phenols Derived from Olive Products (pp 81-91)

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ABSTRACT

Invited Review: The ageing population of many societies has been accompanied by an increase in the incidence of chronic diseases. At the same time, people are more interested in healthy dietary patterns and the use of dietary supplements. It is in this context that olive oil and olive leaf have attracted attention. Both products contain a number of biophenols that have been associated with bioactivity and positive health outcomes. Data indicate that the phenols are absorbed and metabolised and that a minor fraction of the ingested dose is excreted in the urine. This is a necessary pre-requisite to biological activity. However, their metabolic fate remains controversial. The outcomes of in vivo human studies are examined and contrasted with in vitro and animal studies. Furthermore, whether the bioactivity translates into physiological outcomes has not been established conclusively and will depend on development of suitable biomarkers of functionality.

Alejandro Ruiz-Rodriguez, Susana Santoyo, Cristina Soler-Rivas (Spain) Antioxidant Properties of Edible Mushrooms (pp 92-102)

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ABSTRACT

Invited Review: Antioxidants or molecules with radical scavenger capacity gained attention a few years ago because of their potential protective effect against free radical damage. Epidemiological studies have shown that a higher intake of these compounds is associated with lower risk of mortality from cancer and coronary heart disease. Recent scientific studies confirmed that many edible mushrooms, described before by the traditional folklore of Asian culture as medicinal remedies towards a variety of disorders and diseases, indeed contained specific bioactive compounds. These were shown to lower cholesterol levels, to protect against tumours and other disorders, microbes and virus. Most of these properties were directly or indirectly related to the high antioxidant activity exhibited by specific compounds. The bioactive compounds are not yet well defined in all the species. Their antioxidant activity has been associated with minerals such as selenium and zinc. Also biomolecules such as ergothioneine, polysaccharide-protein complexes (β-D-glucans, etc.) phenolic compounds and, in lower quantities, peptides, vitamins A, C, and E (quantification depend on species) have been identified. However, flavonoids and related polyphenols are rare in mushrooms suggesting that these edible fungi might be an interesting source of new bioactive compounds different than plant antioxidants.

David M. Pereira, Patrícia Valentão, Paula B. Andrade (Portugal) Organic Acids of Plants and Mushrooms: Are they Antioxidants? (pp 103-113)

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ABSTRACT

Invited Review: In recent years, it has become evident that significant health risks and benefits are associated with dietary food choice. This association is often attributed to the antioxidants contained in fruits and vegetables. Among those phytochemicals, organic acids may contribute to the protection against various diseases involving oxidative processes, due to their antioxidant potential. In addition, these compounds are well-known for their determinant role in maintaining fruits and vegetables quality and organoleptic characteristics and have also been used in their quality control. Ascorbic acid is, probably, the most widely distributed water soluble antioxidant in plant foods, but other organic acids, like oxalic, tartaric, malic, citric and succinic can also work as antioxidants. In this work, it will be highlighted the potential of organic acids from several matrices (fruits, vegetables, mushrooms and medicinal plants) as antioxidants.