Die phenolischen Inhaltsstoffe des Obstes: I. Bisherige Kenntnisse �ber Vorkommen, Gehalte sowie Ver�nderungen w�hrend des Fruchtwachstums

Enzymatic browning reactions in apple and apple products

This review examines the parameters of enzymatic browning in apple and apple products that is, phenolic compounds, polyphenoloxidases, and other factors (ascorbic acid and peroxidases), both qualitatively and quantitatively. Then the relationships between intensity of browning and the browning parameters are discussed, including a paragraph on the methods used for browning evaluation. Finally, the different methods for the control of browning are presented.

Vegetables, fruit, and cancer. II. Mechanisms

The epidemiologic literature on the relationship between vegetable and fruit consumption and human cancer at a variety of sites was reviewed systematically in Part I. It was concluded that consumption of higher levels of vegetables and fruit is associated consistently, although not universally, with a reduced risk of cancer at most sites, and particularly with epithelial cancers of the alimentary and respiratory tracts. Possible mechanisms by which vegetable and fruit intake might alter risk of cancer are addressed here. A large number of potentially anticarcinogenic agents are found in these food sources, including carotenoids, vitamins C and E, selenium, dietary fiber, dithiolthiones, glucosinolates and indoles, isothiocyanates, flavonoids, phenols, protease inhibitors, plant sterols, allium compounds, and limonene. These agents have both complementary and overlapping mechanisms of action, including the induction of detoxification enzymes, inhibition of nitrosamine formation, provision of substrate for formation of antineoplastic agents, dilution and binding of carcinogens in the digestive tract, alteration of hormone metabolism, antioxidant effects, and others. It appears extremely unlikely that any one substance is responsible for all the associations seen. Possible adverse effects of vegetable and fruit consumption are also examined. One way to consider the relationships reviewed here is to hypothesize that humans are adapted to a high intake of plant foods that supply substances crucial to the maintenance of the organism, but only some of which are currently called 'essential nutrients.' Cancer may be the result of reducing the level of intake of foods that are metabolically necessary--it may be a disease of maladaptation.

Occurrence and content of hydroxycinnamic and hydroxybenzoic acid compounds in foods

Phenolic acid compounds seem to be universally distributed in plants. They have been the subject of a great number of chemical, biological, agricultural, and medical studies. Hydroxycinnamic acid compounds occur most frequently as simple esters with hydroxy carboxylic acids or glucose, while the hydroxybenzoic acid compounds are present mainly in the form of glucosides. Furthermore, phenolic acids may occur in food plants as esters or glycosides conjugated with other natural compounds such as flavonoids, alcohols, hydroxyfatty acids, sterols, and glucosides. Also, hydroxycinnamic acid amides appear to be common constituents. The occurrence of the different natural phenolic acid compounds in foods is reviewed, and data of the content in fruit, vegetables, and spices are given. The distribution of the main phenolic acid compounds in food plants as well as their changes during development and maturation of fruits are considered. Furthermore, the hydroxycinnamic acids bound to cell wall polymers, the phenolic acid compounds in coffee, cereals, oil seed, and tree nuts, and the analysis of phenolic acid derivatives are reviewed.

Polyphenol oxidase and peroxidase in fruits and vegetables

Polyphenol oxidases and peroxidases are among the most studied enzymes in fruits and vegetables. Owing to the deleterious effects of discoloration and off-flavor formation induced by their actions, these enzymes have not ceased to be a matter of concern to food technologists, while their versatility as catalyst and their diversity as protein present a challenge to the biochemist. This article gives an account on the present state of knowledge in this field. The occurrence of polyphenol oxidases and peroxidases in food and food raw materials, and their role and importance in food processing are briefly outlined. Results of biochemical research including catalytic properties, substrate specificity, susceptibility towards pH and temperature, action of inhibitors, isolation, purification, and characteristics of the enzymes are given, with special emphasis on recent achievements based on high resolution separation and isoenzyme techniques. Finally, the behavior of polyphenol oxidase and peroxidase in selected major groups of fruits and vegetables is discussed. Some contradictions found in the literature are pointed out and some questions that have not been given the necessary attention by researchers so far are mentioned.

[On the metabolism of sulphur dioxide in apples (author's transl)]

Apples of the two varieties, Boskoop and Brettacher, were exposed to 35S labeled sulphur dioxide. After storage at several conditions the distribution of 35S-activity among the three fractions, sulphite, sulphate and sulphonate was examined. The major portion of the radioactivity was found in the sulphate fraction. The activity decreased remarkably from the peel towards the core. Appreciable differences in distribution patterns were found between the two apples varieties.

[The phenolics of fruits. VIII. Changes in flavonol concentrations during fruit development (authors transl)]

In black currants the contents of quercetin- and especially of myricetin glycosides increased during ripeness very considerably. The myricetin level in ripe fruits of cultivated blueberries and the quercetin level in ripe berries of privet was higher than in unripe. However, the concentrations of kaempferol and quercetin glycosides were in most of the fruits (e.g. red and white currants, sour cherries, plums, cultivated blueberries, elderberries) smaller than in unripe fruits. Anthocyanin formation is therefore not combined with an accumulation of flavonols (perhaps with the exception of myricetin).

The phenolics of fruits. VII. The phenolics of cherries and plums and the changes in catechins and hydroxycinnamic acid derivatives during the development of fruits

Quantitative data of hydroxycinnamic acids, hydroxybenzoic acids and hydroxycoumarins (after hydrolysis of derivatives) and of catechins are given. -Large quantities of catechins and hydroxycinnamic acid derivatives are found in the young fruit. Related to mg per kg fresh weight these concentrations soon decline sharply, especially during the progressive growth of the fruits. Related to mg per fruit, the concentrations of catechins increase progressively with fruit development, showing a loss when reaching maturity. The concentrations of hydroxycinnamic acids increase in a similar manner, but show in part a remarkable loss when examined after removal of the harder seeds.

[V. The phenolics of strawberries and their changes during development and ripeness of the fruits (author's transl)]

16 strawberry varieties contained ca. 10--70 mg (+)-catechin per kg freshweight, frequently up to 10 mg (-)-epicatechin, seldom (+)-gallocatechin and never (-)-epigallocatechin. The phenolic contents after hydrolysis were up to ca. 10 mg caffeic acid, ca. 10--15 mg p-coumaric acid, ca. 10--35 mg 4-hydroxybenzoic acid, up to 6 mg protocatechuic acid and ca. 10--40 mg gallic acid per 1000 g freshweight. From "Senga Sengana" ca. 10 mg/kg methyl gallate and ellagic acid were isolated. Salicylic acid, gentisic acid and vanillic acid were found in traces (1 mg/kg). The concentrations of all the examined phenolic acids, relating to the whole fruit (mg per fruit) increased, and, relating to fresh weight (mg per kg) decreased during the growth of the fruits with exception of 4-hydroxybenzoic acid. This acid appeared only in a relatively late stage of the fruit. The changes in catechins were similar. In the ripe fruit the catechin level was reduced a little.

[The phenolics of fruits. VI. The phenolics of currants, gooseberries and blueberries. Changes in phenolic acids and catechins during development of black currants (author's transl)]

Black, red, and white currants, gooseberries and cultivated blueberries contained only small amounts of catechins (total up to 30 mg per kg). Hydroxycinnamic acid derivatives, especially of caffeic and p-coumaric acid, occured mostly in higher concentrations. Furthermore, 4-hydroxygenzoic acid, protocatechuic acid and gallic acid were found after hydrolysis in currants and only protocatechuic acid in gooseberries in different levels. Salicyclic and gentisic acid were found in traces up to 2 mg per kg, occassionally vanillic acid, syringic acid or isoferulic acid. The concentrations of the examined phenolic acids in black currants related to the whole fruit (mg per fruit) increased, and related to fresh weight (mg per 1000 g) decreased during the growth of the fruits with the exception of protocatechuic acid, which appeared mostly in a last stage of the fruit.