Bioactive compounds of citrus as health promoters

Citrus are a group of fruit species, quite heterogeneous in many aspects, including chemical composition of the fruit. Since ancient times, some citrus fruits were used to prevent and cure human diseases. In the recent decades, it has been demonstrated that fruits can actually help prevent and cure some diseases and above all, they are essential in a balanced diet. Citrus fruits, as one of the groups of fruit species, with greater importance in the world, have been studied for their effects on human health. Some species of citrus were referred as potential antioxidant based therapy for heart disease, cancer and inflammation. Fruit peels and seeds have also high antioxidant activity. The health benefits of citrus fruit have mainly been attributed to the high level of bioactive compounds, such as phenols (e.g., flavanone glycosides, hydroxycinnamic acids), carotenoids and vitamin C. These compounds are present in the fruit pulp and hence in the juice. But some bioactive compounds can be found in parts of the fruit which usually are not used for human food. The content of bioactive compounds depends on the species and cultivar, but also depends on the production system followed in the orchard. Citrus fruits, their derivatives and their by-products (peel, pulp and oil) are reach in different bioactive compounds and its maturity, postharvest and agroindustry processes influence their composition and concentration. The aim of this chapter was to review the main bioactive compounds of the different components of citrus and their relationship to health.

Differential effects of low-temperature inhibition on the propylene induced autocatalysis of ethylene production, respiration and ripening of 'Hayward' kiwifruit

Previous studies (Stavroulakis and Sfakiotakis, 1993) have shown an inhibition of propylene-induced ethylene production in kiwifruit below a critical temperature range of 11-14.8 degrees C. The aim of this research was to identify the biochemical basis of this inhibition in kiwifruit below 11-14.8 degrees C. 'Hayward' kiwifruit were treated with increasing propylene concentrations at 10 and 20 degrees C. Ethylene biosynthesis pathways and fruit ripening were investigated. Kiwifruit at 20 degrees C in air started autocatalysis of ethylene production and ripened after 19 d with a concomitant increase in respiration. Ethylene production and the respiration rise appeared earlier with increased propylene concentrations. Ripening proceeded immediately after propylene treatment, while ethylene autocatalysis needed a lag period of 24-72 h. The latter event was attributed to the delay found in the induction of 1-aminocyclopropane-1-carboxylate synthase (ACC synthase) activity and consequently to the delayed increase of l-aminocyclopropane l-carboxylic acid (ACC) content. In contrast propylene treatment induced 1-aminocyclopropane-1-carboxylate oxidase (ACC oxidase) activity with no lag period. Moreover, transcription of ACC synthase and ACC oxidase genes was active only in ethylene-producing kiwifruit at 20 degrees C. In contrast, treatment at 10 degrees C with propylene strongly inhibited ethylene production, which was attributed to the low activities of both ACC synthase and ACC oxidase as well as the low initial ACC level. Interestingly, fruit treated with propylene at 10 degrees C appeared to be able to transcribe the ACC oxidase but not the ACC synthase gene. However, propylene induced ripening of that fruit almost as rapidly as in the propylene-treated fruit at 20 degrees C. Respiration rate was increased together with propylene concentration. It is concluded that kiwifruit stored at 20 degrees C behaves as a typical climacteric fruit, while at 10 degrees C behaves like a non-climacteric fruit. We propose that the main reasons for the inhibition of the propylene induced (autocatalytic) ethylene production in kiwifruit at low temperature (less than or equal to 10 degrees C), are primarily the suppression of the propylene-induced ACC synthase gene expression and the possible post-transcriptional modification of ACC oxidase.

Citrus as a component of the Mediterranean Diet

Citrus are native to southeastern Asia, but are present in the Mediterranean basin for centuries. This group of species has reached great importance in some of the Mediterranean countries and, in the case of orange, mandarin and lemon trees, they found here soil and climatic conditions which allows them to achieve a high level of fruit quality, even better than in the regions where they came from. Citrus fruits are present in the diet of the peoples living on the Mediterranean basin, at least since the time of the Roman Empire. In the 20th century they became the main crop in various agricultural areas of the Mediterranean, playing an important role in the landscape, in the diet of the overall population, and also in international trade. They are present in the gardens of palaces and monasteries, but also in the courtyards and orchards of the poorest families. Their fruits are not only a refreshing dessert, but also a condiment, or even a major component of many dishes. Citrus fruits have well-documented nutritional and health benefits. They can actually help prevent and cure some diseases and, above all, they are essential in a balanced and tasty diet.