## 3 Bio-Functional Compounds and Health Benefits of Kiwi Fruit and Its Juice
### Kiwi Nutritional Value and Bioactive Composition
#### 3.2.1 Kiwi Vitamins  
With respect to the nutrients present in kiwi-derived juices, vitamin C, vitamin E, and folate are present in high percentages in these kiwi products (Figure 1). Vitamin C, commonly known as ascorbic acid, is a vital vitamin for humans, which is obtained from various plants and animal products that can synthesize it. Our need for the daily intake of vitamin C stems from the fact that we cannot produce it, due to a gene mutation of an enzyme that is essential in the series of reactions for its formation. The raw material, sugars, and relatively simple chemical synthesis process make understandable, the increased concentration of this vitamin in fruits and vegetables, and in quantitatively large amounts compared to other types of vitamins, especially in kiwi fruit. Its main properties, and according to which it is extremely useful for humans, are its involvement as a co-enzyme in collagen formation, as well as its potent antioxidant capacity, that is, the neutralization of free radicals and particularly reactive oxygen and/or nitrogen species (ROS/RNS), which offers protection from oxidative stress damage. Its deficiency in humans is reported to be associated with signs of fatigue and lethargy, while its additional properties as a co-factor in enzymes have also been reported in dopamine neurotransmission and hormone synthesis pathways [15, 18, 19, 20]. Another important vitamin present in kiwi is vitamin E. This vitamin encompasses a group of fat-soluble compounds referred to as docochromanols, specifically chromatan-6-ols. These can be further classified into tocopherols (\(\alpha\)-, \(\beta\)-, \(\gamma\)-, and \(\delta\)-tocopherol) and tocopherols (\(\alpha\)-, \(\beta\)-, \(\gamma\)-, and \(\delta\)-tocotrienols). Vitamin E consists of each or of all these eight forms, which are produced by plants like kiwi through the utilization of homogentisic acid. It can be defined as a robust chain-breaking antioxidant, which hampers the generation of ROS molecules both when lipid oxidation occurs and in the midst of the dissemination of free radical reactions. The primary effect of \(\alpha\)-tocopherol is to capture and counteract the free radicals present. Consequently, vitamin E can protect against the onset of chronic diseases that are linked to oxidative stress [21]. For some years, it was widely believed that the primary source of vitamin E in kiwi fruit was the seeds, which were thought to contain a significant amount of the vitamin due to their high lipid content. However, the seeds were known to be resistant to digestion, making the vitamin E in them largely unavailable. [PERSON] and colleagues demonstrated that \(\alpha\)-tocopherol is present in the flesh of the kiwi too, potentially linked to the cellular membranes of the fruit cells, with potentially higher bioavailability compared to that of the seeds. The presence of vitamins in the flesh of kiwi has a significant role, as it enhances the organization of membrane lipids, resulting in a more tightly packed membrane. This increased stability of the cell membrane is crucial for the overall health and functioning of the cells in kiwi fruit. Vitamin E plays a vital role in promoting membrane repair in mammalian cells too, by preventing the occurrence of oxidized phospholipids [11, 15, 21].