Vitamin C and the Role of Citrus Juices as Functional Food

Abstract

The literature on the content and stability of vitamin C (ascorbic acid, AA) in citrus juices in relation to industrial practices is reviewed. The role of vitamin C from citrus juices in human diet is also reviewed. Citrus fruits and juices are rich in several types of bioactive compounds. Their antioxidant activity and related benefits derive not only from vitamin C but also from other phytochemicals, mainly flavonoids. During juice processing, temperature and oxygen are the main factors responsible for vitamin C losses. Non-thermal processed juices retain higher levels of vitamin C, but economic factors apparently delay the use of such methods in the citrus industry. Regarding packing material, vitamin C in fruit juice is quite stable when stored in metal or glass containers, whereas juice stored in plastic bottles has a much shorter shelf-life. The limiting step for vitamin C absorption in humans is transcellular active transport across the intestinal wall where AA may be oxidized to dehydroascorbic acid (DHAA), which is easily transported across the cell membrane and immediately reduced back to AA by two major pathways. AA bioavailability in the presence of flavonoids has yielded controversial results. Whereas flavonoids seem to inhibit intestinal absorption of AA, some studies have shown that AA in citrus extract was more available than synthetic ascorbic acid alone. DHAA is reported to possess equivalent biological activity to AA, so recent studies often consider the vitamin C activity in the diet as the sum of AA plus DHAA. However, this claimed equivalence should be carefully reexamined. Humans are one of the few species lacking the enzyme (L-gulonolactone oxidase, GLO) to convert glucose to vitamin C. It has been suggested that this is due to a mutation that provided a survival advantage to early primates, since GLO produces toxic H 2 O 2. Furthermore, the high concentration of AA (and DHAA) in neural tissues could have been the key factor that caused primates (vertebrates with relative big brain) to lose the capacity to synthesize vitamin C. Oxidative damage has many pathological implications in human health, and AA may play a central role in maintaining the metabolic antioxidant response. The abundance of citrus juices in the Mediterranean diet may provide the main dietary source for natural vitamin C.

Dietary factors and pancreatic cancer: The role of food bioactive compounds

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Comparison of ascorbate metabolism in fruits of two citrus species with obvious difference in ascorbate content in pulp

“…Citrus fruit and related products are rich in ASC (Nagy, 1980). They are widely consumed as a functional food in the world and provide an important source of ASC for human health (Martí et al, 2009). The ASC content in citrus fruit juice sacs is 20-100 mg per 100 mL juice, which varies greatly depending on species or variety (Nagy, 1980;Lee and Kader, 2000).…”

Interactions between Vitamin C and Nanocolloidal Silver Particles Studied by Cyclic Voltammetry and UV‐Vis Spectrophotometry

“…The authors have been reported a first‐order kinetics for vitamin C degradation and corresponding activation energy ranging between 12 and 25 kcal ⋅ mol −1 . The initial concentration of dissolved oxygen has a major impact on vitamin C degradation to dehydroascorbic acid and 2,3‐diketogulonic acid . The UV irradiation of fruits and vegetables, before and after harvest may be considered an efficient method for enhancing the content of antioxidant compounds .…”