Biochemical, physiological and transcriptomic strategies to study the relationship between carotenoids, oxidative stress and Citrus fruit quality

Abstract

Citrus fruits are the most cultivated fruit crop for human consumption worldwide, accounting for more than 100 million TM per year. Brazil is responsible for approximately ¼ of that production, mostly oranges. In the Mediterranean, Spain produces around 22 million TM/year with a high diversity of products. Regarding human nutrition, the regular consumption of citrus fruits has been associated with lower occurrence of chronic-degenerative diseases, especially those with a redox-triggering mechanism, involving reactive oxygen/nitrogen species (RONS). At least part of the health benefits provided by regular uptake of citrus fruits in diet comes from their carotenoid (as antioxidants and pro-vitamin A agents) and ascorbic acid (also an antioxidant and a co-factor for hydroxilases) contents. These micronutrients are responsible for preventing cellular oxidative modifications by RONS during regular aerobic metabolism, or under more (oxidative) challenging conditions in pathological processes. A diversity of colors in citrus fruits relates with a vast composition of carotenoids in peel and pulp, e.g. alpha-carotene, beta-carotene, beta-cryptoxanthin, and lycopene. Therefore, different carotenoid/ascorbate contents in citrus could, hypothetically, provide extracts with a wide range of antioxidant activities for human consumption, depending on their form of absorption, bioavailability, etc. The study of carotenogenesis in citrus related to their antioxidant capacity could shed light about their contribution in human nutrition, with a putative implication for preventing redox-mediated diseases. In addition, carotenoids and ascorbic acid are also involved in the prevention of chilling injury in citrus fruits, which is a pivotal issue concerning storage, conservation, and the commercial value of their products. Since 2003, the "Postharvest Physiology and Fruit Quality Laboratories", at the Institute of Agricultural Chemistry and Food Technology (IATA-CSIC, Valencia, Spain) study the biosynthesis and accumulation of carotenoid compounds in citrus, mostly by transcriptomic techniques (RNAseq.) in order to better understand the link between genomic information, regulatory pathways, mutations, and the quality of the end-products. The aims of this project are: (i) evaluate the participation of carotenoids in the preservation of post-harvested citrus fruits against chilling injuries; and (ii) study the antioxidant capacity of carotenoids (in synergism with ascorbic acid) and the nutritional value of citrus fruits, by applying classic biochemical assays (ORAC, ABTS, etc.), but also testing carotenoid-rich extracts from different citrus (including mutational products) in biomimicking membranes (liposomes) loaded with redox-sensitive probes, as C11-BODIPY 581/591. (AU)