Effects of uvb light, wounding stress and storage time on the biosynthesis of betalains, phenolic compounds and ascorbic acid in red prickly pears (opuntia ficus-indica cv. Rojo vigor)

UVB light In the past years, abiotic stresses such as wounding and ultraviolet radiation have been studied as an effective tool to improve the accumulation of bioactive phytochemicals in fresh produce. Postharvest application of UVB-radiation and wounding stress induces the accumulation of secondary metabolites in horticultural crops. However, there are few studies evaluating the combined effects of both stresses Therefore, the present thesis evaluated, on the one hand, the separated and combined effects of UVB radiations and wounding stress on the total content of betalains, phenolic compounds and ascorbic acid in red prickly pear (Opuntia Ficus-Indica cv. Rojo Vigor) treated with UVB light (6.4 W•m-2) for 0, 15, 90 and 180 min, before and after storage (24 h at 16 °C); and on the other hand, the effects of UVB radiations and wounding stress, alone or in combination, on the profile of individual betalains and phenolic compounds, as well as the activity of the enzymes involved in their biosynthesis, in red prickly pear treated with UVB light (6.4 W•m-2) for 0 and 15 min, before and after storage (24 h at 16 °C). The highest phenolic accumulation occurred 24 h after UVB treatment (15 min) in whole pulp and peel, increasing by 125.8% and 33.8%, respectively. In the whole fruit pulp, there was a significant increment in kaempferol (64.5%), sinapoyl malate (187.7%), 1-O-β-D-Glucopyranosyl sinapate (57.7%), rosmarinic acid (584.5%), vanillic acid (15.1%), sinapic acid (23.3%), quercetin3-O-glucoside (28.4%) and kaempferol 3-O-sophoroside-7O-glucoside (57.7%). On the other hand, the whole fruit peel showed an increment in the content of kaempferol (631.5%), sinapoyl malate (172.7%), 1-O-β-D-Glucopyranosyl sinapate (505.7%), rosmarinic acid (394.5%), p-coumaric (53.9%), sinapic acid (639.3%), quercetin3-O-glucoside (133.4%), kaempferol 3-Oglucoside (160.9%), quercetin (425.2%) and kaempferol 3-O-sophoroside-7O-glucoside (63.7%). The increment in the PAL activity (1173.5% in pulp and 239.3% in peel) after 12 h of storage corresponds to the increment in content of phenolics. The highest betalain accumulation occurred 24 h after UVB treatment (15 min) in whole pulp and wounded peel, increasing by 49.8% and 33.1%, respectively. The whole fruit pulp showed a significant increment in muscaaurin VII (293.6%), indicaxanthin (316%), betanin (26.2%) and iso-betanin (70.6%); whereas vulgaxanthin III (-21.1%), betanidin (-78.9%), neobetanidin (-87.3%) and gomphrenin (-55.4%) decreased. On the other hand, the wounded fruit peel showed a significant increment in muscaaurin VII (33.2%), indicaxanthin (159.1%), betanin (161.8) and iso-betanin (98.7%). The increment in the TYR hydroxylase (744.1% in pulp and 332.9% in peel) and TYR oxidase activity (81.6% in pulp and 59.2% in peel), as well as cyclo- Dopa formation (637.2% in pulp and 439.3% in peel) after 12 h of storage corresponds to the increment in content of betalains. The highest ascorbic acid accumulation occurred 24 h after UVB treatment in wounded pulp and peel, increasing by 67.2% and 84.6%, respectively. The increment in the GalLDH activity (85.4% in pulp and 502.3% in peel) after 12 h of storage corresponds to the increment in content of ascorbic acid.Results indicated that the application UVB light alone or combined with wounding stress in red prickly pear can be used as an effective strategy to induce the accumulation of secondary metabolites with potential application in the food, dietary supplements and pharmaceutical industries; since these postharvest treatments are low cost, have no legal restrictions, and do not require complex equipment.