Carotene and Novel Apocarotenoid Concentrations in Orange-Fleshed Cucumis melo Melons: Determinations of β-Carotene Bioaccessibility and Bioavailability

Abstract

Muskmelons, both cantaloupe (Cucumis melo Reticulatus Group) and orange-fleshed honey dew (C. melo Inodorus Group), a cross between orange-fleshed cantaloupe and green-fleshed honey dew, are excellent sources of β-carotene. Although β-carotene from melon is an important dietary antioxidant and precursor of vitamin A, its bioaccessibility/bioavailability is unknown. We compared β-carotene concentrations from previously frozen orange-fleshed honey dew and cantaloupe melons grown under the same glasshouse conditions, and from freshly harvested field-grown, orange-fleshed honey dew melon to determine β-carotene bioaccessibility/bioavailability, concentrations of novel β-apocarotenals, and chromoplast structure of orange-fleshed honey dew melon. β-Carotene and β-apocarotenal concentrations were determined by HPLC and/or HPLC-MS, β-carotene bioaccessibility/bioavailability was determined by in vitro digestion and Caco-2 cell uptake, and chromoplast structure was determined by electron microscopy. The average β-carotene concentrations (μg/g dry weight) for the orange-fleshed honey dew and cantaloupe were 242.8 and 176.3 respectively. The average dry weights per gram of wet weight of orange-fleshed honey dew and cantaloupe were 0.094g and 0.071g, respectively. The bioaccessibility of field-grown orange-fleshed honey dew melons was determined to be 3.2±0.3 percent, bioavailability in Caco-2 cells was about 11%, and chromoplast structure from orange-fleshed honey dew melons was globular (as opposed to crystalline) in nature. We detected β-apo-8’-, β-apo-10’, β-apo-12’-, β-apo-14’-carotenals and β-apo-13-carotenone in orange-fleshed melons (at a level of 1-2% of total β-carotene). Orange-fleshed honey dew melon fruit had higher amounts of β-carotene than cantaloupe. The bioaccessibility/bioavailability of β-carotene from orange-fleshed melons was comparable to that from carrot (Dacus carota).

Two Carotenoid Oxygenases Contribute to Mammalian Provitamin A Metabolism

“…Simultaneously, this BCO1 activity ensures that even long chain ␤-apocarotenoids can be utilized for vitamin A production, thereby providing an explanation for the observed vitamin A activity of these compounds (24). Physiologically, this pathway may play a role after consumption of plants rich in ␤-apocarotenoids such as melons (48). Additionally, it also might be important for the tailoring of asymmetric carotenoids such as ␤-cryptoxanthin for vitamin A production.…”

“…More recently, ␤-apocarotenoids also have been implicated as specific antagonists of these nuclear receptors (26,27). ␤-Apocarotenoids exist in the diet as plant metabolites and/or oxidative breakdown products of carotenoids in food (48,49). Additionally, eccentric oxidative enzymatic cleavage of BC has been proposed as the method to produce these compounds (23).…”

Carotenoid metabolism in mammals, including man: formation, occurrence, and function of apocarotenoids

“…The ability of ␤ -apocarotenoic acids, including ␤ -apo-8 ′ -, ␤ -apo-10 ′ -, ␤ -apo-12 ′ -, and ␤ -apo-14 ′ -carotenoic acid, to inhibit breast tumor cell growth in both estrogen receptor-positive ␤ -Apocarotenoids are present in the diet ( 107,108 ). Processed mango juice, acerola juice, and dried apricots were analyzed by TLC, HPLC, and visible absorption spectra obtained by a photodiode array detector and mass spectra.…”

Naturally Occurring Eccentric Cleavage Products of Provitamin A β-Carotene Function as Antagonists of Retinoic Acid Receptors

“…In mammals, ATRA functions as a hormone agonist for the retinoic acid receptor family of nuclear transcription factors and directly activates several hundred genes, which contain retinoic acid response elements (RAREs) 2 in their promoters (6,7); it is this global effect on the regulation of gene transcription that renders vitamin A essential for embryonic development, growth, and differentiation in mammals, including humans. ␤-Carotene is cleaved eccentrically at double bonds other than the central one to yield ␤-apocarotenals and ␤-apocarotenones (8 -10), molecules that have been detected in foods (11) and in the blood of both humans (12) and animals (13), but whose function in these is unknown. Here, we show that some of these compounds (particularly ␤-apo-14Ј-carotenal, ␤-apo-14Ј-carotenoic acid, and ␤-apo-13-carotenone) function as antagonists of retinoic acid receptors ␣, ␤, and ␥ and block the ATRA-induced activation of endogenous genes that contain RAREs in their promoters.…”