title: Physical barriers to carotenoid bioaccessibility. Ultrastructure survey of chromoplast and cell wall morphology in nine carotenoid-containing fruits and vegetables.
abstract: BACKGROUND
  The ultrastructural characterisation of cellular components is a key element in revealing the bases for differences in nutrient bioaccessibility among fruits and vegetables and their derived products. Together, cell walls and chromoplasts constitute the two major physical barriers to carotenoid release from the food matrix (structure) during digestion. In general, larger cells with thinner cell walls are most likely to fail under mechanical pressure. In relation to chromoplasts, the substructures plastoglobuli, crystals and membranes give decreasing rates of carotenoid solubilisation when exposed to digestive forces.
  
  
  RESULTS
  This paper describes cell wall and chromoplast structures in nine carotenoid-storing raw fruits and vegetables. Watermelon and melon cells were shown to have the largest cells concomitant with thin, non-fibrous cell walls, while carrot, hypodermal grapefruit and sweet potato cells were smallest with fibrous or dense cell walls. Mango fruit showed the highest proportion of globules to other substructures. Carrot, papaya and tomato contained many crystalline structures. Finally, watermelon, mango and butternut squash developed a high proportion of membranous structures.
  
  
  CONCLUSIONS
  A more precise description of the physical characteristics of foods that stand as barriers to bioaccessibility can help in understanding which are more or less inhibitory for particular foods.
authors.affiliation: Microscopy Imaging Center, 2257 TAMU, Texas A&M University, College Station, TX 77843, USA. jenn.l.jeffery@gmail.com
authors.forename: Jennifer
authors.initials: J
authors.lastname: Jeffery
authors.forename: Andreas
authors.initials: A
authors.lastname: Holzenburg
authors.forename: Stephen
authors.initials: S
authors.lastname: King
mesh_terms: D001682:Biological Availability; D002338:Carotenoids / Q000032:analysis*; D002473:Cell Wall / Q000648:ultrastructure*; D004032:Diet; D005638:Fruit / Q000033:anatomy & histology / Q000737:chemistry* / Q000648:ultrastructure*; D006801:Humans; D018087:Plastids / Q000648:ultrastructure*; D014675:Vegetables / Q000033:anatomy & histology / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: D002338:Carotenoids