Total and free amino acids composition of the peel and pulp from the fruits of seven Mexican <i>Opuntia</i> species

Mexico presents the highest diversity of Opuntia species in the world. Determination of the amino acid composition of Opuntia fruits provides interesting information on the nutritional quality, potential health benefits, and industrial applications of these fruits. Hence, the total and free amino acid compositions of the fruits of seven Opuntia species from México have been analyzed by RP-HPLC. These species are O. ficus-indica, O. albicarpa, O. undulata, O. megacantha, O. robusta, O. dillenii, and O. joconostle. Protein contents were, in general, higher in the peel than in the pulp, ranging in the peel from 1.95 % in O. dillenii to 4.91 % in O. robusta, and in the pulp from 0.10 % in O. ficus-indica to 11.91% in O. joconostle. Main amino acids in the peel were Asp, Glu and Leu, and Asp, Glu, and Ala in the pulp. The proteins with the highest nutritional value were found in the peel from O. dillenii, and O. megacantha, and in the pulp from O. albicarpa. The content in free amino acids in the pulp ranged from 0.1% in O. dillenii to 2.71% in O. undulata, while it ranged from 0.11% in O. dillenii to 1.27% in O. undulata in the peel samples. This work shows that although protein content in Opuntia fruits is low, this protein is of good nutritional quality, pointing out a possible use of the peel by-product as a source of quality protein.