Acidity changes and pH-buffering capacity of nopalitos (Opuntia spp.)

Changes in tritratable acidity of 10 variants of "nopalito" (edible young cladodes of flat-stemmed spiny cacti mainly of the Opuntia genus used as vegetables) with high commercial value (Atlixco, Blanco Espinoso, Copena F-1, Copena V-1, Jade, Milpa Alta, Polotitlan, Texas A&I 1308, Toluca and Tovarito) in response to hour of the day of harvest were evaluated. The effect of the elapsed time since harvest on acidity in the Milpa Alta variant and pH-buffering capacity were also evaluated. Significant differences in acidity (factor of 2.7) among the nopalito variants were detected. Differences in acidity among the nopalito variants harvested at 6:00 h (between 0.28 and 0.76%) and at 13:00 h (between 0.21 and 0.36%) were observed. Copena V-1 and Atlixco variants had the lowest acidity content. Variation in postharvest acidity in the Milpa Alta variant depended on the hour of the day of harvest as well as on the light-dark natural periods, at least during the first 48 h. Variations of acidity during 48-h following nopalito harvest indicated that the Crassulacean acid metabolism (CAM) remained active after harvest. Milpa Alta nopalito showed a pH-buffering capacity, largely within the low-pH range that appears to be also dependent on the hour of harvesting, since the more acidic, early morning harvested cladodes had a wider range of buffering activity. This could partially explain the therapeutic effect attributed to nopalitos in gastrointestinal disorders. (C) 2003 Elsevier B.V. All rights reserved.