Physicochemical characterization of nopal pads (Opuntia ficus indica) and dry vacuum nopal powders as a function of the maturation.

This paper presents the physicochemical and nutrimental characterization of fresh nopal (Opuntia ficus indica, Redonda variety) and nopal powder produced at different stages of development. Nopal powder was obtained by dry vacuum technique using 10(2) Torr and low temperature (40 degrees C). The results showed that the nutrimental and mineral composition of nopal changes as a function of the maturation as follow: The ash content increases from 18.41 for nopalitos (60 g of weight) to 23.24% (nopal pads 200 g); calcium content increases from 1.52 to 3.72%, while phosphorous exhibits an opposite trend: 0.43 to 0.27%, respectively. Calcium oxalate was determined by X-ray diffraction and SEM microscopy and quantified by using atomic absorption spectroscopy. Calcium oxalate decreases from 7.95 to 3.47 mg/g and the Ca/P ratio varies from 3.6 to 11. The soluble fibre decreases from 25.22 to 14.91%, while insoluble fibre increases from 29.87 to 41.65%. These results suggest that nopal could be an important source of minerals within the diets of people in Mexico and the rest of Latin America.

Behavior of methamidophos residues in peppers, cucumbers, and cherry tomatoes grown in a greenhouse: evaluation by decline curves.

Residue levels of methamidophos were determined in peppers, cucumbers, and cherry tomatoes grown in commercial greenhouses, up to 6 weeks after being sprayed with Monitor (methamidophos 60%). Mathematically defined decline curves were established by determining optimal relationships between methamidophos residues and time, using different models. Model functions that best fit experimental data were 1st-order function for cucumber, 1.5th-order function for pepper, and 1st-order root function for tomato. However, in all cases, the 1st-order function was legitimized statistically. Half-life times determined from the optimal functions were 8.68 days (cucumber), 13.28 days (pepper), and 2.77 days (tomato), whereas half-life times determined from the 1st-order reaction function were 8.68 days (cucumber), 17.04 days (pepper), and 7.47 days (tomato). In this work, some experiments to determine residue levels of methamidophos in these vegetables after multiple applications were also carried out. The unexpected high residue levels found in all cases after five successive applications seem to indicate that methamidophos presents certain long-term accumulative effects in the three studied vegetables.