Structural polysaccharides in xoconostle (Opuntia matudae) fruits with different ripening stages
Keywords:dietary fiber, soluble fiber, insoluble fiber, mucilage, pectin, hemicelluloses, cellulose.
The objective of this research was to isolate, purify and quantify the content of mucilage, pectins,
hemicelluloses and cellulose of the acidic cactus fruits of Opuntia matudae with commercial
maturity. Fruits were collected in an orchard for commercial production of cactus pear fruit and
pads in San Martin de Las Pirámides, Mexico. Fruits were grouped according to the receptacle
depth, fruit dimensions and proportion of structures. The structural polysaccharides of the
dehydrated and finely crushed skin (edible portion) fruits, were sequentially extracted with water
and aqueous solutions of ammonium oxalate and potassium hydroxide, precipitated with ethanol,
purified by dialyzing or watery washing and gravimetrically quantified after being lyophilized.
Although, fruits were harvested with significantly homogenous size, and identified by the farmer
like adequate for commercialization (with equatorial and polar diameters homogenous between the
fruits, 51.7 mm, 45.2 mm respectively), they were grouped in three depending on receptacle depth
(between 3.8 and 6.9 mm) and other parameters, like total wet biomass (between 64 and 81 g/fruit)
and dry biomass (between 1.9 and 33.3 g/fruit), skin thickness (between 11.3 and 12.7 mm) and
total number of seeds (120 to 205 abortive plus normal seeds/fruit). In addition, also it was
confirmed that fruit ripeness of O. matudae is inversely related to the depth of receptacle.
Mucilage, pectin and cellulose represented a significantly higher amount in the ripe fruits (7.5, 8.0
and 15.4%, respectively) than in the unripe (1.8, 2.5 and 10.0%, respectively); whereas the
hemicelluloses content in all three classified ripe states was significantly similar (in average 3.2 and
1.5 % of loosely and tightly bound hemicelluloses). The results indicate that xoconostle fruits are
rich in soluble (7.8 to 18.6%) and insoluble (11.6 to 16.5%) dietary fiber, and the type of
polysaccharides varies in dependence of fruit ripening.