Fruit quality in almond: chemical aspects for breeding strategies

Almond (Prunus amygdalus Batsch) kernel composition is a basic aspect for almond quality evaluation, but, with the exception of kernel taste, only nut and kernel physical traits have been considered so far in almond evaluation. Kernel bitterness, due to the presence of amygdalin, has been thoroughly studied from the physiological and genetic points of view, but not the other chemical traits, which, however, have a great importance in the organoleptic appreciation of the kernel, in its industrial utilization, in its keeping performance, and in its nutritional and healthy value. The major component of almond kernels is the lipid fraction, ranging from 35 to 70% of the total kernel dry weight. More important is the different proportion of the main fatty acids, with a predominant role of oleic acid, the most interesting from the nutritional and health point of view, ranging from 62 to 78% of the total fatty acids. Some confectioneries, such as nougat, require a high proportion of fatty acids whereas others, such as marzipan and almond flour, require a low proportion. Protein content ranges between 13 and 29%, being inversely proportional to the percentage of fatty acids. Soluble sugars range from 3 to 8%, with a predominant presence of sucrose. Ash residue ranges from 3 to 4.5%, with K, Ca and Mg as predominant elements. Fibre content ranges from 2 to 6%. Mostly interesting is the presence of tocopherols, due to their antioxidant activity. They are the source of vitamin E and also avoid, or retard, the rancidity process in almond kernels. Large differences in tocopherol content have been found between cultivars and selections, allowing an effective selection process for this trait in breeding programmes because of their implication in the industrial, nutritional and healthy value of the almond kernels. All these parameters are more or less heritable and must be considered in the design of crosses and in the evaluation during a breeding programme.