*4.1. Sugars*

Nuts are characterized by low quantities of soluble sugars, that range from 2.6% to 7.9% (Table 1). The soluble sugars fraction suffers important quantitative variations depending mainly on the cultivar, but also on the origin and even harvest time [9,18,69,70]. Most sugars are not reducing, with sucrose representing more than 90% of the total sugars. Raffinose, inositol, sorbitol, fructose and glucose were also detected [55,56,71]. Differences found between commercial and regional cultivars about sugars composition, especially sucrose, may be used to establish a sugar profile as an indicator of almond kernel quality.

Moreover, Nanos et al. [69] found galactose (reducing sugars), melezitose (tri-saccharide) and stachyose (tetrasaccharide). Late-harvested almonds had lower total amounts of these sugars than early-harvested ones.

The fact that the main sugar is sucrose is due to its preferential production and its accumulation in almond kernel during ripening and to the fact that many minor sugars constitute a substrate for the synthesis of sucrose [57]. Kazantzis et al. [55] observed that almond kernels early-harvested (green mesocarp surface at 90%) had a lower content in sucrose and higher content in inositol than more ripened almonds (brown mesocarp surface at 90%). Trees subjected to irrigation and compost treatments also produce almond kernels with the highest content in sucrose and glucose. This could reduce their water content, causing a higher concentration of compounds such as sugars [57]. In contrast, a recent study by Lipan et al. [72] showed that almost all morphological and physical-chemical parameters were unaffected by water stress.

Regarding the total sugars, a value of 4.63 g/100 g of peeled almonds was found, distributed as 4.46 g of sucrose, 0.03 g of glucose and 0.14 g of maltose [43]. A review of a worldwide collection of almond samples found a soluble sugars content ranging from 1.80 to 7.60 g/100 g f.w. [8]. On the other side, when data are referred to almonds with skin, total values fall to 4.35 g/100 g, and are distributed as follows: 3.95 g of sucrose, 0.17 g of glucose and 0.04 g of maltose, appearing with 0.11 g of fructose and 0.07 g of galactose.
