Sensory and textural changes in maturing Omani dates

The astringency and texture of the Omani date variety khalas were examined at progressive levels of maturity. Astringency was measured using descriptive sensory analysis, while texture was measured with a texture meter. The phenolic (referred to as 'tannin') and polygalacturonic acid (referred to as 'pectin') contents of the dates were measured by colorimetry. It was found that astringency closely followed levels of tannin content measured on a fresh weight basis. The most astringent dates were at the kimri and tamar stages of maturity, which also had the highest fresh weight tannin content of 2.8 and 1.5g kg^-1 respectively. The least astringent dates were at the rutab stage of maturity, which also had the lowest fresh weight tannin content (1.0g kg^-1). On a dry weight basis the tannin content decreased as the dates matured. The texture of the dates closely followed the degree of methylation of the date pectin. The softest dates were at the tamar stage of maturity, with a degree of methylation of 39%, while the hardest dates were at the kimri stage, with a degree of methylation of 72%. The polygalacturonic acid content did not appear to affect the texture, since the fresh weight polygalacturonic acid content was higher at the tamar stage (11-13g kg^-1) than at the kimri stage (6-9 g kg^-1) of maturity. Traditionally, dates at the rutab stage are preferred since they are considered the sweetest and softest. Although tamar dates have the highest sugar content, owing to moisture loss, rutab dates may be preferred not necessarily for their great sweetness and soft texture, but rather for their lack of astringency.