VARIATIONS OF CARBOHYDRATE CONTENT AND INVERTASE ACTIVITY IN GREEN AND WHITE ASPARAGUS SPEARS - EFFECTS OF SPEAR LENGTH AND PORTION

Abstract

Spears of asparagus (Asparagus officinalis) are commonly consumed and appreciated because they are low in calories and provide substantial amounts of reducing sugars and very low amounts of fructooligosaccharides (FOS), and these polymers are well-known for health benefits. Many investigations were carried out on asparagus FOS structures, enzymology and molecular biology, while few investigated carbohydrate content of edible spears after harvesting. The objective of our investigation was to assess contents of total soluble sugars (TSS), reducing sugars (RS), and ketoses contents and invertase activity in different portions (top, middle and bottom) of green and white asparagus spears that differed in commercial sizes (long: 25-26 cm, medium: 19-20 cm and short: 14-15 cm). TSS consist mainly of reducing sugars, and small amount of low DP (degree of polymerization) FOS content as 1-kestose and neokestose. TSS content was a little higher in long spears, and decreased from bottom to top portion. RS showed similar variations although TSS and RS contents of white asparagus were higher than those of green asparagus. Ketoses contents showed close similarity to TSS and RS, with little differences between middle and bottom portions. Invertase activity of green asparagus was higher than that of white asparagus. On the other hand, this activity increased from the bottom to the top portion where high activity was noted in both white and green asparagus. Probably, low TSS, RS and ketoses contents, and high invertase activity observed in the top portion of asparagus spears might be related to the high metabolism occurring in this portion which contains the zone of elongation and thus is characterized by intense metabolic activity.