The impact of amylase treatment on characteristics, viscosity and enzymatic modifications of acid-extracted pectin from butternut squash (Cucurbita moschata)

Abstract

The impact of pretreatment with amylase, applied individually or in combination with cell wall degrading enzymes, on characteristics, viscosity and enzymatic modification of acid-extracted pectin from butternut squash was studied. Yield of pectin after treatment of squash mesocarp with amylase, cellulase, and xylanase (104.4 mg/g_DM) was for 50 % higher in comparison to that after treatment with individual amylase. Amylase-assisted acidic extractions delivered pectins with very low starch content (0.2 %) and in average 2.8 higher galacturonic acid content compared to acidic extraction. These pectins also had a lower degree of methoxylation and considerably higher homogalacturonan content (over 65 %) compared to acid-extracted pectin. Flow curves of all pectins showed shear thinning behavior with differences in values of apparent viscosity. Modification with endo-polygalacturonase decreased aggregation and molecular weight, and changed flow characteristics to Newtonian, most distinctively for acid-extracted pectin after pretreatment of individual amylase. Pectin methylesterase increased molecular weight and viscosity of all pectins leading to the most distinctive thixotropic effect for acid-extracted pectin. Modification with combined pectinolytic enzymes potentiated decrease of aggregation and molecular weight in comparison to action of sole endo-polygalacturonase. The effects of combined modification were more intensive on pectins extracted with the assistance of amylase than without it.