Characterization of starch and cell walls from mature-green ambarella (Spondias cytherea Sonnerat) and their enzymatic hydrolysis

Juice from mature-green ambarella contains starch, a characteristic detrimental to its visual appearance due to the white sediment formed upon storage. The purpose of this work was to evaluate the effects of starch and cell wall degrading enzymes on juice residual starch and content in soluble sugars. Starch and cell walls from mature-green ambarella fruits were purified and characterized. Starch was found to contain 21.0% amylose, 78.1% amylopectin and 0.9% other minors compounds. Its average granule size was 20 μm. Its thermal characteristics were: temperatures of onset (To = 57.8 °C), peak (Tp = 65.6 °C), and conclusion (Tc = 72.6 °C) of gelatinization and the endothermic enthalpy (ΔHgelatinisation = 12.4 J g−1). Cell walls represented 2.8% of the edible fresh matter and were mainly constituted of highly methylated (HM) pectic substances and cellulose. The amylolytic preparations we tested, AMG® 300 L and Hazyme® C, showed similar behaviours in terms of starch hydrolysis and profit of Brix degree obtained. With 200 μg g−1 of AMG® 300 L or Hazyme® C, the degree of amylolysis of coarse ambarella puree was close to 50% and its increased up to 70% with enzymes concentrations higher than 1,000 μg g−1 (gelatinization at 75 ± 5 °C for 15 min followed by starch amylolysis at 60 ± 5 °C for 15 min). Total hydrolysis of ambarella starch is possible when pectinolysis occurred before amylolysis treatment, probably because of the fluidification of the medium by the pectocellulolytic enzymes. Pectinex® Ultra SP-L was the most efficient preparation to degrade the ambarella pectins (∼80% of cell wall uronides liberated from 120 mg g−1 of purified cell walls within 1 h at 30 °C, pH 2.7).