Abstract
The mechanisms governing the enzymatic clarification of apple juice were studied by electron microscopy techniques. Full ripe and unripe apple juice samples (Granny Smith) were treated with commercial pectinase (Solvay 5XLHA) and amylase (Röhalase HT) enzymes, respectively. Scanning electron microscopy studies revealed that commercial amylolytic enzymes quickly reduced starch content in unripe apple juice to undetectable values. It was also observed that after pasteurization of this juice (90C, 5 min) all starch granules gelatinized. Using transmission electron microscopy, it was possible to observe pectin bonded to ripe apple juice particles. This protective colloid is known to be responsible for cloudy juice stability. The effect of pectic enzyme to destroy the protective pectin colloid was also detected with this technique. As a result of the enzymatic treatment, average particle size initially increased from 1000 to 1500 nm and decreased thereafter to ≈1100 nm, and Z-potential increased in absolute values from −9.6 to −11.4 mV. It was speculated that the destruction of the weak pectin net by the action of the specific enzyme caused particle aggregation, followed by the collapse of aggregates, increasing the number of particles <500 nm.
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