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Physical and chemical properties of apple juice and apple juice particulate McKenzie, Darrell-Lee


In order to prevent enzymatic oxidation of phenols during the centrifugal extraction of juice from apple purée, a sulfite or ascorbic acid treatment followed by blanching has been proposed. However, juice from blanched puree is more turbid and difficult to clarify than juice processed without blanching. In order to better understand the effect of blanching on juice turbidity as well as to provide more information concerning the effect of cultivar, post-harvest storage and enzyme treatment on juice quality, the chemical and physical properties of apple juice and apple juice particulate from fresh and stored McIntosh, Red Delicious and Spartan apples processed with and without enzyme digestion and with and without blanching were examined. Analysis of juice included measurement of: soluble solids, total sugars (by HPLC), sucrose, glucose, fructose, sorbitol, pH, titratable acidity, total acidity (by HPLC), citric acid, galacturonic acid, malic acid, quinic acid, succinic acid, pectin (as anhydrogalacturonic acid by HPLC) and turbidity (as absorbance at 600 nm). Analysis of particulate included measurement of dry matter weight, pectin, protein and zeta potential as well as thin sectioning, negative staining and shadow casting transmission electron microscopy. Chemical analysis of apple juice showed that the levels of organic acids, sugars and soluble pectin differed between cultivars. However, no varietal differences were observed in the chemical or microscopic analysis of cloud material. Blanching of apple puree, on the other hand, increased apple juice turbidity by increasing the amount of particulate suspended in the juice. Furthermore, blanching stabilized suspended particulate by what appeared to be the formation of a protective colloid which prevented particle aggregation through electrostatic repulsion. Post-harvest apple storage also resulted in changes to juice particulate, which were observed as gel formation during juice storage at 0°C and as a web-like aspect in the microscopic appearance of juice particulate. Treatment of apple purée with Ir-gazyme 100 decreased juice turbidity, resulting in the concomitant decrease in both the level of soluble juice pectin and the amount of suspended cloud material. Use of enzyme treatment and blanching in the processing of apple juice was demonstrated by stepwise discriminant analysis to allow production of four unique apple juice products.

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