title: Effect of thermal treatment on the quality of cloudy apple juice.
abstract: Apple juice from eight different varieties of apples was heated at high-temperature (60-90 degrees C) and short-time (20-100 s) (HTST) combinations. To determine the effect of heating conditions on enzymatic browning and cloud stability in apple juices, the activity of polyphenol oxidase and pectinesterase was analyzed and correlated with the thermal treatment conditions and the quality of the juice. Additional investigations included the measurement of pH value, soluble solid content, titratable acidity, color, and turbidity after 3 and 6 months. The results showed that HTST treatment at 80 degrees C already inactivated polyphenol oxidase, whereas pectinesterase activity was reduced to half and could even at 90 degrees C not be inactivated completely. In fact, highest residual pectinesterase activity was found at 60 degrees C. Heating at 70 degrees C caused stable pectinesterase activity and even a slight increase for 50 and 100 s heating times. Turbidity and lightness increased after HTST treatment. In particular, differences in cloud stability between the varieties were measured. HTST parameters did not correlate with the residual cloud stability after 6 months. The sensory evaluation revealed that only a few combinations were distinguishable. The best stability of cloud and color in relation to heat impact was achieved by HTST treatment between 70 degrees C/100 s and 80 degrees C/20 s.
authors.affiliation: Department of Fruit Processing, Federal College and Institute for Viticulture and Pomology, A-3400 Klosterneuburg, Austria. gottfried.krapfenbauer@hblawo.bmlfuw.gv.at
authors.forename: Gottfried
authors.initials: G
authors.lastname: Krapfenbauer
authors.forename: Mathias
authors.initials: M
authors.lastname: Kinner
authors.forename: Manfred
authors.initials: M
authors.lastname: Gössinger
authors.forename: Regine
authors.initials: R
authors.lastname: Schönlechner
authors.forename: Emmerich
authors.initials: E
authors.lastname: Berghofer
mesh_terms: D001628:Beverages / Q000032:analysis*; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism; D004156:Catechol Oxidase / Q000378:metabolism; D003116:Color; D005638:Fruit; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015416:Maillard Reaction; D027845:Malus; D009391:Nephelometry and Turbidimetry; D012677:Sensation
chemical_list: D004156:Catechol Oxidase; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase