Impact of minimal heat-processing on pectin methylesterase and peroxidase activity in freshly squeezed <Emphasis Type="Italic">Citrus</Emphasis> juices |
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Authors: | Angelika?R?Hirsch Alexandra?Knauss Reinhold?Carle Sybille?Neidhart |
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Affiliation: | (1) Institute of Food Science and Biotechnology, Chair of Plant Foodstuff Technology, Hohenheim University, Garbenstrasse 25, 70599 Stuttgart, Germany; |
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Abstract: | The impact of minimal heat-processing of juices on the activities of endogenous pectin methylesterase (PE) and peroxidase
(POD) was compared between Citrus species. Mono-cultivar juices were produced from three orange (Citrus sinensis (L.) Osbeck cvs. ‘Navelina’, ‘Salustiana’, and ‘Navelate’), two lemon (Citrus limon (L.) Burm. f. cvs. ‘Verna’ and ‘Primofiori’), and two Clementine mandarin varieties (Citrus reticulata Blanco cvs. ‘Marisol’ and ‘Clemenules’). Two mandarin hybrids (cvs. ‘Ortanique’ and ‘Clemenvilla’) were likewise used. The freshly
squeezed juices were subjected to continuous treatments at six different temperatures (42–92 °C) with subsequent re-cooling
on the pilot plant scale. In fresh Citrus juice, POD activities notably varied between 0.2 and 7.5 nkat g−1 of juice, whereas PE activities were more uniform (0.4–1.5 PE units g−1). In all juices, except ‘Ortanique’ juice, heating ≥42 °C for 12 s reduced POD activity below 4.3% of the maximum activity
in fresh Citrus juice. Thermal tolerance of the thermo-labile PE fraction was overall much higher, but varied among juices during heating
at temperatures ≤62 °C. Overall thermal resistance of PE was though comparable, with deactivation exceeding 84%, mostly even
90%, after thermal treatments ≥72 °C. Unlike POD, total PE activity proved to be an indicator of freshness that is universally
applicable to Citrus juices derived from orange, mandarin, and lemon or blends thereof. Freshly squeezed juices can analytically be distinguished
from cold-stored, minimally processed products that display an almost completely inactivated thermo-labile PE fraction and
thus extended shelf life. |
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