Inactivation of Escherichia coli ATCC 25922 and Saccharomyces cerevisiae IMR-R-L 962 in grapefruit [Citrus paradisi (Macf.)] juice by UV-C light: changes in bioactive compounds and quality characteristics
Fecha
2018Autor
La Cava, Enzo L.
Sgroppo, Sonia Cecilia
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The viability of UV-C treatment (0.0-2.36 J/cm²) at 254 nm as a non-thermal preservation
process for grapefruit juice on microbial inactivation, the organic acids and individual
flavonoids, as well as the quality characteristics (pH, ºBrix, titratable acidity, colour, total
phenolics and antioxidant capacity) was evaluated. Additionally, pectin methylesterase (PME)
activity was also measured. The effects of UV-C on microbial inactivation were assessed by
kinetic studies on the inactivation of inoculated grapefruit juice with one strain of Escherichia
coli ATCC 25922 and one strain of Saccharomyces cerevisiae IMR-R-L 962. The suitability
of Weibull distribution and modified Gompertz models was analysed to characterise the
UV-C inactivation kinetics for E. coli and S. cerevisiae in freshly squeezed grapefruit juice.
Likewise, the changes after UV-C treatment in citric (CA), malic (MA), ascorbic (AA) and
tartaric (TA) acids, as well as naringin (NAR), hesperidin (HES) and neohesperidin (NEO),
were quantified by HPLC, whereas the total phenolics and antioxidant capacity (DPPH• and
ABTS•+) were quantified by spectrophotometric methods. Nonlinear inactivation curves were
successfully fitted with Weibull-type and modified Gompertz models. However, the Gompertz
model allowed a better fit and more accurate estimation of the parameters. UV-C treatment
at 1.83 J/cm² achieved a 5.18 ± 0.01 and 2.7 ± 0.15 log CFU/mL reduction in E. coli and
S. cerevisiae, respectively, whereas no significant changes occurred in CA, MA, TA, NAR,
HES, NEO, total phenolics, ABTS•+, pH, ºBrix, titratable acidity and colour of the grapefruit
juices (p>0.05). However, PME was partially inhibited and the AA level and DPPH• decreased
significantly after treatment, with losses up to 15.9 and 8% (at 1.83 J/cm²), respectively, which
were associated with the UV-C dose intensity.
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