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Inactivation of Saccharomyces cerevisiae and polyphenoloxidase in mango nectar treated with UV light
José A Guerrero-Beltrán1, Gustavo V Barbosa-Cánovas
1Biological Systems Engineering Department, Washington State University, Pullman 99164-6120, USA.
Abstract:
Fresh mango nectar was processed by UV light at five flow rates (0.073 to 0.451 liter/min) and five UV light doses (75 to 450 kJ/m2) to evaluate total microbial load, Saccharomyces cerevisiae survival, and polyphenoloxidase activity. UV systems containing an inner mercury lamp (254 nm) each with intensity of 25 mW/cm2 were used as germicidal sources. In addition, mango nectar was treated for 15 min at 0.073 and 0.451 liter/min, stored at 3 degrees C, and evaluated periodically for total microbial count, yeast count, color, and polyphenoloxidase activity. The first-order kinetics modeling found that DUV-values in mango nectar ranged from 27.9 to 10.9 min (R2 > 0.950) and 26.0 to 11.8 min (R2 > 0.962) for total microbial count and yeast count, respectively. The maximum log reduction (CFU per milliliter) was 2.71 and 2.94 for total microbial count and yeast count, respectively, after 30 min of UV treatment at 0.451 liter/min. DUV-values ranging from 156 to 204 min were observed for polyphenoloxidase activity. The remaining polyphenoloxidase activity after 30 min of UV treatment at 0.451 liter/min was 19 +/- 4%. Initial microbial load and yeast in stored mango nectar were reduced in the range 2.86 to 3.41 and 1.82 to 1.97 log (CFU/ml) cycles, respectively. No substantial microbial growth was observed prior to 20 days of storage. Averages of 1,055 +/- 32, 803 +/- 32, and 710 +/- 37 enzyme activity units were observed in mango nectar UV processed at 0, 0.073, and 0.451 liter/min, respectively, during the entire storage period. However, mango nectar treated at 0.073 and 0.451 liter/min maintained a yellow and yellow-orange color, respectively, after 26 days of storage.
Insights
UV processing effectively reduces microbial load and yeast in mango nectar, maintaining quality for up to 20 days. This study optimized UV light doses and flow rates for effective microbial inactivation and enzyme activity control.
Area of Science:
- Food Science and Technology
- Microbiology
- Biochemistry
Background:
- Microbial contamination and enzymatic spoilage are significant challenges in preserving fresh mango nectar.
- Traditional preservation methods can impact sensory attributes and nutritional value.
- Ultraviolet (UV) light processing offers a non-thermal alternative for microbial inactivation.
Purpose of the Study:
- To evaluate the efficacy of UV light processing in reducing microbial load and Saccharomyces cerevisiae in fresh mango nectar.
- To assess the impact of UV treatment on polyphenoloxidase (PPO) activity and color retention.
- To determine optimal UV doses and flow rates for effective preservation of mango nectar.
Main Methods:
- Fresh mango nectar was treated with UV light at varying flow rates (0.073–0.451 L/min) and doses (75–450 kJ/m²).
- Microbial load (total count and yeast) and PPO activity were measured post-treatment.
- Treated mango nectar was stored at 3°C, with periodic evaluations of microbial counts, color, and PPO activity.
Main Results:
- UV treatment significantly reduced total microbial load (up to 2.71 log CFU/mL) and yeast count (up to 2.94 log CFU/mL).
- DUV-values for microbial inactivation ranged from 10.9 to 27.9 min, while for PPO activity, they ranged from 156 to 204 min.
- UV-treated mango nectar maintained desirable color and showed reduced PPO activity (19 ± 4% remaining after 30 min at 0.451 L/min), with no significant microbial growth for 20 days.
Conclusions:
- UV light processing is an effective method for reducing microbial contamination in mango nectar.
- Optimized UV treatment parameters can inactivate microorganisms while preserving sensory qualities like color.
- UV processing shows promise for extending the shelf-life of fresh mango nectar without compromising quality.
