1. Hyperbaric storage of raw watermelon juice with extension of shelf-life up to 58 days
Álvaro T. Lemos1, Ana C. Ribeiro1, Liliana G. Fidalgo1, Ivonne Delgadillo1, Jorge A. Saraiva1
1QOPNA, Department of Chemistry, University of Aveiro, Aveiro, Portugal
Introduction
Watermelon juice is a highly perishable food due to its high pH (>4.6) and high water activity (>0.85) [1], resulting in a short shelf-life due to the easy microbial growth and enzymatic activity, therefore it is necessary to store it under refrigeration, unless it is sterilized.
In the lasts years, hyperbaric storage at room temperature (HS/RT) has been studied as a new preservation method as an alternative to refrigeration (RF). It consists on food preservation under pressure using low/mild pressure levels ( MPa) [2].
The main advantage of this methodology is the possibility of great energy savings, since it only needs energy during compression and no additional energy is used to maintain the product under pressure, allowing food storage with lower energy costs and a reduced carbon footprint comparatively to refrigeration [3].
Results
Samples stored at AP/15 °C and RF showed a quick increase in microbial counts during storage time (Figure 1) reaching the acceptable limit (6.0 log CFU/mL) after 7 days of storage for all microbial counts.
With HS at 50 MPa/15 °C, the microbial growth was less pronounced when compared to RF, while for 62.5 and 75 MPa/15 ºC it was verified a gradual microbial load reduction during all storage time, but more pronounced for the first days.
HS at 75 MPa was capable of maintaining pH and TSS with a slight decrease in cloudiness during 21 days, while the physicochemical analyses showed clear changes in all parameters at 3rd day of storage at AP/15 °C (Figure 2).
After 58 days of storage at 62.5 and 75 MPa at 15 ºC, the juice still presented the characteristic odour of fresh raw watermelon juice.
Figure 1 – Microbial loads variation (Log (N/N0)) of total aerobic mesophiles (TAM) and psychrophiles (TAP), Enterobacteriaceae and Yeasts and Moulds during 58 days of storage under: hyperbaric storage (HS) at 50, 62.5 and 75 MPa, at low room temperature (15 °C); and under atmospheric pressure (0.1 MPa) at refrigerated (RF, 4 °C) and low room temperature (AP/15 °C). Positive or negative microbial variation indicates growth or inactivation, respectively. Unfilled symbols mean that microbial counts were ≥ 300 CFU/mL on the 10-4 dilution of samples or below the detection limit (≤ 1 CFU/mL). N0 correspond to the initial load of each storage condition.
Aim
Evaluate the effect of HS (50, 62.5 and 75 MPa) at 15 ºC up to 58 days, on raw watermelon juice’s microbial load and up to 21 days to physicochemical parameters.
Method
Samples Treatments
and Analysis
Figure 2 – pH, total soluble solids (TSS), cloudiness and total difference color (ΔE) for watermelon juice stored during 21 days of storage under: hyperbaric storage (HS) at 50 and 75 MPa, at low room temperature (15 °C); and under atmospheric pressure (0.1 MPa) at refrigerated (RF, 4 °C) and low room temperature (AP/15 °C).
Statistical analysis:
Analysis of Variance (ANOVA) and Tukey’s HSD test, at a 5% level of significance
Watermelon Juice Storage
HS at 50 and 75 MPa
15 ºC
Up to 58 days
Conclusions
With 50 MPa at 15 °C, the microbial load increased at a lower rate comparatively to RF and at AP/15 °C
HS at MPa at 15 °C of watermelon juice inhibits microbial growth over 58 days of storage, as also led to microbial inactivation comparatively to initial loads.
HS at 62.5 and 75 MPa was also capable to maintain the pH, TSS content, cloudiness and colour at values similar to the initial ones.
These results clearly indicate the potential to preserve foods by HS, with basically no energetic costs and with a clearly considerable extension of shelf-life of watermelon juice at least up to 58 days.
Microbiologic Analysis:
Total aerobic mesophiles
Total aerobic psycrophiles
Enterobacteriaceae
Yeasts and moulds
Physicochemical parameters: pH
Cloudiness
Total Soluble Solids
Colour
References
[1] - Fidalgo, L., Santos, M., Queirós, R., Inácio, R., Mota, M., Lopes, R., Saraiva, J. (2014). Hyperbaric storage at and above room temperature of a highly perishable food. Food Bioprocess Technology, 7(7),
[2] - Lemos, Á. T., Ribeiro, A. C., Fidalgo, L. G., Delgadillo, I., & Saraiva, J. A. (2017). Extension of raw watermelon juice shelf-life up to 58 days by hyperbaric storage. Food Chemistry, 231, 61–69.
[3] - Bermejo-Prada, A., & Otero, L. (2015). Effect of hyperbaric storage at room temperature on color degradation of strawberry juice. Journal of Food Engineering, 169,
Acknowledgements
FCT/MEC for the financial support to QOPNA research Unit (FCT UID/QUI/00062/2013), through national funds and where applicable co-financed by the FEDER, within the PT2020 Partnership Agreement
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