Effects of pulsed-light treatments on shelf-life and decontamination of strawberries and blueberries
Date
2017
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Strawberries and blueberries are highly perishable fruits with short shelf-life.
They are also occasionally contaminated with pathogens such as Salmonella and
human norovirus. In this study, we explored the potential of pulsed light (PL) for
shelf-life extension and decontamination of these two fruits. Screening studies were
conducted to identify effective PL treatments which were further evaluated. Three dry
PL treatments (samples were exposed to PL directly), low intensity PL with a dose of
3 𝐽⁄𝑐𝑚2 (L3), medium intensity PL with a dose of 3 𝐽⁄𝑐𝑚2 (M3), and medium
intensity PL with a dose of 5 𝐽⁄𝑐𝑚2 (M5), were identified for strawberries. These 3
PL treatments along with untreated control were applied to strawberries and
strawberries dip- and spot-inoculated with a cocktail of Salmonella. Strawberries were
then stored at refrigerated storage and analyses were conducted at selected time
intervals. All three PL treatments showed delayed fungal development, slowed down
overall spoilage, better preserved surface glossiness, and delayed anthocyanin
accumulation. Among the three treatments, M3 showed best shelf-life extension effect,
while L3 and M5 achieved slightly better decontamination effect as well as slightly
enhanced surface redness. No significant difference in other quality attributes,
including weight loss, firmness, acid or sugar contents were observed between the
control and PL-treated strawberries. However, although not obviously reflected in
shelf-life, a tendency of accelerated quality degradation was discerned in M5 samples,
suggesting the use of high dose PL treatments should be cautiously executed or
discouraged. For blueberries, two PL treatments, dry low intensity PL with a dose of 6
𝐽⁄𝑐𝑚2 (L6) and water-assisted low intensity PL with a dose of 9 𝐽⁄𝑐𝑚2 (wL9)
(samples were exposed to PL while being washed in agitated water) were identified.
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These 2 PL treatments along with untreated control were applied to blueberries and
blueberries dip- and spot-inoculated with a cocktail of Salmonella. Blueberries were
then stored at room temperature (~22°C) or 5℃ and analyses were conducted at
selected time intervals. Neither dry nor water-assisted PL treatments showed benefits
in extending the shelf-life of blueberries regardless the storage temperature. However,
the two PL treatments significantly reduced the Salmonella population immediately
after treatments and after 7 days of cold storage. Overall, the water-assisted PL
treatment had better decontamination effect than the dry PL treatment. Surface
lightness was directly reduced after both treatments. Reduced firmness was detected in
water-assisted PL samples after 7 days of cold storage, while increased weight loss
was detected during storage after dry PL treatment. The increased weight loss and
decreased surface lightness were the major restrictions of dry PL treatment. Due to the
limitation of our water-assisted PL system, blueberries were in contact with water
much longer than necessary and our system could not provide a rapid drying and
cooling process. In summary, dry PL treatment showed promise in extending shelf-life
and decontamination of strawberries. Although water-assisted PL treatment could
effectively inactivate Salmonella on blueberries, equipment need to be carefully
designed to minimize the time blueberries are in contact with water and provide rapid
drying and cooling of blueberries after water-assisted PL treatment.