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Efficacy of non-thermal technologies and sanitizer solutions on microbial load reduction and quality retention of strawberries

Publication . Alexandre, Elisabete M.C.; Brandão, Teresa R.S.; Silva, Cristina L.M.

The effect of non-thermal technologies (ozone in aqueous solution, ultrasound and ultraviolet C radiation) and washings with chemical solutions (sodium hypochlorite and hydrogen peroxide) on safety and quality features of strawberries was studied. These treatments were applied before fruit storage at two different temperatures (4 and 15 C). The overall impact on microbial loads (total mesophiles, and yeasts and moulds) and selected quality attributes (colour, firmness, pH, total anthocyanins and ascorbic acid content) was assessed. During storage under refrigerated temperature, washing with hydrogen peroxide solutions resulted in strawberries with lower microbial loads, when compared to the other treatments. However, it produced significant key quality attributes losses, such as colour and total anthocyanins content. The results presented show that ozone and ultrasound are promising alternatives to thermal treatments. The application of such technologies, before refrigerated storage of strawberries, allowed a satisfactory retention of all quality characteristics analysed, while being efficient in controlling microbial contamination.

2012Journal article

Restricted access

Influence of aqueous ozone, blanching and combined treatments on microbial load of red bell peppers, strawberries and watercress

Publication . Alexandre, Elisabete M. C.; Santos-Pedro, Dora M.; Brandão, Teresa R. S.; Silva, Cristina L. M.

The effectiveness of ozone in aqueous solution treatment on microbial inactivation was studied for three combinations microorganism/food: Listeria innocua/red bell peppers (artificially inoculated), total mesophiles/strawberries, and total coliforms/watercress, with two concentrations (0.3 and 2.0 ppm). Blanching treatments (50-60 degrees C) were also individually applied and in combination with ozone, for studying possible synergistic effects. In relation to ozone treatments, the highest microbial reductions were obtained for the highest concentration with the highest treatment time (3 min). Under those conditions. L. innocua/peppers, total mesophiles/strawberries and total coliforms/watercress were reduced respectively 2.8 +/- 0.5, 2.3 +/- 0.4 and 1.7 +/- 0.4 log-cycles. However, a substantial portion of the microbial populations were reduced by water washing alone, and the presence of ozone generally added an additional reduction of 0.5-1.0 log-cycles. If ozone at the highest concentration is used, the treatment impacts on L. innocua/peppers and total mesophiles/strawberries load reductions were equivalent to a blanching at 50 degrees C (for the same treatment times). Combining blanching and ozone did not generate synergistic effects, and in some situations microbial reductions were lower than the ones observed when treatments were applied independently.

2011Journal article

Open access

Impact of non-thermal technologies and sanitizer solutions on microbial load reduction and quality factor retention of frozen red bell peppers

Publication . Alexandre, Elisabete M. C.; Brandão, Teresa R. S.; Silva, Cristina L. M.

The effect of non-thermal technologies (ozone in aqueous solution, ultrasounds and ultraviolet C radiation) and washings with chemical solutions (sodium hypochlorite and hydrogen peroxide) on Listeria innocua survival was studied in red bell peppers. Quality attributes such as total colour difference, firmness, pH and ascorbic and dehydroascorbic acid content were also evaluated. The treatments were applied before product storage under frozen conditions (-7 and -30 degrees C). Pre-washings with hydrogen peroxide solutions allowed obtaining frozen shred red bell peppers with lower microbial loads, when compared to the results obtained with the remaining treatments. However, those washings had a negative impact on colour and firmness. Alternatively, ozonation provided microbial reductions significantly higher than water-washings and improved, or at least allowed to preserve, all quality parameters analysed under both storage conditions. Storage at -7 degrees C provided higher microbial reductions in red bell peppers. However, this temperature implied higher colour alterations and ascorbic acid losses. Industrial relevance: The native microbial flora of fresh fruits and vegetables may include pathogens which are dangerous threats to consumers. Thermal treatments are conventionally used to attain safety standards; however, overall quality may be negatively affected by heat. Chemical treatments (environmental friendly) or non-thermal processes such as ozone, UV-C radiation and ultrasonication are promising technologies. From an industrial point of view, these processes may have potential application if safe and high quality produce is to be attained.

2013Journal article

Restricted access