30G-20 |
Efectiveness of ultrasound combined with refrigeration on extending shelf life of fresh fruit juices |
M. Mincz, Industry, Natural and Exact Sciences School, Buenos Aires University, Ciudad Universitaria ., Nuņez, Buenos Aires, 1428, Argentina, S. GUERRERO, Industry. Natural and Exact Sciences School, Buenos Aires University, Ciudad Universitaria, Nuņez, Buenos Aires, 1428, Argentina, and S. M. Alzamora. Traditional preservation methods for fruit juices like thermal pasteurization extend their shelf life assuring safety but may have some detrimental effects on organoleptic properties. Yeasts such as Saccharomyces cerevisiae and Zygosaccharomyces spp. may cause significant spoilage in non pasteurized fruit juice products, leading to economic loss and consumer rejection. In addition, growth of psicrotrophic pathogen microorganisms like Listeria monocytogenes could seriously affect their safety In this regard, ultrasonic technology represents an emerging method accomplishing other preservation factors in order to obtain safe minimally processed products with good organoleptic characteristics. The objective of this research was to investigate the influence of ultrasonic treatment on the behavior of some spoilage microorganisms and on color changes of pineapple and lemon juices stored 15 days at refrigeration temperature. Freshly squeezed lemon and pineapple juices were prepared, filtrated in sterilized bottles and used for further analysis. For microbiological study, 95 mL juice samples were inoculated with S. cerevisiae, Z. bailii , Z. rouxii and L. monocytogenes leading to initial cell concentration of 106 UFC/mL.The juices inoculated or not were immediately sonicated (Vibracell 20kHz,45°C,95 ĩm) and stored in sterilized glass 10-mL containers at 7ēC during 15 days. The microbial population of inoculated samples was monitored by plate counting technique at preset intervals during product storage. Samples without ultrasound treatment were taken as control. Juice color was evaluated in uninoculated and sonicated samples by measuring CIELAB* parameters using a Minolta colorimeter. Changes in pH and aw were also monitored at set intervals up two weeks. Results showed that color changes in the studied fruit juices was strongly represented by lightness( L*). The combined ultrasonic and refrigeration treatment on lemon and pineapple fresh juices was significant in suppressing microbial growth improving color retention without significant changes in pH and aw of pineapple and lemon juices These results show the important role of ultrasound contributing to inhibit microbial growth when it is combined with other traditional technologies
Session 30G, Fruit & Vegetable Product: Processed Fruits and Vegetables
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