HIGH PRESSURE PROCESSING, pH, AND THE EFFECT OF PRESERVATIVES ON THE SURVIVAL OF SPOILAGE FUNGI AND ALICYCLOBACILLUS SPP. IN A DILUTED APPLE JUICE CONCENTRATE AT VARYING WATER ACTIVITIES
Buerman, Elizabeth Claire
Spoilage fungi and bacteria are capable of surviving typical juice pasteurization methods and growth during shelf life. High Pressure Processing (HPP) is a method used to extend the shelf life of foods by subjecting products in their final packaging to extreme pressure. This process leads to protein degradation in microbial cells, membrane degradation, and eventual cell death. Survival of spoilage organisms, especially spore formers, has not been closely considered in regard to the effect of water activity (aw). HPP causes less nutrient and color degradation than traditional thermal processing which results in improved consumer acceptance. The purpose of this study was to determine the effect of pH, sulfites, dimethyl dicarbonate (DMDC) and aw on HPP apple juice to prevent fungal and bacterial spoilage during storage. Spoilage fungi, Aspergillus pseudoglaucus, Aspergillus fischeri, Paecilomyces niveus (Byssochlamys nivea), Penicillium spp., Paecilomyces variotii (asexual form of Byssochlamys spectabilis), Aspergillus niger, Candida parapsilosis, Rhodotorula mucilaginosa, and Torulaspora delbrueckii as well as three strains of spoilage bacterium Alicyclobacillus spp. were inoculated into diluted apple juice concentration adjusted to 0.94, 0.96, 0.98 and 1.0 aw at pH 3.5, 4.6 or 7.0 with either no preservative, 8 ppm sulfite or 0.025% DMDC. These products were processed at 5°C in a commercial HPP unit at 300 MPa for 1.5 min, 450 MPa for 1.5 min, or 600 MPa for 1.5 - 15 min. These products were stored at 5 or 23°C for six months. Results display that processing pressure sensitive fungi at 450 MPa or higher and storing at refrigeration could extend storage up to 26 weeks. Pressure resistant organisms, A. fischeri, A. pseudoglaucus, P. niveus, C. parapsilosis and Alicyclobacillus spp. were capable of surviving the conditions tested. Additionally, using sulfites and DMDC did not significantly improve reductions of spoilage organisms, and storing HPP juices at refrigeration is necessary for extended shelf life.
Alicyclobacillus; HPP; Juice; Fungi; Food science; Spoilage
Padilla-Zakour, Olga I.
Worobo, Randy W.; Davis, Andrew M.
Food Science and Technology
Ph.D., Food Science and Technology
Doctor of Philosophy
dissertation or thesis