Impact of ultra high pressure homogenization on pectin methylesterase activity and microbial characteristics of orange juice: A comparative study against conventional heat pasteurization

The effect of different ultra high pressure homogenization (UHPH) treatments on pectin methylesterase (PME) activity and on the contaminating microorganisms of orange juice was investigated. The treatments consisted in combinations of two inlet temperatures (10 or 20 degrees C), three pressures (100, 200 or 300 MPa) and two holding times (<= 0.7 or 30 s). Results were compared with two thermal pasteurization treatments (1 and 2 min at 90 degrees C). Shelf-life of treated juices was evaluated for a period of 50 days at 4 degrees C. Mean bacterial counts in raw orange juice were: mesophilic aerobic bacteria (MAB) 4.75 +/- 0.48 Log CFU/ml; psychrotrophic aerobic bacteria (PAB) 4.58 +/- 0.30 Log CFU/ml; lactic-acid bacteria (LAB) 4.69 +/- 0.40 Log CFU/ml; yeasts 426 +/- 0.16 Log CFU/ml. UHPH treatments at 200 and 300 MPa reduced significantly the counts of all the microbial groups up to 4.38 Log CFU/ml for MAB; to 4.43 Log CFU/ml for PAB; to 4.69 Log CFU/ml for LAB and to undetectable from the rest of the group. No significant differences were observed with the thermal pasteurization. These treatments also reduced the PME activity above the 96% of its initial activity. The effect of increasing the inlet temperature from 10 to 20 degrees C, or the holding time (time during which the sample remains at the maximum temperature achieved) did not increase the efficacy of treatments above 200 MPa. During the later 50 days of storage at 4 degrees C neither the microbial count nor the PME activity increased their values and no differences were observed with the pasteurized samples during this period. Industrial relevance: Today, consumer demands are more and more directed toward high-quality, additive free, minimally processed, nutritious, and fresh like products. Thermal pasteurization in fruit juice processing has as primary purpose to destroy pathogenic and deteriorative organisms as well as inactivate undesirable enzymes. Nevertheless, high pasteurization temperatures impact negatively on the nutritional quality and taste of orange juice. On the other hand, Ultra-High Pressure Homogenization (UHPH) is an emergent technology based on the application of high pressures, that allows to process in continuous fluid foods and that has been proposed by its germicidal effect as an alternative to the pasteurization for foods with heat-sensitive properties. Recently, several improvements introduced in the design and materials of UHPH equipments allowed to increase the performances of these equipments in order to bring them closer to the industry requests. We believe the article contains new data and information about the UHPH pectin methylesterase and microbial inactivation effects on orange juice and may be relevant to the scientific and industrial community. (C) 2011 Elsevier Ltd. All rights reserved.