R.M. Velázquez-Estrada, M.M. Hernández-Herrero, B. Guamis-López, A.X. Roig-Sagués

Centre Especial de Recerca Planta de Tecnología dels Aliments, Departament de Ciencia Animal i dels Aliments, XaRTA, TECNIO, MALTA Consolider, Facultat de Veterinària, edifici V, Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain.
Abstract

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 °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 °C). Shelf-life of treated juices was evaluated for a period of 50 days at 4 °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 4.26 ± 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 °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 °C neither the microbial count nor the PME activity increased their values and no differences were observed with the pasteurized samples during this period.