Improvement of the Fresh Taste Intensity of Processed Clementine Juice by Separate Pasteurization of its Serum and Pulp

This work describes a process to separate the Clementine juice by centrifugation into two fractions, the larger one ('serum fraction') almost lacking of pulp, and the smaller one ('pulp fraction') enriched in pulp, which are independently pasteurized in conventional plate heat exchangers under different conditions. Both fractions were aseptically blended giving a final product, whose fresh taste did not differ from that of the initial nonheated juice. The larger serum fraction was almost free of pectin methylesterase activity and could be pasteurized under minimal heat conditions, just enough to destroy microorganisms, less heat-resistant than enzymes. Since only a minor part of the juice ( the pulp fraction) received the usual heat treatment, fresh taste was preserved. Destruction of Lactobacillus plantarum inoculated to the serum fraction was fitted accurately by the Weibull model, with a reduction higher than 5 log cycle at 57.5 degrees C for 20 s and no counts were found at 60 degrees C for 10 s. According to this, thermal treatment of the serum fraction (78% of the initial juice) was fixed at 60 degrees C for 15 s. Sensory evaluation of fresh taste intensity showed no significant differences between serum treated at 60 degrees C for 15 s and fresh serum. The pulp fraction (22%) was pasteurized at 85 degrees C for 15 s and at 90 degrees C for 30 s to assure enough enzyme inactivation. No differences were found between the nonpasteurized juice and the blend of pulp and serum pasteurized as explained above, whereas both samples presented fresher taste than the whole juice treated at 90 degrees C for 30 s.