Utilização do micro-ondas na conservação de polpas de frutas: alterações físicas e químicas.

The preservation of fruit pulps is done by applying a heat treatment followed by freezing. However, the intensity of heat treatment may cause undesirable changes in product characteristics, such as thermal degradation of thermolabile nutrients such as vitamins and pigments. The objective of this work was to evaluate the impact of conventional heat pasteurization and microwave pasteurization on the physical and chemical quality parameters of fruit pulps. Passion fruit, guava and orange pulp were subjected to pasteurization (with heat and microwave application). Pulp quality was evaluated for optical microstructure, sedimentation, turbidity, humidity, soluble solids content, titratable acidity and pH, vitamin C and carotenoids content. Data were analyzed by analysis of variance at a significance level of 95% and Tukey test. In the optical microstructure analysis the thermal treatments: conventional and microwave presented significant distinctions only in the passion fruit and orange pulps. Microwave pasteurization provided higher sedimentation rates of passion fruit and orange pulps. In guava pulp, in turn, the application of microwaves did not increase the sedimentation of the pulp. The application of microwaves influenced the increased turbidity of passion fruit and orange pulp. However, in passion fruit pulp, this index was lower than in conventionally treated samples. In guava pulp, the turbidity of the samples submitted to microwave application did not differ statistically from the samples without treatment. Conventional and microwave pasteurization provided an increase in soluble solids content and decreased moisture in the pulp of the three fruits. Regarding the pH content, there was no significant pH difference in passion fruit and orange pulps submitted to different pasteurization treatments. In guava pulp, conventional pasteurization increased the pH content. Microwave application did not alter the titratable acidity of the passion fruit pulp. In conventionally and microwave pasteurized guava pulp, titratable acidity values were statistically similar. In orange pulp, the treatment that increased the most in titratable acidity was conventional pasteurization. The vitamin C content of all pulps was statistically higher with microwave application compared to conventional pasteurization. The carotenoid content in the passion fruit and orange pulps were statistically similar when subjected to conventional and microwave pasteurization. In the guava pulp, the microwave treatment provided lower reduction in carotenoid content compared to conventional thermal pasteurization. Thus, regarding the pasteurization technology that less degraded the initial characteristics of the product, the heat treatment using the microwave was more efficient in the passion fruit, guava and orange pulps compared to the conventional thermal pasteurization.