RHEOLOGICAL BEHAVIOR OF PINEAPPLE JAM FORMULATED WITH DIFFERENT ACIDULANTS

The formation of the gel network in traditional jams is a complex interaction among sugar, pectin, and an acidic environment. In many cases, the addition of acidulants is required to achieve a pH between 3.0 and 3.2 in the jam matrix, ensuring proper gel formation. The rheological behavior of gels is of industrial interest, as these systems possess complex networks, and understanding them can contribute to the development of new products with improved market performance. In this context, the objective of this study was to determine whether differences exist in the rheological profile of gels formed in “pérola” pineapple jams prepared with five different acidulants: (1) acetic acid, (2) citric acid, (3) hydrochloric acid, (4) lactic acid, and (5) tartaric acid. The formulations consisted of 60% pineapple pulp, 40% sucrose (União, São Paulo, Brazil), and 1% pectin (CPKelco – PECTIN LM-102-AS). Based on the initial pH of the pineapple pulp, the amount of each acid to be added to the jam matrix was previously calculated to reach a final pH of 3.0. The cooking process continued until reaching 60 ± 2 °Brix. Rheological behavior was analyzed using a rheometer (Brookfield Model DV-III) equipped with a temperature-controlled bath (Brookfield Model TC-500) at 25 °C, conducted at the Fruit, Vegetable, and Sugar Products Laboratory (LFH) of the School of Food Engineering (FEA), University of Campinas (UNICAMP). The five treatments were analyzed in triplicate, and the following parameters were obtained: viscosity (cP), torque (%), shear stress (Pa), and shear rate (s⁻¹). Measurements were performed at spindle speeds ranging from 1 to 250 RPM, each for 30 s, and the procedure was repeated in reverse order to obtain both ascending and descending curves. All treatments exhibited pseudoplastic fluid behavior, typical of non-Newtonian materials. Thixotropic characteristics were also observed, indicated by gel network breakdown under shear without complete recovery after stress removal. Notably, the jam formulated with lactic acid exhibited more pronounced hysteresis, showing greater sensitivity to structural breakdown compared with the other formulations. This behavior may be associated with lactic acid interference in the crystal network, as reported in other polymeric studies. In conclusion, except for lactic acid, the type of acidulant did not affect the rheological behavior of the gels formed.