Avaliação da termossonicação na inativação da lipoxigenase do extrato hidrossolúvel de soja

Abstract

The soymilk (SM), a drink resulting from the hydration of soybeans, has great nutritional importance and is an alternative among lactose-intolerant consumers and/or those seeking healthier diets. As it is highly perishable, this product needs to undergo a conservation method to ensure food safety and extension of its shelf life. Commonly, the heat treatment applied to SM is defined as a function of its ability to inactivate the lipoxygenase enzyme (LOX), due to its undesirable effects on the product. Although thermosonication (combination of ultrasound and heat) has the potential to reduce the conventional heat treatment intensity, there are still no studies investigating its effect on SM. Thus, this work aimed to evaluate the thermosonication process on the inactivation of the lipoxygenase enzyme in SM, varing ultrasonic amplitudes (70% and 90%). For this, a central composite design (CCD) was used, evaluating the effect of parameters as temperature (62 °C to 83 °C) and thermosonication time (2 to 4 min) on the LOX residual activity (RA, %). The results were submitted to regression analysis, at 5% significance level, and then contour curves were generated to assess the best experimental condition for LOX inactivation. It was found that the variable that most influenced the thermosonication process was temperature, and, regardless of the amplitude, to reach levels of LOX reduction above 70%, it was necessary to use temperatures above 70 °C. The experimental condition with the greatest reduction in LOX (RA = 2.35%) in the amplitude of 70% was at the temperature of 80 °C/2min, while for the amplitude of 90%, it was at the temperature of 83 °C/3min (RA =2.14%). At elevated temperatures, it was observed that thermosonication did not have a synergistic effect on LOX inactivation in the EHS. Fresh SM (without undergoing heat treatment), treated with thermosonication at 70% and 90% amplitude, as well as EHS subjected to a conventional heat treatment (83 °C/3min) were subjected to color analysis (L*, a*, b*), pH, total soluble solids (°Brix) and total phenolic content. The results obtained for the physical and chemical analyzes of the different treatments were compared to each other using the t-test and Dunnett's test, at a 5% significance level. Among the color parameters evaluated, the variable a* showed significant difference (p<0,05) between fresh and thermosonicated SM samples in the amplitude of 70%. The soluble solids content of fresh EHS compared to other treatments showed statistical significant difference (p<0,05). The use of thermosonication showed a low loss of total phenolic content in the EHS compared to conventional heat treatment. This work opens new perspectives for the study of LOX inactivation in other raw materials, using thermosonication under different conditions.