Estudo da concentração de ácido sórbico e de indicadores da reação de Maillard em doce de leite e o uso de permeado de leite como indutor da cristalização de lactose em leite condensado

Abstract

Dulce de leche and sweetened condensed milk are dairy products obtained fromthe partial dehydration of milk and are therefore less perishable than milk. Both needmilk and sucrose to be obtained, with differences in the manufacturing technology. For dulce de leche, besides the concentration, the mixture is cooked, which is usuallydone in an open pan (atmospheric pressure) and this process favors the Maillard Reaction, responsible for characteristics such as color, flavor, and texture of the dulcede leche. The condensed milk is evaporated under vacuum and, unlike the dulce deleche, there is no cooking, which gives it a more fluid viscosity and a lighter color thanthe dulce de leche. Due to the variations that can occur in the manufacture of both and the industrial interest, this dissertation presents studies based on technological issues of the two products. For the dulce de leche matrix, two independent studies were developed, in which the first evaluated the heating stability of the preservative sorbic acid and its salt potassium sorbate in the manufacture of dulce de leche; in thesecond study, the presence of four furfural derivatives (indicators of the Maillard Reaction) were evaluated: 5-hydroxymethylfurfural (HMF), 2-furaldehyde (F), 2-furyl- methylketone (FMC) and 5-methyl-2-furaldehyde (MF) in commercial milk candy samples, both conducted by high-performance liquid chromatography (HPLC). Thesetwo strands of study are based on industrial demands related to the timing of addingpreservatives and better understanding of the Maillard Reaction. The results showedthat for the preservative to be degraded by heating, it is necessary to consider the pHof the medium, especially below the pKa of sorbic acid. This is because, due to the chemical equilibrium, the acid species prevails in acidic medium and this has the ability to be carried by steam, while the sorbate prevails in higher pH and is not lost in evaporation. With the study of the Maillard reaction markers, it was possible to develop and apply a methodology that simultaneously identified and quantified the 4analytes of interest in the matrix, with good sensitivity, in which HMF was detected and quantified in all samples, ranging from 49.79 to 262.0 µmol/kg; F was detected in two samples, but not quantified because it was below the quantification limit of themethod; the others were not detected for any sample, which may be related to the intensity of the thermal treatment and the process of obtaining each product. For sweetened condensed milk, the second matrix of interest, the application of powdered milk permeate, a by-product of dairy products that has a high concentration of lactose,was studied as a lactose crystallization agent. The results revealed that the milk permeate is an excellent inducer of crystallization, since the profile obtained was similar to the crystallization with pure lactose, as evidenced by the analysis of crystalmicroscopies in specific software. In addition, the use of permeate for this purpose iseconomically feasible because it is a by-product generally discarded by industries.