Investigação do espessamento em leite condensado integral: caracterização física, química e microbiológica

Abstract

Sweetened condensed milk is milk product which can be obtained by the partial removal of water from milk with the addition of sugar and is among the five dairy products most exported by Brazil. It’s must meet the sensory characteristics of viscous and semi-liquid consistency, yellowish white color, characteristic odor and flavor, homogeneous texture with no sandiness. Along the shelf life a gradual increase in viscosity is expected, however, the excessive increase in viscosity and gelation de- characterizes the product. This is a defect called thickening. The aim of this search was to characterize condensed milk samples with thickening, obtained from a Brazilian dairy industry. Standard (SCM) and non-standard (NSCM) condensed milk samples were analyzed for optical microscopy, pH, acidity, moisture content (MU), total solids (TS), soluble solids (SS), water activity (Aw) and fat. The profile of protein bands by polyacrylamide gel electrophoresis (SDS-PAGE), protease activity, particle distribution, color, free 5-hydroxymethylfurfural index (HMFf) and rheology were also analyzed. Microbiological analysis was performed to enumerate mesophilic aerobic, coagulase positive Staphylococcus, filamentous fungi and yeasts. The bacterial strains were selected and characterized by biochemical, molecular (rep-PCR) and spectrometric (MALDI-TOF) methods. The results showed that NSCM has an acidity value (0.59 g/100g of lactic acid) and pH (5.37) uncharacteristic for condensed milk, particles and crystals larger (NSCMd90%: 34.88 µm), rheological behavior typical of solids and higher complex viscosity than SCM. Coagulase negative Staphylococcus and yeasts were the main groups of microorganisms isolated from the samples. S. gallinarum demonstrated the ability to produce thickening in sweetened condensed milk, which progressed to a gel state with an increase in acidity and a reduction in pH. The results of this study show that problems with microbial contamination in the production of sweetened condensed milk can cause thicken ing during the shelf life.