Activation And Application Of Lactoperoxidase System

The lactoperoxidase system (LPS) is the natural antimicrobial system presented in milk. It has been used to preserve raw milk quality in the areas where it is not possible to use mechanical refrigeration for technical and/ or economic reasons. The LPS consists of three components: LP, thiocyanate ion (SCN^-), and hydrogen peroxide (H₂O₂).In this paper, the potentials of applying chemical activation of the LPS in extending the shelf life of raw milk were investigated. Raw milk was LPS activated by adding various concentrations (mmol/L) of SCN^-/H₂O₂, denoted as 0.1, 0.25 or 0.5 mmol/L, and stored at 4°C, 25°C or 35°C respectively. The residual concentration of SCN^- in the raw milk was much lower than the concentration in human saliva or in human gastric juices (0.86-5.17 mmol/L and 0.69-0.86 mmol/L, respectively). H₂O₂ was lower than 0.2 mmol/L, which was much lower than the value of FAO/WHO (2.94-8.82 mmol/L), and decreased rapidly during the enzymatic oxidation of thiocyanate to produce the hypothiocyanate ion. Thus the presence of H₂O₂ is not considered a toxicological risk.Under different preserved temperatures (4°C, 25°C, 35°C), the fresh period of the treatments prolonged than the control by 3-4 days, 2.5-4.5 hours, and 3.5-7.5 hours, respectively. By quality index measurement, 0.5 mmol/L was the last treatment to spoil, which suggested that the shelf life of milk increased with increasing concentrations of SCN^-/H₂O₂. All the treated milk samples showed lower microbiological content during storage compared to the control. The total colony counts and coliform counts of all treatments were lower than the control at least by 1-2 log, and improved by 3 hygienic grades. The potentials of applying enzymatic activation of LPS in extending the shelf life of raw milk at temperature 25 or 35°C were investigated. H₂O₂ was produced by GO-G system. The result showed that at 25°C, the fresh period of the control and the treatments of 0.1, 0.25, and 0.5 mmol/L samples were 16.5 h, 6.5 h, 26.5 h, and 33.5 h, respectively. The storage period was increased 19 h at the concentration of 0.5 mmol/L of SCN^-/H₂O₂ at 25°C, and it increased about 4 h at 35°C. Compared with the method which activated the LPS by adding H₂O₂ directly, this method prolonged the storage period 14 h. Enzymatic activation of LPS have a sustaining effect to prolong the shelf life of raw milk, which is better than chemical method. All the treated milk samples showed lower microbiological content during storage compared to the control, and improved the hygienic grade by 3 grades.Yoghurt was prepared using mixed culture and raw milk in which LPS had been chemical activated by adding various concentrations (mmol/L) of SCN^-/H₂O₂ and denoted as 0.25 and 0.5 mmol/L. The result showed that LPS suppressed acid production in the yoghurts during refrigerated storage. The most effective suppression was observed with sample of 0.5 mmol/L. The water-holding capacity of yoghurt was increased by activation of LPS. The rheological properties showed that the apparent viscosity of yoghurt, G' and G'' were also reduced by activation of LPS. The yoghurts had softer and smoother texture than untreated one. The accessibility of SH groups and total SH groups in the LPS activated raw milks were reduced. The SDS-PAGE of heat-treated milks samples showed that the interaction betweenβ-lactoglobulin (β-Lg) andκ-casein (κ-CN) was decreased, and hindered by the LPS activation, which validated the mechanism of the activation of LPS.