Low-Fat Set Yogurt Made from Milk Subjected to Combinations of High Hydrostatic Pressure and Thermal Processing

Abstract

The combined use of high hydrostatic pressure (300 to 676 MPa, 5 min) and thermal treatment (85 degrees C, 30 min) in milk for the manufacture of low-fat yogurt was studied. The objective was to reduce syneresis and improve the rheological properties of yogurt, reducing the need for thickeners and stabilizers. The use of high hydrostatic pressure alone, or after thermal treatment, reduced the lightness and increased the viscosity of skim milk. However, milk recovered its initial lightness and viscosity when thermal treatment was applied after high hydrostatic pressure. The MALDI-TOF spectra of skim milk presented monomers of whey proteins after a treatment of 676 MPa for 5 min. Yogurts made from skim milk subjected to 400 to 500 MPa and thermal treatment showed increased yield stress, resistance to normal penetration, and elastic modulus, while having reduced syneresis when compared to yogurts from thermally treated or raw milks. The combined use of thermal treatment and high hydrostatic pressure assures extensive whey protein denaturation and casein micelle disruption, respectively. Although reaggregation of casein submicelles occurs during fermentation, the net effect of the combined HHP and thermal treatment is the improvement of yogurt yield stress and reduction of syneresis.

Sensory properties of high-pressure-treated milk

“…Similar tendency was established by Naik et al (2013) in skimmed milk after treatment at 250-450 MPa, significant decrease in the L* value was observed, and in ewe`s milk, by Gervilla et al (2001). Also Harte et al (2003) reported that milk subjected to HP treatment and thermal treatment followed by HP, loses its white colour and turns yellowish. Johnston et al (1992) proposed that the decrease in L* value could have been mainly due to disintegration of casein micelles by pressure into small fragments and that might be a possible explanation for obtained results in our research.…”

“…Hunter Luminance value (L* value) of milk is generally used as a measure of whiteness (Harte et al, 2003). The results of colour CIE L*a*b* measurements of the milk samples are shown in Table 2.…”

Effects of High-Pressure Technology on the Functional Properties of Milk and Fermented Milk Products

“…Acid gels, such as yogurt, obtained from HHP (400-500 MPa) homogenized milk showed increased yield stress, resistance to normal penetration, elastic modulus and reduced syneresis with decrease in whey holding capacity and retention of more than 20% whey after centrifugation [36,37]. Similarly, Needs et al [27] recorded lower values of fracture stress in set yoghurts made from pressure-treated milk (60 MPa for 15 min) compared to heat treated milk.…”

“…Acidification of yoghurt milk with GDL (glucono-δ-lactone) at 200 MPa for 20 min resulted in fine coagulum, homogeneous gel than that of heat treated milk [19,22,36].…”

“…Thus, these changes could lead to modifications of the technological parameters of milk used in cheese-making to improve the rennet coagulation properties and cheese yield (Fig. 2) [19,36]. …”