Assessing Set-Style Yogurt Quality After Vibration or Altitude Postproduction Treatment Using Noninvasive Methods

The impact of vibration or altitude on set-style yogurt after production was assessed on a technology platform simulating the conditions encountered during road and air transportation. Rheological (apparent viscosity, firmness, stress relaxation, frequency dependence of elastic, and viscous moduli) and physicochemical (pH and syneresis) properties of yogurts were evaluated for 22 days. Noninvasive methods (visible near-infrared reflectance and nuclear magnetic resonance) were also evaluated. The rheological and physicochemical properties were not significantly affected by altitude or vibration compared with control yogurt (no treatment). Apparent viscosity, firmness, and frequency dependence of both moduli significantly increased by 13%, 5%, and 3%, respectively, during storage, probably due to gel restructuring. The transverse relaxation time constant T₂₁, measured by nuclear magnetic resonance, significantly decreased by 13% in control and altitude conditions after 22 days. Yogurt with vibration condition showed constant T₂₁ values, suggesting that vibration affected the restructuring process of yogurt during storage. Both noninvasive techniques were able to significantly differentiate (p < 0.01) yogurts with postproduction treatments from control (69.2% and 87.0% accuracy) by partial least squares-discriminant analysis. This was not observed with conventional methods. Predicted correlation between conventional and noninvasive methods by partial least squares regression was found with R² cross-validation of 0.69 for visible near-infrared reflectance and pH, 0.83 for stress relaxation, 0.79 for firmness, and 0.73 for apparent viscosity with nuclear magnetic resonance. The better sensitivity of the noninvasive methods compared with conventional analysis offers potential for the detection of quality control deviation in set-style yogurts during transportation.