A study of yogurt production from the perspective of rheology: Introducing passive microrheology

EGEA, FERNANDO; RAMSCH, ROLAND; TORMO, HÉLÈNE; DELGADO, JUAN FRANCISCO

Mar del Plata

Congreso; XVI Congreso Argentino de Ciencia y Tecnología de Alimentos; 2017

Asociación Argentina de Tecnólogos Alimentarios - AATA

Fermentation control in yogurt production is necessary to obtain standardized rheological and sensorial characteristics that consumers desire. Classic forms of rheological characterization consist in the direct interaction with the food, through efforts on them. The passive laser micro-rheology allows to obtain materials properties through the movement of the constituent particles using diffusion wave spectroscopy (DWS) based on the backscattered light, obtaining parameters that are directly linked with the viscoelastic properties of the material (Mean Square Displacement and Elasticity index). The objective of this work was to differentiate, through the passive laser micro-rheology (Rheolaser Master, Formulaction, France) characteristics of the lactic ferments that affect the rheological and texture properties of the final product and to compare the sensitivity with classical rheological measurement equipment (Texturometer TA1, Lloyd, USA and AR-G2 Oscillatory Rheometer, TA Instruments, USA). In addition, it was proposed to find out attributes that allow characterizing the yogurt in early stages from the measurement and analysis of the microstructure. The effect of 4 heat pretreatments (No treatment, 72 ° C - 15 seconds, 85 °C - 15 minutes and 92 °C - 5 minutes), the influence of homogenization (50 MPa at 65 ° C) and milk fat content (0.5 and 3%) in final product characteristics, fixing the starter culture used (YO-MIX495 from Danisco, DuPont, France). Micro-rheology tests were performed at 42 ºC in line and double penetration tests were performed over the final product. In addition, the sensitivity of laser rheometer, oscillatory rheometer (frequency and % strain sweeps) and texturometer (double penetration tests to 20 mm) to the effects produced by other two starters (Y430A and Y456B, Sacco, Italy) were compared. Laser rheometer was able to differentiate the effects of the pretreatments on the samples through the elasticity index with greater sensitivity and anticipation than texturometer. In addition, the evolution of the elasticity index in yogurts allowed differentiating starters without having to wait to final times of fermentation, whereas texturometer and oscillatory rheometer could not differentiate them. Starters produced two different yogurts to the palate. According to obtained results it is possible to predict the final rheological characteristics of yogurt at initial time periods of fermentation through laser micro-rheology.