SENSORY THRESHOLDS OF CONSISTENCY OF SEMILIQUID FOODS: EVALUATION BY SQUEEZING FLOW VISCOMETRY*

Abstract

Identification of subtle textural differences or changes in foods in isolation has been a difficult task because they are usually accompanied by differences or changes in other sensory properties. Textural modification of semi liquid foods can easily be produced by mechanical means without affecting their taste and appearance. The changes can be then quantified using squeezing flow viscometry without introducing new uncontrolled modifications. Comparison of the measurements with sensory evaluations of the same samples can establish the threshold of sensory detection, at least in principle. To test this hypothesis, the consistency of practically intact mayonnaise, tomato paste, yogurt and strawberry jam of two commercial brands each were evaluated by squeezing flow viscometry using an Instron UTM. Other samples of the same brands were stirred mildly to modify their consistency and then compared with the undisturbed samples. The textural differences were expressed in terms of the apparent stress at three compressed specimen heights, and the residual stress after 60 and 120 s at the final height. Relatively large differences, as judged by these mechanical measures were also detected by an untrained sensory panel, but the ‘correct identifications’ never reached a 100%. In the case of the two different brands of yogurt, the panel failed to establish the existence of differences, which were clearly detected by the instrument. This suggests that not every difference, detectable instrumentally, has a corresponding sensory response. Although the number of results in this preliminary work was too small to establish the exact threshold for sensory detection, the methodology seems to be appropriate for such a purpose. This is because of the high reproducibility of the squeezing flow parameters and their sensitivity to even subtle difference in the tested specimens consistency.