26-7 |
Yield stress as predictor of firmness in yogurt |
F. M. HARTE1, S. Clark2, and G. V. Barbosa-Cánovas1. (1) Dept. of Biological Systems Engineering, Washington State Univ., 274 FSHN Bldg., PO Box 646120, Pullman, WA 99164-6120, (2) Dept. of Food Science & Human Nutrition, Washington State Univ., 226 FSHN Bldg., PO Box 646376, Pullman, WA 99164-6376 Yogurt is a very nutritious food with increased demand by consumers. Despite this, no standard procedures are available for the sensory evaluation of the flavor, appearance, and texture of yogurts. While trained panelists use well recognized descriptors for texture of yogurts, the cost associated with training panelist and the difficulties in data analysis makes the search for instrumental measurements a continuous effort by researchers. The objective of this research was to measure the yield stress in laboratory-made and retail yogurts and to correlate this rheological property with the sensory firmness as perceived by trained panelist. Additionally, the apparent residual stress was correlated with the sensory viscosity in pre-stirred samples. Laboratory-made yogurts were prepared using standard procedures and selected concentrations of gums to achieve different firmness. Retail yogurts covering a wide range in firmness were purchased in a local store. The yield stress was measured as the peak stress in a vane rotating at 1 rpm and the apparent residual stress as the average stress during the last 10 seconds of rotation. Five individuals were selected and trained for judging firmness and viscosity of laboratory-made yogurts and 15 individuals for retail yogurts. Yield stress exhibited significant correlation (p<0.001) with the sensory firmness as perceived by panelists in laboratory-made (r=0.99) and retail (r>0.97) yogurts, independently of other physical or sensory properties. The apparent residual stress was significantly correlated with sensory viscosity (r>0.90). Several advantages exist for assessing firmness using the yield stress including (1) less time to run the samples, (2) more power to detect differences, (3) less damage associated with sample handling, (4) avoid use of relatives scales or anchors, (5) simple data analysis (homogeneous variances), (6) avoid costs associated with training and managing panelists, and (7) potential to design products based on a target yield and apparent residual stress.
Session 26, Dairy Foods: General developments in dairy technology
|