Comparisons of methods for measuring yield stresses in potato puree: effect of temperature and freezing

Seven methods for determining yield stress of concentrated suspensions were applied to fresh and frozen/thawed natural and commercial purees at different temperatures, and results were compared. Since potato puree was consistent with Herschel-Bulkley flow behaviour, yield stress was more reliably determined by extrapolation of the flow curves assuming Herschel-Bulkley model than Bingham and Casson models. Methods for determining yield stress by dynamic rheological tests were tedious and are not always applicable. Given the high correlation between Herschel-Bulkley yield stress and that as determined by Bohlin option (R2 = 0.8735), Bohlin's “Yield stress option” appears to be highly useful for direct measurement of this property in potato puree. Temperature influenced yield stresses more in frozen than in fresh purees, both natural and commercial. At equal temperatures, processing reduced yield stresses in natural puree but increased them in commercial puree, showing that their structures were not affected in the same way.