33-3 |
Use of sensory methods in a molecular-genetic study of bitterness in Cheddar cheese |
C. P. BRENNAND and J. R. Broadbent. Dept. of Nutrition & Food Sciences, Utah State Univ., 8700 Old Main Hill, Logan, UT 84322 Bitterness, a significant problem in Cheddar cheeses, may be caused by the accumulation of hydrophobic peptides produced by some starter bacteria. Starter proteinase specificity is the primary determinant in whether or not a starter culture produces bitter peptides, but the relative contribution of distinct proteinases to these reactions remains unclear. The objectives of this study were to define the contribution of starter proteinase-specificity on peptide pools and bitterness in Cheddar cheese, to develop a cheese-based test for bitterness, and to establish factors that influence bitter flavor perception in Cheddar cheese. A series of isogenic strains which differed only in proteinase specificity were constructed by recombinant DNA technology. Reduced-fat Cheddar cheese was manufactured and peptide accumulation in experimental cheeses was confirmed by HPLC analysis. Trained, screened panel members evaluated quinine-spiked cheeses to measure perception of bitterness in full-fat, reduced-fat and no-fat cheese at three serving temperatures. Warm cheese samples received lower bitterness scores than did identical samples at refrigerated or room temperature. Full-fat was rated more bitter than no-fat quinine-spiked cheese. Peptides were synthesized and purified by HPLC to match authentic peptides found in experimental cheese. Model cheese systems were spiked with peptides to elucidate impact and thresholds in a cheese system. Peptide level threshold for bitterness were several levels of magnitude higher in cheese than in water for both b casein (193-209) and as1 (1-9) peptide fragments. The b peptide was rated more bitter at lower levels than the as1. Sensory analysis of experimental cheeses after 2, 4, and 6 mo. of ripening established a clear role for culture specificity in the production of bitter peptides. Strains carrying group a, e, or h proteinase had low, intermediate, or high propensities for bitterness, respectively. Starter culture proteinase specificity is a key determinate of whether or not a cheese will develop bitterness.
Session 33, Sensory evaluation of dairy flavors
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