Relationship of free fatty acids and acid degree values to lipolytic flavor of milk

Free fatty acids were studied in relation to acid degree value (ADV) and rancid flavor (RF) in milk and ADV evaluated as a method for measurement of RF. Selected fatty acids (FA) were blended in milk at .25µmol/ml milk with emulsifier. Recovery of FA was <.63 (C₄-C₈), 1.95-2.33 (C₁₀-C₁₆), 3.24 (C_18:0)» and 4.12µmol/g fat (C_18:1). Significant differences (p<.05) in recovery were found among all groups of FA. Recovery of 5 concentrations (.20, .25, .35, .45, .55 µmol/ml milk) did not differ (p>.05) for C₄ (<.51 µmol/g fat), was proportional to added concentration of Cio with significant differences between low and high concentrations (1.94-4.64 µmol/g fat), and was significantly higher with increasing concentration of C_18:1 (3.91-11.08 µmol/g fat). Fatty acid partitioning into skim (C₄) or fat (C₁₀/ C_18:1), as separated by ADV procedure, was demonstrated by gas chromatography. Detection thresholds for C₄, C_18:1 and C₁₀ were .20, .55, and .55 µmol/ml milk.

A 6-member trained flavor panel scored milk samples collected from east Tennessee farms and laboratory-prepared rancid samples (LPRS) for RF by magnitude estimation. Correlation coefficients between rancidity scores (farm samples and LPRS) and standard methods ADV were .13 (p=.16) and .17 (p=.002). Mean rancidity scores were not significantly different for samples divided into 5 groups based on ADV (<1.26, 1.26-1.75, 1.76-2.30, 2.31- 2.75, >2.75) but LPRS were given higher rancidity scores. A consumer panel detected a difference between farm milk with low ADV (1.57), and high values (5.37, 7.67 meq/100 g fat) using paired comparison method. There was an increase in ADV and rancidity scores with storage (12 days at 4°C). Correlations between concentration of FA and ADV were >.82 (p=.0001) for all major FA in farm milk but, for LPRS, the correlation was moderate (r=.53, p=.07) for total shorter chain (C₄-C₁₀) FA and low (r=.23, p=.47) for total longer chain (C₁₂-C_18:1) FA. C₄, C₁₄, C_16:0, C_18:0, and C_18:1 concentration significantly increased among ADV groups. Correlations between RF and FA concentrations were low (r<.45) for both farm and LPRS. Total FA concentrations were not significantly different among "slightly", "moderately" "very rancid" or "unpalatable" samples.