The Effects of Psychotrophic Contamination and the Addition of Sodium-Citrate on Major Chemical Components and Flavor of Buttermilk.

The main objective of this research was to determine what effect, if any, post-pasteurization contamination and/or sodium citrate would have on major chemical components and flavor of buttermilk. Also, it was of interest to establish chemical profiles of good versus bad buttermilk and to gain information which would aid in the prediction of buttermilk flavor. The research was divided into two parts. In Part I buttermilk was artificially inoculated with psychrotrophs (Pseudomonas fluorescens P27) at time of bottling. Part II examined the effect of psychrotrophic contamination at time of set with a lactic culture. Treatments consisted of buttermilk, both with and without added sodium citrate (.15%), and three inocula of psychrotrophs (0/ml, 10(\u274)/ml and 10(\u276)/ml). After processing, buttermilk was stored at 7(DEGREES)C in plastic 3.78 1 containers and sampled at 0, 3, 5, 10, 15 and 20 d. Volatile organics (acetaldehyde, acetone, ethanol and diacetyl) were determined by gas chromotography with headspace sampling followed by organic acid (orotic, lactic, acetic and propionic) analysis by high performance liquid chromotography. Microbial parameters examined were total lactic streptococci, gram negatives and citrate fermenting bacteria. Flavor evaluations were performed by a three member trained taste panel. The Hull test was used to determine proteolysis. Data revealed no significant changes in volatile organics or organic acids as a result of psychrotrophic contamination at time of bottling. Increases in acetaldehyde and decreases in acetone were observed in buttermilk inoculated with psychrotrophs at time of set with a lactic culture. The addition of sodium citrate to milk prior to fermentation yielded higher levels of diacetyl, acetone, lactic acid, acetic acid and propionic acid. Higher concentrations of these components resulted in a definite improvement in buttermilk flavor. Among the chemical components studied, acetone was that which was most often related to flavor. In addition, regression equations were established which laid a foundation for further study in the area of flavor prediction