Estimation of Potential Shelf Life of Cottage Cheese Utilizing Bacterial Numbers and Metabolites

Abstract

A study was conducted to investigate the use of bacterial numbers and their metabolites as estimators of the potential shelf life of cottage cheese. Dry cottage cheese curd and cream dressing were obtained on the day of processing. Portions of the cream dressing were inoculated with Pseudomonas fluorescens P27 to result in approximate levels of 0, 1,000 and 100,000 bacteria per g in finished cottage cheese after combining the curd and cream. Samples, stored at 7°C, were sensorially evaluated on a daily basis and analyzed every 7 d for up to 35 d. On days of analysis each sample was subjected to preliminary incubation (PI) as follows: none, 21°C for 7 h, 21°C for 14 h, 13°C for 18 h and 18°C for 18 h. For each PI, samples were enumerated by aerobic plate count, modified psychrotrophic bacteria count and gram-negative (CVT) count. Samples were enumerated for the standard psychrotrophic bacteria count without PI. Samples were also exposed to 18°C for 18 h PI in plate count broth for impedance detection measurements. Endotoxin (lipopolysaccharide) concentration and proteolysis were determined by the Limulus amebocyte lysate assay and the o-phthaldialdehyde method, respectively. Bacterial enumerations proved to be of little estimative value as the highest correlation coefficient obtained was −0.61. Endotoxin, proteolysis and impedance detection methods resulted in high correlation coefficients as related to potential shelf life of cottage cheese, with values of −0.81, −0.87 and −0.90, respectively. A prediction equation was formulated from the data.