Effect of temperature

Abstract

The main objective of this research was to study the combined effect of temperature —time (TT) combination and carbon dioxide addition on shelf life extension of chilled pasteurized cow milk. Raw cow milk obtained from the university farm was standardized (3.25% fat), homogenized and pasteurized by High Temperature- Short Time (HTSI) method using different TT combinations {72 °C/15s (TTi), 74.5 °C/13s (TT,). 77 °C/12s (TT,). 79.5 °C/10s (TTJ, 82 °C/8s (TTS). Pasteurized milk was bottled and chilled at 4 °C. Phosphatase test was conducted to detect the efficiency of pasteurization. In a separate study pasteurized milk was treated with carbon dioxide and sensory threshold was determined using ASTM (American Society for Testing and Materials) E 679 Ascending Concentration Series Method of Limits to select the suitable carbon dioxide level that can be added into milk. Pasteurized bottled milk was treated with 3 levels of carbon dioxide (0, 7 and 15 mm) and chilled at 4 °C. Shelf life of pasteurized, carbon dioxide treated milk was determined using microbiological tests. The best sensory threshold level of carbon dioxide was 15.61mM. The reduction of Viable Plate Count (VPC) during TT, TT2, TT3, TT4 and TT5 combinations were 96.2%, 96.6%, 97.3%, 91.5% and 93.9% respectively. VPC (log cfu/ml) increased with the storage period in almost all the treatment combinations. The time needed for pasteurized milk to reach the VPC of 5 x 104 cfu/ml (end of shelf life) varied among the treatment combinations. The longest shelf life of 11 days was obtained by TT3 at 15 mm carbon dioxide level. Addition of carbon dioxide up to 15 mm, increased the shelf life of pasteurized milk treated with TT,, TT2, TT3, TT4 and TTS combinations by 1, 2, 3, 2 and 3 days respectively