Abstract
Pasteurized fresh milk requires an accurate estimation of shelf life under various conditions to minimize the risk of spoilage and product losses. Milk samples were stored for 56 h in an oven at 25°C and for 15 days in a refrigerator at 4°C. Samples were analyzed using an electronic nose (e-nose), total bacterial count, titratable acidity and pH to determine the quality of milk. Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA) were used to analyze e-nose data of milk stored at 25°C, and 4°C. A clear shift in quality was identified by the e-nose, which also appeared in the total bacterial count after 24 h and 12 days for storage at 25 and 4°C, respectively. On the other hand, titratable acidity exceeded the normal limits of 0.14 % - 0.21 % after 24 h for storage at 25°C (0.247 ± 0.006 %) and after 15 days for storage at 4°C (0.25 ± 0.01 %). If pH was a good indicator of quality for samples stored at 25°C, it showed no clear trends for samples stored at 4°C. Based on the microbial count data and e-nose output, the milk had a shelf life of 0.3 day (i.e. 8 h) when stored at 25°C. Shelf life was extended to 9 days when stored at 4°C.
Highlights
Beneficial bacteria are important in the production of fermented dairy products, while pathogens and spoilage bacteria have detrimental effects on milk quality and dairy products
± (0.3 d) of storage at 25 oC when total microbial count was 2.42 0.20 log10 cfu mL−1 (Fig. 1A) (p
Similar values of Total Bacterial Count (TBC) for pasteurized milk stored at ambient temperature after 24 h of storage was observed as 8.18 log10 cfu mL−1 (Labreche et al, 2005)
Summary
Beneficial bacteria are important in the production of fermented dairy products, while pathogens and spoilage bacteria have detrimental effects on milk quality and dairy products. The shelf life of pasteurized milk is around 14 days at chilled temperature and is affected by many factors, such as raw milk quality, production system, hygienic, and storage conditions (Bondoc, 2007). To determine the shelf life of pasteurized milk stored under different conditions, different quality indicators, such as microbial counts, titratable acidity (TA), pH and enzyme activity (i.e. lipase and protease) need to be performed (Ziyaina et al, 2018). The mixture of VOCs represents the aroma characteristics of dairy products; consumers typically sniff milk to estimate its quality or freshness in the headspace of the milk container. The VOCs are a very important component of the sensory quality of processed and stored milk. Specific combinations of VOCs form a kind of fingerprint, which can be used as an indicator of food quality and safety
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