Refrigerated storage of raw milk is a prerequisite in dairy industry. However, temperature abused conditions in the farming and processing environments can significantly affect the microbiological quality of raw milk. Thus, the present study investigated the effect of different refrigeration conditions such as 2, 4, 6, 8, 10 and 12 °C on microbiological quality of raw milk from three different dairy farms with significantly different initial microbial counts. The bacterial counts (BC), protease activity (PA), proteolysis (PL) and microbial diversity in raw milk were determined during storage. The effect of combined heating (75 ± 0·5 °C for 15 s) and refrigeration on controlling those contaminating microorganisms was also investigated. Results of the present study indicated that all of the samples showed increasing BC, PA and PL as a function of temperature, time and initial BC with a significant increase in those criteria ≥6 °C. Similar trends in BC, PA and PL were observed during the extended storage of raw milk at 4 °C. Both PA and PL showed strong correlation with the psychrotrophic proteolytic count (PPrBC: at ≥4 °C) and thermoduric psychrotrophic count (TDPC: at ≥8 °C) compared to total plate count (TPC) and psychrotrophic bacterial count (PBC), that are often used as the industry standard. Significant increases in PA and PL were observed when PPrBC and TDPC reached 5 × 104 cfu/ml and 1 × 104 cfu/ml, and were defined as storage life for quality (SLQ), and storage life for safety (SLS) aspects, respectively. The storage conditions also significantly affected the microbial diversity, where Pseudomonas fluorescens and Bacillus cereus were found to be the most predominant isolates. However, deep cooling (2 °C) and combination of heating and refrigeration (≤4 °C) significantly extended the SLQ and SLs of raw milk.

Plants of Molinia caerulea were grown in sand culture for two seasons. All nitrogen (N) supplied to the plants was enriched with 15N throughout the first season, and at natural isotopic abundance throughout the second season. A series of destructive harvests was taken during the second season. At each harvest, the N mobilized from roots and swollen basal internodes and the protease activity (ability to degrade azocasein) of these storage tissues were measured. The pH response curves of protease activity of both basal internodes and roots exhibited optima at pH 5 throughout the season. The protease activity of roots and basal internodes increased in spring, both on a unit fresh weight and unit protein basis, concomitant with mobilization of N from both these tissues to new shoot growth. In absolute terms more N was mobilized from roots than from basal internodes. However, basal internodes which, compared with roots, showed the greatest protease activity (on a f. wt or unit protein basis) were also the tissues that mobilized a greater proportion of N present in the tissue over winter to new shoot material. Individual clones of M. caerulea varied both in the amount of N mobilized from roots and in root protease activity (per plant). Individuals with a higher protease activity mobilized more N compared with individuals of lower protease activity. Therefore in M. caerulea, relationships between N mobilization and protease activity exist at several levels: (1) between different tissues; (2) temporally throughout the season; and (3) between individual clones.