EFFECT OF STORAGE TEMPERATURES ON CHEMICAL, MICROBIOLOGICAL AND SENSORY PROPERTIES OF RENNET EXTRACTED BY SOAKING AND MECHANICAL PROCESSES

Abstract

A comparison was done among rennet samples extracted from different forms of calves vells (fresh and dried) (sliced or minced) by using soaking and mechanical processes, during storage at room temperature (25-30 o C) and refrigeration +- 5o C) for 90 days. The resultant rennet solutions were tested for milk clotting time (MCT), rennet activity (total rennin units/gram (RU/g), rat of loss % of rennet activity or rennet stability, microbiological assessments and sensory properties. Results show that storage temperature had a highly significant effect on all treatments and led to a continuous decrease in RU/g, yield and the keeping quality of all forms of vells at both temperatures. After 90 days of storage, protective effect and stability of rennet activity were superior when storage was carried out in refrigerator, almost double clotting actively of rennet and an increase in the shelf-life of. The average of rennet actively and rat of activity loss were 107.25 RU/g and 14.96 % respectively, with the storage at refrigerator, whereas the average of the other ones stored at room temp. were 94.04 RU/g and 25.41 % in order. T1 with of dried sliced vells kept at refrigerator had the highest rate of stability (119.62 RU/g), while T3 of fresh minced vells stored at room temperature had the lowest one (95.84 RU/g). T3 of fresh sliced vells stored at room temperatures had the highest rate of activity loss (36.51 %), while C soaking treatment of dried sliced vells stored at room temperature recorded the lowest rate of activity loss (10.28 %). Results show also that the mechanical process was superior than the soaking one and stirring at 100 rpm.(T1) was the perfect treatment for extraction. Microbiologically results revealed that initial bacterial counts (TBC) in all treatments, ranged between 104 to 106. C of all treatments had the lowest TBC followed by T1, T2 and T3 in order. Dried sliced vells recorded the lowest TBC followed by dried minced, fresh sliced and fresh minced vells respectively. No growth of coliform bacteria was detected in all treatments, along the storage period. Yeasts & moulds were absent in C and T1 treatments while appeared in case of T2 and T3treatments. Results of sensory evaluation show considerable differences among treatments. C and T1 were found the best ones, characterized by brown, unique odor, clear and free from sediments.