Storage Stability and Acidification Power of Freeze-dried Streptococcus salivarius ssp. thermophilus
| Autor: | Hsiu-Hua Chen, 陳秀華 |
|---|---|
| Rok vydání: | 2000 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 88 Streptococcus salivarius ssp. thermophilus, occurring in pairs or chains, is a homofermentative microorganism and appears to be important in fermentation because of its acidification property and production of flavors. It is largely employed in food industry, and plays an important role in the fermentation of milk. The traditional way of conservation of starter is usually attained by freeze-drying which is a process in which a solvent is removed from a frozen solution by sublimation. Although freeze-drying could minimize the chemical alteration of the products, but bacteria are often injured in the process of freezing and drying, and the survival and storage stability would therefore be influenced. The purpose of this study is to compare the results of survival and acidification power of S. salivarius ssp. thermophilus after freezing and freeze-drying, and to develop a predicting model for long-term conservation of the freeze-dried products at low temperatures, and to inquire into the effect of the storage stability of bacteria after drying. Results showed that the feed suspension of S. salivarius ssp. thermophilus with 22% nonfat dry milk solids (NFDMS) or 22% maltodextrin (MD) had the best viability after freeze-drying (75%). Samples with MD showed 84% of viability after 120 days storage at 5℃. The survival ratio of S. salivarius ssp. thermophilus estimated by accelerated storage test was similar to that measured experimentally, and Arrhenius equation could be a good comparison tool of efficiency for different cryoprotectants application in freeze-drying. The acidification power of freeze-dried cells showed 63% lower than suspension. It was found that cells with cryoprotectants could be protected from dying, but still injured in the process of freeze-grying. On the other hand, there was no effect of solids content of suspension on Ea. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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