Effect of pH adjustment and phosphate salts addition on heat stability of UHT goat milk
| Autor: | Yu, Yuan-Yuan, 尤圓圓 |
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| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 106 Low heat stability of goat milk limited the application of ultra-high temperature (UHT) sterilization on producing sterilized UHT goat milk from excess goat milk in summer for producing goat dairy products in winter in Taiwan. Therefore, this study aimed to add phosphates in goat milk to increase the heat stability for producing UHT sterilized goat milk in summer for making goat dairy products in winter. The quality of goat milk was measured with aNalysis of pH value, titratable acidity (TA), ionic calcium concentration (iCa), ethanol stability, sediment content, color evaluation (L* a* b*), total bacterial count (TBC) and sensory evaluation. Milk samples were obtained from an Alpine goat farm in Changzh, Pintung, Taiwan. In experiment 1, the pH of raw goat milk was adjusted to 6.7-7.1 with baseline 3 stabilizers, blend of sodium phosphates (Na) (group 1), blend of sodium and potassium phosphates (Sp) (group 2), and 0.5 N NaOH (group 3), respectively. Autoclave sterilization at 135℃ for 4 seconds was applied to investigate the heat stability. In experiment 2, 0.05-0.11% Na and Sp were added to raw goat milk at different seasons before autoclave sterilization at 135℃ 4 sec to investigate the optimal amount of stabilizers addition. In experiment 3, was focused on producing shelf life extened milk (product A) from raw goat milk, which was added with 0.08-0.09% Na and Sp sterilized using UHT pilot plant at 135℃ for 4 sec, then reproduced acid flavor milk (product B) from product A. Results of experiment 1 showed that the addition of NaOH in goat milk before heating increased the pH, ethanol stability, and decreased iCa; however, the addition of phosphates in milk resulted in coagulation after 135℃ 4 sec autoclave heating. It indicated that pH value was not a suitable indicator for adjusting the amount of stabilizers added for stabilizing goat milk. Results of experiment 2 showed that there were seasonal differences in choosing the optimal addition levels of stabilizers. After autoclaved, sediments of goat milk with 0.08-0.09% Na and Sp addition without coagulation found, significantly lower than other treatmens, it is indicated higher heat stability. Results of experiment 3 showed that all treatments after UHT sterilization significant lower L*, but significantly higher a* and b* values. Sediments of goat milk added with 0.08% Na and 0.08% Sp were significantly lower than other treatments. The sensory evaluation was scored on 7 points hedonic scale sensory evaluations results of all groups showed that overall acceptability was higher than 4 points in 60 days of storage.The pH value and titratable acidity of acid flavored goat milk of each group were not significantly different during stored at 4℃ for 21 days. Sensory evaluations all group showed that overall acceptability were higher than 5 points. In summary, the addition of 0.08% blend of sodium phosphates and 0.08% blend of sodium with potassium phosphates to raw goat milk improve heat stability of goat milk in UHT treatment, which can extend the shelf life of excess goat milk in summer for winter use, and therefore suitable for producing acid flavored milk. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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