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고준수 한국낙농학회 1983 韓國酪農學會誌 Vol.5 No.3
Yoghurt는 乳酸박테리아를 多量으로 含有하고 있기 때문에 低溫에서 貯藏하여야 하며 可能한 限 빨리 消費하여야 한다. 요구르트를 長期的 貯藏이 必要할 境遇 熱處理에 依하여 乳酸박테리아數를 減少시킴으로서 保存性을 增進시킬 수 있다. 本 試驗은 Starter culture를 3% 接種하여 3時間 培養製造한 요구르트와 3.5時間 培養 2種의 요구르트의 保存性을 試驗하였으며 그 結果는 다음과 같다. 1. 培養時間을 各各 3時間, 3.5時間으로 하여 製造한 요구르트는 pH가 4.32와 3.92, 滴定酸度는 1.03%과 1.37%, 總乳酸박테리아數는 9.6×10^7/㎖와 7.7×10^8/㎖ 그리고 Streptococci와 Lactobacilli比率은 1.1 : 1과 1.3 : 2로 優秀한 品質의 Set Yogurt를 生産할 수 있었다. 2. 요구르트를 加熱하였을 때 3.5時間 培養하여 製造한 요구르트가 乳酸박테리아의 死滅速度가 더 빨랐으며 60℃에서 30分 加熱하였을 때 3時間 培養製造한 요구르트에 8.5×10^6/㎖, 3.5時間 培養製造한 요구르트에는 2.1×10^5/㎖의 乳酸박테리아가 生存하여 있었으며 Streptococci의 死滅比率이 Lactobacilli보다 더 높았다. 3. 加熱하지 않은 요구르트와 60℃에서 30分 加熱한 요구르트를 各各 4℃, 20℃, 30℃에서 保存하였을 때 pH의 降下速度는 加熱하지 않은 요구르트에서 3.15時間 培養製造한 요구르트가, 加熱한 요구르트는 3時間 培養製造한 요구르트가 더 빨리 低下되었다. 4℃와 20℃에서 30日 保存하였을 때 3.5時間 培養하여 加熱한 요구르트의 pH는 3.8以上, 3時間 培養하여 加熱한 요구르트는 pH가 3.53以上으로 維持되었으며 保存性이 매우 優秀하였다. 4. 貯藏期間이 經過함에 따라 요구르트內의 乳酸박테리아數는 顯著히 減少하여 4℃에서 保存 30日, 30℃에서 保存 20日에 乳酸박테리아가 發見되지 않았다. 3時間 培養하여 加熱한 요구르트는 20℃에서 保存 30日에, 3.5時間 培養하여 加熱한 요구르트는 20℃에서 保存 20日에 乳酸박테리아가 모두 死滅하였으며 保存期間이 經過함에 따라 Lactobacilli의 比率이 增加하였다. 5. 熱處理한 Set yoghurt는 30℃에서 保存 20日까지, 4℃와 20℃에서 30日까지 貯藏이 可能하였으며 3.5時間 培養製造하여 加熱處理한 요구르트가 保存性이 가장 優秀하였다. Yoghurt containing large quantities of lactic acid bacteria has to be stored at refrigeration temperature. If the refrigeration system is not prepared, yoghurt has to be consumed immediately after produced, or heated so as to decrease the number of lactic acid bacteria involved for the preservation. Though the heat treated yoghurt loses the microbiological merits, it can hold nutritive value for a quite long. Set yoghurt was made by inoculating 3% starter culture and incubated for 3 and 3.5 hours at 42℃. The keeping quality of yoghurt by heat treatment was evaluated in this experiment, and the results are summarized as follows: 1. Titratable acidity, pH, total lactic acid bacteria and the ratio of streptococci and lactobacilli of yoghurt produced by incubating for 3 hours (Sample A) were 1.03%, 4.32, 9.6 × 10^7/㎖, 1.1 : 1 and those of yoghurt produced by incubating for 3.5 hours (Sample B) were 1.37%, 3.92, 7.7 × 10^8/㎖, 1.3 : 2. 2. Heating at 60℃ for 30 minutes decreased the number of viable lactic acid bacteria to 8.5 × 10^6/㎖ in sample A, and to 2.1 × 10^5/㎖ in sample B. Thermal death of lactic acid bacteria in Sample B was more serious than in Sample A, and lactobacilli survived heat treatment better than streptococci. 3. When yoghurts were stored at 4℃, 20℃ and 30℃, the change of pH of unheated sample B was faster than that of unheated sample A, and heated sample B was slower in change of pH than heated sample A. The pH of heated sample B stored at 4℃ and 20℃ for 30 days did not fall below 3.8 and showed good keeping quality. Heated sample A stored at 4℃ and 20℃ for 30 days maintained their pH value above 3.53. 4. As the storage time was extended the number of viable lactic acid bacteria was highly decreased. There was no viable lactic acid bacteria at 20th storage day at 30℃, 30th storage day at 4℃ and 20℃ except heated sample B. Heated sample B showed no viable lactic acid bacteria at 20th storage day at 20℃. Lactobacilli disappeared more slowly than streptococci. 5. Set yoghurt treated at 60℃ for 30 minutes could be stored at 30℃ for less than 20 days, however at 4℃ and 20℃ kept good quality for 30 days. Sample B treated at 60℃ for 30 minutes showed the best keeping quality.
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액상유제품(液狀乳製品) Ultrafiltration 속도에 영향하는 요인(종설)
고준수,안종건 한국낙농학회 1983 韓國酪農學會誌 Vol.5 No.3
Ultrafiltration is a process which works on a sieve principles, applicable at molecular size levels. Milk protein and fat can be separated from water, lactose, and ash by ultrafiltration without heat supply as in evaporation saving manufacturing costs and protecting protein from heat denaturation. Ultrafiltration can be applied to soft cheese production saving starter culture and rennet, improving yield and quality. Lactose reduced milk from ultrafiltration will be helpful to lactose intolerant persons. The velocity of ultrafiltration, flux rate, is governed by characterists of membrane, pressure, flow rate, temperature and concentrate which affect formation of deposited layer on the surface of membrane. Ultrafiltration has to be accomplished at suitable conditions of those varients according to membrane and solution treated to reduce formation of deposited layer. In studies, ultrafiltration have been done at pressure less than 10 kgf/㎡ and flow rate of 10∼50ℓ/min. To prevent formation of deposited layer and microbiological defects, it is good to work at temperature of higher than 50℃. However cellulose acetate membrane which is weak at high temperature has to be used at temperature lower than 40℃. Besides the selection of suitable conditions of these operating variants, prefilteration through large pore filter, promoting solubility of salts, elimination of insoluble salts can be also offered to reduce formation of deposited layer. Skimmilk was concentrated by ultrafiltration to retentate of 27.6% T.S., whey to retentate of 22.36%, and whole milk can be concentrated by a concentration factor of 3.3 theoretically. The lactose remaining in retentate produced by direct ultrafiltration can be removed largely by diafiltration.
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