Abstract
The aim of this work to determine the formation of lactulose during heat treatment process as a contribution to the estabilishment of limits of chemical indicators for different types of heat processed milk and analyze of lactulose for the reconstituted milk added samples. The HTST(75$\^{C}$/15s) and UHT(130$\^{C}$/2∼3s) treatment realized with a pilot plant and heat-treated samples were stroed at 4, 10, 30$\^{C}$ for 4 weeks. Changes in lactulose was evaluated at 7 days intervals. The other heat treatment was sealed in glass tube and heated at 75$\^{C}$ for 10 to 120s and heated at 130$\^{C}$ for 2 to 60s in a thermostatically controlled constant temperature bath of glycerol. The reconstituted milk was made with full fat dry milk that reconstituted with deionized water to 10% total solid, and was added to milk at 10, 20, 30% respectively. The samples processed with a HTST pilot plant showed that lactulose was contained at 1.47∼1.52mg/10()ml and 8.19 ∼8.32mg/100ml for UHT-treated samples. Changes in the lactulose content of heat-treated samples during storage at 4 and 10$\^{C}$ for 4 weeks caused a slight increase, however a noticeable increase was observed at 30$\^{C}$ for 4 week. The glass tube samples showed that high correlations between relative increase in content of lactulose and increasing processing times(75$\^{C}$ : r = 0.986, 130$\^{C}$ : r = 0.987, respectively). Added with reconstituted milk would cause a increase of the lactulose content linear with increasing addition amount(r = 0.982). This results observed for lactulose in commercial milk samples would applied to the detection of chemical changes during heat treatment and illegal use of reconstituted milk.
시유의 적정품질관리 지표를 설정하기 위하여 열처리에 따른 lactulose의 생성에 관해 실험하였으며 결과는 다음과 같다. 살균기를 이용하여 HTST 및 UHT로 처리하여 4, 10, 3$0^{\circ}C$에서 각각 4주간 저장하며 lactulose의 함량변화를 측정한 결과 모든 처리구에서 저장기간에 따라 지속적으로 증가 하였으나, 4, 1$0^{\circ}C$에서는 최초 1.5mg/100m1에서 저장 4주째 1.93mg/100m1 및 2.14mg/100m1으로 미량 증가하였으며 3$0^{\circ}C$에서는 저장 4주째 4.88mg/100m1으로 생성량이 높게 나타났다. 또한 glycerol bath를 이용하여 75$^{\circ}C$에서 10~120초, 13$0^{\circ}C$에서 2~60초간 열처리하고 시간에 따른 함량변화를 측정한 결과 각 처리구에서 열처리시간과 lactulose의 증가량간에는 매우 높은 상관관계를 나타내며(75$^{\circ}C$ : r=0.986, P<0.001 ; 13$0^{\circ}C$ r=0.987 P<0.001)지속적으로 증가하였다. 또한 전지환원유의 첨가량을 달리하여 UHT처리 후 lactulose 함량을 측정한 결과 환원유 첨가량과 함량의 증가간에는 높은 상관관계(r=0.982, P<0.001)를 나타내었다. 따라서 현재 미생물학적 방법에 의존하고 있는 시유의 품질관리를 좀더 효율적으로 명확히 하기위해서는 열처리 방법 및 시간과 매우 높은 상관관계를 가지는 화학적 품질관리 지표의 도입이 필요한 것으로 사료된다.