เซลล์จุลินทรีย์ตรึงรูปสำหรับการลดความขมของน้ำมะนาวถนอม / อัจฉรา ปิติปัญญากุล = Immobolized microbial cell for the debittering of preserved lime juice / Auchara Pitipanyakun
In this research, optimal condition for cells immobilization was studied. The bacteria used is corynebacterium fascians (NRRL-B-15096). The optimal conditions for immobilization of cells were determined ; mixing 0.75 g. of cells with K-carrageenan in the ratio of 1:7, the appropriate concentration of K-carrageenan and potassium chloride used for immobilization process were 2.0% and 1.0 M, respectively. The enzymic properties of the immobilized cells in limonin hydrolysis were : optimal pH for the immobilized cells and the free cells were 4.0-5.0 and 5.0-6.0 respectively while the temperatures for the immobilized cells and the free cells were 25-35°C and 25-28°C in respectivel order. Km of the immobilized cells was found to be 3.6x10² mM which was smaller than 6.7x10² mM of the free cells. The storage stability of the immobilized cells was higher than that of the free cells under two conditions; at 10°C and room temperature. Half-life of the free cells stored at room temperature and 8-10°C were 60 days and more than 80 days, respectively while those of the immobilized cells were more than 80 days under the two conditions of storage. The vitamin C and citric acid contents of the debittered lime juice using immobilized cells were lower than those of the non-debittered lime juice. The debittering process using immobilized cells could reduce the limonin contents of pasteurized lime juice from 12.21 ppm to 7.07 ppm. The debittered and the non-debittered lime juices were stored at 8-10°C for a period at four months and samples were analyzed at regular intervals. It was shown that Brix, pH and citric acid contents of the two kinds of lime juices varied little with storage time. The browning reaction of debittered lime juice was less than that of the non-debittered one and the vitamin C contents were reduced to 34% and 58% respectively after 4 months in storage. The limonin countent of the non-debittered lime juice increased with storage time; it increased from 12.29 ppm to 17.12 ppm at the end of 4 months. On the other hand, the limonin content of the debittered lime juice varied littleduring the storage. At the end of 2 and 3.5 months, the debittered and non-debittered lime juices were tested for organoleptic properties by trained taste panels. The non debittered lime juice was rejected whereas the debittered lime juice was still accepted by the taste panel.