加工條件對金柑濃糖果汁理化性質之影響

Abstract

金柑濃糖果汁品質之重大缺失就是色澤的褐化以及黏稠度的下降。本論文之研究目的在以不同加熱條件、不同均質前處理條件以及添加異抗壞血酸鈉，來探討其對金柑濃糖果汁的成分、色澤與黏稠度等理化性質的影響，以作為改善加工製程之理論依據。 金柑濃糖果汁經不同溫度加熱處理後，果汁的可溶性固形物、水溶性果膠含量、總酚含量、亮度、紅色度及黃色度以及黏度會隨著加熱溫度的增加而上升，而總類胡蘿蔔素含量、水溶性蛋白質含量會隨著加熱溫度的增加而下降，尤以90℃加熱30秒及100℃加熱30秒的加熱處理，分別會使果汁之總類胡蘿蔔素含量與水溶性蛋白質含量極顯著下降。因此，以80℃加熱30秒的加熱條件，可抑制總生菌數的滋長，並可避免果汁成分中的總類胡蘿蔔素、水溶性蛋白質含量的大幅下降，以維持果汁的品質。 金柑濃糖果汁分別以500及1000rpm均質前處理，再以80℃加熱30秒，果汁的水溶性果膠含量、亮度、黃色度及黏度上升，而總類胡蘿蔔素、螯合性果膠、鹼溶性果膠含量及紅色度則下降；且隨均質時間的增加，水溶性果膠含量、亮度、黃色度及黏度隨之上升，而總類胡蘿蔔素、螯合性果膠、鹼溶性果膠含量及紅色度亦隨之下降。以500rpm均質前處理時間2-4分鐘、1000rpm均質前處理時間1-4分鐘，會使果汁總類胡蘿蔔素含量大幅下降，影響果汁品質，而以500rpm均質前處理時間1分鐘，可減少總類胡蘿蔔素、鹼溶性果膠含量及亮度的下降，並可提高果汁的鹼溶性果膠含量及黏度，水溶性果膠含量增加為造成果汁黏度上升之主要原因之一。 金柑濃糖果汁以500rpm或1000rpm以均質前處理時間1分鐘，再以80℃加熱30秒，於25℃貯藏期間，兩者處理之果汁的總類胡蘿蔔素、亮度、黃色度及黏度會隨著貯藏時間的增加而下降，紅色度則隨著貯藏時間的增加而上升，其變化趨勢以未添加異抗壞血酸鈉的金柑濃糖果汁較為明顯。 因此，異抗壞血酸鈉可以有效降低果汁在貯藏期間，亮度、黃色度、紅色度及黏度的變化，以維持果汁的品質。金柑濃糖果汁中的揮發性成分主要為檸檬油精 (d-limonene)，其含量比例於貯藏第0天約為95%，經8週貯藏之後，降至約89%，其下降趨勢以未添加異抗壞血酸鈉的金柑濃糖果汁較為明顯。而會造成果汁不良風味的α-terpineol，其含量比例則會隨著貯藏時間的增加而上升，且以未添加異抗壞血酸鈉的金柑濃糖果汁較為顯著。因此，異抗壞血酸鈉可減少金柑濃糖果汁於貯藏8週後，不良風味的產生。

The deficiencies of the kumquat syrup are the color browning and the decrease of viscosity. The objective of this study is to investigate the different thermal treatment、different homogenization pretreatment and addition of sodium erythorbate on the content, color and viscosity of kumquat syrup. By heating at different temperature, the soluble solids, water soluble pectin, total phenol content, L value, a value, b value and viscosity increases as the heating temperature increases. The total carotenoids and water soluble protein content decreases as the heating temperature increases, especially decreases significantly after 90℃ heating for 30 sec or 100℃ heating for 30 seconds. Therefore, in order to control the quality of the juice, heating at 80℃ for 30 sec was able to inhibit the growth of the total microbial counts and avoid the total carotenoids and water soluble protein content from decreasing . Kumquat syrup treated with 500rpm or 1000rpm homogenization pretreatment and 80℃thermal treatment for 30 seconds, would result in water soluble pectin, total phenol content, L value, b value and viscosity increased, and the total carotenoids, oxalate soluble pectin, alkali soluble pectin content and a value decreased. As the homogenization time increases, the water soluble pectin, L value, b value and viscosity increases, and the total carotenoids, oxalate soluble pectin, alkali soluble pectin content and a value decreased. Treated with 500rpm pretreated 1-4 minutes or 1000rpm pretreated 2-4 minutes homogenization would decrease the total carotenoids and the quality of the kumquat syrup. However, treated with 500rpm pretreated 1 minute would decrease the total carotenoids, oxalate soluble pectin and L value of the kumquat syrup. One of the major factor to cause the increase of viscosity of the kumquat syrup might be the increase of the water soluble pectin. After the kumquat syrup treated with 500rpm or 1000rpm homogenization pretreatment for 1 minute and 80℃thermal treatment for 30 seconds then stored at 25℃, the total carotenoids content, L value, b value and viscosity decreases , and a value increases during storage. The variation tendency of the kumquat syrup without adding sodium erythorbate is more obviously. The results show that kumquat syrup with sodium erythorbate addition has a huge effect on reducing variation of L value, a value, b value and viscosity. The major volatile compounds is d-limonene. The initial amount of this compound is 95%, and decrease to 89% after storing for 8 weeks. The decrease tendency of the kumquat syrup without adding sodium erythorbate is more obviously. The amount of α-terpineol which cause off-odor of juice increase as storage time increase. The increase tendency of the kumquat syrup without adding sodium erythorbate is more obviously. Therefore, sodium erythorbate could inhibit off-odor produced after storing for 8 weeks.