不同處理條件對葡萄柚汁及文旦柚汁苦味物含量與品質影響

Abstract

葡萄柚(Citrus paradis Macfad)及文旦柚(Citrus grandis (L.) Osbeck)均為芸香科(Rutaceae)多年生常綠果樹。因為與生俱來之苦味，不管鮮食或加工均受到商業限制。目前已知葡萄柚及柚類水果中，主要的苦味成分是柚苦苷(Naringin)。因此，如何降低苦味產生是許多柑橘加工產業積極研究的方向。柚類水果中柚苦苷酶是降低苦味的重要酵素，溫度介於45-55℃時，將會達到最高的脫苦效率。在園產品採後的處理加工方法中，溫湯處理溫度與之相符，所以結合溫湯處理與柚苦苷酶的作用溫度條件進行探討。另外，近年來高壓處理(High pressure processing, HPP)已漸漸應用於食品工業上，並發現具有修飾酵素的催化作用及微生物殺菌的效果。 本研究探討溫湯處理、高壓處理與傳統熱處理，對於葡萄柚汁及文旦柚汁中苦味物質柚苦苷含量、果汁風味品質及微生物的影響。溫湯處理的葡萄柚汁柚苦苷含量為937.0-1233.6 mg/L，均高於未處理組825.0 ± 16.6 mg/L。雖然柚苦苷酶作用溫度與溫湯處理相符，但是溫湯處理無法降低苦味物質。另外，經過加熱殺菌處理則是無顯著改變柚苦苷含量802.1 ± 0.9 mg/L。 另一方面，葡萄柚汁經過高壓處理100 MPa、200 MPa、300 MPa及400 MPa可顯著降低苦味物質，柚苦苷含量從851.09 ± 17.00 mg/L分別降低至475.64 ± 42.10 mg/L、468.77 ± 36.88 mg/L、539.43 ± 69.21 mg/L及458.34 ± 39.24 mg/L，又因一般人對於柚苦苷的苦味接受度為500 mg/L，所以經過高壓處理可以有效降低葡萄柚汁苦味物質。另一試驗材料，文旦柚汁柚苦苷含量與葡萄柚汁相似為820.64 ± 19.00 mg/L，但是經過加熱及高壓處理並無顯著變化約為804.3-863.4 mg/L。 再者，部分果汁理化性質受到加熱及高壓處理影響，又以加熱處理對果汁外觀及品質影響較大。不同加工處理對葡萄柚汁及文旦柚汁pH值、可溶性固形物及可滴定酸則是沒有顯著影響。綜合上述，加熱處理及高壓處理輕微改變部分果汁理化性質，而高壓處理更能維持果汁原有品質。 最後，在微生物試驗中，葡萄柚汁及文旦柚汁經過加熱殺菌(TP)均能顯著降低總生菌數，從3.25 log CFU/mL及3.78 log CFU/mL降低至1.34 log CFU/mL及0.85 log CFU/mL。另外，高壓200、300、400、500 MPa在30℃處理30分鐘，總生菌數均小於2.3 log CFU/ml，符合飲料衛生標準。 綜合以上，高壓處理不僅能促進去苦味酵素作用，也能達到殺菌功效，而且能夠維持原有果汁外觀、風味及品質。可應用於未來柑橘果汁降低苦味的食品工業，對於未來柑橘加工產業應用潛能無限。

The grapefruit (Citrus paradis Macfad) and the buntan shaddock (Citrus grandis (L.) Osbeck) are evergreen perennials of the family Rutaceae, they also called pumelo, is one of the four original citrus species. They have some limitations on commercial processing due to their inherent bitterness. The major component causing the bitterness of pumelo is naringin, and one of the research areas of citrus processing industry is to investigate how to reduce the bitterness during food processing. The key enzyme to reducing bitterness in pumelo is the naringinase that has the most efficiency of debittering when the temperature is between 45 to 55℃. In the methods of horticulture production postharvest handling, the working temperature of the hot water dip method matches to the optimal temperature of naringinase. The combination of the hot water dip method and the naringinase at optimal temperatures is an innovative method. Moreover, the high pressure processing has been found to have the ability to modify the catalytic behavior of the enzyme and inactivate microorganisms during food processing. This study evaluated the effects of the hot water dip (HWD), the high pressure processing (HPP), and the thermo processing (TP) on the quality, the flavor, the naringin content and the microorganisms of grapefruit juices and buntan shaddock juices. The naringin content in grapefruit juice after HWD was 937.0-1233.6 mg/L, and it was higher than the non-processed control (CON) (825.0 ± 16.6 mg/L). Although the temperature of HWD matches to the optimal temperature of the naringinase, the process of HWD cannot reduce the concentration of naringin. Similarly, the TP had no effects to reduce the concentration of naringin in grapefruit juice that is 802.1 ± 0.9 mg/L after TP. On the other hand, the HPP at 100 MPa, 200 MPa, 300 MPa and 400 MPa significant reduced the concentration of naringin in grapefruit juice, from 851.09 ± 17.00 mg/L to 475.64 ± 42.10 mg/L, 468.77 ± 36.88 mg/L, 539.43 ± 69.21 mg/L and 458.34 ± 39.24 mg/L, respectively. The naringin concentration below 500 mg/L that is the bitter taste threshold. The results suggested that HPP can efficiently reduce the naringin content of grapefruit juice. Another test material is buntan shaddock juice, the naringin content in buntan shaddock juice after TP and HPP was 804.3-863.4 mg/L, and it was similar to the non-processed CON (820.64 ± 19.00 mg/L). Then, some physicochemical properties of juices has changed through TP and HHP. Comparison of TP and HHP, it has a great influence on the appearance and quality of juice after TP. However, there was no significant change in pH, soluble solids and titratable acidity of grapefruit juice and buntan shaddock juice after the TP and the HPP. In such a context, TP and HHP mild affect on physicochemical properties of juices, but the HHP maintained the physicochemical properties of the original juice well. Finally, the microbiological tests shows that thermally treating the grapefruit juice and buntan shaddock juice to 85 ℃ for 45 s reduced the bacteria population from 3.25 log CFU/mL and 3.78 log CFU/mL to 1.34 log CFU/mL and 0.85 log CFU/mL. Pressurization at 200, 300, 400, 500 MPa, 30℃ for 30 min reduced the population levels below 2.3 log CFU/mL, it conforms with the microbiological criteria of beverages in Taiwan. In conclusion, HPP not only promote activity of debittering enzyme but also inactivate bacterial cells. This processing maintain the original juice appearance, flavor and quality. It can be used in the future to reduce the bitterness of citrus juice in the food industry, and the potential applications of HPP is unlimit.