椰汁發酵所生成之細菌纖維素質地分析

Texture Analysis of Bacterial Cellulose Produced from Coconut Water Fermentation by Acetobacter Xylinum

以醋酸菌(Acetobacter xylinum)發酵椰汁所生成之白色纖維素薄膜，一般稱呼為椰汁那塔(Nata de coco)，在東南亞為非常普遍的甜點成分。椰汁那塔的主要成分組成為一種非常細小的纖維素，因又具有特殊質地性質，故為一種良好的膳食纖維來源。本研究目的在於探討椰汁那塔的質地，並探討浸漬液對椰汁那塔之質地影響。將椰汁那塔切片(2cm×2cm×1.5cm)利用物性測定儀，以5mm柱狀探針，5mm/sec速度下壓90%之TPA試驗，測定分析椰汁那塔之物性。並將其分別浸漬於不同pH值(2-10)溶液、10-60%的蔗糖溶液、2-10%氯化鈉溶液、不同比例(0.5-2%)且不同種類的膠體（低甲氧基果膠、高甲氧基果膠、鹿角菜膠及海藻酸）溶液中，觀察椰汁那塔的硬度變化。由TPA分析結果發現椰汁那塔比生鮮烏賊有較高的硬度(3681Kg)，而膠體性質與咀嚼性質則相似生鮮烏賊。經由雷達圖堆疊發現，椰汁那塔除了不具破碎性外，其他質地性質與生鮮烏賊極為相似。而質地與組成分之相關性方面，椰汁那塔的硬度與其纖維素含量呈現正相關，與含水量呈現負相關，至於由纖維含量與水分含量之相關係數(r=-0.97)中可再次說明椰汁那塔成分單純為水與纖維素組成。而將椰汁那塔保存於蔗糖、低甲氧基果膠、高甲氧基果膠或是鹿角菜膠等溶液中時，其硬度會隨溶液濃度的升高而下降；若保存於不同濃度之鹽水或不同pH之溶液下則質地沒有顯著的變化。

The white cellulosic pellicle formed on the surface of coconut water broth by the bacteria of Acetobacter xylinum has become a very popular dessert ingredient in Far East Asian countries. The pellicle, commonly named as ”nata de coco”, contains very fine cellulose fiber and exhibits a unique texture, is a excellent source of dietary fiber. The objectives of this Study are to analyze the textural properties of nata de coco and to investigate the textural changes of nata de coco during formulation. Nata de coco dices (2cm×2cm×1.5cm) obtained from coconut water fermentation by Acetobacter xylinum were analyzed for their textural properties by a Texture Analyzer equipped with a 5mm diameter cylinder probe compressing 90% downward at 5mm/sec. Textural changes of nata samples treated with solutions at different pHs (2-10) and solutions containing; 10-60% sucrose, 2-10% NaCl, and 0.5-2% gums (HM pectin, LM pectin, carrageenan, and alginate). The results of texture profile analysis (TPA) show; that nata de coco dices exhibit slightly higher hardness (3.681Kg) and similar gumminess (0.37Kg) and chewiness (0.36Kg) than diced fresh cuttlefish (3.02Kg, 0.34Kg, and 0.23Kg, respectively). The spider web diagram indicates nata de coco's texture, is close to fresh cuttlefish except with no fracturability exhibited. Analyses of correlations among shear force, moisture content, fiber content, and ash content of the nata de coco indicate that, the shear force is correlated with the fiber content (r≒0.73). Highly negative correlation coefficient (r≒0.97) between moisture content and fiber content demonstrates that nata de coco contains merely water and cellulose fiber. Nata de coco became softer if they were immersed soaking suspend floating in a sucrose, HM pectin, LM pectin, or carrageenan solutions. The change of pH value or ion composition of preserve solution made no significant effect on the hardness of nata de coco.