探討小麥草汁混濁沉澱的形成

Abstract

小麥草是為禾本科植物小麥(Triticum aestivum L.)所生長的嫩莖葉，近年來為極受到重視的功能性食品之一。然而小麥草汁於儲存期間若產生沉澱之現象，將造成品質之下降。本研究主要是探討蒸氣殺菁( 100 ℃，0、0.5、3、5或10分鐘)以及添加不同的金屬鹽類( NaCl、CaCl2 )及酚類( gallic acid、tannic acid )對於小麥草汁儲存期間沉澱混濁現象的形成，以及鑑定混濁活性蛋白/多酚，藉以作為食品加工業者改善小麥草汁品質的參考。結果發現，殺菁及添加澄清劑皆可增加小麥草汁於儲存期間的混濁安定性，並減緩沉澱的形成，可溶性蛋白含量及過氧化酶活性隨之下降; 然而殺菁可使總多酚、單寧酸及果膠含量隨之增加，相反於添加澄清劑者。電泳的結果顯示，當儲存過程中形成混濁沉澱時，小麥草汁上層液之13及51 kDa蛋白質含量下降，且此兩蛋白質對於單寧酸具有很強的親和力。而胺基酸分析亦顯示此二種蛋白質皆屬於疏水性蛋白。其等電點( pI )範圍皆為4-6，由光學顯微鏡觀察結果發現，蛋白質-多酚之沉澱物是由多酚類物質形成網狀結構將蛋白質包覆住，而鈣離子則會與酚類物質及蛋白質形成架橋之結晶狀構形。

Wheat seedling juice pressed from the tender small plant grown from wheat seed (Triticum aestivum L.) is getting lots of interest recently as one of the functional foods. However, the formation of haze/ precipitate during storage may decrease the quality of wheat seedling juice. The objective of this study is to evaluate the effect of steam blanching (100 ℃; 0, 0.5, 3, 5, 10 min) and addition of different salts/phenolic acid prior to juice pressing on the haze/ precipitate formation phenomenon in wheat seedling juice during storage, and identify the haze-active protein/ phenols, which may lead to industrial process for remediation or prevention of this quality defect in wheat grass juice. Blanching or addition of fining prior to juice pressing increased the cloudy stability and prevented precipitate formation in wheat grass juice during storage, accompanied with a decrease of soluble protein content and the peroxidase activity, while the total phenol, tannic acid and pectin content increased. Electrophoretic results revealed that two types of protein with a molecular mass of 13 and 51 kDa, respectively, decreased significantly when the haze and sediments formed during storage. Furthermore, both proteins had a strong tendency to associate with tannic acid. Amino acid analysis show that both proteins were hydrophobic protein. Light microscopy results revealed that protein-phenol haze particles like protein embedded in polymerized phenolics. Calcium can cause chemical cross- linking with protein to form a crystalline structure.