常壓電漿預處理對葡萄乾燥速率及葡萄乾品質之影響

Abstract

葡萄乾因其良好的風味和豐富的營養價值而成為受歡迎的點心，也常被用在其他食品之中。乾燥葡萄來生產葡萄乾是一個非常緩慢且耗能的過程，主要是因為葡萄表皮含有蠟質層結構作為去除水分的屏障，因此難以將水分從葡萄中去除。為了除去蠟質層並縮短乾燥時間，在乾燥之前大多數的葡萄都會經過浸泡化學藥劑的預處理，破壞或溶解葡萄表皮的蠟質層。但是，化學藥劑的使用可能會導致在最終產品中具有殘餘物質。 常壓電漿是一種新興的非熱食品加工技術。電漿屬於電離狀態的中性氣體，由大量不同的物質組成，如電子，正離子和負離子，自由基和氣體原子等。這些活性粒子具有相當大的能量能夠和目標產生碰撞，並且對目標的表面產生快速的化學反應和蝕刻作用。 本研究的目的是透過常壓電漿作為葡萄乾燥的預處理，改變葡萄表面蠟質結構的化學性質來縮短乾燥所需的時間，並與未處理、化學浸泡處理與剝皮處理的組別比較，觀察在70 ℃下進行乾燥，葡萄的乾燥速率和葡萄乾質量參數（如外觀顏色、質地、總酚含量、抗氧化活性）的變化。 研究的結果表明，常壓電漿是一種有效的乾燥預處理方法，能夠在葡萄表面造成蝕刻作用，形成微裂縫進而破壞表皮蠟質層的保護，可有效的縮短15 % - 20 % 的乾燥時間，且隨著電漿處理次數的增加以及處理距離的減少，所得到的效果越佳，尤其是距離1公分處理3次的條件，能與化學浸泡處理得到類似的效果。而且電漿處理也能維持如外觀顏色、質地和抗氧化活性等較高的產品質量，同時也能夠保留相對高的總酚含量。此研究表示，常壓電漿能夠發展成為一種新型的乾燥預處理技術，不僅可以縮短乾燥所需的時間，還能夠保持產品品質，並且對環境友善，將來可以應用於其他含有熱敏感因子或功能性成分食品的乾燥預處理。

Raisins are popular snack due to its abundant flavor and high content of bioactive component. Drying of grapes is a rather slow and energy intensive process since grape contains a waxy peel structure, which serves as a barrier to moisture removal. In order to remove the waxy layer and shorten drying time, several chemical pretreatments have been suggested. However, chemical treatment may lead to the presence of toxic residual in the end product. Atmospheric plasma technology is an emerging non-thermal food processing technology. Plasma is the fourth state of matter, which is an ionized gas composed of various active particles, such as electrons, positive and negative ions, free radicals and neutral molecules. These active particles have great energy that react quickly with the target, on which the surface would be rapidly etched and stripped. Presently, plasma has been gradually applied in the food processing, mostly focuses on the role of disinfection and sterilization with highly reactive gases. To better utilize the benefit of plasma technology, the application of plasma in food processing should be extended to other area such as food drying. The purpose of this study was to study the effect of atmospheric plasma as a pretreatment method on the chemical properties of waxy grapes, as well as the drying rate and nutritional quality of the grapes. The chemical and physical changes on waxy surface of the grape were studied by analytical methods and scanning electron microscopy (SEM). In specific, the effect of plasma pretreatment on the drying rate and other quality parameters including color, texture and phenolic content were determined and compared with raisins that were made after chemical pretreatment, peel removed, or intact. The result from this study showed that atmospheric plasma is an effective drying pretreatment that 15%-20% of the drying time was reduced as a result of the formation of micro-fissures on the surface. For plasma pretreated samples, their microstructure and quality parameter were significantly changed when compared to the chemical pretreatment and untreated control samples. In summary, the atmospheric plasma was successfully developed into a novel pretreatment technology that could be used as a reference for application to other products that contain heat-sensitive functional ingredients.