Studies on the far-infrared vacuum-drying of galangal using response surface methodology

Abstract

Galangal is one of the most important spices used in the BBQ sauce. This study was to compare the dried products of galangal by using air-drying, vacuum-drying and far-infrared vacuum-drying. Experimental results demonstrate that far-Infrared vacuum-drying could obtain better quality and drying efficiency in the galangal drying. This research used three-variable and three-level design method to set up 15 groups of experimental conditions to optimize the parameters of far-infrared vacuum-drying. An analysis by response surface methodology (RSM) was performed. The three independent variables studied were the temperature of far infrared radiator (FIR) (X1), the thickness of sample (X2), and the distance between the far-infrared radiator and the sample (X3). The response variables studied included total color difference (ΔE), Hunter-L,Hunter-a,Hunter-b,rehydration ratio,hardness,drying time,sensory properties of appearance,aroma,taste. The % variability explained (R2) of total color difference (ΔE), Hunter-L,Hunter-a,hardness,drying time,sensory properties of appearance,aroma,taste are all over 80%, The highest % variability explained is drying time (R2 = 98%). These results indicates that all these response variables were comply with this regression analysis. The effect of thickness of the sample and the temperature of FIR radiator were more significant among these three independent variables. As the temperature of the FIR became higher and the thickness of the sample got thinner, the drying time was shorter with higher total color difference (ΔE). When temperature decreased and thickness became thinner, the hardness of the product and sensory property of aroma increased. It was found that the quadratic model of Hunter-a was not significant and this model was not applicable. The best drying conditions for far-infrared vacuum-drying were found to be drying time less than 5.2 hours, hardness below 9.0 g/mm2, aroma evaluation above 7.4 and appearance evaluation above 5.1. The overlapping area was located at the set temperature of FIR at 51-54℃, sample thickness 5-6 mm. Verification results showed that the use of quadratic equations to simulate drying time、thickness、sensory property of aroma is acceptable.南薑(galangal)為沙茶醬中的一種重要香辛料。本研究比較熱風乾燥、真空乾燥及遠紅外線真空乾燥，三種方式來乾燥南薑；發現使用遠紅外線真空乾燥，可提高乾燥效率且保留較佳品質。此外，利用反應曲面法之三因子三階層實驗設計，設定了15組的條件組合來進行試驗，以探討遠紅外線真空乾燥南薑之最適製作條件。三個獨立變數為遠紅外線加熱器設定溫度(X1)、樣品之厚度(X2)及遠紅外線加熱器和樣品表面之距離(X3)；而反應變數則包括總色差（△E）、Hunter-L、Hunter-a、Hunter-b、復水性、硬度、乾燥時間、感官品評外觀、風味及口感，以找出遠紅外線真空乾燥南薑最適製作條件。數據結果顯示在以遠紅外線真空乾燥處理下，總色差（△E）、Hunter-L、Hunter-a、硬度、乾燥時間、感官品評外觀及風味的可解釋之變異度皆達到80％以上，其中最高的為乾燥時間（R2＝98％）， 此表示這些反應變數適合所採用的迴歸分析，而且模式欠合性並不顯著，因此迴歸出來的模式相當合適。在三項獨立變數中，皆以樣品之厚度與遠紅外線加熱器設定溫度這兩個變因較為顯著，其影響趨勢為遠紅外線照射溫度越高且樣品厚度越薄時，可得到越短的乾燥時間及較高的總色差（△E）。溫度下降，厚度越薄，則可使產品硬度、感官品評風味呈上升趨勢。而Hunter-a以二次多項式表示時，其整體模式不具顯著效果，所以此模式不適用。遠紅外線真空乾燥之最適乾燥條件於乾燥時間小於5.2 小時、硬度小於9.0 g/mm2、感官品評風味大於7.4及感官品評外觀大於5.1之間，有一重疊區域（斜線部份），其遠紅外線設定的溫度為51-54℃，樣品厚度為5-6 mm。經驗證試驗發現，用來模擬乾燥時間、硬度、感官品評風味、外觀所使用的二次多項式模式是可以被接受的。頁次 壹、前言…………………………………………………………… 1 貳、文獻整理……………………………………………………… 3 一、薑………………………………………………………… 3 (一)薑的簡介…………………………………………… 3 (二)薑的辣味成分……………………………………… 6 (三)薑之藥理活性之介紹……………………………… 8 (四)南薑…………………………………………………10 (五)南薑加工性…………………………………………14 二、乾燥………………………………………………………16 (一)熱風乾燥……………………………………………20 (二)真空乾燥……………………………………………21 三、遠紅外線…………………………………………………24 (一)波長範圍……………………………………………24 (二)遠紅外線加熱之特性………………………………24 (三)遠紅外線在食品工業上之應用……………………27 四、反應曲面法………………………………………………34 (一)反應曲面法的原理…………………………………34 (二)反應曲面法的特點…………………………………36 五、食品組織的物理特性……………………………………39 六、感官品評的測試…………………………………………42 參、研究目的………………………………………………………44 肆、材料與方法……………………………………………………45 一、試驗材料…………………………………………………45 二、試驗流程…………………………………………………46 三、試驗方法…………………………………………………47 (一)南薑樣品的製備……………………………………47 (二)厚度量測……………………………………………47 (三)乾燥方法……………………………………………47 (四)測定項目……………………………………………51 (五)實驗設計……………………………………………55 伍、結果與討論……………………………………………………60 一、遠紅外線真空乾燥與其他乾燥方式的比較……………60 (一)乾燥時間與品質之比較……………………………60 (二)組織構造之比較……………………………………69 二、反應曲面模式分析………………………………………71 三、反應曲面方程式…………………………………………80 四、各應變數之結果分析……………………………………86 (一)對顏色的影響………………………………………86 (二)硬度…………………………………………………90 (三)乾燥時間……………………………………………90 (四)感官品評……………………………………………90 (五)最適化條件之探討…………………………………94 (六)驗證試驗……………………………………………95 陸、結論……………………………………………………………99 柒、中文摘要………………………………………………………101 捌、英文摘要………………………………………………………102 玖、參考文獻………………………………………………………10