Effects of processing variables on system parameters and physicochemical properties of extrudates during extrusion of barley instant cereal foods and their modeling study

Abstract

本研究是以食品雙軸擠壓技術試製大麥即食穀類食品，探討操作條件 (進料速率、進料水份、套筒溫度與螺軸轉速)、螺旋組態、模口直徑及添加物 (碳酸氫鈉) 等變數對擠壓系統參數 (主馬達電流、模口壓力、模口溫度及比機械能) 與產品理化特性 (視黏度、破碎力、膨發度、水溶性與吸水性指標) 之影響，並比較擠出物經乾燥與磨粉而得之即食榖粉和滾筒乾燥產品的品質 (視黏度、水溶性與吸水性指標) 差異。再者，分析加工變數 (操作條件與系統參數) 間和其與擠出物理化特性間之相關性；進一步以反應曲面 (中心旋轉組合設計) 方法，進行大麥粉擠壓實驗之模式化研究。 實驗結果顯示，進料速率 (58-68 kg/h) 明顯地影響主馬達電流、模口溫度、擠出物視黏度、水溶性指標、破碎力與徑向膨發率。在較高之進料速率 (63 kg/h 以上) 下，主馬達電流、模口溫度、擠出物視黏度與徑向膨發率明顯較高，水溶性指標及破碎力值則反之。套筒溫度影響系統參數，當提高加熱溫度時，產品溫度上升，比機械能則下降；而在較高之套筒溫度 (130-170℃) 下，模口壓力明顯下降；套筒溫度明顯地影響擠出物視黏度與破碎力。進料水分影響所有系統參數及擠出物之理化特性，在較高之進料水分下，各系統參數值均有下降之趨勢，而擠出物之視黏度與破碎力則較高。螺軸轉速愈高時，主馬達電流與模口壓力有下降之趨勢，比機械能、模口溫度與縱向膨發性指標則上升，而在適中的螺軸轉速下，擠出物之視黏度較高。添加碳酸氫鈉，明顯地提高樣品之視黏度。模口直徑 (2 mm與4 mm) 較小時，模口溫度與壓力、產品視黏度和膨發度指標均較高；而破碎力則較低。螺旋組態影響所有系統參數及擠出物之理化特性。以適當之擠壓條件，可製出品質接近於滾筒乾燥即食穀粉之產品。 實驗數據相關性係數之分析結果顯示，操作條件與系統參數間有相關性存在，且進料水分與系統參數間有較高的相關性。操作條件與擠出物理化特性間亦有相關性存在，其相關性高低各異；系統參數與產品品質間有較高的相關性。擠出物冷糊與熱糊之視黏度間、水溶性指標間與吸水性指標間有極高的相關性 (r ³ 0.732, P < 0.01)。視黏度與水溶性指標間呈高負相關性 (r = -0.539 ~ -0.723, P < 0.05)，與吸水性指標有負相關性 (r = -0.205 ~ -0.468)。水溶性指標與吸水性指標間呈正相關性 (r = 0.357 ~ 0.732)。吸水性指標與破碎力間呈弱負相關性，與徑向膨發度有正相關性。破碎力與縱向膨發性指標 (r = -0.846, P < 0.01) 和徑向膨發度 (r = -0.900, P < 0.001) 間均呈高負相關性。縱向膨發性指標和徑向膨發度間則有極高之正相關性 (r = 0.959, P < 0.001)。 大麥粉之擠壓實驗模式化研究結果顯示，加工變數 (操作條件與系統參數) 可用來預測產品理化特性。操作條件之線性 (R2 = 0.61 ~ 0.77) 及二階次複回歸模式 (R2 = 0.67 ~ 0.87)，均能適當地描述擠壓機之性能表現。進料水分對各系統參數，均有顯著性影響效應 (P < 0.05)，其間有中至高度之負相關性。 加工條件 (操作條件與系統參數) 與產品理化特性之線性及二階次複回歸模式已被建立，一般而言，系統參數較能充分地描述產品理化特性之差異，其與產品理化特性之相關性也較高。從這些模式中，可看出影響各項產品理化特性之較重要加工因子與其間交互作用之影響；而較重要之操作條件為進料水分，其幾乎對所有產品理化特性均有顯著性效應。 系統參數之實驗模式分析資料，對於產能放大與技術應用性，較具參考價值與實效性。

The objectives of this study were to investigate the effects of processing conditions such as operating variables (feed rate, FR; feed moisture, FM; barrel temperature, BT and screw speed, SS), screw profiles, die diameters and an additive (sodium bicarbonate) on the system parameters (main motor current, MMC; die pressure, DP; die temperature, DT and specific mechanical energy, SME) and physicochemical properties (apparent viscosity, AV; break force, BF; longitudinal expansion index, LEI; radial expansion ratio, ER; water absorption index, WAI; and water solubility index, WSI) of extrudates in a twin-screw extrusion of instant barley cereal foods. Product properties (AV, WAI and WSI) of instant cereal powders prepared from extrusion and drum dryer processes were also compared. Moreover, the correlation coefficients between processing variables, product properties as well as those between thus two main parameters were analyzed. Further, the study on empirical modeling of well milled barely flour extrusion using a rotatable central composite design of response surface methodology was investigated. The experimental results showed that FR obviously affected MMC, DT, AV, WSI, BF, and ER. In contrast to WSI and BF, higher values of MMC, DT, AV and ER were obtained at an FR of over 63 kg/h. DT increased and SME decreased with the increase of BT. DP apparently decreased at a higher BT (130-170 ℃); BT had effects on AV and BF. FM affected all of the system parameters and physicochemical properties of extrudates. The system parameters decreased while higher values of AV and BF obtained at high levels of FM. MMC and DP decreased as well as SME, DT, and LEI increased with the increase of SS. The value of AV at medium SS (250 min-1) was higher than those obtained at other SS. Addition of sodium bicarbonate could obviously increase AV of extrudates. Comparing effects of die diameters (2mm and 4mm), higher DT, DP, AV, expansion indices and lower BF were obtained as small dies used in extrusion trials. Like FM, screw profiles affected all of the system parameters and product properties. Instant barley powders with quality near conventional drum drying samples were prepared using extrudates. The results of correlation coefficients analyses between experimental data showed that operation variables correlated to system parameters. FM had high correlations with all of system parameters. Operation variables had weak to high correlations with product properties. System parameters highly correlated to product properties. AV, WSI and WAI of cold past highly correlated to those of their hot past respectively (r ³ 0.732, P < 0.01). AV negatively related to WSI (r = -0.539 ~ -0.723, P < 0.05) and WAI (r = -0.205 ~ -0.468). WAI positively related to WSI (r = 0.357 ~ 0.732) but negatively related to BF. BF had highly negative correlations with LEI (r = -0.846, P < 0.01) and ER(r = -0.900, P < 0.001). LEI highly related to ER (r = 0.959, P < 0.001). The results of empirical extrusion modeling study showed that processing conditions (operation variables and system parameters) could be used to predict product properties. The multiple linear (R2 = 0.61 ~ 0.77) and second order (R2 = 0.67 ~ 0.87) regression models for operation variables could adequately account for extruder performance. FM had significant (P < 0.05) effects on all of the system parameters and medium to highly negative correlations with them (P < 0.05). The multiple linear and second order regression models for processing variables with product properties had been established. Generally, system parameters could explain the variation of product properties more sufficiently than operation variables. They also have high correlation coefficients with product properties. From these empirical models, the domination of processing variables and their cross-product effect (interaction) on product properties were clarified. The most important operating variable was FM. It almost significantly affected all of the physicochemical properties of extrudates. The empirical models with system parameters are more useful for future scale-up application and technology transfer.