基于主成分分析优化咖啡微水脱胶工艺

Optimization of Coffee Micro-water Degumming Process Based on Principal Component Analysis

为优化微水脱胶工艺,本文分析机械脱皮脱胶+晒干(A)、机械脱皮脱胶+烘干(B)、手工脱皮+带胶烘干(C)、机械脱皮脱胶+水洗脱胶+烘干(D)及手工脱皮+水洗脱胶+烘干(E)五种不同加工工艺对咖啡生豆中香味前体物质(蛋白质、粗脂肪)、滋味呈味物质(咖啡因、绿原酸、咖啡酸)及挥发性物质相对含量的影响。结果显示,机械脱皮脱胶+烘干处理组相比于手工脱皮+带胶烘干处理组,随着果胶残留量的增加,咖啡生豆中绿原酸、咖啡酸含量显著增加(P<0.05),蛋白质含量显著减少(P<0.05);机械脱皮脱胶+水洗脱胶+烘干处理组相比于机械脱皮脱胶+烘干处理组,咖啡生豆中粗脂肪、咖啡酸含量显著增加(P<0.05);机械脱皮脱胶+烘干处理组相比于机械脱皮脱胶+晒干处理组,咖啡生豆中绿原酸、咖啡酸含量显著增加(P<0.05)。手工脱皮+带胶烘干、手工脱皮+水洗脱胶+烘干处理后咖啡生豆中蛋白质、粗脂肪、咖啡因含量均较低,机械脱皮脱胶+水洗脱胶+烘干处理后咖啡生豆中蛋白质含量最高,达13.71%,粗脂肪含量仅次机械脱皮脱胶+晒干,为9.84%。按照品质指标综合得分由高到低排名:D>B>A>E>C,PCA得分图将样品B、D归在一个象限,其他处理分别位于不同象限,这说明机械脱皮脱胶+烘干与机械脱皮脱胶+水洗脱胶+烘干处理组的咖啡生豆品质差异较小,而其他处理组的咖啡生豆品质差异较大。挥发性物质相对含量分析结果表明手工脱皮+水洗脱胶+烘干处理组咖啡生豆中正十八烷(4.80μg/g)、大马士酮(1.85μg/g)、邻苯二甲酸二丁酯(20.28μg/g)等对风味有主要贡献的化合物含量高于机械脱皮脱胶+水洗脱胶+烘干处理组(1.63、0.94、4.07μg/g),随果胶残留量的减少,咖啡生豆中化合物含量整体呈现减少的趋势。综上所述,充分发挥果胶的作用能得到风味丰富的咖啡生豆,而机械脱皮脱胶+水洗脱胶+烘干的微水脱胶工艺则能得到综合品质最佳的咖啡生豆,这为云南精品咖啡豆及发酵风味咖啡豆的加工提供思路。

To optimize the micro-water degumming process,this study investigated the effects of different processing techniques including mechanical peeling degumming+sun drying(A),mechanical peeling degumming+heat pump drying(B),manual peeling+heat pump drying(C),mechanical peeling degumming+water soaking degumming+heat pump drying(D),and manual peeling+water soaking degumming+heat pump drying(E)on the content of aroma precursors(protein and crude fat),taste-producing substances(caffeine,chlorogenic acid and caffeic acid),and volatile substances in green coffee beans.The results showed that compared to the manual peeling degumming+heat pump treatment group,the mechanical peeling degumming+heat pump drying group exhibited a significantly increased chlorogenic acid and caffeic acid contents in raw coffee beans,a significantly decreased(P<0.05)protein content with the increase in pectin residue(P<0.05).The content of crude fat and caffeic acid in raw coffee beans significantly higher in the mechanical peeling degumming+water soaking degumming+heat pump drying treatment group than in the mechanical peeling degumming+heat pump drying treatment group(P<0.05).Chlorogenic acid and caffeic acid contents in raw coffee beans were significantly higher in the mechanical peeling degumming+heat pump drying treatment group than in the mechanical peeling degumming+sun-drying treatment group(P<0.05).The contents of protein,crude fat,and caffeine in green coffee beans were lower in manual peeling+heat pump drying(C)and manual peeling+water soaking degumming+heat pump drying(E).The protein content in green coffee beans was the highest(13.71%)in mechanical peeling degumming+water soaking degumming+heat pump drying(D),and its crude fat content was only second(9.84%)to mechanical peeling degumming+sun drying(A).According to the overall score of quality indicators from high to low,the 5 treatment groups were ranked as D>B>A>E>C.The PCA score plot grouped samples B and D into one quadrant,and the samples in other treatment groups were located in different quadrants,which indicated a relatively small difference in the quality of raw coffee beans between the mechanical peeling degumming+heat pump drying group and mechanical peeling degumming+water soaking degumming+heat pump drying treatment group,while the difference in quality of raw coffee beans among the other treatment groups was dramatic.The analysis results of the relative content of volatile substances showed that raw coffee beans in the manual peeling+water soaking degumming+heat pump drying treatment group contained more main flavor compounds such as n-octadecane(4.80μg/g),damascenone(1.85μg/g),dibutyl phthalate(20.28μg/g)than those in the mechanical peeling degumming+water soaking degumming+heat pump drying treatment group(1.63,0.94,4.07μg/g),and compounds in raw coffee beans exhibited an overall decreasing trend with decreasing pectin residues.Taken together,rich flavor could be obtained from green coffee beans by taking advantage of pectin,and the optimal comprehensive quality could be obtained from the micro-water degumming process,namely,mechanical peeling degumming+water soaking degumming+heat pump drying.The findings would provide new perspectives for the processing of the Yunnan fine coffee beans and fermented flavor coffee beans.