| Coffee as one of the three biggest drinks in the world is the economical and earning crop in development countries because of medicinal values in active ingredients like caffeine and chlorogenic acid. Drinking coffee can prevent some chronic diseases, including type 2 diabetes, Parkinson's disease, liver disease(cirrhosis, liver cancer), kidney, breast and colorectal cancer, etc.The objective of this article was to search new methods of coffee qualities on the research of drying and roasting processes which were the essential pretreatment steps of coffee beans, evaluate component contents after roasting and design a multilayer belt dryer for Vietnam robusta coffee berries on the basis of hot air drying characteristics, roasting performances and component contents changes in different roasting process. The main conclusions were as follows.1. Coffee drying curve changes were consistent in variable initial moisture. Drying time needed more with higher initial moisture, bigger paving quality, slower wind velocity and lower wind temperature. And qualities of coffee beans declined as beans deterioration, when the wind temperature exceeded maximum temperature.2. Orthogonal test showed optimal parameters of hot wind drying of coffee beans were: wind temperature was 80?, wind velocity was 1.82 m/s and paving quality was 41 kg/m2. The wind temperature was found to have the greatest effect on drying process, followed by paving quality and wind velocity. Logarithmic Model(MR = aexp(-kt)+c) can be used to describe and forecast the hot air drying curve of coffee beans, and its parameters were regressed by Maltab software, the results were:a is equal to 0.922553, k is 0.008928, c is 0.077605.3. During the roasting of Vietnam robusta coffee beans, bean qualities declined with an increase in roasting time.And qualities percentages from American roasting to Spain roasting were 92.89%, 87.66%, 84.33%, 78.3%, 75.71% respectively, and their corresponding color were dark brown, light grey, grey, light dark and dark. When the roasting condition were: total roasting time was constant to 20 minutes, the temperature rose from 210? to 250?, qualities percentages measured in every 10? were 91.45%, 89.00%, 87.26%, 81.88%, and 75.71%, respectively. Meanwhile, coffee beans color changed from brown, dark brown, light grey, grey to black.4. Four kinds of bioactive amines were found in Vietnam robusta coffee beans by HPLC(high performance liquid chromatography)gradient elution method. Putrescine were the most, followed by spermidine, spermine and serotonin. Bioactive total content had a significantly decrease and variable types and contents during roasting. It was least in Viennese roasting, then increased in France roasting, while histamine generated and had a more percentage in following roasting.5. Compared to other varieties, Vietnam robusta coffee beans has a higher protein content average to 14.5g per 100 gram, less fat content average to 7.64 g per 100 gram and slightly more average content of chlorogenic acid and tannic acid were 55.51 and 51.59 mg per 100 gram respectively. Besides the average contend of starch, ash, total sugar, caffeine, trigonelline, and acrylamide in Vietnam robusta green coffee beans were separately 21.10 g, 3.47 g, 4.34 g per 100 gram and 15.3mg per gram, 64.24 mg per 100 gram and 91.36?g per gram, closed to other varieties.6. The content of protein and fat increased to the most(16.99 and 12.5g per 100 gram, respectively) as the roasting level added. While starch added from 16.3g per 100 gram to 25.3g per 100 gram, then declined to the initial value(16.3g per 100 gram) and the highest temparature. Total sugar decreased to 0.602 g per 100 gram at 240?. Ash content increased to 5.233 g per 100 gram as roasting degree increased.7. Nine elements(K, Mg, Ca, Na, Fe, Cu, Mn, Zn, Pb) in variable roasting level and temperature were measured by flame atomic absorption spectrometry(FAAS). And results stated in these nine elements K had the maximum contents in five macro elements of both green and roasting beans, followed by Mg, Ca, Na, Fe. Zn had the most contents in four trace elements, followed by Mn, Cu and Pb. The contents of K,Mg,Ca,Cu,Pb were least in green coffee beans and increased after roasting. Cu contents increased as the roasting temperature increased, in addition, contents changes of other elements were complex. Contents of Ca,Na,Mn,Cu,Pb increased to maximum in the highest roasting degree.8. This research accomplished the design of 5-layer belt dryer of coffee beans, computed material parameters, hot air parameters, and construction size of main components of belt dryer and chose the proper heat exchanger type for belt dryer. |
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