| The taste and flavor of coffee are affected by many factors such as coffee beans’ variety,origin,roasting method,and extraction process.At present,the commercial instant coffee powder or extract is mainly extracted using high-temperature extraction technology,while the cold-water extract and its corresponding freeze-dried powders are becoming a new fashion due to their unique tastes and flavors,and exhibiting huge market potentials.However,the existing cold-water extraction process is timeconsuming,high energy consumption and high cost,which restricts the development of the cold-water extract and freeze-dried powder of coffee in industry.The subject of the present study was to assess the possibility of applying the ultrasonic assisted cold-waterextraction technology to coffee extraction by comparing with the traditional hot-water and cold-water extraction technology in the aspects of extraction yields,the contents of bioactive components and flavors,and analyzing the flavor characteristics of the extract,so as to provide theoretical guidance for the industrial application of the ultrasonic assisted coldwater extraction technology.The main results are as follows:1.The extraction efficiency of ultrasonic-assisted cold-water extraction of coffee was systematically compared with hot-water and cold-water extraction methods,including Espresso,Pour Over coffee,boiling water extraction,cold-water extraction operated at 4°C and 10°C.The results showed that the extraction yields of ultrasonic-assisted cold-water extraction could reach 17.06%.Compared with the cold-water extraction processed at 4°C and 10°C,ultrasonic-assisted cold-water extraction showed higher extraction yields for total oil(4.69%),total protein(3.12%)and total acid(0.83%),but lower extraction yields for total phenolic compounds(1.80%),indicating that the ultrasonic-assisted cold-water extraction method has a good extraction effect on the oil,protein,total acid and polyphenols in coffee,and it can replace or even be better than the conventional cold-water extraction methods at 4℃ and 10℃.2.Compare the content of caffeine,chlorogenic acid and trigonelline in different coffee samples.The results showed that the non-volatile compound content of Pour Over coffee and boiling water extraction was not much different from that of cold brewed coffee.The content of caffeine(0.56 mg/m L)and chlorogenic acid(1.25 mg/m L)in ultrasonic-assisted cold-water extraction coffee are slightly lower than those cold water extraction operated at 4°C and 10°C,and the content of trigonelline(0.42 mg/m L)is between the two,indicating that the content of non-volatile compounds in ultrasonic-assisted coldwater extraction is close to those cold-water extraction operated at 4°C and 10°C.3.The types and contents of volatile compounds in coffee liquor obtained by different extraction processes were compared.With the help of GC-MS,73,58 and 49 compounds were isolated and identified from Espresso,Pour Over coffee and boiling water extraction,and the total content of volatile substances were 51.48 μg/m L,140.39 μg/m L and 146.58 μg/m L,respectively.52,58,and 55 compounds were isolated and identified in cold-water extraction operated at 4°C and 10°C,and ultrasonic assisted coldwater extraction,and the total content of volatile substances were 88.41 μg/m L,63.81 μg/m L and 48.95μg/m L,respectively.Cluster analysis showed that ultrasonic assisted cold-water extraction coffee liquid can be combined with Espresso,cold-water extraction operated at 4°C and 10°C,while Pour Over coffee and boiling water extraction can be combined.A total of 20 aroma active ingredients that contributed to the aroma of ultrasonic-assisted cold-water extracts of coffee were identified by the Odor Activity Value(OAV)method,and their types are slightly lower than Espresso and Pour Over coffee,and slightly higher than that of cold-water extracts at 4℃ and 10℃,indicating that the aroma of ultrasonic-assisted coldwater brew coffee is more monotonous than hot brewed coffee,and richer than cold brewed coffee.Except for the floral and spicy aromas,the other aroma activity values of ultrasonic-assisted cold-water brew coffee are lower than the cold-water extracts at 4℃ and 10℃,which may result in weaker aroma.4.The optimal extraction pareameters of ultrasonic assisted cold-water extraction of coffee were obtained using single factor and orthogonal experiment design as follows: the ratio of powder to water:1:15,extraction time: 60 min,ultrasonic power: 100 w,under which the extraction yields reached 17.72%.Compared with the unoptimized coffee liquid,its caffeine and trigonelline content has increased,and the chlorogenic acid content has decreased.With the help of GC×GC-TOF/MS,196 volatile compounds were detected from the ultrasonic assisted cold-water extraction coffee,with a total content of 279.65 μg/m L,including acidic compounds that were not detected by GC-MS.In summary,the research results of this paper show that the ultrasonic assisted cold-water extraction can replace the conventional cold extraction process,and the content of non-volatile functional components and volatile flavor components in the extracted liquid is similar to traditional hot extraction and conventional cold extraction processes,but the extraction time is shorter and the energy consumption is lower.It has potential application prospects in industrialized large-scale production. |
PDF Full Text Request