| In this paper, a typical commercial instant black tea was selected as raw material, both of the chemical composition and the powder characteristics were analysed and measured; and fluidized bed granulation process was utilized to improve the defect of small particle size and poor flowability, then the optimal process was obtained by CCD optimize experiments; and HS-SPME was combined with GC-MS technique to explore the impact of fluidized bed granulation on instant black tea aroma; besides, moisture adsorption characteristics of the instant black tea granulated by the optimal granulation process was studied and high degree of adsorption models were found. Specific conclusions are as follows:BT209-3type instant black tea chemical components analysis showed that it contained moisture content4.29%, total ash14.00%, reducing sugar content10.10%, total amount of crude protein21.30%, polyphenol content27.28%and caffeine content5.10%; besides,16kinds of basic amino acids including7kinds of essential ami no acids leucine, isoleucine, lysine, phenylalanine, methionine, threonine and valine within were detected. Determination of instant tea powder properties results indicated that the color L*, a*, b*values were40.52,11.57and31.73respectively, sensory overall performance of red-brown, besides average particle diameter was104.94μm, bulk density0.38g/mL, tap density0.60g/mL and CI Index36.67%revealing poor flowability of instant black tea raw material and strong adhesion between particles. The equilibrium moisture content of instant black tea raw materials increases sharply with the increase of the relative humidity, and increases with the storage temperature rises when stored at given relative humidities. During stored at25℃RH33%and40℃RH32%conditions, the equilibrium moisture content of instant black tea was low and moisture adsorption was relatively stable. When stored at25℃RH54%,25℃RH75%,40℃RH50%and40℃RH75%, the amount of moisture adsorption increased sharply in the first24h, then the adsorption rate gradually reduced within24-48h subsequently, and the balance reached after48hours with the maximum moisture adsorption amount.These six factors Fluidized bed fan speed, the fluidized bed peristaltic pump rate, atomization pressure, inlet air temperature, granulation time and binder significantly affect moisture content and the average particle diameter of granulated instant tea particles. The granulation time is longer, the greater the average particle diameter, the deeper the color and deterioration of the organoleptic characteristics of the instant tea particles. Appropriate concentration of the binder significantly increased instant tea particle size, while strong adhesive binder would result in hard and poor solubility instant tea. Through fluidized bed atomizing pressure(X1), the pump speed of the peristaltic pump(X2) and the inlet air temperature(X3)3factors CCD experiment optimization, the moisture content (Y1) and the average particle diameter (Y2) of the secondary response surface regression model were obtained. By response surface analysis, the optimal granulation process parameters of instant tea by fluidized bed was as follows:atomization pressure0.04MPa, peristaltic pump speed7.56, inlet air temperature79.55℃0.1%xanthan gum used as binder, granulation time45min. After testing, the moisture content of the instant tea particle granulation by the optimal process was5.84%, and the average particle diameter was1064μm, which was close to the theoretical predictions.HS-SPME was combined with GC-MS technique to analysis the aroma components of instant black tea raw material and instant tea particles granulation at different processes, the results showed that: Aroma compoments of instant black tea raw material (A), instant tea samples granulated30min at75℃(B), granulated30min at95℃(C) and granulated60min at75℃(D) existed a great degree of consistency, there were8kinds of aroma components as Benzeneacetaldehyde, a-Methyl-a-[4-methyl-3-pentenyl]oxiranemethanol, Methyl salicylate, 1,6-Octadien-3-ol,3,7-dimethyl-,1,5,7-Octatrien-3-ol,3,7-dimethyl-Nonanal,3-Buten-2-one,4-(2,6,6-trimethyl-1-cyclohexen-l-yl)-and Menthol in common, and the amount of these8kinds of aroma components accounted for53.71%,58.98%,59.19%, and68.38%of the total extraction ingredients amount in instant tea samples A, B, C, D respectively. Aroma components of both samples A and B are mainly aldehydes, alcohols and ketones, besides sample A exists unique aroma such as D-Limonene,1R-a-Pinene, Acetophenone, etc, while sample B presents unique aroma jasmine, Methyl tetradecanoate and so on; sample C aroma components are mainly aldehydes, alcohols, esters and ketones, and widely exist alcohols unique aroma, such as1-Octanol,2-butyl-sample D aroma components are mainly alcohols, esters and ketones, besides alcohols aroma component content is as high as70.08%, and exist unique flavor substance Decanal. Dominant aroma substances of samples B, C, D, and raw material are alcohol. On the one hand, granulation significantly increased the relative content of alcohol aroma and its relative content increased with granulation time and granulation temperature increases; on the other hand, granulation decreased aldehydes relative content of tea samples and its content decreased with granulation time extension and the granulation temperature increases. In addition, granulation also improved esters and ketones relative content.Storage characteristics of instant black tea raw material and instant tea particle granulated by the optimal granulation process were studied and specific conclusions were as follows:hydroscopicity of granulated instant black tea particle was lower than raw material. At specific water activity condition, the equilibrium moisture content of both instant tea decreases with temperature rises, besides, rapidly increases with relative humidity increases. The Boltzmann model fitted moisture adsorption data of both raw material and granulated instant tea particle best when stored at25℃, and fitted models were y=85.25-(1.35+85.25)/[1+e(aw-0.95)/0.23], and y=66.16+(0.07-66.16)/[1+e(aw-0.93)/0.19] respectively. When stored at40℃, Allometric model fitted water adsorption data of these two instant black tea well, and fitted models were y=39.49*(aw)2.54and y=37.49*(aw)2.64respectivily. During stored at25℃, relative humidity showed a great impact on moisture content and sensory quality of vacuum-packed instant tea. Only when stored at25℃RH33%condition, the moisture content, sensory quality changed little in the whole storage period. While stored at25℃RH54%,75%conditions, the moisture content gradually increased with storage time increases, color darkened, and reconstitution decreased; Instant black tea had suffered serious aroma losses and sensory quality decrease. |
PDF Full Text Request