农业工程学报
農業工程學報
농업공정학보
2014年
22期
309-315
,共7页
李辉%林河通%林毅雄%袁芳%林福兴
李輝%林河通%林毅雄%袁芳%林福興
리휘%림하통%림의웅%원방%림복흥
贮藏%吸附%热力学性质%荔枝%果肉%等温线%平衡含水率
貯藏%吸附%熱力學性質%荔枝%果肉%等溫線%平衡含水率
저장%흡부%열역학성질%려지%과육%등온선%평형함수솔
storage%sorption%thermodynamic properties%litchi (Litchi Chinensis Sonn.)%pulp%isotherm%equilibrium moisture content
为了解干制“乌叶”荔枝果肉含水率与水分活度、贮藏温度之间的复杂关系，并为干制“乌叶”荔枝果肉贮藏条件的确定提供技术依据，运用吸附原理，在水分活度为0.112～0.976范围内，研究了干制“乌叶”荔枝果肉在20、30和40℃时的水分吸附等温线；采用8种模型对试验数据进行拟合，通过比较模型决定系数（R2）和均方根误差确定用于描述干制“乌叶”荔枝果肉吸附等温线的最适模型；通过不同温度下干制“乌叶”荔枝果肉的吸附等温线数据获得净等量吸附热、焓变、熵变和自由能等热力学性质。结果表明，干制“乌叶”荔枝果肉的水分吸附呈Ⅲ型等温线，在相同水分活度时，平衡含水率随温度的升高而下降。Peleg模型用于描述吸附等温线是较适合的，决定系数为R2为0.9950～0.9979，均方根误差为1.9431～2.7102。热力学性质显示，净等量吸附热随含水率的增加而降低，在较高含水率时趋近于0。焓变与净等量吸附热有相同的值，其范围为0.95～186.98 kJ/mol。熵变随含水率的增加而降低，并没有表现出对温度的依赖性。自由能随含水率和温度的增加而减小。焓-熵补偿理论适用于干制“乌叶”荔枝果肉中的水分吸附过程，此水分吸附过程是焓驱动的。研究结果为干制“乌叶”荔枝果肉的加工和贮藏稳定性提供理论依据。
為瞭解榦製“烏葉”荔枝果肉含水率與水分活度、貯藏溫度之間的複雜關繫，併為榦製“烏葉”荔枝果肉貯藏條件的確定提供技術依據，運用吸附原理，在水分活度為0.112～0.976範圍內，研究瞭榦製“烏葉”荔枝果肉在20、30和40℃時的水分吸附等溫線；採用8種模型對試驗數據進行擬閤，通過比較模型決定繫數（R2）和均方根誤差確定用于描述榦製“烏葉”荔枝果肉吸附等溫線的最適模型；通過不同溫度下榦製“烏葉”荔枝果肉的吸附等溫線數據穫得淨等量吸附熱、焓變、熵變和自由能等熱力學性質。結果錶明，榦製“烏葉”荔枝果肉的水分吸附呈Ⅲ型等溫線，在相同水分活度時，平衡含水率隨溫度的升高而下降。Peleg模型用于描述吸附等溫線是較適閤的，決定繫數為R2為0.9950～0.9979，均方根誤差為1.9431～2.7102。熱力學性質顯示，淨等量吸附熱隨含水率的增加而降低，在較高含水率時趨近于0。焓變與淨等量吸附熱有相同的值，其範圍為0.95～186.98 kJ/mol。熵變隨含水率的增加而降低，併沒有錶現齣對溫度的依賴性。自由能隨含水率和溫度的增加而減小。焓-熵補償理論適用于榦製“烏葉”荔枝果肉中的水分吸附過程，此水分吸附過程是焓驅動的。研究結果為榦製“烏葉”荔枝果肉的加工和貯藏穩定性提供理論依據。
위료해간제“오협”려지과육함수솔여수분활도、저장온도지간적복잡관계，병위간제“오협”려지과육저장조건적학정제공기술의거，운용흡부원리，재수분활도위0.112～0.976범위내，연구료간제“오협”려지과육재20、30화40℃시적수분흡부등온선；채용8충모형대시험수거진행의합，통과비교모형결정계수（R2）화균방근오차학정용우묘술간제“오협”려지과육흡부등온선적최괄모형；통과불동온도하간제“오협”려지과육적흡부등온선수거획득정등량흡부열、함변、적변화자유능등열역학성질。결과표명，간제“오협”려지과육적수분흡부정Ⅲ형등온선，재상동수분활도시，평형함수솔수온도적승고이하강。Peleg모형용우묘술흡부등온선시교괄합적，결정계수위R2위0.9950～0.9979，균방근오차위1.9431～2.7102。열역학성질현시，정등량흡부열수함수솔적증가이강저，재교고함수솔시추근우0。함변여정등량흡부열유상동적치，기범위위0.95～186.98 kJ/mol。적변수함수솔적증가이강저，병몰유표현출대온도적의뢰성。자유능수함수솔화온도적증가이감소。함-적보상이론괄용우간제“오협”려지과육중적수분흡부과정，차수분흡부과정시함구동적。연구결과위간제“오협”려지과육적가공화저장은정성제공이론의거。
In order to reveal the complex relationship among the moisture content, the water activity and the temperature, and to provide technical data for preservation of dried ‘Wuye’ litchi (Litchi Chinensis Sonn. cv. Wuye), the static gravimetric method was used to determine moisture sorption isotherms of dried‘Wuye’ litchi pulp at three temperatures (20, 30, and 40°C) over a range of water activities from 0.112 to 0.976 based on the adsorption theory. The experimental data of dried‘Wuye’ litchi pulp were fitted by eight models (BET, Halsey, Henderson, Peleg, Smith, GAB, Modified Henderson, Oswin) available in the literature. The optimal model used to describe the sorption isotherms of dried ‘Wuye’ litchi pulp was determined by comparing the models’ coefficient of determination (R2) and root mean square error. Thermodynamic properties such as net isosteric heat, enthalpy changes, entropy changes, and free energy that provide a deeper understanding of the properties of water and energy requirements associated with sorption process were determined from moisture adsorption isotherm data of dried‘Wuye’ litchi pulp at different temperatures. The results showed that the moisture sorption isotherms of dried‘Wuye’ litchi pulp exhibited typeⅢsigmoid shape. At low and intermediate water activity, the equilibrium moisture content increased slowly with water activity (0.1-0.4), while at high water activity (>0.4) equilibrium moisture content increased rapidly with water activity. The equilibrium moisture content decreased with the increasing temperature at constant water activity. The Peleg model was found to be the best for describing the relationship between the moisture content, the water activity and temperature. The agreement between experiment and predicted values of this model was excellent (R2 ranging from 0.9950-0.9979,root mean square error ranging from 1.9431-2.7102). The thermodynamic properties of dried‘Wuye’ litchi pulp showed that net isosteric heat of adsorption decreased with an increasing in moisture constant, and approached to zero at high moisture content. enthalpy changes had the same values as the net isosteric heat ranged from 0.95 to 186.98 kJ/mol. entropy changes values ranged from 1.11 to 587.24 J/(mol·K) at moisture levels ranging from 8%-50%for dried‘Wuye’ litchi pulp. These values decreased as moisture content increased and did not show temperature dependence. Free energy ranged from 0.60 to 18.58 kJ/mol for dried ‘Wuye’ litchi pulp. Free energy became smaller as the moisture content and the temperature increased. The plot of the enthalpy versus entropy showed a linear relationship for dried ‘Wuye’ litchi pulp with R2 equal to 0.9999, which indicated the existence of compensation. The values of isokinetic temperature and harmonic mean temperature were 319.34 K and 302.93 K respectively. Therefore, the enthalpy-entropy compensation theory was suitable for water adsorption of dried‘Wuye’ litchi pulp because isokinetic temperature was significantly different from the value of harmonic mean temperature. Since isokinetic temperature>harmonic mean temperature, the mechanism of the adsorption process of dried ‘Wuye’ litchi pulp was enthalpy driven. The results provide a theoretical basis for the processing and storage stability of dried‘Wuye’ litchi pulp.
