الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
This study aimed to establish the influence of drying condition such as pretreatments,the sample thickness,the air temperature and type of drier(oven or solar)on the drying constants
for fig & banana fruits and onion & garlic vegetables.
The kinetic parameters for the color
change during drying using Hunter L-, a-,b- values, chroma, Hue, total color change (∆Ε) values were determined. Zero-order and first-order model were used to calculate K0 (zeroorder
kinetic constant)and K(first-order kinetic constant). The moisture sorption isotherms of fig and banana fruits at room temperature at 25°C was done. Henderson, Chung&Pfost,
Halsey,Smith and BET model equations were applied to fit experimental moisture sorption data for water activity ranged from 0.11 to 0.85.
I-Fig fruits (Conadria):
Fig fruits were subjected to different pre-drying treatment (steam-blanching, waterblanching+sulfuring)and dried either by oven drying at 55, 65 and 75°C or by solar drying.
All drying curves were characterized by two different drying phases; namely constant drying rate and falling drying rate phases. Both drying phases were greatly influenced by the temperature of drying air. The application of Lewis and Page equations resulted in the
drying parameters (K, N) for each pre-treatment of figs and for each drying temperature.
The Lewis and Page equations were successfully applied to fit the drying data of all drying experiments.
The L and b-values were decreased with drying time in all samples, specially
those dried at 75°C, while the a-values were increased strongly. Great differences in chroma-values were found between dried samples(control),steam-blanched,and waterblanched+
sulfured samples dried at 75°C. On the other side, the zero-order model kinetic
constant values (Ko) were higher in all cases than those of the first-order model. While, the moisture sorption of dried fig fruits was determined at room temperature. It was found that in all cases,Halsey equation came in the first rank and had a better fitness than the other applied equations for the sorption data of the tested fig samples.
II-Banana fruits (Maghrabi):
The drying air temperatures(60, 50°C and solar drying),pretreatments and the osmotic pretreatment have positively influenced the drying rate values compared with that of the un-treated or without the osmotic pretreatment samples. Pretreatment of the banana slices by a combination of blanching and osmotic pretreatment (60 Brix) gave the highest attained K-values compared by the single blanching treatment. The color parameters (L),(b)and chroma of the untreated or treated samples were decreased,but(a)and (∆Ε) values were increased with the drying time. The L values were lighter for blanched-slufured or(blanched-ascorbic+citric acid)samples followed by osmotic dehydrated samples compared with the other treated ones. In general,the zero-order model kinetic constant values(Ko)were higher in all cases than those of the first-order model. The moisture
sorption of dried banana fruits was determined at room temperature. It was found that in all cases,Halsey equation came in the first rank and had a better fitness than the other applied
equations for the sorption data of the tested banana samples.
III-Onion(Beheri)and garlic(Baladi) samples: Onion and garlic slices were dried at 70°C,60°C,50°C and by solar drying.
It was noticed that in all drying curves,the constant drying rate period was found to be absent in the drying of sliced onion and garlic samples and the value of moisture content was rapidly
decreased with consequent increase of the drying rate, when air temperature was increased. Page equation having higher R2-values than those calculated for Lewis equation and the smaller samples thickness has positively influenced the drying rate values
compared with that of the highest thickness of onion and garlic samples. It gave the highest attained K-values. The L-, a-, b-values revealed that the color of dried onion and garlic
slices was affected regardless of thickness, the drying temperature, and the drying method.
The L and b-values were decreased with drying time in all samples, specially in those dried at 70 and 60°C, while the a-values were increased strongly when compared with drying at 50°C and solar drying that seemed lighter. The zero-order model constant values (Ko)
were higher in all cases than those of the first-order model(K). The R2 values of both models were different,that is why it is impossible to affirm that one model was superior to the other.