الملخص الإنجليزي
Tomato is one of the extensively produced crop in the world which belongs to
Solanaceae family. Preserving lycopene and β-carotene in plum tomatoes during
processing and storage is significant from the nutritional point of view. There is
limited research conducted on the storage stability of lycopene and β-carotene in fresh
and freeze - dried tomatoes. This makes the current study more important in
characterizing the degradation kinetics of lycopene and β-carotene, thus could help
industrial processors in predicting the suitable processing and storage temperature.
The main objective was to determine the effects of temperature on the stability of
lycopene and β-carotene in fresh and freeze-dried plum tomato during processing and
storage. The other objectives were to determine the physico-chemical characteristics
of fresh plum tomato and to determine the proximate and nutritional compositions of
fresh and freeze-dried plum tomatoes. The proximate composition was determined
using methods of AOAC. Ascorbic acid, total phenolics, total flavonoids and total
carotenoids were determined using colorimetric methods. The storage stability of
lycopene and β-carotene of fresh tomatoes were investigated at -80, -60, -40, -20, -10,
5, 25, 60, 80, 100 and 120 °C. However, the storage stability of lycopene and β carotene of freeze-dried tomatoes were investigated at -80, -60, -40, -20, -10 and 25
°C. Lycopene and β-carotene were extracted using a mixture of ethanol: hexane (4:3,
v/v) and the absorbance readings were determined using spectrophotometer at 445 and
470 nm for lycopene and β-carotene, respectively. There was a significant difference
(p < 0.05) between fresh and freeze-dried tomatoes in moisture, ash, fat and total
carbohydrates. However, there was no significant difference (p > 0.05) in protein
content which revealed high stability of protein towards the effect of freeze drying.
Freeze drying significantly decreased the contents of ascorbic acid (57.96 % loss),
total phenolics (60.63 % loss), total flavonoids (40.12 % loss) and total carotenoids
(49.21 % loss).The initial concentrations of lycopene and β-carotene in fresh plum
tomatoes were 3.97 ± 0.98 and 8.69 ± 1.90 mg /g ds, respectively. Freeze drying
significantly reduced the initial concentrations of lycopene and β-carotene to reach
values of 0.52 ± 0.26 and 1.12 ± 0.71 mg /g ds, respectively with 86.84 % loss of
lycopene and 87.11 % loss of β-carotene. Lycopene and β-carotene exhibited similar
behaviors during storage in which both slow release and decay were observed at low
temperatures (-10, -20, -40, -60, -80 °C), whereas decay was observed at mild
temperatures (5, 25, 60, 80 °C). However, a very fast release followed by decay was
observed at high temperatures (100, 120 °C). There was a significant effect (p < 0.05)
of temperature on the lycopene and β-carotene reaction rates and half times. Lycopene
and β-carotene stabilities in fresh tomatoes were greater than the corresponding
stabilities in freeze-dried tomatoes stored at -10, -20, -40 and -80 °C. The fresh
tomatoes had higher lycopene stability than freeze-dried tomatoes stored at 25 °C.
However, β-carotene exhibited greater stability in freeze –dried tomatoes than fresh
tomatoes at 25 °C. Lycopene and β-carotene in fresh tomatoes were more stable at 25
°C compared to 5 °C. Lycopene and β-carotene in freeze-dried tomatoes were more
stable at 25 °C than -10 and – 20 °C. Lycopene and β-carotene in fresh tomatoes stored
at 100 °C were stable up to 8 h and 5 h, respectively. Both were stable up to 1 h at 120
°C. Therefore, lycopene and β-carotene had greater stabilities at 100 °C than 120 °C,
thus it is recommended for the food processors to avoid processing at 120 °C and if
needed it is better to reduce the time to not more than 1 h. Storage of fresh tomatoes
at temperatures above 25 °C caused an increase of lycopene and β-carotene losses with
increasing temperature and storage time. It is recommended to use mild thermal
processing at 60 or 80 °C to insure retention of more lycopene and β-carotene. Further
research is needed to optimize the freeze drying conditions of tomatoes and to develop
a combined kinetics model of lycopene and β-carotene degradation. Also, further
research is required to study the other factors involved in lycopene and β-carotene
degradation.
