The effect of drying by moisture absorbent materials on the quality properties of saffron

Introduction: The saffron plant is native to Iran. About 90% of the world's saffron is produced in Iran. Drying saffron has a great effect on the qualitative and sensory characteristics of saffron. Saffron drying is done in different ways. In choosing the optimal method and conditions for drying saffron, one should pay attention to points such as regional conditions, pollution level, efficiency, final moisture and product quality indicators. Drying saffron at a temperature of 25 to 60 degrees Celsius will reduce the amount of crocin pigment and the intensity of coloring due to the enzymatic decomposition of crocin (Tsimidou and Biliaderis 1997). Using a temperature higher than 90°C will reduce the intensity of saffron coloring due to the increase in the thermal decomposition and oxidation of crocin (Gregory et al., 2005).The saffron plant is native to Iran. About 90% of the world's saffron is produced in Iran. Drying saffron has a great effect on the qualitative and sensory characteristics of saffron. Saffron drying is done in different ways. In choosing the optimal method and conditions for drying saffron, one should pay attention to points such as regional conditions, pollution level, efficiency, final moisture and product quality indicators. Drying saffron at a temperature of 25 to 60 degrees Celsius will reduce the amount of crocin pigment and the intensity of coloring due to the enzymatic decomposition of crocin (Tsimidou and Biliaderis 1997). Using a temperature higher than 90°C will reduce the intensity of saffron coloring due to the increase in the thermal decomposition and oxidation of crocin (Gregory et al., 2005). The saffron plant is native to Iran. About 90% of the world's saffron is produced in Iran. Drying saffron has a great effect on the qualitative and sensory characteristics of saffron. Saffron drying is done in different ways. In choosing the optimal method and conditions for drying saffron, one should pay attention to points such as regional conditions, pollution level, efficiency, final moisture and product quality indicators. Drying saffron at a temperature of 25 to 60 degrees Celsius will reduce the amount of crocin pigment and the intensity of coloring due to the enzymatic decomposition of crocin (Tsimidou and Biliaderis 1997). Using a temperature higher than 90°C will reduce the intensity of saffron coloring due to the increase in the thermal decomposition and oxidation of crocin (Gregory et al., 2005).International and national standards recommended minimum humidity of 12% and 10% respectively for saffron in order to increase its shelf life. Moisture absorbent materials are based on the principle of moisture transfer due to the difference in vapor pressure between the absorbent material and air. The absorbent material with low moisture content absorbs moisture from the air and reaches a balance with it. The saffron plant is native to Iran. About 90% of the world's saffron is produced in Iran. Drying saffron has a great effect on the qualitative and sensory characteristics of saffron. Saffron drying is done in different ways. In choosing the optimal method and conditions for drying saffron, one should pay attention to points such as regional conditions, pollution level, efficiency, final moisture and product quality indicators. Drying saffron at a temperature of 25 to 60 degrees Celsius will reduce the amount of crocin pigment and the intensity of coloring due to the enzymatic decomposition of crocin (Tsimidou and Biliaderis 1997). Using a temperature higher than 90°C will reduce the intensity of saffron coloring due to the increase in the thermal decomposition and oxidation of crocin (Gregory et al., 2005). International and national standards recommended minimum humidity of 12% and 10% respectively for saffron in order to increase its shelf life. Moisture absorbent materials are based on the principle of moisture transfer due to the difference in vapor pressure between the absorbent material and air. The absorbent material with low moisture content absorbs moisture from the air and reaches a balance with it.The advantages of moisture absorbent materials in drying, in addition to low energy consumption, include continuous drying even in non-sunny hours, increased drying rate due to hot and dry air, very uniform drying, and higher product quality, especially for heat-sensitive products (Dorouzi et al., 2017). There is no research available in the field of using moisture absorbing compounds in drying saffron. The purpose of the research was to investigate the effectiveness of moisture absorbent material on drying saffron and the effect of the characteristics of the air entering the dryer containing moisture absorbent material on the quality indicators (color, aroma and taste) of saffron.
Materials and methods: The stigmas were separated from the saffron petals and prepared for drying. The usual index and sufficiency of saffron drying was considered equal to 10% moisture based on national standard No: 259-2. After drying and reaching laboratory conditions in terms of temperature and humidity, the samples were packed in glass containers and kept at 4 °C for evaluation tests. In the first phase, moisture absorbent materials including silica gel, natural zeolite, clay and bentonite were compared in terms of their effect on the drying speed of saffron. At this stage, these materials were placed in the drying machine and under constant drying conditions (inlet air temperature 40°C and inlet air velocity 0.4 m/s) the time for saffron moisture to reach 10% of the initial value was measured. . To determine the time to reach 10% moisture, direct weighing during drying and comparing it with the moisture content of the original product was used. The adsorbent selected from this step was used in the next step. Then, with the aim of determining the optimal conditions of the incoming air in the drying method using the moisture absorbent material selected from the previous phase, the incoming air with 3 speeds of 0.2, 0.4 and 0.6 m/s and three temperatures of 30, 40 and 50 degrees Celsius after passing through the (selected) moisture absorbent layer, it entered the dryer and the effect of the treatments on the amount of picrocrocin, safranal and crocin of saffron was checked and the optimal speed and temperature of the inlet air was selected. Also, the effect of drying method on the quality of saffron was investigated. In this experiment, saffron was dried using three Spanish methods, dry shade (traditional) and drying with moisture absorbent materials, and the effect of drying method on picrocrocin, safranal and crocin of saffron was investigated. Drying methods included the traditional, Spanish method and the use of moisture absorbent materials. Saffron quality evaluation tests including measuring the values of saffron quality indicators, i.e. picrocrocin, safranal and crocin, were determined based on national standard number 259-2 and with a spectrophotometer and ultraviolet-visible spectrophotometric method. The drying of saffron continued until the moisture content reached 10%.
Results and discussion: The results showed a significant difference between the effects of moisture absorbent materials on the drying time of saffron under the same temperature conditions. The highest drying speed was related to silica gel and the lowest was related to clay. An important issue is the ability to stabilize silica gel in the drying bed and the possibility of reusing it without contamination. The results showed that as the temperature increased from 30°C to 50°C, the amount of picrocrocin gradually decreased. Also, at a constant temperature, the amount of picrocrocin increased with the increase of the inlet air speed. Decreasing the drying temperature along with increasing the incoming air speed can produce saffron with a better aroma. The studied temperature range for drying saffron, i.e. the temperature range of 30°C to 50°C, the amount of crocin increased with increasing temperature. The quality of saffron obtained by drying saffron with moisture absorbent was in competition with the traditional drying method.
Conclusion: Among the three methods of drying saffron, by measuring the qualitative indicators of saffron, the traditional drying method produces saffron with an aroma index (safranal) (48 ± 2.7 unit), taste index (picrocrocin) (96 ± 2.1).The drying method with silica gel moisture absorbent material was after the traditional method in terms of taste index (86.7 ± 1 unit). In terms of saffron color index (crocin), the Spanish method (211.37±3 unit) scored the highest. The use of moisture absorbent materials in the process of drying saffron can significantly help in drying saffron with high quality (taste and aroma). The use of air speed of 0.2 m/s was chosen due to economic efficiency. The highest amount of crocin (235.7±5 unit) was obtained at a temperature of 50 °C and an air velocity of 0.2 m/s. Drying saffron at 30 °C produced saffron with better taste and aroma. To create crocin or more color in saffron, after drying saffron at a temperature of 30°C, at the end of the drying process, it is better to use a high temperature of 50°C.