اثر خشک کردن توسط مواد جاذب رطوبت بر خواص کیفی زعفران

تاثیر مواد جاذب رطوبت بر خشک کردن زعفران بررسی شد. اثرات نوع ماده جاذب رطوبت (سیلیکاژل، زئولیت، خاک‌‌رس و بنتونیت)، سرعت هوای ورودی به خشک‌کن (2/0، 4/0و 6/0 متر بر ثانیه) و دمای هوای ورودی به خشک‌کن (30، 40 و 50 درجه سانتی‌گراد)، پس از عبور از ماده جاذب رطوبت، بر کیفیت زعفران بررسی شدند. مقادیر پیکروکروسین، سافرانال و کروسین زعفران خشک شده با این روش با دو روش خشک کردن اسپانیایی و سایه خشک (سنتی) مقایسه شدند. نتایج نشان داد سامانه خشک کن دارای سیلیکاژل سریع‌تر از بقیه ترکیبات (29 دقیقه) باعث خشک شدن زعفران شد. به دلیل قابلیت استفاده مکرر سیلیکاژل به عنوان ماده جاذب رطوبت انتخاب و در مراحل بعدی مورد استفاده قرار گرفت.

هوای ورودی به خشک کن با دمای 30 درجه سانتی‌گراد و سرعت 6/0 متر بر ثانیه، باعث حفظ بیشترین مقادیر سافرانال (2/51) و پیکروکروسین (7/99) در زعفران شد. بیشترین مقدار کروسین (7/235) نیز در دمای 50 درجه سانتی‌گراد و سرعت 2/0 متر بر ثانیه اندازه گرفته شد. با توجه به تأثیر یکسان سرعت‌های هوای 2/0 ، 4/0 و 6/0 متر بر ثانیه بر کیفیت محصول، سرعت 2/0 متر بر ثانیه به دلیل کاهش مصرف انرژی مناسب‌ تشخیص داده شد. استفاده از دمای º C30 در خشک کردن، محصولی با کیفیت از نظر عطر و طعم ایجاد کرد. برای تولید کروسین (رنگ) بیشتر، نیاز به دمای بالا است. برای این منظور در انتهای خشک کردن زعفران دمای بالاتر (º C50) اعمال شد. کیفیت زعفران در روش استفاده از ماده جاذب رطوبت مشابه روش سنتی خشک کردن زعفران و نسبت به روش اسپانیایی بالاتر بود.

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. 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. Moisture absorbent materials act based on the principle of moisture transfer due to the difference in vapor pressure between the absorbent material and air. 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. 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. 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.

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 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 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.