بررسي اثر نوع برش، بر سينتيك خشك شدن و كيفيت هويج خشك

The effect of slicing type on drying kinetics and quality of dried carrot

با توجه به اهمیت برش در فرآوری محصولات كشاورزی، در این تحقیق اثر برخی پارامترهای برشی بر فرآیند خشك شدن و كیفیت محصول خشك نهایی هویج بررسی شد. آزمایش‌ها به‌صورت طرح كاملاً تصادفی انجام گرفت و در آن اثر ضخامت هویج در دو سطح 3 و 6 میلی‌متر، نوع تیغه در سه مدل تیغه لبه صاف، اره‌ای و كنگره‌دار و جهت برش در سه راستای طولی، عرضی و مورب بر سینتیك خشك شدن، آهنگ تبخیر، چروكیدگی و جذب مجدد آب بررسی شد. نمونه‌ها در آون با دمای 70 درجه سانتی‌گراد تا رسیدن به رطوبت مطلوب 8% خشك شدند. نتایج نشان داد اثر متغیرهای مستقل بر پارامترهای مورد مطالعه در سطح یك درصد معنی‌دار است. كمترین زمان خشك شدن در مدت 200دقیقه و در نمونه‌های برش خورده با تیغه كنگره‌دار و در جهت عرضی، با اختلاف معنی‌دار در سطح 5 درصد بود. بیشترین آهنگ تبخیر 74/0 گرم بر دقیقه در حالت برش با تیغه صاف و در جهت طولی با اختلاف معنی‌دار در سطح 5 درصد با سایر تیمارها به‌دست آمد. همچنین كمترین چروكیدگی نیز برای همین تیمار به میزان 7/36 درصد به‌دست آمد. بیشترین جذب مجدد آب در برش با تیغه صاف و در جهات مورب و طولی به‌ترتیب 96/3 و 88/3 و با اختلاف معنی‌دار نسبت به سایر تیمارها به‌دست آمد. به‌طور كلی با توجه به نتایج این پژوهش، برش هویج با تیغه صاف و در جهت طولی برای تولید هویج خشك با كیفیت بالاتر توصیه می‌شود.

Introduction: Carrot is one of the most common vegetables used for human nutrition because of its high vitamin and fiber contents. Drying improves the product shelf life without addition of any chemical preservative and reduces both the size of package and the transport cost. Drying also aidsto reduce postharvest losses of fruits and vegetables especially, which can be as high as 70%. Dried carrots are used in dehydrated soups and in the form of powder in pastries and sauces. The main aim of drying agricultural products is decrease the moisture content to a level which allows safe storage over an extended period. Many fruits and vegetables can be sliced before drying.because of different tissue of a fruit or vegetable, cutting them in different direction and shape created different tissue slices. Due to drying is the exiting process of the moisture from internal tissue so different tissue slices caused different drying kinetics. Therefore, the study on effect of cutting parameters on drying is necessary. Materials and Methods: Carrots (Daucus carota L.) were purchased from the local market (Kerman, Iran) and stored in a refrigerator at 5°C. The initial moisture contents of the Carrot samples were determined by the oven drying method. The sample was dried in an oven at 105±2°C about 24 hours. The carrots cut by 3 models blade at 3 directions. The samples were dried in an oven at 70°C. Moisture content of the carrot slices were determined by weighting of samples during drying. Volume changes because of sample shrinkage were measured by a water displacement method. Rehydration experiment was performed by immersing a weighted amount of dried samples into hot water 50 °C for 30 min. In this study the effect of some cutting parameters was considered on carrot drying and the quality of final drying product. The tests were performed as a completely random design. The effects of carrot thickness at two levels (3 and 6 mm), blade in 3 models (flat blade, wavy blade and Ridged blade) and the cutting direction at 3 levels (linear, lateral and diagonal) were evaluated on drying kinetics, drying rate, shrinkage and rehydration. Statistic analysis done by SPSS software. Results and Discussion: The results of analysis of variance showed that the effects of cutting parameters were significant on studied parameters (p <0.01) (Table 1). Thin layers dried faster than thick layers because of firmness of surface which it causes slow moisture transfer. The least drying time was 200 minutes at the samples that cut by a wavy blade at the lateral direction with a significant difference (p <0.05) given Fig.3. In these samples surface evaporation is more, because of more surface. The compare means showed drying rate at thick layer is fewer because of the longer distance moisture removal (Fig.6). Also the most drying rate was 0.74 gmin-1 at cutting by flat blade on linear direction with a significant difference (p <0.05).The least shrinkage was obtained on this treatment was 36.7% given Fig.8. The most of tissue of linear slices is woody part that is dense compare with other parts therefore shrinkage decrease at during drying. The most rehydration was 3.96 and 3.88 for cutting by flat blade in diagonal and linear direction with significant difference to other treatments. Rehydration depends on cell damage greatly. Since the slices of carrot that cut by flat blade were damaged fewer than other treatments therefore rehydration was more. Conclusions: The drying behavior of carrot slices was studied at different methods in slicing carrot. The results showed a significant effect of the cutting variables on drying kinetics, drying rate, shrinkage and rehydration. The carrot moisture content decreases continuously over the drying and the fastest drying occurred at thin layers sliced by wavy blade. The slices that were cut by flat blade at linear direction caused the best quality. The results show cutting parameters are significant effect on quality of dried fruits and vegetable. There for the study of drying behavior is necessary for fruits with different tissue because of more quality of production and high efficiency at drying. Also the study of cutting parameter suggest on other fruits and vegetables with different tissue. The results help to manufactures for improvement of production of drying equipment.