Effect Of Different Pretreatment Of Freeze-dried Hawthorn Slices

As a medicinal and food plant,hawthorn is rich in many nutrients and it is widely used for fresh food,processing and medicine.Most traditional hawthorn products have a high sugar content and they are gradually replaced by new hawthorn products.Freeze-dried hawthorn has become a popular product because it maintains original shape and retains many of biological activities.Hawthorn has a high acid content,which leads to higher acidity and poorer taste in freeze-dried.Hawthorn slices and products are less pleasant for consumers.Hawthorn is rich in pectin,resulting in an excessively hard product after freeze-drying,which largely reduces the taste of freeze-dried hawthorn slices and thus affects the market for consumer.Therefore a suitable solution of this problem is needed.Pretreatment can reduce the high acid content of hawthorn and improve the unpleasant sensation.And it is caused by high acidity.And the problems such as excessive hardness of hawthorn after freeze-drying are improve.In this research,we used hawthorn slices as raw material to investigate the effect of different blanching times,number of freeze-thaw cycles,and different permeation solutions and ultrasound-assisted permeation on the quality of freeze-dried hawthorn slices.The main findings are as follows.(1)We researched the effect of blanching time on the quality of freeze-dried hawthorn slices.We compared the colour difference,hardness,crispness,rehydration rate,total acid,total sugar,flavonoids,total phenols,antioxidant activity,microstructure and sensory evaluation of freezedried hawthorn slices with different blanching times.Then we obtained that the colour was closest to the original sample and the rehydration performance was the highest when the blanching time is 0.5 minute.The total acid,total sugar and flavonoid content are highest.The antioxidant activity is best.And the organoleptic score of 90.03.(2)We researched the effects of one,two and three times of freeze-thaw cycles on the vacuum freeze-drying time.And producting quality of hawthorn slices was researched by using hawthorn slices as raw material.The results showed that the freeze-thaw cycle can effectively shortened the drying time.At the same time,it reduced the hardness of the product and the total acid content.And it increased the total phenolic content and the antioxidant activity.In order to obtain freeze-dried hawthorn slices with a short drying time and a good quality product,the freeze-thaw cycle should not be exceeded more than 2 times.(3)We investigated the effects of permeable solution and ultrasound-assisted permeation on the quality of freeze-dried hawthorn slices.The results of single-factor experiments showed that the best sonication conditions were achieved when the sonication power was 360 W and the sonication time was 10 min.The results showed that the samples had the best colour,moderate hardness and brittleness when the permeation solution was Na Cl with or without sonication.The best rehydration performance and the highest content of bioactive substances such as total flavonoids and phenols improved antioxidant capacity.And they also had a certain enhancement effect on volatile substances.However,the sensory scores of the sucrose-treated and the ultrasound-assisted sucrose-treated reached 92.00 and 90.33.So that different substances could be selected as penetrants depended on the actual processing use.(4)We mainly analyzed the physicochemical properties of hawthorn with different concentrations of humic acid solution and found that changing the concentration of humic acid solution would cause some damage to the cell structure of hawthorn.And they resulted in poor colour,reducing hardness,poor rehydration properties.And total sugars,total acids and flavonoids gradually decreased in freeze-dried slices of hawthorn.However,the total phenolic content and antioxidant capacity of hawthorn which were enhanced to a certain extent treated with humic acid.The results showed that the humic acid concentration of 0.1% changed the colour of the hawthorn less.And it caused less loss of nutrients and improved the quality of the hawthorn at the same time.