Effects Of Pretreatment And Compound Drying On Cell Damage During The Preparation Of Purple Sweet Potato Granules

In this paper,fresh purple sweet potatoes(PSP)are used as raw materials,after pretreatment,the effects of different calcium concentration,pre-cooking temperature,pre-cooking time,cooking time,and emulsifier addition amount on cell damage of PSP granules were studied,during the drying process,the effects of different hot air drying temperature,intermediate conversion moisture content,and freeze-drying time on cell damage of PSP granules were studied,at the same time,the physical and chemical properties of different PSP granules were studied.The effects of different calcium concentration,pre-cooking temperature,pre-cooking time,cooking time and emulsifier addition amount on the iodine blue value of PSP granules during the pretreatment process of PSP were studied,at the same time,observed the micro-morphology of the granules particles.According to the single factor test,the optimal levels of various factors in the pretreatment process of PSP are calcium concentration 110?g/mL,pre-cooking temperature 70 ?,pre-cooking time 10 min,cooking time 9 min,and addition of emulsifier 2.0 %.Based on the results of the single-factor test,orthogonal optimization test was performed on each factor,the best process parameters in the pretreatment process of PSP were: calcium concentration 110 ?g/mL,pre-cooking temperature 70 ?,pre-cooking time 11 min,cooking time 10 min,and addition of emulsifier2.5 %.At this time,the PSP granules had the lowest iodine blue value was 5.98,the starch particles in the PSP granules were regular in shape,uniform in size,uniformly dispersed,and there was no sign of serious damage.This shows that the pretreatment process has a strengthening effect on the cell wall of PSP granules,can maintain cell integrity,and has an adverse effect on the damage of PSP granules.The effects of different hot air drying temperature,intermediate conversion moisture content,and freeze-drying time on the PSP granules compound drying process on PSP granules iodine blue value and anthocyanin content were studied.The single factor test results show that the optimal levels of each factor are: hot air drying temperature 60 ?,intermediate conversion moisture content 30 %,and freeze drying time 7 h.The response surface optimization test was used to designed a model using Design-Expert.V8.0.6.1 software,the PSP granules iodine blue value was used as the response value,the optimization results were analyzed to determine the effects of the optimal process parameters of compound drying andthe interaction of various factors on the iodine blue value.The influence of each factor on the iodine blue value was extremely significant,and the order of influence was: hot air drying temperature>freeze drying time>intermediate conversion moisture content,the optimal process parameters for compound drying were: hot air drying temperature 70 ?,intermediate conversion moisture content 25 %,freeze-drying time 7 h,at this time,the iodine blue value of PSP granules was low.This shows that the compound drying method can reduce cell damage and hinder the cell damage of PSP granules.The untreated and compound dried PSP granules was used as a blank control,and PSP granules were prepared according to the optimal process parameters of pretreatment and compound drying,the physical and chemical properties of three PSP granules were investigated.The water-holding and oil-holding capacity,solubility and swelling degree,viscosity value of the optimal pretreated and compound dried PSP granules were higher than those of the blank PSP granules,and the freeze-thaw water dehydration rate and light transmittance were lower than those of the blank PSP granules,the gelation properties was worse than that of the blank PSP granules.In the optical microscope image of the PSP granules,the starch particles of the optimal pretreated and compound dried PSP granules had a regular round shape,no larger volume particles appeared,the particle breakage was smaller,and there was no obvious bonding phenomenon.It shows that the pretreatment and compound drying methods can improve the physical and chemical properties of PSP granules,and further proves that the PSP granules pretreatment and compound drying method are effective in protecting granules cells,enhancing cell wall strength and reducing cell damage.