Study On Effects Of Osmotic Dehydration With Different Saccharides And Drying Methods On Texure Of Dried Apple Chips

In the study,apples were chosen as materials.Apple slices were osmotically pretreated with different saccharides,the osmotic characteristcs,the behavior of hot air combined with instant controlled pressure drop(HA-ICPDD)drying and the texture quality of those apple chips were investigated.Based on the best osmotic solution,the effects of osmotic temperature and time of stachyose on the qualities of the HA-ICPDD apple chips were evaluated.Finally,different drying methods were applied and changes in pectin,and texture of the dried apple chips were investigated.The main conclusions were as follows:1.All the monosaccharide(fructose,glucose),disaccharide(sucrose,maltose),trisaccharide(raffinose),tetrasaccharide(stachyose)selected,significantly increased the hardness and crispness of the samples,among which raffinose and stachyose exhibited the most significant increase in crispness.Samples with different osmotic pretreatments showed less discoloration.Compared with other pretreatments,HA-ICPDD apple chips pretreated by stachyose possessed the highest Tg(29.74?)and porous structure.Besides,HA-ICPDD apple chips pretreated with maltose and stachyose got the highest overall scores by the sensory evalution.According to the results of this study and the advantages of raffinose and stachyose as new functional carbohydrates,it is possible to use stachyose as an alternative to osmotic agents and produce apple chips with crispness and functions.2.The water loss(WL)and solids ganin(SG)of apple slices pretreated with stachyose had positive correlations with osmotic temperature and time.Compared with those with no pretreatment,all the osmotic pretreatments increased the crispness of the HA-ICPDD apple chips significantly.On the other hand,the color of the samples pretreated with 40?and 30 min of osmosis were close to the fresh samples.Moreover,total polyphenol contents of the samples pretreated with 40?and 30 min of osmosis did not decrease compared with those with no osmosis.Taken color,texture and nutriention together,stachyose osmosis with 40?and 30 min combined with HA-ICPDD could be beneficial to improve the overall quality of apple chips.3.The research results showed that hot air drying(AD)and medium and shortwave infrared radiation drying(IR)mainly occurred in the falling rate drying.With the drying temperature increased,the drying rates increased,and the values in volume,rehydration ratios,and crispness of dehydrated apples also increased.Freeze drying(FD)and HA-ICPDD apples chips showed excellent honeycomb structures.The volume and rehydration rations of FD apple chips were 0.76 and 7.55 respectively,while the volume and rehydration rations of apple chips from other drying methods ranged as 0.19~0.31 and4.56~5.48 respectively.FD-dried apple chips exhibited obvious advantages in volume and rehydration rations compared with other drying methods.HA-ICPDD apple chips showed the highest crispness(92),while the FD samples had the lowest(10).4.Among all selected drying methods,samples dried by FD had the highest content of water-soluble(WSP),that was 112.7 mg/g AIR.For AD and IR drying,the content of WSP decreased with the increasing drying temperature.Firstly,the tissue structure was well preserved under the freeze drying.The high content of WSP resulted in low viscosity and low mechanical strength between cells,and thus the FD-dried apple chips showed low values in hardness.On the other hand,The low content of WSP resulted from high temperature during AD,IR and HA-ICPDD drying might reduce glass transition temperatutre(T_g)of samples.When the temperature was higher than Tg,viscoelasticity and plasticity of samples increased.Therefore,high speed of water loss would contribute to the formation of stable porous structures.The degree of esterification of CSP is low and there are many free carboxyl groups that would easily bind metal ions.Such effects contribute to the increase in the porous degree of apple chips.Therefore,the crispness values of the apple chips obtained from AD 90?,IR 90?and HA-ICPDD apple chips were larger than those from drying methods.In summary,WSP content may be one of the factors that affects hardness and microstructure of dried apples,and DE of CSP may influence crispness.