Research On The Osmotic Dehydration And Combined Drying Technology Of Peach Cylinders

In this study, Jiubao peaches were chosen as materials. The osmotic solutions were fructose, glucose, maltose, sucrose, respectively. After osmotic dehydration pretreatment, peach cylinders were dried by hot air combined with explosion puffing drying. Water loss, solute gain and drying quality were evaluated, and then the best osmotic solution was chosen; traditional osmotic dehydration, ultrasound-assisted osmotic dehydration, osmotic dehydration with pulsed vacuum, osmotic dehydration assisted with high hydrostatic pressure were carried out to gain the optimal osmotic mode and time; after different osmotic pretreatments, the drying characteristics, moisture migration and quality analysis were studied by infrared radiation drying, infrared radiation drying combined with explosion puffing drying. This study aimed at providing with technical reference and theoretical support to the development of new fruit and vegetable chips. The main conclusions were as follows:1. Peach cylinders pretreated by osmotic dehydration with maltose had highest water loss, lowest solute gain, and preferable dehydration efficiency. After maltose osmosis, the color of peach cylinders dried by explosion puffing drying significantly improved, hardness decreased, explosion ratio and crispness increased. Based on the scanning electron microscopy, the peach cylinders showed a uniform porous structure. In summary, maltose osmosis combined with explosion puffing drying could be beneficial to improve the efficiency of the osmotic dehydration and enhance overall quality of peach cylinders.2. According to kinetics of traditional osmotic dehydration(OD), the ratio of water loss and solute gain of peach cylinders increased respectively with osmotic time increased. However, the ratio of water loss was much greater than solute gain. After long time of osmotic process(about 400min), the water loss was tended to equilibrium; nevertheless, the solute gain still increased due to the damage of peach organizational structure. According to osmotic dehydration efficiency, the osmotic dehydration time was selected as 90, 180 and 240 min to be the pretreatment condition; ultrasound could increase the moisture migration during osmotic process, but the organizational structure of peach cylinders significantly damaged and corrupted after a long time ultrasonic osmosis treatment(> 70 min) and the gain of solute significantly increased. According to the significant difference, 30 and 60 min should be as the time of ultrasound-assisted osmotic dehydration(ULOD); From the perspective of applicability and efficiency, osmotic dehydration with pulse vacuum and high hydrostatic pressure was not suitable osmotic dehydration of peach cylinders.3. The transverse relaxation time analysised by low field nuclear magnetic resonance showed that ULOD and OD could influence the moisture migration, change moisture state and the moisture redistribution. After all osmotic pretreatments, the content of free water of peach cylinders decreased, the relaxation time of free and immobilized water decreased, and the relaxation time of bound water was relatively stable. However, the proportion of immobilized and bound water increased to different extent. The changes of relaxation time and corresponding content change were correlated with the WL and SG during osmotic pretreatments. Magnetic resonance imaging(MRI) showed that fresh sample present the brightest image signal, after osmotic processing, the signal gradually reduced, the signal of OD for 240 min was weakest.4. The drying tempreture and the time of ULOD and OD would affect the infrared radiation drying rate of peach cylinders. Drying rate and water effective diffusion coefficient decreased as osmotic time increased, improved as drying temperature increased. Mathematical models were used to fit the drying process, and the results showed that Verma et al. model could reflect drying process and describe moisture variation of peach cylinders with drying time. During infrared radiation drying process, the free and immobilized water of samples pretreated by ULOD and OD reduced, and the amplitude of the signal were gradually migrating to the left. When dried to 120 min, the free water of all samples completely removed. And the remaining water was mainly bound water, which was difficult to remove. Samples pretreated by ULOD had a longer shelf life, ULOD and OD could both improve the overall color.5. After different osmotic pretreatments, peach cylinders were dried to 90 min(water content of 25% to 30%) by infrared radiation drying and then combined with explosion puffing drying. Results showed that hardness of peach cylinders increased, crispness reduced, and color improved. Different pretreatments had various influences on the ratio of soluble solid content to titration acid. Through sensory evaluation analysis, peach cylinders dried by OD for 180 min or ULOD 60 min combined with explosion puffing drying had a better overall quality.