Effects Of Drying Methods On Drying Characteristics And Quality Of Housui Pear Slices

With pear as the research object, the variety screening and pretreatment technology were studied and pear varieties appropriate for drying processing were determined. The effects of hot air drying(HAD), medand short- wave infrared radiation drying(MIRD) and vacuum drying(VD) on the drying characteristics and physical quality of Housui pear slices were studied. Based on the above results, experiments of single factor and response surface optimization were carried out by hot air- pulsed instant decompression flashing combined drying technology, and the optimal technological conditions were determined. From the pre-stage test, the effects of different drying methods on the quality of housui pear chips were studied. The research results are as follows:(1) Based on the contrastive analysis of physical quality of dried products from six pear varieties housui pear were were chosen as the best breed for drying. In color pretreatment experiments, it was found that housui pear slices can also maintain good color without color pretreatment. In dipping pretreatment experiments, it was found that dried housui pear slices of Blank-2 were the best on its quality, that is, the quality of housui pear products by direct drying is better than that with pre-treatment.(2) The research results showed that HAD, MIRD and VD mainly occurs in the falling rate drying. The drying temperature showed significant effects on drying featurs and quality of housui pear. The drying time of housui pear decreased with the increase of drying temperature, but the drying rate and effective moisture diffusivity were increased. The radiation power and radiation distance on the influence of the drying rate was not obvious. The L value of housui pear slices decreased with the increase of drying temperature, while the ΔE value increased. By model fitting, it was found that the fitting degree of Page Model to the drying process is better. Comprehensively, when the HAD temperature is 65℃, MIRD temperature is 65℃, radiation power is 1350 W, radiation distance is 120 mm, VD temperature is 65℃, and the drying time is appropriate, the quality of housui pear slices is better.(3) Based on the single factor experiment and quadratic orthogonal composite experiment, the optimal technical parameters were obtained as follows: puffing temperature of 85.08~95.73℃, vacuum temperature of 61.89~66.68℃, vacuum time of 1.77~2.03 h. The high qualified housui pear slices can be obtained from the above drying conditions.(4) In order to understand the influence of drying methods on hosui pear chips, the effects of drying methods including HAD, HA-PIDFD, MIRD, MIR-PIDFD, VD and FD on color, ascorbic acid, total phenolics, total flavonoids and antioxidant capacity(ABTS, DPPH and FRAP) of dried hosui pear were investigated. The results showed that the contents of gallic acid, protocatechuic acid, neochlorogenic acid, pcoumaric acid, rutin and quercetin of the hosui pear dried by different methods were significantly increased(P<0.05), and the chlorogenic acid, caffeic acid, epicatechin, ferulic acid and catechin content were significantly decreased(P<0.05). The color, ascorbic acid, total phenolic, total flavonoids and antioxidant capacity were significant different(P<0.05) among the hosui pear chips dried by different methods. The drying time of the MIR-PIDFD was the shortest. The highest total phenolic and antioxidant properties were showed in MIR-PIDFD and HA-PIDFD dried pears. In addition, The microstructure of MIR-PIDFD and FD products similar with fresh samples. The three principal components, which contained 95.823% information of the initial 14 indexes, were extracted by principal component analysis(PCA). The MIR-PIDFD, VD, HA-PIDFD products have the higher comprehensive appraise score. The PIDFD can be used in industry as a suitable method for processing high quality hosui pear.