The Experimental Study Of Chinese Yam Low Temperature Preservation Drying

Chinese yam has gained an outstanding reputation for its rich nutritional value andhealth benefits of Medicinal and Edible. But its unique viscous material, high moisturecontent and irregular shape makes it impossible to provide long-term storage and long-distance transport. Dried Chinese yam can not only solve the above problems but alsoimprove product value. Low-temperature preservation drying is use Low temperaturedrying method such as heat drying, vacuum drying, freeze drying to process foodmaterials for achieving lower nutrient loss, stored longer and the better sensory qualityproduct by reducing the loss of thermosensitive substance. In this paper, the dryingcharacteristics and drying quality of Chinese yam in heat drying and vacuum dryingwere studied. The main conclusions are as follows:Drying technology of Chinese yam were studied used the two drying method ofheat drying and vacuum drying. The optimal drying parameters of Chinese yam weretemperature40℃, slice thickness5mm, air speed3.0m/s in heat drying andtemperature60℃, vacuum pressure0.09Mpa, slice thickness3mm in vacuum drying.The result of drying characteristics showed that heat drying and vacuum drying had anotable difference on drying rate. The sensory evaluation of vacuum drying productwas higher than heat drying.This study was to measured total phenol content of Chinese yam by FolinCiocalteu methods. The results showed that ultrasonic extraction of phenolics fromChinese yam organic reagents chose60%ethanol solution. And volume fraction,liquid-to-material ratio, extraction temperature, extraction times had a non-significanteffect on the phenol extraction of Chinese yam. The orthogonal test results showedthat investigated parameters could be ranked in decreasing order of importance intheir effects as follows: liquid-to-material ratio, ultrasonic power, extraction time.The optimal extraction technology condition of Chinese yam was20:1(mL/g) ofliquid-to-material ratio treated with200W ultrasonic for25min. The analysis of material was carried out before quality detection of Low-temperature preservation-drying Chinese yam. The moisture content at drying-endpoint of heat drying and vacuum drying was both setted45%士1％、30%士1％and15%士1％. The optimal drying method was confirmed by comparing the wateractivity, total plate count at15d and30d in store process, polysaccharide content,rehydration ratio and sensory evaluation of dried Chinese yam. The result showed thatthe best drying method of Chinese yam was heat drying and the moisture content was30%at the drying-end point. By comparing the relationship of phenol in heat dryingand vacuum drying, the result showed that the brown of Chinese yam in heat dryingwas caused by enzymatic browning, and the brown of Chinese yam in vacuum dryingwas caused by non-enzymatic browning.