Effect Of Processing On The Quality Of Dehydrated Toona Sinensis

Toona sinensis is an unique and traditional woody vegetable in China and contains unique flavor, various nutritional and bioactive componends. However, the browning and the loss of nutrition, affects the appearance, taste and nutritional value seriously occur generally in the conventional Toona Sinensis products. The dehydrated Toona Sinensis is preferred as its small size, light weight and easy transportation. In order to provide technical basis for reasonable utilization of Toona sinensis, the effects of processing on quality of dehydrated Toona Sinensis were studied. The main conclusions are as follows:The protein content of Toona Sinensis decreased with the collecting time and length prolong, while the content of fiber and fat were increased. The contents of Fe and Zn were lower than those of K, Ca, Mg, and Na is the lowest in minerals. All the highest contents of minerals were found in the first collecting period except Fe. The total amount of amino acids and essential amino acids peaked in the 5-10 cm of the first collecting period, and followed by the 10-15 cm of the second collecting period. With the collecting time prolonging, harvest, the contents of total phenol(TP), total flavonoids(TF) and antioxidant activity of Toona Sinensis increased gradually. Compared with collecting length, The collecting time got a greater impact on the contents of phenolic compounds, which peaked in the length of 5-10 cm of the third collecting period.Better brightness, greenness, TP, TF, antioxidant activity, phenolic compounds, characteristic aroma and safety assurance were gained by hot water blanching and steam blanching. The polyphenol oxidase(PPO) and peroxidase(POD) activity were inhibited more effectively by microwave blanching, but it caused the greatest loss of phenolic components and antioxidant activity. Blanching treatment had no significant effect on the contents of gallic acid, quercetin and kaempferol, but methyl gallate, rutin, hyperoside, isoquercitrin, astragalin and afzelin showed a great loss of Toona sinensis, and astragalin got a minimum retention followed by rutin. Overall, hot water blanching caused a minimal loss of quality, followed by steam blanching.Vacuum freeze drying(FD) would take a longer time than hot air drying(CD) and microwave-vacuum drying(MVD), but it offered a better protection of color, rehydration ratio, TP, TF, antioxidant activity, phenolic compounds, characteristic aroma. Dehydrated Toona Sinensis by FD attained the highest contents of phenolic compounds(except gallic acid), and remained closer aroma of fresh Toona Sinensis, followed with CD and MVD. Contents of gallic acid, methyl gallate, hypericum, quercitrin extracted from dehydrated Toona Sinensis were higher than fresh sample, while all drying processing lowered the contents of other phenolic compounds. DPPH · scavenging activity showed closely relation with TP and TF of dehydrated Toona Sinensis, but the reduction of iron(FRAP) had a good correlation with TP only.The heating temperature, thickness and slitting size were considered to be the most important factors affecting the dehydrated Toona Sinensis, as well as quality characteristics of final products(TP, TF, FRAP).Central composite design(CCD) and response surface methodology(RSM) were employed to optimize the conditions for FD of Toona Sinensis. The optimal conditions as follows: 51.2 ℃ of heating temperature, 15.6 mm of thick apple slices and 16.7mm of slitting size; orthogonal design were employed to optimize the conditions for CD of Toona Sinensis. The optimal conditions as follows: 50 ℃ of heating temperature,15 mm of thick apple slices and 10 mm of slitting size.Rehydration temperature of 40℃ could be favorable to the retention of the characteristic and major aromatic components of dehydrated Toona Sinensis. Rehydration temperature had a significant effect on the value of a* and b*,which decreased at the beginning of rehydration and increased subsequently. The L* of dehydrated Toona Sinensis reduced with prolonging of rehydration time. Dehydrated Toona Sinensis, rehydrated at temperature 40℃, ratio of solid to liquid 1:60(g:m L), soaking time 30-40 min, were profitable for protecting color, aroma and nutrient, and also ensuring higher rehydration ratio and safety of rehydrated Toona sinensis.