Effect Of Osmo-dehydrofreezing And Glassy State Storage On The Quality Attributes Of Frozen Mango And Dynamic Simulation

The objectives of this study were to use the combining osmotic dehydration pre-treatment with freezing technique to improve the quality of frozen mango. The effects of different pre-treatments on the quality attributes, phenolic compounds and volatile flavor compositions of frozen mango were investigated. Moreover, in order to simulate the whole processes of osmotic dehydration and freezing, a successive one-dimensional mass and heat transfer modeling approach based on mango cell as a basic unit was developed. In addition, glass transition temperature and state diagram of mango were investigated to predict the storage stability of frozen mangoes. Moreover, the effects of storage at glassy state and osmo-dehydrofreezing on the quality attributes of frozen mangoes during storage were also investigated. The main results and conclusions were made as follows:(1) The osmo-dehydrofrozen mangoes obtained a shorter freezing time, a lower melting point and a higher freezing rate than that of the conventionally frozen samples. The osmotic dehydration pretreatment significantly improved the quality attributes of frozen mango in terms of color, hardness, drip loss, vitamin C content and other physical properties compared with the untreated or the blanched ones. In addition, the osmo-dehydrofreezing can inhibit the polyphenol oxidase activity, but activate the peroxidase activity.(2) Freezing time of the osmotic-dehydrated mangoes was reduced by increasing osmotic concentration due to less water to be frozen. The melting temperature of mango cuboids dehydrated in glucose and maltose solutions was lower than that of fresh samples and samples in sucrose solution. In addition, the dehydrofrozen samples pretreated in maltose had higher quality in vitamin C content (increasing by23.5-73.0%), color (color change reducing by2.6-39.2%) and drip loss (reducing by0.7～9.7%) than those pretreated in other osmotic solutions. The cuboids pretreated in glucose displayed higher hardness (increasing by16.4-36.2%). Based on principal component analysis (PCA) and group distance, osmotic dehydration in45%maltose was proposed as the most favorable freezing conditions.(3) The osmo-dehydrofreezing could prevent total phenolic losses of mangoes compared with conventional freezing. The dehydrofrozen samples pretreated in glucose had higher content of total phenolic than other sugars. After different freezing processes, there were significant differences (p<0.05) in the content of individual phenolic compounds; some phenolic compounds (including gallic acid, quercetin, and sinapic acid) decreased, while others (including p-hydroxybenzoic acid and p-coumaric acid) increased. The current work indicates osmo-dehydrofreezing improves the content of individual phenolic compounds in frozen mangoes.(4) The new volatile compounds were present in osmotically pretreated mangoes after freezing. Some compounds present in fresh samples tended to decrease or disappear after conventional freezing. The osmo-dehydrofreezing could improve the esters and other major aroma compounds of frozen mangoes compared with conventional freezing. The dehydrofrozen samples pretreated in maltose had more volatile compounds identified than other sugars.(5) The one-dimensional mass balance equations and thermal balance equations were established. And a good agreement was obtained between the simulated and experimental results, proving that two models were practical. Numerical results could describe the distribution of water and sucrose in the intracellular and extracellular volumes of mangoes during osmotic dehydration. The distribution of water in the intracellular was similar with that of water in the extracellular volumes. The density of water in the extracellular volumes was lower than in the intracellular volumes. In addition, the density of sucrose in the extracellular volumes was higher when the distance was close to the interface, and it gradually become lower when the distance was close to the center.(6) The water sorption isotherm of freeze-dried mango (25℃) was established by GAB model and the monolayer moisture content was found to be0.109g water/g sample (d.b.) as the stability criteria by water activity concept. The state diagram provided an estimate of maximal-freeze-concentrated solutes at0.84g solids/g sample (w.b.)(Xs’) with the characteristic temperature of end point of freezing (Tm’) being-33.0℃and the characteristic glass transition temperatures Tg’being-54.6℃. Other characteristic glass transition temperatures Tg "and Tg’"were-43.2℃and-36.8℃, respectively. The unfreezable water in mango was obtained as0.16g water/g sample (w.b.)(1-Xs’). The state diagram can be used in predicting the storage stability of frozen and dried mangoes as well as in providing the optimum processing conditions.(7) The osmotic dehydration pretreatment can improve the quality attributes of frozen mango in terms of color (total color difference reducing by12.5～36.8%), hardness (increasing by35.8～65.5%), drip loss (reducing by11.3～44.5%) and vitamin C content (increasing by21.2～134.8%) compared with the untreated ones after6months of frozen storage (-18℃). Pretreatment with higher solution concentration showed smaller alterations in the quality attributes of samples. Through comprehensive analysis, dehydration in osmotic solution of concentration40%was considered as the optimum pretreatment conditions for frozen storage. In addition, the quality was better maintained in shaded side (firmer) of mangoes than the sun-exposed side (softer). With progression of storage time, although there was a reduction in the quality of samples, mangoes pretreated by osmotic dehydration showed less reduction than the untreated. The quality attributes of frozen mango could be improved at glassy state during frozen storage (-55℃).