Abstract
The influence of osmotic dehydration (OD) in combination with vacuum impregnation (VI) technique on the mass transfer behavior of “Phulae” pineapple was investigated. Pineapple slices of 10 mm thick were immersed in sucrose solution at concentrations of 55 and 65oBrix under atmospheric pressure or vacuum pressures at 250 mmHg (VOD-250) and 450 mmHg (VOD-450). The results deduced that 65o Brix of sucrose solution for 300 min and the vacuum pressure of VI at 450 mmHg were necessitated to increase solute uptake to 14.79 g/100 g when compared to other treatments. Surprisingly, the effect of OD and VI on water loss was not much different. Scanning electron microscope (SEM) showed that the pore sizes of pineapple slices were decreased when the impregnation period increased implying the higher adsorption of sucrose into the fruit structure. Subsequently, calcium lactate (Ca-L) at 2, 4 and 6% (w/w) was incorporated in sucrose solution prior to drying at 60oC in a conventional hot air dryer. It was observed that increasing concentration of Ca-L led to a significant decrease in moisture content (17.74 to 15.53%) and water activity (0.58 to 0.56) whereas calcium content was increased (24.472 to 676.317 mg/100g). However, it should be noted that high concentration of Ca-L had adverse effect on sensory property where overall actability decreased from 7.09 to 5.65 as well as total phenolic content (TPC) (17.74 to 15.53 gGAE/100g), DPPH (223.51 to 159.7 µmol Trolox/100g) and FRAP (380.65 to 291.57 µmol ascorbic acid/100g) values.
Highlights
Pineapple is one of tropical fruits that are most consumed worldwide
The water loss and solute gain were calculated based on mass balance technique
The water loss value (Figure 1a) was superior compared with solute gain (Figure 1b) when the same impregnation period was considered
Summary
Pineapple is one of tropical fruits that are most consumed worldwide. It holds the third most world production tropical fruit, after only bananas and mangoes.[1] Among various varieties, Ananas comosus (L.) Merr. Known as “Phulae” pineapple is a Geographical Indication (GI) fruit which can grow only some areas in Chiang Rai, Thailand. This pineapple cultivar is becoming popular as fresh-cut product exported to other countries. Conventional hot air drying drastically causes negative changes in the sensory properties, nutritive values, chemical constituents and mechanical properties of products.[5]
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