Vacuum frying line is
an integral process which consists of pre-treatment, frying, and
post-treatment.
The pre-treatment plays a crucial role in the improvement of final product quality. For example, fruits have high initial water content, that requires a long frying time. The problem of final product with high oil absorptions, burnt and low crispness will be occurred. Pre-treatment such as blanching/pre-drying/ drying after steeping and freezing can limit these problems.
In addition to choosing professional pre-treatment equipment suppliers, you should also choose professional and reliable process providers, only by combining the two parts, can we produce excellent products.
Blanching
Function: minimize enzymatic browning and limit oil
uptake
Steeping
Actually steeping is a mass transfer process, which removes partially water and increases the soluble solid content of fruit and vegetable by steeping in solution. The solution is made by water and maltose syrup. The process results in modification of the fruit and vegetable tissue which can be tailored toward compositional, textural, and sensorial quality of vacuum fried fruits and vegetables.
Freezing
Freezing is an alternative pre-treatment strategy to achieve a crispy fruit matrix in vacuum-frying processing.
In fact, due to fast heat transfer to frozen tissue, ice crystal inside the frozen cells sublimed under vacuum condition leaving pores in the food matrix, accelerated the moisture loss and sequentially decrease the final moisture content.
Freezing rate could affect vacuum-fried fruit and vegetables. Slow freezing produces big size crystal, which damages the cell. Then it could increase oil penetration. Thus fast freezing is preferred to minimize oil uptake.
Vacuum frying post-treatment—de-oiling/centrifugation
Centrifugation for removing the surface oil is an important part of the post-frying process and can be part of the frying equipment. Centrifugation done while the pressure is still low, and the oil could penetrate the porous product when breaking the vacuum. In general, increasing centrifugation speed decreased the oil uptake, but maybe damage product shape.
Thus the centrifugation speed has to be limited according to the product hardness to prevent product breakage.