The role of fructose at a range of concentration on the texture and microstructure of freeze-dried pectin–cellulose matrix cryogel

Abstract

Freeze-dried (FD) fruit and vegetable materials with a large amount of sugar are unstable. With the aim to understand the structure formation of FD products, the effects of fructose content on the texture and microstructure of FD matrix were investigated by using pectin–cellulose cryogel model. Cryogels containing fructose of 0–40% were produced using freeze-drying at three different primary drying temperatures of −40, −20, and 20°C. The resultant cryogels were characterized by texture profile analyzer, scanning electron microscope, and μCT. Results indicated that at drying temperature of −40°C, increasing fructose concentration promoted the hardness of the cryogels, and cryogels of 16% fructose obtained maximum hardness. Excessive fructose (≥20%) weakened the described hardness, while exhibiting stronger springiness and resilience. The microstructure showed that dense pores and increased wall thickness due to fructose aggregation were critical factors responsible for increased hardness. The porous structure as well as relatively large pore size were necessary for crispness, in addition, rigid pore wall with certain strength were also required. At the drying temperature of 20°C, large hetero-cavities dominated the microstructure of cryogels with 30% and 40% fructose, caused by melting inside during FD process. In this situation, lower T_m (−15.48 and −20.37°C) were responsible for cryogels’ melting In conclusion, if possible, regulating fructose content and state may enable the precision texture design of FD fruit and vegetable foods.