Rheological properties of β-fat gel made of binary mixtures of high-melting and low-melting fats

Abstract

Rheological analysis was conducted to study the physical properties of the mixtures of high-melting (HM) and low-melting (LM) fats. The HM and LM fats examined in the present work were fully hydrogenated rapeseed oil with a high amount of behenic acid (FHR-B), and sal fat olein (SFO). Gel-like behavior of the FHR-B/SFO fat mixture with FHR-B concentration of 1.5–4.0 wt% indicated the existence of many small FHR-B crystals of β polymorph that were formed by the following thermal treatment: rapid cooling ( V c=10 °C/min) from 70 °C to crystallization temperature ( T c=20 °C), and heating from T c to final temperature ( T f=38 °C) where the fat mixture was held for 60 min. These results were obtained: (1) FHR-B/SFO fat mixture exhibiting gel-like behavior formed by V c=10 °C/min exhibited pseudo-plastic flow properties with the apparent yield value at T f=38 °C. Storage moduli G ′ showed approximately the same values during the frequency scanned. Loss moduli G″, which were smaller than G ′, decreased with increasing frequency in the measured range, whereas the gel-like fat was not formed at V c=1.5 °C/min. In this mixture, G ′ and G″ were increased with increasing frequency, resulting in smaller values than those of the rapid cooling. Additionally, G″ dominated the viscoelasticity, which corresponds to liquid-like behavior. (2) At the FHR-B concentration of 1.5 wt% or higher, the FHR-B/SFO fat mixtures exhibited gel-like behavior with proper thermal treatment, whereas G ′ and G″ showed liquid-like behavior when FHR-B concentration was less than 1.5 wt%. (3) G ′ and G″ of gel-like behavior of FHR-B (2.0 wt%)/SFO (98.0 wt%) decreased drastically around T f=38 °C, and rheological behavior changed from gel-like to liquid-like at 43 °C. (4) The many small β crystals of FHR-B crystallized by proper thermal treatment may play decisive roles in viscoelastic behavior of β-fat gel.