Effects of konjac oligo-glucomannan on the physicochemical properties of frozen surimi from red gurnard (Aspitrigla cuculus)

In this study, the effects of konjac oligo-glucomannan (KOG) on the physicochemical properties of frozen surimi from red gurnard (Aspitrigla cuculus) during frozen storage at -18 degrees C for 50 days were investigated. An aliquot of 0.5% (w/w) of KOG was added into the surimi and subjected to frozen storage (KOG group), and 8% of a conventional cryoprotectant (4% sorbitol and 4% sucrose, w/w) was used as a positive control (S group). The salt soluble protein content, the Ca2+-ATPase activity, total sulfhydryl (SH) content, gel strength, thiobarbituric acid (TBA) value, and whiteness of frozen surimi were determined. After storage for 50 days at -18 degrees C, the contents of salt soluble protein of KOG group and S group were 14.81% and 21.27% higher than the control, respectively, and the total SH contents of KOG group and S group were 6.90% and 8.46% higher than the control, respectively, and the gel strengths of KOG group and S group were 10.85% and 11.89% higher than the control, respectively. Although the activities of Ca2+-ATPase of KOG group and S group reached to 0.10 +/- 0.02 mu mol Pi/mg.min(-1) and 0.11 +/- 0.01 mu mol Pi/mg.min(-1) after 50 days, respectively, they are significantly different from the control (0.04 +/- 0.02) mu mol Pi/mg.min(-1), which indicated a strong cryoprotective effect of KOG. KOG exhibited more powerful antioxidant activity with lower TBA values than S group. It can be concluded that the addition of conventional cryoprotectant and KOG can inhibit protein denaturation and reduce the decrease of gel strength, but KOG displayed a stronger antioxidant activity with a small addition amount of only 0.5%, despite having no effect to improve the whiteness. These make KOG a promising cryoprotectant candidate using in frozen surimi industry.