Solution properties of laccase-treated pectic polysaccharides derived from steam-dried sugar beet pulp

Authors: WAKISAKA, NODOKA - Obihiro University; KOBAYASHI, WAKANA - Obihiro University; ABE, TASUYA - Nippon Beet Sugar Mfg Co, Ltd; NODA, KOTA - Nippon Beet Sugar Mfg Co, Ltd; NAGURA, TAIZO - Nippon Beet Sugar Mfg Co, Ltd; SUGAWARA, MASAYUKI - Obihiro University; Ikeda, Shinya

Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2023
Publication Date: 12/30/2023
Citation: Wakisaka, N., Kobayashi, W., Abe, T., Noda, K., Nagura, T., Sugawara, M., Ikeda, S. 2023. Solution properties of laccase-treated pectic polysaccharides derived from steam-dried sugar beet pulp. Food Hydrocolloids. 150(2024) 109712. https://doi.org/10.1016/j.foodhyd.2023.109712.
DOI: https://doi.org/10.1016/j.foodhyd.2023.109712

Interpretive Summary: Sugar beet pectin is widely used as a processing aid in food processing to control the quality and stability of various food products because it has an ability to provide not only viscosity but also stability to emulsions and foams. Sugar beet pectin is conventionally produced based on acid extraction from sugar beet pulp which is dried using a rotary drum dryer operated typically at 650–1000 °C. Steam-drying of sugar beet pulp at a temperature of operation around 150–180 °C is an innovative technology, allowing hot water extraction of pectin without the use of acids with much higher yields and lower environmental impacts. The major drawback of the technology is that the resulting pectin is more hydrolyzed and functionally inferior. The objective of the present study was to increase the viscosity of sugar beet pectin derived from steam-dried pulp using an enzyme that catalyzes the crosslinking reaction between the molecular chains of sugar beet pectin. The average molecular weight of the sugar beet pectin increased in a dose dependent manner, accompanied by dose dependent increases in viscosity. Additionally, the sugar beet pectin exhibited solution properties distinctively different from various other polysaccharides, including weaker molecular weight dependences of the intrinsic viscosity, weaker concentration dependences of the specific viscosity in the semi-dilute region, higher critical concentrations, and lower coil overlap parameters. These results demonstrated that the enzyme-mediated crosslinking is a useful approach to improving the functionality of the sugar beet pectin derived from steam-dried sugar beet pulp.

Technical Abstract: Steam-drying of sugar beet pulp enables hot water extraction of pectic polysaccharides without adding acid to the extraction medium with a yield higher than the conventional preparation method but a lower molecular weight. The objective of the present study was to investigate the effect of laccase treatment on the molecular weight and solution properties of the pectic polysaccharides derived from steam-dried sugar beet pulp using hot water extraction. The weight average molecular weight and intrinsic viscosity of the pectic polysaccharides increased from 97.1 kDa to147 kDa and from 0.383 dL/g to 0.525 dL/g due to isopropanol fractionation to remove low molecular weight fractions, respectively, and then to 661 kDa and 0.832 dL/g by the laccase treatment at the highest laccase rate examined, respectively. The intrinsic viscosity values showed a power-law relationship with the molecular weight, the exponent value of which was found to be 0.32 prior to the isopropanol fractionation or 0.38 after the isopropanol fractionation. These values were much lower than that derived theoretically for a random coil (0.5) and closer to that for a sphere (0.33). Compared to the results previously reported for various polysaccharides, the concentration dependence of the specific viscosity in the semi-dilute region was weaker, the critical concentration which is the threshold between dilute and semi-dilute solutions was higher, and the so-called coil overlap parameter was lower. The present results indicate that the pectic polysaccharides examined in this study had highly branched, compact, and spherical molecular structure.