Direct Isomaltulose Synthesis From Beet Molasses by Immobilized Sucrose Isomerase

Qin-Qing Wang,Jian-Hua Hao,Ming Yang,Zai-Chao Ma

doi:10.3389/fbioe.2021.691547

Abstract

Isomaltulose is becoming a focus as a functional sweetener for sucrose substitutes; however, isomaltulose production using sucrose as the substrate is not economical. Low-cost feedstocks are needed for their production. In this study, beet molasses (BM) was introduced as the substrate to produce isomaltulose for the first time. Immobilized sucrose isomerase (SIase) was proved as the most efficient biocatalyst for isomaltulose synthesis from sulfuric acid (H2SO4) pretreated BM followed by centrifugation for the removal of insoluble matters and reducing viscosity. The effect of different factors on isomaltulose production is investigated. The isomaltulose still achieved a high concentration of 446.4 ± 5.5 g/L (purity of 85.8%) with a yield of 0.94 ± 0.02 g/g under the best conditions (800 g/L pretreated BM, 15 U immobilized SIase/g dosage, 40°C, pH of 5.5, and 10 h) in the eighth batch. Immobilized SIase used in repeated batch reaction showed good reusability to convert pretreated BM into isomaltulose since the sucrose conversion rate remained 97.5% in the same batch and even above 94% after 11 batches. Significant cost reduction of feedstock costs was also confirmed by economic analysis. The findings indicated that this two-step process to produce isomaltulose using low-cost BM and immobilized SIase is feasible. This process has the potential to be effective and promising for industrial production and application of isomaltulose as a functional sweetener for sucrose substitute.

Highlights

Molasses is a viscous by-product of sugar refineries with a sweet taste and color ranging from brown to dark-brown, which mainly includes cane molasses (CM), soy molasses (SM), and beet molasses (BM)
Sucrose-Isomerase Converting Molasses to Isomaltulose discharged in China in the past years, and only a little amount was used as grinding aid, feed, and carbon source (Gao et al, 2011; Yan et al, 2011), aggravating BM waste and causing serious environmental concerns
Pretreatment can reduce the content of those metal ions in BM, increasing the isomaltulose yield and the immobilization of enzyme notably reduced the enzyme demand. These results indicated that the bioprocess using pretreated BM and immobilized sucrose isomerase (SIase) is a feasible alternative approach for isomaltulose production

Summary

Introduction

Molasses is a viscous by-product of sugar refineries with a sweet taste and color ranging from brown to dark-brown, which mainly includes cane molasses (CM), soy molasses (SM), and beet molasses (BM). The molasses is rich in sucrose and is composed of a minimum amount of carbohydrates (like glucose) and other components (e.g., proteins, vitamins, and heavy metals) (Wang et al, 2019a; Palmonari et al, 2020). Sucrose-Isomerase Converting Molasses to Isomaltulose discharged in China in the past years, and only a little amount was used as grinding aid, feed, and carbon source (Gao et al, 2011; Yan et al, 2011), aggravating BM waste and causing serious environmental concerns. BM has attracted increasing attention for different industrial applications worldwide, including China, due to its higher sucrose content (about 50%) than those (about 30–50%) of other molasses (Álvarez-Cao et al, 2019; Ozdal and Basaran Kurbanoglu, 2019; Wang et al, 2019a; Zheng et al, 2019; Palmonari et al, 2020; Zhan et al, 2020)

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