Cost-effective Production of tagatose as a beneficial sugar substitute from sour whey

Tagatose is an excellent sugar substitute in terms of sweetening power and calories. The new method describes a cost-effective production process from sour whey.

New arabinose isomerase:

• High activity in the pH range 4-7 (relative activity ≥ 70%)
• Temperature maximum at 75° C
• Half-life of ~6 h at 60 °C in skimmed milk ultrafiltration permeate pH 4.5
• Maximum galactose-tagatose isomerization of 50 % achievable
• Production in GRAS organisms possible

Tagatose as a sugar substitute:

• comparable sweetness to sucrose
• significantly fewer calories than sucrose (12.5 kJ/g tagatose, 17 kJ/g sucrose)
• suitable for diabetics as it has a glycemic index of 3 (sucrose 65)
• prebiotic, only 15-20% is absorbed in the intestine
• does not promote tooth decay
• approved as a novel food in Europe since 2005
• already used in various products (e.g. coating agents, diet drinks)

Foods containing sugar are very popular with consumers, although high sugar consumption can lead to health problems such as obesity, diabetes and cardiovascular disease. However, conventional sugar substitutes and sweeteners, which are typically used in calorie-reduced confectionery, soft drinks or diet products, often differ in taste from natural sugars or have to be declared as additives, which is met with skepticism by consumers.

The food industry is faced with the challenge of offering products with a reduced sugar content that have a convincing taste and are perceived as natural. The simple sugar tagatose could be a sensible alternative with advantageous properties: it has a sweetening power comparable to that of sucrose, with a lower physiological calorific value (tagatose = 12.5 kJ/g; sucrose = 17 kJ/g). Tagatose can be obtained by a chemical process in which the disaccharide lactose is first hydrolyzed into the two monosaccharides galactose and glucose. The purified galactose can then be isomerized to tagatose under alkaline conditions. However, this process is commercially unattractive due to the high production costs and the formation of undesirable by-products. Enzymatic conversion could reduce production costs and the formation of by-products, but there is currently no commercially available enzyme for converting galactose to tagatose.

A process for the enzymatic conversion of lactose to tagatose was developed at the University of Hohenheim. The bi-enzymatic reaction using the enzymes β-galactosidase and L-arabinose isomerase produces a mixture of the monosaccharides glucose, galactose and tagatose. Lactose-rich whey, especially sour whey, is used as a raw material, which is produced in large quantities in dairies as a by-product stream that has hardly been utilized to date. The purely enzymatic conversion is made possible by a new L-arabinose isomerase, which converts galactose to tagatose. The new arabinose isomerase from Lentilactobacillus parakefiri is characterized by a special pH stability and activity in the acidic range, which distinguishes it from conventional L-arabinose isomerases and their usual activities in the neutral or alkaline range. Due to this special property, the L-arabinose isomerase can be used directly in sour whey without having to process the whey beforehand.

Multi-Enzymsystem zur Herstellung eines alternativen Zuckersirups, Sabine Lutz-Wahl et al., BIOspektrum, 2020