Short communication: Development of a rapid laboratory method to polymerize lactose to nondigestible carbohydrates

Nondigestible carbohydrates with a degree of polymerization between 3 and 10 (oligosaccharides) are commonly used as dietary fiber ingredients in the food industry, once they have been confirmed to have positive effects on human health by regulatory authorities. These carbohydrates are produced through chemical or enzymatic synthesis. Polylactose, a polymerization product of lactose and glucose, has been produced by reactive extrusion using a twin-screw extruder, with citric acid as the catalyst. Trials using powdered cheese whey permeate as the lactose source for this reaction were unsuccessful. The development of a laboratory method was necessary to investigate the effect of ingredients present in permeate powder that could be inhibiting polymerization. A Mars 6 Microwave Digestion System (CEM Corp., Matthews, NC) was used to heat and polymerize the sugars. The temperatures had to be lowered from extrusion conditions to produce a caramel-like product and not decompose the sugars. Small amounts of water had to be added to the reaction vessels to allow consistent heating of sugars between vessels. Elevated levels of water (22.86 and 28.57%, vol/wt) and calcium phosphate (0.928 and 1.856%, wt/wt) reduced the oligosaccharide yield in the laboratory method. Increasing the citric acid (catalyst) concentration increased the oligosaccharide yield for the pure sugar blend and when permeate powder was used. The utility of the laboratory method to predict oligosaccharide yields was confirmed during extrusion trials of permeate when this increased acid catalyst concentration resulted in similar oligosaccharide concentrations.