Rapid Determination of Lactose and Its Hydrolyzates in Whey and Whey Permeate by High Performance Liquid Chromatography

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Abstract
A rapid method is presented for the quantitative analysis of lactose, glucose, and galactose in whey and whey permeate by high performance liquid chroma- tography. Samples were prepared by heating to precipitate most proteins and by eluting through a Sep-Pak TM cartridge to remove lipids, chromophores, and residual proteins. Sugars were separated on an Altex ~t-Spherogel Carbohydrate column and measured by a refractive index detector. Recovery of added carbohydrates averaged 98.0% for lactose and 101.5% for glucose and galactose. Coefficients of variation for recovery ranged from .27 to 3.20%. Reproducibility was demonstrated by our monitoring rate of enzymatic hydrolysis of lactose in whey permeate. Sample preparation time was 15 min; chromatographic separation was within 15 min. versatility, and specificity. Several workers reported HPLC procedures for carbohydrates in such dairy products as milk (4, 14, 18), butter- milk (14), yogurt (4, 14), ice cream (18), and dried whey (14). Samples for these HPLC analyses were prepared either by coagulating proteins in milk and other dairy products with ethanol (14, 18) or those in milk with tri- chloroacetic acid (4). Those methods, however, are inadequate for analysis of carbohydrates in liquid whey and whey permeate mainly because of the high dilution of samples by ethanol for protein precipitation or the harmful effect of trichloracetic acid on resin-based columns that are advantageous for separating glucose and galactose. This study presents a rapid sample preparation procedure for HPLC analysis of lactose, glucose, and galactose in liquid whey and whey permeate, particularly in lactose- hydrolyzed products.