Semi-micro method for the quantitative determination of gellan gum in food products

Abstract

A reagent consisting of 0.1% thiourea in concentrated H 2SO 4 and cysteine hydrochloride at a final concentration of 600 μg/ml was used to determine gellan gum in pudding mix, salad dressings, dog food, orange drink mix, milk, milk products and pineapple pie filling in the presence of other food hydrocolloids. Proteins and starch were removed by digestion with papain and amyloglucosidase respectively. Gellan gum and other hydrocolloids in the clarified digest were precipitated with cetylpyridinium chloride (CPC) and the mixed CP-hydrocolloid complex trapped on a Celite column, washed to remove soluble sugars and the gellan gum eluted with boiling 2% sodium hexametaphosphate. The color developed by reacting an aliquot of the eluate with the reagent was measured at 455 nm and the amount present determined from a standard curve. The rhamnose moiety of the gum gives the specific color response. Maximum color development occurred after 4 h at 26 ± 2°C and remained relatively constant for 24 h. Using ‘product’ blanks the average recovery from milk was 90% with a reproducibility of 2.6% for high-clarity gellan gum. With low-clarity gellan gum the average recovery was 86.4% with a reproducibility of 3%. Pudding, pie fillings (high starch) and salad dressings (high oil content) gave lower recoveries.