Methods of Analyzing Starch and Modified Starch in Food

There are no reliable ways to identify modified starches in food because the composition of food is so diverse. The European Starch Industry Association (AAF) explains that even though it is theoretically possible to develop a product-specific identification method, it is not practical due to the wide variety of food matrices to which modified starches are added. Similarly, developing a general identification method based on the modification of starch is not feasible as the degree of substitution (DS) is usually low and modified starches are often used in combination in food products. (Documentation provided to EFSA n.1).

To detect modified starch identifiers, specific compositional parameters like phosphorous and aluminium content, and carboxyl, acetyl, adipate, hydroxypropyl and octenyl-succinyl groups can be analyzed. However, there are missing data to define specifications for some modified starches, including suitable tests to identify specific groups and evaluate cross-linking, according to the 82nd JECFA meeting. (JECFA, 2016a, 2016b)

In the 1980s and 1990s, methods were developed to analyze starches and modified starches in foods. Enzymatic treatments were becoming more popular than chemical methods because the latter were not very specific and relied on dangerous reagents (Karkalas, 1985).

Karkalas (1985) developed a method to analyze starch and modified starches in different foods. The method used enzymes to break down the starch and measure glucose levels through colorimetry. Native normal and waxy starches and distarch phosphate could be measured accurately, but oxidized starch could not due to its dicarboxylic groups. Acetylated distarch phosphate, high-amylose starch, and retrograded amylose required an additional alkaline pretreatment step. The method was found to be precise, quick, and useful in determining starch content in foods, but could not distinguish between native starch and modified versions.

Chatel et al. (1996) used dialysis to remove sucrose and preserve starch in sweetened fruit preparations. They tested experimental parameters like membrane cut-off, treatment time, temperature, and water renewal, and found a yield of 99.4% (RSD 0.1%) sucrose elimination for strawberry preparations. Enzymatic hydrolysis with a-amylase and amyloglucosidase was then used to break down the starch, and the glucose produced was measured using hexokinase and glucose-6-phosphate dehydrogenase. By using this method, they could determine the starch content in strawberry preparations containing 3.0% (w/w) acetylated distarch adipate with an accuracy of 92% (RSD, 3.1%). The method was considered efficient, specific, and reproducible for the samples analysed.

Chatel et al. (1997) improved the method for identifying and quantifying starch in sweetened fruit preparations by optimising the dialysis and gelatinisation steps, and using infrared (IR) identification of starch chemical modifications. The low concentration, heterogeneous, gelified and highly sweetened nature of the medium made identification and quantification of starch difficult. Starches were first identified by optical microscopy, and acetyl and hydroxypropyl modifications were characterised by Fourier transform IR spectroscopy (FT-IR). Starch was extensively purified by dialysis to remove most of the sucrose. The experimental conditions of this step were optimised, and a previous gelatinisation treatment improved the enzymatic hydrolysis of starch and the quantification of the released glucose. The method was found to allow reliable determinations of distarch phosphate, acetylated distarch phosphate and acetylated distarch adipate, and was considered to be appropriate for hydroxypropylated distarch phosphate.

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