Troubleshooting the biological degradation of a child's toy

A case of applying basic biochemistry

BT&C Inc.

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Lebanon, NJ 08833

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One of our early consulting/contract projects involved fixing a childrenís toy.  This project epitomizes the type of project accepted by BT&C as it is different and intriguing. 

BT&C was contacted by the manufacturer of colored modeling dough made for kids.  The dough, which is a mixture of flour, water, latex coloring, and an anti-microbial preservative, was designed to be rubbery moldable dough.  Though this product passed all quality control tests before release, once children began playing with the dough, it was reported that the dough lost its rubber-like consistency and became mushy. 

A thorough review of the product by process engineers failed to identify any flaws in the manufacturing that would result in a faulty product.  Consequently, the company contacted BT&C to help troubleshoot the problem.  The customer provided BT&C with samples of new and failed product.  The new product was firm and malleable while the failed product was soft and sticky. 

As the main component of the dough is flour, and flour is primarily made of starch, this is where the investigation began.  Any cook book tells us that starch is a thickening agent, therefore it was logical to conclude that the rubber texture of dough was due to the starch.  The starch also made the dough a non-Newtonian solution.  Starch is composed of chains of glucose in a linear sequence called amylose, or in a branched pattern called amylopectin.  The end glucose in the starch chain is a reducing sugar, which means that in an alkaline environment, the sugar forms a ketone or aldehyde.

Using the Nelson-Somogyi method for measuring reducing sugars the new dough was compared to failed product.  The analysis demonstrated that the failed product contained more reducing sugars than new product.  Since only the end glucose molecule in amylose reacts during a Nelson-Somogyi reaction, the observation indicates that the starch molecules are degrading thus creating multiple smaller chains each with its own terminal reducing sugar.

Carbohydrate chains, such as amylose, can breakdown as a result of enzymatic activity or chemical hydrolysis.  The latter requires harsh acids, so making the assumption that strong acids are not available to children while playing, enzymatic degradation was investigated.  Starch, specifically amylose, is enzymatically degraded by amylase.  This enzyme is found throughout nature, but very obviously it is a major enzyme in saliva.

Itís no shock to parents that children put toys in their mouths or slobber on them.  Thus, the simple hypothesis was made that the dough is degrading as it is being contaminated with amylase from the children.  To test this idea, saliva was added to the dough and as expected, it became mushy.  The question that remained was whether this was the real problem, and if so, how could it be prevented?

Preventing the supposed cause of the degradation involved applying some basic biochemistry.  Human amylase has an optimum pH near 7.0.  It was proposed that by dropping the pH of the dough to approximately 3 with a weak acid that the amylase would be sufficiently inactive so to prevent degradation of the starch. 

Test product was made with the addition of lactic acid and then test marketed with children.  Indeed the modified product remained stable after handling by children.  The change in formulation was consequently adopted which resolved the problem.