Reformulating the Snack Bar
A food technology class is reformulating a muesli bar. The current bar contains 38 g of sugar per 100 g, mostly from glucose syrup and dried fruit, and 22 g of fat per 100 g, mostly from added vegetable fat. The brief is to reduce sugar to below 15 g per 100 g and keep the bar acceptable in texture and shelf life. Trial 1 replaced glucose syrup with maltitol and reduced dried fruit; the bar was crumbly and had a laxative warning issue at high intake. Trial 2 used polydextrose and more nuts; the bar was oily and went rancid after 6 weeks. The class has 4 weeks and a budget for 3 more trials.
1. Evaluate the two trials against the brief and recommend what the third trial should change, with reasons grounded in food chemistry.
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Trial 1. Replacing glucose syrup with maltitol lowers sugar and calories, but glucose syrup does more than sweeten: it is a humectant and an amorphous glass that binds the bar and keeps it soft. Removing it left the bar crumbly. Maltitol also has a laxative effect at high intake, which is a labelling and consumer-acceptability problem. Dried fruit reduction removed both sugar and moisture, worsening the crumbliness. So Trial 1 meets the sugar target but fails texture and creates a warning issue.
Trial 2. Polydextrose is a bulking agent that adds fibre and lowers sugar, and more nuts raises protein and healthy fat. But the bar was oily and rancid by 6 weeks. Nuts are high in polyunsaturated fat, which oxidises; without an antioxidant or protective packaging, rancidity is expected. The oily surface also suggests fat was not bound by the matrix, since the sugar glass that helped emulsify it was reduced.
Recommendation for Trial 3. Combine the best of both: use a mix of polydextrose and a small amount of glucose syrup or isomalt to restore binding and humectancy, keep some dried fruit for flavour and moisture, and add a natural antioxidant such as tocopherol or use oxygen-barrier packaging. Reduce the proportion of very high-polyunsaturated nuts or use almonds, which are more oxidatively stable. Check the sugar target by calculation before making the batch, and test texture with a simple bend and bite test plus a 6-week storage trial. The key principle is that sugar and fat are functional, not just nutritional - replacing them requires replacing their functions.
2. Explain how the class should design the remaining trials and evaluate the final product, given only 4 weeks and 3 trials.
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Design logic. With only three trials, each must test a clear variable and build on the last. Trial 3 should test the reformulated binder system (polydextrose plus isomalt plus reduced dried fruit) while holding nuts constant. Trial 4 should test antioxidant and packaging changes against the Trial 3 formula. Trial 5 should be a confirmatory batch at the final formula, made in duplicate for shelf-life testing.
Variables to control. Keep bar weight, baking time and cooling conditions constant so texture differences can be attributed to formulation. Record everything: ingredient weights, water activity if a meter is available, and sensory scores.
Measurements. Use objective tests where possible - a bend test for flexibility, a visual score for oil on the surface, and a simple peroxide value or smell test for rancidity at 0, 3 and 6 weeks. Use a small trained panel with a hedonic scale for liking, and a ranking test for preference between formulas. Because the class is small, keep the panel consistent across trials.
Shelf-life testing. Four weeks is too short for a full shelf life, so use accelerated storage: keep samples at elevated temperature (for example 35 °C) to speed oxidation and predict rancidity. Compare against a refrigerated control.
Evaluation against the brief. The final product must meet the sugar target (below 15 g per 100 g), be acceptable in texture and flavour, and not go rancid within the intended shelf life. If the sugar target is met but texture fails, the product is not acceptable. The class should present a decision matrix scoring each trial on sugar, texture, flavour, cost and shelf life, and justify the chosen formula with evidence rather than preference.